U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2018–5136

Prepared in cooperation with the Bureau of Reclamation and the 

Oklahoma Water Resources Board

Simulation of Groundwater Flow and Analysis of Projected 

Water Use for the Rush Springs Aquifer, Western Oklahoma
Cover photograph: Wheat field irrigated by the Rush Springs aquifer, between Weatherford and Thomas, Oklahoma, March 27, 2012. 

Photograph courtesy of Chris Neel, Oklahoma Water Resources Board.
Simulation of Groundwater Flow and Analysis of Projected 

Water Use for the Rush Springs Aquifer, Western Oklahoma

By John H. Ellis

Prepared in cooperation with the Bureau of Reclamation and the 

Oklahoma Water Resources Board

Scientific Investigations Report 2018–5136

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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Suggested citation:

Ellis, J.H., 2018, Simulation of groundwater flow and analysis of projected water use for the Rush Springs aquifer, western Oklahoma: U.S. Geological Survey Scientific Investigations Report 2018–5136, 156 p., https://doi.

org/10.3133/sir20185136.

ISSN 2328-031X (print)

ISSN 2328-0328 (online)

ISBN 978-1-4113-4268-2
iii

Acknowledgments

The project documented in this report was conducted by the U.S. Geological Survey (USGS) in 

cooperation with the Bureau of Reclamation (Reclamation) and the Oklahoma Water Resources 

Board (OWRB). Appreciation is extended to Collins Balcombe (Reclamation) for initiating and 

supporting this project and to Anna Hoag (Reclamation) for assistance with data compilation and 

analysis for the Foss and Fort Cobb Reservoirs. The author also thanks Polly Edwards with the 

Caddo Nation, whose initiative led to the installation of the five continuous-observation wells 

used in this study. Since installation, funding for the five continuous-observation wells has been 

provided by the U.S. Bureau of Indian Affairs. The Reclamation Native American Affairs Technical Assistance to Tribes Program funded data collection and analysis for previous studies about 

the Rush Springs aquifer.

The author also thanks Michael Fienen (USGS) for his assistance with the uncertainty analysis 

and Nicole Paizis (USGS) for assistance with report figures. 
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Study Area..............................................................................................................................................6

Conceptualization of Groundwater-Flow System..........................................................................12

Geologic Units ............................................................................................................................12

Recharge.....................................................................................................................................15

Using the RORA Method to Estimate Recharge ..........................................................15

Using the Soil-Water-Balance Code to Estimate Recharge......................................15

Recharge from Crop Irrigation........................................................................................20

Saturated-Zone Evapotranspiration .......................................................................................20

Streamflow Characteristics and Seepage ............................................................................20

Lateral Groundwater Flows......................................................................................................21

Water Use ...................................................................................................................................21

Seeps and Springs.....................................................................................................................22

Reservoir.....................................................................................................................................22

Groundwater Storage Change.................................................................................................22

Conceptual Water Budget........................................................................................................25

Simulation of Groundwater Flow...............................................................................................................25

Spatial and Temporal Discretization................................................................................................27

Hydrologic Boundaries ......................................................................................................................27

Recharge.....................................................................................................................................27

Lateral Groundwater Flow, Seeps, and Springs ...................................................................27

Streams........................................................................................................................................31

Reservoir.....................................................................................................................................33

Saturated-Zone Evapotranspiration .......................................................................................35

Groundwater Use.......................................................................................................................35

Model Calibration................................................................................................................................35

Calibration Parameters.............................................................................................................37

Calibration Targets.....................................................................................................................40

Groundwater-Level Observations ..................................................................................40

Fort Cobb Reservoir Stage Observations......................................................................40

Base-Flow and Stream-Seepage Estimates ................................................................45

Calibration-Target Uncertainty and Weighting............................................................45

Calibrated Model Fit ..................................................................................................................47

Groundwater Levels .........................................................................................................47

Base Flow...........................................................................................................................58

Reservoir Stage and Water Budget...............................................................................63

Calibrated Water Budget.................................................................................................66

Calibrated Parameter Values...................................................................................................70

Calibrated GHB and Drain Conductance ......................................................................70
v

Calibrated Recharge ........................................................................................................70

Calibrated Evapotranspiration from Groundwater......................................................73

Calibrated Reservoir Inputs ............................................................................................73

Calibrated Hydraulic Conductivity and Vertical Anisotropy ......................................73

Storage Parameters .........................................................................................................78

Sensitivity and Identifiability....................................................................................................82

Groundwater Availability Scenarios.........................................................................................................84

Equal Proportionate Share................................................................................................................84

Uncertainty in Equal-Proportionate-Share Results ......................................................................89

Projected (50-Year) Groundwater Use ............................................................................................91

Hypothetical (10-Year) Drought ........................................................................................................99

Model Limitations and Assumptions ......................................................................................................106

Summary......................................................................................................................................................108

References Cited .......................................................................................................................................110

Figures

1. Map showing the Rush Springs aquifer study area, western Oklahoma............................3

2. Map showing the surficial geologic units of the Rush Springs aquifer study 

area, western Oklahoma .............................................................................................................4

3. Stratigraphic chart showing surficial geologic and hydrogeologic units of the 

Rush Springs aquifer study area, western Oklahoma............................................................5

4. Map showing land-surface altitudes of the Rush Springs aquifer study area, 

western Oklahoma........................................................................................................................7

5. Map showing land and crop cover over the Rush Springs aquifer, western 

Oklahoma, 2011–15 .....................................................................................................................13

6. Pie charts showing land and crop cover over the Rush Springs aquifer, 

western Oklahoma, 2011–15 .....................................................................................................14

7. Graph showing annual precipitation and recharge computed by using the 

Soil-Water-Balance code for the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................17

8. Graphs showing mean monthly precipitation and recharge computed by 

using the Soil-Water-Balance code for the Rush Springs aquifer, western 

Oklahoma, 1979–2015 .................................................................................................................18

9. Map showing mean annual groundwater recharge computed by using the 

Soil-Water-Balance code for the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................19

10. Map showing locations of permitted groundwater wells and surface-water 

diversions for the Rush Springs aquifer, western Oklahoma, 1979–2015..........................23

11. Map showing locations of long-term and continuous groundwater-level 

observation wells for the Rush Springs aquifer, western Oklahoma, 1979–2015.............24

12. Graphs showing depth to water for selected wells in Rush Springs aquifer 

and Fort Cobb Reservoir surface watershed, western Oklahoma, 1974–2016 .................26

13. Map showing hydrogeologic units of the Rush Springs aquifer study area, 

western Oklahoma......................................................................................................................28

14. Vertical cross section of the Rush Springs groundwater-flow model, 

western Oklahoma......................................................................................................................29
vi

15. Map showing active area, hydrologic boundaries, and selected parameter 

zones for the numerical groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma......................................................................................................................30

16. Map showing Streamflow-Routing package stream channel widths for 

the numerical groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma......................................................................................................................32

17. Graph showing Fort Cobb Reservoir volume, surface area, and stage relationship ......33

18. Lake package cross-section and discretization for the Rush Springs aquifer, 

western Oklahoma......................................................................................................................34

19. Graph showing monthly water demand by groundwater-use type for the 

Rush Springs aquifer, western Oklahoma ..............................................................................35

20. Map showing spatial distribution of recharge zones for the Rush Springs 

aquifer model, western Oklahoma, 1979–2015.......................................................................38

21. Map showing spatial distribution of pilot points for the Rush Springs aquifer 

model, western Oklahoma, 1979–2015 ....................................................................................39

22. Pie charts showing components of the objective function for the calibration 

of the numerical groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma, 1979–2015 .................................................................................................41

23. Map showing spatial distribution of groundwater-level observations in 

layers 1 and 2 for the Rush Springs aquifer model, western Oklahoma............................42

24. Graph showing number of groundwater-level observations for each well 

for the Rush Springs aquifer model, western Oklahoma, 1979–2015 .................................43

25. Map showing spatial distribution of groundwater-level observations per 

well for the Rush Springs aquifer model, western Oklahoma, 1979–2015.........................44

26. Graphs showing annual and monthly distribution of groundwater-level 

observations for the Rush Springs aquifer model, western Oklahoma, 1979–2015.........45

27. Graph showing temporal distribution of streamflow observations used for the 

calibration of the Rush Springs aquifer model, western Oklahoma, 1979–2015 ..............46

28. Graphs showing observed and simulated groundwater levels and groundwaterlevel residual distributions for the numerical groundwater-flow model of the 

Rush Springs aquifer, western Oklahoma, 1979–2015 ..........................................................47

29. Graphs showing residuals by quality category, weighted residuals by quality 

category, residuals by layer, and weighted residuals by layer for the numerical 

groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................49

30. Map showing spatial distribution of mean groundwater-level residuals for 

the numerical groundwater-flow model of the Rush Springs aquifer, western 

Oklahoma, 1979–2015 .................................................................................................................50

31. Map showing spatial distribution of mean weighted groundwater-level 

residuals for the numerical groundwater-flow model of the Rush Springs 

aquifer, western Oklahoma, 1979–2015...................................................................................52

32. Graph showing temporal distribution of mean, minimum, and maximum 

groundwater-level residuals for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015 ...................................................53

33. Graphs showing observed and simulated groundwater levels in long-term 

and continuous groundwater-level observation wells for the Rush Springs 

aquifer, western Oklahoma, 1979–2015...................................................................................54
vii

34. Graphs showing observed streamflow, estimated base flow, and simulated 

base flow at Hammon streamgage on Washita River; Clinton streamgage 

on Washita River; Carnegie streamgage on Washita River; Anadarko 

streamgage on Washita River; Bridgeport streamgage on Canadian River; 

Cement streamgage on Little Washita River; Cobb Creek streamgage on 

Cobb Creek; Lake Creek streamgage on Lake Creek; and Willow Creek 

streamgage on Willow Creek for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015 ...................................................59

35. Graphs showing Fort Cobb Reservoir observed and simulated stage and 

storage for the numerical groundwater-flow model of the Rush Springs 

aquifer, western Oklahoma, 1979–2015...................................................................................64

36. Graphs showing annual reservoir inflows and outflows and change in storage 

for Fort Cobb Reservoir in the numerical groundwater model of the Rush Springs 

aquifer, western Oklahoma, 1979–2015...................................................................................65

37. Pie charts showing mean annual calibrated water budget for the numerical 

groundwater model of the Rush Springs aquifer, western Oklahoma, 1979–2015...........66

38. Map and pie chart showing simulated stream seepage for the numerical 

groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................68

39. Graphs showing annual mean inflows and outflows and annual change in 

groundwater storage for the numerical groundwater-flow model of the 

Rush Springs aquifer, western Oklahoma, 1979–2015 ..........................................................69

40. Graphs showing mean monthly aquifer inflows and outflows and mean monthly 

change in groundwater storage for the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................71

41. Map showing calibrated mean annual recharge for the numerical groundwaterflow model of the Rush Springs aquifer, western Oklahoma, 1979–2015 ..........................72

42. Graph showing change from initial Lake package inputs for the numerical 

groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................73

43. Maps showing calibrated horizontal hydraulic conductivity of the Cloud Chief 

Formation, alluvium and terrace, and lower Whitehorse Group for the Rush 

Springs aquifer numerical groundwater-flow model, western Oklahoma........................74

44. Histograms showing horizontal hydraulic conductivity and calibrated horizontal 

hydraulic conductivity for Canadian River alluvium and terrace and lower 

Whitehorse Group for the groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma......................................................................................................................77

45. Histograms showing specific yield for the Cloud Chief Formation; Canadian 

River alluvium and terrace; and lower Whitehorse Group for the Rush Springs 

aquifer, western Oklahoma .......................................................................................................78

46. Maps showing specific yield of the Cloud Chief Formation, alluvium and 

terrace, and lower Whitehorse Group for the Rush Springs aquifer numerical 

groundwater-flow model, western Oklahoma .......................................................................79

47. Graph showing observation group sensitivity by parameter group in the numerical 

groundwater-flow model for the Rush Springs aquifer, western Oklahoma ....................82

48. Graph showing parameter identifiability in the numerical groundwater-flow 

model for the Rush Springs aquifer, western Oklahoma......................................................83
viii

49. Map showing simulated saturated thickness and simulated base flow after 

20 years of continuous equal-proportionate-share groundwater pumping in 

the Rush Springs aquifer, western Oklahoma........................................................................86

50.Vertical cross section of the Rush Springs groundwater-flow model after 

20 years of equal-proportionate-share groundwater pumping in the Rush 

Springs aquifer, western Oklahoma ........................................................................................87

51. Graphs showing changes in simulated groundwater storage during 20, 40, 

and 50 years of continuous equal-proportionate-share groundwater pumping 

in the Rush Springs aquifer, western Oklahoma ...................................................................88

52. Graph showing changes in simulated base flow in Cobb, Lake, and Willow 

Creeks and in simulated stage in Fort Cobb Reservoir during 20 years of 

continuous equal-proportionate-share groundwater pumping in the Rush 

Springs aquifer, western Oklahoma ........................................................................................89

53. Graphs showing parameter distribution of layer 3 specific yield multiplier 

and recharge zone 12 multiplier for the equal-proportionate-share uncertainty 

analysis for the Rush Springs aquifer, western Oklahoma..................................................90

54. Graph showing probabilistic equal-proportionate-share pumping rates for the 

Rush Springs aquifer, western Oklahoma ..............................................................................91

55. Graphs showing simulated groundwater storage during 50 years of groundwater 

use at selected rates for the Rush Springs aquifer and Fort Cobb Reservoir 

watershed, western Oklahoma ................................................................................................93

56. Maps showing simulated change in saturated thickness after 50 years of no 

groundwater use; mean groundwater use, 1979–2015; increasing groundwater 

use; and 2015 groundwater use for the Rush Springs aquifer, western Oklahoma.........94

57. Graphs showing simulated annual mean base flow through 50 years of groundwater 

use at selected rates in the Rush Springs aquifer, western Oklahoma.............................98

58. Graph showing change in groundwater storage during a hypothetical 10-year 

drought for the Rush Springs aquifer, western Oklahoma, 1979–2007 ............................100

59. Map showing simulated change in saturated thickness after a hypothetical 

10-year drought for the Rush Springs aquifer, western Oklahoma, 1979–2007..............101

60. Graphs showing changes in simulated base flow at Hammon streamgage on 

Washita River; Clinton streamgage on Washita River; Carnegie streamgage 

on Washita River; Anadarko streamgage on Washita River; Bridgeport 

streamgage on Canadian River; Cement streamgage on Little Washita River; 

Cobb Creek streamgage; Lake Creek streamgage; and Willow Creek 

streamgage for the numerical groundwater-flow model of the Rush Springs 

aquifer, western Oklahoma, 1979–2007.................................................................................10

2

61. Graphs showing changes in Fort Cobb Reservoir stage and Fort Cobb Reservoir 

storage during a hypothetical 10-year drought for the Rush Springs aquifer, 

1979–2007 ...................................................................................................................................107
ix

Tables

1. Location, period of record, and coefficient of variation for selected streamgages

in the Rush Springs aquifer study area, western Oklahoma.................................................8

2. Mean annual streamflow and mean annual base flow for selected streamgages 

in and near the Rush Springs aquifer study area, western Oklahoma, 1979–2015............9

3. Conceptual water budget for the Rush Springs aquifer, western Oklahoma, 

1979–2015 .....................................................................................................................................14

4. Selected climate stations in and near the Rush Springs aquifer study area,

western Oklahoma......................................................................................................................16

5. Components of the objective function for the automated calibration of the 

numerical groundwater-flow model of the Rush Springs aquifer, western 

Oklahoma, 1979–2015 .................................................................................................................36

6. Calibration parameters, parameter values, parameter sensitivity, and parameter 

identifiability for the automated calibration of the numerical groundwater-flow

model of the Rush Springs aquifer, western Oklahoma, 1979–2015.................................114

7. Selected groundwater-level observation wells in the Rush Springs aquifer study 

area, western Oklahoma .........................................................................................................142

8. Statistical summary of groundwater-level residuals for the numerical groundwaterflow model of the Rush Springs aquifer, western Oklahoma, 1979–2015 ..........................48

9. Statistical summary of base-flow residuals for the numerical groundwater-flow 

model of the Rush Springs aquifer, western Oklahoma, 1979–2015...................................58

10. Statistical summary of Fort Cobb Reservoir stage residuals for the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015 ..............64

11. Mean annual calibrated water budget for the numerical groundwater-flow model 

of the Rush Springs aquifer, western Oklahoma, 1979–2015...............................................66

12. Equal-proportionate-share (EPS) pumping rates for the Rush Springs aquifer, 

western Oklahoma, 1979–2015 .................................................................................................84

13. Changes in groundwater storage after 50 years of groundwater use at selected 

rates for the Rush Springs aquifer, western Oklahoma .......................................................92
x

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

section (640 acres or 1 square mile) 259.0 square hectometer (hm2

) 

square mile (mi2

) 259.0 hectare (ha)

Volume

gallon (gal) 0.003785 cubic meter (m3

) 

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Flow rate

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3

/yr)

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year (hm3

/yr)

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Leakance

foot per day per foot [(ft/d)/ft] 1 meter per day per meter

Transmissivity

foot squared per day (ft2

/d) 0.09290 meter squared per day (m2/d)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 32) / 1.8.
xi

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88). Vertical coordinate information for Foss and Fort Cobb Reservoirs is referenced to 

the National Geodetic Vertical Datum of 1929 (NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Abbreviations

BFI base-flow separation code 

DEM digital elevation model

EPS equal proportionate share

ET evapotranspiration

ETg saturated-zone evapotranspiration

GHB General-Head Boundary

GPS Global Positioning System

Kh horizontal hydraulic conductivity

MAY maximum annual yield

NHDPlus National Hydrography Dataset Plus

NWIS National Water Information System

OWRB Oklahoma Water Resources Board

Reclamation Bureau of Reclamation

RMSE root-mean-square error

SFR Streamflow-Routing package, version 2 

Ss specific storage

SVD singular value decomposition

SVDA singular value decomposition-assist

SWB soil-water-balance

Sy specific yield

USGS U.S. Geological Survey

Simulation of Groundwater Flow and Analysis of 

Projected Water Use for the Rush Springs Aquifer, 

Western Oklahoma

By John H. Ellis

Abstract

The U.S. Geological Survey, in cooperation with the 

Bureau of Reclamation and the Oklahoma Water Resources 

Board, (1) quantified the groundwater resources of the 

Rush Springs aquifer in western Oklahoma by developing a 

numerical groundwater-flow model, (2) evaluated the effects 

of estimated equal-proportionate-share (EPS) pumping rates 

on aquifer storage and streamflow for time periods of 20, 

40, and 50 years into the future, (3) assessed the uncertainty 

in the EPS scenario results, and (4) evaluated the effects of 

(a) projected groundwater-use rates extended 50 years into

the future and (b) sustained hypothetical drought conditions

over a 10-year period on stream base flow and groundwater

in storage.

The Rush Springs aquifer is an important source of 

water for municipal and irrigation use by many communities 

and agricultural users in the study area. The study area is 

composed of about 4,970 square miles (3,181,003 acres) of 

Rush Springs aquifer bedrock deposits located in 14 counties. 

The study area also includes the alluvium and terrace deposits 

of the Canadian and Washita Rivers, as well as alluvium along 

the Little Washita River, Deer Creek, and a number of smaller 

tributaries of the Washita River that overlie the bedrock. 

A numerical groundwater-flow model of the Rush Springs 

aquifer was constructed by using MODFLOW with the 

Newton solver. Groundwater flow was simulated for January 

1979–December 2015 by using monthly stress periods, and an 

initial steady-state stress period was configured to represent 

mean annual inflows and outflows. The model was calibrated 

to groundwater-level observations at selected wells, monthly 

base flow at nine streamgages, stream seepage as estimated for 

the conceptual water budget, and Fort Cobb Reservoir stage. 

The EPS scenarios for the Rush Springs aquifer were run 

for periods of 20, 40, and 50 years. The 20-, 40-, and 50-year 

EPS pumping rates under normal recharge conditions were 

0.82, 0.49, and 0.43 acre-foot per acre per year, respectively. 

Given the 2,954,545-acre aquifer area used for the EPS 

scenarios, the 20-year rate corresponds to an annual yield of 

about 2,422,727 acre-feet per year. Groundwater storage at 

the end of the 20-year EPS scenario was about 13,321,000 

acre-feet, or about 31,516,437 acre-feet (70 percent) less than 

the starting EPS scenario storage. This decrease in storage 

was equivalent to a mean groundwater-level decline of about 

152 feet. Water availability under the EPS pumping rate was 

primarily from the western area of the model. Saturation was 

sustained though the entire EPS scenario where the aquifer 

was sufficiently thick or a shallow hydraulic gradient was 

present. Fort Cobb Reservoir stage was below the dead-pool 

stage after about 5 years of 20-year EPS pumping.

An uncertainty analysis was conducted to assess the 

uncertainty in the EPS scenario results. An ensemble of 

400 random sets of possible parameter values was performed 

for the uncertainty analysis by using a multivariate normal 

distribution centered on the calibrated parameter values. The 

parameter bounds for the uncertainty analysis were determined 

by using the posterior covariance matrix, which allows for 

the incorporation of knowledge gained during the calibration 

process as well as observation uncertainty and the correlation 

between estimated parameters. The uncertainty results indicate 

a 95-percent confidence interval for the 20-year EPS pumping 

rate between 0.73 and 0.95 acre-foot per acre per year.

Projected 50-year pumping scenarios were used to 

simulate the effects of selected well withdrawal rates on 

groundwater storage of the Rush Springs aquifer. The effects 

of well withdrawals were evaluated by comparing changes 

in groundwater storage between four 50-year scenarios using 

(1) no groundwater use, (2) mean groundwater use for the

study period (1979–2015), (3) increasing groundwater use,

and (4) groundwater use at the 2015 rate. The increasinguse scenario assumed a 38-percent increase in pumping over

50 years on the basis of 2010–60 demand projections for

western Oklahoma. Simulated groundwater storage changes

ranged between an increase of 6.3 percent for the scenario

with no groundwater use, and 0.9 percent for the scenario

with 2015 groundwater-use rates. For the Fort Cobb Reservoir

surface watershed, simulated groundwater storage changes

ranged between an increase of 23.6 percent for the scenario
2 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

with no groundwater use and a decrease of 4.0 percent for 

the increasing groundwater-use scenario. Groundwaterlevel changes were generally greater in areas with a large 

concentration of groundwater wells and groundwater use such 

as the Fort Cobb Reservoir surface watershed. 

A hypothetical 10-year drought scenario was used to 

simulate the effects of a prolonged period of reduced recharge 

on the Rush Springs aquifer groundwater storage and Fort 

Cobb Reservoir stage and storage. Drought effects were 

quantified by comparing the results of the drought scenario 

to those of the calibrated numerical model. To simulate the 

hypothetical drought, recharge in the calibrated numerical 

model was reduced by 50 percent during the simulated drought 

period (1983–1992), and upstream inflows to the Canadian 

and Washita Rivers and associated tributaries were reduced by 

37 percent. Groundwater storage at the end of the hypothetical 

drought period in December 1992 was about 42,983,000 

acre-feet, or about 3,525,000 acre-feet (7.6 percent) less than 

the groundwater storage of the calibrated numerical model. 

This change in groundwater storage is equivalent to a mean 

groundwater-level decline of 15.8 feet. Simulated mean baseflow declines at the Canadian and Washita River streamgages 

were between 39 and 59 percent during the drought period. 

The minimum stage in Fort Cobb Reservoir at the end of 

the hypothetical drought period was 1,311 feet, indicating a 

storage capacity of only 10 percent of active conservation 

pool storage. The Fort Cobb Reservoir storage declines mostly 

resulted from reduced base flows in Cobb, Lake, and Willow 

Creeks upstream from the reservoir. 

Introduction

The 1973 Oklahoma Water Law (82 OK Stat § 

82-1020.5) requires the Oklahoma Water Resources Board 

(OWRB) to conduct hydrologic investigations of the State’s 

aquifers (called groundwater basins by the OWRB) to 

determine the maximum annual yield (MAY) for each aquifer. 

The MAY is defined as the total amount of fresh groundwater 

that can be withdrawn annually from an aquifer while ensuring 

a minimum 20-year life of that aquifer. For bedrock aquifers, 

the aquifer-life requirement is satisfied if, after 20 years of 

MAY withdrawals, 50 percent of the aquifer retains a saturated 

thickness of 15 feet (ft). When a MAY has been established, 

the amount of land owned or leased by a permit applicant 

determines the annual volume of water allocated to that permit 

applicant. The annual volume of water allocated per acre of 

land is known as the equal-proportionate-share (EPS) pumping 

rate.

Prior to the OWRB determination of the MAY, a 

hydrologic investigation is needed to obtain data and 

information related to the geology, hydrogeologic framework, 

and hydrogeology of an aquifer. To address this need, the 

hydrologic investigation for the Rush Springs aquifer includes 

Neel and others (2018) and the study documented in this 

report by the U.S. Geological Survey (USGS) in cooperation 

with Bureau of Reclamation (Reclamation) and OWRB. 

Neel and others (2018) described the climate, geology, 

hydrogeology, hydraulic properties, water use, streamflow, 

base flow, and groundwater quality of the Rush Springs 

aquifer. Data from Neel and others (2018) were used in the 

conceptualization of the groundwater-flow system and in 

the construction of a numerical groundwater-flow model 

(hereinafter, “groundwater model”) that was used to simulate 

groundwater flow and run groundwater availability scenarios 

during this study. 

This study also was conducted to evaluate water 

management issues in Fort Cobb Reservoir. Water demands 

are projected to increase substantially by 2060 for all uses 

in west-central Oklahoma (OWRB, 2012); thus, there is a 

need to estimate long-term water supplies from this reservoir. 

Additionally, the growing recognition of coupled surfacewater and groundwater interaction has prompted an evaluation 

of the flows between the Rush Springs aquifer and Fort Cobb 

Reservoir and the effects of pumping on surface-water inflows 

and groundwater levels surrounding the reservoir. 

Purpose and Scope

The purpose of this report is to describe the simulation 

of groundwater flow and analysis of projected water use for 

the Rush Springs aquifer. Specifically, the report (1) quantifies 

the groundwater resources of the Rush Springs aquifer 

simulated by using a groundwater model, (2) presents the 

effects of estimated EPS pumping on aquifer storage and 

streamflow for time periods of 20, 40, and 50 years into the 

future, (3) presents the uncertainty in the EPS scenario results, 

and (4) presents the effects of (a) projected groundwater-use 

rates extended 50 years into the future, and (b) sustained 

hypothetical drought conditions on stream base flow and 

groundwater in storage over a 10-year period. The study 

period, for which a water-budget analysis was performed, 

includes years 1979–2015. 

The geographic extent of the Rush Springs aquifer (fig. 1), 

as defined in this report, is composed of the Rush Springs 

Formation and Marlow Formation bedrock units (Whitehorse 

Group) and the overlying alluvium and terrace deposits 

collectively referred to as the Rush Springs aquifer (figs. 2–3). 

Although previous reports have defined the base of the Rush 

Springs aquifer as the top of the Marlow Formation, this unit 

is included as a part of the aquifer in this investigation based 

on Neel and others (2018). Thus, the base of the Rush Springs 

aquifer is the top of the Dog Creek Shale, which is a member 

of the El Reno Group (Neel and others, 2018) (fig. 3).
Introduction 3

laf18-0888_fig 01

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

Alfalfa

Bridgeport

Camargo

Carnegie

Cement

Clinton

Eakly

Fay

Fort Cobb

Chickasha

Anadarko

Hammon

Hinton

Marlow

Rush Springs

Seiling

Taloga

Thomas

Weatherford

Hydro

Alfalfa

Bridgeport

Camargo

Carnegie

Cement

Clinton

Eakly

Fay

Fort Cobb

Chickasha

Anadarko

Hammon

Hinton

Marlow

Rush Springs

Seiling

Taloga

Thomas

Weatherford

Hydro 07228500

07324200

07325000

07326000

07325800

07326500

07325500

07325850

07325860

07327447

07324400

07228500

07324200

07325000

07326000

07325800

07326500

07325500

07325850

07325860

07327447

07324400

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb 

Reservoir

Stinking

Creek

Rainy Mountain

Creek

Stinking

Creek

Rainy Mountain

Creek

North Fork Red RiverNorth Fork Red River

North Canadian River North Canadian River

OKLAHOMA

Study area

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Rush Springs aquifer boundary

Western extent of equal­proportionate­share 

aquifer boundary—Modified from Neel 

and others (2018)

Streamgage and number (USGS, 2017c)

EXPLANATION

07325500

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

Figure 1. The Rush Springs aquifer study area, western Oklahoma.
4 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 2. The surficial geologic units of the Rush Springs aquifer study area, western Oklahoma.

laf18-0888_fig 02

Base modified from U.S. Geological Survey digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003)

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

GARVIN

MCCLAIN

JACKSON

HARMON

TILLMAN

Lake 

Creek

Little Washita River

Stinking

Creek Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

North Fork Red River

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Rainy Mountain

Creek

North Canadian River

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Stinking

Creek Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

North Fork Red River

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Rainy Mountain

Creek

North Canadian River

Canadian River

Turkey

Creek

Cavalry

Creek

Qal

Qal

Qal

Qt

Qt

Qt

Qt

Qt

Qt

To

Qt

Qt

Qt

Qt

Qt

Qt

Qt

Qt

Qt

Qt

Qal

Pcc

Pdy

Pdy

Pdy

Pd

Pdc

Qal

Qal

Qal

Phy

Phy

Phy

Qal

Qal

Qt

Qt

Pb

Pb

Pdc

Pdc

Pw

Pw

Pw

Pw

Pw

Pw Pw

Pu

Pf

Pcc

Pu

Pdc

Pf

Pcc

Pcc

Pec

To

To

Qal

Qal

Pcc

Pd

Pu

Pd

Pu

Pd

Phy Phy

Ou

i

Pf Pb

Pdc

Pcc

Pu

Qal

Qt

Pd

Qt

Pw

Pf Pf

i

i

Pu

Pu

Pd Pw

Qal

Pec

Pcc

Pb

Pb

Pb

Pb

Pb

Phy

Phy

Pd

i

i

i i

i

Pf

Ppo

Ppo

Ppo Ppo Ppo

Ppo

Pu

Ou

i

Pf

Pd

Phy

Ppo

Pdy

Pdc

Pw

Pcc

Pb

Qt

Qal

To

Pec Rush Springs aquifer boundary

Permian rocks, undivided

Ordovician rocks, undivided

Wichita Granite Group (Cambrian)

Flower-pot Shale (Permian)

Duncan Sandstone of the 

El Reno Group (Permian)

Hennessey Group (Permian) 

Post Oak Conglomerate (Permian)

Doxey Shale (Permian)

Cloud Chief Formation (Permian)

Whitehorse Group (Permian)

Dog Creek Shale (Permian)

Blaine Formation (Permian)

Alluvium (Quaternary)

Terrace deposits (Quaternary)

Ogallala Formation (Tertiary)

Elk City Sandstone (Permian)

Geologic unit

EXPLANATION

0 10 20 30 MILES

0 10 20 30 KILOMETERS

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'
Introduction 5

Figure 3. Surficial geologic and hydrogeologic units of the Rush Springs aquifer study area, western Oklahoma.

laf18-0888_fig 03

a

Ellis and others, 2017

b

Tanaka and Davis, 1963

c

Becker and Runkle, 1998

d

Fay, 1978

e

Carr and Bergman, 1976

System Hydrogeologic

unit 

Thickness,

in feet Description

Quaternary 0–130a,b,c

Silt, sand, and clay deposited by North Fork Red River

and tributaries often reworked by wind; occasionally 

containing quartzitic gravel and slightly cemented by 

calcium carbonate

Tertiary

High Plains 

(Ogallala) 

aquifer

0–600

Brown to light tan to salmon, mostly unconsolidated clay, 

silt, sand, and gravel with zones of caliche near the 

surface

Elk City

Sandstone 

Reddish-brown, fine-grained sandstone with silt and 

clay, weakly cemented by iron oxide, calcium carbonate, 

and gypsum

Doxey Shale Reddish-brown, silty shale and siltstone

0–300b,c

Reddish-brown to orange-brown shale interbedded with 

siltstone and sandstone; some dolomite and much 

gypsum near base

Rush Springs

Formation 0–560d Reddish-brown to orange-brown cross-bedded

sandstonee

Marlow

Formation 0–128b Orange-brown, fine-grained sandstone and siltstone with 

some dolomite and gypsum

Dog Creek 

Shale 

Dog Creek 

confining unit 0–400 Red, brown, and green gypsiferous shales with several 

beds of siltstone, sandstone, and dolomite

Blaine 

Formation 0–140

Beds of white massive gypsum and thin beds of gray 

medium-grained dolomite or dolomitic limestone 

separated by well-defined units of red and green shale

Flower-pot

Shale 0–150

Red, brown. and maroon blocky shales with green and 

gray shales and thin beds of gypsum and dolomite; 

satin spar gypsum occurs throughout

Duncan

Sandstone

of the

El Reno Group 

0–40

Grayish-brown to buff, indurated, highly cross-bedded, 

ripple-marked, nonfossiliferous, silty to fine-grained 

dolomitic sandstone with interbedded shale

0–500

Yellowish-gray to buff nonfossiliferous shale with 

calcareous fine-grained siltstone and limestone 

conglomerate

Cambrian

Ordovician

Igneous rocks of Wichita uplift

Geologic unit

Alluvium and terrace 

deposits

Ogallala Formation 

Permian

Quartermaster 

Formation 

Hennessey Group or

Post Oak Conglomerate

0–400

Cloud Chief Formation Whitehorse Group El Reno Group

Wichita Granite Group

Cloud Chief 

confining unit

Rush Springs 

aquifer

Alluvial aquifers 

or Rush Springs 

aquifer where 

overlying the 

Whitehorse Group

Limestone and conglomerate with abundant quartz sand

and cherty zones

Cool Creek or McKenzie

Hill Formations
6 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Study Area

The Rush Springs aquifer includes about 4,970 square 

miles (mi2

) (3,181,003 acres) of bedrock and alluvium 

and terrace deposits located in Blaine, Caddo, Canadian, 

Comanche, Custer, Dewey, Ellis, Grady, Kiowa, Major, Roger 

Mills, Stephens, Washita, and Woodward Counties (fig. 1). 

The physiography of the Rush Springs aquifer is characterized 

by gently rolling hills that are dissected by incised deep 

drainage channels and surface-water features. Gypsum beds 

in the western part of the study area create erosion-resistant 

caprocks that form steep-sided ledges when located near 

alluvial valleys (Becker and Runkle, 1998). Land-surface 

altitudes in the Rush Springs aquifer (fig. 4) range from about 

1,100 to 2,400 ft above the North American Vertical Datum of 

1988 (NAVD 88) (USGS, 2017a). 

The northern and northeastern boundary of the Rush 

Springs aquifer includes the water-bearing portions of the 

Marlow Formation (Neel and others, 2018) situated west 

of the North Canadian River alluvium and terrace deposits 

(fig. 2). The northwestern boundary is the Ogallala Formation 

of Tertiary age. The southwestern boundary is the geologic 

contact with the Dog Creek Shale of Permian age. The 

southern and southeastern boundaries are the erosional extent 

of the Rush Springs Formation defined by Becker and Runkle 

(1998). The Rush Springs aquifer dips south-southwest and 

becomes buried westward. Neel and others (2018) defined 

the western boundary of this aquifer based on an increase in 

total dissolved solids, but that boundary was modified for this 

study to align with the overlying surface-watershed boundaries 

defined by the National Hydrography Dataset (USGS, 2017b). 

This modification was used so that the groundwater model 

could account for runoff that would otherwise have been 

routed outside the aquifer area.

The primary streams that drain the Rush Springs aquifer 

include the Canadian and Washita Rivers (fig. 1) (Tanaka 

and Davis, 1963; Ellis and others, 2017; Neel and others, 

2018). Additionally, the Rush Springs aquifer includes a 

number of smaller streams and tributaries to these rivers. 

Mean annual streamflow data (USGS, 2017c) recorded 

at streamgages (fig. 1; table 1) are summarized in table 2. 

Although the Bridgeport streamgage (07228500) is located 

about 2.5 miles (mi) downstream from the study area, flows 

from this streamgage are included because it is near the 

aquifer. Streamgage data are not available for tributaries of 

the Washita River other than for the Fort Cobb streamgage 

below the Fort Cobb Reservoir (07326000) (fig. 1; table 1); 

however, it is estimated that these tributaries carry only minor 

streamflows. 

The climate of the study area is classified as semi-arid, 

and mean annual temperatures for the period 1905–2015 

ranged from about 58 degrees Fahrenheit in the northern part 

of the study area to 61 degrees Fahrenheit in the southern 

part (Neel and others, 2018). The mean annual precipitation 

for the period 1905–2015 was 28.2 inches (in.), with a period 

of above-mean annual precipitation between 1985 and 2008 

(Neel and others, 2018). For the period 1905–2015, the 

greatest mean monthly precipitation (4.4 in.) occurred in May, 

and the least mean monthly precipitation (1.0 in.) occurred in 

January (Neel and others, 2018). 
Introduction 7

laf18-0888_fig 04

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

0 10 20 30 MILES

0 10 20 30 KILOMETERS

High: 2,404

Low: 1,107

Land­surface altitude, in feet above North 

American Vertical Datum of 1988

Rush Springs aquifer boundary

EXPLANATION

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Stinking

Creek Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

North Fork Red River

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Rainy Mountain

Creek

North Canadian River

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Stinking

Creek Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

North Fork Red River

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Rainy Mountain

Creek

North Canadian River

Canadian River

Turkey

Creek

Cavalry

Creek

Figure 4. Land-surface altitudes of the Rush Springs aquifer study area, western Oklahoma.
8 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 1. Location, period of record, and coefficient of variation for selected streamgages in the Rush Springs aquifer study area, 

western Oklahoma.

[USGS, U.S. Geological Survey; M/Y, month/year; --, no analysis performed]

USGS 

station 

number 

(fig. 1)

Station 

identifier Station name

Latitude

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain gaps) 

Coefficient of 

variation of 

streamgage 

data during 

study period 

(1979–2015)

Begin End

Continuous-record streamgages (USGS, 2017c)

07228500 Bridgeport 

streamgage

Canadian River at Bridgeport, Okla. 35.26422 -100.24179 10/1944 present 0.08

07324200 Hammon streamgage Washita River near Hammon, Okla. 35.47310 -100.12095 10/1969 present 0.08

07324400 Foss streamgage Washita River near Foss, Okla. 35.65644 -99.30621 3/1956 present --

07325000 Clinton streamgage Washita River near Clinton, Okla. 35.42227 -99.96928 10/1935 present 0.08

07325500 Carnegie streamgage Washita River at Carnegie, Okla. 35.16811 -99.50731 5/1947 9/2006 0.08

07325800 Cobb Creek 

streamgage

Cobb Creek near Eakly, Okla. 34.88950 -99.30700 10/1968 present 0.09

07325850 Lake Creek 

streamgage

Lake Creek near Eakly, Okla. 35.01172 -99.90371 10/1969 present 0.08

07325860 Willow Creek 

streamgage

Willow Creek near Albert, Okla. 34.91423 -99.11397 10/1970 present 0.08

07326000 Fort Cobb streamgage Cobb Creek near Fort Cobb, Okla. 35.29061 -98.59423 10/1939 present --

07326500 Anadarko streamgage Washita River at Anadarko, Okla. 34.63813 -99.10369 1/1903 present 0.08

07327447 Cement streamgage Little Washita River near Cement, 

Okla.

34.63785 -98.99869 2/1992 present 0.08
Introduction 9

Table 2. Mean annual streamflow and mean annual base flow for selected streamgages in and near the Rush Springs aquifer study 

area, western Oklahoma, 1979–2015.—Continued

[Annual base flow computed by using a base-flow separation code (BFI; Wahl and Wahl, 1995) integrated into the U.S. Geological Survey Groundwater 

Toolbox (Barlow and others, 2015); ft3/s, cubic feet per second; %, percent; acre-ft/yr, acre-feet per year; --, data not available or not applicable]

Year

Bridgeport streamgage 

(07228500) on the 

Canadian River

Hammon streamgage 

(07324200) on the 

Washita River

Foss streamgage 

(07324400) on the 

Washita River

Clinton streamgage 

(07325000) on the 

Washita River

Mean 

streamflow

(ft3

/s)

Mean 

base flow

Mean 

streamflow

(ft3/s)

Mean 

base flow

Mean 

streamflow

(ft3/s)

Mean 

base flow

Mean 

streamflow

(ft3/s)

Mean 

base flow

ft3

/s % 

(BFI) ft3

/s % 

(BFI) ft3

/s % 

(BFI) ft3

/s % 

(BFI)

1979 180.1 63.4 35.2 29.4 16.9 57.6 19.1 5.9 30.9 48.2 19.3 40.0

1980 221.2 73.5 33.2 37.3 14.1 37.7 46.2 9.9 21.3 71.4 31.5 44.1

1981 135.4 56.4 41.7 4.5 1.6 35.1 9.9 7.1 71.5 26.3 14.3 54.6

1982 346.5 100.1 28.9 106.9 19.4 18.2 116.2 49.4 42.5 199.9 103.7 51.9

1983 456.5 139.7 30.6 47.7 29.4 61.6 101.0 57.8 57.3 157.4 89.8 57.1

1984 160.7 131.9 82.1 21.0 13.2 62.9 7.4 6.6 89.1 30.3 24.6 81.0

1985 146.8 64.1 43.7 14.8 8.9 60.1 10.5 9.3 88.5 22.1 16.4 74.3

1986 557.2 117.1 21.0 77.6 32.2 41.4 56.5 12.5 22.0 217.4 60.8 28.0

1987 801.1 254.8 31.8 -- -- -- 246.3 121.4 0.0 336.3 181.6 54.0

1988 472.7 189.1 40.0 -- -- -- -- -- -- 174.7 127.6 73.1

1989 424.7 123.2 29.0 -- -- -- 9.1 8.8 0.0 279.2 177.1 63.4

1990 260.2 136.7 52.5 96.7 44.9 46.5 73.5 32.9 44.7 145.3 100.2 68.9

1991 136.9 90.7 66.3 32.1 20.6 64.0 36.7 11.5 31.2 82.3 44.1 53.6

1992 229.3 130.5 56.9 35.7 26.2 73.3 40.3 12.7 31.5 90.8 53.8 59.3

1993 416.5 176.8 42.5 65.6 46.3 70.6 104.6 53.4 51.0 183.8 123.5 67.2

1994 184.7 102.3 55.4 20.3 13.4 65.8 5.6 4.4 78.7 36.8 20.7 56.2

1995 483.7 164.5 34.0 80.2 31.3 39.0 95.4 40.7 42.6 270.8 119.0 43.9

1996 382.2 170.1 44.5 86.7 49.3 56.9 143.4 60.1 41.9 341.5 173.7 50.9

1997 619.3 249.1 40.2 294.4 184.9 62.8 390.5 188.1 48.2 692.3 471.1 68.0

1998 450.8 251.7 55.8 209.3 153.8 73.5 221.4 106.0 47.9 345.1 222.9 64.6

1999 411.1 230.9 56.2 119.1 88.3 74.1 120.0 53.7 44.7 190.2 114.6 60.3

2000 383.1 192.9 50.3 77.2 51.7 66.9 69.3 24.7 35.6 127.4 71.3 56.0

2001 372.0 227.1 61.1 112.1 68.9 61.5 150.0 73.8 49.2 211.3 150.8 71.4

2002 218.9 144.9 66.2 47.9 28.8 60.2 6.3 5.2 82.4 32.4 21.4 66.1

2003 170.3 118.7 69.7 54.7 32.6 59.6 47.4 14.1 29.7 65.0 35.8 55.0

2004 248.3 119.7 48.2 43.2 26.5 61.4 25.8 11.8 45.7 59.7 29.9 50.1

2005 300.2 162.1 54.0 55.4 37.2 67.2 79.1 29.8 37.6 116.3 70.8 60.8

2006 82.6 45.4 55.0 14.6 9.0 61.8 11.1 10.1 90.4 24.2 19.5 80.6

2007 718.7 191.2 26.6 128.5 57.8 44.9 142.3 52.7 37.1 234.1 101.4 43.3

2008 431.8 156.6 36.3 103.7 55.1 53.1 84.6 18.4 21.7 167.5 80.4 48.0

2009 261.5 149.1 57.0 51.4 38.3 74.4 52.7 13.9 26.4 97.4 46.1 47.3

2010 207.7 114.3 55.0 62.0 35.0 56.4 40.9 18.4 45.0 77.0 46.8 60.8

2011 68.0 40.2 59.1 12.5 10.6 84.7 13.0 12.5 96.2 22.0 19.4 88.2

2012 103.3 56.3 54.5 3.0 0.6 20.2 5.8 5.0 86.1 12.6 8.1 64.1

2013 112.6 49.3 43.8 0.9 0.0 0.6 4.5 3.4 76.4 7.4 4.3 57.6

2014 82.7 34.9 42.1 0.4 0.0 0.0 3.5 2.8 79.7 7.4 3.5 47.4

2015 554.0 177.3 32.0 95.9 34.3 35.7 31.6 4.5 14.2 117.6 28.9 24.6

Mean 318.7 135.0 46.8 66.0 37.7 53.2 72.8 32.0 48.3 143.8 81.9 57.7

Mean, in 

acre-ft/yr

230,756 97,761 47,754 27,270 52,719 23,186 104,122 59,261
10 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 2. Mean annual streamflow and mean annual base flow for selected streamgages in and near the Rush Springs aquifer study 

area, western Oklahoma, 1979–2015.—Continued

[Annual base flow computed by using a base-flow separation code (BFI; Wahl and Wahl, 1995) integrated into the U.S. Geological Survey Groundwater 

Toolbox (Barlow and others, 2015); ft3/s, cubic feet per second; %, percent; acre-ft/yr, acre-feet per year; --, data not available or not applicable]

Year

Carnegie streamgage 

(07325500) on the 

Washita River

Cobb Creek streamgage 

(07325800) on 

Cobb Creek 

Lake Creek streamgage 

(07325850) on 

Lake Creek 

Willow Creek streamgage 

(07325860) on 

Willow Creek 

Mean 

streamflow

(ft3

/s)

Mean 

base flow

Mean 

streamflow

(ft3/s)

Mean 

base flow

Mean 

streamflow

(ft3/s)

Mean 

base flow

Mean 

streamflow

(ft3/s)

Mean 

base flow

ft3

/s % 

(BFI) ft3

/s % 

(BFI) ft3

/s % 

(BFI) ft3

/s % 

(BFI)

1979 208.0 70.2 33.8 11.3 7.2 64.2 -- -- -- -- -- --

1980 288.0 99.5 34.5 20.4 7.0 34.3 -- -- -- -- -- --

1981 151.1 46.9 31.0 18.1 6.3 34.9 -- -- -- -- -- --

1982 570.4 286.8 50.3 30.6 9.9 32.4 -- -- -- -- -- --

1983 491.3 175.9 35.8 23.2 9.1 39.2 -- -- -- -- -- --

1984 97.5 75.9 77.8 9.3 8.5 91.6 -- -- -- -- -- --

1985 237.2 95.5 40.3 16.0 9.2 57.1 -- -- -- -- -- --

1986 793.8 238.6 30.1 60.8 16.1 26.4 -- -- -- -- -- --

1987 868.4 465.5 53.6 60.6 20.3 33.5 -- -- -- -- -- --

1988 526.9 307.4 58.3 22.2 11.9 53.8 -- -- -- -- -- --

1989 683.3 298.2 43.6 35.4 15.2 42.9 -- -- -- -- -- --

1990 533.8 273.1 51.2 27.5 18.8 68.5 -- -- -- -- -- --

1991 347.1 116.7 33.6 22.4 14.1 63.0 -- -- -- -- -- --

1992 482.8 195.6 40.5 37.6 18.8 50.1 -- -- -- -- -- --

1993 918.0 457.7 49.9 52.4 21.8 41.7 -- -- -- -- -- --

1994 225.3 103.8 46.1 31.4 16.9 54.0 -- -- -- -- -- --

1995 949.3 337.5 35.6 60.2 23.6 39.2 -- -- -- -- -- --

1996 696.7 383.3 55.0 32.0 19.0 59.3 -- -- -- -- -- --

1997 1,295.8 884.8 68.3 55.6 26.6 47.8 -- -- -- -- -- --

1998 674.0 440.3 65.3 34.9 20.9 59.7 -- -- -- -- -- --

1999 429.8 254.1 59.1 30.4 18.4 60.4 -- -- -- -- -- --

2000 468.5 208.5 44.5 41.3 18.4 44.6 -- -- -- -- -- --

2001 446.2 290.5 65.1 30.8 18.8 61.1 -- -- -- -- -- --

2002 173.1 94.3 54.5 24.5 16.0 65.1 -- -- -- -- -- --

2003 189.4 114.9 60.7 16.4 12.8 77.8 -- -- -- -- -- --

2004 355.1 116.8 32.9 28.2 14.2 50.4 -- -- -- -- -- --

2005 318.3 171.3 53.8 35.2 15.7 44.8 8.4 3.8 45.3 2.8 1.8 64.8

2006 -- -- -- 15.5 12.3 79.1 3.4 2.6 76.6 1.7 1.3 79.3

2007 -- -- -- 77.3 29.2 37.8 22.1 5.9 26.9 8.3 3.0 36.7

2008 -- -- -- 47.8 23.3 48.7 17.0 8.3 48.8 6.9 3.4 48.3

2009 -- -- -- 27.4 17.2 62.6 10.5 6.1 58.4 4.7 2.9 62.0

2010 -- -- -- 19.1 14.7 76.7 6.5 5.3 80.7 3.4 2.2 64.6

2011 -- -- -- 13.8 8.6 62.4 3.8 2.5 66.8 2.6 1.6 63.9

2012 -- -- -- 12.6 8.6 68.4 2.8 1.8 65.3 2.0 1.2 57.2

2013 -- -- -- 14.3 8.9 62.1 5.6 2.0 34.6 2.3 1.2 49.5

2014 -- -- -- 11.8 7.0 59.7 4.2 2.1 50.2 2.8 1.5 53.4

2015 -- -- -- 32.9 13.1 39.8 12.2 3.8 31.2 -- -- --

Mean 497.0 244.6 48.3 30.8 15.1 53.9 8.8 4.0 53.2 3.8 2.0 58.0

Mean, in 

acre-ft/yr

359,814 177,060 22,329 10,924 6,351 2,914 2,715 1,453
Introduction 11

Table 2. Mean annual streamflow and mean annual base flow for selected streamgages in and near the Rush Springs aquifer study 

area, western Oklahoma, 1979–2015.—Continued

[Annual base flow computed by using a base-flow separation code (BFI; Wahl and Wahl, 1995) integrated into the U.S. Geological Survey Groundwater 

Toolbox (Barlow and others, 2015); ft3/s, cubic feet per second; %, percent; acre-ft/yr, acre-feet per year; --, data not available or not applicable]

Year

Fort Cobb streamgage 

(07326000) below the 

Fort Cobb Reservoir

Anadarko streamgage 

(07326500) on the 

Washita River

Cement streamgage 

(07327447) on the 

Little Washita River

Mean 

streamflow

(ft3

/s)

Mean 

base flow Mean 

streamflow

(ft3

/s)

Mean 

base flow

Mean 

streamflow

(ft3

/s)

Mean 

base flow

ft3

/s % 

(BFI) ft3

/s % 

(BFI) ft3

/s % 

(BFI)

1979 2.8 2.21 80.5 234.0 96.0 41.0 -- -- --

1980 11.9 2.12 17.8 318.0 132.7 41.7 -- -- --

1981 2.3 1.66 71.7 161.1 73.7 45.8 -- -- --

1982 62.6 9.68 15.5 685.9 463.5 67.6 -- -- --

1983 20.8 2.03 9.8 625.7 197.0 31.5 -- -- --

1984 9.0 3.37 37.2 141.3 119.0 84.2 -- -- --

1985 3.8 2.13 56.8 264.9 126.9 47.9 -- -- --

1986 78.7 5.1 6.5 913.4 424.3 46.5 -- -- --

1987 109.2 30.37 27.8 1,172.7 763.7 65.1 -- -- --

1988 44.1 4.29 9.7 648.4 412.1 63.5 -- -- --

1989 83.4 5.02 6.0 943.4 468.9 49.7 -- -- --

1990 78.0 2.93 3.8 685.9 360.3 52.5 -- -- --

1991 41.3 2.92 7.1 456.3 183.6 40.2 -- -- --

1992 57.6 11.92 20.7 615.3 307.2 49.9 48.7 28.7 --

1993 111.1 16.06 14.5 1,092.6 594.5 54.4 44.2 29.6 62.2

1994 45.7 14.51 31.7 312.7 169.7 54.3 18.0 12.9 64.5

1995 121.9 21.42 17.6 1,170.0 483.4 41.3 30.8 19.2 55.9

1996 34.8 3.03 8.7 771.9 450.6 58.4 13.3 10.0 69.2

1997 85.5 5.91 6.9 1,452.3 1,026.8 70.7 24.0 15.1 57.5

1998 54.0 5.47 10.1 820.9 534.8 65.1 40.1 28.0 65.7

1999 24.1 2.99 12.4 493.0 287.8 58.4 22.0 12.6 53.1

2000 56.2 4.86 8.6 593.2 231.3 39.0 22.4 11.6 40.5

2001 35.7 2.99 8.4 517.0 334.7 64.7 21.0 15.8 68.7

2002 9.0 2.53 27.9 212.5 116.7 54.9 9.4 6.4 61.6

2003 9.9 4.91 49.6 209.3 147.3 70.3 7.1 4.7 59.6

2004 14.7 3.05 20.7 405.0 138.2 34.1 8.7 5.5 52.1

2005 22.6 2.34 10.4 384.4 194.4 50.6 8.1 6.5 74.1

2006 6.4 1.75 27.4 146.6 87.8 59.9 7.2 2.7 32.7

2007 137.4 28.52 20.8 1,486.6 558.7 37.6 51.4 20.7 30.8

2008 65.0 4.68 7.2 628.3 314.4 50.0 18.0 12.0 61.5

2009 34.8 6.64 19.1 391.6 222.8 56.9 22.2 11.1 34.3

2010 23.4 2.36 10.1 315.7 164.8 52.2 17.1 10.3 49.8

2011 1.9 1.21 62.8 121.5 65.3 53.8 5.0 3.5 63.0

2012 2.1 1.52 71.4 111.6 54.1 48.4 5.5 2.9 45.5

2013 2.4 1.39 57.0 97.9 42.6 43.6 12.1 3.3 15.8

2014 1.9 0.95 50.8 73.2 37.6 51.3 3.3 2.0 49.6

2015 21.7 12.57 57.9 809.5 311.7 38.5 31.6 13.4 21.9

Mean 41.3 6.4 26.6 553.6 289.2 52.3 20.5 12.0 51.7

Mean, in 

acre-ft/yr

29,892 4,645 400,796 209,337 14,817 8,694
12 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Land-cover data for the Rush Springs aquifer were 

obtained from the CropScape database (National Agricultural 

Statistics Service [NASS], 2017) (figs. 5–6). This database 

included information about land-cover characteristics at a 

30-meter resolution for land overlying the Rush Springs 

aquifer for the period 2011–15. During this period, land 

cover was primarily for grass/pasture (52.2 percent) and 

cropland (31.7 percent). Winter wheat, which accounted for 

80.3 percent of cropland by area, was the dominant crop type 

overlying the Rush Springs aquifer. Cotton (2.8 percent), 

alfalfa (2.8 percent), rye (1.8 percent), and sorghum 

(1.8 percent) were the only other crop types accounting 

for at least 1 percent of cropland by area (figs. 5–6). About 

4.7 percent of cropland by area was fallow or idle. Although 

crop types may change on the basis of economic conditions 

and hydrologic factors such as flooding or drought conditions, 

the percentages of total crop land cover and individual crop 

types did not change much during the period 2011–15 for 

which data were available (NASS, 2017).

