Scientific Investigations Report 2016–5180

Version 1.1, March 2017

U.S. Department of the Interior

U.S. Geological Survey

Hydrogeology and Simulation of Groundwater Flow and 

Analysis of Projected Water Use for the Canadian River 

Alluvial Aquifer, Western and Central Oklahoma

Prepared in cooperation with the Oklahoma Water Resources Board

Hydrogeology and Simulation of Groundwater Flow and 

Analysis of Projected Water Use for the Canadian River 

Alluvial Aquifer, Western and Central Oklahoma
Cover, Canadian River near Highway 283 in Roger Mills County, Oklahoma. Photograph by Kevin Smith, 

U.S. Geological Survey, Oklahoma, January 2013.
Hydrogeology and Simulation of 

Groundwater Flow and Analysis of 

Projected Water Use for the Canadian 

River Alluvial Aquifer, Western and Central 

Oklahoma

By John H. Ellis, Shana L. Mashburn, Grant M. Graves, Steven M. Peterson, 

S. Jerrod Smith, Leland T. Fuhrig, Derrick L. Wagner, and Jon E. Sanford

Prepared in cooperation with the Oklahoma Water Resources Board

Scientific Investigations Report 2016–5180

Version 1.1, March 2017

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2017

First release: 2017

Revised: March 2017 (ver 1.1) 

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Suggested citation:

Ellis, J.H., Mashburn, S.L., Graves, G.M., Peterson, S.M., Smith, S.J., Fuhrig, L.T., 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 (ver. 1.1, March 2017): U.S. Geological Survey Scientific Investigations 

Report 2016–5180, 64 p., 7 pls., https://doi.org/10.3133/sir20165180.

ISSN 2328-031X (print) 

ISSN 2328-0328 (online)
iii

Acknowledgments

The Canadian River alluvial aquifer study was conducted as a part of the U.S. Geological Survey 

(USGS) Cooperative Water Program in cooperation with the Oklahoma Water Resources Board 

(OWRB). The authors thank the board members of the OWRB for their support of this study and 

the OWRB technical studies section, who provided datasets and field assistance. 

The authors thank USGS employee Lynette Brooks for her help in conceptual flow model 

analysis and design. The authors thank Mike Fienen for support with parameter estimation 

(PEST) settings, singular value decomposition, and regularization. Additionally, the authors 

thank the Wisconsin and Nebraska Water Science Centers for use of their high-performance 

computing networks to perform the PEST calibration for the two groundwater-flow models. 

The authors also thank USGS employee Kevin Smith for his extensive field work and site data 

collection. Finally, the authors thank the many landowners who provided access to their land 

and groundwater wells, without whose assistance this study would not have been possible. 

v

Contents

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

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

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

Purpose and Scope .............................................................................................................................4

Study Area Description .......................................................................................................................4

Land Use ................................................................................................................................................4

Climate ...................................................................................................................................................5

Reported Water Use ............................................................................................................................5

Geology of the Canadian River Alluvial Aquifer .......................................................................................8

Quaternary-Age Alluvial and Terrace Deposits ..............................................................................8

Bedrock Units .......................................................................................................................................8

Tertiary-Age Bedrock Units .....................................................................................................10

Permian-Age Bedrock Units ...................................................................................................10

Pennsylvanian-Age Bedrock Units ........................................................................................10

Hydrogeologic Framework of the Canadian River Alluvial Aquifer ....................................................11

Lithologic-Log Standardization ........................................................................................................11

Aquifer Areal and Vertical Extent ....................................................................................................12

Hydraulic Profiling and Sediment Coring .......................................................................................12

Percent-Coarse Value and Hydraulic Properties .........................................................................12

Hydrogeology of the Canadian River Alluvial Aquifer ..........................................................................13

Groundwater .......................................................................................................................................13

Temporal Water-Level Fluctuations .......................................................................................14

Water-Table Surface in 2013 ...................................................................................................14

Groundwater Flow to and from Bedrock Units ....................................................................14

Water Quality .............................................................................................................................17

Surface Water ....................................................................................................................................17

Streamflow Characteristics and Trends ...............................................................................17

Stream Base Flow .....................................................................................................................21

2013 Seepage Run ...........................................................................................................21

Base-Flow Separation ....................................................................................................22

Streambed Hydraulic Properties ............................................................................................23

Recharge .............................................................................................................................................23

Water-Table Fluctuation Method ...........................................................................................25

Soil-Water-Balance Code ........................................................................................................25

Evapotranspiration from Groundwater ..........................................................................................26

Conceptual Flow Model of the Canadian River Alluvial Aquifer .........................................................28

Hydrogeologic Boundaries ..............................................................................................................28

Conceptual Water Budget ................................................................................................................28

Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer ..........................................30

Model Extents and Configuration ....................................................................................................30

Discretization ......................................................................................................................................30

Boundary Conditions .........................................................................................................................30

Groundwater Recharge ...........................................................................................................31
vi

Water-Table Evapotranspiration ............................................................................................31

Streamflow .................................................................................................................................31

Lateral Flow ................................................................................................................................32

Groundwater Use ......................................................................................................................32

Model Calibration ...............................................................................................................................32

Calibration Parameters ............................................................................................................33

Calibration Targets ....................................................................................................................34

Calibration-Target Uncertainty and Weighting ....................................................................34

Calibration Results ....................................................................................................................35

Comparison of Simulated and Observed Values ........................................................35

Reach I ......................................................................................................................35

Reach II ....................................................................................................................37

Water Budget ...................................................................................................................41

Calibrated Parameters ....................................................................................................44

Sensitivity Analysis ...................................................................................................................47

Equal Proportionate Share Scenarios ............................................................................................47

Estimated Reach I Equal Proportionate Share ....................................................................49

Estimated Reach II Equal Proportionate Share ...................................................................49

Projected Water Use .........................................................................................................................51

Fifty-Year Water Use ................................................................................................................51

Sustained Drought ....................................................................................................................54

Stream Base Flow ............................................................................................................54

Groundwater in Storage .................................................................................................54

Assumptions and Limitations ...........................................................................................................55

Summary .......................................................................................................................................................58

References Cited .........................................................................................................................................60

Plates

[Available at https://doi.org/10.3133/sir20165180.]

1. Map showing Canadian River alluvial aquifer extent, geologic units, continuous 

recorder wells, hydraulic-profiling tool test holes, streambed-hydraulic property 

sites, seepage-run sites, and wastewater-treatment plant outflows.

2. Map showing altitude of the base of the Canadian River alluvial aquifer, Oklahoma.

3. Map showing water-table surface contours and general direction of groundwater 

flow of the Canadian River alluvial aquifer, Oklahoma, 2013.

4. Map showing recharge estimated by using the soil-water-balance (SWB) code 

for the Canadian River alluvial aquifer.

5. Map showing boundary conditions used for the Canadian River alluvial aquifer 

groundwater-flow models.

6. Map showing horizontal hydraulic conductivity zones used for the Canadian 

River alluvial aquifer groundwater-flow models.

7. Map showing equal-proportionate-share pumping saturated thickness for 

Reach I and Reach II of the Canadian River alluvial aquifer groundwater-flow 

models.
vii

Figures

1. Map showing extent of the Canadian River watershed upstream from Eufaula, 

Oklahoma, and climate divisions, climate stations, and streamgages ...............................3

2. Pie charts showing land cover and crop types on the Canadian River alluvial 

aquifer, Oklahoma ........................................................................................................................4

3. Graph showing average annual precipitation for the period 1896–2014, 5-year 

moving average, and the number of cooperative observer stations recording 

during each year in the Canadian River alluvial aquifer study area ...................................6

4. Graph showing average monthly precipitation during the time periods of 1947–80 

and 1981–2014 for the Taloga, Norman 3SSE, and Sallisaw 2 NW cooperative 

observer stations in the Canadian River alluvial aquifer study area ..................................6

5. Graphs showing groundwater use by type for the Canadian River alluvial aquifer, 

Oklahoma, 1967–2013 ..................................................................................................................7

6. Stratigraphic chart showing geologic and hydrogeologic units of the Canadian 

River alluvial aquifer study area ................................................................................................9

7. Graph showing frequency distribution of depth of lithologic logs used for the 

hydrogeologic framework in the Canadian River alluvial aquifer, Oklahoma ..................11

8. Graph showing frequency distribution of depth to bedrock (base of alluvial 

aquifer) determined from lithologic logs ................................................................................11

9. Chart showing percent-coarse multiplier values for the standardized lithologic 

categories used to obtain horizontal hydraulic conductivity for the Canadian 

River alluvial aquifer, Oklahoma ..............................................................................................11

10. Graph showing frequency distribution of horizontal hydraulic conductivity 

determined from lithologic logs ...............................................................................................13