Conceptualization of Groundwater-Flow System

The Rush Springs aquifer conceptualized groundwaterflow system is a simplified description of the aquifer system 

accounting for (1) the definition of the aquifer geologic units, 

(2) major inflow and outflow sources between the aquifer and 

surrounding units (hydrologic boundaries), and (3) the amount 

of water that moves between each boundary (conceptual water 

budget) during the study period (table 3). The information 

from these components was used in the design, construction, 

and simulation of the groundwater model. 

Geologic Units

The Rush Springs aquifer includes alluvium and terrace 

deposits of Quaternary age and bedrock of Permian age; 

overlying and underlying confining units are of Permian age 

(figs. 2–3). The units of Quaternary age include the alluvium 

and terrace deposits of the Canadian and Washita Rivers and 

associated tributaries. The primary hydrogeologic units of 

Permian age include the Cloud Chief Formation, Whitehorse 

Group, and Dog Creek Shale. 

The Quaternary alluvium and terrace deposits of the 

Canadian River and Washita River and associated tributaries 

consist of sand, silt, and clay deposits (Tanaka and Davis, 

1963) that typically yield 200–400 gallons per minute (gal/min) 

but can yield as high as 1,000 gal/min (Fay, 1978). These 

deposits were formed by an initial period of downcutting of 

the stream channels into the bedrock units of Permian age 

and gradual filling with sand, silt, and clay sediments through 

subsequent cycles of erosion and deposition. The estimated 

thickness of the Canadian River alluvium and terrace deposits 

is about 120 ft (Ellis and others, 2017). The estimated 

thickness of the Washita River alluvium and terrace deposits 

is about 130 ft in Custer County (Fay, 1978) and as much as 90 ft

in Caddo County (Tanaka and Davis, 1963). The maximum 

thickness of the Deer Creek alluvium deposits is estimated to 

be 40 ft (Fay, 1978). The thickness of the alluvium underlying 

other tributaries to the Washita River has not been studied but 

is estimated to be 30 ft. 

The bedrock units of Permian age, or “red beds,” underlie 

most of the Quaternary alluvium and terrace deposits in the 

study area (figs. 2–3). These bedrock units are generally 

fine grained and are composed of reddish-brown to orangebrown fine- to very fine-grained sandstone, shale, and 

siltstone interbedded with gypsum and dolomite (Miller and 

Stanley, 2004). The Cloud Chief Formation is described as 

an interbedded reddish-brown to orange-brown shale (Carr 

and Bergman, 1976) that is not a substantial water source 

and only yields a few gallons of water per day (Tanaka and 

Davis, 1963). The estimated thickness of the Cloud Chief 

Formation ranges from 100 ft (Becker and Runkle, 1998) to 

more than 300 ft (Tanaka and Davis, 1963; Fay, 1978). The 

Cloud Chief Formation is exposed in Custer, Dewey, Roger 

Mills, and Washita Counties as erosional remnants on hills and 

upland areas and is a confining unit where it overlies the Rush 

Springs Formation. 

Stratigraphically below the Cloud Chief Formation is the 

Rush Springs Formation of the Whitehorse Group, which is 

the principal hydrogeologic unit of the Rush Springs aquifer. 

Well yields are spatially variable, ranging from less than 

50 gal/min in the western half of Custer County to between 

200 and 700 gal/min in eastern Custer County (Fay, 1978) 

and more than 1,000 gal/min in Caddo County (Tanaka and 

Davis, 1963). The Rush Springs Formation is typically a redto orange-brown cross-bedded sandstone (Carr and Bergman, 

1976) with calcite- or gypsum-cemented fine- to very finegrained quartz grains (Becker and Runkle, 1998). The Rush 

Springs Formation is between 200 and 560 ft thick in the 

western and southeastern parts of Custer County, respectively 

(Fay, 1978). 

The Marlow Formation of the Whitehorse Group 

underlies the Rush Springs Formation and consists of 

interbedded sandstones, siltstones, mudstones, gypsumanhydrite, and dolomite (Becker and Runkle, 1998). The 

Marlow Formation forms the lower part of the Rush Springs 

aquifer, is typically well-cemented, has low hydraulic 

conductivity, and in most areas yields only 1–2 gal/min (Tanaka 

and Davis, 1963). As a result, the Marlow Formation—

generally 0.5–1.0 mi wide—limits the water that is exchanged 

laterally with adjoining hydrogeologic units. The Marlow 

Formation thickness can be as great as 128 ft in the study area 

(Tanaka and Davis, 1963).

The Dog Creek Shale consists of red clay and shale with 

intermixed gypsum and dolomite (Six, 1930) and, therefore, 

has a very low permeability and is not a predominant source 

of water (Mogg and others, 1960; Wood and Stacy, 1965). 

The Dog Creek Shale forms the underlying confining unit 

to the Rush Springs aquifer and is about 400 ft thick in 

Blaine County and about 90 to 115 ft thick in Caddo and 

Grady Counties.
Introduction 13

laf18-0888_fig 05

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Land cover from National Agricultural Statistics Service (2017);

Shaded relief derived from USGS (2017a)

0 10 20 30 MILES

0 10 20 30 KILOMETERS

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir 

surface watershed

boundary (USGS, 2017b) 

Grass/pasture

Developed

Forest

Shrubs/range

Other (water, wetland)

Winter wheat

Cotton

Alfalfa

Rye

Sorghum

Fallow/idle

Other crops

Land cover (2011–15 average) Crop cover (2011–15 average),

by type

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Figure 5. Land and crop cover over the Rush Springs aquifer, western Oklahoma, 2011–15.
14 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 06

Crop-cover type, 2011–15, in percent

Total area: 1,006,250 acres

Land-cover type, 2011–15, in percent

Total area: 3,172,746 acres

Other crops 

5.7

Alfalfa 

Sorghum 

Cotton Rye

Fallow/idle 

Winter wheat

80.3

4.7

1.8 2.8 2.8 1.8

Other

0.4

Crops

31.7

Grass/pasture

52.2

Shrubs/

range Developed 

Forest 

8.4

4.9 2.4

Note: Components may not sum to totals because of rounding. 

Land­cover type, 2015 (National 

 Agriculture Statistics

 Service, 2017)

 Developed

 Forest

 Shrubs/range

 Grass/pasture

 Other (water, wetland)

 Crops—2011–2015 average

 Winter wheat

 Cotton

 Alfalfa

 Rye

 Sorghum

 Fallow/idle

 Other crops

EXPLANATION

Figure 6. Land and crop cover over the Rush Springs aquifer, western Oklahoma, 2011–15.

Table 3. Conceptual water budget for the Rush Springs aquifer, 

western Oklahoma, 1979–2015.

[--, negligible change or amount; outflows do not sum to total because of 

rounding]

Water-budget category

Amount

(acre-feet 

per year)

Percentage 

of inflows 

or outflows1

Inflows

Recharge2 556,675 97%

Lateral flow1 16,700 3%

Lakebed seepage -- --

Total inflow 573,375 100%

Outflows

Stream seepage1 259,161 45%

Seeps and springs 155,507 27%

Saturated-zone evapotranspiration (ETg) 92,945 16%

Groundwater use 65,763 11%

Net change in groundwater storage -- --

Total outflow 573,376 100%

1

Stream seepage and lateral flow represent net terms. 

2

Equals about 2.1 inches per year over the aquifer area of 3,181,003 acres.
Introduction 15

Recharge

Groundwater recharge, in this report, is defined as water 

that infiltrates from the land surface through the unsaturated 

zone and to the top of the water table. Other processes that 

may be included in a broader definition of recharge, such 

as stream seepage, lateral groundwater flow from adjacent 

hydrogeologic units, or lakebed seepage, are accounted 

for separately in the Rush Springs aquifer conceptual 

water budget. 

Recharge rates are controlled by a number of factors, 

including precipitation rates, evapotranspiration (ET) rates, 

unsaturated-zone permeability and moisture capacity, and 

slope of the land surface. Although recharge rates are difficult 

to measure because of high spatial and temporal variability, 

methods using a mass balance, streamflow-hydrograph 

techniques, environmental tracers, physical measurements, 

and computer code have been used to estimate recharge rates. 

Estimates of recharge for the study area were obtained from 

Neel and others (2018) and the soil-water-balance (SWB) code 

(Westenbroek and others, 2010), a mass-balance method. 

Using the RORA Method to Estimate Recharge

Neel and others (2018) used the RORA method to 

estimate annual recharge to the Rush Springs aquifer. Selected 

sites included streamgages on Barnitz Creek, Cobb Creek 

(07325800), Deer Creek, Lake Creek (07325850), Little 

Washita River, and Willow Creek (07325860). The RORA 

method uses a streamflow-recession-curve displacement 

method to estimate groundwater recharge (Rorabaugh, 1964; 

Rutledge, 1998). This method assumes an idealized aquifer 

with uniform hydraulic parameters and thickness and a fully 

penetrating stream where the streambed altitude is equal to 

the aquifer-base altitude. Mean annual recharge rates ranged 

from 0.24 in. at Barnitz Creek for the period 1946–63 to 

2.26 in. at Little Washita River for the periods 1969–78 and 

2005–15 (Neel and others, 2018). Recharge at the Barnitz 

Creek streamgage may be low because of the presence of the 

Cloud Chief Formation confining unit that may limit areal 

recharge in the area of the streamgage (Neel and others, 2018). 

The aquifer-base altitude is generally at least 100 ft below 

the streambed altitude at each streamgage; therefore, the 

streambed is not fully penetrating through the aquifer.

Using the Soil-Water-Balance Code to Estimate Recharge

Spatially distributed recharge to the Rush Springs 

aquifer was computed for each month of the study period 

by using the SWB code (Westenbroek and others, 2010). 

The SWB code is based on a modified Thornthwaite-Mather 

method (Thornthwaite and Mather, 1957) and requires 

gridded climatological and landscape-characteristic data 

inputs including precipitation, temperature, soil-water storage 

capacity, hydrologic soil group, land-surface gradient, and 

land-cover type. The SWB code uses a mass-balance approach 

to compute gridded recharge as the difference between 

sources and sinks for each grid cell, while accounting for the 

cumulative effects of the change in soil moisture. The massbalance equation (modified from Westenbroek and others, 

2010) has the form:

R P = + ( ) S R + i o − + ( ) Int R + P S et − ∆ m 

(1)

where

R is recharge,

P is precipitation,

S is snowmelt,

Ri is surface runoff inflow,

Int is plant interception,

Ro is surface runoff outflow,

Pet is potential evapotranspiration, and

ΔSm is the change in soil moisture.

SWB-estimated recharge for the Rush Springs aquifer 

was previously computed by Neel and others (2018). 

However, because the aquifer areal extent for this report 

was larger than that of Neel and others (2018), SWBestimated recharge was recomputed by using the same input 

datasets for this larger areal extent. Daily climate data, 

including precipitation (P) and minimum and maximum air 

temperature, were obtained for 33 climate stations (National 

Climatic Data Center, 2017; Oklahoma Mesonet, 2017) 

(table 4) and interpolated to a grid using a 500-ft uniform 

spacing. Soil properties (soil-water storage capacity and 

hydrologic soil group) and land cover were derived from 

the Digital General Soil Map database (STATSGO; Natural 

Resources Conservation Service, 2015), which is an inventory 

of generalized soil characteristics at a 1:250,000 scale. 

Precipitation and snowmelt (S) were differentiated, based on 

the daily minimum and maximum air temperatures. Surface 

runoff inflow (Ri

) was calculated by using a flow-direction 

grid derived from a digital elevation model (DEM) (USGS, 

2017a) whereby values representing land-surface altitudes 

were assigned to each SWB grid cell and runoff was routed to 

downslope cells. To ensure correct routing of surface runoff 

and to eliminate areas of internal drainage that can result in 

unrealistic amounts of recharge, depressions in the DEM 

(USGS, 2017a) were filled. Plant interception (Int) occurs 

when precipitation is captured by vegetation prior to reaching 

the top of the soil profile, and Int was specified for each landcover type during the growing season. Surface runoff outflow 

(Ro

) was calculated by using Natural Resources Conservation 

Service curve numbers that relate rainfall and runoff 

(Westenbroek and others, 2010). Potential evapotranspiration 

(Pet) in the SWB code was calculated by using methods from 

Hargreaves and Samani (1985), discussed further in the 

“Saturated-Zone Evapotranspiration” section of this report.
16 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 4. Selected climate stations in and near the Rush Springs aquifer study area, western Oklahoma.

[M/D/Y, month/day/year. Present is defined as 2015 for the period of record]

Station 

identifier Station name Latitude(decimal degrees)

Longitude

(decimal degrees)

Period of record (may contain gaps) 

or single measurement date 

(M/D/Y)

Begin End

Climate stations (Oklahoma Mesonet, 2017) used by the Soil-Water-Balance code (Westenbroek and others, 2010)

ACME Acme Mesonet 34.80833 -98.02325 1/1/2009 present 

APAC Apache Mesonet 34.91418 -98.29216 2/1/2009 present 

BESS Bessie Mesonet 35.40185 -99.05847 2/1/2009 present 

BUTL Butler Mesonet 35.59150 -99.27059 2/2/2009 present 

CAMA Camargo Mesonet 36.02866 -99.34652 2/1/2009 present 

CHIC Chickasha Mesonet 35.03236 -97.91446 2/1/2009 present 

ELRE El Reno Mesonet 35.54848 -98.03654 2/1/2009 present 

FAIR Fairview Mesonet 36.26353 -98.49766 2/1/2009 present 

FTCB Fort Cobb Mesonet 35.14887 -98.46607 2/1/2009 present 

HINT Hinton Mesonet 35.48439 -98.48151 2/1/2009 present 

HOBA Hobart Mesonet 34.98971 -99.05283 2/1/2009 present 

KETC Ketchum Ranch Mesonet 34.52887 -97.76484 2/1/2009 present 

MINC Minco Mesonet 35.27225 -97.95553 2/1/2009 present 

NINN Ninnekah Mesonet 34.96774 -97.95202 2/1/2009 present 

PUTN Putnam Mesonet 35.89904 -98.96038 2/1/2009 present 

RETR Retrop Mesonet 35.12275 -99.36001 2/1/2009 present 

SEIL Seiling Mesonet 36.19033 -99.04030 2/1/2009 present 

WATO Watonga Mesonet 35.84185 -98.52615 2/1/2009 present 

WEAT Weatherford Mesonet 35.50830 -98.77509 2/1/2009 present 

WOOD Woodward Mesonet 36.42329 -99.41682 2/1/2009 present 

Climate stations (National Climatic Data Center, 2017) used by the Soil-Water-Balance code (Westenbroek and others, 2010)

USC00340224 Anadarko 35.3392 -99.8769 12/31/1892 present 

USC00340260 Apache 35.2164 -99.8628 6/30/1909 present 

USC00340332 Arnett 35.0522 -99.5125 3/22/1911 present 

USW00003932 Clinton-Sherman Airport 35.6103 -100.1022 8/16/1958 present 

USC00342039 Colony 34.8847 -99.2964 8/31/1983 present 

USC00342125 Cordell 34.9003 -99.8614 6/30/1936 present 

USC00343497 Geary 34.9578 -99.9414 11/1/1911 present 

USC00345090 Leedey 35.3061 -99.6275 7/31/1941 present 

USC00345581 Marlow 35.2 -100.25 10/1/1900 present 

USC00349086 Union City 35.3008 -98.9958 4/17/1914 present 

USC00349364 Watonga 35.215 -100.2503 10/31/1902 present 

USC00349422 Weatherford 35.0258 -99.1058 12/31/1904 present 

USC00349760 Woodward 34.9894 -99.0525 9/30/1895 present 
Introduction 17

Root-zone depths represent the maximum depth to 

which various types of vegetation will grow and are classified 

based on land-cover and soil type. Greater plant root-zone 

depths result in the increased uptake of water in the soilmoisture zone, thus decreasing recharge, whereas smaller 

values increase recharge to the water table. Winter wheat, 

the dominant crop type overlying the Rush Springs aquifer 

(NASS, 2017; figs. 5–6), has mean and maximum rooting 

depths of about 1.0 and 4.6 ft, respectively, in Oklahoma 

(Patrignani and others, 2012; David Marburger, Oklahoma 

State University, written commun., 2018). To account for this 

root-zone depth range, the default root-zone depth for each 

land-cover type was scaled by 70 percent, which resulted in 

root-zone depths for crops between 1.4 and 2.1 ft. 

The SWB-estimated mean annual recharge for the study 

period was about 1.7 inches per year (in/yr), or 5.6 percent of 

the mean annual precipitation of 30 in. (fig. 7). For the Fort 

Cobb Reservoir surface watershed (hereafter, “Fort Cobb 

Reservoir watershed”)—defined by a 10-digit hydrologic 

unit code (USGS, 2017b)—the mean annual recharge for the 

study period was about 1.8 in/yr. The minimum and maximum 

SWB-estimated annual recharge for the study period were 

about 0.03 in/yr (2003) and 4.6 in/yr (2007), respectively 

(fig. 7). Mean monthly recharge tended to be greatest from 

January through March and in May (fig. 8B). Recharge in 

these months corresponds to between 12 and 15 percent 

of mean annual precipitation. Mean monthly recharge was 

least between July and September. Recharge in these months 

corresponds to between 1 and 4 percent of mean annual 

precipitation. 

Spatially, mean annual recharge for the study period was 

greatest in the southeastern part of the aquifer, the alluvium, 

0

275

550

825

1,100

1,375

1,650

1,925

2,200

0

1

2

3

4

5

6

7

8

0

6

12

18

24

30

36

42

48

1979198219851988199119941997200020032006200920122015

Annual recharge, in thousands of acre-feet

Annual precipitation, in inches

Annual recharge, in inches

Year

Mean annual recharge (1979–2015)

Mean annual precipitation (1979–2015)

Annual mean precipitation

Annual mean recharge

EXPLANATION

Figure 7. Annual precipitation and recharge computed by using the Soil-Water-Balance code 

(Westenbroek and others, 2010) for the Rush Springs aquifer, western Oklahoma, 1979–2015. 
18 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

and the terrace between the Canadian and North Canadian 

Rivers (fig. 9); this terrace contains windblown sand deposits 

and dunes that allow for rapid infiltration of precipitation (Six, 

1930; Fay, 1962). Greater recharge occurred in the alluvial 

and terrace deposits than in the bedrock deposits because of a 

more sandy soil type in the alluvium and terrace deposits that 

had a lower available water capacity (Westenbroek and others, 

2010, table 7). Recharge was least where the Cloud Chief 

Formation was present (fig. 2), particularly in western Custer, 

southwestern Dewey, and eastern Roger Mills Counties (fig. 9). 

Soil-water properties are generalized on a county scale in the 

STATSGO database; thus, changes in recharge can occur at 

county boundaries between hydrologic soil or available water 

capacity groups, such as the recharge change in an area where 

the Canadian River runs parallel to the North Canadian River 

in western Blaine County (fig. 9). 

Mean annual recharge rates estimated from the SWB 

code were compared to published estimates of mean annual 

recharge. Tanaka and Davis (1963) estimated mean annual 

recharge for the Fort Cobb Reservoir watershed to be 2.8 in/yr, 

or about 10 percent of mean annual precipitation for the 

period 1953–56. Precipitation during three of the four years 

(1953–56) of the Tanaka and Davis (1963) study was below 

the mean annual precipitation for the period of 1905–2015 

(28.2 in/yr) estimated from Neel and others (2018). Becker 

and Runkle (1998) estimated mean annual recharge between 

March 1989 and January 1991 to be 1.8 in/yr, or about 

7 percent of mean annual precipitation for that period. That 

recharge value was based on the assumption that aquifer 

recharge was equal to stream discharge between March 1989 

and January 1991 (Becker and Runkle, 1998). The mean 

annual precipitation between March 1989 and January 1991 

was estimated at 29 in/yr (Becker and Runkle, 1998), which 

is about 3 percent greater than mean annual precipitation 

from Neel and others (2018). Becker (1998) estimated a mean 

recharge of 1.3 in/yr for the Rush Springs aquifer through 

calibration of a steady-state groundwater model. Wyatt and 

others (2017) estimated a mean annual recharge of 2.6 in/yr by 

using soil-moisture drainage rates at a 60-centimeter (23.6 in.) 

depth below land surface to approximate recharge based on 

soil-moisture data from five climate stations between 1998 

and 2014. This recharge estimate is about 9 percent of mean 

annual precipitation estimated from Neel and others (2018). 

The soil-moisture-based drainage results could overstate 

recharge in locations where plant root-zone depths exceed 

23.6 in., or where the water table is near this depth below 

land surface. 

The mean annual recharge rate estimated by using 

the SWB code for this study is generally lower than these 

published estimates of recharge for the Rush Springs aquifer. 

The average of mean annual recharge rates from Tanaka and 

Davis (1963), Becker and Runkle (1998), Becker (1998), and 

Wyatt and others (2017) is about 2.1 in/yr, or approximately 

7 percent of precipitation from Neel and others (2018). When 

applied across the land-surface area of the Rush Springs 

aquifer (3,181,003 acres), the mean annual recharge of 2.1 in/yr

A

B

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Month

Mean monthly precipitation, in inches per month Mean monthly recharge, in inches per month

Month

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Study period (1979–2015)

Study period (1979–2015)

Figure 8

0

0.05

0.10

0.15

0.20

0.25

0.30

EXPLANATION

EXPLANATION

Figure 8. Mean monthly A, precipitation and B, recharge 

computed by using the Soil-Water-Balance code 

(Westenbroek and others, 2010) for the Rush Springs 

aquifer, western Oklahoma, 1979–2015.
Introduction 19

laf18-0888_fig 09

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

0 10 20 30 MILES

0 10 20 30 KILOMETERS

EXPLANATION

Mean annual recharge (1979–2015), in inches

0.01 to 0.50

0.51 to 1.00

1.01 to 2.00

2.01 to 4.00

> 4.00

Rush Springs aquifer boundary

Western extent of equal­proportionate­share 

aquifer boundary—Modified from Neel 

and others (2018)

Fort Cobb Reservoir surface watershed

boundary (USGS, 2017b) 

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Fort Cobb 

Reservoir

Foss

Reservoir

Figure 9. Mean annual groundwater recharge computed by using the Soil-Water-Balance code (Westenbroek and 

others, 2010) for the Rush Springs aquifer, western Oklahoma, 1979–2015.
20 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

corresponds to a mean annual recharge volume of about 

556,675 acre-feet per year (acre-ft/yr), or about 97 percent of 

aquifer inflows in the conceptual water budget (table 3). 

Recharge from Crop Irrigation

Additional recharge from crop irrigation (sometimes 

called irrigation return flows) could also be expected to 

infiltrate through the unsaturated zone to the water table. 

Tanaka and Davis (1963) determined that recharge from 

irrigation was probably small in the Rush Springs aquifer 

study area because the irrigation method used is application 

of water from sprinklers to only the upper few inches of soil. 

However, studies in Nebraska have found that irrigation 

increases groundwater recharge (Roark and Healy, 1998; 

McMahon and others, 2011), and recharge rates are greater 

in irrigated cropland areas compared to natural rangeland or 

nonirrigated cropland (Scanlon and others, 2005). Stanton 

and others (2010) described annual increases in recharge of 

0.13–0.30 in/yr in irrigated cropland compared to nonirrigated 

cropland (Dugan and Zelt, 2000) and 1.3–1.6 in/yr in irrigated 

cropland compared to rangeland (McMahon and others, 2006). 

However, the soil properties (soil-water storage capacity and 

hydrologic soil group), irrigation methods, and irrigation 

rates in Nebraska may differ from cropland areas in the Rush 

Springs aquifer. A constrained range for the recharge from 

crop irrigation could not be established; thus, this term was not 

quantified in the conceptual water budget. 

Saturated-Zone Evapotranspiration

ET is the process by which water is transferred to the 

atmosphere directly by evaporation or indirectly by plant 

transpiration. This process occurs in both the saturated 

and soil-moisture (unsaturated) zones typically in areas 

where the water table is at or near land surface, such as 

lakes or wetlands. The soil-moisture-zone component of 

ET was not considered to be a part of the conceptual water 

budget because it occurs before infiltrating precipitation 

has become groundwater recharge. For this investigation, 

evapotranspiration by plants from the saturated zone—or 

saturated-zone evapotranspiration (ETg)—was quantified in 

the water budget. The ETg rate was estimated by using the 

SWB code, a daily groundwater-level fluctuation method 

from White (1932), and previously published literature. The 

ETg area (63,734 acres) was defined by using the National 

Wetlands Inventory (U.S. Fish and Wildlife Service, 2017). 

ETg rates were assumed to be proportional to the 

difference between potential ET (Pet; eq. 1) and actual ET (Aet) 

computed by using the SWB code. Pet was calculated by using 

the Hargreaves and Samani (1985) method and represents the 

maximum rate at which groundwater could be evapotranspired 

with unlimited soil-moisture availability. The SWB code 

computes the change in soil moisture whereby Pet is subtracted 

from daily precipitation. If the resulting value is positive, Aet

equals Pet. If the resulting value is negative, Aet is limited to 

the change in soil moisture and is less than Pet. Because SWB 

computes soil-moisture-zone ET without regard to the location 

of groundwater levels in relation to land surface, the difference 

between Pet and Aet can be used to approximate ETg. The 

mean annual ETg rate (Pet – Aet), computed by using the SWB 

code, was 24.5 in/yr.

White (1932) estimated annual ETg rates by using 

specific yield (Sy) from soil columns and groundwater levels 

measured every hour from a continuous well. This method 

was applied for undisturbed salt grass cover in southwest 

Utah with a mean depth to water of 12–24 in. By using this 

method, the mean annual ETg was estimated as 16 in/yr. By 

comparison, a mean annual ETg of 12 in/yr was obtained 

by using the same method for the North Fork Red River in 

Oklahoma (Smith and others, 2017). 

The ETg rates from the SWB code (24.5 in/yr), 

White (1932) (16 in/yr), and Smith and others (2017) 

(12 in/yr) were averaged to obtain a mean annual ETg rate 

of 17.5 in/yr. When applied across the ETg area, this ETg 

rate was 92,945 acre-ft/yr, or about 16 percent of aquifer 

outflows (table 3). This annual ETg rate was expected to be a 

reasonable balance between the various ETg estimates for the 

Rush Springs aquifer.

Streamflow Characteristics and Seepage

Base flow, or the part of streamflow that is not from 

runoff and is discharged from aquifers adjoining a stream, was 

quantified over the study period 1979–2015 for the studyarea streamgages by using a base-flow separation code (BFI; 

Wahl and Wahl, 1995) integrated into the USGS Groundwater 

Toolbox (Barlow and others, 2015) (table 1). This technique 

identifies the minimum streamflow for user-specified n-day 

moving increments and compares this streamflow to adjacent 

minimums to determine turning points on a base-flow 

hydrograph. The ratio of base flow to the total streamflow is 

the base-flow index. A base-flow index of 1 indicates that all 

streamflow occurs from groundwater, and a base-flow index of 

0 indicates that no streamflow occurs from groundwater.

The Canadian River is regulated by an upstream surfacewater reservoir in Texas, but no releases from the reservoir 

were recorded during the study period. The Washita River is 

regulated by Foss Reservoir and Fort Cobb Reservoir, and 

a number of reservoir releases to the Washita River were 

recorded during the study period. Thus, BFI may overestimate 

base flows at regulated streamgages on the Washita River 

(fig. 1), and long-term trends in base flows may be masked by 

reservoir releases that are indistinguishable from base flows.

The BFI-estimated base flows calculated at streamgages 

located on the Canadian River, Washita River, Little Washita 

River, and Fort Cobb Reservoir tributaries (Cobb, Lake, and 

Willow Creeks) were used to estimate annual stream seepage 

between the Rush Springs aquifer and these streams. Base 

flow from the Canadian River upstream from the aquifer 

was estimated from Ellis and others (2017). Based on the 

increase in streamflow between streamgages (table 2), the 
Introduction 21

estimated mean annual stream seepage is predominantly from 

the Rush Springs aquifer to the study-area streams. Although 

flow from the study-area streams, such as Cobb Creek, to 

the Rush Springs aquifer may occur (Mashburn and Smith, 

2014), the substantial increases in mean downstream base flow 

suggest that this flow is small in comparison to flow from the 

aquifer to the study-area streams. 

Mean annual stream seepage for streams with available 

streamgage data was calculated as the sum of the mean annual 

stream seepage from the Canadian (51,016 acre-ft/yr), Washita 

(146,914 acre-ft/yr), and Little Washita (9,915 acre-ft/yr) 

Rivers and Cobb (12,392 acre-ft/yr), Lake (3,644 acre-ft/yr), 

and Willow (1,476 acre-ft/yr) Creeks during the study period. 

For the Washita River downstream from Foss Reservoir, the 

mean annual stream seepage was based on the difference 

between the base flow at the Anadarko (07326500) and 

Foss (07324400) streamgages and an estimated 3 cubic 

feet per second (ft3

/s; 2,173 acre-ft/yr) of base flow from 

five tributaries (Turkey, Boggy, Cavalry, Rainy Mountain, 

and Stinking Creeks; fig. 1), surface-water diversions, and 

releases from Fort Cobb Reservoir. Base flow in the Washita 

River at the upstream Rush Springs aquifer boundary was 

estimated as 66 percent of the base flow at the Hammon 

streamgage (07324200). Thus, mean annual stream seepage 

for the Washita River upstream from Foss Reservoir was 

the difference of these flows adjusted upward by 8 percent 

for the 3.9-mi distance downstream to Foss Reservoir. The 

Little Washita River originates in the Rush Springs aquifer; 

therefore, the stream seepage was set as the base flow at this 

gage adjusted upward by 14 percent for the 4.3-mi distance 

downstream to the Rush Springs aquifer boundary. Mean 

annual stream seepages for Cobb, Lake, and Willow Creeks 

were estimated by using the same methods, with upward 

flow adjustments for Cobb Creek and Lake Creek of 12 and 

20 percent, respectively, made to account for the distance 

between the streamgages and Fort Cobb Reservoir. 

Stream seepage is assumed to occur at the numerous 

ungaged streams in the study area. Because no data are 

available for these streams, the seepage contribution from 

these streams was estimated at 15 percent of the mean annual 

stream seepage for streams with available streamgage data. 

Thus, mean annual stream seepage for the Rush Springs 

aquifer—including gaged (225,357 acre-ft/yr) and ungaged 

streams (33,804 acre-ft/yr)—was estimated at 259,161 acre-ft/yr, 

or about 45 percent of aquifer outflows (table 3).

Lateral Groundwater Flows

The bedrock deposits of the Ogallala Formation (fig. 2), 

which are situated upgradient from the Rush Springs aquifer, 

were assumed to exchange lateral groundwater flow with this 

aquifer. The flow from the Ogallala Formation to the Rush 

Springs aquifer is shown by potentiometric-surface contours in 

this area parallel to the aquifer boundary during 1986 and 

1991 (Becker and Runkle, 1998) and during 2013 (Neel and 

others, 2018), or perpendicular to the direction of lateral 

groundwater flow. 

To the southwest and west of the Rush Springs aquifer, 

the surrounding bedrock units are composed predominantly 

of shale and siltstone. Potentiometric-surface contours for 

this area are generally perpendicular to the aquifer boundary 

(Neel and others, 2018); thus, lateral groundwater flows in 

these areas were assumed to be negligible. Additionally, to the 

northeast and east, seepage is assumed to occur from the Rush 

Springs aquifer to the North Canadian alluvium and terrace 

deposits based on potentiometric-surface contours that are 

parallel to this boundary (Ryter and Correll, 2016; Neel and 

others, 2018). The low-permeability Dog Creek Shale at the 

base of the Rush Springs aquifer is expected to impede flow 

from the Rush Springs aquifer into underlying units or to the 

aquifer from underlying units. 

No estimates of lateral groundwater flow from the 

Ogallala Formation to the Rush Springs aquifer are available 

in published literature; however, based on the configuration 

of the published potentiometric-surface contours, the lateral 

groundwater flow from the Ogallala Formation to the Rush 

Springs aquifer is expected to be small. Thus, mean 

annual lateral groundwater flow was assumed to be about 

3 percent of recharge to the Rush Springs aquifer, or about 

16,700 acre-ft/yr (table 3). 

Water Use

Water use in Oklahoma, with the exceptions of 

groundwater use of less than 5 acre-ft/yr for domestic and 

agricultural purposes and groundwater use for irrigation of less 

than 3 acres of land, is regulated by the OWRB. Groundwaterand surface-water-use data are self-reported annually to the 

OWRB by permitted users, and the OWRB staff reviewed 

water-use data described in this report to ensure the quality 

and completeness of the data. 

During the study period (1979–2015), groundwater use 

was estimated for 1,891 irrigation, public supply, industrial, and 

temporary permits (OWRB, 2017). Mean annual groundwater use 

for the study period totaled 65,763 acre-ft/yr, or about 11 percent 

of aquifer outflows (table 3). This groundwater-use total includes 

58,821 acre-ft/yr for irrigation (89 percent), 5,854 acre-ft/yr for 

public supply (9 percent), and 1,088 acre-ft/yr for all other use 

types (2 percent). Mean annual groundwater use was similar 

to that of the period of record 1967–2015, during which mean 

annual groundwater use was 68,719 acre-ft/yr including 

62,501 acre-ft/yr for irrigation (91 percent), 5,362 acre-ft/yr 

for public supply (8 percent), and 855 acre-ft/yr for all other 

use types (1 percent). 

Groundwater-use permits for irrigation were 

predominantly in agricultural land located in Caddo and 

eastern Washita Counties (figs. 5, 10), whereas groundwateruse permits for public supply were predominantly in eastern 

Custer County, central and western Caddo County, and 

southern Grady County (fig. 10). Irrigation permits account 
22 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

for 89 percent of all groundwater use, and annual groundwater 

use for the Rush Springs aquifer is, therefore, concentrated 

during summer months. About 85 percent of annual irrigation 

groundwater use occurs between June and September of each 

year, and about 60 percent occurs between July and August 

(OWRB, 2012). 

The Fort Cobb Reservoir watershed contained the largest 

concentration of groundwater use in the Rush Springs aquifer 

(fig. 10). Although this watershed contains only 6.7 percent 

of the Rush Springs aquifer surface area (213,895 out of 

3,181,003 acres), mean annual groundwater use from this 

watershed accounts for 52 percent (34,521 acre-ft/yr) of the 

mean annual groundwater use in the aquifer (65,763 acre-ft/yr, 

table 3). Additionally, 98 percent of the groundwater 

permits in this watershed are for irrigation purposes; thus, 

the groundwater use in this area is concentrated in June–

September of each year. Mean annual groundwater use in the 

Fort Cobb Reservoir watershed was greater than the mean 

annual recharge in this watershed estimated by using the 

SWB code.

Reported surface-water use in the Rush Springs 

aquifer consists of permitted diversions along the Washita 

River, Little Washita River, and Deer Creek and associated 

tributaries (fig. 10). The mean annual withdrawal rate for all 

surface-water permitted diversions during the study period 

was 156 acre-ft/yr (OWRB, 2017). During the study period, 

30 permitted diversions had mean annual withdrawal rates 

between 3 and 628 acre-ft/yr. This total withdrawal includes 

all active and temporary permits in the boundaries of the Rush 

Springs aquifer for the study period.

Seeps and Springs

Seeps and springs are commonly present in the Rush 

Springs aquifer along deeply incised drainage channels 

(Mashburn and Smith, 2014). One of the primary conduits 

for groundwater outflows from this aquifer (other than 

stream seepage) is likely to be seeps and springs along the 

southeastern boundary of the aquifer (Tanaka and Davis, 

1963). That boundary is often parallel to potentiometricsurface contours from Neel and others (2018), indicating that 

groundwater flows from the Rush Springs aquifer to seeps and 

springs along that boundary. A total of 25 discharging springs 

were documented during 2011 (Mashburn and Smith, 2014), 

although below-mean precipitation during 2011 and several 

prior years precluded additional springs being located that 

likely existed. Because spring flow occurred during drought 

conditions, these springs are likely perennial but are estimated 

to flow less than 1 ft3

/s. 

Although discharge data are generally unavailable for 

seeps and springs in the study area, a substantial component of 

aquifer outflows is expected to occur along the entire eastern 

and southeastern boundary of the Rush Springs aquifer, or 

effectively half of the aquifer boundary—is expected to 

result in a substantial component of aquifer outflows. Becker 

(1998) used a steady-state groundwater model to estimate 

that discharge to seeps and minor streams originating in 

the Rush Springs aquifer was approximately 82 percent of 

aquifer outflows. However, this model covered a smaller 

areal extent and made no delineation between discharge to 

seeps and seepage to minor streams. Based on the balance 

of inflows (recharge and lateral groundwater flow) and other 

outflows (stream seepage, ETg, and groundwater use), mean 

annual discharge to seeps and springs is estimated to be 

155,507 acre-ft/yr, or about 27 percent of aquifer outflows in 

the conceptual water budget (table 3). 

Reservoir

Streamflows from Cobb Creek, Lake Creek, and Willow 

Creek are the primary source of surface-water inflow to Fort 

Cobb Reservoir (fig. 1), a Reclamation reservoir constructed 

in 1959 for flood control, water supply, and recreation. Fort 

Cobb Reservoir provides municipal and industrial water to 

the Public Service Company of Oklahoma, Western Farmers 

Electric Cooperative, the City of Anadarko, and the City 

of Chickasha. The active conservation pool storage of Fort 

Cobb Reservoir is 71,696 acre-ft (Reclamation, 2017a), 

and the reservoir has mean annual permitted surface-water 

withdrawals of about 18,000 acre-ft/yr (OWRB, 2012). 

Flow to and from Fort Cobb Reservoir and the Rush 

Springs aquifer (termed “lakebed seepage”) was expected 

to vary seasonally with changes in precipitation and water 

use. Stage in Fort Cobb Reservoir is generally highest in 

the early summer after spring rainfall and lowest in the fall 

after the cumulative effects of increased evaporation and 

permitted surface-water withdrawals during summer months 

(Reclamation, 2017a). Thus, lakebed seepage may occur as an 

inflow to or an outflow from the Rush Springs aquifer during 

various times of the year.

Streamflow from the Washita River is the primary 

source of surface-water inflow to Foss Reservoir (fig. 1), a 

Reclamation reservoir constructed in 1961 for flood control, 

water supply, and recreation. The active conservation pool 

storage of Foss Reservoir is 168,732 acre-ft (Reclamation, 

2017b), and the reservoir has mean annual permitted surfacewater withdrawals of about 18,000 acre-ft/yr (OWRB, 2012).

Groundwater Storage Change

To estimate groundwater storage change for the Rush 

Springs aquifer, an analysis was performed for groundwater 

levels at 19 of the 26 long-term or continuous observation 

wells (fig. 11) completed in the unconfined portion of the Rush 

Springs aquifer. Changes in groundwater levels occur because 

of changes in the volume of water stored in the aquifer. Longterm changes determined over many years can be indicative 

of an imbalance between inflows, such as recharge and lateral 

groundwater flow, and outflows, such as stream seepage, 

groundwater use, evapotranspiration, or seeps and springs. 
Introduction 23

laf18-0888_fig 10

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Groundwater well, by permitted use (OWRB, 2017)

Permitted surface­water diversion (OWRB, 2017)

Public supply

Irrigation

Other

OWRB, Oklahoma Water Resources Board

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 10. Locations of permitted groundwater wells and surface-water diversions for the Rush Springs aquifer, 

western Oklahoma, 1979–2015.
24 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 11

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Long­term groundwater­level observation well—

Numeral indicates map number from table 7

Continuous groundwater­level observation well—

Numeral indicates map number from table 7

22

5

0 10 20 30 MILES

0 10 20 30 KILOMETERS

1

2

3

4

5

6

7 8

9

11

12

13 14

15 16 17

18

19

20

21

10

22

24

25

23

26

Figure 11. Locations of long-term and continuous groundwater-level observation wells for the Rush Springs 

aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 25

The analysis period began in 1979, after a transition 

to developed conditions had occurred in the aquifer (Neel 

and others, 2018), and ended in early 2016. This analysis 

examined groundwater-level observations conducted during 

base-flow conditions (generally December to March), when 

seasonal groundwater use and ETg are minimal. This analysis 

included only wells for which no pumping was recorded at 

the time of the groundwater-level observations in the National 

Water Information System (NWIS) database (USGS, 2017c) 

or OWRB database (OWRB, 2017). 

The results from the analysis of groundwater levels in 

19 wells (fig. 12) indicated 

• generally stable to slightly declining groundwater 

levels during an early period with somewhat belownormal precipitation (1979–81; fig. 7), 

• increasing groundwater levels during a period with 

above-normal precipitation (1985–2000; fig. 7), and 

• decreasing groundwater levels during periods of belownormal precipitation (2001–06; fig. 7) and drought 

(2009–14; fig. 7) in western Oklahoma. 

For the 19 wells analyzed, mean groundwater levels increased 

during the analysis period by 3.4 ft, including mean increases 

of 2.6 ft for long-term wells 1–3, 21.9 ft for long-term wells 

4–6, and 8.9 ft for long-term wells 7, 8, 10, and 20 (fig. 12). 

Mean groundwater levels decreased during the analysis period 

by 4.9 ft for wells in the Fort Cobb Reservoir watershed (longterm wells 11, 12, 14–18, 22, and 25). This groundwater-level 

decrease corresponds to a groundwater storage change of 

73,366 acre-ft for the Fort Cobb Reservoir watershed. This 

groundwater storage change was calculated by multiplying the 

groundwater-level change by the Sy (0.07; determined as the 

mean Sy for the Rush Springs aquifer from Neel and others 

[2018]) and the area of the Fort Cobb Reservoir watershed 

(213,895 acres). 

Based on the similarity of groundwater-levels in 1979 

and 2016 from this analysis and Neel and others (2018), it was 

expected that the groundwater storage change for the analysis 

period would be negligible for the purposes of calculating 

the conceptual water budget for the study period (table 3). 

Although groundwater levels in some areas of the aquifer 

increased during the analysis period (fig. 12A), these increases 

were offset by decreases in groundwater levels in the Fort 

Cobb Reservoir watershed (fig. 12B).

Conceptual Water Budget

A conceptual water budget for the Rush Springs aquifer 

(table 3) was developed to quantify the amount of water that 

moves between each boundary of the aquifer and to guide the 

construction and calibration of the groundwater model. This 

water budget provides a generalized estimate of mean annual 

inflows and outflows for the Rush Springs aquifer during the 

study period 1979–2015 (table 3). The Rush Springs aquifer 

bedrock units as well as the alluvium and terrace deposits 

in the study area are considered a single hydrogeologic unit 

(Rush Springs aquifer, fig. 3). Water that flows from the Rush 

Springs aquifer to the study area streams is considered an 

aquifer outflow, whereas the reverse constitutes an inflow to 

the aquifer. 

Approximately 97 percent of inflows to the Rush Springs 

aquifer occurred as recharge during the study period, and 

net lateral flow was estimated to be 3 percent of the aquifer 

inflow (table 3). Net lakebed seepage at Fort Cobb Reservoir 

was expected to be a relatively small (less than 1 percent) 

component of the water budget; thus, this term was not 

quantified in table 3. 

The largest aquifer outflow (45 percent) was net stream 

seepage (table 3). The remaining aquifer outflows were seeps 

and springs (27 percent), ETg (16 percent), and groundwater 

use (11 percent). The amount of surface-water use (mean for 

30 permits of 156 acre-ft/yr) is small and variable from year 

to year and, therefore, is not accounted for in the conceptual 

water budget (table 3).

Simulation of Groundwater Flow

A groundwater model of the Rush Springs aquifer was 

constructed by using MODFLOW-2005 (Harbaugh, 2005) 

with the Newton solver (MODFLOW-NWT; Niswonger 

and others, 2011). MODFLOW-NWT uses finite-difference 

methods to solve the three-dimensional groundwater-flow 

equation and includes more advanced capabilities to solve 

nonlinear simulations compared to MODFLOW-2005. In the 

modular design of MODFLOW, each hydrologic boundary, 

such as stream seepage, recharge, or groundwater use, is 

included as a package that, when activated, adds new inflow 

and outflow terms to the groundwater-flow equation being 

solved. Model space is discretized into orthogonal cells, and 

the cell size is the finest resolution at which spatially varying 

properties may be represented and varied. Model time is 

discretized into time steps within stress periods. The stress 

period length is the finest resolution at which temporally 

varying inflows and outflows may be represented and varied, 

and the time step length is the finest length of time for which 

model outputs may be written. The calibrated groundwater 

model inputs and outputs are available in Ellis (2018).
26 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 12

Depth to water, in feet below land surface Depth to water, in feet below land surface

Date

1974197619781980198219841986198819901992199419961998200020022004200620082010201220142016

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

0

10

20

30

40

50

60

70

80

90

100

110

120

Study period 1979–2015

Dry period Wet 

period

Drought period

Dry period Wet period Dry period Wet 

period

Dry period Wet period

Drought period

Well 1

Well 2

Well 3

Well 4

Well 5

Well 6

Well 7

Well 8

Well 10

Well 11

Well 12

Well 14

Well 15

Well 16

Well 17

Well 18

Well 20

Well 22

Well 25

Study area climate periods from Neel and others 

(2018) based on a 5-year moving average

A. Observation wells in the Rush Springs aquifer

B. Observation wells in the Fort Cobb Reservoir surface watershed

Figure 12. Depth to water for selected wells in A, Rush Springs aquifer and B, Fort Cobb Reservoir surface watershed, 

western Oklahoma, 1974–2016.
Simulation of Groundwater Flow 27

Spatial and Temporal Discretization

The Rush Springs aquifer groundwater-model grid was 

spatially discretized into 1,362 rows and 1,083 columns 

containing 500-ft by 500-ft cells without rotation of the grid. 

Three layers were used to represent geologic units in the 

study area (figs. 13–14), and the active area was defined by 

the boundaries discussed in the “Purpose and Scope” section 

(fig. 1). The top layer (layer 1) represented the Cloud Chief 

Formation located in the western part of the study area and 

was inactive where that geologic unit was absent. The middle 

layer (layer 2) represented the alluvium and terrace deposits 

(hereafter, “alluvium and terrace”) as well as the upper 30 ft of 

the Whitehorse Group (hereafter, “upper Whitehorse Group”). 

This configuration was used to allow lateral groundwater 

flow to occur between the upper Whitehorse Group and the 

alluvium and terrace and between the upper Whitehorse Group 

and Fort Cobb Reservoir. Areas of the terrace outside of those 

areas shown on figure 13 were determined to be unsaturated 

based on an analysis of available well logs. The bottom layer 

(layer 3) represented the remainder of the Whitehorse Group 

(hereafter, “lower Whitehorse Group”). All model layers were 

assigned as a convertible-type layer, whereby each layer can 

convert between confined and unconfined conditions. 

The groundwater-model period was temporally 

discretized into 444 monthly transient stress periods with 

1 time step each, representing the period of January 1979 

to December 2015. The monthly transient stress periods 

were used to capture seasonally variable processes such as 

recharge, ETg, and groundwater use. A lack of sufficient 

water data prior to the mid-1970s precluded the establishment 

of predevelopment groundwater levels and flow conditions; 

therefore, an initial 365-day steady-state stress period was 

configured to represent mean annual inflows and outflows 

from the Rush Springs aquifer to establish initial conditions 

for the study period. 

Hydrologic Boundaries

Hydrologic boundaries in the groundwater model 

represent the locations where the inflow or outflow of water 

may occur (fig. 15) and include specified-flux and headdependent boundaries. For a specified-flux boundary, a 

user-specified discharge rate governs groundwater exchange 

at that boundary. Simulated specified-flux boundaries 

include groundwater use and recharge, as well as the no-flow 

boundary established at the bottom of layer 3. A no-flow 

boundary was also established at some locations in each 

layer where adjoining hydrogeologic units do not yield water 

to the Rush Springs aquifer (fig. 15). A head-dependent 

boundary simulates flow based on the difference between a 

user-specified groundwater level and the groundwater level 

in model cells. Simulated head-dependent boundaries include 

ETg, lateral groundwater flow, seeps and springs, stream 

seepage, and lakebed seepage at Fort Cobb Reservoir.

Recharge

Areally distributed recharge from the SWB code was 

simulated as a specified-flux boundary by using the Recharge 

package (Harbaugh, 2005). The steady-state simulation used a 

mean recharge value calculated for the model period, and the 

transient simulation used recharge values calculated for each 

month of the model period. Spatial adjustment of recharge 

occurred during the calibration phase to obtain better matches 

between simulated and observed calibration targets. Recharge 

was applied to the highest active cell, or layer 1 in the area 

where the Cloud Chief Formation is present and layer 2 in all 

other locations. 

Lateral Groundwater Flow, Seeps, and Springs

Lateral groundwater flows between the Rush Springs 

aquifer and the Ogallala Formation in the northwest 

model area and between the Rush Springs aquifer and 

Foss Reservoir (fig. 2) were simulated as head-dependent 

boundaries by using the General-Head Boundary (GHB) 

package (Harbaugh, 2005) (fig. 15). The GHB package uses 

a linear relation between flux and the water-table altitude 

(or water head), and a user-specified reference groundwater 

level and conductance. Conductance is defined as the 

product of hydraulic conductivity of the model cell and 

the cross-sectional area perpendicular to flow, divided by 

the distance between the general-head boundary and the 

model cell. When the simulated groundwater level is lower 

than the reference groundwater level, water flows into the 

groundwater model. When the simulated groundwater level 

is higher than the reference groundwater level, water flows 

out of the groundwater model. The reference groundwater 

level for each GHB cell simulating flow from the Ogallala 

Formation was determined from the mean of the nearest 

measured groundwater levels during the model period (USGS, 

2017c). The reference groundwater level for each GHB cell 

simulating flow between Foss Reservoir and the Rush Springs 

aquifer was determined as the mean of the reservoir stage 

(Reclamation, 2017b) during the model period.

Seeps and springs along the model boundary were 

simulated as a head-dependent boundary by using the Drain 

package (Harbaugh, 2005). Flow between the aquifer and 

drain cells is similar to the flow in the GHB package, except 

that (1) no flow to the drain occurs when the groundwater level 

in the aquifer is less than the altitude of the drain and (2) flow 

does not occur from the drain to the aquifer. The altitude of the 

drains simulating the spring discharge were set at the altitudes 

recorded for the springs in the NWIS database (USGS, 2017c). 

In layer 2, the spring altitudes for 3 of the 25 springs were 

increased because these altitudes occurred below the bottom 

of the cell. Lateral groundwater flows, springs, and seeps were 

simulated in layers 2 and 3 of the model. 
28 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 13

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017); Model layer 1—Cloud Chief Formation Shaded relief derived from USGS (2017a)

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower part 

of Whitehorse Group represented by model layer 3

Rush Springs aquifer boundary

A'A Line of section—Model row 585 (fig. 14)

EXPLANATION

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

0 10 20 30 MILES

0 10 20 30 KILOMETERS

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb 

Reservoir

A A'

Figure 13. Hydrogeologic units of the Rush Springs aquifer study area, western Oklahoma.
Simulation of Groundwater Flow 29

laf18-0888_fig 14

A A' FEET

2,000

1,900

1,800

1,700

1,600

1,500

1,400

1,300

1,200

WEST EAST

Model column

54 75 150 225 300 375 450 525 600 675 726

0 5 10 15 MILES

0 5 10 15 KILOMETERS

VERTICAL SCALE GREATLY EXAGGERATED

DATUM IS NORTH AMERICAN VERTICAL DATUM OF 1988

Washita RiverFoss Reservoir

Barnitz Creek

Beaver Creek

Deer Creek

Canadian River

Washita River

EXPLANATION

Line of section for A–A' (model row 585) shown on figure 13

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Whitehorse Group

Upper 30 feet (layer 2)

Lower part (layer 3)

Dog Creek Shale and other bedrock (not modeled)

Potentiometric surface (2013; Neel and others, 2018)

Figure 14. Vertical cross section of the Rush Springs groundwater-flow model, western Oklahoma.
30 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 15

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Shaded relief derived from USGS (2017a)

EXPLANATION

Rush Springs aquifer model—The edge of the active model

area is a no-flow boundary unless specified otherwise

Streamflow routing

Evapotranspiration

Lake

General-head-boundary

(table 6)

Drain (table 6)

Rush Springs aquifer boundary—

Active model area boundary

ghb1 Well

drn5

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

0 10 20 30 MILES

0 10 20 30 KILOMETERS

ghb1

ghb2

ghb3

ghb4

ghb5

drn1

drn1

drn2

drn3

drn4

drn5

drn6

drn6

drn6

ghb7

drn7

drn8

drn9

drn10

drn11

ghb1

ghb2

ghb3

ghb4

ghb5

drn1

drn1

drn2

drn3

drn4

drn5

drn6

drn6

drn6

ghb7

drn7

drn8

drn9

drn10

drn11

Figure 15. Active area, hydrologic boundaries, and selected parameter zones for the numerical groundwaterflow model of the Rush Springs aquifer, western Oklahoma.
Simulation of Groundwater Flow 31

Streams

The major streams and associated tributaries in the 

study area (figs. 15–16) were simulated as a head-dependent 

boundary by using the Streamflow-Routing package, version 

2 (SFR) (Niswonger and Prudic, 2005). SFR exchanges flow 

between the aquifer and the stream according to Darcy’s Law 

(Darcy, 1856); stream seepage is the product of the streambed 

conductance and the difference between the groundwater 

level and the stream stage. The streambed conductance is 

the product of the hydraulic conductivity of the streambed 

sediments and the area of the stream channel divided by the 

streambed thickness. Stream stage is calculated by using 

Manning’s Equation, in which stream stage is a function of 

flow based on the geometry of the stream channel. Where 

groundwater levels are lower than stream stage, inflow to 

the aquifer from the stream occurs (termed “seepage from 

streams”). Where groundwater levels are higher than stream 

stage, outflow from the aquifer to the stream occurs at a 

specified streambed conductance rate from the aquifer (termed 

“seepage to streams”).