11. Graphs showing continuous water levels recorded in wells and precipitation in 

Reach I of the Canadian River alluvial aquifer, Oklahoma ..................................................15

12. Graphs showing continuous water levels recorded in wells and precipitation in 

Reach II of the Canadian River alluvial aquifer, Oklahoma .................................................16

13. Piper diagrams showing water types in wells completed in the Canadian River 

alluvial aquifer, Oklahoma, in 2013 ..........................................................................................20

14. Graph showing stream base-flow measurements from the March 2013 seepage 

run conducted for the Canadian River alluvial aquifer and underlying bedrock 

units ..............................................................................................................................................22

15. Graphs showing average annual Base-Flow Index for streamgages along the 

Canadian River, Oklahoma, 1981–2013 ...................................................................................24

16. Graphs showing annual recharge from 1981 to 2013 by using the soil-waterbalance (SWB) code for A, Reach I; B, Reach II; and C, Reaches I and II of the 

Canadian River alluvial aquifer, Oklahoma ............................................................................27

17. Graphs showing observed and simulated depth to water for water-table 

observations in Oklahoma Water Resources Board (OWRB) wells A, 9666, and 

B, 9591, in the Canadian River alluvial aquifer, Oklahoma ..................................................29

18. Graphs showing observed and simulated water-table altitudes for A, Reach I, 

and C, Reach II, and histograms showing water-table residuals for B, Reach I, 

and D, Reach II, of the Canadian River alluvial aquifer, Oklahoma ...................................36

19. Graph showing observed streamflow, observed stream base flow, and 

simulated stream base flow at the Canadian River at Bridgeport, Oklahoma 

streamgage (07228500) for Reach I of the Canadian River alluvial aquifer, 

Oklahoma, 1981–2013 ................................................................................................................38
viii

20. Graph showing observed and simulated average stream base flow, estimated 

average base-flow gain, simulated average base-flow gain, and confidence 

intervals for Reach I and Reach II of the Canadian River alluvial aquifer, 

Oklahoma, 1981–2013 ................................................................................................................39

21. Graphs showing observed streamflow, observed stream base flow, and 

simulated stream base flow at the Canadian River at A, Norman, Oklahoma 

(07229050); B, Canadian River at Purcell, Oklahoma (07229200); and C, Canadian 

River at Calvin, Oklahoma (07231500), streamgages for Reach II of the Canadian 

River alluvial aquifer, Oklahoma, 1981–2013 ..........................................................................40

22. Graphs showing average monthly aquifer inflow, outflow, and change in 

storage for A, Reach I, and B, Reach II, of the Canadian River alluvial aquifer, 

Oklahoma, 1981–2013 ................................................................................................................44

23. Graphs showing precalibration recharge, calibrated recharge, and average 

recharge multipliers for A, Reach I, and B, Reach II, of the Canadian River 

alluvial aquifer, Oklahoma, 1981–2013 ....................................................................................45

24. Graphs showing calibrated average parameter zone values and ranges for A, Reach I, and B, Reach II of the Canadian River alluvial aquifer, 1981–2013 ...............46

25. Bar charts showing observation group sensitivity by parameter group in the 

numerical groundwater-flow models for A, Reach I, and B, Reach II, of the 

Canadian River alluvial aquifer, Oklahoma ............................................................................48

26. Graphs showing percentage of A, Reach I, and B, Reach II, of the Canadian 

River alluvial aquifer, Oklahoma, with less than 5 feet of saturated thickness 

after 20 years of continuous equal-proportionate-share groundwater pumping ...........50

27. Graphs showing net change in groundwater in storage and groundwater 

pumping for A, Reach I, and B, Reach II, of the Canadian River alluvial aquifer, 

Oklahoma, during 20 years of continuous equal-proportionate-share 

groundwater pumping ...............................................................................................................52

28. Graphs showing percentage of A, Reach IIa, and B, Reach IIb, of the Canadian 

River alluvial aquifer, Oklahoma, with less than 5 feet of saturated thickness 

after 20 years of continuous equal-proportionate-share groundwater pumping ...........53

29. Graph showing changes in stream base flow in Reach I of the Canadian River 

at the Bridgeport, Oklahoma streamgage (07228500) during a hypothetical 

10-year drought for the Canadian River alluvial aquifer, Oklahoma ..................................55

30. Graphs showing changes in stream base flow in Reach II of the Canadian River 

at A, Purcell, Oklahoma (07229200), and B, Calvin, Oklahoma (07231500), 

streamgages during a hypothetical 10-year drought for the Canadian River 

alluvial aquifer, Oklahoma ........................................................................................................56

31. Graphs showing change in groundwater storage during a hypothetical 10-year 

drought in A, Reach I, and B, Reach II, for the Canadian River alluvial aquifer, 

Oklahoma ....................................................................................................................................57
ix

Tables

1. Data collection time periods of average annual precipitation at selected 

cooperative observer climate stations used in the Canadian River alluvial aquifer 

study area .....................................................................................................................................5

2. Reported annual groundwater-use statistics for the Canadian River alluvial 

aquifer, Oklahoma, 1967–2013 ....................................................................................................7

3. Summary statistics of water-quality constituent values for groundwater samples 

collected August–September 2013 from the Canadian River alluvial aquifer, 

Oklahoma ....................................................................................................................................18

4. Summary statistics of daily-averaged monthly streamflow and Base-Flow 

Index (BFI) stream base flow at streamgages in the Canadian River alluvial 

aquifer study area ......................................................................................................................21

5. Conceptual water budget for the Canadian River alluvial aquifer, Oklahoma, 

1981–2013 ....................................................................................................................................28

6. Components of the objective function prior to calibration by using parameter 

estimation for Reach I and Reach II of the Canadian River alluvial aquifer, 

Oklahoma ....................................................................................................................................33

7. Comparison of observed and simulated water-table altitudes for the Canadian 

River alluvial aquifer, Oklahoma, 1981–2013 ..........................................................................37

8. Comparison of observed and simulated average stream base flow for the 

Canadian River alluvial aquifer, Oklahoma, 1981–2013 ........................................................38

9. Average annual water budget for the Reach I and Reach II numerical 

groundwater-flow models of the Canadian River alluvial aquifer, Oklahoma, 

1981–2013 ....................................................................................................................................41

10. Numerical groundwater-flow model annual calibrated water budget for Reach I 

of the Canadian River alluvial aquifer, Oklahoma, 1981–2013 ............................................42

11. Numerical groundwater-flow model annual calibrated water budget for Reach II 

of the Canadian River alluvial aquifer, Oklahoma, 1981–2013 ............................................43

12. Equal-proportionate-share pumping for Reach I and Reach II of the Canadian 

River alluvial aquifer, Oklahoma ..............................................................................................51

13. Changes in groundwater storage after 50 years of groundwater pumping at 

the 2013 rate for the Canadian River alluvial aquifer, Oklahoma .......................................54
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 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

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

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

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)

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)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32) / 1.8.

Datum

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

(NAVD 88).

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.
xi

Abbreviations

BFI base-flow index

DEM digital elevation model

EPS equal proportionate share

ET evapotranspiration

GHB General Head Boundary

HPT Hydraulic Profiling Tool

IDW Inverse Distance Weighting

MAY maximum annual yield

NHDPlus National Hydrography Dataset

NWIS National Water Information System

OWRB Oklahoma Water Resources Board

PEST parameter estimation

RMSE root-mean-square error

SFR Streamflow-Routing Package version 2

SVDA singular value decomposition-assist

SWB soil-water balance

USGS U.S. Geological Survey

WTF water-table fluctuation

Hydrogeology and Simulation of Groundwater Flow and 

Analysis of Projected Water Use for the Canadian River 

Alluvial Aquifer, Western and Central Oklahoma

By John H. Ellis, Shana L. Mashburn, Grant M. Graves, Steven M. Peterson, S. Jerrod Smith, Leland T. Fuhrig, 

Derrick L. Wagner, and Jon E. Sanford

Abstract

This report describes a study of the hydrogeology and 

simulation of groundwater flow for the Canadian River 

alluvial aquifer in western and central Oklahoma conducted 

by the U.S. Geological Survey in cooperation with the 

Oklahoma Water Resources Board. The report (1) quantifies 

the groundwater resources of the Canadian River alluvial 

aquifer by developing a conceptual model, (2) summarizes the 

general water quality of the Canadian River alluvial aquifer 

groundwater by using data collected during August and 

September 2013, (3) evaluates the effects of estimated equal 

proportionate share (EPS) on aquifer storage and streamflow 

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

using numerical groundwater-flow models, and (4) evaluates 

the effects of present-day groundwater pumping over a 

50-year period and sustained hypothetical drought conditions 

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

in storage by using numerical flow models. The Canadian 

River alluvial aquifer is a Quaternary-age alluvial and terrace 

unit consisting of beds of clay, silt, sand, and fine gravel 

sediments unconformably overlying Tertiary-, Permian-, and 

Pennsylvanian-age sedimentary rocks. For groundwater-flow 

modeling purposes, the Canadian River was divided into 

Reach I, extending from the Texas border to the Canadian 

River at the Bridgeport, Okla., streamgage (07228500), and 

Reach II, extending downstream from the Canadian River 

at the Bridgeport, Okla., streamgage (07228500), to the 

confluence of the river with Eufaula Lake. The Canadian River 

alluvial aquifer spans multiple climate divisions, ranging from 

semiarid in the west to humid subtropical in the east. The 

average annual precipitation in the study area from 1896 to 

2014 was 34.4 inches per year (in/yr).

A hydrogeologic framework of the Canadian River 

alluvial aquifer was developed that includes the areal and 

vertical extent of the aquifer and the distribution, texture 

variability, and hydraulic properties of aquifer materials. The 

aquifer areal extent ranged from less than 0.2 to 8.5 miles 

wide. The maximum aquifer thickness was 120 feet (ft), and 

the average aquifer thickness was 50 ft. Average horizontal 

hydraulic conductivity for the Canadian River alluvial aquifer 

was calculated to be 39 feet per day, and the maximum 

horizontal hydraulic conductivity was calculated to be 100 feet 

per day.

Recharge rates to the Canadian River alluvial aquifer 

were estimated by using a soil-water-balance code to estimate 

the spatial distribution of groundwater recharge and a watertable fluctuation method to estimate localized recharge rates. 

By using daily precipitation and temperature data from 

39 climate stations, recharge was estimated to average 

3.4 in/yr, which corresponds to 8.7 percent of precipitation as 

recharge for the Canadian River alluvial aquifer from 1981 to 

2013. The water-table fluctuation method was used at one site 

where continuous water-level observation data were available 

to estimate the percentage of precipitation that becomes 

groundwater recharge. Estimated annual recharge at that site 

was 9.7 in/yr during 2014. 

Groundwater flow in the Canadian River alluvial aquifer 

was identified and quantified by a conceptual flow model for 

the period 1981–2013. Inflows to the Canadian River alluvial 

aquifer include recharge to the water table from precipitation, 

lateral flow from the surrounding bedrock, and flow from 

the Canadian River, whereas outflows include flow to the 

Canadian River (base-flow gain), evapotranspiration, and 

groundwater use. Total annual recharge inflows estimated 

by the soil-water-balance code were multiplied by the area 

of each reach and then averaged over the simulated period 

to produce an annual average of 28,919 acre-feet per year 

(acre-ft/yr) for Reach I and 82,006 acre-ft/yr for Reach 

II. Stream base flow to the Canadian River was estimated 

to be the largest outflow of groundwater from the aquifer, 

measured at four streamgages, along with evapotranspiration 

and groundwater use, which were relatively minor discharge 

components. 

Objectives for the numerical groundwater-flow models 

included simulating groundwater flow in the Canadian River 

alluvial aquifer from 1981 to 2013 to address groundwater 

use and drought scenarios, including calculation of the EPS 

pumping rates. The EPS for the alluvial and terrace aquifers 

is defined by the Oklahoma Water Resources Board as the 

amount of fresh water that each landowner is allowed per year 

per acre of owned land to maintain a saturated thickness of 
2 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

at least 5 ft in at least 50 percent of the overlying land of the 

groundwater basin for a minimum of 20 years. 

The groundwater-flow models were calibrated to watertable altitude observations, streamgage base flows, and 

base-flow gain to the Canadian River. The Reach I watertable altitude observation root-mean-square error was 6.1 ft, 

and 75 percent of residuals were within ±6.7 ft of observed 

measurements. The average simulated stream base-flow 

residual at the Bridgeport streamgage (07228500) was 

8.8 cubic feet per second (ft3/s), and 75 percent of residuals 

were within ±30 ft3/s of observed measurements. Simulated 

base-flow gain in Reach I was 8.8 ft3/s lower than estimated 

base-flow gain. The Reach II water-table altitude observation 

root-mean-square error was 4 ft, and 75 percent of residuals 

were within ±4.3 ft of the observations. The average simulated 

stream base-flow residual in Reach II was between 35 and 

132 ft3/s. The average simulated base-flow gain residual in 

Reach II was between 11.3 and 61.1 ft3/s.

Several future predictive scenarios were run, including 

estimating the EPS pumping rate for 20-, 40-, and 50-year 

life of basin scenarios, determining the effects of current 

groundwater use over a 50-year period into the future, 

and evaluating the effects of a sustained drought on water 

availability for both reaches. The EPS pumping rate was 

determined to be 1.35 acre-feet per acre per year ([acre-ft/

acre]/yr) in Reach I and 3.08 (acre-ft/acre)/yr in Reach II for 

a 20-year period. For the 40- and 50-year periods, the EPS 

rate was determined to be 1.34 (acre-ft/acre)/yr in Reach I and 

3.08 (acre-ft/acre)/yr in Reach II. Storage changes decreased 

in tandem with simulated groundwater pumping and were 

minimal after the first 15 simulated years for Reach I and the 

first 8 simulated years for Reach II.

Groundwater pumping at year 2013 rates for a period of 

50 years resulted in a 0.2-percent decrease in groundwaterstorage volumes in Reach I and a 0.6-percent decrease in the 

groundwater-storage volumes in Reach II. The small changes 

in storage are due to groundwater use by pumping, which 

composes a small percentage of the total groundwater-flow 

model budgets for Reaches I and II.

A sustained drought scenario was used to evaluate the 

effects of a hypothetical 10-year drought on water availability. 

A 10-year period was chosen where the effects of drought 

conditions would be simulated by decreasing recharge by 

75 percent. In Reach I, average simulated stream base flow 

at the Bridgeport streamgage (07228500) decreased by 58 

percent during the hypothetical 10-year drought compared to 

average simulated stream base flow during the nondrought 

period. In Reach II, average simulated stream base flows at 

the Purcell streamgage (07229200) and Calvin streamgage 

(07231500) decreased by 64 percent and 54 percent, 

respectively. In Reach I, the groundwater-storage drought 

scenario resulted in a storage decline of 30 thousand acre-feet, 

or an average decline in the water table of 1.2 ft. In Reach II, 

the groundwater-storage drought scenario resulted in a storage 

decline of 71 thousand acre-feet, or an average decline in the 

water table of 2.0 ft.

Introduction

The Canadian River alluvial aquifer in western and 

central Oklahoma is an unconfined alluvial aquifer derived 

from erosion and redeposition of sediments by the river 

that are composed of clay, silt, sand, and fine gravel (pl. 1). 

The Canadian River alluvial aquifer underlies the Canadian 

River, which originates in Colorado, flows through New 

Mexico and Texas, and then flows into Oklahoma to 

Eufaula Lake in McIntosh County, Oklahoma (fig. 1). 

Groundwater in approximately 606 square miles (mi2) of 

this aquifer is used for irrigation, municipal use, mining 

(oil and gas), livestock, and domestic supply. Groundwater 

from the Canadian River alluvial aquifer is used by several 

municipalities including Lexington, Noble, and Tuttle, Okla. 

(Oklahoma Water Resources Board, 2012a). Flow in the 

Canadian River has been regulated since 1964 by Sanford 

Dam (fig. 1), which impounds Lake Meredith in Hutchinson 

County, Tex. 

The 1973 Oklahoma Water Law (82 OK Stat 

§ 82-1020.5) requires the Oklahoma Water Resources 

Board (OWRB) to conduct hydrologic surveys of the State’s 

aquifers to determine the maximum annual yield (MAY) 

over the life of the basin. The MAY is the total amount of 

fresh groundwater that may be pumped from a groundwater 

basin for a minimum 20-year life of such basin. The equalproportionate-share (EPS) is the MAY of groundwater 

allocated to each acre of land overlying the basin. The 

life of the basin is the period of time during which at least 

50 percent of the total overlying land will retain a saturated 

thickness, allowing pumping of the MAY for a minimum 

20-year life of the basin. Saturated thickness for alluvial 

and terrace aquifers shall remain at least 5 feet (ft) by law. 

To determine the MAY of a major groundwater basin, an 

investigation is conducted to obtain data and information 

related to the geology, hydrogeologic framework, and 

hydrogeology of an aquifer. A numerical groundwater-flow 

model can be developed by using these data and information 

to conceptualize the flow system and evaluate effects of 

water use on the aquifer. The study described in this report to 

evaluate the Canadian River alluvial aquifer was a cooperative 

effort between the U.S. Geological Survey (USGS) and the 

OWRB. 