Streamflows are calculated for each part of the stream, 

known as reaches, contained in a model cell until the end of a 

segment, or group of reaches with uniform or linear hydraulic 

properties, is reached during each time step. A stream-water 

balance computes the amount of water available in each 

stream reach and the amount of water exchanged between the 

stream and the aquifer in groundwater-model simulations. 

Calculation of flows repeats downstream in this manner until 

water is routed out of the model active area. Inflows (Qin) to 

each stream reach are calculated as

∑ + Q Q in= sp Q Q tr + + ro Q Q pr gwi − 

 

(2)

where

Qsp is the specified inflow at the beginning of the 

first reach of a segment;

Qtr is the sum of tributary inflow;

Qro is direct overland runoff;

Qpr is direct precipitation; and

Qgwi is seepage to streams.

Specified inflows (Qsp) at the beginning of each stream 

reach include specified flows at the model boundary from the 

Canadian and Washita Rivers based on Ellis and others (2017) 

and flow at the Hammon streamgage (07324200; USGS, 

2017c), respectively. Additionally, specified inflows include 

releases from Fort Cobb and Foss Reservoirs (Reclamation, 

2017a, b) to the first downstream segment. Tributary inflows 

(Qtr) are based on flow routed from upstream segments, which 

includes the small tributaries associated with the alluvium 

and terrace of the Canadian and Washita Rivers. A tributary 

inflow rate of 3 ft3

/s at the model boundary was included for 

five tributaries: Turkey, Boggy, Cavalry, Rainy Mountain, 

and Stinking Creeks (fig. 1). All other tributaries at the model 

boundary were either assumed to be intermittent or ephemeral, 

with no specified inflows. Tributaries originating in the 

model active area were assumed to drain the Rush Springs 

aquifer and were simulated primarily to route groundwater 

flow to the Canadian River or Washita River. The model 

is simulated under base-flow conditions; therefore, direct 

overland runoff (Qro) and precipitation (Qpr) were not applied 

to the stream channel. Groundwater discharge from the aquifer 

simulated by using MODFLOW is a negative value; thus, the 

groundwater inflow (Qgwi) term is subtracted from the other 

inflow components. Outflows (Qout) from each stream reach 

are calculated as

∑ + Q Q out= str d Q Q iv + + et Qgwo 

 

(3)

where

Qstr is streamflow out of a reach;

Qdiv is specified diversions;

Qet is evapotranspiration; and

Qgwo is seepage from streams.

Streamflow out of each reach (Qstr) was routed downstream in 

all areas except for the stream segments directly above Foss 

and Fort Cobb Reservoirs, where streamflow was routed into 

these reservoirs, and stream segments located at the boundary 

of the model. During the model period, 12 of 30 permitted 

surface-water diversions had mean annual withdrawal rates 

(Qdiv) greater than 218 acre-ft (0.3 ft3

/s), and only those 

diversions were simulated in the model. Diversions can be 

simulated only from the last reach in any segment; thus, 

this location may differ somewhat from the actual diversion 

location. The discrepancies between the actual and simulated 

diversion locations were not substantial, however, and the 

diversion rates represented only a small percentage of flow in 

the SFR cells. Surface-water diversions located on intermittent 

or ephemeral streams were considered to be supplied from 

surface runoff and were not included. No evaporative 

processes (Qet) were applied by using the SFR package, 

although ETg is simulated by using the Evapotranspiration 

package (Harbaugh, 2005) for alluvium cells that include 

stream segments. 

The extent of the streams (fig. 16) was modified from 

the National Hydrography Dataset Plus (NHDPlus; Horizon 

Systems Corporation, 2015), a 1:100,000-scale geospatial 

dataset of surface-water features. Streams having a stream 

order (Strahler, 1952) of one—defined as headwater 

streams that are dominated by runoff—were excluded from 

the stream extent. Differences in stream channel location 

occurred between the DEM (USGS, 2017a) and the NHDPlus 

streamline because of the resampling of DEM cells and 

migration of the stream channel in the alluvial valleys over 

time. To ensure correct surface-water routing in the stream, the 

stream location was adjusted to ensure that the stream channel 

altitude decreased in a downstream direction in each segment. 

For segments where the streambed slope was zero, either the 
32 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 16

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017);

Shaded relief derived from USGS (2017a) EXPLANATION

Rush Springs aquifer boundary

Stream channel width, in feet

3.0 to 9.9

10.0 to 19.9

20.0 to 39.9

40.0 to 79.9

80.0 to 119.9

120.0 to 150.0

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layer 2—Lake

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower part

of Whitehorse Group represented by model layer 3

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

0 10 20 30 MILES

0 10 20 30 KILOMETERS

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb 

Reservoir

Figure 16. Streamflow-Routing package stream channel widths for the numerical groundwater-flow model of the 

Rush Springs aquifer, western Oklahoma.
Simulation of Groundwater Flow 33

upstream altitude was slightly increased, or the downstream 

altitude was slightly decreased. 

The SFR streambed thickness was set to 2 ft, and a 

rectangular channel was used to define the stream geometry 

in all segments of the model. The streambed altitude was 

derived from a 10-meter DEM, and stream segments were 

incised between 1 and 5 ft in relation to the DEM altitude. 

Stream channel widths (fig. 16) were estimated from 2013 

aerial photographs (Natural Resources Conservation Service, 

2015) and ranged from 100 to 150 ft for the Canadian River, 

from 21 to 55 ft for the Washita River, and from 3 to 20 ft for 

the tributaries (fig. 16). Although the streambed conductivity 

could be expected to vary based on location and discharge 

rates, the streambed conductivity was set at 5 feet per day 

(ft/d) based on Ellis and others (2017). Out of 167 stream 

segments, 164 were assigned to layer 2 of the model; the 

remaining 3 segments were assigned to layer 1 of the model. 

Reservoir

Fort Cobb Reservoir was simulated as a head-dependent 

boundary by using the Lake package (Merritt and Konikow, 

2000; Niswonger and Prudic, 2005). Lake package cells 

exchange water with adjacent and underlying active 

model cells based on the lakebed leakance and simulated 

groundwater levels for both the reservoir and surrounding 

active model cells. The Lake package computes a water 

budget independent of MODFLOW during each time step for 

the simulated lake, described as

h h t p e rnf w sp Q Q

A l

n

l

n si so

s

= + −1 − + − − + − ∆

 

(4)

where

h h l

n

l

n = −1 are lake (reservoir) stage from the current and 

previous time steps, respectively;

∆t is the time step length;

p is the rate of precipitation applied to the lake;

e is the rate of evaporation from the lake;

rnf is the rate of surface runoff to the lake;

w is the rate of water withdrawals from the lake;

sp is the net rate of lakebed seepage between the 

lake (reservoir) and the aquifer;

Qsi is the rate of stream inflow to the lake;

Qso is the rate of stream outflow from the lake; 

and

As is the surface area of the lake.

Fort Cobb Reservoir bathymetry and stage-storage 

relation data (fig. 17) were digitized from a 2007 

sedimentation survey (FTN Associates, 2009) and were used 

by the Lake package to determine reservoir volume and area 

for a given stage. Only minor differences between the volume 

and area relation from the sedimentation study and the relation 

used in the Lake package occurred; thus, the simulated 

curves are not shown in figure 17. Because layer 1 is inactive 

where Fort Cobb Reservoir is simulated, that reservoir was 

simulated by using 697 cells in layer 2; those cells exchange 

water laterally with other cells in layer 2 and vertically with 

cells in layer 3 that are directly under the lakebed (fig. 18). 

These 697 cells correspond to a surface area of 4,000 acres 

(As

), which is slightly larger than the active conservation 

pool surface area of 3,779 acres (Reclamation, 2017a) due to 

discretization caused by using square cells. The rate of lakebed 

leakance (sp)—or the quotient of the hydraulic conductivity 

and thickness between the aquifer and lake—was set at 

0.5 day−1. This leakance rate governs the lakebed seepage 

between the aquifer and simulated reservoir. 

The rates of precipitation (p), evaporation (e), and 

withdrawals (w; which include permitted use and floodcontrol releases) during the model period were obtained 

from Reclamation (2017a). The mean annual precipitation 

to Fort Cobb Reservoir for the model period was 31.3 in/yr, 

estimated at Reclamation weather stations in the reservoir 

area. The mean annual precipitation, when applied over the 

area of the Lake package cells, was about 10,430 acre-ft/

yr. The mean annual evaporation for the model period was 

69.4 in/yr, measured at an evaporation pan (Reclamation, 

2017a). The mean annual evaporation, when applied over the 

area of the Lake package cells, was about 23,130 acre-ft/yr. 

Mean annual withdrawals (w) during the model period totaled 

36,562 acre-ft/yr (Reclamation, 2017a), including permitted 

use of 10,765 acre-ft/yr and releases of 25,797 acre-ft/yr. Fort 

Cobb Reservoir flood-control releases were estimated by using 

data from Reclamation (2017a). Some estimated releases 

were greater than the flow recorded at Cobb Creek below Fort 

Cobb Reservoir (07326000) (fig. 1; table 1) about 2 miles 

downstream from the reservoir; thus, the reported releases 

were reduced to the flow recorded at this gage during these 

months. Releases from Fort Cobb Reservoir may occur when 

the reservoir stage is at the top of the active conservation pool 

(1,342 ft above the National Geodetic Vertical Datum of 1929 

[NGVD 29]).

Figure 17. Fort Cobb Reservoir volume, surface 

area, and stage relationship.

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

0

50,000

100,000

150,000

200,000

250,000

300,000

1,290 1,300 1,310 1,320 1,330 1,340 1,350 1,360 1,370

Reservoir surface area, in acres

Reservoir volume, in acre-feet

Reservoir volume

EXPLANATION

Reservoir surface area

Elevation, in feet above National Geodetic

 Vertical Datum of 1929
34 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 18

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

0 10 20 30 MILES

0 10 20 30 KILOMETERS

WOODWARD GARFIELD

ELLIS

MAJOR

BLAINE KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Model layer 1—Cloud Chief

Formation

Model layer 2—Alluvium and

terrace deposits

Model layers 2 and 3—Upper 30 feet

of Whitehorse Group represented

by model layer 2 and lower part 

of Whitehorse Group (not shown

at land surface) represented by

model layer 3

Rush Springs aquifer boundary

Line of section

EXPLANATION

B'B

Area enlarged

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadia n River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadia n River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb Reservoir

B B'

B B' 1,530

1,450

1,370

1,130

1,290

1,210

1,530

1,450

1,370

1,130

1,290

1,210

FEET

0 8,000 16,000 24,000 32,000 40,000 0 8,000 16,000 24,000 32,000 40,000

Distance, in feet

DATUM IS NORTH AMERICAN VERTICAL DATUM OF 1988 VERTICAL SCALE GREATLY EXAGGERATED

DATUM IS NORTH AMERICAN VERTICAL DATUM OF 1988

Whitehorse Group

Upper 30 feet (layer 2)

Lower part (layer 3)

Bedrock (not modeled)

Water exchange between

model cells for Fort Cobb

Reservoir simulation

EXPLANATION WEST EAST

Bedrock

Layer 3

Layer 2

Fort Cobb

Reservoir

35°15'

35°12'

35°09'

98°33’ 98°30’ 98°27'

B B'

Numerical model grid 

cell, by type

Lake

Streamflow routing

Alluvium and terrace

Line of section

EXPLANATION

B'B

Figure 18. Lake package cross-section and discretization for the Rush Springs aquifer, western Oklahoma.
Simulation of Groundwater Flow 35

Surface runoff (rnf) was estimated at 26,895 acre-ft/yr 

and includes BFI-estimated runoff and overland flows entering 

Fort Cobb Reservoir that were not captured by BFI. The 

BFI-estimated runoff was calculated by using streamflow data 

from the Cobb (07325800), Lake (07325850), and Willow 

(07325860) Creek streamgages (fig. 1, table 1). Streamflow 

data were only available for 1969–78 and 2005–15 at the Lake 

Creek (07325850) and Willow Creek (07325860) streamgages 

(table 2); thus, the runoff components at these gages for 

1979–2004 were calculated by using ratios of streamflow 

between Cobb Creek (07325800) and these streamgages. 

Mean recharge during the model period was 43 percent 

greater that mean recharge during years when streamgage data 

were available (1969–78, 2005–15). Therefore, the runoff 

components from these streamgages during the 1979–2004 

period were adjusted upwards by 43 percent. Mean annual 

BFI-estimated runoff for Fort Cobb Reservoir during the 

model period was estimated at 17,930 acre-ft/yr. Overland 

flows from the topographically higher land area adjacent to the 

reservoir was initially set at 50 percent of the BFI-estimated 

runoff. 

Stream inflows (Qsi ) to Fort Cobb Reservoir occurred 

from SFR stream segments representing Cobb, Lake, and 

Willow Creeks. Mean annual surface-water inflows during 

the model period were estimated at 15,337 acre-ft between 

1979 and 2004. Because the reservoir is managed, releases 

are passed to stream segments downstream from the reservoir; 

therefore, the stream outflow term (Qso ) is zero. 

Saturated-Zone Evapotranspiration

ETg was simulated as a head-dependent boundary by 

using the Evapotranspiration package (Harbaugh, 2005). In 

this package, ETg decreases linearly with decreases in the 

simulated groundwater level, and no ETg occurs when the 

simulated groundwater level is below a user-specified rootzone depth. The root-zone depth for the groundwater model 

was set equal to the SWB root-zone depth for each land-cover 

type. ETg was not expected to occur from the bedrock because 

depths to groundwater in the bedrock commonly exceed 30 ft; 

therefore, the Evapotranspiration package (fig. 15) was limited 

to the ETg area defined by wetlands (U.S. Fish and Wildlife 

Service, 2017), which are included in the layer 2 alluvium and 

terrace (fig. 13).

Groundwater Use

Well withdrawals were simulated as a specified-flux 

boundary by using the Well package (Harbaugh, 2005). 

Annual reported groundwater use for each permit was split 

equally among all the wells attached to a permit (fig. 10) 

(OWRB, 2017). These annual well withdrawals were then 

distributed into monthly well withdrawals by using monthly 

demand distributions (fig. 19) for Basin 19 in the Oklahoma 

Comprehensive Water Plan (OWRB, 2012). Annual irrigation 

well withdrawals were multiplied by the monthly irrigation 

demand (as a percentage of annual groundwater use), and 

annual public-supply well withdrawals were multiplied by 

the monthly public-supply demand. Annual well withdrawals 

for other purposes were distributed evenly to all months of 

the year. Domestic withdrawals, which are not regulated or 

reported by the OWRB, were not simulated; these withdrawals 

were expected to be a minor component of total withdrawals.

Groups of wells attached to a single permit were 

not allowed to exceed the permitted annual withdrawal 

amount. Reported annual well withdrawals for 70 irrigation 

wells (4 percent of all simulated wells) were greater than 

807 acre-ft/yr (500 gal/min) and were reduced to this value to 

avoid the simulation of unrealistic pumping rates. Steady-state 

well withdrawals were determined as the mean of withdrawals 

during the model period.

Model Calibration

Model calibration is the process of adjusting initial model 

input values to improve the fit between model-simulated data 

and observed or estimated data (calibration targets). During 

model calibration, the inputs to be adjusted are updated to 

new values that reduce the discrepancy, or residual, between 

the observed and simulated data. Calibration outcomes 

were evaluated based on the reduction of this residual and 

Irrigation

Basin 19

Public supply

0

5

10

15

20

25

30

35

40

45

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Monthly water demand, as a percentage of annual groundwater use

Month

Other

Modified from Oklahoma Water Resources Board (2012)

Figure 19. Monthly water demand by groundwater-use 

type for the Rush Springs aquifer, western Oklahoma.
36 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

the fit of the calibrated groundwater-model water-budget 

components to those components of the conceptual water 

budget. The calibration process for the Rush Springs aquifer 

model included (1) manual adjustment of model inputs by 

trial and error, followed by (2) automated adjustment of model 

inputs (parameters) by using a combination of the nonlinear 

regression codes PEST (Doherty, 2010) and PEST++ (Welter 

and others, 2015). The PEST code uses the Gauss-MarquardtLevenberg algorithm to adjust user-specified parameters to 

minimize a sum of squared weighted residuals, or objective 

function (table 5). The objective function (Φ) is expressed as 

Φ [ ( ) 2

1

 

n

ii i

i

ω s o == −  ∑  

(5)

where

n is the number of observations,

ωi is the observation weight,

si is the simulated value, and

oi is the observed or estimated value.

PEST automates calibration by running the model as 

many times as needed to determine the best parameter values 

while automatically updating the parameter values during 

each step of the process. This iterative approach allows for the 

optimal values of many parameters to be estimated together 

with greater speed than that of a traditional manual calibration 

approach. Prior to automated calibration, the calibration 

targets were weighted to account for error in each type 

of observation. 

The automated calibration approach concurrently 

applied subspace regularization techniques by using singular 

value decomposition (SVD; Tonkin and Doherty, 2005) 

in conjunction with singular value decomposition-assist 

(SVDA; Tonkin and Doherty, 2005) to reduce automated 

calibration run time and ensure calibration stability. SVD 

was implemented with PEST to identify combinations of 

parameters that are most responsive to the dataset, thus 

separating parameters that may be useful for calibration from 

those parameters that are actually useful and have an effect 

on modeled outputs. To decrease the run time associated with 

a large number of parameters, SVDA was also implemented 

Table 5. Components of the objective function for the automated calibration of the numerical groundwater-flow model of the Rush 

Springs aquifer, western Oklahoma, 1979–2015. Note: components may not sum to totals because of rounding.

Observation 

group Description Number of observations

Total observations in each 

group

Group 

contribution 

(percent)

Objective 

function components

Groundwater-level 

observations

Good quality 3,418

Fair quality 1,730 5,412 29 3,917,565

Poor quality 264

Fort Cobb Reservoir 

stage observations Fort Cobb stage observations 445 445 23 3,142,620

Base-flow estimates

Anadarko streamgage (07326500) 445

2,667 33 4,355,590

Bridgeport streamgage (07228500) 445

Cobb Creek streamgage (07325800) 445

Lake Creek streamgage (07325850) 133

Willow Creek streamgage (07325860) 133

Carnegie streamgage (07325500) 334

Clinton streamgage (07325000) 445

Cement streamgage (07327447) 287

Stream-seepage 

estimates

Canadian River upstream boundary to 

Bridgeport streamgage

1

8 15 2,005,830

Foss Reservoir to Clinton streamgages 1

Clinton to Carnegie streamgages 1

Carnegie to Anadarko streamgages 1

Little Washita River 1

Cobb Creek 1

Lake Creek 1

Willow Creek 1

8,532 101 13,421,605
Simulation of Groundwater Flow 37

with PEST. SVDA computes a user-specified combination of 

parameters, or “super parameters,” that enables a reduction 

in the number of parameters used during calibration. PEST 

requires that the model be run one or two times for either each 

adjustable parameter or super parameter used in the calibration 

process multiplied by typically five to seven parameter 

optimization iterations. Thus, the reduction in the number of 

parameters by using super parameters resulted in significant 

time savings during the Rush Springs model calibration. To 

further reduce the run time associated with the calibration 

process, model runs were performed in parallel on a highperformance computing cluster using the HTCondor run 

management software (Condor Team, 2012). 

Calibration Parameters

For the Rush Springs aquifer model, 9 parameter groups 

representing 842 parameters were defined for the automated 

calibration (table 6, at end of report). These parameter groups 

are GHB conductance, drain conductance, recharge rate 

multipliers, ETg rate and ETg root-zone depth multipliers 

(1 group), streambed conductance, lakebed leakance, Sy, 

specific storage (Ss), and horizontal hydraulic conductivity 

(Kh) and vertical anisotropy pilot points (1 group). The Kh, 

vertical anisotropy, and Sy values in layer 1 (Cloud Chief 

Formation, fig. 13) were obtained from Neel and others (2018) 

and were not adjusted during automated calibration. 

The GHB and drain cells were grouped into parameter 

zones for the adjustment of conductance values. The 6 GHB 

and 11 drain parameter zones (fig. 15) were created to account 

for variations in hydraulic properties of bedrock units adjacent 

to the Rush Springs aquifer. Recharge from the SWB code 

was divided into zones (fig. 20) based on hydrologic soil 

group and available water capacity data used as an input to 

the SWB code. Recharge rate multiplier parameters were 

applied uniformly across each stress period to adjust recharge 

for each of these zones. The ETg multiplier parameters were 

adjusted in the same manner during manual calibration, with 

zones created for the alluvium and terrace of the Canadian, 

Washita, and Little Washita Rivers. During automated 

calibration, entire-array multiplier parameters were used to 

adjust the ETg rate and ETg root-zone depth uniformly in 

each transient stress period. A single streambed conductivity 

parameter was set for all stream segments. A single lakebed 

leakance parameter was adjusted within a range of values that 

improved model stability of the reservoir while reducing the 

stage residual. The initial Sy for pilot points in the layer 2 

(Canadian River) alluvium and terrace used values obtained 

from Ellis and others (2017), which ranged from 0.06 to 0.32. 

A Sy value of 0.12 was set for the alluvium and terrace of 

the Washita River and other model-area tributaries where no 

storage information was available. The initial Sy for pilot 

points in layer 3 used values from the lithologic-log analysis 

from Neel and others (2018) and ranged from 0.03 to 0.23. 

The Ss for all three layers was set as a static value of 1×10–5, 

which was comparable to values used by Ryter and Correll 

(2016) and Ellis and others (2017) for Permian bedrock units 

in Oklahoma.

Kh and vertical anisotropy, or the ratio of horizontalto-vertical hydraulic conductivity, were represented by using 

pilot point interpolation in the groundwater model in layers 

2 and 3 (fig. 21). Pilot points provide a balance between the 

manipulation of values by parameter zones, often defined 

where values are thought to be relatively constant, and the 

manipulation of values in individual model cells, which 

may require more detailed data than are typically available. 

Exponentially weighted kriging was used to interpolate the 

Kh and vertical anisotropy value at each pilot point in each 

geologic unit of layers 2 and 3. Kh and vertical anisotropy 

were interpolated independently. 

Pilot points representing the alluvium in layer 2 were 

spaced at 7,500-ft intervals, and pilot points representing the 

bedrock in layers 2 and 3 were spaced at 25,000-ft intervals. 

Because the division of the Whitehorse Group into layers 

2 and 3 was arbitrary and not based on a geologic contact 

or change in hydraulic parameters, the pilot point Kh and 

vertical anisotropy values representing the Whitehorse Group 

in layer 2 were tied to the respective pilot points in layer 3 

directly underneath. 

An initial Kh value of 45 ft/d was set for pilot points in 

layer 2 representing the alluvium and terrace of the Canadian 

and Washita Rivers, and a value of 30 ft/d was set for the 

alluvium of the model-area tributaries. This 45-ft/d value 

is the calibrated mean Kh of the Canadian River alluvium 

and terrace from the Ellis and others (2017) Reach I model. 

Although literature describing the Kh of the Washita River 

alluvium and terrace inside the model active area is limited, 

this alluvium and terrace was assumed to be lithologically 

similar to the Canadian River alluvium and terrace; thus, the 

same initial Kh values were applied. An initial Kh of 6.3 ft/d 

was set for the pilot points in layers 2 and 3 representing the 

Whitehorse Group. This mean value was calculated from 

the lithologic-log analysis from Neel and others (2018) and 

was applied to the larger aquifer extent from this report. The 

minimum and maximum Kh for all pilot points were set at 

6×10–4 and 90 ft/d, respectively. The value of 6×10–4 ft/d 

represents the mean of siltstone and claystone values from 

Morris and Johnson (1967). The maximum Kh of 90 ft/d was 

modified from the fine-gravel Kh value (100 ft/d) used in Ellis 

and others (2017). Pilot point vertical anisotropy values for the 

interpolation zones in both layers were set to an initial value of 

10, indicating a horizontal-to-vertical Kh ratio of 10:1.
38 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 20

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Shaded relief derived from USGS (2017a)

Recharge zone area and recharge

multiplier zone number (table 6)

No parameter zone

Rush Springs aquifer boundary

EXPLANATION

18

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

17

17

17

17

7

2

12

12

23

23

1

1

19

19

15

15

20

20

15

15

19

18

18

19

19

4

4

19

3

3

3 12 12

12

12

3

3

3 13

15

22

22

18

5

5

5

14

14

18

6 6

6

6

21

21

21

21

6

10

10

3

8

12

12

7

7

7

9

9

9

9

18

18

14 14

14

11

14

3

3

16

16

16

5

16

5

5

9

18

22

14

19

17

17

17

17

18

21

6

19

8

2

2

6

12 12

12

12

23

21

21

5

14 14

14

5

18

11

11

11

14

13

13

21

21

16

16

15

15 10

19

15

10

14

15 21

15

15 15

16

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 20. Spatial distribution of recharge zones for the Rush Springs aquifer model, western Oklahoma, 

1979–2015.
Simulation of Groundwater Flow 39

laf18-0888_fig 21

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

Horizontal hydraulic conductivity

Layer 2 pilot point interpolation zone

Layer 2 and layer 3 pilot point 

interpolation zones

Rush Springs aquifer boundary

EXPLANATION

Horizontal hydraulic conductivity

pilot point, by layer

Layer 2

Layer 3

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Foss

Reservoir

Fort Cobb 

Reservoir

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 21. Spatial distribution of pilot points for the Rush Springs aquifer model, western Oklahoma, 

1979–2015.
40 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Calibration Targets

Calibration targets for the Rush Springs aquifer model 

included groundwater-level (OWRB, 2017; USGS, 2017c) 

and reservoir-stage (Reclamation, 2017a) observations, as well 

as base-flow (table 2) and stream-seepage estimates. For the 

automated calibration, these targets were weighted and placed 

into observation groups of the same name (table 5, fig. 22). 

Groundwater levels at the 25 springs identified from Mashburn 

and Smith (2014) were also used as calibration targets in 

the initial stages of model calibration. Because these springs 

are expected to be perennial and flow as much as 1 ft3

/s, the 

groundwater levels in cells representing these springs were set 

at land surface. Seepage from these springs was assessed by 

using the Drain Observation package (Harbaugh, 2005).

Groundwater-Level Observations

The groundwater model was calibrated to 5,412 groundwaterlevel observations (table 5) at 508 wells in the study area 

(table 7, at end of report); this total included 505 groundwaterlevel observations for the steady-state simulation and 

4,907 groundwater-level observations (table 7) for the 

transient simulation. A total of 5,301 groundwater-level 

observations at 481 wells were completed in layer 3, and the 

remaining 111 groundwater-level observations at 27 wells 

were completed in the alluvium and terrace in layer 2 (fig. 23). 

Although most wells have less than 4 observations during the 

model period (fig. 24), wells with more than 20 observations 

were distributed across the model active area (fig. 25). 

Few groundwater-level observations were available in the 

part of the Whitehorse Group confined by the Cloud Chief 

Formation (fig. 25); thus, the groundwater model has a greater 

uncertainty in this area. 

A median of 84 groundwater-level observations per year 

were available for the model period, but 53 percent of all 

observations occurred in the first 12 years of the model period 

(fig. 26A). Therefore, a bias toward the 1979–90 period was 

incurred during the model calibration. About 58 percent of the 

observations were measured between January and March of 

each year (fig. 26B); thus, most observations were minimally 

affected by local well withdrawals for irrigation that typically 

occur between March and September (fig. 19).

When available, screened-interval data were analyzed 

to ensure that observation wells were completed in the 

Rush Springs aquifer. All groundwater-level observations 

were originally collected as depth-to-water measurements; 

groundwater altitudes were calculated by subtracting the 

measured depth to water from the land-surface altitude 

specified in the NWIS (USGS, 2017a) or OWRB (2017) 

databases. The land-surface altitude specified in the NWIS 

database was compared to the altitude obtained from a DEM, 

and observations with large land-surface altitude discrepancies 

were discarded.

Fort Cobb Reservoir Stage Observations

The groundwater model was calibrated to 445 Fort 

Cobb Reservoir stage observations (table 5), which included 

444 monthly stage observations (Reclamation, 2017a) 

and 1 steady-state (averaged) stage observation. At active 

conservation pool stage (1,342 ft above NGVD 29), Fort Cobb 

Reservoir storage was about 71,696 acre-ft; at dead-pool stage 

(1,300 ft above NGVD 29), storage was about 1,015 acre-ft. 

Because the dead-pool storage was relatively small, it was not 

removed from estimates of Fort Cobb Reservoir storage used 

in this report.
Simulation of Groundwater Flow 41 laf18-0888_fig 22

Calibration target contribution to the 

groundwater-level observations 

group, in percent

Observation group contribution to the 

objective function, in percent

Calibration target contribution 

to the base-flow estimates 

group, in percent

Calibration target contribution to the 

stream-seepage estimates group, 

in percent

Note: U.S. Geological Survey streamgage number in parentheses

Base-flow

estimates

33

Groundwater-level

observations

29

Fort Cobb Reservoir

stage observations

23

Stream-seepage

estimates

15

Good quality

66

Fair quality

26

Poor quality

8

Canadian River

17

 Foss Reservoir to

Clinton streamgage

17

Clinton to Carnegie

streamgages

17

Carnegie to

Anadarko

streamgages

17

Little Washita River

Cobb Creek

8

Lake Creek

8

Willow Creek

8

Lake Creek

(07325850)

19

Carnegie (07325500)

Clinton (07325000)

Cement (07327447)

Willow Creek

(07325860)

Anadarko

(07326500)

19

Bridgeport

(07228500)

19

Cobb Creek

(07325800)

19

8

6

6

6

6

Figure 22. Components of the objective function for the calibration of the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.
42 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 23

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017);

EXPLANATION Shaded relief derived from USGS (2017a)

Groundwater­level observation well, by model

layer representing the hydrogeologic unit

in which completed

Layer 2

Layer 3

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower part 

of Whitehorse Group represented by model layer 3

Rush Springs aquifer boundary

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Foss

Reservoir

Fort Cobb 

Reservoir

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 23. Spatial distribution of groundwater-level observations in layers 1 and 2 for the Rush Springs 

aquifer model, western Oklahoma.
Simulation of Groundwater Flow 43

Figure 24

Number of groundwater wells

Number of groundwater-level observations per well

0

50

100

150

200

250

300

350

1 to 4 5 to 9 10 to 19 20 to 29 30 to 39 40 to 289

Figure 24. Number of groundwater-level observations for each 

well for the Rush Springs aquifer model, western Oklahoma, 

1979–2015.
44 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 25

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017); EXPLANATION Shaded relief derived from USGS (2017a)

Number of groundwater­level 

observations per well

1 to 4

5 to 9

10 to 19

20 to 29

30 to 39

40 to 289

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower part 

of Whitehorse Group represented by model layer 3

Rush Springs aquifer boundary

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Foss

Reservoir

Fort Cobb 

Reservoir

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 25. Spatial distribution of groundwater-level observations per well for the Rush Springs aquifer model, 

western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 45

Base-Flow and Stream-Seepage Estimates

The groundwater model was manually 

calibrated to base-flow estimates at 9 streamgages 

but the automated calibration used 2,667 baseflow estimates at 8 streamgages (table 5, fig. 27), 

including 2,659 monthly estimates and 8 steadystate (averaged) estimates. Base-flow estimates 

were available during each stress period for five 

streamgages and for shorter periods at the remaining 

streamgages (fig. 27). For periods when streamflow 

data were not available—either prior to installation 

of a streamgage, or when streamflow records were 

unavailable after installation—weighting was 

set to zero and no base-flow calibration targets 

were established. 

The groundwater model was calibrated to 

eight stream-seepage estimates (table 5, fig. 22). 

The simulated stream seepage was determined as 

the sum of the “Flow to Aquifer” column in the 

SFR secondary output file (Ellis, 2018) divided 

by the 444 monthly stress periods for the transient 

simulation. Therefore, this value represents the 

mean stream seepage across the model period.

Calibration-Target Uncertainty and Weighting

The calibration targets, with the exception of 

lake-stage observations, were weighted by using 

error-based weighting from Hill and Tiedeman 

(2007). Groundwater-level observation weights 

were defined as ωi 1/ = σi , where σi is the error 

associated with each observation. Base-flow 

and stream seepage weights were defined as 

ωi = × 1/( ) cv o i i , where cvi is the coefficient of 

variation and oi is the observed or estimated value.

Three sources of uncertainty contributing to 

the error of the groundwater-level observations 

are (1) the location accuracy, or how precisely the 

coordinates of the observation wells were known; 

(2) the altitude accuracy, which is based on the 

method used to determine the land-surface altitude 

at observation wells; and (3) the temporal variability 

of groundwater levels at each observation well. By 

using methods from Hill and Tiedeman (2007), the 

error (σi) of each groundwater-level observation 

was calculated as follows:

222 σ σσσ i l at = ++ (6)

where

σl is the location accuracy uncertainty expressed 

as a standard deviation,

σa is the altitude accuracy uncertainty expressed 

as a standard deviation, and

σt is the temporal variability uncertainty 

expressed as a standard deviation.

Figure 26

Number of groundwater-level observations per year Percentage of groundwater-level observations in each month

Year

Month

Median number of groundwaterlevel observations (84)

0

100

200

300

400

500

1979198219851988199119941997200020032006200920122015

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

0

5

10

15

20

25

A.

B.

Figure 26. A, Annual and B, monthly distribution of groundwaterlevel observations for the Rush Springs aquifer model, western 

Oklahoma, 1979–2015.
46 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

The location and altitude accuracy values recorded in 

the NWIS and OWRB databases are based on the method 

used to obtain each observation, typically by using a Global 

Positioning System (GPS) or a topographic map. The location 

accuracy of each observation well, as recorded in the NWIS 

and OWRB databases, was between 0.01 and 10 seconds of 

latitude or longitude for all but two wells, which had a location 

accuracy of 60 seconds. Methods from Clark and Hart (2009) 

were used to determine the location accuracy uncertainty. A 

radius equal to the location accuracy was created for each 

observation well, and the standard deviation of the landsurface altitude in that radius was calculated. The standard 

deviation of the altitude accuracy was calculated by dividing 

half of the altitude accuracy code (in feet) by the critical value 

of a 95-percent confidence interval (Hill and Tiedeman, 2007).

The temporal variability at each observation well was 

determined by using methods from Hill and Tiedeman (2007). 

The groundwater-level range for each observation well was 

determined by using either the observed seasonal groundwaterlevel range for wells with four or more observations per 

year, or a mean value approximating the maximum seasonal 

groundwater-level range (seasonal approximation) for wells 

with less than four observations per year. The seasonal 

approximation was obtained from six observation wells 

(table 7) that were not coded in NWIS as pumping during the 

observation and that included observations during each quarter 

of the year. A value of 1.9 ft was obtained for the seasonal 

approximation, which included data from 54 annual periods 

representing 20 of the 32 years in the model period. Assuming 

that the groundwater-level range represents a 

95-percent confidence interval, the temporal 

variability uncertainty was calculated as the 

groundwater-level range divided by 4 (Hill 

and Tiedeman, 2007).

The error (standard deviation of 

groundwater levels) at each observation 

well was between about 0.3 and 33 ft, 

with a mean of 5.7 ft (table 7). About 

50 percent of these wells had a standard 

deviation of groundwater levels of less 

than 3.9 ft, and about 90 percent had 

a standard deviation of groundwater 

levels of less than 13 ft. The largest error 

component was the location accuracy; 

approximately half of the groundwaterlevel observations were measured prior to 

1990 when survey-grade GPS equipment 

became commonly available. Based on the 

error, the groundwater-level observations 

were grouped into three quality categories 

(“good,” “fair,” and “poor”) representing the 

value of the groundwater-level observations 

(fig. 22). The “good,” “fair,” and “poor” 

groundwater levels were those observations 

with standard deviations ranging between 

0.3 and 4.9 ft, between 5.0 to 14.9 ft, and 

more than 14.9 ft, respectively (table 7). 

The “good,” “fair,” and “poor” transient groundwater-level 

groups contained 3,418; 1,730; and 264 groundwater levels, 

respectively (table 5).

An additional source of uncertainty concerns groundwater 

levels affected by pumping at the measured well, or a nearby 

well, as coded in the NWIS database. For the “good,” “fair,” 

and “poor” groundwater-level groups, 3, 16, and 14 percent of 

groundwater levels, respectively, were coded as pumping at 

the time of an observation. Because of the difficulty associated 

with determining a standard deviation for pumping conditions, 

this error is not included in the error for each groundwaterlevel observation, but is noted where the observed values were 

difficult to simulate in the groundwater model.

Base-flow weights were determined based on the 

accuracy of field streamflow measurements at each 

streamgage. Most of these measurements collected during 

the model period were rated as “fair” in NWIS, which 

corresponds to a 95-percent confidence interval of plus or minus 

(±)15 percent of true streamflow (USGS, 2017c). The standard 

deviation of the base-flow estimates at each streamgage was 

calculated as 15 percent of the base-flow estimate, divided 

by the critical value of a 95-percent confidence interval. The 

coefficient of variation was then defined as this standard 

deviation divided by the mean base flow at each streamgage 

(table 1). Based on stream order (Strahler, 1952), in which 

lower order streams drain small groundwater basins and are 

most susceptible to variations in local properties, the assigned 

coefficients of variation for Cobb, Lake, and Willow Creeks 

Figure 27

07228500

07325000

07325500

07325800

07325850

07325860

07326500

07327447

07324200

Streamgage station number 

Year

1979198219851988199119941997

20002003

20062009

20122015

See table 1 for information pertaining to each streamgage

and figure 1 for the spatial location of each streamgage

1

 Used for automated groundwater-flow model calibration 2

 Used for manual groundwater-flow model calibration

1, 2

2

1, 2

1, 2

1, 2

1, 2

1, 2

1, 2

1, 2

Figure 27. Temporal distribution of streamflow observations used for the 

calibration of the Rush Springs aquifer model, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 47

(stream orders 2–4) may understate the uncertainty in the 

flows for these streams compared the coefficients of variation 

for the Canadian and Washita Rivers (stream orders 6–7).

Weights for the stream seepage between streamgages 

were assigned by using methods from Hill and Tiedeman 

(2007) and were given a 95-percent confidence interval of 

±15 percent of actual flow. Coefficients of variation ranged 

from 0.11 for the Washita River between the Foss and 

Anadarko streamgages to 0.71 for the Washita River between 

the Carnegie and Anadarko streamgages.

Prior to the automated calibration process, the 

observation weights for the calibration targets in each group 

were adjusted by using methods from Doherty and Hunt 

(2010). An observation group contribution to the objective 

function was set through a series of trial runs in which various 

combinations of observation-group weights were tested to 

determine the best weighting arrangement to reduce the 

objective function.

Calibrated Model Fit

The calibrated model fit was evaluated based on the 

reduction of calibration-target residuals and the fit of the 

calibrated water-budget components to the components of 

the conceptual water budget. Residuals were calculated as 

observed minus simulated values; positive residuals indicate 

lower simulated than observed values (underpredicted), and 

negative residuals indicate higher simulated than observed 

values (overpredicted). Residuals multiplied by the error-based 

weights discussed in the “Calibration-Target Uncertainty and 

Weighting” section are referred to as weighted residuals. The 

root-mean-square error (RMSE) of residuals was calculated by 

using the following equation:

( )2

1

1 n

i i

i

RMSE o s n == − ∑ 

(7)

where

n is the number of observations,

oi is the observed (or estimated) value, and 

si is the simulated value.

Groundwater Levels

A good agreement between the observed and simulated 

groundwater levels was obtained as shown on a 1:1 plot, 

where the values generally fall along a straight line (fig. 28A). 

The combined groundwater-level mean residual for steadystate and transient simulations was –2.3 ft, indicating that 

simulated groundwater levels were slightly overpredicted on 

average (table 8). The combined groundwater-level RMSE 

was 26.3 ft, and 75 percent of residuals were within ±27.4 ft 

(table 8). The simulated water-table relief was 1,095 ft, and the 

combined RMSE as a percentage of this water-table relief was 

2.4 percent (table 8). Groundwater-level observations in the 

Figure 28

Frequency

Groundwater−level residual (observed minus simulated), in feet

[NAVD 88, North American Vertical Datum of 1988]

Simulated groundwater level, in feet above NAVD 88

Observed groundwater level, in feet above NAVD 88

B

A

Groundwater levels, good

Groundwater levels, fair

Groundwater levels, poor

1,100

1,300

1,500

1,700

1,900

2,100

2,300

1,100 1,300 1,500 1,700 1,900 2,100 2,300

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

less than −105

 −90 to −105

 −75 to −90 −60 to −75 −45 to −60 −30 to −45 −15 to −30

0 to −15

0 to 15

15 to 3030 to 4545 to 6060 to 7575 to 90

90 to 105

105 to 120

greater than 120

Groundwater levels, good

Groundwater levels, fair

Groundwater levels, poor

EXPLANATION

EXPLANATION

Figure 28. A, Observed and simulated groundwater 

levels and B, groundwater-level residual distributions 

for the numerical groundwater-flow model of the Rush 

Springs aquifer, western Oklahoma, 1979–2015.
48 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

“fair” and “poor” quality categories tended to exhibit larger 

residuals (simulated values both above and below observed 

values) compared to the wells in the “good” quality category 

(figs. 28, 29A). About 85 percent of residuals in the “good” 

category were between ±30 ft, compared to 73 percent and 

63 percent of residuals for the “fair” and “poor” categories, 

respectively (fig. 29A). A total of 99 percent of residuals in the 

“good” category were between ±60 ft, compared to 94 percent 

and 93 percent residuals for the “fair” and “poor” categories, 

respectively (fig. 29A).

If groundwater-level observation weights reasonably 

represent the error inherent in each observation, the weighted 

groundwater-level residual distribution should be random 

around a horizontal line (Hill and Tiedeman, 2007). The 

weighted residuals show a mostly random distribution 

above and below zero, although some clusters of positive 

and negative residuals occur with respect to the simulated 

groundwater levels even after accounting for the quality of the 

data through the weighting process (figs. 29B). 

The overall distribution of groundwater-level residuals 

was reasonable, although wells in some parts of the model 

exhibited positive or negative bias in residuals (fig. 30). 

Overpredicted groundwater levels in layer 3 typically occurred 

in wells in the central, eastern, and southeastern parts of the 

model (fig. 30). One of these wells (long-term well 21; fig. 11) 

includes overpredicted groundwater levels at elevations 

around 1,250 ft NAVD 88 (fig. 29A), where the mean 

residual was −94 ft during the simulation period (fig. 30). No 

completion or screening information was available for the 

well, but the well depth recorded in the NWIS database and 

the aquifer thickness of 100 ft in this area suggest that the 

well may have been completed in a geologic unit other than 

the Whitehorse Group. Overpredicted groundwater levels also 

occurred east of Fort Cobb Reservoir near the model boundary 

(fig. 30). Deeply incised drainage channels in this area have 

rapid changes in altitude and hydraulic gradients of as much 

as 100 feet per mile in some locations. Underpredicted 

groundwater levels in layer 3 typically occurred in three parts 

of the model: (1) the confined western part of the model, 

where the Cloud Chief Formation overlies the Whitehorse 

Group, (2) the Fort Cobb Reservoir watershed, where pumping 

wells are most concentrated (fig. 10), and (3) the southern part 

of the model. 

Table 8. Statistical summary of groundwater-level residuals for the numerical groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma, 1979–2015.

[±, plus or minus; RMSE, root-mean-square error]

All observations

Statistic Steady-state simulation Transient simulation Combined

Observation count 505 4,907 5,412

Mean residual, in feet 1.2 −2.6 −2.3

75-percentile residual range, in feet ±32.2 ±25.6 ±27.4

RMSE, in feet 29.5 25.9 26.3

RMSE percentage of water-table relief (1,095 feet) 2.7 2.4 2.4

Alluvium and terrace (Layer 2)

Statistic Steady-state simulation Transient simulation Combined

Observation count 26 85 111

Mean residual, in feet −0.2 1.2 0.9

75-percentile residual range, in feet ±10.2 ±13.5 ±13.4

RMSE, in feet 11.6 13.6 13.1

RMSE percentage of water-table relief (546 feet) 2.1 2.5 2.4

Rush Springs Formation (Layer 3)

Statistic Steady-state simulation Transient simulation Combined

Observation count 479 4,822 5,301

Mean residual, in feet 1.3 −2.7 −2.6

75-percentile residual range, in feet ±32.8 ±25.8 ±26.5

RMSE, in feet 30.2 26.1 26.5

RMSE percentage of water-table relief (1,095 feet) 2.8 2.4 2.5
Simulation of Groundwater Flow 49

Figure 29

A. B.

C. D.

200

150

100

50

0

–50

–100

–150

–200

200

150

100

50

0

–50

–100

–150

–200

200

150

100

50

0

–50

–100

–150

–200

200

150

100

50

0

–50

–100

–150

–200

1,100 1,300 1,500 1,700 1,900 2,100 2,300 1,100 1,300 1,500 1,700 1,900 2,100 2,300

Residual, in feet

Weighted residual, in feet Weighted residual, in feet

Simulated groundwater level, in feet above NAVD 88

1,100 1,300 1,500 1,700 1,900 2,100 2,300

Residual, in feet

Simulated groundwater level, in feet above NAVD 88

Simulated groundwater level, in feet above NAVD 88

1,100 1,300 1,500 1,700 1,900 2,100 2,300

Simulated groundwater level, in feet above NAVD 88

Groundwater levels, layer 3

Groundwater levels, layer 2

[NAVD 88, North American Vertical Datum of 1988]

Groundwater levels, good

Groundwater levels, fair

Groundwater levels, poor

EXPLANATION

EXPLANATION

Groundwater levels, layer 3

Groundwater levels, layer 2

EXPLANATION

Groundwater levels, good

Groundwater levels, fair

Groundwater levels, poor

EXPLANATION

Residuals by quality category Weighted residuals by quality category

Residuals by layer Weighted residuals by layer

Figure 29. A, Residuals by quality category, B, weighted residuals by quality category, C, residuals by layer, and 

D, weighted residuals by layer for the numerical groundwater-flow model of the Rush Springs aquifer, western 

Oklahoma, 1979–2015.
50 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 30

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017);

Shaded relief derived from USGS (2017a)

Mean groundwater­level residual (observed minus simulated),

in feet, 1979–2015—Numeral indicates map number for

long-term groundwater-level observation well from table 7

Less than −80

−80 to −40

−39 to −20

−19 to −10

−9 to 10

11 to 20

21 to 40

41 to 80

Greater than 80

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower part 

of Whitehorse Group represented by model layer 3

Rush Springs aquifer boundary

EXPLANATION

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb 

Reservoir

0 10 20 30 MILES

0 10 20 30 KILOMETERS

21

Figure 30. Spatial distribution of mean groundwater-level residuals for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 51

For the transient simulation, the mean residual in the 

layer 2 alluvium and terrace was 1.2 ft (table 8). Groundwater 

levels in the layer 2 alluvium and terrace generally were 

underpredicted in the alluvium and terrace in areas closer to 

the surrounding bedrock, whereas groundwater levels were 

overpredicted near the stream channel (fig. 30) because of the 

inability to simulate the full amount of ETg estimated from 

the SWB code. More wells were completed near the stream 

channel than near the surrounding bedrock, and those wells 

near the stream channel contain only a few groundwater-level 

observations each, shown as scattered negative residuals; the 

fewer wells near the surrounding bedrock generally contain 

6–10 observations each, shown as clustered positive residuals 

(figs. 29C, 30). 

The distribution of the mean weighted residuals from 

each observation well is shown on figure 31. Approximately 

half of the largest positive and negative weighted residuals 

occurred in wells located at or near a model boundary; thus, 

structural error may account for these residuals. Large positive 

weighted residuals occurred in a small number of wells 

(fig. 31) including (1) continuous wells 24 and 25 shown 

as vertical clusters at elevations around 1,380 and 1,550 ft 

NAVD 88 (figs. 29B, D), respectively, that had observations 

mostly during drought conditions in 2011–14, and (2) wells 

located near Fort Cobb Reservoir, also shown as vertical 

clusters at elevations around 1,400 ft NAVD 88 (figs. 29B, D), 

where irrigation demand is greatest. Large negative weighted 

residuals (fig. 31) occurred in a greater number of wells than 

the large positive weighted residuals. However, only 1 of the 

15 wells with the largest negative weighted residuals had more 

than 9 groundwater-level observations (fig. 25), and 12 of the 

15 largest negative weighted residuals occurred for wells with 

groundwater-level observations taken only during 2011–14 

when drought conditions were present. The largest negative 

residuals occurred mostly between (1) the Canadian River and 

the model boundary in Blaine County and (2) between Fort 

Cobb Reservoir and the model boundary in eastern Caddo 

County (fig. 31). 
52 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 31

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017); EXPLANATION Shaded relief derived from USGS (2017a)

Mean weighted groundwater­level residual (observed

minus simulated), in feet, 1979–2015

Less than −80

−80 to −40.1

−40 to −20.1

−20 to −10.1

−10 to 0.1

0 to 19.9

20 to 39.9

40 to 79.9

Greater than 80

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower part 

of Whitehorse Group represented by model layer 3

Rush Springs aquifer boundary

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb 

Reservoir

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 31. Spatial distribution of mean weighted groundwater-level residuals for the numerical groundwater-flow 

model of the Rush Springs aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 53

Groundwater-level residuals for each year of the transient 

simulation are shown in figure 32. The mean residual in most 

years was between ±11 ft (fig. 32). The transient simulation 

contained larger negative groundwater-level residuals 

between 1983 and 1989 compared to the subsequent years of the 

simulation. Those larger residuals are probably caused by (1) the 

transition from averaged groundwater-level observations 

used for the steady-state stress period, (2) the overprediction 

of groundwater-level changes as a result of above-mean 

recharge during 1986–87, and (3) the greater number of 

groundwater-level observations prior to 1990 compared to the 

remaining period (fig. 26A). The 75-percent residual range 

for each month generally varied by less than 6 ft, suggesting 

that groundwater-level observations during summer months 

(defined as June–August) do not show a systemic bias in 

underpredicting groundwater levels other than the area around 

Fort Cobb Reservoir. The 35 groundwater levels in 1999 were 

all measured at 27 wells in a 4-mi radius immediately north of 

Fort Cobb Reservoir where observed groundwater levels are 

underpredicted through the simulation period because of the 

large irrigation use in this area. These levels were measured 

in August when irrigation demand was greatest (fig. 19), 

whereas most groundwater levels for the model period were 

measured between January and March of each year (fig. 26B). 

Groundwater levels were also generally underpredicted 

between 2010 and 2014, when drought conditions were 

prevalent (fig. 32). During this period, only five wells had 

more than seven groundwater-level observations; thus, more 

than half of the observations between 2011 and 2015 occurred 

at these five wells (continuous wells 22–26, fig. 11). As a 

result, although positive and negative residuals were spatially 

distributed during the drought period, the mean residual was 

biased towards the underpredicted groundwater levels in these 

five wells.

Simulated well hydrographs generally match the 

trends of observed well hydrographs, but the magnitude 

of the simulated groundwater-level changes was typically 

greater than the observed changes for most wells (fig. 33). 

The overpredicted groundwater-level changes occurred for 

(1) substantial changes in inflow, such as the large recharge 

events in 2007 and 2015, and (2) changes in outflow, such 

as the 60- to 90-percent decrease in well pumping in a 1-mi 

radius around long-term well 18 (figs. 11, 33) between 2007 

and 2010. 

Year

Groundwater-level residual, in feet

Groundwater­level residual range

EXPLANATION

75­percent residual range

Mean groundwater­level residual

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

150

125

100

75

50

25

0

–25

–50

–75

–100

–125

–150

The Oklahoma Water Resources Board (OWRB) groundwater levels 

(OWRB, 2017) from 1999 were mistakenly omitted in this analysis.

Figure 32. Temporal distribution of mean, minimum, and maximum groundwater-level residuals for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.
54 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

1 5

2 6

3 7

4 8

Groundwater level, in feet above North American Vertical Datum of 1988 

2,010

2,030

2,050

2,070

2,090

2,110

2,130

1,720

1,740

1,760

1,780

1,800

1,820

1,840

2,120

2,140

2,160

2,180

2,200

2,220

2,240

1,680

1,700

1,720

1,740

1,760

1,780

1,810

1,830

1,850

1,870

1,890

1,910

1,930

1,780

1,800

1,820

1,840

1,860

1,880

1,900

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

1,520

1,540

1,560

1,580

1,600

1,620

1,640

1,500

1,520

1,540

1,560

1,580

1,600

1,620

Long-term well map number (fig. 11; table 7)

Figure 33_part1

Year Year

1,660

19791983198719911995199920032007201120151979198319871991199519992003200720112015

Figure 33. Observed and simulated groundwater levels in long-term and continuous groundwater-level observation 

wells for the Rush Springs aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 55

Figure 33. Observed and simulated groundwater levels in long-term and continuous groundwater-level 

observation wells for the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

Groundwater level, in feet above North American Vertical Datum of 1988 

1,490

1,510

1,530

1,550

1,570

1,590

1,610

1,470

1,490

1,510

1,530

1,550

1,570

1,590

1,460

1,480

1,500

1,520

1,540

1,560

1,580

1,480

1,460

1,500

1,520

1,540

1,560

1,580

1,400

1,420

1,440

1,460

1,480

1,500

1,520

1,400

1,420

1,440

1,460

1,480

1,500

1,520

1,380

1,400

1,420

1,440

1,460

1,480

1,500

1,440

1,460

1,480

1,500

1,520

1,540

1,560

Long-term well map number (fig. 11; table 7)

EXPLANATION EXPLANATION

EXPLANATION

EXPLANATION EXPLANATION

EXPLANATION EXPLANATION

EXPLANATION

Observed

Simulated

Observed

Simulated

Observed

Simulated

Observed

Simulated

Observed

Simulated

Observed

Simulated

Observed

Simulated

Observed

Simulated

Figure 33_part2

9 13

10 14

11 15

12 16

Year Year

1979198319871991199519992003200720112015

1979198319871991199519992003200720112015
56 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma Groundwater level, in feet above North American Vertical Datum of 1988 

1,370

1,390

1,410

1,430

1,450

1,470

1,490

1,320

1,340

1,360

1,380

1,400

1,420

1,440

1,410

1,430

1,450

1,470

1,490

1,510

1,530

1,250

1,270

1,290

1,310

1,330

1,350

1,370

1,100

1,140

1,180

1,220

1,260

1,300

1,340

Long-term well map number (fig. 11; table 7)

17 20

18 21

19

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Year

Year

1979198319871991199519992003200720112015

1979198319871991199519992003200720112015

Figure 33_part3

Figure 33. Observed and simulated groundwater levels in long-term and continuous groundwater-level 

observation wells for the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued
Simulation of Groundwater Flow 57

Figure 33. Observed and simulated groundwater levels in long-term and continuous groundwater-level 

observation wells for the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

Groundwater level, in feet above North American Vertical Datum of 1988 

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

Observed

EXPLANATION

Simulated

1,480

1,500

1,520

1,540

1,560

1,580

1,600

1,500

1,520

1,540

1,560

1,580

1,600

1,620

1,410

1,430

1,450

1,470

1,490

1,510

1,530

1,320

1,340

1,360

1,380

1,400

1,420

1,440

1,260

1,280

1,300

1,320

1,340

1,360

1,380

Figure 33_part4

22 25

23 26

24

Continuous well map number (fig. 11; table 7)

Year

Year

1979198319871991199519992003200720112015

1979198319871991199519992003200720112015
58 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

In the northern model area (long-term wells 1–3; fig. 11), 

simulated groundwater levels reasonably matched observed 

levels (fig. 33). Simulated groundwater levels in northern 

Caddo County northeast and northwest of Lake Creek (longterm wells 7–11; fig. 11) were overpredicted, while simulated 

levels near Fort Cobb Reservoir (long-term wells 15, 17, 18, 

20, and continuous wells 24–26; fig. 11) generally were 

underpredicted (fig. 33) because of the high pumping rate in 

this area. The location of long-term well 9 was interpolated 

from a topographic map; thus, there was more uncertainty 

for groundwater-level observations from this well than the 

other long-term wells. The Sy across the model area was 

generally similar; therefore, the simulated groundwater-level 

response is less likely to be caused by the variability in the 

storage parameters. 

Base Flow

The pattern of simulated base flows was similar to that 

of estimated base flows at the nine streamgages used in the 

calibration, but mean simulated base flows were slightly 

lower than estimated mean base flows (fig. 34). With the 

exception of the Bridgeport streamgage (07228500), the mean 

base-flow residual was between 14.3 and –1.1 ft3

/s for each 

streamgage (table 9). The mean base-flow residual at the 

Bridgeport streamgage (07228500) was –23.4 ft3

/s, primarily 

because of overpredicted simulated stream seepage west 

of Taloga (fig. 1). For the four Washita River streamgages, 

the RMSE was less than or equal to 9.0 percent of the 

range in estimated base flow, and the mean base flow was 

slightly underpredicted for the Clinton (07325000), Carnegie 

(07325500), and Anadarko (07326500) streamgages (table 9). 

For the Fort Cobb Reservoir tributary streamgages, the RMSE 

was between 7.6 and 26.1 percent of the range in estimated 

base flow because of small mean estimated base flows 

(2.0–15.1 ft3

/s) at these streamgages that were difficult to 

reproduce at the scale of the model (table 9).

Table 9. Statistical summary of base-flow residuals for the numerical groundwater-flow model of the Rush Springs aquifer, western 

Oklahoma, 1979–2015.

[Residual is calculated as the estimated value minus the simulated value; thus, a negative number indicates higher simulated than estimated values. All units are in 

cubic feet per second; RMSE, root-mean-square error; ±, plus or minus]

Station 

number 

(fig. 1)

Station identifier

Estimated base flow Simulated base flow Base-flow residuals RMSE 

percentage of 

range in 

estimated 

base flow

Minimum

Mean Maximum

Minimum

Mean MaximumMean RMSE

75th 

percentile 

range

07228500 Bridgeport 

streamgage on 

Canadian River

0.0 136.0 648.0 45.0 159.0 428.0 −23.4 82.9 ±84.1 12.8

07324200 Hammon streamgage 

on Washita River

0.0 39.3 463.4 3.5 38.3 333.8 −1.1 16.5 ±11.1 3.6

07325000 Clinton streamgage 

on Washita River

0.4 82.0 1,052.3 16.6 80.0 628.4 2.0 62.0 ±30.2 5.9

07325500 Carnegie streamgage 

on Washita River

10.5 240.0 1,851.6 102.9 225.6 780.1 14.3 164.9 ±105.6 9.0

07325800 Cobb Creek 

streamgage on 

Cobb Creek

1.3 15.1 88.2 3.1 15.6 55.1 −0.4 6.6 ±5.8 7.6

07325850 Lake Creek 

streamgage on 

Lake Creek

0.2 4.0 16.6 1.7 4.7 21.3 −0.7 2.8 ±2.0 17.1

07325860 Willow Creek 

streamgage on 

Willow Creek

0.2 2.0 4.8 0.1 1.8 12.4 0.3 1.2 ±1.0 26.1

07326500 Anadarko 

streamgage on 

Washita River

7.9 289.3 2,699.2 99.3 281.3 1,186.5 8.0 203.1 ±106.2 7.5

07327447 Cement streamgage 

on Little Washita 

River

0.0 11.9 74.9 5.1 12.6 49.1 −0.4 6.3 ±5.7 8.4
Simulation of Groundwater Flow 59

A. Hammon streamgage (07324200) on Washita River

B. Clinton streamgage (07325000) on Washita River

Base flow, in cubic feet per second

Streamflow, in cubic

feet per second

Streamflow, in cubic

feet per second

0

800

1,600

0

200

400

600

800

1,000

1,200

Base flow, in cubic feet per second

Year

0

400

800

0

100

200

300

400

500

600

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

Base flow, estimated

Base flow, simulated

Streamflow, observed

Releases from Foss

Reservoir

EXPLANATION

Base flow, estimated

Base flow, simulated

Streamflow, observed

EXPLANATION

Figure 34AB

Figure 34. Observed streamflow, estimated base flow, and simulated base flow at A, Hammon streamgage 

(07324200) on Washita River; B, Clinton streamgage (07325000) on Washita River; C, Carnegie streamgage 

(07305500) on Washita River; D, Anadarko streamgage (07326500) on Washita River; E, Bridgeport 

streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; G, 

Cobb Creek streamgage (07325800) on Cobb Creek; H, Lake Creek streamgage (07325850) on Lake Creek; 

and I, Willow Creek streamgage (07325860) on Willow Creek for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015.
60 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Base flow, estimated

Base flow, simulated

Streamflow, observed

Releases from Foss

Reservoir

EXPLANATION

Base flow, estimated

Base flow, simulated

Streamflow, observed

Releases from Foss and

Fort Cobb Reservoirs

EXPLANATION

C. Carnegie streamgage (07325500) on Washita River

D. Anadarko streamgage (07326500) on Washita River

Base flow, in cubic feet per second

Streamflow, in cubic

feet per second

0

3,000

6,000

Streamflow, in cubic

feet per second

0

3,000

6,000

0

500

1,000

1,500

2,000

2,500

3,000

Base flow, in cubic feet per second

Year

0

400

800

1,200

1,600

2,000

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

Figure 34CD

Figure 34. Observed streamflow, estimated base flow, and simulated base flow at A, Hammon streamgage 

(07324200) on Washita River; B, Clinton streamgage (07325000) on Washita River; C, Carnegie streamgage 

(07305500) on Washita River; D, Anadarko streamgage (07326500) on Washita River; E, Bridgeport 

streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; G, 

Cobb Creek streamgage (07325800) on Cobb Creek; H, Lake Creek streamgage (07325850) on Lake Creek; 

and I, Willow Creek streamgage (07325860) on Willow Creek for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued
Simulation of Groundwater Flow 61

Figure 34. Observed streamflow, estimated base flow, and simulated base flow at A, Hammon streamgage 

(07324200) on Washita River; B, Clinton streamgage (07325000) on Washita River; C, Carnegie streamgage 

(07305500) on Washita River; D, Anadarko streamgage (07326500) on Washita River; E, Bridgeport 

streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; G, 

Cobb Creek streamgage (07325800) on Cobb Creek; H, Lake Creek streamgage (07325850) on Lake Creek; 

and I, Willow Creek streamgage (07325860) on Willow Creek for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

Base flow, estimated

Base flow, simulated

Streamflow, observed

EXPLANATION

Base flow, estimated

Base flow, simulated

Streamflow, observed

EXPLANATION

E. Bridgeport streamgage (07228500) on Canadian River

F. Cement streamgage (07327447) on Little Washita River

Base flow, in cubic feet per second

Streamflow, in cubic

feet per second

0

70

140

Streamflow, in cubic

0

feet per second

2,000

4,000

0

10

20

30

40

50

60

70

80

Base flow, in cubic feet per second

Year

0

100

200

300

400

500

600

700

800

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

Figure 34EF
62 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 34. Observed streamflow, estimated base flow, and simulated base flow at A, Hammon streamgage 

(07324200) on Washita River; B, Clinton streamgage (07325000) on Washita River; C, Carnegie streamgage 

(07305500) on Washita River; D, Anadarko streamgage (07326500) on Washita River; E, Bridgeport 

streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; G, 

Cobb Creek streamgage (07325800) on Cobb Creek; H, Lake Creek streamgage (07325850) on Lake Creek; 

and I, Willow Creek streamgage (07325860) on Willow Creek for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

Base flow, estimated

Base flow, simulated

Streamflow, observed

EXPLANATION

Base flow, estimated

Base flow, simulated

Streamflow, observed

EXPLANATION

Year

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

G. Cobb Creek streamgage (07325800) on Cobb Creek

H. Lake Creek streamgage (07325850) on Lake Creek

Base flow, in cubic feet per second

Streamflow, in cubic

feet per second

0

50

100

Streamflow, in cubic

feet per second

0

200

400

0

5

10

15

20

25

Base flow, in cubic feet per second

0

20

40

60

80

100

Figure 34GH
Simulation of Groundwater Flow 63

Base flows were somewhat overpredicted during 

periods of lower base flows (winter and summer months) and 

underpredicted during periods of higher base flows (fall and 

spring months). Overpredicted base flows were likely the 

result of undersimulated ETg because increases in ETg in the 

model reduced summer low-flow residuals. Underpredicted 

base flows at the Washita River streamgages during highflow periods indicate that estimated base flows probably 

were overestimated by BFI because of reservoir releases 

from Foss or Fort Cobb Reservoirs that could not easily be 

removed from the base-flow estimates. Reservoir releases 

from Foss and Fort Cobb Reservoirs did not occur for about 

half of the total number of stress periods. For these stress 

periods when reservoir releases did not occur, the RMSE for 

the Clinton (07325000), Carnegie (07325500), and Anadarko 

(07326500) streamgages decreased by 65 percent, 54 percent, 

and 68 percent, respectively; the 75-percent residual range 

decreased by 38 percent, 27 percent, and 28 percent, 

respectively. Thus, the model generally simulates patterns 

in estimated base flow with more error present in months 

in which reservoir releases occur. Recharge processes such 

as bank storage flow or interflow that mostly operate on a 

submonthly time scale also could contribute to underpredicted 

base flows. Bank storage flows (Chen, 2003), by which 

floodwater infiltrates the aquifer and is released days to weeks 

after the floodwater recedes, may increase base flows during 

periods of no new recharge. The primary source of water to the 

aquifer is recharge, so large positive base-flow residuals also 

could be caused by underpredicted or incorrectly distributed 

recharge. Additionally, maximum base-flow differences of 

1,000–2,000 ft3

/s between consecutive stress periods could not 

easily be reproduced in the model.

Reservoir Stage and Water Budget

The mean Fort Cobb Reservoir stage residual was 0.1 ft 

(table 10), indicating that the mean simulated stage was 

slightly lower than the mean observed stage (fig. 35A). The 

RMSE of Fort Cobb Reservoir stage residuals was 0.6 ft, and 

75 percent of the simulated reservoir stage values were within 

±0.7 ft of the observed stage values (table 10). The minimum 

simulated stage was 0.1 ft lower than the minimum observed 

stage, and the maximum simulated stage was 0.2 ft higher than 

Figure 34. Observed streamflow, estimated base flow, and simulated base flow at A, Hammon streamgage 

(07324200) on Washita River; B, Clinton streamgage (07325000) on Washita River; C, Carnegie streamgage 

(07305500) on Washita River; D, Anadarko streamgage (07326500) on Washita River; E, Bridgeport 

streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; G, 

Cobb Creek streamgage (07325800) on Cobb Creek; H, Lake Creek streamgage (07325850) on Lake Creek; 

and I, Willow Creek streamgage (07325860) on Willow Creek for the numerical groundwater-flow model of 

the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

Base flow, estimated

Base flow, simulated

Streamflow, observed

EXPLANATION

Year

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

I. Willow Creek streamgage (07325860) on Willow Creek

Base flow, in cubic feet per second

Streamflow, in cubic

feet per second

0

20

40

0

2

4

6

8

10

12

14

Figure 34I
64 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

the maximum observed stage. The largest Fort Cobb Reservoir 

stage residuals occurred in late 1984 and early 1986 when the 

observed reservoir stage was relatively low (fig. 35A). Fort 

Cobb Reservoir stage was also slightly overpredicted during 

drought conditions in 2011–14 when base flows at the Cobb 

Creek (07325800), Lake Creek (07325850), and Willow 

Creek (07325860) streamgages were generally overpredicted 

(figs. 34G–I and 35A). 

Simulated storage in Fort Cobb Reservoir increased by 

about 4,000 acre-ft during the study period (fig. 36B). Storage 

in Fort Cobb Reservoir between 2001 and 2007 reflected 

precipitation trends, where large shifts in precipitation 

occurred during each subsequent year (fig. 7); thus, the 

stage and water budget in Fort Cobb Reservoir for these 

years tended to oscillate on a year-to-year basis more than in 

other periods. Between 2011 and 2014, actual withdrawals 

averaged about 60 percent of the permitted withdrawal volume 

Table 10. Statistical summary of Fort Cobb Reservoir stage 

residuals for the numerical groundwater-flow model of the Rush 

Springs aquifer, western Oklahoma, 1979–2015.

[Observed and simulated stage values for Fort Cobb Reservoir are in feet relative to the North American Vertical Datum of 1988; RMSE, root-mean-square 

error; ±, plus or minus]

Observation Fort Cobb Reservoir stage

Minimum Mean Maximum

Observed 1,334.8 1,341.2 1,349.3

Simulated 1,334.7 1,341.1 1,349.5

Mean residual, in feet 0.1

RMSE, in feet 0.6

75-percentile residual 

range, in feet ±0.7

A

B

Year

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

1,332

1,334

1,336

1,338

1,340

1,342

1,344

1,346

1,348

1,350

1,352

40,000

50,000

60,000

70,000

80,000

90,000

100,000

110,000

Observed stage

Simulated stage

Active conservation

pool stage 

Observed storage

Simulated storage

Active conservation 

pool storage

Fort Cobb Reservoir storage, 

in acre-feet

Fort Cobb Reservoir stage, in feet above 

National Geodetic Vertical Datum of 1929

EXPLANATION

EXPLANATION

Figure 35. Fort Cobb Reservoir observed and simulated A, stage and B, storage for the numerical 

groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 65

(18,000 acre-ft/yr), and stage in Fort Cobb Reservoir dropped 

to about 1,335 ft in 2014, or 68 percent of active conservation 

pool storage (fig. 35). This stage was the lowest since 1961 

(Reclamation, 2017a). This decrease in stage corresponds 

with a decrease in base flow to Cobb, Lake, and Willow 

Creeks during this period (table 2). Because more than half of 

the streamflow in Cobb, Lake, and Willow Creeks upstream 

from Fort Cobb Reservoir occurs as base flow (table 2), 

groundwater-level declines in the aquifer upgradient from Fort 

Cobb Reservoir greatly affect stage and storage. Therefore, 

Fort Cobb Reservoir storage for permitted withdrawals is 

dependent on base-flow inflows.

Fort Cobb Reservoir and the surrounding Rush Springs 

aquifer are hydrologically connected; therefore, declines 

in Fort Cobb Reservoir stage and storage were expected to 

occur during periods of declining groundwater levels in the 

aquifer. Although the simulated groundwater levels in the 

aquifer adjacent to the reservoir were lower than the observed 

A

B

Year

Annual Fort Cobb Reservoir inflow or outflow,

 in acre-feet 

Annual net change in storage

Cumulative net change in storage

Change in Fort Cobb Reservoir storage, 

inacre-feet

Reservoir outflow Reservoir inflow

–140,000

–120,000

–100,000

–80,000

–60,000

–40,000

–20,000

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

Precipitation

Surface runoff

Stream inflow

Net lakebed 

seepage

Evaporation

Withdrawals

(permitted use 

and releases)

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

–24,000

–20,000

–16,000

–12,000

–8,000

–4,000

0

4,000

8,000

12,000

16,000

20,000

24,000

28,000

EXPLANATION

EXPLANATION

EXPLANATION

Figure 36

Figure 36. A, Annual reservoir inflows and outflows and B, change in storage for Fort Cobb Reservoir in the 

numerical groundwater model of the Rush Springs aquifer, western Oklahoma, 1979–2015.
66 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

groundwater levels (fig. 30), mean monthly lakebed seepage 

was less than 17 percent of the reservoir inflows or outflows 

in 95 percent of the stress periods. Additionally, the annual 

imbalances between lakebed seepage to the reservoir, which 

was greatest in April and September when the stage was 

typically low, and lakebed seepage from the reservoir, which 

was greatest in May and June when the stage was typically 

highest, were not large. Thus, simulated groundwater-level 

declines adjacent to Fort Cobb Reservoir had a lesser effect on 

stage and storage than declines in base flow.

Calibrated Water Budget

The calibrated water budget for the Rush Springs aquifer 

model (table 11; fig. 37) lists mean annual inflows and 

outflows for the model period. Simulated recharge was the 

largest inflow (91 percent); lateral groundwater inflow was 

about 5 percent, seepage from streams was about 4 percent, 

and lakebed seepage was less than 1 percent of total inflows. 

Seepage to streams was the largest outflow (56 percent); seeps 

and springs were about 20 percent, ETg was about 13 percent, 

groundwater use was about 9 percent, lateral groundwater 

outflow was about 2 percent, and lakebed seepage was less 

than 1 percent of total outflows.

The mean annual recharge for the calibrated water budget 

(578,676 acre-ft/yr; table 11) was about 4 percent greater 

than that of the conceptual water budget (556,675 acre-ft/yr; 

table 3). This difference corresponds to a rate of 0.1 in/yr. 

Table 11. Mean annual calibrated water budget for the 

numerical groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma, 1979–2015.

[Net budget totals are calculated as inflow minus outflow; therefore, positive 

values indicate net inflow, and negative numbers indicate net outflow; may not 

sum to totals because of rounding; %, percent; <, less than]

Water-budget category

Amount

(acre-feet 

per year)

Percentage 

of water 

budget

Inflow

Recharge1 578,676 91%

Lateral groundwater inflow 30,586 5%

Seepage from streams 24,415 4%

Lakebed seepage 1,244 <1%

Total inflow 634,921 100%

Outflow

Seepage to streams 353,329 56%

Seeps and springs 122,779 20%

Saturated-zone evapotranspiration 

(ETg) 78,319 13%

Groundwater use 57,719 9%

Lateral groundwater outflow 12,349 2%

Lakebed seepage 1,873 <1%

Total outflow 626,368 100%

Net water-budget totals

Stream seepage −328,914

Lakebed seepage −629

Lateral groundwater flow 18,237

Change in groundwater storage 8,553

1

Equals about 2.2 inches per year over the aquifer area of 3,181,003 acres.

Rush Springs aquifer inflows, in percent (table 11)

Rush Springs aquifer outflows, in percent (table 11)

56

20

9

Groundwater

use

2

Lateral

groundwater

outflow 

Seepage to streams 

Seeps and springs

< 1

Lakebed

seepage 

91

< 1

Recharge

Lateral

groundwater

inflow 

Seepage

from

streams 

Lakebed

seepage 

Saturated-zone

evapotranspiration (ETg)

13

5

4

Note: Components may not sum to totals because of rounding. 

Figure 37. Mean annual calibrated water budget for 

the numerical groundwater model of the Rush Springs 

aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 67

Mean annual stream seepage (fig. 38) for the calibrated 

water budget (328,914 acre-ft/yr; table 11) was about 

27 percent greater than that of the conceptual water budget 

(259,161 acre-ft/yr; table 3). However, this stream seepage 

value for the calibrated water budget includes several ungaged 

streams in various areas of the model that are not tributaries 

to the Canadian or Washita Rivers (fig. 38). The sum of the 

calibrated mean annual stream seepage (258,465 acre-ft/yr; 

fig. 38) for the gaged streams (Washita River and tributaries, 

Canadian River and tributaries, Little Washita River and 

tributaries, and Fort Cobb Reservoir tributaries) was about 

15 percent greater than the BFI-estimated mean annual stream 

seepage (225,357 acre-ft/yr; see “Streamflow Characteristics 

and Seepage” section).

The simulated mean annual stream seepage for the 

Canadian River and tributaries (69,688 acre-ft/yr; fig. 38) was 

about 37 percent greater than that of the BFI-estimated mean 

annual stream seepage (51,016 acre-ft/yr). Similar patterns 

occurred between the simulated stream seepage and seepage 

measurements conducted in 2013 (Ellis and others, 2017, 

fig. 14). When compared with the seepage measurements, the 

simulated stream seepage was overpredicted west of Taloga 

(fig. 1) and underpredicted between Taloga and the Bridgeport 

streamgage (07228500) (fig. 38). The two stream segments 

north of the confluence of Deer Creek and the Canadian River 

are the only losing stream segments in the model located on a 

gaged stream other than a segment between the Willow Creek 

streamgage (07325860) and Fort Cobb Reservoir (fig. 38). 

The simulated losing stream segments were caused by 

underpredicted groundwater levels in the area that are below 

the bottom of the streambed in these segments. 

The simulated mean annual stream seepage for the 

Washita River (150,956 acre-ft/yr; fig. 38) was within 

3 percent of the BFI-estimated mean annual stream seepage 

(146,914 acre-ft/yr). The simulated stream seepage was 

underpredicted between the Clinton (07325000) and Carnegie 

(07305500) streamgages, and overpredicted between the 

Carnegie (07325500) and Anadarko (07326500) streamgages. 

Stream seepage in the northeastern, eastern, southeastern, 

southern, and western areas of the model (fig. 38) were 

typically less than 1 ft3

/s (724 acre-ft/yr) in each segment 

with the exception of several stream segments located at 

the northern and southern extremes of the model. These 

segments drained areas that had persistently high simulated 

groundwater levels. 

Simulated seeps and springs (122,779 acre-ft/yr; table 11) 

were about 21 percent less than that of the conceptual water 

budget (155,507 acre-ft/yr; table 3), reflecting uncertainty 

in estimating this component for which published discharge 

rates were unavailable. Mean annual net lateral groundwater 

flow for the calibrated model (18,237 acre-ft/yr; table 11) 

was about 9 percent greater than that of the conceptual water 

budget (16,700 acre-ft/yr; table 3). Mean annual ETg for 

the calibrated model (78,319 acre-ft/yr; table 11) was about 

16 percent less than that of the conceptual water budget 

(92,945 acre-ft/yr; table 3). Because unreasonably long model 

run times are associated with larger ETg areas and rates, the 

area where ETg was simulated and the simulated ETg rate 

were decreased in the simulation. 

The mean simulated annual groundwater use 

(57,719 acre-ft/yr; table 11) was about 12 percent less than 

the conceptual water budget (65,763 acre-ft/yr; table 3) 

because of the threshold applied to large pumping rates 

and because of a lack of saturation in some cells where 

groundwater use occurred. Additionally, groundwater use may 

be overestimated for the Rush Springs aquifer, particularly 

the Fort Cobb Reservoir watershed (fig. 10), where 52 percent 

of mean annual groundwater use occurs. Groundwater use 

for the irrigation of winter wheat, which is the predominant 

crop overlying the Rush Springs aquifer and the Fort Cobb 

Reservoir watershed (NASS, 2017), may be overestimated by 

approximately 10 percent (Masoner and others, 2003). 

Simulated groundwater storage at the end of the 

model period (2015) was 44,837,437 acre-ft, and mean 

simulated groundwater storage for the model period was 

44,830,760 acre-ft (Ellis, 2018). Because of the difficulty 

associated with estimating total recoverable groundwater—

whereby groundwater pumping cannot extract the entire 

volume of water from the aquifer—these simulated 

groundwater storage values represent theoretical volumes. 

However, these values are useful for comparisons of changes 

in groundwater storage caused by aquifer stresses. 

For the model period 1979–2015, mean annual simulated 

inflows exceeded outflows by 8,553 acre-ft/yr (table 11). 

This difference corresponds to a cumulative net storage 

increase of about 353,581 acre-ft (fig. 39), or a cumulative net 

groundwater-level increase of 1.6 ft. This increase in storage 

occurred largely as a result of (1) a period of sustained greater 

than mean annual recharge between 1985 and 2000 and 

(2) recharge in 2007 and 2015, which are the first and third 

largest recharge events during the model period (fig. 39) that 

were substantially greater than the mean annual recharge.
68 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 38

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Geology from Heran and others (2003), Ellis and others (2017)

EXPLANATION

Simulated mean annual stream seepage (1979–2015), in acre­feet per year

−17,494 to −10,001

−10,000 to −5,001

−5,000 to −2,501

−2,500 to −1,251

−1,250 to 0

1 to 249

250 to 1,537

Seepage to streams Seepage from streams

Rush Springs aquifer boundary

Surface watershed boundary

(USGS, 2017b)

Streamgage and number

07325500

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Upper 30 feet of Whitehorse

Group represented by model layer 2 and lower 

part of Whitehorse Group represented by model 

layer 3

WOODWARD

GARFIELD

MAJOR

BLAINE

KINGFISHER

DEWEY

CANADIAN

CADDO

GRADY

KIOWA

GREER

COMANCHE

CUSTER

WASHITA

JACKSON

WOODS

GARVIN

MCCLAIN

35°00'

98°00'

98°00'

98°30'

99°00'

99°30'

36°00'

35°30'

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Beaver Creek

Washita River

Foss

Reservoir

Fort Cobb 

Reservoir

0 10 20 30 MILES

0 10 20 30 KILOMETERS

07228500

07324200

07325000

07325500

07325800

07325850

07326500

07327447

07325860

07324400

07228500

07324200

07325000

07325500

07325800

07325850

07326500

07327447

07325860

07324400

Canadian River 

and tributaries 

Washita River

and tributaries

Northeastern 

area streams

Western 

area streams

Southeastern 

area streams

Eastern 

area streams

Southern 

area streams

Canadian River 

and tributaries 

Washita River

and tributaries

Northeastern 

area streams

Western 

area streams

Southeastern 

area streams

Eastern 

area streams

Southern 

area streams

21.2 percent

Total: 328,914 acre-feet per year

Canadian River

and tributaries

69,688 

Rush Springs simulated mean annual stream seepage

(1979–2015), in acre­feet per year (1979–2015), in acre feet per year

6.1 percent

20,018

8.2 percent

26,847

7.4 percent

24,206

4.1 percent

Southeastern 

area

13,591

1.3 percent

Western 

area

4,258

0.5 percent

Eastern 

area

1,547

5.4 percent

17,803

45.9 percent

Washita River

and tributaries

150,956 Little Washita 

River and tributaries

Components may not sum to totals

because of rounding

Ft. Cobb Reservoir

tributaries

Southern 

area

Northeastern 

area

Rush Springs aquifer zone

Washita River and tributaries

Canadian River and tributaries

Little Washita River and tributaries

Ft. Cobb Reservoir tributaries

Southern area

Northeastern area

Southeastern area

Western area

Eastern area

EXPLANATION

Figure 38. Simulated stream seepage for the numerical groundwater-flow model of the Rush Springs aquifer, western 

Oklahoma, 1979–2015.
Simulation of Groundwater Flow 69

Simulated annual groundwater storage changes reflect 

climatic trends during the model period (fig. 39). From 1979 

to 1984, cumulative storage decreased (fig. 39) because of a 

period of mean to lower than mean precipitation (fig. 7). A 

relatively long period of above-mean precipitation occurred 

between 1985 and 2000 (fig. 7), which provided a substantial 

amount of recharge to the aquifer, resulting in a cumulative 

storage increase (fig. 39). This period was followed by a 

period of generally below-mean precipitation between 2001 

and 2006 (fig. 7), whereby cumulative storage decreased 

(fig. 39). The drought conditions between 2009 and 2014 

(fig. 7) resulted in a sustained decrease of groundwater in 

storage (fig. 39). By comparison, the cumulative storage 

change between 2009 and 2014 (about 1,376,000 acre-ft; fig. 39) 

is slightly greater than 19 times the volume of water stored in 

Fort Cobb Reservoir at the active conservation pool stage. 

Recharge composes 91 percent of the total simulated 

inflow to the aquifer (fig. 39; table 11). Therefore, precipitation 

A

B

Year

Aquifer inflow or outflow, in thousands of acre-feet 

Annual net change in storage

Cumulative net change in storage

Groundwater storage change, in thousands of acre-feet

Aquifer outflow Aquifer inflow

−1,000,000

−800,000

−600,000

−400,000

−200,000

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1,800,000

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015

−1,000,000

−800,000

−600,000

−400,000

−200,000

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1,800,000

EXPLANATION

EXPLANATION

Net lateral

groundwater flow

Recharge

Saturated­zone

evapotranspiration

Springs and seeps

Groundwater use

Net stream seepage

The lakebed seepage terms are small compared to the other 

budget components and cannot be viewed at this scale.

Figure 39

Figure 39. A, Annual mean inflows and outflows and B, annual change in groundwater storage for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.
70 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

changes greatly affect groundwater storage and the annual 

water budget, which is several times larger in years with 

substantial precipitation events compared with years of belowmean precipitation. During extended periods of below-mean 

precipitation, groundwater use substantially increased—such 

as during 2014 and 2015, when groundwater use was 92 and 

53 percent greater, respectively, than the average (Neel and 

others, 2018, fig. 16)—which compounded the effects on 

groundwater storage. Because simulated groundwater levels 

were overpredicted during and after large precipitation 

events, the simulated inflows in these years may also 

be overestimated. 

Mean simulated aquifer inflows, primarily from recharge 

and seepage from streams, tended to be greatest during 

January through March (fig. 40A), which corresponds to 

months of above-mean recharge (fig. 8B). Mean simulated 

aquifer outflows, primarily from seepage to streams, ETg, and 

groundwater use, were greatest in July and August (fig. 40A). 

During those summer months, seepage to streams was reduced 

by groundwater-level declines from large ETg outflows and 

groundwater use, which was primarily for irrigation. Mean 

monthly outflows exceeded mean monthly inflows in 4 of 

12 months (fig. 40B).

Calibrated Parameter Values

The calibrated parameter values for the model (table 6) 

represent updates to the initial values estimated from available 

hydraulic data or from the conceptual water budget. Only 

753 of 842 parameters remained adjustable throughout the 

calibration process (table 6). A total of 89 parameters were 

fixed during the calibration process—mostly because of 

stability-related issues. Five of the 753 parameters had no 

effect on model calibration; each of these parameters were in 

the Washita River alluvium (layer 2) in the western part of the 

model where few calibration targets were available (fig. 25). 

Calibrated GHB and Drain Conductance

Calibrated mean and maximum GHB conductances 

for the six GHB conductance zones (fig. 15) were 660 and 

2,000 ft2

/d, respectively (table 6). Increases in the GHB 

conductance resulted in increased flow to the western area of 

the model underlying the Cloud Chief Formation, where most 

groundwater levels were underpredicted. However, these GHB 

conductance increases also resulted in (1) larger base flow and 

stream seepage residuals for the Canadian River, when the 

simulated base flow could not match the lower estimated base 

flow (fig. 34E), and (2) larger groundwater-level residuals in 

the northern area of the model where most groundwater levels 

were somewhat overpredicted (fig. 30). 

Calibrated mean and maximum drain conductances 

for the 11 drain conductance zones were 207 and 501 ft2

/d, 

respectively (table 6). Although drain conductance increases 

for zone 10 (drn10; fig. 15) reduced the groundwater-level 

residuals near that zone, increases in the groundwater-level 

residuals occurred for simulated groundwater levels around 

Fort Cobb Reservoir. A similar number of groundwater-level 

observations were available for the Fort Cobb Reservoir 

watershed, where groundwater levels were underpredicted, 

and the area around zone 10, where levels were overpredicted 

(fig. 30). However, the 445 monthly stage observations at 

Fort Cobb Reservoir provided a greater contribution to the 

objective function than these groundwater-level observations; 

therefore, no objective function improvement was seen when 

this drain conductance was increased. 

Calibrated Recharge

Calibrated recharge was increased from the conceptual 

water budget by using recharge multipliers applied to the 

23 recharge zones (fig. 20). Calibrated recharge was increased 

and decreased in 11 zones each and was unchanged in 1 zone 

(table 6). The recharge multiplier zones were substantially 

different in areal extent, whereby 4 of the 23 zones (zones 14, 

15, 17, and 19; fig. 20) account for just over half of the aquifer 

area. Although spatially distributed recharge could have been 

further discretized into smaller zones, there was no apparent 

geologic or hydrologic basis for doing so. Additionally, further 

increases in the number of parameters, when combined with 

the lengthy model run times (approximately 9 hours), would 

have been impractical.

Spatially, calibrated mean annual recharge (fig. 41) 

decreased from the initial mean annual recharge (fig. 9) in 

the northern, eastern, and alluvium and terrace areas because 

groundwater levels were mostly overpredicted in those areas 

(fig. 30). Calibrated recharge increased in the southern and 

western model areas and Fort Cobb Reservoir watershed 

because groundwater levels were mostly underpredicted 

in those areas (fig. 30). These calibrated recharge changes 

generally resulted in increased recharge in areas of greater 

groundwater development and decreased recharge in areas 

of lesser development. Calibrated mean annual recharge 

in the Fort Cobb Reservoir watershed was 3.6 in/yr. The 

increase in mean annual recharge from the initial SWB 

estimate (1.8 in/yr) to the calibrated value (3.6 in/yr) was 

comparable but slightly greater than the mean annual increase 

in estimated recharge from crop irrigation (1.3 to 1.6 in/yr) 

compared to rangeland (McMahon and others, 2006) that is 

not irrigated. Therefore, when accounting for the effects of 

recharge from irrigation, the calibrated mean annual recharge of 

3.6 in/yr may be more indicative of recharge to the Fort Cobb 

Reservoir watershed.
Simulation of Groundwater Flow 71

A

B

Aquifer inflow or outflow, in acre-feet

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Change in groundwater storage (inflows

minus outflows), in acre-feet

Month

Aquifer outflow Aquifer inflow

0

The lakebed seepage terms are small compared to the other 

budget components and cannot be viewed at this scale.

–800,000

–600,000

–400,000

–200,000

0

200,000

400,000

600,000

Change in storage

Seepage to streams

Seeps and springs

Saturated­zone

evapotranspiration

Lateral groundwater

outflow

Groundwater use

Lateral groundwater

inflow

Seepage from streams

Recharge

EXPLANATION

EXPLANATION

EXPLANATION

–1,000,000

–800,000

–600,000

–400,000

–200,000

200,000

400,000

600,000

800,000

1,000,000

1,200,000

Figure 40 Figure 40. A, Mean monthly aquifer inflows and outflows and B, mean monthly change in groundwater 

storage for the Rush Springs aquifer, western Oklahoma, 1979–2015.
72 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 41

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Foss

Reservoir

Fort Cobb 

Reservoir

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Calibrated mean annual recharge 

(1979–2015), in inches

0.01 to 0.50

0.51 to 1.00

1.01 to 2.00

2.01 to 4.00

> 4.00

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 41. Calibrated mean annual recharge for the numerical groundwater-flow model of the Rush Springs 

aquifer, western Oklahoma, 1979–2015.
Simulation of Groundwater Flow 73

Calibrated Evapotranspiration from Groundwater

The calibrated ETg rate multiplier was reduced to a 

value of 0.4 (40 percent) (table 6) in all areas where ETg 

was simulated. Although further increases in the ETg rate 

multiplier may have improved the calibration to base flows 

and groundwater levels, larger ETg rates could not be 

simulated without model stability issues. Because of these 

stability issues and extended run times during automated 

calibration, the following changes were made during 

calibration: (1) the ETg area—originally defined by using 

National Wetlands Inventory data (U.S. Fish and Wildlife 

Service, 2017)—was reduced to a narrower zone adjoining the 

simulated stream channel in the alluvium, and (2) an annual 

threshold of 75 in/yr was applied to the ETg rate.

Following the automated calibration, the rate multipliers 

for the Canadian River, Fort Cobb Reservoir tributaries, and 

the Little Washita River ETg areas were adjusted by using 

manual calibration zones to further reduce base-flow and 

groundwater-level residuals. In these ETg areas where manual 

adjustments occurred, the final rate multiplier was equivalent 

to a value between 0.8 (80 percent) and 1.2 (120 percent) of 

the initial ETg rate.

Calibrated Reservoir Inputs

Precipitation, evaporation, surface runoff, and withdrawal 

inputs for Fort Cobb Reservoir were adjusted manually 

following the automated calibration. During each stress 

period, precipitation and evaporation were varied between 

±20 percent until a match was obtained between the 

observed and simulated stage. Because of the uncertainty 

inherent in estimating surface runoff to Fort Cobb 

Reservoir—particularly overland flows—surface runoff 

was varied between ±30 percent in each stress period.

Fort Cobb Reservoir stage was generally 

underpredicted during summer months (fig. 35); thus, 

precipitation and surface runoff were increased and 

evaporation was decreased during these months (fig. 42). 

The required increase in surface runoff, particularly in 

May and June when precipitation was greatest (fig. 8A), 

suggests that this input was underestimated—or that 

ETg was overestimated—during the generation of 

inputs to the Lake package. During the 2009–14 

drought period, stream inflows from Cobb Creek, Lake 

Creek, and Willow Creek to Fort Cobb Reservoir were 

overpredicted (fig. 34G–I). Therefore, recharge and 

surface runoff were decreased, and evaporation was 

increased in order to match the observed stage (fig. 42). 

Large reservoir releases during 12 of the 445 stress 

periods between 1989 and 1991 were reduced by an 

average of 50 percent because of substantial declines in the 

simulated reservoir stage that occurred when the full release 

amount was simulated. 

Calibrated Hydraulic Conductivity and Vertical Anisotropy

Layer 1 was minimally saturated throughout the 

simulation; thus, Kh in this layer was not adjusted during 

calibration and represents interpolated values from Neel and 

others (2018). The mean Kh for layer 1 was 1.6 ft/d, and the 

values ranged between 0.1 and 4.0 ft/d (fig. 43A). 

Mean calibrated Kh from the interpolated pilot points in 

the layer 2 alluvium and terrace was 48.6 ft/d, and the values 

ranged from 0.74 to 90.0 ft/d (fig. 43B). Spatially, Kh was 

greatest in the Washita River alluvium, particularly between 

the Clinton (07325000) and Carnegie (07325500) streamgages 

where simulated stream seepage was underpredicted (fig. 43B). 

Layer 2 Kh values were generally lower in the Canadian River 

alluvium, where simulated stream seepage was overpredicted 

(fig. 38). 

Literature describing the Kh of the alluvium and terrace 

of the Washita River or Fort Cobb Reservoir tributaries was 

limited. Therefore, calibrated Kh for the Canadian River 

alluvium and terrace was compared between this model and 

the Reach I model from Ellis and others (2017) (fig. 44A). 

The mean calibrated Kh for the Canadian River alluvium 

and terrace (45.6 ft/d) was within 3.4 percent of the mean 

calibrated Kh (44.1 ft/d) from Ellis and others (2017). A 

greater number of cells had calibrated Kh values between 80.0 

and 90.0 ft/d in this model than in the Reach I model (Ellis and 

others, 2017) (fig. 44A). A number of these Kh values were at 

the upper Kh boundary of 90.0 ft/d, indicating that additional 

Change from initial lake parameter values, in percent

Month

−20

−15

−10

−5

0

5

10

15

20

Jan. Feb. Mar. Apr. May. June July Aug. Sept. Oct. Nov. Dec.

Precipitation multiplier

Evaporation multiplier

Runoff multiplier

EXPLANATION

Figure 42. Change from initial Lake package inputs for the 

numerical groundwater-flow model of the Rush Springs aquifer, 

western Oklahoma, 1979–2015.
74 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 43. Calibrated horizontal hydraulic conductivity (Kh) of the A, Cloud Chief Formation (layer 1), 

B, alluvium and terrace (layer 2), and C, lower Whitehorse Group (layer 3) for the Rush Springs aquifer numerical 

groundwater-flow model, western Oklahoma.

laf18-0888_fig 43a

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Fort Cobb 

Reservoir

Foss

Reservoir

EXPLANATION

Rush Springs aquifer

boundary 

Horizontal hydraulic conductivity (Kh) of the 

Cloud Chief Formation (layer 1), in feet

per day

0.1 to 0.4

0.5 to 0.9

1.0 to 1.9

2.0 to 2.9

3.0 to 4.0

0 10 20 30 MILES

0 10 20 30 KILOMETERS

A. Cloud Chief Formation (layer 1)
Simulation of Groundwater Flow 75

Figure 43. Calibrated horizontal hydraulic conductivity (Kh) of the A, Cloud Chief Formation (layer 1), 

B, alluvium and terrace (layer 2), and C, lower Whitehorse Group (layer 3) for the Rush Springs aquifer numerical 

groundwater-flow model, western Oklahoma.—Continued

laf18-0888_fig 43b

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Fort Cobb 

Reservoir

Foss

Reservoir

EXPLANATION

Rush Springs aquifer

boundary

Layer 2 pilot point location 

Calibrated horizontal hydraulic conductivity 

(Kh) of the alluvium and terrace deposits

(layer 2), in feet per day

0.74 to 20

20.1 to 40

40.1 to 60

60.1 to 80

80.1 to 90

0 10 20 30 MILES

0 10 20 30 KILOMETERS

B. Alluvium and terrace deposits (layer 2)
76 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 43c

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

EXPLANATION

Rush Springs aquifer

boundary

Layer 3 pilot point location 

Calibrated horizontal hydraulic conductivity 

(Kh) of the lower part of Whitehorse 

Group (layer 3), in feet per day

0.01 to 4.9

5 to 9.9

10 to 19.9

20 to 39.9

40 to 90—Visible

in inset

0 10 20 30 MILES

0 10 20 30 KILOMETERS

C. Lower part of Whitehorse Group (layer 3)

Inset

Inset

Figure 43. Calibrated horizontal hydraulic conductivity (Kh) of the A, Cloud Chief Formation (layer 1), 

B, alluvium and terrace (layer 2), and C, lower Whitehorse Group (layer 3) for the Rush Springs aquifer numerical 

groundwater-flow model, western Oklahoma.—Continued
Simulation of Groundwater Flow 77

upward adjustment of these Kh values using PEST may 

have yielded an improved calibration. In the Ellis and others 

(2017) groundwater model of the Canadian River, maximum 

calibrated Kh in the Reach I model was 176 ft/d; thus, an 

increase in Kh may be reasonable. However, without the 

application of regularization techniques for the Kh values in 

the model, setting an upper limit greater than 90.0 ft/d may 

have resulted in an excessive percentage of Kh values greater 

than 90.0 ft/d. 

Mean calibrated vertical anisotropy in the 

alluvium and terrace was 9.9 (9.9:1 horizontal-tovertical ratio), and the values ranged from 8.7 to 20. 

The vertical anisotropy of 9.7 for the Canadian River 

alluvium and terrace was greater than that of Ellis and 

others (2017), which was 3. 

Mean calibrated Kh for the lower Whitehorse 

Group was 6.6 ft/d, and the values ranged from 

0.01 to 90.0 ft/d (fig. 43C). This mean Kh is within 

5 percent of the initial mean Kh of 6.3 ft/d obtained 

from Neel and others (2018). The mean calibrated 

Kh for the lower Whitehorse Group under the 

Cloud Chief Formation was 8.3 ft/d. Although the 

groundwater levels in this area were underpredicted, 

whereby Kh values would be expected to be lowered 

to compensate, the more numerous underpredicted 

monthly streamflow observations at the Carnegie 

streamgage (07225000) (fig. 34C) resulted in a slight 

increase in calibrated Kh in this area during automated 

calibration. The mean calibrated Kh for the lower 

Whitehorse Group where not overlain by the Cloud 

Chief Formation was 6.0 ft/d. 

The distribution of calibrated Kh values differed 

from Neel and others (2018) through (1) an increase 

in the number of cells with Kh values between 0.01 

and 3.0 ft/d and between 9.1 and 30.0 ft/d, and 

(2) a decrease in the number of cells with Kh values 

between 3.1 and 9.0 ft/d (fig. 44B). Of the Kh values 

from this calibrated model and from Neel and others 

(2018), 99 percent are less than 30 ft/d (fig. 44B); thus, 

the majority of Kh-value adjustments occurred within 

a constrained range.

The mean calibrated Kh of 6.6 ft/d is similar 

to most values from available aquifer-test results 

conducted in the Rush Springs aquifer. Although the 

results from these aquifer tests provide hydraulic 

parameter information pertaining to a relatively 

localized area, aquifer-test values in various locations 

of the aquifer were informative of overall aquifer 

properties. Kh values from these tests were (1) 1.6 ft/d 

for the town of Hydro (fig. 1) production well (Neel 

and others, 2018), (2) 6.4 ft/d for a single-well aquifer 

test in southern Grady County (Neel and others, 

2018), (3) 3.8–4.4 ft/d for aquifer tests in Weatherford, OK 

(fig. 1) (Becker and Runkle, 1998), (4) 5.4 ft/d for a 2-week 

multi-well aquifer test in Caddo County (Neel and others, 

2018), and (5) 45 ft/d for a Grady County production well 

(Neel and others, 2018). The higher Kh value for the Grady 

County production well aquifer test relative to the others may 

be indicative of an uncemented sand versus more common 

descriptions of loosely cemented sand from published 

literature (Tanaka and Davis, 1963; Becker and Runkle, 1988; 

Neel and others, 2018).

Mean calibrated vertical anisotropy in the lower 

Whitehorse Group was 11.2 (11.2:1 horizontal-to-vertical 

ratio), or slightly greater than the initial 10:1 vertical 

0

10

20

30

40

50

60

0

10

20

30

40

50

60

Percent of estimated values Percent of estimated values

Horizontal hydraulic conductivity, in feet per day

Horizontal hydraulic conductivity, in feet per day

0.01 to 3.0 3.1 to 6.0 6.1 to 9.0 9.1 to 12.0 12.1 to 15.0 15.1 to 30.0 30.1 to 90.0

Horizontal hydraulic conductivity

from Neel and others (2018)

Calibrated horizontal hydraulic

conductivity

0.74 to 19.9 20.0 to 39.9 40.0 to 59.9 60.0 to 79.9 80.0 to 90.0

Horizontal hydraulic conductivity

from Ellis and others (2017)

Calibrated horizontal hydraulic

conductivity

EXPLANATION

EXPLANATION

Figure 44

B. Lower Whitehorse Group (layer 3)

A. Canadian River alluvium and terrace (layer 2)

Figure 44. Horizontal hydraulic conductivity and calibrated horizontal 

hydraulic conductivity for A, Canadian River alluvium and terrace and 

B, lower Whitehorse Group for the groundwater-flow model of the Rush 

Springs aquifer, western Oklahoma.
78 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

anisotropy, and the calibrated values ranged 

from 7.4 to 20. Cores examined from previous 

studies show subangular to subround grains and a 

moderate degree of cross bedding and cementation 

(Tanaka and Davis, 1963; Becker and Runkle, 

1998; Neel and others, 2018); therefore, these 

values are thought to be reasonable. 

Storage Parameters

The calibrated Sy values for each layer were 

unchanged from the initial Sy values from Neel 

and others (2018). The mean and maximum Sy 

values for layer 1 were 0.05 and 0.08, respectively 

(figs. 45A and 46A). The mean values are similar 

to those of Johnson (1967), which lists values 

of 0.05 and 0.03 for silt and clay, respectively, 

based on a laboratory sediment analysis. The 

mean and maximum calibrated Sy values for the 

alluvium and terrace in layer 2 were 0.07 and 0.29, 

respectively (figs. 45B and 46B). The calibrated Sy 

values for the Canadian River alluvium and terrace, 

for which the mean and maximum calibrated 

Sy values were 0.16 and 0.29 (Ellis and others, 

2017), were somewhat greater than the Sy values 

for the Washita River alluvium and terrace and 

the Little Washita River alluvium (fig. 46B). The 

Washita River incises the fine-grained Cloud Chief 

Formation and relatively fine-grained Whitehorse 

Group, whereas the Canadian River incises coarser 

grained materials such as the Ogallala Formation 

(Hendricks, 1937); therefore, Sy values for the 

Washita River alluvium and terrace were expected 

to be lower than the Sy values for the Canadian 

River alluvium and terrace. 

The mean and maximum Sy values for 

layer 3 were 0.07 and 0.23, respectively, and 

99 percent of the values were less than 0.11 

(figs. 45C and 46C). Although Sy depends on the 

sorting, dominant size, and cementation of aquifer 

materials—textural properties that cannot always 

be derived from the lithologic logs analyzed—the 

Sy values used in the model also agree with the 

aquifer tests described in the “Calibrated Hydraulic 

Conductivity and Vertical Anisotropy” section of 

this report. The Sy values obtained from these tests 

were 0.09 (town of Hydro production well; Neel 

and others, 2018), 0.09 (single-well test in southern 

Grady County; Neel and others, 2018), 0.08 

(aquifer test in Weatherford; Becker and Runkle, 

1998), 0.07 (multi-well test in Caddo County; Neel 

and others, 2018), and 0.04 (Grady County production 

well; Neel and others, 2018).

A. Cloud Chief Formation

B. Alluvium and terrace (Canadian River)

C. Lower Whitehorse Group

0

5

10

15

20

25

30

35

40

45

50

0.01 to 0.04 0.04 to 0.05 0.05 to 0.06 0.06 to 0.07 0.07 to 0.08

Specific yield

Specific yield

Specific yield

Percent of estimated values

0

5

10

15

20

25

30

35

40

45

50

Percent of estimated values Percent of estimated values

0.01 to 0.06 0.06 to 0.12 0.12 to 0.15 0.15 to 0.18 0.18 to 0.21 0.21 to 0.29

0

5

10

15

20

25

30

35

40

0.01 to 0.05 0.05 to 0.06 0.06 to 0.07 0.07 to 0.08 0.08 to 0.09 0.09 to 0.23

Figure 45

Figure 45. Specific yield for the A, Cloud Chief Formation; B, Canadian 

River alluvium and terrace; and C, lower Whitehorse Group for the Rush 

Springs aquifer, western Oklahoma.
Simulation of Groundwater Flow 79

Figure 46. Specific yield of the A, Cloud Chief Formation (layer 1), B, alluvium and terrace (layer 2), and C, 

lower Whitehorse Group (layer 3) for the Rush Springs aquifer numerical groundwater-flow model, western 

Oklahoma.

laf18-0888_fig 46a

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Fort Cobb 

Reservoir

Foss

Reservoir

Specific yield of the Cloud Chief

Formation (layer 1)

0.01 to 0.039

0.04 to 0.049

0.05 to 0.059

Rush Springs aquifer boundary

0.06 to 0.069

0.07 to 0.080

EXPLANATION

0 10 20 30 MILES

0 10 20 30 KILOMETERS

A. Cloud Chief Formation (layer 1)
80 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 46b

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Fort Cobb 

Reservoir

Foss

Reservoir

EXPLANATION

Specific yield of the alluvium and

terrace deposits (layer 2)

0.01 to 0.059

0.06 to 0.119

0.12 to 0.149

Rush Springs aquifer boundary

0.15 to 0.179

0.18 to 0.209

0.21 to 0.287

0 10 20 30 MILES

0 10 20 30 KILOMETERS

B. Alluvium and terrace deposits (layer 2)

Figure 46. Specific yield of the A, Cloud Chief Formation (layer 1), B, alluvium and terrace (layer 2), and C, 

lower Whitehorse Group (layer 3) for the Rush Springs aquifer numerical groundwater-flow model, western 

Oklahoma.—Continued
Simulation of Groundwater Flow 81

Figure 46. Specific yield of the A, Cloud Chief Formation (layer 1), B, alluvium and terrace (layer 2), and C, 

lower Whitehorse Group (layer 3) for the Rush Springs aquifer numerical groundwater-flow model, western 

Oklahoma.—Continued

laf18-0888_fig 46c

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

EXPLANATION

Specific yield of the lower part of 

Whitehorse Group (layer 3)

0.01 to 0.049

0.05 to 0.059

0.06 to 0.069

Rush Springs aquifer boundary

0.07 to 0.079

0.08 to 0.089

0.09 to 0.230

0 10 20 30 MILES

0 10 20 30 KILOMETERS

C. Lower part of Whitehorse Group (layer 3)
82 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Sensitivity and Identifiability

Several analyses were performed to ensure that the 

parameters used were effective in reducing the objective 

function and to evaluate the correlation among parameters 

and identify parameters informed by the calibration process. 

During automated calibration, PEST computed the sensitivities 

of each parameter with respect to all observations by using 

1-percent changes in parameters, which are contained in 

the Jacobian matrix. These sensitivities are a dimensionless 

measure of the change in residuals affected by adjustments to 

a parameter; thus, calibration-target residuals are more easily 

reduced by parameters with larger sensitivities. Sensitivities 

were calculated by using the Jacobian matrix output from 

PEST (table 6) and summed for each parameter group 

(fig. 47).

The observation groups were generally most sensitive 

to changes in recharge and hydraulic conductivity (fig. 47). 

Recharge was the largest aquifer inflow (table 11), which—

along with the pilot points used to adjust hydraulic 

conductivity and specific yield—affected the groundwater 

levels, base flows, stream seepage, and reservoir stage 

throughout the model. Out of the highest parameter 

sensitivities, recharge parameter zones represented the six 

largest. Two of the three most sensitive parameters, recharge 

zones 14 and 5 (table 6; fig. 20), were located in the Fort 

Cobb Reservoir watershed, which contained the largest 

concentration of base-flow estimates and groundwater-level 

observations in the model (figs. 1, 10) as well as the Fort Cobb 

Reservoir stage observations. Adjustments to Sy occurred as 

an entire-layer multiplier; thus, adjustments in this manner 

also resulted in a higher sensitivity relative to other parameter 

groups. 