The objectives of the study were to (1) conduct a 

hydrologic survey to quantify the groundwater resources of the 

Canadian River alluvial aquifer by using groundwater-level 

and streamflow data collected during 2013–16 and 1981–2013, 

respectively; (2) summarize the general water quality of the 

Canadian River alluvial aquifer groundwater; (3) evaluate the 

effects of estimated EPS on aquifer storage and streamflow; 

and (4) evaluate the effects of present-day groundwater 

pumping and sustained hypothetical drought conditions on 

stream base flow and groundwater in storage. The scope of this 

study was the Canadian River alluvial aquifer and adjoining 

bedrock units.
COLORADO

KANSAS

NEW MEXICO

OKLAHOMA

TEXAS

Amarillo

Oklahoma

City

Tu

Wichita

Amarillo

Oklahoma

City

Tu

Wichita

SANFORD DAMSANFORD DAM

Central

Oklahoma Climate

Division 5

West central

Oklahoma Climate

Division 4

Central

Oklahoma Climate

Division 5

West central

Oklahoma Climate

Division 4

104° 102° 100° 98° 

37°36°35°34°

Base modified from U.S Geological Survey digital dataAlbers Equal-Area Conic projectionNorth American Datum of 1983

0 50 100 150

0 50 100 150

200 MILES

200 KILOMETERS

USGS

Camargo well

TALOGA

07229050

Boundary of climate divisions (Oklahoma Climatological Survey, 2015f)Boundary of Canadian River watershed upstream from Eufaula, Okla.U.S. Geological Survey (USGS) streamgage and number (U.S. Geological Survey, 2013a)Climate station and identifier (National Climatic Data Center, 2015; Oklahoma Climatological Survey, 2015e)USGS continuous recorder well and name

EXPLANATION

Canadian River

Lake

Meredith

Red River

Canadian River

Lake

Meredith

Red River

Beaver Harper

Cimarron Woods

Grant Kay Alfalfa Texas

Woodward 

Noble Garfield Ellis Major 

Payne Blaine

Kingfisher

Dewey

Logan 

Roger Mills 

Lincoln

Custer

Canadian

Okfuske

Beckham Caddo Seminole Washita 

Grady

Hug

Kiowa Greer

Harmon Pontotoc Jackson Comanche Garvin Coal

Stephens

Tillman Murray

Cotton Carter Johnston Jefferson

Pottawatomie McClain

Creek

Pawnee

Osage

Cleveland

Hutchinson

TALOGA

NORMAN3 SSE

07227500

07228000

07228500

07229050

07229200

07227500

07228000

07228500

07229050

07229200

USGS

Camargo well

Canadian River

watershed upstream

from Eufaula, Okla.

NEW

MEXICO

COLORAD

Reach I extends from the Texas border to the Bridgeport seepage-run site and streamgage (07228500);Reach II extends from the Bridgeport seepage-run site to Eufaula Lake; Reach IIa extends from the Bridgeportseepage-run site to the eastern boundary of Cleveland County; Reach IIb extends from the eastern boundary ofCleveland County to Eufaula Lake.

Figure 1. Extent of the Canadian River watershed upstream from Eufaula, Oklahoma, and climate divisions, climate stations, and streamgages.
4 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Purpose and Scope

The purpose of this report is to describe the hydrogeology 

and simulation of groundwater flow for the Canadian River 

alluvial aquifer in western and central Oklahoma. The report 

(1) quantifies the groundwater resources of the Canadian 

River alluvial aquifer by developing a conceptual model; 

(2) summarizes the general water quality of the Canadian 

River alluvial aquifer groundwater by using data collected 

during August and September 2013; (3) evaluates the effects 

of estimated EPS on aquifer storage and streamflow for 

time periods of 20, 40, and 50 years into the future by using 

numerical groundwater-flow models; and (4) evaluates the 

effects of present-day groundwater pumping over a 50-year 

period and sustained hypothetical drought conditions over 

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

storage by using numerical flow models. 

Study Area Description

The study area is the extent of the Canadian River alluvial 

aquifer in Oklahoma from the Texas border to Eufaula Lake, 

as well as the adjoining bedrock units as shown in plate 1. The 

Canadian River alluvial aquifer underlies approximately 606 

mi2 of land in 14 Oklahoma counties along the Canadian River 

from the Texas border to Eufaula Lake (fig. 1). The western 

part of the study area near the Texas border is characterized 

by gently sloping hills surrounding the bends of the Canadian 

River (Kitts and Black, 1959). The central part of the study 

area contains grass-covered plains and sandstone hills (Wood 

and Burton, 1968). The eastern part of the study area consists 

of grass-covered plains and northeast-trending cuestas cut 

by stream valleys (Weaver, 1954). The study area includes 

substantial changes in elevation from west to east, ranging 

from 2,150 ft above the North American Vertical Datum of 

1988 (NAVD 88) in the west (Kitts and Black, 1959) to about 

500 ft above NAVD 88 near Eufaula Lake (Oakes and Koontz, 

1967). 

For the study described in this report, the Canadian River 

alluvial aquifer was divided into two sections: Reach I, which 

is 242 mi2 and extends from the Texas border to the Canadian 

River at the Bridgeport, Okla., streamgage (07228500); and 

Reach II, which is 364 mi2 and extends from the Canadian 

River at the Bridgeport, Okla., streamgage (07228500) to 

Eufaula Lake (fig. 1). 

Land Use

Land-use data for the Canadian River alluvial aquifer 

were obtained from the CropScape database (National 

Agricultural Statistics Service, 2015) (fig. 2). That database 

includes information about land-use characteristics at a 

30-meter resolution. Land uses overlying the total reported 

alluvial aquifer area of approximately 388,000 acres (606 

mi2) were composed of grass/pasture (52.3 percent), crops 

(23.7 percent), and forest (13.3 percent) in 2015. The 

remaining acreage included developed land (4.2 percent), 

shrubs (1.9 percent), and other uses (4.7 percent). The crops 

grown in this area were mostly winter wheat (61.3 percent of 

the total crop area) and alfalfa or other hay (17.9 percent of the 

total crop area). Corn, soybeans, and cotton were each grown 

in less than 4 percent of the total crop area. About 4 percent 

of the total crop area was fallow or idle, and 7.1 percent of the 

total crop area was allocated to other crops.

4.4

3.9

2.9

2.5

7.1

Winter

wheat

61.3

Soybeans (2.9)

Cotton (2.5)

Fallow/idle

Other crops

Forest

13.3

4.2

4.7 Other

Developed

Shrubs Grass/pasture 1.9

52.3

Crops

23.7

Alfalfa or

other hay

17.9 Corn

Crop type, 2010–15, in percent

Total area: 92,000 acres

Land cover type, in percent

Total area: 388,000 acres

Land cover type, 2015 (CropScape, National

 Agriculture Statistics Service, 2015)

 Developed

 Barren

 Forest

 Shrubs

 Grass/pasture

 Other (water, wetland, barren)

 Crops

 Winter wheat

 Alfalfa or other hay

 Corn

 Soybeans

 Cotton

 Fallow/idle

 Other crops

EXPLANATION

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

Figure 2. Land cover and crop types on the Canadian River alluvial aquifer, Oklahoma.
Introduction 5

Climate

Climate in the area underlain by the Canadian River 

alluvial aquifer ranges from semiarid in the western part of 

the study area to humid subtropical in the eastern part of the 

study area (Oklahoma Climatological Survey, 2015a). Average 

annual precipitation and temperatures generally increase from 

west to east across the aquifer (Oklahoma Climatological 

Survey, 2015a). Daily air temperatures ranged from 44.4 to 

71.6 degrees Fahrenheit (°F) in Roger Mills County, from 49.7 

to 72.7 °F in Cleveland County, and from 52.2 to 72.8 °F in 

McIntosh County (Oklahoma Climatological Survey, 2015b, 

2015c, and 2015d).

Climate data for three cooperative observer stations 

distributed across the extent of the Canadian River alluvial 

aquifer were obtained from the Oklahoma Climatological 

Survey’s Web site (Oklahoma Climatological Survey, 

2015e). These stations were chosen for data representing 

long-term climate conditions for the western, central, and 

eastern parts of the aquifer. The three stations used in this 

study were Taloga (western), Norman 3SSE (central), 

and Sallisaw 2 NW (eastern) (fig. 1, table 1). Some data 

were missing from the periods of record of these stations, 

and data from years containing less than 10 months of 

precipitation data were omitted from the calculation of 

average precipitation. Average annual precipitation increased 

by 2.5 inches per year (in/yr). during the period 1981–2014 

compared to 1947–80 (table 1). 

Table 1. Data collection time periods of average annual 

precipitation at selected cooperative observer climate stations 

used in the Canadian River alluvial aquifer study area.