Changes in ETg applied to the alluvium and 

terrace (fig. 13) had a lesser effect on groundwater-level 

observations because most of the observations are distant 

from Evapotranspiration package cells. Changes in ETg 

also resulted in sensitivity for the Fort Cobb Reservoir stage 

observations because stream inflows contributed a large 

percentage of inflow to this reservoir. Drain cells representing 

seeps and springs compose a majority of the northeastern, 

eastern, and southeastern boundaries of the model (fig. 15). 

As a result, most observation groups were sensitive to 

changes in drain conductance. The “good” groundwaterlevel observations and base-flow estimates composed about 

71 percent of all calibration targets in the model (table 5); 

1

10

100

1,000

10,000

100,000

1,000,000

Recharge Hydraulic

conductivity

Specific 

yield

Saturated-zone

evapotranspiration

Drain 

conductance

Streambed

conductance

General-head

boundary

conductance

Specific 

storage

Dimensionless sensitivities

Parameter group

Lake stage

Groundwater levels, good

Base flow

Groundwater levels, fair

Stream seepage

Groundwater levels, poor

Observation group

EXPLANATION

Figure 47. Observation group sensitivity by parameter group in the numerical groundwater-flow model for 

the Rush Springs aquifer, western Oklahoma.
Simulation of Groundwater Flow 83

thus, these two calibration-target observation groups had 

among the highest sensitivities of any observation group. The 

sensitivities for the lakebed leakance were nearly zero for 

every observation group; therefore, they were not shown on 

figure 47.

Parameter sensitivities provide some insight regarding 

their value in the calibration process. However, they do not 

reflect the (1) degree of parameter correlation, whereby 

changes in one parameter value are offset by changes in 

another, negating any advantage in using these parameters 

to improve model fit, or (2) the ability to uniquely estimate 

each parameter based on the calibration dataset (Doherty 

and Hunt, 2009). Thus, another statistic—parameter 

identifiability—is used for highly parameterized models to 

quantify parameter correlation and the amount of information 

gained from the calibration dataset. Outputs using this 

method use a normalized scale range between zero and one. 

An identifiability of zero reveals that no information for a 

parameter is provided from the calibration dataset, resulting in 

(1) insensitivity of model outputs to changes in a parameter, 

and (2) a lack of reduction in the parameter uncertainty 

from the calibration process. An identifiability value of one 

indicates that a parameter incorporates substantial calibration 

information and that potential parameter error is caused by 

noise associated with the calibration-target dataset (Doherty 

and Hunt, 2009). Values between zero and one indicate some 

degree of parameter correlation whereby information is shared 

between parameters. Parameters with a high identifiability, 

and thus a lower uncertainty, can be viewed as favorable to 

the calibration process, but parameters with low identifiability 

retain prior uncertainty and are uninformed by the calibration 

process. Therefore, expert knowledge is required to assign 

values for parameters with lower identifiabilities. An 

identifiability value of 0.7 was chosen as a cutoff between 

parameters that are identifiable and those parameters that are 

not based on a similar cutoff chosen in other studies (Doherty 

and Hunt, 2009; Masterson and others, 2016). 

Singular values identified by using SVD are associated 

with unit vectors that span parameter space (Doherty and 

Hunt, 2009). Parameter space includes the solution space, 

which contains parameters and parameter combinations 

that can be estimated, and the null space, which contains 

parameters that cannot be estimated. The number of 

identifiable parameters is directly related to the number of 

singular values contained in the solution space (Doherty 

and Hunt, 2009). A singular value boundary of 80 singular 

values identified by SVD was chosen to characterize the 

solution space by using pyEMU (White and others, 2016) 

and the PEST utility IDENTPAR (Doherty, 2010). Eighty 

super parameters were used for model calibration; thus, this 

analysis suggests that the super parameters associated with 

these singular values contained information from the model 

calibration dataset. 

The singular value contributions to identifiability for 

each of the 24 parameters with an identifiability of greater 

than 0.7 are shown in figure 48. Identifiability is the sum of 

0

0.2

0.4

0.6

0.8

1.0

0

8

16

24

32

40

48

56

64

72

80

rch5

ss3

sy3

hkpp973

rch14

rch6

rch18

rch20rch15

sfrmul

rch3

hkpp1039

sy2

spring10

rch21rch11drn10rch19

rch9

evtmult

rch22

hkpp984

hkpp1462

rch16

Identifiability

Number of singular values considered

Parameter

Figure 48. Parameter identifiability in the numerical groundwater-flow model for the Rush Springs aquifer, 

western Oklahoma.
84 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

the contribution of the singular values—each represented 

by a separate color in figure 48—to each parameter. Warm 

colors (reds, oranges, and yellows) denote identifiability 

attributable to more informative singular values, and the cool 

colors (greens and blues) indicate identifiability attributable to 

less informative singular values. The identifiability (total bar 

height) and singular value composition (individual bar colors) 

between two parameters can be compared whereby bars 

containing mostly warm colors indicate that these parameters 

can be estimated with less potential for error than those 

parameters with mostly cool colors.

The calibration parameters had a large range of 

identifiability (table 6). Some values were nearly equal to 

one, but other values were near zero, indicating little to no 

identifiability. Ten parameters were nearly identifiable (values 

near or at 1.0), and 14 parameters were identifiable (greater 

than 0.7), based on the calibration-target dataset (fig. 48). 

The recharge zones had 6 of the 10 largest identifiabilities 

because the spatial extent of these particular zones (fig. 20) 

encompassed a large percentage of the groundwater-level 

targets, generally near Fort Cobb Reservoir. Pilot points near 

Fort Cobb Reservoir (hkpp973, hkpp1039; table 6) were most 

identifiable, while the remainder of the pilot points were less 

identifiable because they were located further from calibration 

targets. The sensitivity analysis suggests that many parameters 

are useful for calibration. By comparison, the results of the 

identifiability analysis indicate that (1) the recharge and 

storage parameters were well informed and (2) some degree 

of correlation is present among many of the calibration 

parameters. The recharge and storage parameters are important 

controls on groundwater flow in the aquifer; therefore, a large 

identifiability for these parameters provides greater certainty 

in the modeled scenario results. 

Groundwater Availability Scenarios

Three types of scenarios were formulated for the 

calibrated groundwater model. These scenarios were used 

to (1) estimate the EPS pumping rate that guarantees a 

minimum 20-year life of the aquifer, (2) quantify the effects 

of projected groundwater-use rates on aquifer storage over a 

50-year period, and (3) evaluate the effects of (a) projected 

groundwater-use rates extended 50 years into the future and 

(b) sustained hypothetical drought conditions over a 10-year 

period on base flow and groundwater in storage. Additionally, 

an uncertainty analysis was performed for the EPS scenario.

Equal Proportionate Share

The EPS for the Rush Springs aquifer was defined as the 

pumping rate at which fresh groundwater can be withdrawn 

so that, after a minimum of 20 years of continuous EPS 

withdrawals, 50 percent of the aquifer retains a saturated 

thickness of at least 15 ft. To compute the EPS for the Rush 

Springs aquifer, a similar approach to that of the model 

calibration was implemented. Whereas automated calibration 

of the Rush Springs aquifer model involved the adjustment of 

many model parameters based on available calibration targets, 

the determination of the EPS was based only on a uniform 

pumping rate parameter (EPS pumping rate) and an aquifer 

saturated thickness calibration target (15 ft). The EPS pumping 

rate parameter was composed of a hypothetical well placed 

in each active cell in layer 3. During each iteration of the 

calibration process, the pumping rate parameter was adjusted 

until the objective function was zero—when 50 percent of 

the basin retained a saturated thickness of 15 ft. The EPS 

was computed for time periods of 20, 40, and 50 years into 

the future.

The layer 2 alluvium and terrace was considered as a 

separate aquifer for the purposes of the EPS scenarios; thus, 

the EPS scenarios were evaluated for layer 3 only. The EPS 

scenarios also were evaluated based only on the modified 

extent of Neel and others (2018), which includes an area of 

about 4,616 mi2

 (2,954,545 acres).

Annual stress periods with calibrated model mean 

stresses were used in the EPS scenarios instead of monthly 

stress periods to (1) shorten transient simulation run times, 

(2) minimize the iterative variability in the EPS pumping 

rate caused by monthly or seasonal stresses, and (3) improve 

model stability. The 2015 simulated water table from the 

calibrated groundwater model was used as the starting water 

table in each EPS scenario. The calibrated model mean 

recharge is referred to as “normal recharge” conditions. To 

account for potential climate variability, the EPS scenarios 

were run with recharge increased and decreased by 10 percent.

The 20-, 40-, and 50-year EPS pumping rates under 

normal recharge conditions were 0.82, 0.49, and 0.43 acrefoot per acre per year (acre-ft/acre/yr), respectively (table 12). 

Given the 2,954,545-acre aquifer area from Neel and others 

(2018), these rates correspond to annual yields of about 

2,422,727, 1,447,727, and 1,270,454 acre-ft/yr, respectively. 

Increasing and decreasing recharge by 10 percent resulted 

in 20-year EPS pumping rates of 0.84 (2.4-percent increase) 

and 0.81 acre-ft/acre/yr (1.2-percent decrease), respectively. 

Increasing and decreasing recharge by 10 percent resulted 

in 40-year EPS pumping rates of 0.51 (4.1-percent increase) 

and 0.48 acre-ft/acre/yr (2.0-percent decrease), respectively. 

Increasing and decreasing recharge by 10 percent resulted in 

Table 12. Equal-proportionate-share (EPS) pumping rates for the 

Rush Springs aquifer, western Oklahoma, 1979–2015.

Period 

(years)

EPS pumping rate 

(acre-feet per acre per year)

Recharge 

reduced by 

10 percent

Normal recharge

Recharge 

increased by 

10 percent

20 0.81 0.82 0.84

40 0.48 0.49 0.51

50 0.41 0.43 0.45
Groundwater Availability Scenarios 85

50-year EPS pumping rates of 0.45 (4.7-percent increase) and 

0.41 acre-ft/acre/yr (4.7-percent decrease), respectively.

At the end of the 20-year EPS scenario, saturated 

thickness remained primarily in the western parts of the 

aquifer (fig. 49). In most areas of Washita and Custer 

Counties, where the aquifer is thickest and had a shallow 

hydraulic gradient, saturated thickness remained through the 

end of the 20-year EPS scenario (figs. 49–50). Areas along 

the Canadian and Washita Rivers in Roger Mills, Ellis, and 

Dewey Counties remained saturated because of SFR stream 

inflows and corresponding seepage from streams (figs. 49–50). 

Other parts of the aquifer generally were unsaturated except 

for the area located between the Canadian and North Canadian 

Rivers, which remained saturated because of the (1) thickness 

of the sediment, (2) increase in calibrated recharge compared 

to the conceptual budget, and (3) reduction in drain cell 

outflows from the reduced groundwater levels.

In each EPS scenario, substantial percentages of 

groundwater storage were removed by the simulated wells in 

each model cell (fig. 51). Annual EPS groundwater pumping 

decreased as the thinner areas of the aquifer, including most 

of the alluvium and terrace, were dewatered and dropped 

below 15 ft of saturated thickness or went dry (figs. 49–50). 

Annual groundwater storage changes decreased as annual 

EPS groundwater pumping decreased, whereby groundwater 

storage changes were more moderate during the last few years 

of each scenario (fig. 51). Therefore, the 40- and 50-year EPS 

pumping rates were closer in value than either of those rates 

compared to the 20-year EPS pumping rate. 

 Groundwater storage at the end of the 20-year EPS scenario 

was about 13,321,000 acre-ft, or about 31,516,437 acre-ft 

(70 percent) less than the starting storage (fig. 51). Given 

the 4,616-mi2

 (2,954,545-acre) aquifer area modified from 

Neel and others (2018) and a mean Sy of 0.07, this decrease 

in storage was equivalent to a mean groundwater-level 

decline of about 152 ft. This groundwater-level decline was 

generally greater than the aquifer thickness in the eastern and 

southern areas of the model where the aquifer was dewatered 

(figs. 49–50).

At the end of the 20-year EPS scenario, base flow had 

decreased to 0 ft3

/s in most model-area stream segments 

except the Washita River upstream of the Hammon streamgage 

(07324200) and below Foss Reservoir, and the Canadian 

River near the upstream model boundary where SFR inflows 

sustained streamflows (fig. 49). The aquifer groundwater level 

was below the bottom of the streams during most of the EPS 

scenarios promoting seepage from streams to the aquifer. 

This seepage is demonstrated near model column 75 (fig. 50) 

where the EPS groundwater altitude is greatest directly below 

the Washita River. By comparison, the Washita River near 

column 175 is dry; thus, no seepage occurs from the stream to 

the aquifer.

Fort Cobb Reservoir stage was below the dead-pool stage 

of 1,300 ft after about 5.5 years of pumping in the 20-year 

EPS scenario (fig. 52). The drying of the reservoir was caused 

by (1) the cessation of stream inflows from Cobb, Lake, and 

Willow Creeks—which constituted about one-third of inflows 

to Fort Cobb Reservoir—after about 2 years (fig. 52), and 

(2) the decline of groundwater levels around the reservoir 

compared to the calibrated model (fig. 49), resulting in large 

lakebed seepage outflows to the aquifer. Surface-water inflows 

composed a much larger percentage of the total reservoir 

inflow than lakebed seepage; thus, the precipitous decline in 

reservoir stage in the first 5 years is largely the result of the 

Fort Cobb Reservoir tributaries ceasing to flow. Precipitation 

and evaporation also decreased as cells representing Fort 

Cobb Reservoir became dry, but these decreases tended 

to offset each other. When the EPS scenarios were run 

without simulating Fort Cobb Reservoir, the change in EPS 

pumping rate was negligible; therefore, the 40- and 50-year 

EPS scenarios were run without the Lake package to save 

computation time. 
86 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 49

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

0 10 20 30 MILES

0 10 20 30 KILOMETERS

07228500

07324200

07325000

07326000

07325800

07326500

07325500

07325850

07325860

07327447

07324400

07228500

07324200

07325000

07326000

07325800

07326500

07325500

07325850

07325860

07327447

07324400

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

07325500

Rush Springs aquifer boundary

Western extent of equal­proportionateshare aquifer boundary—Modified 

from Neel and others (2018)

Line of section—Model row 585 (fig. 50)

Streamgage and number (USGS, 2017c)

A A'

Base flow, in cubic feet per second, after

20 years of equal­proportionate­share 

groundwater pumping

0

0.1 to 5.1

5.1 to 10.0

10.1 to 20.0

20.1 to 40.0

40.1 to 63.2

Saturated thickness, in feet, after 20 years

of equal­proportionate­share

groundwater pumping

0 to 15.0

15.1 to 30.0

30.1 to 45.0

45.1 to 60.0

60.1 to 90.0

90.1 to 120.0

Greater than 120.0

EXPLANATION

A A'

Figure 49. Simulated saturated thickness and simulated base flow after 20 years of continuous equal-proportionate-share 

groundwater pumping in the Rush Springs aquifer, western Oklahoma.
Groundwater Availability Scenarios 87

laf18-0888_fig 50

A A' FEET

2,000

1,900

1,800

1,700

1,600

1,500

1,400

1,300

1,200

WEST EAST

Model column

54 75 150 225 300 375 450 525 600 675 726

0 5 10 15 MILES

0 5 10 15 KILOMETERS

VERTICAL SCALE GREATLY EXAGGERATED

DATUM IS NORTH AMERICAN VERTICAL DATUM OF 1988

Washita RiverFoss Reservoir

Barnitz Creek

Beaver Creek

Deer Creek

Canadian River

Washita River

150 feet

EXPLANATION

Line of section for A–A' (model row 585) shown on figure 49

Model layer 1—Cloud Chief Formation

Model layer 2—Alluvium and terrace deposits

Model layers 2 and 3—Whitehorse Group

Upper 30 feet (layer 2)

Lower part (layer 3)

Dog Creek Shale and other bedrock (not modeled)

Potentiometric surface (2013; Neel and others, 2018)

20­year equal­proportionate­share potentiometric surface

Figure 50. Vertical cross section of the Rush Springs groundwater-flow model after 20 years of equal-proportionate-share 

groundwater pumping in the Rush Springs aquifer, western Oklahoma.
88 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 51

0

20

40

60

80

100

Cumulative simulated change in

groundwater storage,

in percent

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

Simulated groundwater storage, 

in acre-feet 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

Year

0

20

40

60

80

100

Cumulative simulated change in

groundwater storage,

in percent

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

Simulated groundwater storage, 

in acre-feet 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Year

0

20

40

60

80

100

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cumulative simulated change in

groundwater storage,

in percent

Simulated groundwater storage, 

in acre-feet 

Year

A. 20­year equal­proportionate­share scenario

B. 40­year equal­proportionate­share scenario

C. 50­year equal­proportionate­share scenario

Starting groundwater storage: 44,837,437 acre-feet

Starting groundwater storage: 44,837,437 acre-feet

Starting groundwater storage: 44,837,437 acre-feet

Figure 51

Figure 51. Changes in simulated groundwater storage during A, 20, B, 40, and C, 50 years 

of continuous equal-proportionate-share groundwater pumping in the Rush Springs aquifer, 

western Oklahoma.
Groundwater Availability Scenarios 89

Uncertainty in Equal-Proportionate-Share 

Results

A probabilistic approach was used to assess the 

uncertainty in the EPS scenario results. Uncertainty in the 

EPS results is related to uncertainty in the model, such as 

simplifications of the modeled natural system, spatial and 

temporal discretization, or uncertainty in the hydraulic 

parameter value estimates. Additionally, the process of inverse 

modeling, whereby parameter values are estimated from a 

limited amount of data, produces non-unique solutions. Thus, 

the scenario outputs can be viewed as more “probabilistic” 

than “deterministic” and may have a range of possible results. 

By exploring different combinations of likely parameter 

distributions—which correspond to possible scenario 

outcomes—the uncertainty can be expressed numerically.

A combined approach using Schur’s compliment for 

linear analysis (Tarantola, 2005; Doherty, 2010; Fienen and 

others, 2010) to estimate the posterior covariance matrix 

followed by the Monte Carlo nonlinear-uncertainty technique 

was applied for the EPS scenario uncertainty analysis by using 

pyEMU (White and others, 2016). The posterior covariance 

matrix ( ∑θ ), which incorporates information gained during 

the calibration process, is

] 1

 T T

θ θθ θ θ

−

∑ = ∑ −∑ ∑ +∑ ∑ 

 JJ J J (8)

where

∑θ is the prior covariance matrix,

∑ is the observation-noise covariance matrix,

T indicates the vector transpose, and

J is the Jacobian matrix.

The prior covariance matrix ( ∑θ ) contains uncertainty 

associated with adjustable parameters independent of the 

calibration process. By using pyEMU, the parameter 

distributions for this matrix were generated from the usersupplied parameter upper and lower bounds used during the 

PEST calibration that constitute reasonable value ranges 

for each parameter and reflect the expert knowledge of 

the parameters prior to calibration. The upper and lower 

bounds were the same for all similar parameter types in each 

parameter group during calibration. The observation-noise 

covariance matrix ( ∑ ) contains uncertainty in the calibration 

targets based on the observation weights discussed in the 

“Calibration-Target Uncertainty and Weighting” section of 

this report. The Jacobian matrix (J ) contains the derivatives of 

each observation with respect to each parameter. 

The posterior covariance matrix (eq. 8) generated 

by using Schur’s complement is a full covariance matrix 

containing the posterior parameter uncertainty (as variances) 

and off-diagonal terms that characterize the correlation among 

parameters. That matrix was used to generate an ensemble 

of 400 sets (or “realizations”) of possible random parameter 

values by using a multivariate normal distribution centered 

on the calibrated parameter values. While the Monte Carlo 

technique often uses realizations derived solely from the prior 

covariance matrix, use of the posterior covariance matrix 

Figure 52

1,264

1,272

1,280

1,288

1,296

1,304

1,312

1,320

1,328

1,336

1,344

1,352

10 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Fort Cobb Reservoir simulated stage, in feet above NGVD 29 

during equal-proportionate-share groundwater pumping

Simulated base flow, in cubic feet per second

Year

Reservoir stage 

below deadpool stage

Surface-water 

inflows cease

Reservoir stage 

at bottom of 

reservoir

Fort Cobb Reservoir stage

EXPLANATION

Cobb Creek streamgage (07325800) on Cobb Creek

Lake Creek streamgage (07325850) on Lake Creek

Willow Creek streamgage (07325860) on Willow Creek

NGVD 29; National Geodetic Vertical Datum of 1929

0

1

2

3

4

5

6

7

8

Figure 52. Changes in simulated base flow in Cobb, Lake, and Willow Creeks and in simulated stage in Fort 

Cobb Reservoir during 20 years of continuous equal-proportionate-share groundwater pumping in the Rush 

Springs aquifer, western Oklahoma.

∑
90 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

allowed for the incorporation of knowledge gained during the 

calibration process. 

The assumptions underlying the linear analysis include 

a normal parameter distribution and a linear sensitivity 

function between parameters and observations. The parameter 

distributions for calibrated Kh (fig. 43), vertical anisotropy, 

recharge, Sy (fig. 46), Ss, ETg rate multiplier, and SFR 

conductance were assumed to be normal and were included in 

the uncertainty analysis. The parameter distributions for other 

parameters, such as drain and GHB conductance, 

were not assumed to be normal. Additionally, with 

the exception of one drain parameter (drn10), 

identifiability values for these parameters were small 

(table 6) and were not included in the uncertainty 

analysis. 

Comparison of the prior and posterior 

distributions provides an understanding of how well 

the observation dataset used in the model calibration 

informs the model parameters. The prior and posterior 

distributions for two selected parameters—layer 3 

Sy multiplier (sy3) and the recharge multiplier for 

recharge zone 15 (rch15)—are shown in figure 53. 

These two parameters are representative of parameters 

where either (1) the height is increased and the width 

is decreased for the posterior distribution compared to 

the prior distribution, or (2) the posterior distribution 

is shifted laterally compared to the prior distribution. 

The prior distribution for the layer 3 Sy 

multiplier was 0.8 to 1.3 (fig. 53A), equivalent to 

mean Sy values between 0.06 and 0.09. The Sy from 

four of the five pump tests from Neel and others 

(2018) was between 0.07 and 0.09; therefore, this 

constrained range was considered to best approximate 

Sy based on field-test data. The prior distribution 

for this parameter, whereby the parameter bounds 

are wider and the frequency (probability) is lower 

than the posterior, indicates a higher variance, and 

correspondingly, a higher parameter uncertainty. 

The posterior distribution for this parameter had a 

narrower calibration-constrained range between 0.8 

and 1.2 (fig. 53A), equivalent to mean Sy values 

between 0.06 and 0.08. The posterior distribution for 

this parameter, which incorporates information from 

the calibration process, had slightly more constrained 

parameter bounds and a higher probability, indicating 

a lower variance, and correspondingly, a lower 

parameter uncertainty. Thus, this parameter was 

highly estimable by the calibration process, which 

is also reflected in an identifiability of 1.0 (fig. 48; 

table 6). 

The posterior distribution for the recharge zone 

15 multiplier was shifted laterally compared to the 

prior distribution (fig. 53B). Lateral shifts in the 

posterior distribution in either direction occurred for most 

recharge zones in order to increase or decrease recharge 

to match the model calibration targets. The posterior 

distribution was much narrower and had a much greater 

probability than the prior distribution, indicating a greater 

level of certainty in the estimation of this parameter. This 

recharge zone (fig. 20) was the largest of 23 recharge zones 

and contained many groundwater-level observation wells 

(fig. 23) and base-flow estimates; thus, this parameter was 

both highly estimable (fig. 53B) and highly identifiable (0.99; 

fig. 48; table 6).

Frequency Frequency

B. Recharge zone 12 multiplier (rch15)

0

5

10

15

20

25

30

35

40

45

50

A. Layer 3 specific yield multiplier (sy3)

Parameter value

Parameter value

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

Prior distribution

Posterior distribution

EXPLANATION

Prior distribution

Posterior distribution

EXPLANATION

0

10

20

30

40

50

60

70

80

Figure 53

0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3

Figure 53. Parameter distribution of A, layer 3 specific yield 

multiplier and B, recharge zone 12 multiplier for the equalproportionate-share uncertainty analysis for the Rush Springs 

aquifer, western Oklahoma.
Groundwater Availability Scenarios 91

Following the linear analysis, parameter files were 

created from the 400 realizations generated by using the 

posterior covariance matrix. These parameter files contained 

the random sets of possible parameter values that would 

be used by PEST for each realization and account for the 

correlation among parameters. The PEST control file was 

then modified so that all parameters except for the EPS 

pumping rate parameter were fixed, and their values were 

kept constant at the assigned random value generated for 

each realization from the posterior covariance matrix. Each 

realization was then run by using the same PEST setup as 

the EPS scenarios and by using the HTCondor software to 

coordinate run scheduling and manage output files. Output 

files for the 400 realizations were about 3.3 gigabytes each; 

therefore, all of the output files from each realization could not 

be saved because of storage limitations. Only the MODFLOW 

and PEST run records listing the value of the calibrated EPS 

pumping rate parameter were necessary for the analysis. 

The 95-percent confidence interval (±2σ) for the 20-year 

EPS pumping rate, which is a common measure of uncertainty, 

was between 0.73 and 0.95 acre-ft/acre/yr (fig. 54). The 

68-percent confidence interval (±1σ) for the 20-year EPS 

pumping rate was between 0.79 and 0.86 acre-ft/acre/yr. 

The distribution of the Monte Carlo results is approximately 

normal. The generation of more realizations, which were 

limited by the availability of processing cores and run time, 

may be needed. The largest frequency of realizations were 

clustered around the 20-year EPS result, indicating a high 

probability that the EPS pumping rate is closer to this result 

than for the less-frequent realizations that occurred near the 

boundaries of the 95-percent confidence interval. 

Projected (50-Year) Groundwater Use

Projected 50-year groundwater-use scenarios were used 

to simulate the effects of selected well withdrawal rates on 

groundwater storage in the Rush Springs aquifer. The effects 

of well withdrawals were evaluated by comparing changes 

in groundwater storage between four 50-year scenarios 

using (1) no groundwater use, (2) mean groundwater use 

for the model period, (3) increasing groundwater use, and 

(4) groundwater use at the 2015 rate. The increasing-use 

scenario assumed a 38-percent increase in pumping over 

50 years based on 2010–60 demand projections for western 

0.70 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96

0

20

40

60

80

100

120

95-percent confidence interval

68-percent confidence interval

±10-percent change in recharge

20-year EPS

pumping rate

(0.82)

20-year equal-proportionate-share (EPS) groundwater pumping rate, in acre-feet per acre per year

Frequency

Figure 54. Probabilistic equal-proportionate-share pumping rates for the Rush Springs aquifer, 

western Oklahoma.
92 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Oklahoma (West Central Region, OWRB, 2012). Model 

stresses were configured as the mean of stresses in each month 

from the calibrated model, and the scenarios assumed that 

future climate conditions were similar to the climate of the 

1979–2015 model period. The projected storage calculation 

uses the same method as the EPS scenarios, whereby the 

model Sy is multiplied by the saturated thickness in each 

active model cell.

For the Rush Springs aquifer, simulated groundwater 

storage at the end of the projected 50-year groundwater-use 

scenarios increased by 6.3 percent for the no groundwater-use 

scenario, 2.3 percent for the mean groundwater-use scenario, 

1.3 percent for the increasing groundwater-use scenario, and 

0.9 percent for the 2015 groundwater-use scenario (table 13; 

fig. 55A). The increase in groundwater storage that occurred 

for the no groundwater-use scenario was expected given that 

approximately 9 percent of the calibrated water budget is 

composed of groundwater use (table 11).

For the Fort Cobb Reservoir watershed, simulated 

groundwater storage at the end of the projected 50-year 

groundwater-use scenarios increased by 23.6 percent for the 

no groundwater-use scenario, increased by 1.2 percent for the 

mean groundwater-use scenario, decreased by 4.0 percent for 

the increasing groundwater-use scenario, and decreased by 

3.5 percent for the 2015 groundwater-use scenario (table 13; 

fig. 55B). 

The disparity in the simulated groundwater storage 

changes between the Rush Springs aquifer and the Fort Cobb 

Reservoir watershed is caused by (1) the large percentage 

of groundwater use occurring in the Fort Cobb Reservoir 

watershed relative to the size of the Rush Springs aquifer 

(compared to the lower percentage of groundwater use relative 

to the size of the Rush Springs aquifer) and (2) the differences 

in groundwater-use rates in the Fort Cobb Reservoir 

watershed compared with those of the Rush Springs aquifer. 

Substantially more groundwater wells are completed in the 

Fort Cobb Reservoir watershed (2.6 wells per mile) compared 

to other areas of the Rush Springs aquifer (0.2 wells per mile) 

(fig. 10). Additionally, 52 percent of groundwater withdrawn 

from the Rush Springs aquifer is from the Fort Cobb Reservoir 

watershed. Thus, greater groundwater-level changes occurred 

primarily in the Fort Cobb Reservoir area and in other 

areas with large concentrations of groundwater wells and 

groundwater use. 

For the scenario with no groundwater use, a simulated 

groundwater-level recovery occurred in nearly all areas of 

the aquifer (fig. 56A), particularly in the Fort Cobb Reservoir 

watershed where the mean groundwater-level recovery 

resulted in simulated groundwater levels approximately at 

or slightly above land surface. Groundwater storage also 

increased substantially in the area northeast of the Canadian 

River. Base flows for this scenario increased between 8.0 ft3

/s 

(50 percent) at the Cobb Creek streamgage (07325800) 

and 5.5 ft3

/s (354 percent) at the Willow Creek streamgage 

(07325860) (fig. 57).

Table 13. Changes in groundwater storage after 50 years of groundwater use at selected rates for the Rush Springs aquifer, western 

Oklahoma.

[Rush Springs aquifer area is 3,181,003 acres; Fort Cobb Reservoir surface watershed is 213,895 acres]

Rush Springs aquifer

50-year groundwateruse scenario

Groundwater storage at beginning 

of scenario

(acre-feet)

Groundwater storage at end 

of scenario

(acre-feet)

Change in groundwater storage

(acre-feet)

Change in groundwater storage

(percent)

Mean change 

in groundwater 

levels

(feet)

No groundwater use 43,998,000 46,790,000 2,792,000 6.3 12.5

Mean groundwater use, 

1979–2015

43,998,000 44,992,000 994,000 2.3 4.5

Increasing groundwater use 

(38-percent increase)

43,992,000 44,567,000 575,000 1.3 2.6

2015 groundwater use 43,998,000 44,374,000 376,000 0.9 1.7

Fort Cobb Reservoir surface watershed of the Rush Springs aquifer

50-year groundwateruse scenario

Groundwater storage at beginning 

of scenario

(acre-feet)

Groundwater storage at end 

of scenario

(acre-feet)

Change in groundwater storage

(acre-feet)

Change in groundwater storage

(percent)

Mean change 

in groundwater 

levels

(feet)

No groundwater use 3,942,000 4,874,000 932,000 23.6 62.2

Mean groundwater use, 

1979–2015

3,942,000 3,988,000 46,000 1.2 3.1

Increasing groundwater use 

(38-percent increase)

3,939,000 3,781,000 −158,000 −4.0 −10.6

2015 groundwater use 3,942,000 3,805,000 −137,000 −3.5 −9.2
Groundwater Availability Scenarios 93

Figure 55

44,000

43,500

43,000

44,500

45,000

45,500

46,000

46,500

47,000

47,500

Simulated groundwater storage, in thousands of acre-feet Simulated groundwater storage, in thousands of acre-feet 

0 10 20 30 40 50

Time elapsed, in years

A. Rush Springs aquifer

B. Fort Cobb Reservoir surface watershed

3,200

3,400

3,600

3,800

4,000

4,200

4,400

4,600

4,800

5,000

5,200

Loss of storage Gain in storage Loss of storage Gain in storage

Groundwater use at 2015 rate

Mean groundwater use, 1979–2015

No groundwater use

EXPLANATION

Increasing groundwater use 

(38­percent increase over 50 years)

Figure 55. Simulated groundwater storage during 50 years of groundwater use at selected rates for the A, 

Rush Springs aquifer and B, Fort Cobb Reservoir watershed, western Oklahoma.
94 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

laf18-0888_fig 56a

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Change in saturated thickness, in feet, after

50 years of no groundwater use

Greater than 60.0

60.0 to 30.1

30.0 to 10.1

10.0 to 0

0 to −10.0

−10.1 to −12.8

0 10 20 30 MILES

0 10 20 30 KILOMETERS

A

Figure 56. Simulated change in saturated thickness after 50 years of A, no groundwater use; B, mean 

groundwater use, 1979–2015; C, increasing groundwater use; and D, 2015 groundwater use for the Rush 

Springs aquifer, western Oklahoma.
Groundwater Availability Scenarios 95

Figure 56. Simulated change in saturated thickness after 50 years of A, no groundwater use; B, mean 

groundwater use, 1979–2015; C, increasing groundwater use; and D, 2015 groundwater use for the Rush 

Springs aquifer, western Oklahoma.—Continued

laf18-0888_fig 56b

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Change in saturated thickness, in feet, after

50 years of model period (1979–2015) mean

groundwater use

Greater than 60.0

60.0 to 30.1

30.0 to 10.1

10.0 to 0

0 to −10.0

−10.1 to −33.6

0 10 20 30 MILES

0 10 20 30 KILOMETERS

B
96 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 56. Simulated change in saturated thickness after 50 years of A, no groundwater use; B, mean 

groundwater use, 1979–2015; C, increasing groundwater use; and D, 2015 groundwater use for the Rush 

Springs aquifer, western Oklahoma.—Continued

laf18-0888_fig 56c

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Change in saturated thickness, in feet, after

50 years of increasing groundwater use

Greater than 60.0

60.0 to 30.1

30.0 to 10.1

10.0 to 0

0 to −10.0

−10.1 to −30.0

−30.1 to −132.2

0 10 20 30 MILES

0 10 20 30 KILOMETERS

C
Groundwater Availability Scenarios 97

Figure 56. Simulated change in saturated thickness after 50 years of A, no groundwater use; B, mean 

groundwater use, 1979–2015; C, increasing groundwater use; and D, 2015 groundwater use for the Rush 

Springs aquifer, western Oklahoma.—Continued

laf18-0888_fig 56d

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Change in saturated thickness, in feet, after

50 years of groundwater use at the 2015

rate

Greater than 60.0

60.0 to 30.1

30.0 to 10.1

10.0 to 0

0 to −10.0

−10.1 to −30.0

−30.1 to −148.8

0 10 20 30 MILES

0 10 20 30 KILOMETERS

D
98 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

0 10 20 30 40 50

Time elapsed, in years

EXPLANATION

0

4

8

12

16

20

24

28

32

36

0

2

4

6

8

10

12

14

0

1

2

3

4

5

6

7

8

A. Cobb Creek streamgage (07325800)

B. Lake Creek streamgage (07325850)

C. Willow Creek streamgage (07325860)

2015 groundwater­use rate scenario

Mean groundwater­use rate (1979–2015) scenario

No groundwater use scenario

Increasing demand groundwater­use rate scenario 

(38­percent increase over 50 years)

Base flow, in cubic feet per second Base flow, in cubic feet per second Base flow, in cubic feet per second

Figure 57 Figure 57. Simulated annual mean base flow through 50 years of groundwater use at selected rates in 

the Rush Springs aquifer, western Oklahoma.
Groundwater Availability Scenarios 99

For the mean groundwater-use scenario, groundwater 

storage increased slightly in most areas (fig. 56B), but 

increased the most in the area northeast of the Canadian River. 

A decrease in simulated storage occurred in a small area 

south of Fort Cobb Reservoir where high-capacity simulated 

pumping wells are concentrated. The mean pumping rate for 

these wells during the model period was more than double the 

mean pumping rate for all simulated wells in the aquifer. Base 

flows for this scenario increased between 0.6 ft3

/s (3.7 percent) at 

the Cobb Creek streamgage (07325800) and 0.4 ft3

/s (27 percent) 

at the Willow Creek streamgage (07325860) (fig. 57).

For the increasing-use scenario, groundwater storage 

in most parts of the aquifer was similar to storage at the 

beginning of the scenario, with increases occurring in the 

less-developed northern and southern areas of the aquifer 

(fig. 56C). Minor groundwater storage declines of about 1–3 ft 

occurred throughout the central area of the aquifer, and storage 

declines were more pronounced in the vicinity of the Fort 

Cobb Reservoir watershed (fig. 56C). After about 10 years 

when groundwater-use rates had increased by about 6 percent 

in this area, groundwater storage losses began and continued 

through the end of the scenario (fig. 56C). Base flow for this 

scenario decreased between 1.9 ft3

/s (12.7 percent) at the Cobb 

Creek streamgage (07325800) and 0.5 ft3

/s (32 percent) at the 

Willow Creek streamgage (07325860) (fig. 57). 

For the scenario using groundwater-use rates from 

2015, groundwater storage changes were similar to changes 

in the increasing-use scenario (fig. 56D). However, greater 

groundwater storage declines—particularly between the 

Canadian River and Deer Creek, and between the Canadian 

River and Lake Creek—occurred in the eastern area of the 

aquifer compared to the increasing-use scenario. The mean 

groundwater-use rate for the Rush Springs aquifer in 2015 was 

48 percent greater than the mean groundwater-use rate for the 

model period; therefore, groundwater storage declines were 

expected in areas with large concentrations of wells (fig. 10). 

However, the mean groundwater-use rate in 2015 for the 

Fort Cobb Reservoir watershed was only 29 percent greater 

than the mean groundwater-use rate for the model period. 

Thus, groundwater-level declines in the Fort Cobb Reservoir 

watershed were smaller than the declines in the increasinguse scenario. The base-flow changes for this scenario ranged 

between a 0.2-ft3

/s increase (1.2 percent) at the Cobb Creek 

streamgage (07325800) and a 0.6 ft3

/s decrease (14 percent) at 

the Lake Creek streamgage (07325850) (fig. 57).

Hypothetical (10-Year) Drought

A hypothetical (10-year) drought scenario was used to 

simulate the effects of a prolonged period of reduced recharge 

on groundwater storage in the Rush Springs aquifer and Fort 

Cobb Reservoir stage and storage. The 10-year period of 

January 1983 to December 1992 was chosen as the drought 

period because mean annual base flows and recharge for that 

period were similar to those of the 1979–2015 model period 

and facilitates comparison of the hypothetical drought effects 

to assumed mean hydrologic conditions. Drought effects were 

quantified by comparing the results of the drought scenario 

to the calibrated model. To simulate the hypothetical drought, 

recharge in the calibrated model was reduced by 50 percent 

during the simulated drought period. Upstream inflows to the 

Canadian and Washita Rivers and associated tributaries were 

reduced by 37 percent, which was the mean decrease in annual 

base flow during the drought of years 1976–81 (Shivers and 

Andrews, 2013). The simulation was continued 15 years past 

the end of the drought period until 2007 to assess the recovery 

of aquifer storage. 

The rates of precipitation, evaporation, and surface runoff 

to Fort Cobb Reservoir were unchanged from the calibrated 

groundwater model. Observed reservoir releases for each 

month prior to and during the drought period were included in 

the simulation. To assess the recovery of Fort Cobb Reservoir 

stage following the drought period, reservoir releases were 

suspended until the stage reached the top of the active 

conservation pool (1,342 ft). Once this stage was reached, 

reservoir releases were again included in the simulation. 

Groundwater storage at the end of the drought 

period in December 1992 was about 42,983,000 acre-ft, 

or about 3,525,000 acre-ft (7.6 percent) less than the 

groundwater storage of the calibrated groundwater model 

(about 46,508,000 acre-ft) (fig. 58). Based on the 4,970-mi2

(3,181,003-acre) aquifer area and specific yield of 0.07, this 

change in groundwater storage was equivalent to a mean 

groundwater-level decline of 15.8 ft. By comparison, the 

drought conditions of 2009–14 resulted in a mean simulated 

groundwater-level decline of 9.5 ft between January 2009 and 

December 2014. Although mean annual recharge during the 

hypothetical drought (1.05 in/yr) was greater than the mean 

annual recharge during the 2009–14 drought (0.6 in/yr), the 

extended length of the hypothetical drought resulted in greater 

groundwater-level declines than the 2009–14 drought. During 

the hypothetical drought, at the 72-month point (December 

1988) when the length of the hypothetical drought equaled 

the length of the 2009–14 drought, the change in groundwater 

storage for the Rush Springs aquifer was about 1,669,000 

acre-ft (fig. 58), or the equivalent of a mean groundwater-level 

decline of 7.5 ft. Thus, if the recharge during the hypothetical 

drought was set to the recharge during the actual drought, the 

decrease in groundwater levels between the hypothetical and 

actual drought would most likely be similar. 

Groundwater storage at the end of the hypothetical 

drought for the Fort Cobb Reservoir watershed was about 

3,729,000 acre-ft, or about 303,000 acre-ft (about 7.5 percent) 

less than the groundwater storage of the calibrated groundwater 

model (4,032,000 acre-ft). Based on the 213,895-acre Fort 

Cobb Reservoir watershed area and specific yield of 0.07, 

this change in groundwater storage was equivalent to a mean 

groundwater-level decline of 20.2 ft. In comparison, for the 

Fort Cobb Reservoir watershed, the drought of 2009–14 
100 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

resulted in a mean simulated groundwater-level decline of 

15.4 ft between January 2009 and December 2014. At the 

72-month point (December 1988) of the hypothetical drought, 

the change in groundwater storage for the Fort Cobb Reservoir 

watershed was about 190,000 acre-ft, or the equivalent of a 

mean groundwater-level decline of 12.7 ft.

At the end of the hypothetical drought, the largest 

changes in saturated thickness occurred in the area northeast 

of the Canadian River, the area south of the Little Washita 

River, and in the Fort Cobb Reservoir watershed (fig. 59). In 

the area northeast of the Canadian River and south of the Little 

Washita River, groundwater storage was supplied entirely by 

recharge, so decreases in recharge had substantial effects on 

groundwater levels. The decreased saturated thickness in some 

areas resulted in a reduction in simulated well withdrawals as 

compared to the calibrated groundwater model. The saturated 

thickness of areas near the streams and associated tributaries 

changed little during the hypothetical drought; however, 

simulated base flows decreased at each simulated streamgage.

After the first 2 years of the hypothetical drought, baseflow declines at the Canadian and Washita River streamgages 

were similar (fig. 60). At the end of the hypothetical drought, 

simulated flows at the Bridgeport (07228500), Hammon 

(07324200), Clinton (07325000), Carnegie (07325500), and 

Anadarko (07326500) streamgages declined 39, 42, 48, 45, 

and 44 percent, respectively, during this period compared to 

the calibrated groundwater model. At the end of the 10-year 

hypothetical drought period, base-flow declines for the Fort 

Cobb Reservoir tributaries were the largest of the declines 

at model-area streamgages; base flow declined at the Cobb 

(07325800), Lake (07325850), and Willow (07325860) Creek 

streamgages by 53, 58, and 59 percent, respectively. Although 

groundwater-level declines in the immediate vicinity of the 

Fort Cobb Reservoir tributaries were not particularly large 

(fig. 59), these streams were relatively small; thus, minor 

groundwater-level changes have an effect on base flows. 

Simulated low-flow conditions in some months may be 

overpredicted during the drought scenario because periods of 

Simulated groundwater storage, in acre-feet

Year

EXPLANATION

1979

19801981198219831984198519861987198819891990199119921993199419951996

19971998

1999

20002001200220032004200520062007

Difference in groundwater

storage, in percent

Hypothetical 10-year 

drought period

Simulated groundwater storage, no drought

Simulated groundwater storage, with drought

(recharge reduced 50 percent from calibrated model)

Difference in simulated groundwater storage

1

Years after beginning of simulated drought 

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 21 22 23 24 25

10

5

0

19 20

41,000,000

42,000,000

43,000,000

44,000,000

45,000,000

46,000,000

47,000,000

48,000,000

Figure 58

Figure 58. Change in groundwater storage during a hypothetical 10-year drought for the Rush Springs 

aquifer, western Oklahoma, 1979–2007.
Groundwater Availability Scenarios 101

laf18-0888_fig 59

Base modified from U.S. Geological Survey (USGS) digital data

Albers Equal-Area Conic projection

North American Datum of 1983

Rush Springs aquifer boundary modified from Neel and others (2018);

Hydrography modified from Horizon Systems Corporation (2015);

Shaded relief derived from USGS (2017a)

35°00'

34°30'

99°30' 99°00' 98°30' 98°00'

36°00'

35°30'

WOODWARD

GARFIELD

ELLIS

MAJOR

BLAINE

KINGFISHER

DEWEY

ROGER

MILLS

CANADIAN

CADDO

BECKHAM

GRADY

KIOWA

GREER

COMANCHE

STEPHENS

CUSTER

WASHITA

JACKSON

WOODS

HARMON

TILLMAN

GARVIN

MCCLAIN

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

Lake 

Creek

Little Washita River

Willow

Creek

Foss

Reservoir

Fort Cobb 

Reservoir

Washita River

Barnitz Creek

Deer Creek

Creek

Cobb

Boggy Creek

Canadian River

Turkey

Creek

Cavalry

Creek

EXPLANATION

Rush Springs aquifer

boundary

Fort Cobb Reservoir surface 

watershed boundary 

(USGS, 2017b) 

Change in saturated thickness, in feet, after

10 years of hypothetical drought conditions

Less than −40.1

−40.0 to −20.1

−20.0 to −10.1

−10.0 to −5.1

−5.0 to 0

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Figure 59. Simulated change in saturated thickness after a hypothetical 10-year drought for the Rush Springs 

aquifer, western Oklahoma, 1979–2007.
102 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

A. Hammon streamgage (07324200) on Washita River 

B. Clinton streamgage (07325000) on Washita River 

50

40

30

20

10

0

Percentage decrease

in simulated flow

Percentage decrease

in simulated flow

60

40

20

0

EXPLANATION

1

Years after beginning of simulated drought 

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Hypothetical 10-year drought period

19791980198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007

Year

Figure 60AB

800

700

600

500

400

300

200

100

0

1,200

1,000

800

600

400

200

0

Base flow, in cubic feet per second Base flow, in cubic feet per second

Base flow, no drought

Base flow, with drought

Decrease in base flow

Figure 60. Changes in simulated base flow at A, Hammon streamgage (07324200) on Washita River; B, Clinton streamgage 

(07325000) on Washita River; C, Carnegie streamgage (07305500) on Washita River; D, Anadarko streamgage (07326500) on 

Washita River; E, Bridgeport streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; 

G, Cobb Creek streamgage (07325800); H, Lake Creek streamgage (07325850); and I, Willow Creek streamgage (07325860) for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2007.
Groundwater Availability Scenarios 103

Figure 60. Changes in simulated base flow at A, Hammon streamgage (07324200) on Washita River; B, Clinton streamgage 

(07325000) on Washita River; C, Carnegie streamgage (07305500) on Washita River; D, Anadarko streamgage (07326500) on 

Washita River; E, Bridgeport streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; 

G, Cobb Creek streamgage (07325800); H, Lake Creek streamgage (07325850); and I, Willow Creek streamgage (07325860) for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2007.—Continued 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

20062007

Year

C. Carnegie streamgage (07325500) on Washita River

0

200

400

600

800

1,000

1,200

1,400

1,600

0

250

500

750

1,000

1,250

1,500

1,750

2,000

2,250

2,500

D. Anadarko streamgage (07326500) on Washita River

Percentage decrease

in simulated flow

Percentage decrease

in simulated flow

60

40

20

0

Figure 60CD

Base flow, in cubic feet per second Base flow, in cubic feet per second

Base flow, no drought

Base flow, with drought

Decrease in base flow

EXPLANATION

1

Years after beginning of simulated drought 

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

50

40

30

20

10

0
104 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Figure 60. Changes in simulated base flow at A, Hammon streamgage (07324200) on Washita River; B, Clinton streamgage 

(07325000) on Washita River; C, Carnegie streamgage (07305500) on Washita River; D, Anadarko streamgage (07326500) on 

Washita River; E, Bridgeport streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; 

G, Cobb Creek streamgage (07325800); H, Lake Creek streamgage (07325850); and I, Willow Creek streamgage (07325860) for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2007.—Continued

E. Bridgeport streamgage (07228500) on Canadian River

F. Cement streamgage (07327447) on Little Washita River

Base flow, in cubic feet per second

Percentage decrease

in simulated flow

Percentage decrease

in simulated flow

0

10

20

30

40

50

60

70

80

90

100

Base flow, in cubic feet per second

0

100

200

300

400

500

600

700

800

900

1,000

40

30

20

10

0

19791980198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007

Year

50

40

30

20

10

0

Figure 60EF

Base flow, no drought

Base flow, with drought

Decrease in base flow

EXPLANATION

1

Years after beginning of simulated drought 

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Groundwater Availability Scenarios 105

Figure 60. Changes in simulated base flow at A, Hammon streamgage (07324200) on Washita River; B, Clinton streamgage 

(07325000) on Washita River; C, Carnegie streamgage (07305500) on Washita River; D, Anadarko streamgage (07326500) on 

Washita River; E, Bridgeport streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; 

G, Cobb Creek streamgage (07325800); H, Lake Creek streamgage (07325850); and I, Willow Creek streamgage (07325860) for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2007.—Continued

G. Cobb Creek streamgage (07325800) on Cobb Creek

H. Lake Creek streamgage (07325850) on Lake Creek

60

40

20

0

Base flow, in cubic feet per second

Percentage decrease

in simulated flow

Percentage decrease

in simulated flow

Base flow, in cubic feet per second

19791980198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007

Year

0

20

40

60

80

100

120

60

40

20

0

0

5

10

15

20

25

30

35

1

Years after beginning of simulated drought 

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Figure 60GH

Base flow, no drought

Base flow, with drought

Decrease in base flow

EXPLANATION
106 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

nearly zero flow periodically occur in the model period that 

could not be reproduced in the calibrated groundwater model.

Substantial decreases in the Fort Cobb Reservoir 

stage began in October 1986 in conjunction with baseflow decreases of more than 50 percent at the Cobb Creek 

(07325800), Lake Creek (07325850), and Willow Creek 

(07325860) streamgages (figs. 60–61). Annual lakebed seepage 

for Fort Cobb Reservoir was similar for the first 4 years 

of the hypothetical drought compared to the nondrought 

conditions. From July 1988 until the end of the hypothetical 

drought, the Fort Cobb Reservoir stage was below 1,331 ft 

(fig. 61A), which was generally below the groundwater levels 

in the surrounding bedrock. Thus, lakebed seepage between 

July 1988 and the end of the hypothetical drought was 

predominantly to the reservoir. However, as with the transient 

model simulation, lakebed seepage represented a relatively 

small percentage of the Fort Cobb Reservoir water budget. 

The minimum stage in Fort Cobb Reservoir was 1,311 ft in 

October 1992 (fig. 61A), near the end of the hypothetical 

drought period, indicating a storage capacity of only 10 percent 

of active conservation pool storage. 

Large precipitation events totaling 14 in. in April and 

May 1993 (Reclamation, 2017a) resulted in a stage recovery 

to 1,339 ft at Fort Cobb Reservoir by June 1993. Similarly, 

large precipitation events occurred between April and May for 

1995–1997 for Fort Cobb Reservoir; therefore, a rapid stage 

and storage recovery would have still occurred over a 60- to 

90-day period if the drought scenario timeframe had been 

shifted to end during these years. 

Model Limitations and Assumptions

The Rush Springs aquifer groundwater model is a 

simplification of a complex groundwater-flow system and, 

therefore, incorporates necessary limitations and assumptions. 

The model contains features such as the StreamflowRouting package, the Lake package, and a grid size that may 

represent localized features, but the model is best used to 

support groundwater management decisions at a regional 

to subregional scale. The 37-year model period included 

hydrologic and climatic variability. However, results from 

the groundwater model may not be representative of past 

hydrologic conditions and future climatic variability. 

Although the spatial distribution of groundwater-level 

observations (fig. 25) was reasonable, some areas of the 

Figure 60. Changes in simulated base flow at A, Hammon streamgage (07324200) on Washita River; B, Clinton streamgage 

(07325000) on Washita River; C, Carnegie streamgage (07305500) on Washita River; D, Anadarko streamgage (07326500) on 

Washita River; E, Bridgeport streamgage (07228500) on Canadian River; F, Cement streamgage (07327447) on Little Washita River; 

G, Cobb Creek streamgage (07325800); H, Lake Creek streamgage (07325850); and I, Willow Creek streamgage (07325860) for the 

numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2007.—Continued

I. Willow Creek streamgage (07325860) on Willow Creek

Base flow, in cubic feet per second

0

2

4

6

8

10

12

14

16

18

100

80

60

40

20

0

Percentage decrease

in simulated flow

19791980198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007

Year

Figure 60I

Base flow, no drought

Base flow, with drought

Decrease in base flow

EXPLANATION
Model Limitations and Assumptions 107

A

B

Fort Cobb Reservoir simulated 

storage, in acre-feet

Year

Fort Cobb Reservoir simulated stage, in feet above 

National Geodetic Vertical Datum of 1929

Figure 61

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

110,000

Years after beginning of simulated drought 

Simulated, no drought

EXPLANATION

Simulated, with drought

Active conservation pool

1,308

1,312

1,316

1,320

1,324

1,328

1,332

1,336

1,340

1,344

1,348

1,352

19791980198119821983198419851986198719881989199019911992199319941995

1 2 3 4 5 6 7 8 9 10 11 12 13

Hypothetical 10-year drought period

Figure 61. Changes in A, Fort Cobb Reservoir stage and B, Fort Cobb Reservoir storage during a hypothetical 

10-year drought for the Rush Springs aquifer, 1979–2007.
108 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

model—particularly near the western boundary—had few 

or no observations. Additionally, layer 1 did not contain 

any groundwater-level observations. The simulated water 

table in the western area of the model is in an expected 

water-table altitude range; however, more site-specific and 

local calibration-target data would facilitate a more detailed 

characterization of water-table conditions. As a result, in the 

western model areas, the calibration was only constrained by 

base-flow estimates, and any uses of the model simulation 

with regards to layer 1 are limited. The temporal distribution 

of groundwater observations resulted in a calibration bias 

towards earlier years in the model period (fig. 26A) and 

January–March (fig. 26B) of each year. Additionally, the 

groundwater levels have inherent uncertainty, some of 

which is discussed in the “Calibration-Target Uncertainty 

and Weighting” section of this report. The majority of wells 

had four or fewer observations during the model period 

(fig. 25) and had substantial location and altitude accuracy 

uncertainty, particularly for older observations. As a result, 

the groundwater-level mean calculated standard deviation 

was 4.9 ft, and about 95 percent of groundwater levels had a 

standard deviation as much as 12 ft; therefore, the simulation 

may be less representative of actual conditions in areas or 

time periods where data are less commonly available, and 

the uncertainties associated with the observation data are 

propagated into the modeled results.

Some uncertainties exist for input data used to estimate 

recharge for the Rush Springs aquifer with the SWB code. 

Soil properties from the STATSGO database used with 

the SWB code are generalized on a county scale and may 

not be representative of soil properties at a smaller scale. 

Surface-runoff routing is based on a 10-meter DEM (USGS, 

2017a), which may contain inaccuracies in altitude and 

surface depressions even after postprocessing with digital 

mapping tools. Additionally, the climate data were not evenly 

distributed throughout each year; thus, uncertainty exists in 

the interpolated climate data used to estimate recharge. The 

SWB code also does not account for lag between precipitation 

and recharge caused by the distance between the plant root 

zone and the water-table surface. In the Rush Springs aquifer, 

the water-table altitude is commonly 30 to 50 ft below the 

land-surface altitude. Therefore, the travel time for recharge to 

reach the water-table surface, which could be substantial some 

areas, is not incorporated. Additionally, the SWB code may 

not provide accurate estimates of recharge where the water 

table is near land surface; thus, recharge may be overestimated 

in these areas. As a result of these uncertainties, although 

the SWB-derived recharge agrees well with other estimates, 

the overall distribution of recharge from this method may be 

more accurate than the actual recharge values estimated at any 

given location. 

Streamflow, and thus base-flow estimates, for Lake 

Creek and Willow Creek were not available until 2005 

(table 2; fig. 27); therefore, base-flow inflows to Fort Cobb 

Reservoir contained in the Lake package from these creeks 

were estimated for the majority of the simulation period. 

Additionally, the regulation of streamflow from upstream 

reservoirs alters the natural streamflow. Because regulation 

results in the more gradual and controlled release of water 

compared to a storm peak, it can introduce inaccuracies in 

base-flow separation techniques. As a result, surface runoff 

may be understated, while base flow may be overestimated for 

the Rush Springs aquifer conceptual water budget.

Exact amounts of annual groundwater use are unknown 

because groundwater wells are not metered, and groundwateruse data are based on estimates provided by the OWRB from 

permit holders. Additionally, groundwater use by domestic 

wells, though assumed to be relatively small, was not included 

in the groundwater model. Even if these wells were simulated, 

no known groundwater-use records exist for individual 

domestic wells for the Rush Springs aquifer.

Groundwater models representing hydrologic systems 

are discretized spatially and temporally. The model grid 

was spatially discretized with a cell size of 500 ft × 500 ft, 

and hydraulic properties are uniform in each cell. Hydraulic 

properties that change rapidly, such as hydraulic conductivity 

and land-surface altitude, are generalized and may not be fully 

represented. Monthly stress periods were assumed to provide 

an adequate temporal resolution to assess changes in storage, 

groundwater levels, and base flows. As a result, simulation of 

features or processes at a scale smaller than 500 ft or less than 

1 month in length would require model refinement.

The stream network used in the groundwater model is 

a simplification of the actual stream geometry and hydraulic 

properties. More could be done to refine the stream channel 

width, characterize the channel geometry, and estimate the 

streambed conductance and stream seepage exchange with 

the aquifer; these properties can vary substantially at the local 

scale. The groundwater model was calibrated primarily to 

base-flow estimates; therefore, collection of more streamflow 

data would further reduce uncertainty in simulation results. 

Laboratory-determined Sy values for sandstone generally 

are larger than the mean Sy used in the groundwater model. 

The laboratory-derived Sy values may be more useful for 

evaluating groundwater reserves over a long period of time 

instead of evaluating shorter term groundwater-level responses 

to well pumping (Neuman, 1987). The determination of the 

aquifer response to groundwater use was investigated during 

this study; thus, the model mean Sy of 0.07 may provide a 

better estimate than the Sy value determined in the laboratory.

Summary

The U.S. Geological Survey, in cooperation with the 

Bureau of Reclamation and the Oklahoma Water Resources 

Board, (1) quantified the groundwater resources of the 

Rush Springs aquifer in western Oklahoma by developing a 

numerical groundwater-flow model, (2) evaluated the effects 

of estimated equal-proportionate-share (EPS) pumping rates 

on aquifer storage and on streamflow for time periods of 20, 
Summary 109

40, and 50 years into the future, (3) assessed the uncertainty 

in the EPS scenario results, and (4) evaluated the effects of 

(a) projected groundwater-use rates extended 50 years into 

the future and (b) sustained hypothetical drought conditions 

over a 10-year period on stream base flow and groundwater 

in storage. 

The study area is composed of about 4,970 square miles 

(3,181,003 acres) of Rush Springs aquifer bedrock deposits 

located in 14 counties in Oklahoma. The study area includes 

the alluvium and terrace of the Canadian and Washita Rivers, 

as well as alluvium along the Little Washita River, Deer 

Creek, and a number of smaller tributaries of the Washita 

River that overlie the bedrock. The Rush Springs aquifer is 

an important source of water for municipal and irrigation 

use by many communities and agricultural users in the study 

area. Streamflow from Cobb, Lake, and Willow Creeks is the 

primary source of stream inflow to Fort Cobb Reservoir, a 

Bureau of Reclamation reservoir constructed to provide flood 

control, water supply, and recreation.

A conceptual water budget for the study period 

was developed for the Rush Springs aquifer to guide the 

construction and calibration of a groundwater model. 

The primary aquifer inflow was recharge derived from 

precipitation. Mean annual recharge estimated from the SoilWater-Balance code adjusted to 7 percent of precipitation 

was 2.1 inches. Stream seepage was the predominant outflow 

from the Rush Springs aquifer, primarily to the Washita and 

Canadian Rivers. 

The numerical groundwater-flow model of the Rush 

Springs aquifer was constructed by using MODFLOW with 

the Newton solver. The groundwater model grid was spatially 

discretized into 1,362 rows, 1,083 columns, and 3 layers 

without rotation. Groundwater flow was simulated for January 

1979–December 2015 by using monthly stress periods, and an 

initial steady-state stress period was configured to represent 

mean annual inflow and outflow. The model was calibrated 

to groundwater-level observations at selected wells, monthly 

base flow at nine streamgages, stream seepage as estimated for 

the conceptual water budget, and Fort Cobb Reservoir stage. 

Equal proportionate share (EPS) scenarios for the 

Rush Springs aquifer were run for periods of 20, 40, and 50 

years. The 20-, 40-, and 50-year EPS pumping rates under 

normal recharge conditions were 0.82, 0.49, and 0.43 acrefoot per acre per year (acre-ft/acre/yr), respectively. Given 

the 2,954,545-acre aquifer area used for the EPS scenarios, 

the 20-year rate corresponds to an annual yield of about 

2,422,727 acre-feet per year (acre-ft/yr). Groundwater 

storage at the end of the 20-year EPS scenario was about 

13,321,000 acre-ft, or about 31,516,437 acre-ft (70 percent) 

less than the starting EPS scenario storage. This decrease in 

storage was equivalent to a mean groundwater-level decline of 

about 152 feet (ft). Water availability under the EPS pumping 

rate was primarily from the western area of the model. 

Saturation was sustained though the entire EPS scenario 

where the aquifer was sufficiently thick or a shallow hydraulic 

gradient was present. Fort Cobb Reservoir stage was below the 

dead-pool stage after about 5 years of EPS pumping.

An uncertainty analysis was conducted to assess the 

uncertainty in the EPS scenario results. An ensemble of 

400 random sets of possible parameter values was performed 

for the uncertainty analysis by using a multivariate normal 

distribution centered on the calibrated parameter values. The 

parameter bounds for the uncertainty analysis were determined 

by using the posterior covariance matrix, which allows for 

the incorporation of knowledge gained during the calibration 

process as well as observation uncertainty and the correlation 

between estimated parameters. The uncertainty results indicate 

a 95-percent confidence interval for the 20-year EPS pumping 

rate between 0.73 and 0.95 acre-foot per acre per year.

Projected 50-year pumping scenarios were used to 

simulate the effects of selected well withdrawal rates on 

groundwater storage of the Rush Springs aquifer. The effects 

of well withdrawals were evaluated by comparing changes 

in groundwater storage between four 50-year scenarios using 

(1) no groundwater use, (2) mean groundwater use for the 

study period (1979–2015), (3) increasing groundwater use, 

and (4) groundwater use at the 2015 rate. The increasinguse scenario assumed a 38-percent increase in pumping over 

50 years based on 2010–60 demand projections for western 

Oklahoma. Simulated groundwater storage changes ranged 

between an increase of 6.3 percent for the scenario with 

no groundwater use and 0.9 percent for the scenario with 

2015 groundwater-use rates. For the Fort Cobb Reservoir 

surface watershed, simulated groundwater storage changes 

ranged between an increase of 23.6 percent for the scenario 

with no groundwater use and a decrease of 4.0 percent for 

the increasing groundwater-use scenario. Groundwaterlevel changes were generally greater in areas with a large 

concentration of groundwater wells and groundwater use such 

as the Fort Cobb Reservoir surface watershed.

A hypothetical 10-year drought scenario was used to 

simulate the effects of a prolonged period of reduced recharge 

on the Rush Springs aquifer groundwater storage and Fort 

Cobb Reservoir stage and storage. Drought effects were 

quantified by comparing the results of the drought scenario 

to those of the calibrated numerical model. To simulate the 

hypothetical drought, recharge in the calibrated numerical 

model was reduced by 50 percent during the simulated 

drought period (1983–92), and upstream inflows to the 

Canadian and Washita Rivers and associated tributaries were 

reduced by 37 percent. Groundwater storage at the end of the 

hypothetical drought period was about 42,983,000 acre-ft, or 

about 3,525,000 acre-ft (7.6 percent) less than the groundwater 

storage of the calibrated numerical model. This change in 

groundwater storage is equivalent to a mean groundwaterlevel decline of 15.8 ft. Mean simulated base-flow declines at 

the Canadian and Washita River streamgages were between 

39 and 59 percent during the drought period. The minimum 

stage in Fort Cobb Reservoir at the end of the hypothetical 

drought period was 1,311 ft, indicating a storage capacity of 

only 10 percent of active conservation pool storage. The Fort 

Cobb Reservoir storage declines mostly resulted from reduced 

base flows in Cobb, Lake, and Willow Creeks upstream from 

the reservoir.
110 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

References Cited 

Barlow, P.M., Cunningham, W.L., Zhai, Tong, and Gray, 

Mark, 2015, U.S. Geological Survey Groundwater Toolbox, 

a graphical and mapping interface for analysis of hydrologic 

data (version 1.0)—User guide for estimation of base flow, 

runoff, and groundwater recharge from streamflow data: 

U.S. Geological Survey Techniques and Methods, book 3, 

chap. B10, 27 p., accessed July 19, 2016, at https://dx.doi.

org/10.3133/tm3B10.

Becker, M.F., 1998, Steady-state simulation of ground-water 

flow in the Rush Springs aquifer, western Oklahoma: 

U.S. Geological Survey Water-Resources Investigations 

Report 98–4082, 88 p.

Becker, M.F., and Runkle, D.L., 1998, Hydrogeology, water 

quality, and geochemistry of the Rush Springs aquifer, 

western Oklahoma: U.S. Geological Survey WaterResources Investigations Report 98–4081, 37 p. [Also 

available at https://pubs.er.usgs.gov/publication/wri984081.]

Bureau of Reclamation [Reclamation], 2017a, Reservoir 

release, storage, evaporation, and precipitation data for Fort 

Cobb Reservoir, Oklahoma, accessed March 15, 2017, at 

https://www.usbr.gov/gp-bin/custom.pl?SWE221A&cobb.

Bureau of Reclamation [Reclamation], 2017b, Reservoir 

release, storage, evaporation, and precipitation data for Foss 

Reservoir, Oklahoma, accessed March 15, 2017, at https://

www.usbr.gov/gp-bin/custom.pl?SWE221A&foss.

Carr, J.E., and Bergman, D.L, 1976, Reconnaissance of the 

water resources of the Clinton quadrangle, west-central 

Oklahoma: Oklahoma Geological Survey Hydrologic 

Atlas 5, 4 sheets, scale 1:250,000.

Chen, X., 2003, Stream water infiltration, bank storage, and 

storage zone changes due to stream-stage fluctuations: 

Journal of Hydrology, v. 280, p. 246–264.

Clark, B.R., and Hart, R.M., 2009, The Mississippi 

Embayment Regional Aquifer Study (MERAS)—

Documentation of a groundwater-flow model constructed 

to assess water availability in the Mississippi embayment: 

U.S. Geological Survey Scientific Investigations 

Report 2009–5172, 61 p.

Condor Team, 2012, Condor version 7.6.6 manual: Madison, 

Wisc., University of Wisconsin.

Darcy, H., 1856, Les Fontances publiques de la ville de Dijon: 

Paris, Victor Dalmont.

Doherty, J.E., 2010, PEST, model-independent parameter 

estimation and uncertainty analysis—Addendum to 

user manual (5th ed.): Brisbane, Australia, Watermark 

Numerical Computing, accessed March 5, 2012, at http://

pesthomepage.org/. 

Doherty, J.E., and Hunt, R.J., 2009, Two statistics 

for evaluating parameter identifiability and error 

reduction: Journal of Hydrology, v. 366, no. 1–4, 

p. 119–127, accessed October 3, 2017, at https://doi.

org/10.1016/j.jhydrol.2008.12.018.

Doherty, J.E., and Hunt, R.J., 2010, Approaches to highly 

parameterized inversion—A guide to using PEST for 

groundwater-model calibration: U.S. Geological Survey 

Scientific Investigations Report 2010–5169, 59 p.

Dugan, J.T., and Zelt, R.B., 2000, Simulation and analysis of 

soil-water conditions in the Great Plains and adjacent areas, 

central United States, 1951–80: U.S. Geological Survey 

Water-Supply Paper 2427, 81 p.

Ellis, J.H., 2018, MODFLOW model used in simulation 

of groundwater flow and analysis of projected water use 

for the Rush Springs aquifer, western Oklahoma: U.S. 

Geological Survey data release, https://doi.org/10.5066/

F7Q52NXK.

Ellis, J.H., Mashburn, S.L, Graves, G.M., Peterson, S.M., 

Smith, S.J., Fuhrig, L.F., Wagner, D.L., and Sanford, J.E., 

2017, Hydrogeology and simulation of groundwater flow 

and analysis of projected water use for the Canadian 

River alluvial aquifer, western and Central Oklahoma: 

U.S. Geological Survey Scientific Investigations 

Report 2016–5180, 64 p.

Fay, R.O., 1962, Stratigraphy and general geology of Blaine 

County, part 1 of Geology and mineral resources of 

Blaine County, Oklahoma: Oklahoma Geological Survey 

Bulletin 89, 258 p.

Fay, R.O., 1978, Geology and mineral resources (exclusive 

of petroleum) of Custer County, Oklahoma: Oklahoma 

Geological Survey Bulletin 114, 88 p.

Fienen, M.N., Doherty, J.E., Hunt, R.J., and Reeves, H.W., 

2010, Using prediction uncertainty analysis to design 

hydrologic monitoring networks: Example applications 

from the Great Lakes Water Availability Pilot Project: 

U.S. Geological Survey Scientific Investigations 

Report 2010–5159, 44 p.

FTN Associates, 2009, Fort Cobb Reservoir 2007 

sedimentation survey analysis. 16 p.

Harbaugh, A.W., 2005, MODFLOW-2005, The U.S. 

Geological Survey modular ground-water model—

the Ground-Water Flow Process: U.S. Geological 

Survey Techniques and Methods, book 6, chap. A16 

[variously paged].

Hargreaves, G.H., and Samani, Z.A., 1985, Reference crop 

evapotranspiration from temperature: Applied Engineering 

in Agriculture, v. 1, no. 2, p. 96–99.
References Cited 111

Hendricks, T.A., 1937, History of the Canadian River of 

Oklahoma as indicated by the Gerty Sand: Geological 

Society of America Bulletin 48, no. 3, p. 365–372.

Heran, W.D., Green, G.N., and Stoeser, D.B., 2003, A digital 

geologic map database for the State of Oklahoma: U.S. 

Geological Survey Open-File Report 03–247, 10 p.

Hill, M.C., and Tiedeman, C.R., 2007, Effective groundwater 

model calibration—With analysis of data, sensitivities, 

predictions, and uncertainty: New York, Wiley and Sons, 

455 p.

Horizon Systems Corporation, 2015, National Hydrography 

Dataset Plus (NHDPlus): Horizon Systems Corporation, 

accessed November 1, 2010, at http://www.horizonsystems.com/nhdplus/.

Johnson, A.I., 1967, Sy—Compilation of Sys for various 

materials: U.S. Geological Survey Water-Supply 

Paper 1662–D, 74 p.

Mashburn, S.L., and Smith, S.J., 2014, Evaluation of 

groundwater and surface-water interactions in the 

Caddo Nation Tribal Jurisdictional Area, Caddo County, 

Oklahoma, 2010–13: U.S. Geological Survey Scientific 

Investigations Report 2014–5082, 54 p.

Masoner, J.R., Mladinich, C.S., Konduris, A.M., and Smith, 

S.J., 2003, Comparison of irrigation water use estimates 

calculated from remotely sensed irrigated acres and 

State reported irrigated acres in the Lake Altus drainage 

basin, Oklahoma and Texas, 2000 growing season: U.S. 

Geological Survey Water-Resources Investigations 

Report 03–4155, 38 p.

Masterson, J.P., Pope, J.P., Fienen, M.N., Monti, Jack, Jr., 

Nardi, M.R., and Finkelstein, J.S., 2016, Documentation of 

a groundwater flow model developed to assess groundwater 

availability in the Northern Atlantic Coastal Plain aquifer 

system from Long Island, New York, to North Carolina 

(ver. 1.1, December 2016): U.S. Geological Survey 

Scientific Investigations Report 2016–5076, 70 p., accessed 

September 13, 2017, at https://doi.org/10.3133/sir20165076.

McMahon, P.B., Dennehy, K.F., Bruce, B.W., Böhlke, J.K., 

Michel, R.L., Gurdak, J.J., and Hurlbut, D.B., 2006, Storage 

and transit time of chemicals in thick unsaturated zones 

under rangeland and irrigated cropland, High Plains, United 

States: Water Resources Research, v. 42, accessed October 19, 

2017, at https://doi.org/10.1029/2005WR004417.

McMahon, P.B., Plummer, L.N., Böhlke, J.K., Shapiro, S.D., 

and Hinkle, S.R., 2011, A comparison of recharge rates in 

aquifers of the United States based on groundwater-age 

data: Hydrogeology Journal, v. 19, accessed June 22, 2017, 

at https://doi.org/10.1007/s10040-011-0722-5.

Merritt, M.L., and Konikow, L.F., 2000, Documentation of a 

computer program to simulate lake-aquifer interaction using 

the MODFLOW ground-water flow model and the MOC3D 

solute-transport model: U.S. Geological Survey WaterResources Investigations Report 00–4167, 146 p.

Miller, G.W., and Stanley, T.M., comps., 2004, Geologic map 

of the Anadarko 30’ X 60’ quadrangle, Caddo, Canadian, 

Custer, Grady, Kiowa and Washita Counties, Oklahoma: 

Oklahoma Geological Survey Geologic Quadrangle Map 

OGQ-58, scale 1:100,000, accessed March 15, 2017, at 

http://ogs.ou.edu/docs/OGQ/OGQ-58-color.pdf.

Mogg, J.L., Schoff, S.L., and Reed, E.W., 1960, Groundwater resources of Canadian County, Oklahoma: Oklahoma 

Geological Survey Bulletin 87, 112 p.

Morris, D.A., and Johnson, A.I., 1967, Summary of hydrologic 

and physical properties of rock and soil materials, as 

analyzed by the Hydrologic Laboratory of the U.S. 

Geological Survey, 1948–60: U.S. Geological Survey 

Water-Supply Paper 1839–D, 42 p.

National Agricultural Statistics Service [NASS], 2017, 

CropScape—Cropland data layers, 2010–15, accessed 

February 5, 2017, at https://nassgeodata.gmu.edu/

CropScape/.

National Climatic Data Center, 2017, Climate data online, 

accessed March 25, 2017, at https://www7.ncdc.noaa.gov/

CDO/CDODivisionalSelect.jsp.

Natural Resources Conservation Service, 2015, Geospatial 

Data Gateway: Natural Resources Conservation Service, 

accessed March 14, 2013, at http://datagateway.nrcs.usda.

gov/.

Neel, C.R., Wagner, D.L., Correll, J.S., Sanford, J.E., 

Hernandez, R.J., Spears, K.W., and Waltman, P.B, 2018, 

Hydrologic Investigations Report of the Rush Springs 

aquifer in west-central Oklahoma: Oklahoma Water 

Resources Board, accessed August 2, 2018, at http://www.

owrb.ok.gov/reports/studies/RushSprings2015.pdf.

Neuman, S.P., 1987, On methods of determining specific 

yield: Ground Water, v. 25, no. 6, p. 683.

Niswonger, R.G., Panday, S., and Ibaraki, M., 2011, 

MODFLOW-NWT, A Newton formulation for 

MODFLOW-2005: U.S. Geological Survey Techniques and 

Methods, book 6, chap. A37, 44 p.

Niswonger, R.G., and Prudic, D.E., 2005, Documentation 

of the Streamflow-Routing (SFR) package to include 

unsaturated flow beneath streams—A modification to SFR1: 

U.S. Geological Survey Techniques and Methods, book 6, 

chap. A13, 50 p.
112 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Oklahoma Mesonet, 2017, Daily data retrieval, accessed 

March 25, 2017, at http://www.mesonet.org/index.php/

weather/daily_data_retrieval.

Oklahoma Water Resources Board [OWRB], 2012, Oklahoma 

comprehensive water plan: West-Central Watershed 

Planning Region Report, 168 p. 

Oklahoma Water Resources Board [OWRB], 2017, Data & 

maps—Groundwater: Oklahoma Water Resources Board, 

accessed February 2017 at http://www.owrb.ok.gov/maps/

pmg/owrbdata_GW.html.

Patrignani, A., Godsey, C.B., Ochsner, T.E., and Edwards., 

J.T., 2012, Soil water dynamics of conventional and no-till 

wheat in the southern great plains: Soil Science Society of 

America Journal, v. 76, p. 1768–1775, accessed December 11, 

2017, at https://doi.org/10.2136/sssaj2012.0082.

Roark, D.M., and Healy, D.F., 1998, Quantification of deep 

percolation from two flood-irrigated alfalfa fields, Roswell 

Basin, New Mexico: U.S. Geological Survey WaterResources Investigations Report 98–4096, 32 p.

Rorabaugh, M.I., 1964, Estimating changes in bank storage 

and groundwater contribution to streamflow: International 

Association of Scientific Hydrology, publication 63, 

p. 432–441.

Rutledge, A.T., 1998, Computer programs for describing the 

recession of ground-water discharge and for estimating 

mean ground-water recharge and discharge from streamflow 

records—Update: U.S. Geological Survey Water-Resources 

Investigations Report 98–4148, 43 p.

Ryter, D.W., and Correll, J.S., 2016, Hydrogeological 

framework, numerical simulation of groundwater flow, 

and effects of projected water use and drought for the 

Beaver-North Canadian River alluvial aquifer, northwestern 

Oklahoma: U.S. Geological Survey Scientific Investigations 

Report 2015–5183, 63 p. [Also available at https://dx.doi.

org/10.3133/sir20155183.]

Scanlon, B.R., Reedy, R.C., Stonestrom, D.A., Prudic, D.E., 

and Dennehy, K.F., 2005, Impact of land use and land 

cover change on groundwater recharge and quality in the 

southwestern U.S.: Global Change Biology, v. 11, p. 1,577–

1,593. [Also available at https://doi.org/10.1111/j.1365-

2486.2005.01026.x]

Shivers, M.J., and Andrews, W.J., 2013, Hydrologic drought 

of water year 2011 compared to four major drought periods 

of the 20th century in Oklahoma: U.S. Geological Survey 

Scientific Investigations Report 2013–5018, 52 p., accessed 

August 9, 2017, at http://pubs.usgs.gov/sir/2013/5018/.

Six, R.L., 1930, Oil and gas in Oklahoma; Blaine, Dewey, 

Custer, and Roger Mills Counties: Oklahoma Geological 

Survey, Bulletin 40-UU, p. 22–23.

Smith, S.J., Ellis, J.H., Wagner, D.L., and Peterson, S.M., 

2017, Hydrogeology and simulated groundwater flow and 

availability in the North Fork Red River aquifer, southwest 

Oklahoma, 1980–2013: U.S. Geological Survey Scientific 

Investigations Report 2017–5098, 107 p., accessed May 3, 

2017, at https://doi.org/10.3133/sir20175098.

Stanton, J.S., Peterson, S.M., and Fienen, M.N., 2010, 

Simulation of groundwater flow and effects of groundwater 

irrigation on stream base flow in the Elkhorn and 

Loup River Basins, Nebraska, 1895–2055—Phase 

two: U.S. Geological Survey Scientific Investigations 

Report 2010–5149, 78 p.

Strahler, A.N., 1952, Hypsometric (area-altitude) analysis of 

erosional topology: Geological Society of America Bulletin, 

v. 63, no. 11, p. 1117–1142.

Tanaka, H.H., and Davis, L.V., 1963, Ground-water resources 

of the Rush Springs sandstone in the Caddo County area, 

Oklahoma: Oklahoma Geological Survey Circular 61, 63 p.

Tarantola, Albert, 2005, Inverse problem theory and methods 

for model parameter estimation: Society for Industrial and 

Applied Mathematics, 342 p.

Thornthwaite, C.W., and Mather, J.R., 1957, Instructions and 

tables for computing potential evapotranspiration and the 

water balance: Centerton, N.J., Laboratory of Climatology, 

Publications in Climatology, v. 10, no. 3, p. 185–311.

Tonkin, M.J., and Doherty, J.E., 2005, A hybrid regularized 

inversion methodology for highly parameterized 

environmental models: Water Resources Research, 

v. 41, W10412, accessed July 10, 2017, at https://doi.

org/10.1029/2005WR003995.

U.S. Fish and Wildlife Service, 2017, National Wetlands 

Inventory—Download seamless wetlands data by State, 

accessed May 5, 2017, at http://www.fws.gov/wetlands/

Data/State-Downloads.html.

U.S. Geological Survey [USGS], 2017a, National Elevation 

Dataset, accessed January 2017 at http://ned.usgs.gov/

index.html.

U.S. Geological Survey [USGS], 2017b, National 

Hydrography Dataset: U.S. Geological Survey database, 

accessed September 14, 2016, at http://nhd.usgs.gov/

data.html.
References Cited 113

U.S. Geological Survey [USGS], 2017c, U.S. Geological 

Survey water data for Oklahoma: U.S. Geological Survey 

National Water Information System database, accessed 

March 14, 2017, at http://waterdata.usgs.gov/ok/nwis/.

Wahl, K.L., and Wahl, T.L., 1995, Determining the flow of 

Comal Springs at New Braunfels, Texas, in Proceedings 

of Texas Water ‘95, A Component Conference of the First 

International Conference on Water Resources Engineering, 

San Antonio, Texas, August 16–17, 1995: American Society 

of Civil Engineers, p. 77–86.

Welter, D.E., White, J.T., Hunt, R.J., and Doherty, J.E., 

2015, Approaches in highly parameterized inversion—

PEST++ Version 3, a Parameter ESTimation and uncertainty 

analysis software suite optimized for large environmental 

models: U.S. Geological Survey Techniques and Methods, 

book 7, chap. C12, 54 p.

Westenbroek, S.M., Kelson, V.A., Dripps, W.R., Hunt, 

R.J., and Bradbury, K.R., 2010, SWB—A modified 

Thornthwaite-Mather Soil-Water-Balance code for 

estimating groundwater recharge: U.S. Geological Survey 

Techniques and Methods, book 6, chap. A31, 60 p.

White, J.T., Fienen, M.N., and Doherty, J.E., 2016, 

pyEMU—A python framework for environmental model 

uncertainty analysis, version .01: U.S. Geological Survey 

software release, accessed July 13, 2018, at https://dx.doi.

org/10.5066/F75D8Q01.

White, W.N., 1932, A method of estimating ground-water 

supplies based on discharge by plants and evaporation 

from soil—Results of investigations in Escalante Valley, 

Utah: U.S. Geological Survey Water-Supply Paper 659–A, 

p. 1–105, accessed April 20, 2017, at https://pubs.er.usgs.

gov/publication/wsp659A.

Wood, P.R., and Stacy, B.L., 1965, Geology and ground-water 

resources of Woodward County, Oklahoma: Oklahoma 

Water Resources Board Bulletin 21, 79 p.

Wyatt, B.M., Ochsner, T.E., Fiebrich, C.A., Neel, C.R., and 

Wallace, D.S., 2017, Useful drainage estimates obtained 

from a large-scale soil moisture monitoring network by 

applying the unit-gradient assumption: Vadose Zone 

Journal, v. 16, no. 6, accessed June 9, 2017, at https://doi.

org/10.2136/vzj2017.01.0016.
114 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

GHB conductance1 ghb1 GHB conductance zone 1 500 5.0 ft2

/d 0.27 0.05

ghb2 GHB conductance zone 2 500 5.0 0.30 0.07

ghb3 GHB conductance zone 3 500 198 0.19 0.04

ghb4 GHB conductance zone 4 500 42.9 0.26 0.03

ghb5 GHB conductance zone 5 500 2,000 0.24 0.04

ghb7 GHB conductance zone 7 500 1,707 0.30 0.16

Drain conductance1 drn1 Drain conductance zone 1 500 500 ft2

/d 0.22 0.04

drn2 Drain conductance zone 2 500 58 0.18 0.02

drn3 Drain conductance zone 3 500 501 0.30 0.06

drn4 Drain conductance zone 4 500 31 0.31 0.03

drn5 Drain conductance zone 5 500 343 0.32 0.03

drn6 Drain conductance zone 6 500 195 0.28 0.04

drn7 Drain conductance zone 7 500 41 0.19 0.03

drn8 Drain conductance zone 8 500 51 0.26 0.03

drn9 Drain conductance zone 9 500 46 0.22 0.04

drn10 Drain conductance zone 10 500 10 0.31 0.55

drn11* Drain conductance zone 11 500 500 -- --

Recharge rate 

multipliers2

rch1 Recharge multiplier zone 1 1.0 0.5 multiplier 0.30 0.03

rch2 Recharge multiplier zone 2 1.0 2.0 0.30 0.06

rch3 Recharge multiplier zone 3 1.0 0.9 0.30 0.88

rch4 Recharge multiplier zone 4 1.0 0.5 0.24 0.03

rch5 Recharge multiplier zone 5 1.0 2.0 1.41 1.00

rch6 Recharge multiplier zone 6 1.0 2.0 0.27 0.98

rch7 Recharge multiplier zone 7 1.0 0.5 0.28 0.19

rch8 Recharge multiplier zone 8 1.0 0.5 0.29 0.05

rch9 Recharge multiplier zone 9 1.0 0.5 0.32 0.40

rch10 Recharge multiplier zone 10 1.0 0.5 0.25 0.05

rch11 Recharge multiplier zone 11 1.0 1.5 1.23 0.92

rch12 Recharge multiplier zone 12 1.0 0.5 0.25 0.27

rch13 Recharge multiplier zone 13 1.0 0.5 0.05 0.03
Table 6 115

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Recharge rate 

multipliers2

—

Continued

rch14 Recharge multiplier zone 14 1.0 2.0 multiplier 2.32 0.99

rch15 Recharge multiplier zone 15 1.0 2.0 0.99 0.99

rch16 Recharge multiplier zone 16 1.0 1.0 0.13 0.63

rch17 Recharge multiplier zone 17 1.0 0.5 0.33 0.21

rch18 Recharge multiplier zone 18 1.0 2.0 0.89 0.99

rch19 Recharge multiplier zone 19 1.0 2.0 0.32 0.87

rch20 Recharge multiplier zone 20 1.0 1.5 0.31 0.97

rch21 Recharge multiplier zone 21 1.0 1.3 1.57 0.94

rch22 Recharge multiplier zone 22 1.0 2.0 0.30 0.83

rch23 Recharge multiplier zone 23 1.0 0.5 0.04 0.03

Evapotranspiration 

multipliers

evtmult Rate multiplier 1.0 0.4 multiplier 0.48 0.80

evtextd Root-zone depth multiplier 1.0 1.0 0.29 0.04

Streambed conductance sfrmul Streambed conductance 5.0 5.0 ft/d 0.30 0.98

Lakebed leakance lakcond Lakebed leakance 0.5 0.5 ft-1 0.29 0.02

Specific yield sy2 Layer 2 specific yield 1.0 1.0 multiplier 0.28 0.97

sy3 Layer 3 specific yield 1.0 1.0 0.43 1.00

Specific storage ss2 Layer 2 specific storage 1.00E-05 1.00E-05 ft-1 0.24 0.05

ss3 Layer 3 specific storage 1.00E-05 1.00E-05 0.21 1.00

Horizontal hydraulic 

conductivity and 

vertical anisotropy

hkpp900 Layer 2 Kh 45.0 44.8 ft/d 0.23 0.16

hkpp901 Layer 2 Kh 45.0 32.4 0.38 0.19

hkpp902 Layer 2 Kh 45.0 25.5 0.32 0.17

hkpp903 Layer 2 Kh 45.0 40.1 0.31 0.05

hkpp904 Layer 2 Kh 45.0 25.7 0.39 0.06

hkpp905 Layer 2 Kh 45.0 80.9 0.24 0.03

hkpp906 Layer 2 Kh 45.0 49.8 0.20 0.05

hkpp907 Layer 2 Kh 45.0 42.0 0.22 0.04

hkpp908 Layer 2 Kh 45.0 57.6 0.29 0.04

hkpp909 Layer 2 Kh 45.0 38.1 0.36 0.16

hkpp910 Layer 2 Kh 45.0 25.0 0.14 0.04

hkpp911 Layer 2 Kh 45.0 31.7 0.24 0.15
116 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp912 Layer 2 Kh 45.0 29.5 ft/d 0.33 0.16

hkpp913 Layer 2 Kh 45.0 39.6 0.33 0.23

hkpp914 Layer 2 Kh 45.0 25.8 0.35 0.04

hkpp915 Layer 2 Kh 45.0 32.8 0.22 0.03

hkpp916 Layer 2 Kh 45.0 28.1 0.32 0.05

hkpp917 Layer 2 Kh 45.0 31.9 0.30 0.06

hkpp918 Layer 2 Kh 45.0 47.6 0.32 0.05

hkpp919 Layer 2 Kh 45.0 50.8 0.20 0.06

hkpp920 Layer 2 Kh 45.0 42.7 0.22 0.05

hkpp921 Layer 2 Kh 45.0 45.6 0.27 0.04

hkpp922 Layer 2 Kh 45.0 62.5 0.28 0.04

hkpp923 Layer 2 Kh 45.0 38.7 0.30 0.05

hkpp924 Layer 2 Kh 45.0 36.3 0.25 0.04

hkpp925 Layer 2 Kh 45.0 36.4 0.29 0.05

hkpp926 Layer 2 Kh 45.0 25.7 0.15 0.03

hkpp927 Layer 2 Kh 45.0 64.2 0.25 0.03

hkpp928 Layer 2 Kh 45.0 56.9 0.31 0.04

hkpp929 Layer 2 Kh 45.0 93.0 0.23 0.03

hkpp930 Layer 2 Kh 45.0 92.5 0.23 0.03

hkpp931 Layer 2 Kh 45.0 38.7 0.15 0.04

hkpp932 Layer 2 Kh 45.0 32.2 0.24 0.03

hkpp933 Layer 2 Kh 45.0 26.8 0.14 0.02

hkpp934 Layer 2 Kh 45.0 21.1 0.29 0.04

hkpp935 Layer 2 Kh 45.0 91.3 0.31 0.12

hkpp936 Layer 2 Kh 45.0 50.9 0.23 0.02

hkpp937 Layer 2 Kh 45.0 39.7 0.23 0.03

hkpp938 Layer 2 Kh 45.0 84.8 0.36 0.04

hkpp939 Layer 2 Kh 45.0 89.4 0.17 0.02

hkpp940 Layer 2 Kh 45.0 52.7 0.22 0.06

hkpp941 Layer 2 Kh 45.0 24.0 0.23 0.04
Table 6 117

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp942 Layer 2 Kh 45.0 25.6 ft/d 0.29 0.05

hkpp943 Layer 2 Kh 45.0 42.6 0.19 0.03

hkpp944 Layer 2 Kh 45.0 97.4 0.30 0.02

hkpp945 Layer 2 Kh 45.0 96.3 0.25 0.03

hkpp946 Layer 2 Kh 45.0 35.7 0.29 0.04

hkpp947 Layer 2 Kh 45.0 23.1 0.33 0.05

hkpp948 Layer 2 Kh 45.0 37.1 0.34 0.03

hkpp949 Layer 2 Kh 45.0 96.1 0.27 0.06

hkpp950 Layer 2 Kh 45.0 41.4 0.26 0.05

hkpp951 Layer 2 Kh 45.0 41.4 0.41 0.05

hkpp952 Layer 2 Kh 45.0 23.6 0.17 0.04

hkpp953 Layer 2 Kh 45.0 37.7 0.22 0.03

hkpp954 Layer 2 Kh 45.0 87.9 0.31 0.04

hkpp955 Layer 2 Kh 45.0 41.5 0.26 0.04

hkpp956 Layer 2 Kh 45.0 26.1 0.26 0.04

hkpp957 Layer 2 Kh 45.0 37.8 0.25 0.02

hkpp958 Layer 2 Kh 45.0 35.2 0.28 0.04

hkpp959 Layer 2 Kh 45.0 84.1 0.23 0.02

hkpp960 Layer 2 Kh 45.0 32.6 0.27 0.04

hkpp961 Layer 2 Kh 45.0 31.4 0.26 0.07

hkpp962 Layer 2 Kh 45.0 38.6 0.14 0.03

hkpp963 Layer 2 Kh 45.0 33.4 0.23 0.03

hkpp964 Layer 2 Kh 45.0 94.1 0.24 0.03

hkpp965 Layer 2 Kh 30.0 39.4 0.27 0.03

hkpp966 Layer 2 Kh 45.0 60.9 0.17 0.03

hkpp967 Layer 2 Kh 30.0 38.6 0.35 0.08

hkpp968 Layer 2 Kh 45.0 30.8 0.24 0.04

hkpp969 Layer 2 Kh 30.0 46.9 0.22 0.04

hkpp970 Layer 2 Kh 45.0 18.8 0.20 0.04

hkpp971 Layer 2 Kh 30.0 19.1 0.31 0.04
118 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp972 Layer 2 Kh 45.0 11.7 ft/d 0.26 0.05

hkpp973 Layer 2 Kh 45.0 13.5 0.31 0.99

hkpp974 Layer 2 Kh 30.0 62.5 0.20 0.03

hkpp975 Layer 2 Kh 30.0 27.8 0.30 0.58

hkpp976 Layer 2 Kh 45.0 41.4 0.18 0.04

hkpp977 Layer 2 Kh 45.0 46.7 0.21 0.05

hkpp978* Layer 2 Kh 45.0 59.4 -- --

hkpp979 Layer 2 Kh 45.0 48.9 0.26 0.05

hkpp980* Layer 2 Kh 46.0 52.8 -- --

hkpp981 Layer 2 Kh 30.0 38.4 0.24 0.04

hkpp982 Layer 2 Kh 30.0 33.8 0.18 0.05

hkpp983 Layer 2 Kh 30.0 34.7 0.24 0.07

hkpp984 Layer 2 Kh 45.0 51.4 0.35 0.48

hkpp985 Layer 2 Kh 45.0 39.0 0.20 0.04

hkpp986 Layer 2 Kh 45.0 35.6 0.30 0.04

hkpp987 Layer 2 Kh 45.0 36.7 0.22 0.05

hkpp988 Layer 2 Kh 45.0 49.0 0.22 0.04

hkpp989 Layer 2 Kh 30.0 35.1 0.17 0.03

hkpp990 Layer 2 Kh 30.0 29.2 0.22 0.03

hkpp991 Layer 2 Kh 30.0 26.5 0.31 0.04

hkpp992 Layer 2 Kh 45.0 46.5 0.22 0.04

hkpp993 Layer 2 Kh 45.0 41.3 0.33 0.06

hkpp994 Layer 2 Kh 45.0 41.3 0.26 0.03

hkpp995 Layer 2 Kh 45.0 99.0 0.26 0.02

hkpp996 Layer 2 Kh 45.0 54.1 0.24 0.04

hkpp997 Layer 2 Kh 30.0 43.6 0.27 0.05

hkpp998 Layer 2 Kh 30.0 20.3 0.25 0.08

hkpp999 Layer 2 Kh 45.0 73.0 0.31 0.05

hkpp1000 Layer 2 Kh 30.0 21.5 0.16 0.03

hkpp1001 Layer 2 Kh 45.0 49.4 0.31 0.06
Table 6 119

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1002 Layer 2 Kh 45.0 44.7 ft/d 0.23 0.03

hkpp1003 Layer 2 Kh 30.0 22.4 0.36 0.04

hkpp1004 Layer 2 Kh 30.0 57.8 0.19 0.03

hkpp1005 Layer 2 Kh 45.0 35.9 0.24 0.03

hkpp1006 Layer 2 Kh 45.0 37.8 0.33 0.06

hkpp1007 Layer 2 Kh 45.0 41.1 0.26 0.03

hkpp1008 Layer 2 Kh 45.0 39.2 0.27 0.04

hkpp1009 Layer 2 Kh 45.0 42.0 0.17 0.03

hkpp1010 Layer 2 Kh 45.0 23.9 0.28 0.06

hkpp1011 Layer 2 Kh 45.0 100.0 0.31 0.03

hkpp1012 Layer 2 Kh 30.0 14.0 0.31 0.08

hkpp1013 Layer 2 Kh 45.0 56.2 0.28 0.04

hkpp1014 Layer 2 Kh 45.0 52.8 0.14 0.04

hkpp1015 Layer 2 Kh 45.0 99.0 0.27 0.04

hkpp1016 Layer 2 Kh 45.0 99.0 0.14 0.01

hkpp1017 Layer 2 Kh 45.0 97.7 0.24 0.03

hkpp1018 Layer 2 Kh 45.0 24.7 0.23 0.03

hkpp1019 Layer 2 Kh 45.0 100.0 0.15 0.03

hkpp1020 Layer 2 Kh 45.0 20.8 0.29 0.03

hkpp1021 Layer 2 Kh 45.0 12.4 0.28 0.03

hkpp1022 Layer 2 Kh 45.0 9.8 0.10 0.03

hkpp1023 Layer 2 Kh 45.0 100.0 0.22 0.04

hkpp1024 Layer 2 Kh 45.0 33.5 0.26 0.04

hkpp1025 Layer 2 Kh 45.0 19.3 0.16 0.03

hkpp1026 Layer 2 Kh 45.0 100.0 0.32 0.07

hkpp1027 Layer 2 Kh 45.0 100.0 0.25 0.03

hkpp1028 Layer 2 Kh 45.0 100.0 0.00 0.00

hkpp1029 Layer 2 Kh 45.0 100.0 0.00 0.00

hkpp1030 Layer 2 Kh 45.0 100.0 0.31 0.10

hkpp1031* Layer 2 Kh 30.0 99.0 -- --
120 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1032 Layer 2 Kh 45.0 100.0 ft/d 0.00 0.00

hkpp1033 Layer 2 Kh 30.0 95.5 0.26 0.04

hkpp1034 Layer 2 Kh 30.0 85.1 0.31 0.03

hkpp1035 Layer 2 Kh 45.0 100.0 0.31 0.10

hkpp1036 Layer 2 Kh 30.0 43.7 0.18 0.03

hkpp1037 Layer 2 Kh 45.0 100.0 0.00 0.00

hkpp1038 Layer 2 Kh 45.0 100.0 0.22 0.03

hkpp1039 Layer 2 Kh 30.0 36.0 0.34 0.98

hkpp1040 Layer 2 Kh 45.0 100.0 0.33 0.03

hkpp1041 Layer 2 Kh 45.0 100.0 0.15 0.03

hkpp1042 Layer 2 Kh 45.0 100.0 0.21 0.03

hkpp1043 Layer 2 Kh 30.0 80.4 0.28 0.03

hkpp1044 Layer 2 Kh 45.0 100.0 0.32 0.03

hkpp1045 Layer 2 Kh 30.0 81.2 0.29 0.06

hkpp1046 Layer 2 Kh 30.0 49.0 0.16 0.03

hkpp1047 Layer 2 Kh 30.0 43.1 0.23 0.02

hkpp1048 Layer 2 Kh 30.0 100.0 0.31 0.03

hkpp1049 Layer 2 Kh 45.0 100.0 0.00 0.00

hkpp1050 Layer 2 Kh 30.0 76.9 0.25 0.05

hkpp1051 Layer 2 Kh 30.0 42.0 0.22 0.04

hkpp1052 Layer 2 Kh 45.0 100.0 0.31 0.10

hkpp1053 Layer 2 Kh 45.0 100.0 0.31 0.10

hkpp1054 Layer 2 Kh 45.0 96.8 0.31 0.10

hkpp1055* Layer 2 Kh 45.0 99.0 -- --

hkpp1056* Layer 2 Kh 45.0 99.0 -- --

hkpp1057* Layer 2 Kh 45.0 99.0 -- --

hkpp1058 Layer 2 Kh 45.0 99.0 0.19 0.03

hkpp1059* Layer 2 Kh 45.0 99.0 -- --

hkpp1060* Layer 2 Kh 45.0 99.0 -- --

hkpp1061 Layer 2 Kh 45.0 98.8 0.31 0.03
Table 6 121

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1062 Layer 2 Kh 45.0 60.7 ft/d 0.27 0.04

hkpp1063 Layer 2 Kh 45.0 5.4 0.31 0.06

hkpp1064 Layer 2 Kh 45.0 89.1 0.22 0.03

hkpp1065 Layer 2 Kh 45.0 35.9 0.24 0.03

hkpp1066 Layer 2 Kh 45.0 28.6 0.17 0.04

hkpp1067 Layer 2 Kh 45.0 52.2 0.27 0.03

hkpp1068 Layer 2 Kh 45.0 67.9 0.34 0.03

hkpp1069 Layer 2 Kh 45.0 67.1 0.21 0.04

hkpp1070 Layer 2 Kh 45.0 73.0 0.16 0.04

hkpp1071 Layer 2 Kh 45.0 68.8 0.18 0.04

hkpp1072 Layer 2 Kh 45.0 67.4 0.29 0.03

hkpp1073 Layer 2 Kh 45.0 84.4 0.23 0.03

hkpp1074 Layer 2 Kh 45.0 87.4 0.28 0.03

hkpp1075 Layer 2 Kh 45.0 86.5 0.24 0.03

hkpp1076 Layer 2 Kh 45.0 80.5 0.24 0.03

hkpp1077 Layer 2 Kh 45.0 88.4 0.23 0.04

hkpp1078 Layer 2 Kh 45.0 81.1 0.25 0.03

hkpp1079 Layer 2 Kh 30.0 30.1 0.30 0.04

hkpp1080 Layer 2 Kh 30.0 13.3 0.22 0.04

hkpp1081 Layer 2 Kh 30.0 29.3 0.24 0.03

hkpp1104 Layer 3 Kh 6.3 16.5 0.34 0.04

hkpp1106 Layer 3 Kh 6.3 6.9 0.19 0.04

hkpp1108 Layer 3 Kh 6.3 24.2 0.19 0.04

hkpp1118 Layer 3 Kh 6.3 13.6 0.26 0.07

hkpp1120 Layer 3 Kh 6.3 8.8 0.19 0.03

hkpp1122 Layer 3 Kh 6.3 13.6 0.22 0.17

hkpp1133 Layer 3 Kh 6.3 3.4 0.31 0.05

hkpp1135 Layer 3 Kh 6.3 7.0 0.32 0.04

hkpp1137 Layer 3 Kh 6.3 15.3 0.30 0.03

hkpp1139 Layer 3 Kh 6.3 5.0 0.31 0.07
122 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1141 Layer 3 Kh 6.3 16.5 ft/d 0.20 0.05

hkpp1160 Layer 3 Kh 6.3 0.1 0.32 0.06

hkpp1162* Layer 3 Kh 6.3 2.8 -- --

hkpp1164 Layer 3 Kh 6.3 13.7 0.25 0.05

hkpp1166 Layer 3 Kh 6.3 4.7 0.31 0.16

hkpp1168 Layer 3 Kh 6.3 4.8 0.24 0.05

hkpp1170 Layer 3 Kh 6.3 7.3 0.36 0.07

hkpp1172 Layer 3 Kh 6.3 10.0 0.24 0.11

hkpp1174 Layer 3 Kh 6.3 10.5 0.31 0.17

hkpp1197* Layer 3 Kh 6.3 1.1 -- --

hkpp1199* Layer 3 Kh 6.3 2.2 -- --

hkpp1201* Layer 3 Kh 6.3 2.2 -- --

hkpp1203 Layer 3 Kh 6.3 6.5 0.32 0.05

hkpp1205* Layer 3 Kh 6.3 1.1 -- --

hkpp1207 Layer 3 Kh 6.3 1.2 0.28 0.14

hkpp1209 Layer 3 Kh 6.3 2.0 0.23 0.04

hkpp1211 Layer 3 Kh 6.3 2.6 0.26 0.18

hkpp1213 Layer 3 Kh 6.3 2.6 0.10 0.12

hkpp1215 Layer 3 Kh 6.3 5.4 0.32 0.12

hkpp1217 Layer 3 Kh 6.3 18.6 0.19 0.06

hkpp1243* Layer 3 Kh 6.3 5.3 -- --

hkpp1245 Layer 3 Kh 6.3 3.1 0.34 0.05

hkpp1247 Layer 3 Kh 6.3 4.6 0.25 0.07

hkpp1249 Layer 3 Kh 6.3 3.1 0.14 0.02

hkpp1251 Layer 3 Kh 6.3 2.4 0.18 0.04

hkpp1253 Layer 3 Kh 6.3 1.3 0.21 0.14

hkpp1255 Layer 3 Kh 6.3 0.1 0.26 0.05

hkpp1257 Layer 3 Kh 6.3 0.4 0.25 0.04

hkpp1259 Layer 3 Kh 6.3 2.3 0.29 0.15

hkpp1261 Layer 3 Kh 6.3 2.1 0.13 0.11
Table 6 123

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1263 Layer 3 Kh 6.3 4.8 ft/d 0.30 0.12

hkpp1290 Layer 3 Kh 6.3 3.7 0.15 0.03

hkpp1292 Layer 3 Kh 6.3 4.5 0.29 0.04

hkpp1294* Layer 3 Kh 6.3 4.4 -- --

hkpp1296 Layer 3 Kh 6.3 3.7 0.23 0.04

hkpp1298* Layer 3 Kh 6.3 0.9 -- --

hkpp1300* Layer 3 Kh 6.3 1.1 -- --

hkpp1302 Layer 3 Kh 6.3 6.3 0.30 0.14

hkpp1304 Layer 3 Kh 6.3 6.8 0.23 0.06

hkpp1306 Layer 3 Kh 6.3 8.8 0.30 0.15

hkpp1308 Layer 3 Kh 6.3 2.8 0.14 0.08

hkpp1310 Layer 3 Kh 6.3 2.1 0.28 0.30

hkpp1312 Layer 3 Kh 6.3 4.3 0.26 0.31

hkpp1340 Layer 3 Kh 6.3 7.8 0.03 0.03

hkpp1342 Layer 3 Kh 6.3 13.2 0.25 0.07

hkpp1344 Layer 3 Kh 6.3 2.5 0.26 0.04

hkpp1346 Layer 3 Kh 6.3 1.2 0.26 0.04

hkpp1348 Layer 3 Kh 6.3 3.3 0.26 0.04

hkpp1350* Layer 3 Kh 6.3 2.2 -- --

hkpp1352* Layer 3 Kh 6.3 0.9 -- --

hkpp1354 Layer 3 Kh 6.3 17.2 0.20 0.08

hkpp1356 Layer 3 Kh 6.3 8.6 0.24 0.04

hkpp1358 Layer 3 Kh 6.3 13.4 0.27 0.04

hkpp1360 Layer 3 Kh 6.3 6.6 0.27 0.06

hkpp1362 Layer 3 Kh 6.3 4.4 0.16 0.04

hkpp1364 Layer 3 Kh 6.3 5.8 0.26 0.04

hkpp1392 Layer 3 Kh 6.3 10.4 0.18 0.03

hkpp1394 Layer 3 Kh 6.3 10.9 0.28 0.04

hkpp1396 Layer 3 Kh 6.3 17.3 0.27 0.04

hkpp1398 Layer 3 Kh 6.3 2.2 0.25 0.04
124 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1400* Layer 3 Kh 6.3 0.8 ft/d -- --

hkpp1402* Layer 3 Kh 6.3 1.1 -- --

hkpp1404 Layer 3 Kh 6.3 1.9 0.22 0.04

hkpp1406 Layer 3 Kh 6.3 2.1 0.29 0.05

hkpp1408 Layer 3 Kh 6.3 4.1 0.34 0.30

hkpp1410 Layer 3 Kh 6.3 18.5 0.18 0.08

hkpp1412 Layer 3 Kh 6.3 8.5 0.22 0.08

hkpp1414* Layer 3 Kh 7.3 1.1 -- --

hkpp1416 Layer 3 Kh 6.3 16.7 0.19 0.04

hkpp1444 Layer 3 Kh 6.3 6.1 0.28 0.03

hkpp1446* Layer 3 Kh 6.3 4.8 -- --

hkpp1448 Layer 3 Kh 6.3 7.5 0.27 0.05

hkpp1450 Layer 3 Kh 6.3 39.3 0.21 0.05

hkpp1452 Layer 3 Kh 6.3 5.9 0.18 0.04

hkpp1454 Layer 3 Kh 6.3 3.3 0.36 0.09

hkpp1456 Layer 3 Kh 6.3 41.6 0.28 0.04

hkpp1458* Layer 3 Kh 6.3 3.7 -- --

hkpp1460 Layer 3 Kh 6.3 5.1 0.27 0.53

hkpp1462 Layer 3 Kh 6.3 7.4 0.27 0.71

hkpp1464 Layer 3 Kh 6.3 0.3 0.32 0.17

hkpp1466 Layer 3 Kh 6.3 0.4 0.30 0.11

hkpp1468* Layer 3 Kh 6.3 1.2 -- --

hkpp1470 Layer 3 Kh 6.3 9.2 0.23 0.05

hkpp1499 Layer 3 Kh 6.3 10.1 0.20 0.04

hkpp1500 Layer 3 Kh 6.3 46.0 0.31 0.05

hkpp1502 Layer 3 Kh 6.3 16.9 0.30 0.05

hkpp1504 Layer 3 Kh 6.3 8.0 0.22 0.07

hkpp1506 Layer 3 Kh 6.3 2.1 0.28 0.04

hkpp1508 Layer 3 Kh 6.3 10.0 0.25 0.14

hkpp1510 Layer 3 Kh 6.3 6.4 0.27 0.06
Table 6 125

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1512 Layer 3 Kh 6.3 0.3 ft/d 0.25 0.11