[Data from Oklahoma Climatological Survey, 2015e. All units are in inches 

per year]

Station 

number

Station 

name

Period 

of 

record1

Number 

of 

years

1947–80 

average

1981–

2014 

average

8708 TALOGA 1900–

2015

66 25.8 27.3

6386 NORMAN 3SSE 1895–

2015

101 34.7 37.4

7862 SALLISAW 2NW 1893–

2015

81 45.0 48.4

Average 35.2 37.7

1

Not continuous.

Average annual precipitation in the study area from 

1896 to 2014 was 34.4 in/yr. (fig. 3). Precipitation trends 

indicate (1) below-average precipitation from the late 1890s 

through the early 1920s, (2) above-average precipitation from 

the late 1920s to the late 1940s, (3) variable precipitation 

between 1950 and the early 1980s, (4) above-average 

precipitation from the mid-1980s to 2010, and (5) belowaverage precipitation from 2010 to 2014 (fig. 3). On average, 

the greatest amounts of precipitation occurred in May, and the 

least amounts occurred in January (fig. 4).

Reported Water Use

Water use in Oklahoma is regulated by the OWRB, and 

permitted water users are required to submit annual water-use 

reports to the OWRB. Water use was reported for 754 permits 

submitted to the OWRB by permitted groundwater users of 

the Canadian River alluvial aquifer for the 1967–2013 period 

(Oklahoma Water Resources Board, 2015a).

The average annual groundwater use from 1967 to 

2013 was 11,887 acre-feet per year (acre-ft/yr) (table 2). 

The annual groundwater-use data show a period of greater 

use during the period of 1967–79, followed by a period of 

lower use during 1980–99 (fig. 5). During 2000–13, there 

was an increasing trend in groundwater use, with a peak of 

23,380 acre-ft/yr in 2012 (fig. 5, table 2). The average annual 

groundwater use decreased from 12,919 acre-ft/yr during the 

period of 1967–79 to 9,392 acre-ft/yr during 1980–99 (fig. 5, 

table 2). That decrease may be a result of a change in the 

method of groundwater use reporting in 1980. Prior to 1980, 

irrigation use was based on crop type, acres, and frequency 

of application (Oklahoma Water Resources Board, 2002). In 

1980, the method was changed to include inches applied to 

increase accuracy (Oklahoma Water Resources Board, 2002). 

Average annual groundwater use increased to 14,461 acre-ft/yr 

during the period of 2000–13 (fig. 5, table 2).

The greatest average groundwater use during the period 

of 1967–2013 was for irrigation, with 8,476 acre-ft/yr, or 

about 71.3 percent of average groundwater use (fig. 5). Public 

supply was the second largest use of groundwater during 

the period of 1967–2013, with 2,466 acre-ft/yr, or about 

20.7 percent (fig. 5). The power, mining, and recreation, fish, 

wildlife use types combined accounted for 799 acre-ft/yr, or 

about 6.7 percent of groundwater use (fig. 5). All other use 

types, which includes self-supplied domestic, composed only 

146 acre-ft/yr, or about 1.2 percent of groundwater use, during 

the period of 1967–2013.
6 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Year

Number of stations

0

10

20

30

40

50

60

70

Precipitation, in inches per year

0

1

2

3

4

119-year average = 34.4 inches

Above historical average (5-year moving average)

Below historical average (5-year moving average)

Annual precipitation

EXPLANATION

[Precipitation data for the Taloga, Norman 3SSE, and

Sallisaw 2 NW cooperative observer stations]

Figure 3. Average annual precipitation for the period 1896–2014, 5-year moving average, and the number of cooperative observer 

stations recording during each year in the Canadian River alluvial aquifer study area.

0

2

4

6

Average precipitation, in inches per month

Month

January February March April May June July August September October November December

1947–80

1981–2014

EXPLANATION

Figure 4. Average monthly precipitation during the time periods of 1947–80 and 1981–2014 for the Taloga, Norman 3SSE, and Sallisaw 2 

NW cooperative observer stations in the Canadian River alluvial aquifer study area.
Introduction 7

Table 2. Reported annual groundwater-use statistics for the 

Canadian River alluvial aquifer, Oklahoma, 1967–2013.

Reported annual groundwater use 

(acre-feet per year)

Statistic 1967–2013 1967–79 1980–99 2000–13

Average 11,887 12,919 9,392 14,461

Median 11,019 12,705 9,121 12,679

Minimum 6,763 8,088 6,763 9,562

Maximum 23,380 17,891 13,648 23,380

19671968196919701971197219731974197519761977197819791980

1981198219831984198519861987198819891990199119921993199419951996

1997

199819992000

2001

20022003

2004

2005

2006

2007

2008

2009201020112012

2013

Year

0

5,000

10,000

15,000

20,000

25,000

Reported groundwater use, in acre-feet per year

30,000

Industrial

(0.6 percent)

72 acre-feet per year

Power

(3.3 percent)

393 acre-feet per year

Mining

(1.8 percent)

213 acre-feet per year

Commercial

(0.1 percent)

13 acre-feet per year

Recreation, fish, wildlife

(1.6 percent)

193 acre-feet per year

Agriculture

(0.2 percent)

28 acre-feet per year

Other

(0.3 percent)

33 acre-feet per year

Irrigation

(71.3 percent)

8,476 acre-feet per year

Public supply

(20.7 percent)

2,466 acre-feet per year

Groundwater use, by type

 Irrigation

 Public supply

 Industrial

 Power

 Mining

 Commercial

 Recreation, fish, wildlife

 Agriculture

 Other

EXPLANATION

Figure 5. Groundwater use by type for the Canadian River alluvial aquifer, Oklahoma, 1967–2013.
8 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Geology of the Canadian River Alluvial 

Aquifer

The geologic units in the study area include Quaternaryage alluvial and terrace deposits of the Canadian River 

alluvial aquifer and Tertiary-, Permian-, and Pennsylvanianage sedimentary bedrock (pl. 1, fig. 6). The clay, silt, sand, 

and fine gravel sediment of the alluvial and terrace deposits 

unconformably overlie the bedrock units.

Quaternary-Age Alluvial and Terrace Deposits

The Canadian River alluvial aquifer originated as the 

Rocky Mountains were uplifted (Fay and others, 1962), with 

the river channel developing in outwash during subsequent 

continental glaciation and regression of the Pleistocene Epoch 

(Johnson and Luza, 2008). Downcutting of the river channel 

occurred, forming major valleys through the Permian-age 

bedrock units, possibly along the path of older stream channels 

(Fay and others, 1962). These valleys were gradually filled 

with sand and fine gravel eroded from the Rocky Mountains 

or the Tertiary-age Ogallala Formation (Hendricks, 1937). 

Multiple deposition and erosion cycles continued with streams 

cutting through and removing previously deposited material 

followed by infill from older terrace deposits and bedrock 

sediment (Davis, 1955). During years of slow glacial ice 

melt, older alluvial sediment remained to form various terrace 

shelves (Fay and others, 1962).

In the present-day alluvial flood plain, sediment with 

a total thickness up to 100 ft (Oakes and Koontz, 1967) 

constitutes the majority of aquifer material deposited during 

the most recent cycle of downcutting of the river (Davis, 

1955). The alluvial deposits in western Oklahoma primarily 

consist of sand and fine gravel with traces of clay and caliche 

(Mogg and others, 1960). Substantial meanders in the 

alluvial deposits are present in western Oklahoma and form 

the boundaries for Roger Mills County and Dewey County. 

The sand and fine gravel are typically composed of quartz 

with varying amounts of quartzite, chert, flint, jasper, and 

mineralized wood (Davis, 1955). The Canadian River alluvial 

deposits in western Oklahoma overlie the Rush Springs and 

Marlow Formations and closely follow the southeastern 

strike of the Permian-age beds, a trend that continues through 

Oklahoma County (Wood and Burton, 1968). The streamchannel gradient in western Oklahoma is between 4 and 5 feet 

per mile (ft/mi) (Kitts and Black, 1959; Fay and others, 1962).

The alluvial deposits average 2 miles (mi) in width in 

central Oklahoma and widen to approximately 3 mi in width 

northwest of Norman (Wood and Burton, 1968). Alluvial 

deposits in central Oklahoma contain an abundance of quartz, 

quartzite, chert, flint, jasper, and silicified wood (Davis, 1955). 

The alluvial channel dissects sandstone hills with relief from 

50 to 200 ft (Wood and Burton, 1968). 

In east-central Oklahoma, incised meanders of the 

Canadian River are present, possibly because of low 

topographic relief (Tanner, 1956). This area has a poorly 

defined flood plain of less than a mile in width (Tanner, 

1956). In contrast to western Oklahoma, the river and 

surrounding alluvial deposits in east-central Oklahoma cross 

the strike of the underlying bedrock at right angles, with the 

exception of an area near the confluence of the Canadian 

River and Little River (Tanner, 1956), which is located about 

52 miles upstream from Eufaula Lake in Hughes County 

(pl. 1). 