hkpp1514 Layer 3 Kh 6.3 0.1 0.21 0.11

hkpp1516 Layer 3 Kh 6.3 0.3 0.37 0.12

hkpp1518 Layer 3 Kh 6.3 3.7 0.35 0.04

hkpp1520 Layer 3 Kh 6.3 9.0 0.29 0.05

hkpp1544 Layer 3 Kh 6.3 100.0 0.25 0.04

hkpp1546 Layer 3 Kh 6.3 8.5 0.31 0.03

hkpp1548 Layer 3 Kh 6.3 13.2 0.23 0.04

hkpp1550 Layer 3 Kh 6.3 27.1 0.24 0.65

hkpp1552 Layer 3 Kh 6.3 50.8 0.24 0.06

hkpp1554 Layer 3 Kh 6.3 4.7 0.22 0.07

hkpp1556 Layer 3 Kh 6.3 3.7 0.27 0.20

hkpp1558 Layer 3 Kh 6.3 0.5 0.20 0.07

hkpp1560 Layer 3 Kh 6.3 3.8 0.27 0.07

hkpp1562 Layer 3 Kh 6.3 16.3 0.21 0.08

hkpp1564 Layer 3 Kh 6.3 9.7 0.21 0.07

hkpp1565 Layer 3 Kh 6.3 4.1 0.26 0.06

hkpp1589 Layer 3 Kh 6.3 10.3 0.21 0.04

hkpp1591 Layer 3 Kh 6.3 10.0 0.20 0.03

hkpp1593 Layer 3 Kh 6.3 12.5 0.27 0.05

hkpp1595 Layer 3 Kh 6.3 5.1 0.25 0.06

hkpp1597 Layer 3 Kh 6.3 13.0 0.30 0.09

hkpp1599 Layer 3 Kh 6.3 13.0 0.27 0.10

hkpp1601 Layer 3 Kh 6.3 3.6 0.12 0.13

hkpp1603 Layer 3 Kh 6.3 2.7 0.24 0.14

hkpp1605 Layer 3 Kh 6.3 6.4 0.24 0.14

hkpp1607 Layer 3 Kh 6.3 23.6 0.20 0.15

hkpp1609 Layer 3 Kh 6.3 18.4 0.26 0.18

hkpp1611 Layer 3 Kh 6.3 3.1 0.26 0.04

hkpp1635 Layer 3 Kh 6.3 11.7 0.27 0.06
126 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1637 Layer 3 Kh 6.3 33.6 ft/d 0.31 0.09

hkpp1639 Layer 3 Kh 6.3 10.8 0.17 0.07

hkpp1641 Layer 3 Kh 6.3 99.0 0.31 0.14

hkpp1643 Layer 3 Kh 6.3 1.2 0.37 0.16

hkpp1645 Layer 3 Kh 6.3 17.9 0.31 0.17

hkpp1647 Layer 3 Kh 6.3 8.0 0.29 0.15

hkpp1649 Layer 3 Kh 6.3 1.3 0.13 0.20

hkpp1651 Layer 3 Kh 6.3 38.1 0.26 0.12

hkpp1653 Layer 3 Kh 6.3 3.1 0.17 0.05

hkpp1676 Layer 3 Kh 6.3 38.8 0.22 0.05

hkpp1678 Layer 3 Kh 6.3 17.1 0.29 0.08

hkpp1680 Layer 3 Kh 6.3 11.9 0.17 0.08

hkpp1682 Layer 3 Kh 6.3 5.2 0.24 0.08

hkpp1684 Layer 3 Kh 6.3 4.4 0.24 0.10

hkpp1686 Layer 3 Kh 6.3 0.7 0.33 0.15

hkpp1688 Layer 3 Kh 6.3 4.3 0.35 0.15

hkpp1690 Layer 3 Kh 6.3 4.0 0.16 0.10

hkpp1693 Layer 3 Kh 6.3 14.5 0.24 0.05

hkpp1718 Layer 3 Kh 6.3 12.5 0.17 0.06

hkpp1720 Layer 3 Kh 6.3 88.9 0.18 0.07

hkpp1722 Layer 3 Kh 6.3 2.7 0.27 0.05

hkpp1724 Layer 3 Kh 6.3 0.6 0.19 0.07

hkpp1726 Layer 3 Kh 6.3 0.1 0.32 0.11

hkpp1728 Layer 3 Kh 6.3 88.7 0.22 0.13

hkpp1730 Layer 3 Kh 6.3 1.2 0.32 0.11

hkpp1732* Layer 3 Kh 6.3 0.8 -- --

hkpp1734 Layer 3 Kh 6.3 5.2 0.30 0.04

hkpp1736 Layer 3 Kh 6.3 5.2 0.35 0.03

hkpp1761 Layer 3 Kh 6.3 9.1 0.32 0.04

hkpp1763 Layer 3 Kh 6.3 17.7 0.18 0.03
Table 6 127

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1765 Layer 3 Kh 6.3 10.0 ft/d 0.27 0.28

hkpp1767 Layer 3 Kh 6.3 17.4 0.29 0.29

hkpp1769 Layer 3 Kh 6.3 99.0 0.29 0.06

hkpp1771 Layer 3 Kh 6.3 3.7 0.18 0.05

hkpp1773 Layer 3 Kh 6.3 15.3 0.29 0.05

hkpp1775* Layer 3 Kh 6.3 1.2 -- --

hkpp1777 Layer 3 Kh 6.3 0.0 0.35 0.10

hkpp1779 Layer 3 Kh 6.3 39.6 0.37 0.11

hkpp1781 Layer 3 Kh 6.3 0.3 0.29 0.06

hkpp1782 Layer 3 Kh 6.3 4.0 0.19 0.04

hkpp1783 Layer 3 Kh 6.3 8.4 0.03 0.03

hkpp1812 Layer 3 Kh 6.3 10.0 0.25 0.27

hkpp1814 Layer 3 Kh 6.3 19.6 0.20 0.28

hkpp1816 Layer 3 Kh 6.3 8.8 0.28 0.04

hkpp1818 Layer 3 Kh 6.3 7.2 0.37 0.06

hkpp1820 Layer 3 Kh 6.3 9.7 0.33 0.05

hkpp1822 Layer 3 Kh 6.3 2.5 0.03 0.04

hkpp1824 Layer 3 Kh 6.3 40.9 0.17 0.05

hkpp1826* Layer 3 Kh 6.3 1.0 -- --

hkpp1828 Layer 3 Kh 6.3 5.7 0.27 0.05

hkpp1830 Layer 3 Kh 6.3 0.5 0.25 0.04

hkpp1846 Layer 3 Kh 6.3 4.9 0.18 0.03

hkpp1848 Layer 3 Kh 6.3 3.6 0.26 0.05

hkpp1850* Layer 3 Kh 6.3 1.2 -- --

hkpp1852 Layer 3 Kh 6.3 10.5 0.17 0.03

hkpp1854 Layer 3 Kh 6.3 29.6 0.19 0.04

hkpp1867 Layer 3 Kh 6.3 10.3 0.23 0.03

hkpp1869 Layer 3 Kh 6.3 17.1 0.36 0.05

hkpp1871 Layer 3 Kh 6.3 13.4 0.31 0.03

hkpp1872 Layer 3 Kh 6.3 6.1 0.26 0.04
128 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1885 Layer 3 Kh 6.3 11.4 ft/d 0.20 0.03

hkpp1887 Layer 3 Kh 6.3 17.7 0.33 0.03

hkpp1889 Layer 3 Kh 6.3 5.7 0.26 0.03

hkpp1891* Layer 3 Kh 6.3 1.0 -- --

hkpp1893 Layer 3 Kh 6.3 7.4 0.20 0.03

hkpp1904 Layer 3 Kh 6.3 15.5 0.30 0.03

hkpp1906 Layer 3 Kh 6.3 91.4 0.25 0.04

hkpp1908 Layer 3 Kh 6.3 23.0 0.29 0.04

hkpp1911 Layer 3 Kh 6.3 2.7 0.20 0.03

hkpp1923 Layer 3 Kh 6.3 89.7 0.30 0.03

hkpp1925 Layer 3 Kh 6.3 14.6 0.33 0.05

hkpp1927 Layer 3 Kh 6.3 2.7 0.30 0.04

hkpp1929 Layer 3 Kh 6.3 1.7 0.22 0.04

hkpp1942 Layer 3 Kh 6.3 70.2 0.16 0.05

hkpp1944 Layer 3 Kh 6.3 7.8 0.17 0.05

hkpp1946 Layer 3 Kh 6.3 5.1 0.29 0.06

hkpp1948 Layer 3 Kh 6.3 4.8 0.25 0.05

hkpp1950 Layer 3 Kh 6.3 6.3 0.25 0.03

hkpp1959 Layer 3 Kh 6.3 15.2 0.24 0.04

hkpp1961 Layer 3 Kh 6.3 6.6 0.22 0.04

hkpp1963 Layer 3 Kh 6.3 2.7 0.20 0.06

hkpp1965 Layer 3 Kh 6.3 2.6 0.31 0.06

hkpp1967* Layer 3 Kh 6.3 6.6 -- --

hkpp1972 Layer 3 Kh 6.3 6.5 0.28 0.05

hkpp1973 Layer 3 Kh 6.3 5.9 0.28 0.04

hkpp900_vk Layer 2 vertical anisotropy 10.0 9.6 Horizontal 

to vertical 

ratio

0.27 0.03

hkpp901_vk Layer 2 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp902_vk Layer 2 vertical anisotropy 10.0 9.7 0.14 0.03

hkpp903_vk Layer 2 vertical anisotropy 10.0 10.0 0.20 0.04

hkpp904_vk Layer 2 vertical anisotropy 10.0 10.0 0.34 0.06
Table 6 129

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp905_vk Layer 2 vertical anisotropy 10.0 9.3 Horizontal 

to vertical 

ratio

0.32 0.03

hkpp906_vk Layer 2 vertical anisotropy 10.0 9.5 0.34 0.08

hkpp907_vk Layer 2 vertical anisotropy 10.0 9.5 0.17 0.03

hkpp908_vk Layer 2 vertical anisotropy 10.0 9.7 0.23 0.03

hkpp909_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp910_vk Layer 2 vertical anisotropy 10.0 9.1 0.23 0.04

hkpp911_vk Layer 2 vertical anisotropy 10.0 9.5 0.05 0.03

hkpp912_vk Layer 2 vertical anisotropy 10.0 9.0 0.29 0.03

hkpp913_vk Layer 2 vertical anisotropy 10.0 9.3 0.19 0.03

hkpp914_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp915_vk Layer 2 vertical anisotropy 10.0 9.5 0.24 0.03

hkpp916_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp917_vk Layer 2 vertical anisotropy 10.0 10.0 0.28 0.02

hkpp918_vk Layer 2 vertical anisotropy 10.0 9.3 0.24 0.04

hkpp919_vk Layer 2 vertical anisotropy 10.0 10.0 0.22 0.03

hkpp920_vk Layer 2 vertical anisotropy 10.0 10.2 0.30 0.03

hkpp921_vk Layer 2 vertical anisotropy 10.0 10.1 0.28 0.06

hkpp922_vk Layer 2 vertical anisotropy 10.0 9.8 0.14 0.02

hkpp923_vk Layer 2 vertical anisotropy 10.0 9.6 0.34 0.04

hkpp924_vk Layer 2 vertical anisotropy 10.0 9.5 0.29 0.03

hkpp925_vk Layer 2 vertical anisotropy 10.0 9.8 0.26 0.03

hkpp926_vk Layer 2 vertical anisotropy 10.0 9.3 0.09 0.02

hkpp927_vk Layer 2 vertical anisotropy 10.0 9.5 0.28 0.02

hkpp928_vk Layer 2 vertical anisotropy 10.0 9.1 0.10 0.02

hkpp929_vk Layer 2 vertical anisotropy 10.0 9.4 0.22 0.03

hkpp930_vk Layer 2 vertical anisotropy 10.0 9.1 0.35 0.04

hkpp931_vk Layer 2 vertical anisotropy 10.0 9.8 0.22 0.03

hkpp932_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp933_vk Layer 2 vertical anisotropy 10.0 10.0 0.35 0.03

hkpp934_vk Layer 2 vertical anisotropy 10.0 9.7 0.34 0.04
130 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp935_vk* Layer 2 vertical anisotropy 10.0 10.0 Horizontal 

to vertical 

ratio

-- --

hkpp936_vk Layer 2 vertical anisotropy 10.0 9.4 0.23 0.03

hkpp937_vk Layer 2 vertical anisotropy 10.0 9.4 0.20 0.04

hkpp938_vk Layer 2 vertical anisotropy 10.0 9.7 0.26 0.03

hkpp939_vk Layer 2 vertical anisotropy 10.0 8.9 0.26 0.04

hkpp940_vk Layer 2 vertical anisotropy 10.0 9.1 0.26 0.03

hkpp941_vk Layer 2 vertical anisotropy 10.0 9.5 0.05 0.04

hkpp942_vk Layer 2 vertical anisotropy 10.0 9.5 0.19 0.04

hkpp943_vk Layer 2 vertical anisotropy 10.0 9.1 0.33 0.04

hkpp944_vk Layer 2 vertical anisotropy 10.0 9.5 0.14 0.03

hkpp945_vk Layer 2 vertical anisotropy 10.0 9.5 0.31 0.04

hkpp946_vk Layer 2 vertical anisotropy 10.0 10.1 0.26 0.05

hkpp947_vk Layer 2 vertical anisotropy 10.0 9.3 0.19 0.03

hkpp948_vk Layer 2 vertical anisotropy 10.0 9.0 0.22 0.03

hkpp949_vk Layer 2 vertical anisotropy 10.0 9.2 0.23 0.05

hkpp950_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp951_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp952_vk Layer 2 vertical anisotropy 10.0 9.4 0.23 0.03

hkpp953_vk Layer 2 vertical anisotropy 10.0 9.2 0.28 0.03

hkpp954_vk Layer 2 vertical anisotropy 10.0 9.0 0.28 0.03

hkpp955_vk Layer 2 vertical anisotropy 10.0 9.8 0.27 0.04

hkpp956_vk Layer 2 vertical anisotropy 10.0 10.2 0.29 0.04

hkpp957_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp958_vk Layer 2 vertical anisotropy 10.0 9.7 0.28 0.03

hkpp959_vk Layer 2 vertical anisotropy 10.0 9.9 0.14 0.02

hkpp960_vk Layer 2 vertical anisotropy 10.0 9.8 0.29 0.04

hkpp961_vk Layer 2 vertical anisotropy 10.0 10.1 0.30 0.05

hkpp962_vk Layer 2 vertical anisotropy 10.0 9.8 0.25 0.03

hkpp963_vk Layer 2 vertical anisotropy 10.0 9.4 0.29 0.06

hkpp964_vk Layer 2 vertical anisotropy 10.0 10.1 0.22 0.03
Table 6 131

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp965_vk Layer 2 vertical anisotropy 10.0 9.6 Horizontal 

to vertical 

ratio

0.28 0.04

hkpp966_vk Layer 2 vertical anisotropy 10.0 10.4 0.23 0.03

hkpp967_vk Layer 2 vertical anisotropy 10.0 10.7 0.28 0.03

hkpp968_vk Layer 2 vertical anisotropy 10.0 9.3 0.14 0.04

hkpp969_vk Layer 2 vertical anisotropy 10.0 9.5 0.22 0.05

hkpp970_vk Layer 2 vertical anisotropy 10.0 10.0 0.20 0.03

hkpp971_vk Layer 2 vertical anisotropy 10.0 9.2 0.21 0.04

hkpp972_vk Layer 2 vertical anisotropy 10.0 9.8 0.27 0.03

hkpp973_vk Layer 2 vertical anisotropy 10.0 9.8 0.22 0.04

hkpp974_vk Layer 2 vertical anisotropy 10.0 10.3 0.23 0.03

hkpp975_vk Layer 2 vertical anisotropy 10.0 9.8 0.24 0.02

hkpp976_vk Layer 2 vertical anisotropy 10.0 10.0 0.26 0.04

hkpp977_vk Layer 2 vertical anisotropy 10.0 9.8 0.32 0.04

hkpp978_vk Layer 2 vertical anisotropy 10.0 10.0 0.26 0.06

hkpp979_vk Layer 2 vertical anisotropy 10.0 9.7 0.14 0.05

hkpp980_vk Layer 2 vertical anisotropy 10.0 9.7 0.16 0.03

hkpp981_vk Layer 2 vertical anisotropy 10.0 9.7 0.24 0.04

hkpp982_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp983_vk Layer 2 vertical anisotropy 10.0 10.4 0.21 0.07

hkpp984_vk Layer 2 vertical anisotropy 10.0 9.5 0.24 0.03

hkpp985_vk Layer 2 vertical anisotropy 10.0 10.2 0.17 0.03

hkpp986_vk Layer 2 vertical anisotropy 10.0 9.7 0.11 0.04

hkpp987_vk Layer 2 vertical anisotropy 10.0 9.1 0.26 0.03

hkpp988_vk Layer 2 vertical anisotropy 10.0 9.8 0.33 0.07

hkpp989_vk Layer 2 vertical anisotropy 10.0 9.5 0.24 0.03

hkpp990_vk Layer 2 vertical anisotropy 10.0 10.4 0.23 0.04

hkpp991_vk Layer 2 vertical anisotropy 10.0 10.1 0.23 0.04

hkpp992_vk Layer 2 vertical anisotropy 10.0 9.5 0.30 0.03

hkpp993_vk Layer 2 vertical anisotropy 10.0 10.1 0.26 0.07

hkpp994_vk Layer 2 vertical anisotropy 10.0 9.9 0.18 0.03
132 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp995_vk Layer 2 vertical anisotropy 10.0 9.4 Horizontal 

to vertical 

ratio

0.16 0.03

hkpp996_vk Layer 2 vertical anisotropy 10.0 9.1 0.35 0.05

hkpp997_vk Layer 2 vertical anisotropy 10.0 9.9 0.23 0.03

hkpp998_vk Layer 2 vertical anisotropy 10.0 10.2 0.27 0.03

hkpp999_vk Layer 2 vertical anisotropy 10.0 9.8 0.28 0.03

hkpp1000_vk Layer 2 vertical anisotropy 10.0 8.9 0.31 0.04

hkpp1001_vk Layer 2 vertical anisotropy 10.0 9.7 0.28 0.03

hkpp1002_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1003_vk Layer 2 vertical anisotropy 10.0 10.1 0.29 0.07

hkpp1004_vk Layer 2 vertical anisotropy 10.0 9.4 0.23 0.02

hkpp1005_vk Layer 2 vertical anisotropy 10.0 9.5 0.26 0.07

hkpp1006_vk Layer 2 vertical anisotropy 10.0 9.9 0.12 0.03

hkpp1007_vk Layer 2 vertical anisotropy 10.0 9.5 0.32 0.02

hkpp1008_vk Layer 2 vertical anisotropy 10.0 10.1 0.24 0.04

hkpp1009_vk Layer 2 vertical anisotropy 10.0 10.4 0.17 0.03

hkpp1010_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1011_vk Layer 2 vertical anisotropy 10.0 9.3 0.18 0.02

hkpp1012_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1013_vk Layer 2 vertical anisotropy 10.0 10.1 0.24 0.03

hkpp1014_vk Layer 2 vertical anisotropy 10.0 10.3 0.21 0.03

hkpp1015_vk Layer 2 vertical anisotropy 10.0 9.3 0.28 0.03

hkpp1016_vk Layer 2 vertical anisotropy 10.0 9.5 0.04 0.03

hkpp1017_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1018_vk Layer 2 vertical anisotropy 10.0 9.2 0.28 0.05

hkpp1019_vk Layer 2 vertical anisotropy 10.0 9.8 0.25 0.04

hkpp1020_vk Layer 2 vertical anisotropy 10.0 9.5 0.19 0.04

hkpp1021_vk Layer 2 vertical anisotropy 10.0 8.8 0.32 0.04

hkpp1022_vk Layer 2 vertical anisotropy 10.0 10.4 0.25 0.08

hkpp1023_vk Layer 2 vertical anisotropy 10.0 9.4 0.26 0.05

hkpp1024_vk Layer 2 vertical anisotropy 10.0 9.1 0.29 0.03
Table 6 133

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1025_vk* Layer 2 vertical anisotropy 10.0 10.0 Horizontal 

to vertical 

ratio

-- --

hkpp1026_vk Layer 2 vertical anisotropy 10.0 10.2 0.20 0.03

hkpp1027_vk Layer 2 vertical anisotropy 10.0 9.9 0.30 0.09

hkpp1028_vk Layer 2 vertical anisotropy 10.0 9.6 0.35 0.04

hkpp1029_vk Layer 2 vertical anisotropy 10.0 8.9 0.26 0.08

hkpp1030_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1031_vk Layer 2 vertical anisotropy 10.0 9.9 0.26 0.03

hkpp1032_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1033_vk Layer 2 vertical anisotropy 10.0 9.8 0.28 0.03

hkpp1034_vk Layer 2 vertical anisotropy 10.0 9.0 0.27 0.03

hkpp1035_vk Layer 2 vertical anisotropy 10.0 10.3 0.25 0.04

hkpp1036_vk Layer 2 vertical anisotropy 10.0 10.2 0.24 0.02

hkpp1037_vk Layer 2 vertical anisotropy 10.0 9.2 0.25 0.04

hkpp1038_vk Layer 2 vertical anisotropy 10.0 9.4 0.25 0.03

hkpp1039_vk Layer 2 vertical anisotropy 10.0 10.0 0.27 0.04

hkpp1040_vk Layer 2 vertical anisotropy 10.0 9.4 0.28 0.04

hkpp1041_vk Layer 2 vertical anisotropy 10.0 9.2 0.33 0.06

hkpp1042_vk Layer 2 vertical anisotropy 10.0 9.9 0.24 0.04

hkpp1043_vk Layer 2 vertical anisotropy 10.0 9.9 0.22 0.04

hkpp1044_vk Layer 2 vertical anisotropy 10.0 9.5 0.28 0.04

hkpp1045_vk Layer 2 vertical anisotropy 10.0 10.3 0.27 0.04

hkpp1046_vk Layer 2 vertical anisotropy 10.0 9.4 0.19 0.03

hkpp1047_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1048_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1049_vk Layer 2 vertical anisotropy 10.0 9.8 0.32 0.04

hkpp1050_vk Layer 2 vertical anisotropy 10.0 9.3 0.19 0.03

hkpp1051_vk Layer 2 vertical anisotropy 10.0 20.0 0.31 0.07

hkpp1052_vk Layer 2 vertical anisotropy 10.0 9.7 0.27 0.05

hkpp1053_vk Layer 2 vertical anisotropy 10.0 9.4 0.23 0.04

hkpp1054_vk Layer 2 vertical anisotropy 10.0 9.5 0.27 0.04
134 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1055_vk Layer 2 vertical anisotropy 10.0 9.5 Horizontal 

to vertical 

ratio

0.10 0.02

hkpp1056_vk Layer 2 vertical anisotropy 10.0 9.0 0.25 0.03

hkpp1057_vk Layer 2 vertical anisotropy 10.0 10.0 0.18 0.03

hkpp1058_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1059_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1060_vk Layer 2 vertical anisotropy 10.0 9.4 0.16 0.04

hkpp1061_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1062_vk Layer 2 vertical anisotropy 10.0 9.9 0.19 0.13

hkpp1063_vk Layer 2 vertical anisotropy 10.0 9.8 0.35 0.04

hkpp1064_vk Layer 2 vertical anisotropy 10.0 10.0 0.23 0.03

hkpp1065_vk Layer 2 vertical anisotropy 10.0 10.0 0.34 0.04

hkpp1066_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1067_vk Layer 2 vertical anisotropy 10.0 9.4 0.14 0.04

hkpp1068_vk Layer 2 vertical anisotropy 10.0 9.7 0.23 0.04

hkpp1069_vk Layer 2 vertical anisotropy 10.0 10.0 0.29 0.02

hkpp1070_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1071_vk Layer 2 vertical anisotropy 10.0 9.6 0.27 0.03

hkpp1072_vk Layer 2 vertical anisotropy 10.0 9.7 0.19 0.04

hkpp1073_vk Layer 2 vertical anisotropy 10.0 9.8 0.28 0.03

hkpp1074_vk Layer 2 vertical anisotropy 10.0 9.8 0.28 0.03

hkpp1075_vk Layer 2 vertical anisotropy 10.0 9.9 0.26 0.04

hkpp1076_vk Layer 2 vertical anisotropy 10.0 9.8 0.29 0.03

hkpp1077_vk Layer 2 vertical anisotropy 10.0 9.6 0.20 0.03

hkpp1078_vk Layer 2 vertical anisotropy 10.0 10.1 0.26 0.03

hkpp1079_vk* Layer 2 vertical anisotropy 10.0 10.0 -- --

hkpp1080_vk Layer 2 vertical anisotropy 10.0 10.0 0.21 0.05

hkpp1081_vk Layer 2 vertical anisotropy 10.0 10.0 0.14 0.02

hkpp1104_vk Layer 3 vertical anisotropy 10.0 9.9 0.23 0.03

hkpp1106_vk Layer 3 vertical anisotropy 10.0 9.3 0.27 0.03

hkpp1108_vk Layer 3 vertical anisotropy 10.0 10.0 0.17 0.03
Table 6 135

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1118_vk Layer 3 vertical anisotropy 10.0 8.9 Horizontal 

to vertical 

ratio

0.26 0.03

hkpp1120_vk Layer 3 vertical anisotropy 10.0 10.1 0.17 0.07

hkpp1122_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1133_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1135_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.03

hkpp1137_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.03

hkpp1139_vk Layer 3 vertical anisotropy 10.0 9.5 0.19 0.03

hkpp1141_vk Layer 3 vertical anisotropy 10.0 9.4 0.19 0.03

hkpp1160_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1162_vk Layer 3 vertical anisotropy 10.0 9.6 0.23 0.03

hkpp1164_vk Layer 3 vertical anisotropy 10.0 8.8 0.30 0.04

hkpp1166_vk Layer 3 vertical anisotropy 10.0 9.3 0.28 0.03

hkpp1168_vk Layer 3 vertical anisotropy 10.0 9.8 0.21 0.04

hkpp1170_vk Layer 3 vertical anisotropy 10.0 9.6 0.24 0.03

hkpp1172_vk Layer 3 vertical anisotropy 10.0 9.3 0.24 0.04

hkpp1174_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1197_vk Layer 3 vertical anisotropy 10.0 9.7 0.29 0.03

hkpp1199_vk Layer 3 vertical anisotropy 10.0 9.0 0.30 0.03

hkpp1201_vk Layer 3 vertical anisotropy 10.0 8.8 0.27 0.03

hkpp1203_vk Layer 3 vertical anisotropy 10.0 10.0 0.19 0.04

hkpp1205_vk Layer 3 vertical anisotropy 10.0 9.4 0.32 0.04

hkpp1207_vk Layer 3 vertical anisotropy 10.0 10.2 0.26 0.04

hkpp1209_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1211_vk Layer 3 vertical anisotropy 10.0 9.3 0.25 0.03

hkpp1213_vk Layer 3 vertical anisotropy 10.0 9.5 0.29 0.04

hkpp1215_vk Layer 3 vertical anisotropy 10.0 8.8 0.29 0.03

hkpp1217_vk Layer 3 vertical anisotropy 10.0 9.3 0.32 0.03

hkpp1243_vk Layer 3 vertical anisotropy 10.0 9.9 0.29 0.04

hkpp1245_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1247_vk Layer 3 vertical anisotropy 10.0 9.2 0.27 0.04
136 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1249_vk Layer 3 vertical anisotropy 10.0 9.3 Horizontal 

to vertical 

ratio

0.26 0.03

hkpp1251_vk Layer 3 vertical anisotropy 10.0 9.0 0.21 0.05

hkpp1253_vk Layer 3 vertical anisotropy 10.0 7.4 0.24 0.05

hkpp1255_vk Layer 3 vertical anisotropy 10.0 9.4 0.36 0.08

hkpp1257_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1259_vk Layer 3 vertical anisotropy 10.0 9.9 0.26 0.04

hkpp1261_vk Layer 3 vertical anisotropy 10.0 9.8 0.36 0.06

hkpp1263_vk Layer 3 vertical anisotropy 10.0 9.6 0.29 0.03

hkpp1290_vk Layer 3 vertical anisotropy 10.0 10.3 0.20 0.05

hkpp1292_vk Layer 3 vertical anisotropy 10.0 10.1 0.23 0.03

hkpp1294_vk Layer 3 vertical anisotropy 10.0 9.1 0.21 0.03

hkpp1296_vk Layer 3 vertical anisotropy 10.0 9.9 0.18 0.04

hkpp1298_vk Layer 3 vertical anisotropy 10.0 8.9 0.05 0.04

hkpp1300_vk Layer 3 vertical anisotropy 10.0 9.8 0.11 0.03

hkpp1302_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1304_vk Layer 3 vertical anisotropy 10.0 10.8 0.29 0.04

hkpp1306_vk Layer 3 vertical anisotropy 10.0 10.0 0.22 0.03

hkpp1308_vk Layer 3 vertical anisotropy 10.0 9.3 0.33 0.03

hkpp1310_vk Layer 3 vertical anisotropy 10.0 9.2 0.21 0.03

hkpp1312_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1340_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1342_vk Layer 3 vertical anisotropy 10.0 9.0 0.20 0.03

hkpp1344_vk Layer 3 vertical anisotropy 10.0 10.4 0.30 0.03

hkpp1346_vk Layer 3 vertical anisotropy 10.0 9.2 0.27 0.03

hkpp1348_vk Layer 3 vertical anisotropy 10.0 9.9 0.34 0.04

hkpp1350_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1352_vk Layer 3 vertical anisotropy 10.0 10.5 0.24 0.04

hkpp1354_vk Layer 3 vertical anisotropy 10.0 10.2 0.19 0.04

hkpp1356_vk Layer 3 vertical anisotropy 10.0 10.2 0.34 0.05

hkpp1358_vk Layer 3 vertical anisotropy 10.0 9.6 0.24 0.07
Table 6 137

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1360_vk Layer 3 vertical anisotropy 10.0 9.9 Horizontal 

to vertical 

ratio

0.28 0.03

hkpp1362_vk Layer 3 vertical anisotropy 10.0 9.5 0.05 0.02

hkpp1364_vk Layer 3 vertical anisotropy 10.0 10.0 0.26 0.03

hkpp1392_vk Layer 3 vertical anisotropy 10.0 9.5 0.20 0.03

hkpp1394_vk Layer 3 vertical anisotropy 10.0 9.3 0.09 0.05

hkpp1396_vk Layer 3 vertical anisotropy 10.0 9.8 0.09 0.03

hkpp1398_vk Layer 3 vertical anisotropy 10.0 10.4 0.28 0.04

hkpp1400_vk Layer 3 vertical anisotropy 10.0 9.8 0.27 0.04

hkpp1402_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1404_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.02

hkpp1406_vk Layer 3 vertical anisotropy 10.0 10.5 0.30 0.04

hkpp1408_vk Layer 3 vertical anisotropy 10.0 10.3 0.26 0.03

hkpp1410_vk Layer 3 vertical anisotropy 10.0 10.4 0.27 0.05

hkpp1412_vk Layer 3 vertical anisotropy 10.0 9.7 0.18 0.03

hkpp1414_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1416_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1444_vk Layer 3 vertical anisotropy 10.0 9.9 0.16 0.02

hkpp1446_vk Layer 3 vertical anisotropy 10.0 9.3 0.28 0.04

hkpp1448_vk Layer 3 vertical anisotropy 10.0 9.1 0.15 0.02

hkpp1450_vk Layer 3 vertical anisotropy 10.0 10.0 0.30 0.03

hkpp1452_vk Layer 3 vertical anisotropy 10.0 8.7 0.09 0.02

hkpp1454_vk Layer 3 vertical anisotropy 10.0 9.5 0.30 0.05

hkpp1456_vk Layer 3 vertical anisotropy 10.0 9.9 0.22 0.03

hkpp1458_vk Layer 3 vertical anisotropy 10.0 10.2 0.17 0.51

hkpp1460_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1462_vk Layer 3 vertical anisotropy 10.0 20.0 0.29 0.08

hkpp1464_vk Layer 3 vertical anisotropy 10.0 10.0 0.22 0.04

hkpp1466_vk Layer 3 vertical anisotropy 10.0 10.2 0.24 0.12

hkpp1468_vk Layer 3 vertical anisotropy 10.0 10.0 0.32 0.05

hkpp1470_vk Layer 3 vertical anisotropy 10.0 9.9 0.28 0.03
138 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1499_vk Layer 3 vertical anisotropy 10.0 9.4 Horizontal 

to vertical 

ratio

0.32 0.04

hkpp1500_vk Layer 3 vertical anisotropy 10.0 20.0 0.32 0.03

hkpp1502_vk Layer 3 vertical anisotropy 10.0 20.0 0.24 0.04

hkpp1504_vk Layer 3 vertical anisotropy 10.0 20.0 0.29 0.05

hkpp1506_vk Layer 3 vertical anisotropy 10.0 8.8 0.17 0.04

hkpp1508_vk Layer 3 vertical anisotropy 10.0 10.0 0.25 0.03

hkpp1510_vk Layer 3 vertical anisotropy 10.0 20.0 0.17 0.04

hkpp1512_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1514_vk Layer 3 vertical anisotropy 10.0 20.0 0.34 0.05

hkpp1516_vk Layer 3 vertical anisotropy 10.0 10.0 0.23 0.03

hkpp1518_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1520_vk Layer 3 vertical anisotropy 10.0 10.0 0.26 0.06

hkpp1544_vk Layer 3 vertical anisotropy 10.0 20.0 0.30 0.03

hkpp1546_vk Layer 3 vertical anisotropy 10.0 20.0 0.26 0.03

hkpp1548_vk Layer 3 vertical anisotropy 10.0 8.8 0.23 0.04

hkpp1550_vk Layer 3 vertical anisotropy 10.0 9.0 0.29 0.05

hkpp1552_vk Layer 3 vertical anisotropy 10.0 20.0 0.37 0.04

hkpp1554_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.03

hkpp1556_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1558_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.04

hkpp1560_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1562_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1564_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1565_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1589_vk Layer 3 vertical anisotropy 10.0 20.0 0.27 0.03

hkpp1591_vk Layer 3 vertical anisotropy 10.0 20.0 0.22 0.04

hkpp1593_vk Layer 3 vertical anisotropy 10.0 8.8 0.20 0.03

hkpp1595_vk Layer 3 vertical anisotropy 10.0 8.0 0.30 0.05

hkpp1597_vk Layer 3 vertical anisotropy 10.0 8.2 0.20 0.02

hkpp1599_vk Layer 3 vertical anisotropy 10.0 20.0 0.20 0.03
Table 6 139

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1601_vk Layer 3 vertical anisotropy 10.0 10.0 Horizontal 

to vertical 

ratio

0.16 0.04

hkpp1603_vk Layer 3 vertical anisotropy 10.0 10.0 0.35 0.04

hkpp1605_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.04

hkpp1607_vk Layer 3 vertical anisotropy 10.0 10.0 0.20 0.04

hkpp1609_vk Layer 3 vertical anisotropy 10.0 10.0 0.23 0.02

hkpp1611_vk Layer 3 vertical anisotropy 10.0 10.0 0.29 0.04

hkpp1635_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1637_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1639_vk Layer 3 vertical anisotropy 10.0 20.0 0.25 0.07

hkpp1641_vk Layer 3 vertical anisotropy 10.0 20.0 0.27 0.04

hkpp1643_vk Layer 3 vertical anisotropy 10.0 10.4 0.18 0.04

hkpp1645_vk Layer 3 vertical anisotropy 10.0 10.0 0.17 0.04

hkpp1647_vk Layer 3 vertical anisotropy 10.0 10.0 0.19 0.04

hkpp1649_vk Layer 3 vertical anisotropy 10.0 10.0 0.20 0.08

hkpp1651_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1653_vk Layer 3 vertical anisotropy 10.0 10.0 0.17 0.04

hkpp1676_vk Layer 3 vertical anisotropy 10.0 8.5 0.27 0.04

hkpp1678_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1680_vk Layer 3 vertical anisotropy 10.0 10.1 0.14 0.04

hkpp1682_vk Layer 3 vertical anisotropy 10.0 10.1 0.27 0.04

hkpp1684_vk Layer 3 vertical anisotropy 10.0 10.0 0.23 0.04

hkpp1686_vk Layer 3 vertical anisotropy 10.0 20.0 0.18 0.03

hkpp1688_vk Layer 3 vertical anisotropy 10.0 10.0 0.22 0.05

hkpp1690_vk Layer 3 vertical anisotropy 10.0 10.0 0.10 0.04

hkpp1693_vk Layer 3 vertical anisotropy 10.0 10.0 0.27 0.03

hkpp1718_vk Layer 3 vertical anisotropy 10.0 8.9 0.30 0.07

hkpp1720_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1722_vk Layer 3 vertical anisotropy 10.0 10.7 0.28 0.03

hkpp1724_vk Layer 3 vertical anisotropy 10.0 10.0 0.29 0.05

hkpp1726_vk Layer 3 vertical anisotropy 10.0 10.0 0.19 0.03
140 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1728_vk Layer 3 vertical anisotropy 10.0 10.0 Horizontal 

to vertical 

ratio

0.24 0.05

hkpp1730_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.04

hkpp1732_vk Layer 3 vertical anisotropy 10.0 10.0 0.29 0.03

hkpp1734_vk Layer 3 vertical anisotropy 10.0 10.0 0.23 0.05

hkpp1736_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.07

hkpp1761_vk Layer 3 vertical anisotropy 10.0 9.4 0.23 0.02

hkpp1763_vk Layer 3 vertical anisotropy 10.0 9.5 0.28 0.03

hkpp1765_vk Layer 3 vertical anisotropy 10.0 9.2 0.21 0.04

hkpp1767_vk Layer 3 vertical anisotropy 10.0 8.7 0.32 0.03

hkpp1769_vk Layer 3 vertical anisotropy 10.0 8.8 0.22 0.04

hkpp1771_vk Layer 3 vertical anisotropy 10.0 10.0 0.17 0.05

hkpp1773_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1775_vk Layer 3 vertical anisotropy 10.0 10.3 0.28 0.04

hkpp1777_vk Layer 3 vertical anisotropy 10.0 10.0 0.22 0.04

hkpp1779_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1781_vk Layer 3 vertical anisotropy 10.0 10.0 0.22 0.04

hkpp1782_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1783_vk Layer 3 vertical anisotropy 10.0 10.0 0.23 0.03

hkpp1812_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1814_vk Layer 3 vertical anisotropy 10.0 9.3 0.28 0.04

hkpp1816_vk Layer 3 vertical anisotropy 10.0 9.0 0.26 0.04

hkpp1818_vk Layer 3 vertical anisotropy 10.0 10.0 0.20 0.03

hkpp1820_vk Layer 3 vertical anisotropy 10.0 9.7 0.26 0.02

hkpp1822_vk Layer 3 vertical anisotropy 10.0 9.9 0.21 0.03

hkpp1824_vk Layer 3 vertical anisotropy 10.0 10.0 0.17 0.04

hkpp1826_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1828_vk Layer 3 vertical anisotropy 10.0 10.0 0.23 0.03

hkpp1830_vk Layer 3 vertical anisotropy 10.0 10.0 0.32 0.03

hkpp1846_vk Layer 3 vertical anisotropy 10.0 10.7 0.34 0.06

hkpp1848_vk Layer 3 vertical anisotropy 10.0 10.3 0.16 0.03

hkpp1850_vk Layer 3 vertical anisotropy 10.0 10.0 0.25 0.04
Table 6 141

Table 6. Calibration parameters, parameter values, parameter sensitivity, and parameter identifiability for the automated calibration of 

the numerical groundwater-flow model of the Rush Springs aquifer, western Oklahoma, 1979–2015.—Continued

[GHB, General-Head Boundary; ft2/d, foot squared per day; ft, foot; ft/d, foot per day; --, not computed; Kh, horizontal hydraulic conductivity. Layer 2 Kh and 

vertical anisotropy refer only to the pilot points in the alluvium and terrace; *, parameter with a fixed value during model calibration]

Parameter 

group

Parameter 

name

Parameter 

description

Initial 

value

Calibrated 

value Units

Sensitivity 

(dimensionless)

Identifiability 

(dimensionless)

Horizontal hydraulic 

conductivity and 

vertical anisotropy—

Continued

hkpp1852_vk Layer 3 vertical anisotropy 10.0 10.0 Horizontal 

to vertical 

ratio

0.27 0.04

hkpp1854_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1867_vk Layer 3 vertical anisotropy 10.0 10.0 0.17 0.04

hkpp1869_vk Layer 3 vertical anisotropy 10.0 10.0 0.19 0.03

hkpp1871_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.04

hkpp1872_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1885_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1887_vk Layer 3 vertical anisotropy 10.0 10.0 0.31 0.03

hkpp1889_vk Layer 3 vertical anisotropy 10.0 10.0 0.26 0.03

hkpp1891_vk Layer 3 vertical anisotropy 10.0 10.0 0.24 0.03

hkpp1893_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.04

hkpp1904_vk Layer 3 vertical anisotropy 10.0 10.0 0.31 0.03

hkpp1906_vk Layer 3 vertical anisotropy 10.0 10.0 0.32 0.03

hkpp1908_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1911_vk Layer 3 vertical anisotropy 10.0 10.0 0.22 0.06

hkpp1923_vk Layer 3 vertical anisotropy 10.0 10.0 0.20 0.04

hkpp1925_vk Layer 3 vertical anisotropy 10.0 10.0 0.24 0.04

hkpp1927_vk Layer 3 vertical anisotropy 10.0 10.0 0.21 0.03

hkpp1929_vk Layer 3 vertical anisotropy 10.0 10.0 0.21 0.02

hkpp1942_vk Layer 3 vertical anisotropy 10.0 10.0 0.24 0.03

hkpp1944_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.04

hkpp1946_vk Layer 3 vertical anisotropy 10.0 10.0 0.28 0.03

hkpp1948_vk Layer 3 vertical anisotropy 10.0 10.0 0.34 0.03

hkpp1950_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1959_vk Layer 3 vertical anisotropy 10.0 10.0 0.18 0.03

hkpp1961_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1963_vk Layer 3 vertical anisotropy 10.0 10.0 0.25 0.03

hkpp1965_vk Layer 3 vertical anisotropy 10.0 10.0 0.29 0.03

hkpp1967_vk Layer 3 vertical anisotropy 10.0 10.0 0.26 0.03

hkpp1972_vk* Layer 3 vertical anisotropy 10.0 10.0 -- --

hkpp1973_vk Layer 3 vertical anisotropy 10.0 10.0 0.20 0.03

1

See figure 15.

2

See figure 20.
142 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Long-term groundwater-level observation wells (Oklahoma Water Resources Board, 2017; U.S. Geological Survey, 2017c)

361833099192201 5385 1 21N-20W-10 DBD 1 36.30921 -99.32316 10/1979 01/2016 58 34 7.46

361610099070901 9871 2 21N-18W-27 BCB 1 36.26948 -99.11955 10/1955 01/2014 54 41 0.60

360759099195601 9293 3 19N-20W-09 DDB 1 36.13310 -99.33261 12/1979 01/2013 430 28 13.70

360454098395601 9290 4 19N-14W-35 BDB 1 36.08171 -98.66592 03/1978 01/2018 291 43 4.46

360316098442001 9289 5 18N-14W-07 BBD 1 36.05449 -98.73926 03/1979 01/2018 400 51 1.40

355816098432401 9288 6 17N-14W-05 CCC 1 35.97115 -98.72537 03/1976 01/2018 350 48 4.64

352924098335601 9160 7 12N-13W-27 BAC 1 35.49005 -98.56590 04/1955 01/2018 300 36 1.05

352922098225801 9159 8 12N-11W-29 ACA 1 35.48950 -98.38312 02/1956 01/2018 260 41 10.30

352551098343901 9157 9 11N-13W-16 ACA 1 35.43089 -98.57784 07/1955 02/2013 353 54 15.80

352515098263001 9156 10 11N-12W-14 CDC 1 35.42089 -98.44201 01/1956 01/2018 320 57 1.26

352225098274001 9151 11 10N-12W-03 BBD 1 35.37367 -98.46145 11/1955 01/2018 335 35 4.80

352107098273801 4017 12 10N-12W-10 CCA 1 35.35200 -98.46089 06/1955 01/2013 340 54 1.69

352017098401701 27649 13 10N-14W-15 CAC 1 35.33811 -98.67173 06/1981 01/2018 300 34 8.75

351939098394101 9844 14 10N-14W-22 ADD 1 35.32755 -98.66173 03/1979 01/2016 -- 48 11.40

351952098332801 9146 15 10N-13W-22 AAC 1 35.33117 -98.55812 06/1956 01/2018 328 46 6.47

352015098253001 9147 16 10N-12W-13 CCA 1 35.33756 -98.42534 06/1954 01/2018 350 38 8.37

351730098300301 9140 17 10N-12W-31 DDB 2 35.29172 -98.50117 02/1956 01/2013 307 45 10.39

351623098312001 3899 18 09N-13W-12 AAC 1 35.27311 -98.52256 12/1974 01/2018 285 33 2.92

351308098395701 9842 19 09N-14W-27 DCD 1 35.21895 -98.66618 05/1955 01/2018 312 53 5.48

350902098235501 9133 20 08N-11W-19 CAC 1 35.15061 -98.39895 01/1955 01/2018 287 36 5.37

344630098083201 9274 21 04N-09W-33 DAA 1 34.77507 -98.14255 03/1983 01/2018 700 45 10.46

Continuous groundwater-level observation wells (U.S. Geological Survey, 2017c)

352423098341701* 22 Eakly 11N-13W-21 

DDD 1

35.40686 -98.57116 04/1965 present 210 183 0.52

352802098191601 23 Hinton 12N-11W-36 

CCA 1

35.46732 -98.32112 08/2010 present 225 35 0.28

351727098290401* 27655 24 Core 2 10N-12W-32 

DDD 1

35.29080 -98.48389 12/1989 present 257 69 1.26

351308098341601* 25 Alfalfa 09N-13W-28 

DDD 1

35.21887 -98.57098 08/1948 present 335 153 0.52

350748098231101 26 Gracemont 08N11W-32 BBA 135.13006 -98.38644 08/2010 present 350 36 0.28

Groundwater-level observation wells from the Mass Measurement Program (Oklahoma Water Resources Board, 2017)

351302098351501 9135 09N-13W-33 BBB 1 35.21728 -98.58784 04/1948 02/1997 199 42 3.93

361856099112401 9876 21N-19W-12 BBD 1 36.31559 -99.19038 09/1949 03/2000 30 24 1.33

353210098423001 43007 12N-14W-08 BBA 1 35.53616 -98.70869 01/1955 03/2010 425 10 14.50

351950098263601 9145 10N-12W-23 BBD 1 35.33061 -98.44367 08/1955 03/2007 288 50 1.56
Table 7 143

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells from the Mass Measurement Program (Oklahoma Water Resources Board, 2017)—Continued

350832098282101 9132 08N-12W-28 BDB 1 35.14228 -98.47284 08/1955 02/1997 245 34 2.68

352046098285901 4039 10N-12W-17 AAD 1 35.34617 -98.48340 12/1955 02/2003 328 33 5.17

352017098263301 9148 10N-12W-14 CBD 1 35.33811 -98.44284 01/1956 05/1988 320 10 2.79

352316098284101 9154 11N-12W-04 CAC 1 35.38783 -98.47840 06/1956 03/2006 309 41 6.52

351805098281201 4093 10N-12W-33 ABC 1 35.30144 -98.47034 06/1956 03/2000 290 28 1.47

351923098291301 9144 10N-12W-20 DAC 1 35.32311 -98.48728 06/1956 02/1996 340 22 1.52

351630098432401 9843 09N-14W-07 BAA 1 35.27506 -98.72368 06/1956 01/1998 52 43 5.28

353137098265801 9162 12N-12W-10 DAD 1 35.52700 -98.44979 06/1956 01/1990 -- 14 2.39

350930098352501 9134 08N-13W-20 ABA 1 35.15839 -98.59062 06/1958 01/1995 300 36 6.31

352715098234901 9158 11N-11W-06 DAC 1 35.45422 -98.39728 07/1964 02/1998 285 39 16.93

352514098223501 9075 11N-11W-21 BBB 1 35.42061 -98.37673 03/1971 01/2010 120 39 9.74

351755098265801 9142 10N-12W-34 ADD 1 35.29867 -98.44978 01/1973 01/1995 268 33 3.85

344349097575801 4627 03N-07W-17 CBC 1 34.73035 -97.96643 02/1973 03/2010 165 38 3.92

351439098263401 9137 09N-12W-23 BAC 1 35.24422 -98.44311 12/1974 02/1998 235 18 2.60

351459098260201 9138 09N-12W-14 DDB 1 35.24978 -98.43422 12/1974 02/2003 294 22 1.97

352229098300901 9152 10N-12W-06 AAD 1 35.37478 -98.50284 12/1974 01/1995 306 13 2.22

351748098264201 9141 10N-12W-35 CBA 1 35.29672 -98.44534 12/1974 10/1988 230 13 5.91

354401098434901 9286 15N-14W-31 BDD 1 35.73366 -98.73064 02/1976 02/1998 -- 40 5.35

361611099171401 5407 21N-20W-25 ACA 1 36.27171 -99.28761 03/1977 03/2004 125 14 13.28

353613099065601 9216 13N-18W-16 ACD 1 35.60366 -99.11592 12/1977 03/1997 500 15 16.32

354015098423001 9212 14N-14W-20 DCA 1 35.67088 -98.70869 01/1978 03/2010 225 27 4.42

352603098453701 27651 11N-15W-14 BBA 1 35.43422 -98.76063 08/1978 01/1996 365 8 4.92

344446097551501 9427 03N-07W-10 DBB 1 34.74618 -97.92115 03/1979 03/2010 180 45 8.10

344222098030101 4686 03N-08W-28 BCA 1 34.70618 -98.05060 03/1979 01/2004 670 25 3.12

352749098422001 9847 11N-14W-05 BAA 1 35.46422 -98.70313 03/1979 01/2006 -- 37 8.55

352229098384601 9846 10N-14W-02 AAC 1 35.37478 -98.64646 03/1979 03/1988 352 10 2.77

360850099141001 9294 19N-19W-04 CCA 1 36.14726 -99.23649 08/1979 02/1998 85 13 10.00

355552098404301 23373 17N-14W-22 CBD 1 35.93115 -98.67897 09/1979 01/2010 295 20 5.88

361221099182601 5275 20N-20W-14 CCA 1 36.20587 -99.30761 10/1979 02/1998 180 20 9.93

353119098273501 9029 12N-12W-15 BAB 1 35.52200 -98.46007 01/1980 01/2010 238 38 1.98

352203098472201 9845 10N-15W-04 DBD 1 35.36755 -98.78980 03/1980 03/1988 -- 5 2.64

354555098593001 9249 15N-17W-22 ACA 1 35.76532 -98.99204 03/1980 03/2010 360 26 2.84

353504099003201 9220 13N-17W-21 DBD 1 35.58449 -99.00926 03/1980 03/2002 362 12 5.36

352834098415201 9246 12N-14W-32 AAC 1 35.47616 -98.69813 12/1981 03/2010 320 27 3.68

353616098334601 9204 13N-13W-15 ADA 1 35.60449 -98.56313 01/1982 03/1998 275 11 18.71

352948098443101 9241 12N-15W-24 CDB 1 35.49672 -98.74230 02/1982 03/1997 400 14 5.01
144 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells from the Mass Measurement Program (Oklahoma Water Resources Board, 2017)—Continued