Three distinct terrace shelves (high, intermediate, and 

low) occur along the Canadian River from Roger Mills County 

in the west to Hughes County in the east, ranging from more 

than 220 ft to less than 15 ft above the alluvial flood plain 

(Weaver, 1954; Kitts and Black, 1959). In western Oklahoma, 

the high and intermediate terraces are eroded on the northern 

side of the river in Roger Mills County (Kitts and Black, 1959) 

but are still present towards the east through Dewey County 

and Blaine County. In central Oklahoma, two or three sets of 

terrace shelves occur along the river, for a total thickness of 

up to 100 ft (Wood and Burton, 1968). The high terrace units 

occur in well-exposed bluffs and are easily distinguishable 

from underlying Permian-age units by color and composition; 

the low terrace can be distinguished from nearby alluvial 

deposits, with difficulty in some areas (Mogg and others, 

1960). 

In eastern Oklahoma, the slow erosional rate that forms 

terrace shelves did not regularly occur, resulting in lessdefined terrace shelves, although three distinct terraces occur 

in some areas (Weaver, 1954).

Eolian dune sands, which have been shifted by southerly 

winds, occur in the terrace units throughout the study 

area. Dune sand is typically above the water table and not 

a separate zone or unit of the aquifer, but because of the 

high permeability, dune sand can facilitate infiltration of 

precipitation and thus increase recharge to the aquifer (Wood 

and Burton, 1968).

Bedrock Units

The bedrock underlying and surrounding the Canadian 

River alluvial aquifer is composed of Tertiary-, Permian-, and 

Pennsylvanian-age units (pl. 1, fig. 6). Outcrops occur in the 

alluvial and terrace deposits where the bedrock surface has 

been exposed by weathering or other events. 
Geology of the Canadian River Alluvial Aquifer 9

System Hydrogeologic 

unit Group Formation Thickness (feet) Description

Quaternary Canadian River 

alluvial aquifer

Alluvial, terrace, and dune 

deposits 0–120 Silt, sand, and clay deposited by the Canadian River and tributaries

Tertiary High Plains

(Ogallala) aquifer Ogallala Formation 1

0–400 Brown to light tan, mostly unconsolidated clay, silt, sand, 

and gravel with zones of caliche near the surface

Permian

Cloud Chief Formation 20–100 Reddish-brown to orange-brown shale interbedded with 

Red to pink massive very-fine-grained gypsiferous

 sandstone

siltstone and sandstone, and dolomite

Rush Springs 

aquifer

Whitehorse 

Group

Rush 

Springs

2

0–300 Formation 

Marlow 

Formation gypsiferous

El Reno Group

Dog Creek 

Shale 2

0–190 Red, brown, and green gypsiferous shales with several 

beds of siltstone, sandstone, and dolomite

Blaine 

Formation 2

0–100 Beds of white gypsum and thin beds of gray mediumgrained dolomite or dolomitic limestone

Chickasha 

Formation 3

150–200 Mudstone conglomerate and red-brown to orange-brown 

silty shale and siltstone

Duncan 

Sandstone 3

150–200 mudstone conglomerate and shale

Hennessey Group 3

600–650 Mostly reddish-brown shale with reddish-brown to 

Cross-bedded fine-grained sandstone with interbedded

 shale and mudstone

reddish-orange siltstone

Central Oklahoma 

(GarberWellington) 

aquifer

Sumner 

Group

Garber 

Sandstone 3

0–400

Wellington 

Formation 3

0–700 Mostly reddish-brown shale with reddish-brown to 

reddish-orange siltstone

Chase, Council Grove, and 

Admire Groups 4

0–500+ grained sandstone with shale and siltstone

Pennsylvanian

Vanoss Formation 50–250 arkosic sandstone

Vamoosa-Ada 

aquifer

Ada Formation 5

0–100

Vamoosa Formation 5125 Alternating layers of shale, sandstone, and chert 

conglomerates

Pre-Vamoosa bedrock units, 

undifferentiated 5

36–680 Shale, with sandstone and limestone

1

Morton, 1980.

Modified from Miser, 1954.

2

Fay and others, 1962.

3

Wood and Burton, 1968.

4

Christenson and others, 1992.

5

Tanner, 1956.

Figure 6. Geologic and hydrogeologic units of the Canadian River alluvial aquifer study area.
10 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Tertiary-Age Bedrock Units

In the western part of Roger Mills County, the Canadian 

River alluvial aquifer unconformably overlies the Tertiary-age 

Ogallala Formation, the principal geologic unit of the High 

Plains (Ogallala) aquifer. The Ogallala Formation consists 

of fine- to medium-grained, well-sorted, yellow-brown 

quartz sands with calcium-carbonate cement present in small 

quantities (Kitts and Black, 1959). The average thickness of 

the Ogallala Formation in the study area is approximately 

150 ft, and the maximum thickness is approximately 400 ft 

(Morton, 1980). The Ogallala Formation rests unconformably 

on Permian-age formations (Kitts and Black, 1959). In Roger 

Mills County, the Ogallala Formation and high terrace contact 

is 140–160 ft above the Canadian River alluvial flood plain 

(Kitts and Black, 1959). 

Permian-Age Bedrock Units

The Permian-age bedrock units underlying the Canadian 

River alluvial aquifer in western and central Oklahoma are 

commonly referred to as “red beds” because of the distinctive 

red color that comes from sandstone containing iron-oxide 

minerals (Breit, 1998). Four bedrock units underlie the 

Canadian River alluvial aquifer between Roger Mills County 

and western Canadian County, including the Cloud Chief, 

Rush Springs, and Marlow Formations, and the Dog Creek 

Shale (pl. 1, fig. 6). The Cloud Chief Formation consists of 

gypsum-cemented shale and siltstone, and minor amounts of 

fine sandstone. In Dewey County, the Cloud Chief Formation 

forms the surface of about one-third of the county and 

forms heavy gypsum ledges (Six, 1930). The Rush Springs 

Formation consists of orange-brown fine-grained sandstone 

and siltstone, with interbedded red-brown shale, silty shale, 

and gypsum (Wood and Stacy, 1965). The Marlow Formation 

consists of siltstone and very fine-grained sandstone with clay 

and gypsum (Mogg and others, 1960). The Dog Creek Shale 

is a red-brown shale with discontinuous bands of silt and thin 

layers of dolomite, has very low permeability, and is not a 

predominant source of water (Mogg and others, 1960; Wood 

and Stacy, 1965). 

The Blaine Formation, Chickasha Formation, Duncan 

Sandstone, Hennessey Group, Garber Sandstone, Wellington 

Formation, and Chase, Council Grove, and Admire Groups 

(pl. 1, fig. 6) underlie the Canadian River alluvial aquifer 

from the eastern extent of Canadian County to Pottawatomie 

County. The Blaine Formation consists mostly of thin gypsum 

beds in the study area with thin beds of dolomite below each 

gypsum layer, interbedded with red-brown shale (Fay and 

others, 1962; Bingham and Moore, 1975). The Chickasha 

Formation consists of mudstone conglomerate and redbrown to orange-brown silty shale and siltstone (Wood and 

Burton, 1968) (pl. 1, fig. 6). Some of the siltstone beds of the 

Chickasha Formation form ledges along the alluvial valleys 

(Davis, 1955) at the edge of terrace bluffs. The Duncan 

Sandstone, with a thickness of 150–200 ft (Wood and Burton, 

1968), is a red-brown to orange-brown sandstone with 

shale and conglomerated mudstone (Bingham and Moore, 

1975) that underlies the Canadian River alluvial aquifer. 

The Hennessey Group is characterized by red shales, which 

are thin and weather to a dark, rich loam. This group has 

a thickness of 600–650 ft in most places in Cleveland and 

Oklahoma Counties (Wood and Burton, 1968). The Garber 

Sandstone, Wellington Formation, and Chase, Council Grove, 

and Admire Groups (water-bearing units of the Central 

Oklahoma aquifer) are the oldest Permian units underlying the 

Canadian River. These Permian units are composed of deepred to reddish-orange massive and cross-bedded fine-grained 

sandstone interbedded with shale and siltstone (Wood and 

Burton, 1968). 

Pennsylvanian-Age Bedrock Units

In eastern Oklahoma, the bedrock units are 

predominantly Pennsylvanian in age (pl. 1, fig. 6) and do not 

share the same red color as the Permian-age units (Aurin, 

1917). The Vanoss, Ada, and Vamoosa Formations underlie the 

Canadian River alluvial aquifer in western Seminole County, 

whereas the Belle City Limestone and Francis (also known as 

Coffeyville), Seminole, and Holdenville Formations underlie 

the aquifer in eastern Seminole County (pl. 1). Most of the 

information regarding Pennsylvanian-age bedrock units is 

from Tanner (1956).

The Vanoss Formation crosses the western part of 

Seminole County in a north-south strip and is approximately 

4 mi wide at the intersection with the Canadian River. 

The Vanoss Formation is composed of shales, sandstones, 

conglomerates, and a few thin limestones. Arkosic sandstones 

and conglomerates are prominent in the southern part of the 

county near the Canadian River. The Vanoss Formation is 

about 250 ft thick in the vicinity of Konawa, just north of 

the Canadian River. In Seminole County, the Ada Formation 

includes shale, sandstone, and siltstone of various colors and 

conglomerated limestone. The shales can be discerned from 

the Vanoss Formation in most areas except the northern part 

of the county. The Vamoosa Formation (major water-bearing 

formation) primarily consists of shales and, to a lesser degree, 

sandstones, which thin southward. The Vamoosa Formation 

is 125 ft thick in the area where it is crossed by the Canadian 

River. 

The pre-Vamoosa Formation bedrock units of the 

Pennsylvanian System in the Canadian River alluvial aquifer 

study area include the Belle City Limestone, Nellie Bly 

Formation, Francis Formation, Seminole Formation, and 

Holdenville Formation in Seminole County and the Wewoka 

Formation, Wetumka Shale, Calvin Sandstone, and Senora 

Formation in Hughes County (Weaver, 1954; Tanner, 1956; 

Oakes and Koontz, 1967). These formations typically consist 

of limestone, shale, and sandstone and range from 36 to 680 ft 

in thickness (Weaver, 1954; Tanner, 1956; Oakes and Koontz, 

1967). These formations have outcrop widths of up to 2 mi 

(Weaver, 1954; Tanner, 1956; Oakes and Koontz, 1967).
Hydrogeologic Framework of the Canadian River Alluvial Aquifer 11

Hydrogeologic Framework of the 

Canadian River Alluvial Aquifer

A hydrogeologic framework of the Canadian River 

alluvial aquifer was developed to provide a three-dimensional 

representation of the aquifer and of underlying and 

surrounding bedrock units. The hydrogeologic framework 

includes the aquifer areal and vertical extent, as well as the 

distribution, texture variability, and hydraulic properties of 

aquifer materials. The hydrogeologic framework was used to 

construct the numerical groundwater-flow models described in 

this report. 

Lithologic-Log Standardization

Approximately 1,400 lithologic logs (Oklahoma Water 

Resources Board, 2015a) were used to characterize the 

alluvial and terrace deposits of the aquifer (pl. 2). These 

logs were recorded by well drillers and report the physical 

characteristics of geologic units encountered during drilling. 

The median depth of the lithologic logs was 60 ft, and 10 

percent of those logs penetrated deeper than 100 ft below land 

surface (fig. 7). Most of the lithologic logs penetrated the base 

of the alluvial aquifer and the top of the underlying bedrock 

unit (fig. 8). 

Techniques based on Mashburn and others (2013) were 

used to simplify the lithologic descriptions and to facilitate 

construction of the hydrogeologic framework of the aquifer. 

The lithologic logs were simplified by reducing the number 

of log interval descriptions from 3,300 unique terms to 

237 standardized terms. These standardized terms were 

classified into five generalized lithologic categories, shown in 

figure 9 (clay/silt, fine sand, medium sand, coarse sand, fine 

gravel).

0

50

100

150

200

250

300

350

400

450

500

Number of lithologic logs

Depth of lithologic logs, in feet

0 to 20 20 to 40 40 to 60 60 to 80 80 to 100 100 to 120 120 to 140

Figure 7. Frequency distribution of depth of lithologic logs used 

for the hydrogeologic framework in the Canadian River alluvial 

aquifer, Oklahoma. 

0

50

100

150

200

250

300

Number of lithologic logs

0 to 10

10 to 2020 to 3030 to 40

40 to 5050 to 60

60 to 7070 to 80

80 to 90

90 to 100

100 to 110110 to 120

Depth to bedrock, in feet

Figure 8. Frequency distribution of depth to bedrock (base of 

alluvial aquifer) determined from lithologic logs.

10 30 50 70 90

Lithologic category Clay/silt Fine sand Medium sand Coarse sand Fine gravel

Percent coarse multiplier

Figure 9. Percent-coarse multiplier values for the standardized lithologic categories used to obtain horizontal hydraulic conductivity 

for the Canadian River alluvial aquifer, Oklahoma. 
12 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Aquifer Areal and Vertical Extent

The aquifer areal extent was determined by using 

1:24,000-scale geologic maps (Stanley and Miller, 2001; 

Suneson and Stanley, 2001a; Suneson and Stanley, 2001b; 

Stanley and Miller, 2002), 1:100,000-scale geologic maps 

(Stanley, 2002; Miller and Stanley, 2004; Chang and 

Stanley, 2010; Fay, 2010a; Fay, 2010b), and 1:250,000-scale 

geologic maps (Heran and others, 2003). The aquifer areal 

extent ranged from less than 0.2 to 8.5 mi wide. Some areas 

designated as “alluvium” or “terrace” from the geologic 

maps were removed from the aquifer extent on the basis of 

an analysis of lithologic-log data. Other terrace deposits were 

excluded because they were either discontinuous or considered 

to be part of the groundwater-flow system of bedrock aquifers. 

The high terrace of the Canadian River alluvial aquifer 

was not included in the active area because of the lack of 

hydrologic connection with the lower terraces (Davis, 1955) 

and difficulty in differentiating between the high terrace and 

the Tertiary-age Ogallala Formation in western Oklahoma 

(pl. 1).

The bedrock surface of the Canadian River alluvial 

aquifer was constructed by using lithologic logs where 

the bedrock contact could be determined. Permian- and 

Pennsylvanian-age lithologic units were identified by terms 

denoting red or consolidated materials such as “red bed,” 

“red clay,” or “bedrock.” The contact with bedrock units was 

defined where a continuous boundary was identified across 

a range of lithologic logs, regardless of the confining nature 

of the bedrock unit. Therefore, a red sand or an impervious 

red clay sequence adjoining an alluvial sand would define 

the aquifer boundary. Minor or interbedded intervals where 

bedrock was identified in alluvial or terrace deposits were 

discarded, and an approximate boundary determined where the 

contacts were gradational. 

The lithologic-log bedrock contacts were then contoured 

by using professional judgment and geologic information from 

previous publications (pl. 2). The maximum aquifer thickness 

was 120 ft, and the average aquifer thickness was 50 ft. The 

bedrock contact is approximate at the western end of the 

Canadian River alluvial aquifer near the Texas-Oklahoma 

border, where there were fewer lithologic logs available to 

determine the bedrock contact. 

Hydraulic Profiling and Sediment Coring

A direct-push Geoprobe Hydraulic Profiling Tool (HPT; 

Geoprobe Systems, 2007) as used to obtain 24 profiles of 

continuous horizontal hydraulic conductivity of the saturated 

zone of the Canadian River alluvial and terrace deposits 

(pl. 1). Locations of the HPT test holes were based on site 

access and proximity to locations of lithologic logs. Six of 

these locations were chosen for 2.25-in.-diameter sedimentcore sampling to analyze and compare the described 

lithologic-core properties to the horizontal hydraulic 

conductivity profile values obtained from the HPT. The six 

sediment cores were described in 1-in. increments, noting 

grain size, sorting, and Munsell (1912) color. The lithologic 

descriptions from sediment cores were grouped into the 

five lithologic categories (fig. 9) from the lithologic-log 

standardization. Saturated horizontal hydraulic conductivity 

values from the HPT profiles were then matched to each 

described core depth interval to determine the relation between 

lithology and horizontal hydraulic conductivity. An average 

horizontal hydraulic conductivity was determined for the 

lithologic categories contained in each core. 

Percent-Coarse Value and Hydraulic Properties

To determine the hydraulic conductivity of the Canadian 

River alluvial aquifer, each lithologic category determined 

from the lithologic logs was assigned a percent-coarse range. 

The percent-coarse ranges were 0–20 percent (clay/silt), 21–40 

(fine sand), 41–60 (medium sand), 61–80 (coarse sand), and 

81–100 (fine gravel). A percent coarse multiplier was based on 

the midpoint of each category (fig. 9), and was used to assign 

a percent-coarse value to each lithologic log depth interval. 

The percent-coarse value for each lithologic log was then 

computed as the thickness-weighted average of percent-coarse 

values assigned to the lithologic categories in each log.