353319098393401 9234 13N-14W-35 CAD 1 35.55533 -98.65980 02/1982 01/2006 285 24 2.09

353926098505801 9211 14N-16W-25 DBD 1 35.65727 -98.84981 04/1982 06/1990 400 5 5.06

353346098582301 9217 13N-17W-35 AAC 1 35.56283 -98.97342 06/1982 03/1997 470 12 7.72

352306098282401 9067 11N-12W-33 ACC 1 35.38505 -98.47367 07/1982 01/1995 275 30 3.80

344630098095901 9275 04N-09W-32 DBB 1 34.77507 -98.16671 01/1983 03/2010 640 24 11.67

352804098401801 9244 12N-14W-34 CCA 1 35.46783 -98.67202 04/1983 03/2010 440 27 8.95

355114099011101 9309 16N-17W-21 BBD 1 35.85393 -99.02010 09/1983 01/2010 400 25 17.83

353033099014801 9238 12N-17W-18 DDD 1 35.50922 -99.03036 09/1983 02/2000 520 19 11.49

353645098440401 9235 13N-14W-07 CCA 1 35.61255 -98.73480 12/1983 03/2010 300 28 8.93

354545098514101 9248 15N-16W-24 BCC 1 35.76255 -98.86176 01/1984 03/1997 305 16 4.47

353436098464201 9225 13N-15W-27 ACA 1 35.57672 -98.77869 02/1984 03/2010 360 26 2.21

354949099062101 9308 16N-18W-27 CDB 1 35.83032 -99.10621 07/1984 01/2010 405 22 11.06

355500098590001 19912 17N-17W-26 DAC 1 35.91671 -98.98371 09/1984 01/2010 400 19 18.77

354311098540401 24882 15N-16W-33 DDB 1 35.71977 -98.90148 07/1986 03/2010 280 25 7.54

353019098501801 9240 12N-16W-24 AAB 1 35.50533 -98.83869 08/1986 03/2010 300 26 14.41

352238098384301 9194 10N-14W-02 AAB 1 35.37728 -98.64562 05/1988 01/2010 395 40 4.26

360256098373101 9196 18N-13W-07 BBA 1 36.04893 -98.62564 06/1988 03/1995 85 13 9.72

353241098500201 9243 12N-15W-06 BCC 1 35.54477 -98.83425 06/1988 03/2010 340 28 4.55

355352098391401 9310 16N-14W-02 ABA 1 35.89782 -98.65425 11/1988 02/2000 253 22 6.41

361525099104101 25665 21N-19W-36 CAA 1 36.25337 -99.18510 01/1989 04/1998 120 7 4.22

351340098234701 9028 09N-11W-30 ADA 1 35.22784 -98.39672 01/1989 01/2010 266 20 3.20

360243098484401 27665 18N-15W-09 BCC 1 36.04532 -98.81259 01/1989 01/2010 360 18 14.30

361742099103301 25661 21N-19W-13 AAD 1 36.30226 -99.17621 02/1989 01/2010 80 18 6.31

361604099080801 25660 21N-18W-28 DCB 1 36.26782 -99.13593 02/1989 01/2010 180 16 4.73

361137099064501 25659 20N-18W-22 ABC 1 36.19948 -99.10538 02/1989 01/2010 180 19 6.13

360959099020501 25652 20N-17W-32 CCA 1 36.16143 -99.04149 02/1989 03/2000 160 10 8.59

360015098573601 9252 18N-17W-25 DBD 1 36.00421 -98.96037 10/1989 03/1997 -- 13 8.76

344807097575101 9191 CORE 4 04N-07W-20 

CBCD 1

34.80174 -97.96532 10/1989 03/2010 197 21 10.79

350153098212101 27653 CORE 5 07N-11W-34 

CCB 1

35.03132 -98.35626 11/1989 01/2011 135 29 0.52

354109098431501 9214 CORE 6 14N-14W-18 

DADD 1

35.68588 -98.72119 03/1990 01/2006 148 16 6.06

354238099094801 9209 CORE 1 14N-18W-07 

BBBB 1

35.71060 -99.16371 03/1990 01/2006 186 17 7.50

352307098583401 27652 CORE 3 11N-17W-34 

DAAA 1

35.38533 -98.97647 04/1990 02/1998 670 10 7.04
Table 7 145

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells from the Mass Measurement Program (Oklahoma Water Resources Board, 2017)—Continued

354950098583301 24883 16N-17W-26 DBC 1 35.83060 -98.97621 08/1990 01/2006 460 21 6.52

351032098523201 27648 OW-5 08N-16W-10 

CDC 1

35.17561 -98.87590 08/1990 01/2010 305 20 5.04

350658098350801 27654 OW-4 07N-13W-04 

BBBB 1

35.11617 -98.58590 08/1990 03/2000 114 9 11.50

352240098440101 27650 OW-3 10N-15W-01 

AAB 1

35.37783 -98.73396 09/1990 01/2010 400 24 24.85

353907098525101 24881 14N-16W-34 AAA 1 35.65199 -98.88120 01/1991 03/2010 420 17 15.11

353321098553901 24880 13N-16W-32 CAC 1 35.55588 -98.92786 01/1991 03/2010 400 16 14.44

354933099050601 24884 16N-18W-35 AAB 1 35.82588 -99.08537 01/1991 02/1998 278 5 10.58

350829098180301 3572 08N-10W-30 BCB 1 35.14145 -98.30116 02/2001 01/2010 200 10 0.92

352435098491501 20923 11N-15W-19 DDB 1 35.40978 -98.82119 02/2001 01/2010 520 10 1.83

345437098125901 3471 05N-10W-14 AAD 1 34.91034 -98.21672 02/2001 01/2010 110 10 3.40

351744098233501 3994 10N-11W-32 CBC 1 35.29561 -98.39339 02/2001 01/2010 268 10 2.04

351828098193001 39787 10N-10W-26 DDA 1 35.30783 -98.32533 02/2001 03/2006 130 6 4.84

352012098104801 3952 10N-09W-17 CCA 1 35.33672 -98.18033 02/2001 03/2010 180 10 3.55

360423098370301 4944 19N-13W-32 CCC 1 36.07310 -98.61786 03/2001 01/2006 200 5 0.60

354432098325601 4894 15N-13W-26 DCA 1 35.74227 -98.54924 03/2001 01/2006 300 6 0.64

354142098323001 4858 14N-13W-14 AAA 1 35.69505 -98.54202 03/2001 01/2010 145 10 4.79

345851098143701 3499 06N-10W-22 BDA 1 34.98090 -98.24394 03/2001 01/2010 205 10 1.37

353821098364501 31405 14N-13W-32 CCC 1 35.63922 -98.61285 03/2001 01/2008 294 8 0.60

344914098081601 21771 04N-09W-10 CCA 1 34.82062 -98.13810 03/2001 01/2010 80 10 1.59

360737098570701 20143 19N-16W-18 BBD 1 36.12699 -98.95232 03/2001 01/2010 200 10 3.05

355721099024201 29012 17N-17W-18 AAA 1 35.95588 -99.04538 03/2001 01/2006 80 6 1.37

360127099173701 20075 18N-20W-23 ADA 1 36.02421 -99.29399 03/2001 01/2010 47 10 1.88

360332099080901 20049 18N-18W-05 DDC 1 36.05893 -99.13621 03/2001 01/2010 345 9 1.73

360051098581801 20044 18N-17W-25 BBB 1 36.01421 -98.97204 03/2001 01/2006 150 6 2.81

355820099171001 19943 17N-20W 01 CDC 2 35.97227 -99.28649 03/2001 01/2010 276 10 0.84

355821099171001 19943 17N-20W-01 CDC 1 35.97255 -99.28649 03/2001 03/2001 276 1 1.63

355544099162201 19934 17N-19W-19 CCC 2 35.92893 -99.27316 03/2001 01/2010 95 10 1.02

355544099162301 19934 17N-19W-19 CCC 1 35.92893 -99.27344 03/2001 03/2001 95 1 1.61

352504098395001 20907 11N-14W-22 ABD 1 35.41783 -98.66424 01/2003 03/2010 327 8 1.68

352759098173801 5066 12N-10W-31 DCA 1 35.46644 -98.29423 03/2003 01/2010 180 8 6.38

Groundwater-level observation wells (U.S. Geological Survey, 2017c)

344656098031401* 04N-08W-33 BBB 1 34.782294 -98.054210 06/1948 10/1995 254 176 2.21

353252098401901 12N-14W-03 BBD 1 35.547830 -98.672296 07/1953 01/1986 275 7 0.57

352933098340701 12N-13W-27 BBA 1 35.49255 -98.56896 04/1955 05/1990 267 21 4.33
146 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

351342098240001 09N-11W-30 ACA 1 35.228391 -98.400335 05/1955 02/1988 266 8 0.61

351334098234701 09N-11W-30 ADD 1 35.226169 -98.396724 05/1955 05/1990 266 23 2.21

352828098475401 12N-15W-33 BDBC 1 35.474497 -98.795076 07/1955 03/1988 335 8 4.67

354112098430601* 14N-14W-17 CBD 1 35.686716 -98.718692 03/1971 08/1995 320 194 3.61

361256099102101* 20N-19W-13 ABB 1 36.215874 -99.177880 02/1972 09/1990 40 289 1.45

352321098281001 11N-12W-33 AAC 1 35.389221 -98.469785 12/1974 03/1988 400 10 6.20

352203098322401 10N-13W-02 DAC 1 35.367554 -98.540342 12/1975 01/1986 300 5 1.62

355328098441301 16N-14W-06 CBB 1 35.891156 -98.737309 03/1976 03/1985 217 2 1.93

344353097572201 03N-07W-17 DBB 1 34.731463 -97.956428 12/1976 02/1986 -- 7 4.11

361643099103001 21N-19W-24 DDA 1 36.278650 -99.175380 01/1978 05/1979 38 5 4.01

361249099042801 20N-18W-13 BAC 1 36.213651 -99.074822 01/1978 02/1979 77 2 4.58

362139099155101 22N-19W-30 AAD 1 36.360871 -99.264549 01/1978 05/1979 36 5 3.34

361615099071401 21N-18W-27 BCB 2 36.270872 -99.120934 02/1978 05/1979 48 5 2.75

360834098544101 19N-16W-09 BAA 1 36.142818 -98.911761 02/1978 05/1979 60 5 3.32

360659098373701 19N-13W-18 DCC 1 36.116428 -98.627307 03/1978 05/1979 100 4 3.84

360753098423001 19N-14W-08 DDD 1 36.131686 -98.708250 03/1978 10/2012 42 29 0.28

360931098515801 20N-16W-36 CCC 1 36.158800 -98.866481 03/1978 01/2012 11 1 0.49

360644098455301 19N-15W-23 ABD 1 36.112263 -98.765090 03/1978 05/1979 260 4 7.33

360340098370901 18N-13W-06 DDA 1 36.061151 -98.619529 03/1978 05/1979 46 5 2.82

350844098281901 08N-12W-28 BAB 1 35.145615 -98.472281 04/1978 06/1991 238 11 6.56

362044099125401 22N-19W-34 ABD 1 36.345594 -99.215381 03/1979 03/1979 68 1 4.40

353650098430901 13N-14W-08 CBC 1 35.613940 -98.719523 03/1979 06/1989 265 21 3.37

353920098415701 14N-14W-28 CCA 1 35.655606 -98.699523 03/1979 03/1988 332 8 1.56

353927098402101 14N-14W-27 DBD 1 35.657550 -98.672856 03/1979 01/1986 315 5 3.18

354144098410901 14N-14W-16 AAA 1 35.695605 -98.686191 03/1979 03/1979 -- 1 2.89

353716098384501 13N-14W-12 BBD 1 35.621161 -98.646187 03/1979 03/1988 240 9 1.54

360039098454001 18N-15W-26 AAD 1 36.010876 -98.761479 03/1979 03/1986 260 4 3.77

355803098472901 17N-15W-10 B 1 35.967544 -98.791757 06/1979 06/1979 220 1 20.07

352637098175401 11N-10W-07 BDA 1 35.443664 -98.298669 07/1979 05/1990 300 25 6.61

360846099205401 19N-20W-05 DDB 1 36.146153 -99.348718 08/1979 08/1979 101 1 2.56

361530099233401 21N-21W-36 AAC 1 36.258373 -99.393164 08/1979 08/1979 -- 1 9.84

361047099201101 20N-20W-28 DBB 1 36.179764 -99.336773 10/1979 10/1979 102 1 6.57

361239099185601 20N-20W-15 ACD 1 36.210874 -99.315940 10/1979 10/1979 220 1 4.31

360447099110801 19N-19W-36 CBB 1 36.079765 -99.185936 12/1979 12/1979 -- 1 3.99

360640099130701 19N-19W-22 BAC 1 36.111153 -99.218992 12/1979 03/1983 290 3 6.05

360903099110201 19N-19W-02 DAA 1 36.150875 -99.184269 12/1979 03/1983 68 3 6.77
Table 7 147

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

344453097551801 03N-07W-10 ACC 1 34.748129 -97.921983 01/1980 01/1980 122 1 8.27

355850098522701 17N-16W-02 ACB 1 35.980599 -98.874538 03/1980 08/1995 240 33 12.34

361452099230401 21N-20W-31 CDC 1 36.247818 -99.384830 04/1980 04/1980 200 1 4.88

355730099060501 17N-18W-10 DDC 1 35.958377 -99.101766 08/1980 08/1980 220 1 24.48

360708099174801 19N-20W-14 DDB 1 36.118931 -99.297050 10/1980 10/1980 465 1 12.33

360457099113601 19N-19W-35 ACB 1 36.082543 -99.193714 10/1980 10/1980 450 1 9.68

361955099181301 21N-20W-11 ADB 1 36.331983 -99.303995 10/1980 10/1980 335 1 2.30

352308098241101 11N-11W-31 ACC 1 35.385610 -98.403394 01/1981 01/1987 246 4 2.83

353012098225901 12N-11W-20 ACA 1 35.503385 -98.383396 01/1981 05/1988 240 9 8.68

360913099174101 19N-20W-02 ADD 1 36.153653 -99.295106 02/1981 03/1988 136 4 9.85

355546098390001 17N-14W-24 CCA 1 35.929488 -98.650362 02/1981 03/1983 -- 1 4.04

360132098525301 18N-16W-23 BBD 1 36.025598 -98.881760 02/1981 03/1983 -- 1 2.72

345536098101601 05N-09W-08 ABB 1 34.926733 -98.171437 03/1981 03/1981 360 1 16.26

353222098385401 12N-14W-02 DCB 1 35.539496 -98.648684 03/1981 03/1981 240 1 6.33

344426098095101 03N-09W-08 DCD 1 34.740627 -98.164491 03/1981 03/1982 -- 1 3.75

355501098444901 17N-15W-25 D 1 35.916989 -98.747310 07/1981 07/1981 320 1 20.11

354140098442501 14N-15W-13 AA 1 35.694494 -98.740637 01/1982 01/1982 357 1 6.63

353319098554401 13N-16W-32 C 1 35.555328 -98.929251 03/1982 06/1991 400 13 7.43

355041098465901 16N-15W-22 CAD 1 35.844769 -98.783421 03/1982 03/1982 240 1 21.03

344710097580501 04N-07W-30 DDA 1 34.786183 -97.968374 05/1982 05/1982 210 1 7.96

345857098055401 06N-09W-24 ABD 1 34.982565 -98.098658 05/1982 05/1982 140 1 18.87

350925098113201 08N-09W-19 B 1 35.157005 -98.192551 07/1982 07/1982 130 1 16.64

355107098474601 16N-15W-21 A 1 35.851991 -98.796477 10/1982 10/1982 280 1 29.60

355648098580401 17N-17W-13 CAC 1 35.946710 -98.968151 11/1982 11/1982 360 1 25.54

344926097553901 04N-07W-15 BBD 1 34.823960 -97.927818 12/1982 12/1982 260 1 17.81

355439099085801 17N-18W-32 BBC 1 35.910878 -99.149822 12/1982 12/1982 500 1 25.63

344407097591501 03N-08W-13 ADB 1 34.735351 -97.987818 04/1983 04/1983 200 1 15.61

345112097585201 04N-07W-06 BBD 1 34.853403 -97.981431 06/1983 06/1983 72 1 20.53

355737098580701 17N-17W-12 C 1 35.960321 -98.968985 08/1983 08/1983 420 1 4.99

350250098083101 07N-09W-27 CBD 1 35.04728549 -98.1422709 11/1983 11/1983 200 1 22.16

350253098271701 07N-12W-27 CAD 1 35.04811658 -98.4550579 11/1983 11/1983 207 1 15.58

344414097553301 03N-07W-15 BAC 1 34.73729585 -97.9261496 12/1983 12/1983 160 1 9.53

355705098562301 17N-16W-18 AD 1 35.95143265 -98.9400947 12/1983 12/1983 380 1 33.15

355531099074601 17N-18W-28 BBD 1 35.92532256 -99.1298218 02/1984 02/1984 520 1 10.88

355754099072901 17N-18W-09 BDD 1 35.96504419 -99.1251002 02/1984 02/1984 415 1 12.81

355358098441401 17N-15W-36 AC 1 35.89948956 -98.7375871 03/1984 03/1984 218 1 6.02
148 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

355355098575601 16N-17W-01 BBA 1 35.8986558 -98.965928 05/1984 05/1984 200 1 3.94

360934098592801 20N-17W-34 DDD 1 36.15948457 -98.9914859 06/1984 06/1984 60 1 9.25

353249098404401 12N-14W-03 BDB 2 35.5469962 -98.6792408 06/1984 06/1984 160 1 3.91

352854098183701 12N-11W-25 DDB 1 35.48171894 -98.3106149 08/1984 08/1984 240 1 2.02

353254098405201 12N-14W-04 ABD 1 35.54838509 -98.6814631 08/1984 08/1984 160 1 4.98

353216098404601 12N-14W-04 DDC 1 35.5378297 -98.679796 09/1984 09/1984 180 1 3.88

355345098450501 16N-15W-01 B 1 35.89587868 -98.7517543 10/1984 10/1984 180 1 9.10

355345098450502 16N-15W-01 B 2 35.89587868 -98.7517543 10/1984 10/1984 165 1 9.10

354914099082501 16N-18W-32 BDC 1 35.82060186 -99.1406535 11/1984 11/1984 405 1 15.26

350639098250801 07N-12W-01 BDC 1 35.11089338 -98.4192238 12/1984 12/1984 250 1 25.06

352058098080801 10N-09W-10 DCD 1 35.349501 -98.1358853 12/1984 12/1984 56 1 4.38

352157098142401 10N-10W-03 DDB 1 35.3658888 -98.2403328 12/1984 12/1984 138 1 4.76

352529098145401 11N-10W-15 CAC 2 35.424776 -98.2486674 12/1984 12/1984 160 1 2.76

355341098454201 16N-15W-02 ACA 1 35.89476756 -98.7620324 12/1984 12/1984 180 1 19.45

350927098174501 08N-10W-19 BBC 1 35.15756004 -98.2961648 12/1984 12/1984 200 1 1.45

351310098102501 09N-09W-29 DCC 1 35.2195043 -98.17394 12/1984 12/1984 100 1 3.68

351544098143401 09N-10W-10 DCC 1 35.26228059 -98.2431087 12/1984 12/1984 60 1 3.34

351714098100001 09N-09W-05 AAD 1 35.28728047 -98.1669962 12/1984 12/1984 75 1 4.36

352146098192001 10N-11W-12 BBB 1 35.36283305 -98.3225574 12/1984 12/1984 168 1 1.77

352234098140801 10N-10W-02 BBB 1 35.3761663 -98.2358884 12/1984 12/1984 46 1 2.30

352437098100201 11N-09W-20 DAD 1 35.41033235 -98.1675538 12/1984 12/1984 129 1 1.98

352542098192701 11N-11W-14 ADDD 1 35.42838696 -98.3245032 12/1984 12/1984 77 1 5.44

352933098192801 12N-11W-26 AAA 1 35.492552 -98.3247822 12/1984 12/1984 127 1 2.09

352646098382901 11N-14W-11 ADAA 1 35.44616434 -98.6417364 12/1984 12/1984 133 1 1.64

353030098392101 12N-14W-14 CCC 1 35.5083857 -98.656183 12/1984 12/1984 130 1 2.73

353455098344601 13N-13W-21 DDD 1 35.5819951 -98.5797938 12/1984 12/1984 143 1 0.71

353755098364901 13N-13W-05 BCC 1 35.6319943 -98.6139635 12/1984 12/1984 123 1 1.36

354205098431501 14N-14W-07 DAD 1 35.7014383 -98.7211924 12/1984 12/1984 104 1 1.49

352150098352601 10N-13W-05 DDC 1 35.36394334 -98.5908992 12/1984 12/1984 65 1 3.16

352500098403201 11N-14W-21 AADD 1 35.41672029 -98.6759035 12/1984 12/1984 190 1 3.86

352926098285201 12N-12W-28 BBC 1 35.49060784 -98.481454 12/1984 12/1984 140 1 1.50

350834098295801 08N-12W-30 AACCC 35.1428366 -98.4997819 01/1985 01/1985 300 1 1.49

351108098211201 08N-11W-10 BCB 1 35.18561464 -98.3536667 01/1985 01/1985 107 1 1.42

351109098252201 08N-12W-12 BBC 1 35.1858919 -98.4231132 01/1985 01/1985 260 1 4.44

351116098335901 08N-13W-09 AAA 1 35.18783528 -98.5667286 01/1985 01/1985 300 1 0.55

351451098184301 09N-11W-13 DCD 1 35.2475582 -98.312277 01/1985 01/1985 43 1 2.49
Table 7 149

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

351657098234201 09N-11W-06 DAA 1 35.2825568 -98.3953356 01/1985 01/1985 258 1 1.42

350255098212601 07N-11W-28 DAD 1 35.04867278 -98.3575549 01/1985 01/1985 127 1 1.48

350339098272201 07N-12W-22 CDB 1 35.0608941 -98.4564469 01/1985 01/1985 64 1 3.28

350459098333001 07N-13W-15 ACB 1 35.0831151 -98.5586722 01/1985 01/1985 120 1 1.61

350515098292001 07N-12W-08 CDD 2 35.08756 -98.4892258 01/1985 01/1985 60 1 1.75

350758098450401 08N-15W-26 CDC 1 35.1328349 -98.7514559 01/1985 01/1985 48 1 2.61

350832098400501 08N-14W-27 BCB 1 35.1422798 -98.668398 01/1985 01/1985 160 1 1.22

345450098171701 05N-10W-07 DDD 1 34.91395434 -98.288385 01/1985 01/1985 86 1 2.02

345800098135901 06N-10W-26 BCB 1 34.96673104 -98.2333837 01/1985 01/1985 32 1 1.92

350000098243601 06N-12W-13 AAA 1 35.00006225 -98.410334 01/1985 01/1985 40 1 1.42

350019098170901 06N-10W-08 CBC 1 35.00534075 -98.2861634 01/1985 01/1985 131 1 2.04

350524098170101 07N-10W-08 CCC 1 35.0900614 -98.2839418 01/1985 01/1985 47 1 3.19

345724098055201 06N-09W-25 DCD 1 34.9567324 -98.098102 01/1985 01/1985 77 1 3.39

345959098043301 06N-08W-07 DDD 1 34.99978687 -98.0761575 01/1985 01/1985 41 1 2.24

350050098112601 06N-09W-07 BAA 1 35.01395239 -98.190883 01/1985 01/1985 107 1 3.98

350234098062601 07N-09W-36 BBA 1 35.0428414 -98.1075477 01/1985 01/1985 124 1 2.34

350320098094701 07N-09W-28 BBC 1 35.0556185 -98.1633826 01/1985 01/1985 46 1 2.84

344930098123201 04N-10W-13 BBA 1 34.82506859 -98.209215 01/1985 01/1985 45 1 1.77

345302098140801 05N-10W-27 AAB 1 34.88395557 -98.235883 01/1985 01/1985 62 1 2.24

345353098073501 05N-09W-23 BBB 1 34.89812278 -98.1267133 01/1985 01/1985 110 1 2.08

345542098114201 05N-09W-06 CCD 1 34.9283991 -98.1953267 01/1985 01/1985 10845 1 1.73

344702098540201 04N-07W-26 DDC 1 34.7839613 -97.900872 01/1985 01/1985 78 1 1.77

344748098065401 04N-09W-26 ABBB 1 34.79673696 -98.1153228 01/1985 01/1985 144 1 1.45

344810098010801 04N-08W-23 CBC 1 34.8028488 -98.0192086 01/1985 01/1985 44 1 3.35

344931098041701 04N-08W-17 BBB 1 34.82534764 -98.0717106 01/1985 01/1985 79 1 1.91

344936098565201 04N-07W-16 BBB 1 34.82673754 -97.948096 01/1985 01/1985 90 1 2.38

345028098091801 04N-09W-04 CCD 1 34.84117974 -98.1553246 01/1985 01/1985 50 1 2.17

345306098562001 05N-07W-21 DDC 1 34.88506924 -97.9392079 01/1985 01/1985 126 1 2.48

353441098391901 13N-14W-26 ABD 1 35.57810666 -98.6556299 07/1985 07/1985 140 1 13.92

350035098115701 06N-10W-12 ADA 1 35.00978574 -98.1994943 10/1985 10/1985 140 1 11.27

361235099034101 20N-17W-18 BCC 1 36.20976187 -99.0617657 11/1985 11/1985 140 1 3.89

345816098003001 06N-08W-23 DDC 1 34.97117714 -98.0086553 06/1986 06/1986 86 1 7.27

345441098012201 05N-08W-15 AAA 1 34.9114566 -98.0230992 06/1986 06/1986 229 1 12.04

345732098064801 06N-09W-26 DDB 1 34.95895444 -98.113658 06/1986 06/1986 90 1 10.34

345833098042401 06N-08W-20 CBB 1 34.9758987 -98.0736572 06/1986 06/1986 50 1 7.30

344159097572701 03N-07W-29 DCB 1 34.6997968 -97.9578164 06/1986 06/1986 109 1 8.67
150 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

344211097544601 03N-07W-26 CBB 1 34.7031303 -97.9130932 06/1986 06/1986 100 1 9.45

344433097545301 03N-07W-10 DDA 1 34.7425735 -97.9150384 06/1986 06/1986 90 1 8.13

344433097572501 03N-07W-08 DCB 1 34.74257329 -97.9572616 06/1986 06/1986 100 1 7.44

345448098071401 05N-09W-11 CDD 1 34.91340016 -98.1208799 06/1986 06/1986 57 1 13.17

345602098035201 05N-08W-05 DCC 1 34.93395558 -98.0647674 06/1986 06/1986 122 1 10.19

344709097575301 04N-07W-33 BAB 1 34.78590529 -97.9650402 06/1986 06/1986 50 1 6.59

345812098102401 06N-09W-29 BAA 1 34.97006475 -98.1736598 06/1986 06/1986 195 1 10.01

344939097554201 04N-07W-22 BBA 1 34.82757099 -97.9286512 06/1986 06/1986 126 1 11.77

345815098160601 06N-10W-28 BBB 1 34.9708973 -98.2686626 06/1986 06/1986 157 1 8.13

344939097575601 04N-07W-08 CCC 1 34.8275707 -97.9658743 07/1986 07/1986 74 1 8.07

345055097545701 04N-07W-03 ADD 1 34.84868159 -97.9161513 07/1986 07/1986 375 1 16.57

345517098160501 05N-10W-09 BCC 1 34.92145427 -98.2683844 07/1986 07/1986 78 1 6.10

344701098031101 04N-08W-28 CCC 1 34.78368239 -98.0533761 07/1986 07/1986 131 1 6.03

344703097591501 04N-08W-25 DDC 1 34.7842385 -97.9878185 07/1986 07/1986 150 1 8.44

344939098000701 04N-08W-11 DDD 1 34.82757044 -98.002264 07/1986 07/1986 61 1 14.64

345445098144301 05N-11W-14 ABB 1 34.9125658 -98.2456058 07/1986 07/1986 58 1 3.90

345750098201801 06N-11W-26 CBB 1 34.9639526 -98.3386648 07/1986 07/1986 40 1 2.93

344946098041101 04N-08W-08 CCB 1 34.8295142 -98.070044 07/1986 07/1986 135 1 10.31

345054098072301 04N-09W-02 BCC 2 34.84840204 -98.1233792 07/1986 07/1986 87 1 6.55

350235098082401 07N-09W-34 BAB 1 35.0431189 -98.1403263 07/1986 07/1986 102 1 16.14

344147098032801 03N-08W-29 DDC 1 34.6964628 -98.058097 07/1986 07/1986 400 1 2.41

344234098003601 03N-08W-26 ABB 1 34.7095184 -98.0103178 07/1986 07/1986 58 1 10.71

350043098094301 06N-09W-09 BCB 1 35.0120082 -98.162271 07/1986 07/1986 46 1 12.29

350053098074901 06N-09W-10 DDC 1 35.01478617 -98.1306036 07/1986 07/1986 78 1 4.81

344431098031801 03N-08W-08 DDA 1 34.74201696 -98.05532 07/1986 07/1986 105 1 9.02

344442098001001 03N-08W-11 DAD 1 34.74507294 -98.003096 07/1986 07/1986 100 1 9.18

344509098070801 03N-09W-11 BAB 1 34.75257155 -98.1192113 07/1986 07/1986 188 1 7.86

344715098072101 04N-09W-26 CBC 1 34.78757049 -98.122823 07/1986 07/1986 109 1 8.45

350542098135901 07N-10W-10 DAA 1 35.09506167 -98.2333848 07/1986 07/1986 40 1 26.61

345201098031601 05N-08W-29 DCD 1 34.8670132 -98.0547662 07/1986 07/1986 59 1 14.40

345212097572301 05N-07W-29 DDD 1 34.8700695 -97.956708 07/1986 07/1986 500 1 8.45

350626098260401 07N-12W-02 CAD 1 35.1072822 -98.4347798 07/1986 07/1986 74 1 11.54

350253098263701 07N-12W-26 CBC 1 35.04811665 -98.4439465 07/1986 07/1986 115 1 6.35

350319098284901 07N-12W-29 AAD 1 35.05533849 -98.4806143 07/1986 07/1986 49 1 11.15

344743098132401 04N-10W-26 BAA 1 34.79534707 -98.2236597 07/1986 07/1986 70 1 2.47

344747098101401 04N-09W-29 BAB 1 34.79645866 -98.1708802 07/1986 07/1986 58 1 5.07
Table 7 151

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

350002098231301 06N-11W-08 CDC 1 35.00061795 -98.3872778 07/1986 07/1986 36 1 8.56

350519098232501 07N-11W-07 DDD 1 35.08867179 -98.3906117 07/1986 07/1986 78 1 6.19

344936098131301 04N-10W-11 DCC 1 34.8267351 -98.2206044 07/1986 07/1986 84 1 4.66

350254098191801 07N-11W-26 DAD 1 35.04839525 -98.3219982 07/1986 07/1986 39 1 9.34

350310098230001 07N-11W-29 BDA 1 35.05283919 -98.3836668 07/1986 07/1986 156 1 6.50

350525098170101 07N-10W-08 CCB 1 35.09033917 -98.2839418 07/1986 07/1986 67 1 11.07

350549098315701 07N-11W-12 BCC 1 35.0970039 -98.5328382 07/1986 07/1986 90 1 9.40

350831098390801 08N-14W-26 BCB 1 35.14200217 -98.6525642 07/1986 07/1986 123 1 4.97

351125098384301 08N-14W-02 CDD 1 35.1903347 -98.6456199 07/1986 07/1986 225 1 8.14

350312098161801 07N-10W-29 ADB 1 35.0533955 -98.2719967 07/1986 07/1986 131 1 22.91

350516098292001 07N-12W-08 CDD 1 35.08783779 -98.4892258 07/1986 07/1986 98 1 8.06

351311098102401 09N-09W-26 DCC 1 35.21978208 -98.1736622 07/1986 07/1986 50 1 12.51

351345098140601 09N-10W-26 BBC 1 35.2292258 -98.2353304 07/1986 07/1986 96 1 18.26

351109098130401 08N-10W-11 AAC 1 35.18589345 -98.2181074 07/1986 07/1986 72 1 13.08

350819098191101 08N-11W-26 DAA 1 35.13867134 -98.3200543 07/1986 07/1986 191 1 3.58

351027098285301 08N-12W-17 AAB 1 35.174225 -98.4817259 07/1986 07/1986 101 1 10.24

351049098221901 08N-11W-08 DAD 1 35.1803368 -98.3722783 07/1986 07/1986 145 1 3.81

351332098254701 09N-12W-26 DAA 1 35.2256133 -98.430058 07/1986 07/1986 123 1 2.19

351357098201001 09N-11W-26 BAB 1 35.2325583 -98.3364443 07/1986 07/1986 240 1 5.93

350753098330001 08N-13W-34 AAB 1 35.13144758 -98.5503389 07/1986 07/1986 125 1 3.41

350819098254701 08N-11W-26 DBA 1 35.13867055 -98.4300576 07/1986 07/1986 49 1 7.78

350845098284101 08N-12W-29 AAA 1 35.14589228 -98.4783924 07/1986 07/1986 131 1 2.59

351112098350101 08N-13W-08 AAD 1 35.18672408 -98.5839513 07/1986 07/1986 126 1 4.54

350516098361501 07N-13W-07 DDD 1 35.08783685 -98.6045068 07/1986 07/1986 96 1 4.39

351308098330801 09N-13W-26 CCC 1 35.2189459 -98.5525616 07/1986 07/1986 268 1 7.91

351401098381601 09N-14W-24 CCD 1 35.2336673 -98.63812 07/1986 07/1986 116 1 3.94

345234098115601 05N-10W-25 DAA 1 34.87617834 -98.1992152 07/1986 07/1986 94 1 6.54

345302098125801 05N-10W-26 AAA 1 34.88395574 -98.216438 07/1986 07/1986 120 1 9.01

345342098105201 05N-09W-19 AAD 1 34.89506655 -98.2147714 07/1986 07/1986 110 1 9.02

345245098130601 05N-10W-26 ADB 1 34.8792336 -98.2186603 07/1986 07/1986 97 1 10.53

345251098123601 05N-10W-25 BAC 1 34.8809003 -98.2103267 07/1986 07/1986 117 1 10.04

345346098125801 05N-10W-23 AAD 1 34.8961776 -98.2164382 07/1986 07/1986 -- 1 13.04

352626098361501 11N-13W-08 CBC 1 35.44060884 -98.6045127 08/1986 08/1986 104 1 6.37

352937098320701 12N-13W-23 DDD 1 35.49366345 -98.5356227 08/1986 08/1986 90 1 3.17

353208098290501 12N-12W-08 AAB 1 35.53560684 -98.4850666 08/1986 08/1986 111 1 4.08

353211098232001 12N-11W-08 BAB 1 35.5364399 -98.38923 08/1986 08/1986 82 1 3.02
152 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

351548098351301 09N-13W-09 CCC 1 35.26338934 -98.5872855 08/1986 08/1986 97 1 7.84

351902098383501 10N-14W-26 AAC 1 35.31727719 -98.6433998 08/1986 08/1986 100 1 7.71

352059098412701 10N-14W-09 CCD 1 35.3497766 -98.69118 08/1986 08/1986 115 1 8.58

352407098320601 11N-13W-26 ADA 1 35.40199836 -98.5353427 08/1986 08/1986 91 1 12.89

352742098413701 11N-14W-05 AAD 1 35.46171975 -98.6939609 08/1986 08/1986 109 1 13.44

352934098383001 12N-14W-26 AAA 1 35.49283038 -98.6420154 08/1986 08/1986 162 1 13.23

351914098255101 10N-12W-23 DDD 1 35.32061134 -98.4311708 08/1986 08/1986 103 1 8.52

352425098392501 11N-14W-23 CCC 1 35.4069982 -98.6572915 08/1986 08/1986 85 1 13.51

351852098331201 10N-13W-27 ADA 1 35.31449979 -98.5536745 08/1986 08/1986 84 1 6.73

351907098070101 10N-09W-26 AAB 1 35.31866877 -98.1172733 08/1986 08/1986 70 1 9.66

352314098075601 11N-09W-34 ADA 1 35.38727767 -98.1325525 08/1986 08/1986 56 1 15.86

353206098352101 12N-13W-08 AAD 1 35.53505166 -98.5895148 08/1986 08/1986 128 1 3.00

351610098234001 09N-11W-07 ADD 1 35.26950155 -98.3947798 08/1986 08/1986 177 1 2.12

351630098043701 09N-08W-08 BBB 1 35.2750593 -98.0772717 08/1986 08/1986 53 1 12.10

352056098360301 10N-13W-08 CDC 1 35.34894354 -98.601177 08/1986 08/1986 98 1 12.25

352145098232101 10N-11W-08 BAB 1 35.36255505 -98.3895038 08/1986 08/1986 145 1 12.27

352145098290201 10N-12W-08 AAA 1 35.3625547 -98.4842289 08/1986 08/1986 229 1 8.79

351637098275101 09N-12W-03 CCC 1 35.2770009 -98.4645042 08/1986 08/1986 210 1 12.96

351908098220101 10N-11W-28 AAB 1 35.318945 -98.36728 08/1986 08/1986 157 1 13.42

352056098095901 10N-09W-08 DDD 1 35.3489453 -98.1667194 08/1986 08/1986 55 1 9.02

352216098162101 10N-10W-05 ADD 1 35.3711663 -98.2728338 08/1986 08/1986 167 1 10.82

352338098283001 11N-11W-27 DDA 1 35.393943 -98.4753405 08/1986 08/1986 149 1 4.11

352517098230401 11N-11W-17 DCC 1 35.4214426 -98.3847827 08/1986 08/1986 135 1 22.37

352604098172201 11N-10W-18 AAAA 1 35.43449794 -98.28978 08/1986 08/1986 142 1 9.38

352655098290501 11N-12W-08 AAA 1 35.4486642 -98.4850643 08/1986 08/1986 260 1 10.02

352843098202701 12N-11W-26 CCC 1 35.47866349 -98.3411714 08/1986 08/1986 105 1 3.10

352435098140901 11N-10W-23 CBCC 1 35.4097765 -98.2361668 08/1986 08/1986 131 1 6.14

353217098410701 12N-14W-04 CDD 1 35.5381075 -98.6856296 08/1986 08/1986 151 1 1.69

350018098031301 06N-08W-09 CBD 1 35.0050647 -98.0539348 08/1986 08/1986 23 1 13.91

353356098333601 13N-13W-35 CCC 1 35.56560647 -98.5603481 08/1986 08/1986 140 1 1.76

353725098364401 13N-13W-08 CCC 1 35.6236611 -98.6125743 08/1986 08/1986 132 1 1.91

351109098104601 08N-09W-07 AAD 1 35.18589377 -98.1797731 08/1986 08/1986 56 1 11.23

351655098424001 09N-14W-05 CBB 1 35.28199956 -98.7114567 08/1986 08/1986 172 1 2.77

351724098155501 09N-10W-04 BAB 1 35.29005745 -98.2656099 08/1986 08/1986 47 1 14.29

352427098254801 11N-12W-23 DDD 1 35.40755396 -98.4303394 08/1986 08/1986 38 1 10.71

352846098263601 12N-12W-26 CCD 1 35.4794969 -98.4436748 08/1986 08/1986 140 1 2.49
Table 7 153

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

354225098111201 08N-14W-07 AAD 1 35.1867232 -98.7072884 08/1986 08/1986 85 1 13.75

361741099112901 21N-19W-13 CBC 2 36.29476109 -99.1917693 02/1987 02/1987 75 1 3.38

355032098541401 16N-16W-21 DCD 1 35.8422682 -98.9042583 05/1989 05/1989 200 1 5.63

355254098573201 16N-17W-12 ABC 1 35.8817117 -98.9592608 05/1989 05/1989 166 1 6.17

354417098461301 15N-15W-35 BDA 1 35.7381045 -98.7706402 05/1989 05/1989 79 1 11.27

354549098552501 15N-16W-20 DCC 1 35.76365858 -98.9239797 05/1989 05/1989 240 1 7.91

352754098453301 12N-15W-35 CDC 1 35.465053 -98.7595189 06/1989 06/1989 157 1 9.65

353555098420801 13N-14W-16 CBC 1 35.5986621 -98.7025768 06/1989 06/1989 91 1 6.56

353755099001901 13N-17W-04 ADA 1 35.6339373 -99.0050899 06/1989 06/1989 119 1 6.06

355936098533701 18N-16W-34 BDD 1 35.99337629 -98.893983 06/1989 06/1989 -- 1 6.68

352935098172001 12N-10W-19 DDD 1 35.4931075 -98.2892255 06/1989 06/1989 75 1 12.01

353357098570202 13N-16W-31 BBB 2 35.56588298 -98.950919 06/1989 06/1989 150 1 8.26

353909098524901 OW-2 14N-16W-34 

AAAA 1

35.65254928 -98.8806413 07/1990 07/1990 420 1 9.38

354936099043801 OW-1 16N-18W-35 

AAB 1

35.8267127 -99.0775965 07/1990 07/1990 278 2 8.15

351322098285701 9N-12W-29 DAD 1 35.22283518 -98.4828373 12/1998 08/1999 -- 2 4.69

351409098283901 9N-12W-21 CDB 1 35.2358905 -98.4778372 12/1998 08/1999 305 2 2.02

351411098290401 9N-12W-20 DD 1 35.236446 -98.4847818 12/1998 08/1999 305 2 2.87

351416098275301 9N-12W-21 DAD 1 35.23777778 -98.4647222 12/1998 08/1999 75 2 1.36

351453098295801 9N-12W-17 CCC 1 35.2481123 -98.4997823 12/1998 08/1999 100 2 4.13

351514098285301 9N-12W-16 CBB 1 35.2541111 -98.4815833 12/1998 08/1999 -- 2 1.36

351328098285801 9N-12W-29 DAA 1 35.2245018 -98.483115 12/1998 08/1999 150 2 3.95

351414098295801 9N-12W-20 CBC 1 35.2372222 -98.4994444 12/1998 08/1999 150 2 2.33

351453098290701 9N-12W-17 DDC 1 35.24866798 -98.4856152 12/1998 08/1999 100 2 3.45

351454098290501 9N-12W-17 DD 1 35.2483902 -98.4850597 12/1998 08/1999 -- 2 1.36

351505098291401 9N-12W-17 D 1 35.25089015 -98.487282 12/1998 12/1998 315 1 1.80

351543098285701 9N-12W-8 DDD 1 35.26219444 -98.4825833 12/1998 08/1999 150 2 1.36

351555098291101 9N-12W-8 D 1 35.2653343 -98.4867267 12/1998 08/1999 300 2 5.45

351628098284401 9N-12W-9 BB 1 35.27450087 -98.4792267 12/1998 08/1999 300 2 2.59

351633098292601 9N-12W-8 ABB 1 35.27588966 -98.4897826 12/1998 08/1999 100 2 3.27

351635098300301 9N-12W-5 CCC 1 35.2767229 -98.4986718 12/1998 08/1999 -- 2 1.81

351507098284101 9N-12W-16 C 1 35.25144576 -98.4783928 12/1998 08/1999 -- 2 1.36

351512098295501 9N-12W-17 CBB 1 35.2533333 -98.4988611 12/1998 08/1999 -- 2 1.36

351523098285501 9N-12W-16 BCB 1 35.25644564 -98.482282 12/1998 08/1999 -- 2 6.92

351608098274901 9N-12W-10 CBBB 1 35.2690833 -98.4636389 12/1998 08/1999 -- 2 1.36
154 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

351618098285301 9N-12W-9 BCB 1 35.2717231 -98.4817267 12/1998 08/1999 -- 2 2.75

351622098294201 9N-12W-8 B 1 35.2728341 -98.4953383 12/1998 08/1999 300 2 3.92

351630098275301 9N-12W-09 AAA 1 35.2751111 -98.4647778 12/1998 08/1999 150 2 1.36

351650098285301 9N-12W-4 CBC 1 35.28061185 -98.481727 12/1998 08/1999 100 2 3.91

351712098284101 9N-12W-4 B 1 35.28672286 -98.4783937 12/1998 12/1998 305 1 3.51

351341098285401 9N-12W-28 BCB 1 35.22811286 -98.4820039 12/1998 12/1998 -- 1 2.41

351421098285301 9N-12W-21 CBB 1 35.23927778 -98.4814722 12/1998 08/1999 -- 2 1.36

351421098285302 9N-12W-21 CBB 2 35.23927778 -98.4814722 12/1998 12/1998 320 1 1.36

351531098310101 9N-12W-18 BBC 1 35.25866759 -98.517283 12/1998 08/1999 -- 2 7.34

351607098310201 9N-13W-12 DAA 1 35.26880556 -98.5174722 12/1998 08/1999 -- 2 1.36

351452098290601 09N-12W-17 DDD 1 35.24783467 -98.4853374 04/1999 07/2000 73 13 2.29

351542098282501 MW-C 9N-12W-16 

BAAA 1 

35.2614456 -98.4739485 04/2000 04/2000 70 1 1.42

351545098285701 MW-B 9N-12W-8 

DDD 2 

35.2625566 -98.4828377 04/2000 04/2000 72 1 1.50

351502098284001 BD-3 9N-12W-16 C 2 35.2508902 -98.478115 04/2000 04/2000 55 1 4.64

351506098284001 BD-1 9N-12W-16 

CBAD 1 

35.2531124 -98.4783929 04/2000 04/2000 55 1 1.72

351504098284601 BD-2 9N-12W-16 

CB 1 

35.25311238 -98.4806152 04/2000 04/2000 55 1 2.17

352515098312001 11N-13W-13 DCD 1 35.42109444 -98.5224361 07/2010 01/2011 240 7 0.28

352907098230501 12N-11W-29 DBB 1 35.48554444 -98.3847472 07/2010 01/2011 208 7 0.28

353014098202601 12N-11W-23 BBC 1 35.50410278 -98.3407083 07/2010 12/2010 88 6 2.00

351850098171901 10N-10W-29 BCC 1 35.314025 -98.2886583 07/2010 01/2011 124 7 0.52

351850098283301 10N-12W-28 BDD 2 35.31395556 -98.47595 07/2010 08/2010 320 2 0.49

353002098340701 12N-13W-22 BCC 1 35.5006722 -98.568775 07/2010 01/2011 200 7 0.76

345443098061701 05N-09W-13 BAB 1 34.91217778 -98.1049083 07/2010 01/2011 77 7 0.28

345633098141901 06N-10W-34 DCD 1 34.94266389 -98.2388417 07/2010 01/2011 56 7 0.52

345728098185401 06N-11W-25 CDC 1 34.9579861 -98.3150389 07/2010 01/2011 50 7 0.76

350157098082501 07N-09W-34 CDB 1 35.03261944 -98.1403972 07/2010 01/2011 -- 7 2.75

350211098222701 07N-11W-33 BCC 1 35.03649444 -98.3741889 07/2010 01/2011 120 7 0.28

350510098332501 07N-13W-15 ABB 1 35.0862333 -98.55695 07/2010 01/2011 130 7 0.28

350856098253101 08N-12W-23 DDA 1 35.14914444 -98.4255111 07/2010 01/2011 70 7 0.28

351243098141201 09N-10W-34 ADD 1 35.21212778 -98.2366944 07/2010 01/2011 60 7 0.28

351907098074201 10N-09W-26 BBB 1 35.318775 -98.1283528 07/2010 01/2011 92 7 0.28

352039098121801 10N-10W-13 ADB 1 35.3442972 -98.2050889 07/2010 01/2011 206 6 0.28

351005098332001 08N-13W-15 ACC 1 35.16816667 -98.5558306 07/2010 01/2011 370 7 0.28

352143098310601 10N-13W-12 AAA 1 35.3620333 -98.5185889 07/2010 01/2011 137 7 0.49
Table 7 155

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

352315098265501 11N-12W-34 ADA 1 35.38753889 -98.4487972 07/2010 01/2011 185 7 0.28

352812098244401 12N-12W-36 DAA 1 35.4702722 -98.4124278 07/2010 01/2011 178 7 0.52

351442098182401 09N-11W-24 AAD 1 35.24517778 -98.30685 07/2010 01/2011 35 7 0.28

351620098234101 09N-11W-07 ADA 1 35.27230556 -98.3949083 07/2010 01/2011 160 7 0.28

350933098172101 08N-10W-19 ABA 1 35.15937778 -98.2893472 07/2010 01/2011 170 7 0.28

351100098232501 08N-11W-07 ADD 1 35.1834111 -98.3903722 07/2010 01/2011 130 7 0.28

352147098195401 10N-11W-02 DCC 1 35.36319444 -98.3316694 07/2010 01/2011 100 7 0.76

345357098181101 05N-10W-18 CCC 1 34.89941667 -98.3031139 07/2010 01/2011 120 7 2.50

345910098233701 06N-11W-18 DDD 1 34.98622778 -98.3937833 07/2010 01/2011 95 8 0.52

350714098232701 08N-11W-31 DDA 1 35.12064167 -98.3908944 08/2010 08/2010 82 1 0.49

350757098230401 08N-11W-29 CDC 1 35.13269167 -98.3845222 08/2010 01/2011 145 7 0.28

350804098230501 08N-11W-29 CDB 1 35.13451389 -98.3847306 08/2010 08/2010 232 1 0.49

350809098230401 08N-11W-29 CAC 1 35.13585278 -98.3845528 08/2010 08/2010 400 1 0.49

352423098221601 11N-11W-21 CDC 1 35.4065333 -98.3711667 08/2010 01/2011 120 7 0.28

351726098353801 09N-13W-05 ABA 0 35.2905611 -98.5939528 07/2011 08/2012 7 6 0.48

351726098353501 09N-13W-05 ABA 5 35.2906083 -98.5932056 09/2011 08/2012 34 6 0.48

351726098353601 09N-13W-05 ABA 3 35.2905833 -98.5935028 09/2011 08/2012 43 6 0.48

351726098353701 09N-13W-05 ABA 2 35.29058056 -98.593675 09/2011 08/2012 23 6 0.48

351727098353801 10N-13W-32 DCD 1 35.2908972 -98.5938833 09/2011 07/2012 21 5 0.48

351727098353701 10N-13W-32 DCD 4 35.2909722 -98.5935806 12/2011 07/2012 46 4 0.48

360809098443501 19N-15W-12 DAA 2 36.13595556 -98.7430833 01/2012 01/2012 -- 1 0.49

360835098475401 19N-15W-09 AAA 1 36.1431861 -98.7982 01/2012 01/2012 51 1 0.49

360842098514201 19N-16W-01 CDC 1 36.1448972 -98.861725 01/2012 01/2012 90 1 0.49

360931098533701 19N-16W-03 ABB 1 36.1586111 -98.8936528 01/2012 10/2012 48 2 0.49

362035099123901 22N-19W-34 ADD 1 36.343 -99.2109472 02/2012 02/2012 54 1 0.49

355909099200801 18N-20W-33 CCD 1 35.98606389 -99.3357389 01/2013 01/2014 250 2 0.49

355221099341001 16N-22W-07 DAC 1 35.87260556 -99.5696944 02/2013 01/2014 36 2 0.49

355256099335901 16N-22W-08 BBB 1 35.88231389 -99.5665083 02/2013 01/2014 24 2 0.49

360050099194701 18N-20W-28 AAA 1 36.01396389 -99.3298278 02/2013 01/2014 53 2 0.49

360128099211501 18N-20W-20 ACB 1 36.02449444 -99.3542056 02/2013 01/2014 60 2 0.49

355242099064001 16N-18W-10 BCD 1 35.8784722 -99.1113861 02/2013 01/2014 183 2 0.49

355304099100401 16N-18W-06 CCC 1 35.8844861 -99.1678278 02/2013 01/2014 36 2 0.49

355424099143501 17N-19W-32 ADC 1 35.9068861 -99.2431722 02/2013 02/2013 89 1 0.49

355441099145101 17N-19W-32 ABB 1 35.9115333 -99.2475667 02/2013 01/2014 41 2 0.49

355500099144701 17N-19W-29 DCB 1 35.9168361 -99.2466167 02/2013 01/2014 78 2 0.49

355538099145901 17N-19W-29 BAA 1 35.92734444 -99.2499333 02/2013 01/2014 72 2 0.49
156 Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

Table 7. Selected groundwater-level observation wells in the Rush Springs aquifer study area, western Oklahoma.—Continued

[OWRB ID is the well identifier used by the Oklahoma Water Resources Board (OWRB) and the U.S. Geological Survey (USGS) databases; Some differences may 

occur for the long-term groundwater-level observation well begin and end dates between the OWRB and the USGS well databases; the number of groundwater-level 

observations does not include the period of record averaged observation used in the steady-state groundwater-flow model; MM/YYYY, month/year; --, not available; 

*, observation well used for approximating the maximum seasonal groundwater-level range (seasonal approximation)]

Well 

number 

OWRB 

ID

Map 

number 

(fig. 11)

Station name

Latitude 

(decimal 

degrees)

Longitude

(decimal 

degrees)

Period of record 

(may contain 

gaps) or single 

measurement 

date 

(MM/YYYY)

Well 

or hole 

depth

(feet)

Number 

of groundwaterlevel observations during study 

period 

(1979–2015)

Standard 

deviation 

of groundwater-level 

observations during 

study period 

(1979–2015) Begin End

Groundwater-level observation wells (U.S. Geological Survey, 2017c)—Continued

355759099141801 17N-19W-09 BCB 1 35.96643056 -99.2386056 02/2013 01/2014 51 2 0.49

355831099155101 17N-19W-06 DBC 1 35.9752833 -99.2642306 02/2013 02/2013 68 1 0.49

355934099161301 18N-19W-31 BDC 1 35.992875 -99.2703222 02/2013 01/2014 41 2 0.49

355358099154901 17N-19W-31 DCC 1 35.8995583 -99.2637083 02/2013 01/2014 92 2 0.49

355558099162901 17N-20W-24 DAD 1 35.9330111 -99.2747333 02/2013 02/2013 -- 1 0.49

353310098223101 13N-11W-33 DCC 1 35.55281944 -98.3753917 03/2013 01/2014 18 2 0.49

355725098584701 17N-17W-11 DCD 1 35.95701944 -98.9798667 03/2013 03/2013 -- 1 0.49

360052098590701 18N-17W-26 BAB 1 36.0146 -98.9854333 03/2013 01/2014 65 2 0.49

355113098363001 16N-13W-20 BAB 1 35.8537083 -98.6086 03/2013 01/2014 250 2 0.49

355305098461501 16N-15W-02 DDC 1 35.88488889 -98.7709417 03/2013 03/2013 62 1 0.49

355307098402901 16N-14W-03 DCC 1 35.8853333 -98.6748333 03/2013 01/2014 250 2 0.49

355359098491101 17N-15W-32 DCD 1 35.89994444 -98.8199528 03/2013 01/2014 130 2 0.49

355523098495501 17N-15W-30 ADA 1 35.92309444 -98.8320944 03/2013 01/2014 132 2 0.49

355559098464401 17N-15W-22 DAA 1 35.9332722 -98.7790583 03/2013 01/2014 107 2 0.49

355803098505601 17N-15W-07 ABC 1 35.9676222 -98.8490833 03/2013 01/2014 56 2 0.49

360012098525801 18N-16W-26 CCB 1 36.00351944 -98.8828083 03/2013 01/2014 91 2 0.49

360014098525801 18N-16W-26 CBC 1 36.00395 -98.8827861 03/2013 03/2013 139 1 0.49

360022098525501 Taloga 18N-16W-26 

CBA 1

36.0060472 -98.8820222 10/2014 04/2016 19 6 0.49

360110099215001 Camargo 18N20W-20 CBC 1 36.01950556 -99.3640139 10/2014 04/2016 24 6 0.49

353215099004101 WSH05 12N-17W-09 

BBB 1 

35.5374611 -99.0113056 04/2015 03/2017 124 3 1.36

354022099202701 WSH04 14N-21W-21 

CDC 1 

35.6728 -99.3409139 04/2015 03/2017 75 2 1.36
For more information about this report, contact

Director, U.S. Geological Survey

202 NW 66th Street, Building 7

Oklahoma City, OK 73116

https://www.usgs.gov/centers/ok-water/

Publishing support provided by

Lafayette Publishing Service Center

Lafayette, Louisiana
Ellis—Simulation of Groundwater Flow and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma—Scientific Investigations Report 2018–5136

ISSN 2328-0328 (print)

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185136

ISBN 978-1-4113-4268-2

9 7 81411 342682