A horizontal hydraulic conductivity of 0.1 feet per day 

(ft/d) was assigned to the clay/silt standardized category, and 

a horizontal hydraulic conductivity of 100 ft/d was assigned 

to the fine gravel standardized category on the basis of the 

weighted-average horizontal hydraulic conductivity values 

calculated for each lithologic category across each of the six 

sediment cores determined by HPT profiles. This range spans 

the expected grain sizes encountered in the Canadian River 

alluvial and terrace material. By assuming that a horizontal 

hydraulic conductivity of 0.1 ft/d and 10 percent-coarse value 

represent the clay/silt standardized category, that a horizontal 

hydraulic conductivity of 100 ft/d and 90 percent-coarse 

value represent the fine gravel standardized category, and that 

the relation between the two parameters is linear, average 

horizontal hydraulic conductivity for the aquifer material was 

assumed to be 

K P h s = × ( . 1 25 1 ) . − 2 4 (1)

where 

Kh is the horizontal hydraulic conductivity in feet 

per day (ft/d), and

Ps is the percent-coarse value.

The frequency distribution of the horizontal hydraulic 

conductivity is shown in figure 10. The average, minimum, 

and maximum horizontal hydraulic conductivities for the 

Canadian River alluvial aquifer were calculated to be 39 ft/d, 

0.1 ft/d, and 100 ft/d, respectively. These values are similar to 

those of Scholl and Christenson (1998) in which the average, 
Hydrogeology of the Canadian River Alluvial Aquifer 13

0

50

100

150

200

250

300

350

400

Number of lithologic logs

Horizontal hydraulic conductivity, in feet per day

0 to 12

12 to 2424 to 3636 to 48

48 to 6060 to 7272 to 8484 to 96

96 to 100

Figure 10. Frequency distribution of horizontal hydraulic 

conductivity determined from lithologic logs.

minimum, and maximum horizontal hydraulic conductivities 

for the Canadian River alluvial aquifer were determined 

to be 19 ft/d, 0.24 ft/d, and 79 ft/d. The Canadian River 

alluvial aquifer materials become finer grained with distance 

downstream to the east, possibly because of the longer 

average distance from the source of the sediment, or possibly 

due to a decline in the streambed elevation gradient. Local 

heterogeneities in the percent-coarse values of alluvial aquifer 

materials may be related to variations in the depositional 

environment and history or the variability in the lithologic-log 

descriptions provided by well drillers. Horizontal hydraulic 

conductivity for the underlying bedrock units was estimated 

by using values from Morris and Johnson (1967) to assign 

a uniform horizontal hydraulic conductivity of 0.2 ft/d for 

the bedrock units, which consisted predominantly of fine 

sandstone.

At the time this report was written (2016), no 

publications were available describing multiwell aquifer tests 

in the Canadian River alluvial aquifer; therefore, a specific 

storage value of 0.0001-1 was chosen from Domenico and 

Mifflin (1965), and a specific yield for each lithology category 

was chosen from Morris and Johnson (1967). The specificyield values chosen were 6 percent for clay/silt deposits, 33 

percent for fine sand, 32 percent for medium sand, 30 percent 

for coarse sand, and 28 percent for fine gravel. The specific 

yield for each lithologic log was then determined as the 

thickness-weighted average of specific yield assigned to the 

lithologic categories in each lithologic log. An average specific 

yield of 22 percent was calculated for the Canadian River 

alluvial aquifer. The specific-yield values used from Morris 

and Johnson (1967) were based on a laboratory determination 

of specific yield. Laboratory-determined specific yield is often 

much larger than values obtained from aquifer tests and may 

be more applicable for the evaluation of long-term aquifer 

yields than groundwater changes from pumping (Neuman, 

1987). 

Spatial interpolation of the percent-coarse values and 

specific-yield values was accomplished by using the Inverse 

Distance Weighting (IDW) method between lithologiclog locations, whereby values closest to the location to be 

interpolated are assigned the greatest weights (Esri, 2015). 

The IDW method assumes that nearby values provide more 

accurate data, which is appropriate for an aquifer where 

localized lithological trends may not continue for more than 

short distances. The IDW interpolation used a power function 

of two, which represents the exponent to which the inverse 

of the distance between the interpolated location and nearby 

values is raised. Additionally, an IDW search radius of 2 mi 

was applied to limit interpolations in areas where the distance 

between values was substantial, such as areas near the Texas 

border.

Hydrogeology of the Canadian River 

Alluvial Aquifer

This section describes the hydrogeology of the Canadian 

River alluvial aquifer. The information described in this 

section was used to create the conceptual flow model and 

forms the basis of the groundwater-flow models described in 

the “Simulation of Groundwater Flow in the Canadian River 

Alluvial Aquifer” section.

Groundwater

Groundwater in the Canadian River alluvial aquifer refers 

to water in the saturated zone between the water table and the 

underlying bedrock. The movement of groundwater in the 

saturated zone is described by Darcy’s Law (Darcy, 1856), by 

which groundwater flows from areas of high hydraulic head 

to areas of low hydraulic head through a porous medium. 

Groundwater inflows to the Canadian River alluvial aquifer 

include recharge to the water table from precipitation 

and groundwater lateral flow from the terrace contact 

with surrounding bedrock. Groundwater outflows include 

evapotranspiration (ET), groundwater use by wells, and some 

groundwater lateral flow from the terrace to the surrounding 

bedrock.
14 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Temporal Water-Level Fluctuations

Depth to water was recorded continuously in eight 

wells (continuous recorder wells) in the Canadian River 

alluvial aquifer study area during the period 2014–16 (pl. 1, 

figs. 11 and 12). Water levels in the Canadian River alluvial 

aquifer can fluctuate 2–10 ft on a timescale of days, depending 

on distance from the river. Stressors affecting these water 

levels in the alluvial aquifer are precipitation, ET, groundwater 

use by wells, and streamflow. Water levels measured in 

wells in Reach I of the Canadian River alluvial aquifer near 

Crawford, Camargo, Taloga, and Bridgeport show a correlative 

response to precipitation data (fig. 11) from west-central 

Oklahoma Climate Division 4 (fig. 1). All continuous recorder 

wells, except for two, were completed in the alluvial deposits. 

Wells in Reach II were located near Purcell, Norman (Indian 

Hills), Norman (NLF TS5), and Konawa. These wells also 

show a correlative response to precipitation data (fig. 12) 

from central Oklahoma Climate Division 5 (fig. 1). The well 

near Konawa is completed in alluvial deposits but is also 

open below the alluvial deposits into the Pennsylvanian-age 

Vanoss Formation. The well near Norman (Indian Hills) is 

completed in the terrace deposits of the alluvial aquifer. The 

highest water levels in both reaches occurred in May 2015 

(figs. 11 and 12) which corresponds to the greatest average 

monthly precipitation during the study period (fig. 4). Water 

levels also show a correlative response to below-average 

precipitation over the summer months and groundwater use 

by wells that are pumped during the crop-growing season 

(April to September). The lowest groundwater levels were 

measured in both reaches in October 2014, which was at the 

end of the 2014 growing season during this 2-year period 

(figs. 11 and 12). Groundwater levels were also low in both 

reaches in September 2015; however, more rain fell during 

the April–June 2015 period compared to the April–June 

2014 period, buffering water levels from declining to the 

previous September–October levels. The range in water 

levels in the well near Konawa is less variable than the 

water levels in wells completed in the alluvial deposits. 

The well near Norman (Indian Hills) had less variable 

water levels than the other wells completed in the alluvial 

aquifer but showed similar trends as the groundwater 

levels measured in other wells in Reach II in response to 

precipitation (fig. 12).

Water-Table Surface in 2013

The water-table surface, which is usually interpolated 

or contoured from water-level altitude measurements at 

many individual wells, approximates the top of the zone of 

saturation. Water levels were measured between January and 

March 2013 in 140 wells completed in the Canadian River 

alluvial aquifer. Most of these wells were constructed with 

slotted polyvinyl chloride or steel casings with sand backfill 

on the outside of the well casings. The water-table surface in 

the Canadian River alluvial aquifer was shallow, typically less 

than 30 ft below land surface. The measured water levels were 

supplemented by additional water levels from OWRB wellcompletion reports (Oklahoma Water Resources Board, 2015a) 

which specified the depth interval at which water was first 

encountered during drilling.

Analysis of the 2013 water-table surface map (pl. 3) 

indicates that groundwater in the terrace deposits flows 

from the surrounding bedrock units and towards the alluvial 

deposits and main river channel. Higher water levels in the 

surrounding bedrock than in the alluvial deposits indicates that 

the Canadian River has incised down into the bedrock, with 

base-flow seepage from bedrock units through the alluvial 

deposits to the river being part of this hydrologic system. This 

incision was not observed in the Beaver-North Canadian River 

alluvial aquifer (Ryter and Correll, 2016). Groundwater in the 

alluvial deposits typically flows subparallel and downstream 

with streamflow. In areas where the water-table contours 

created a “V” more sharply upstream (the western part of the 

aquifer), groundwater discharges more readily to the river. The 

Canadian River is generally a gaining stream (deriving part of 

its flow from groundwater seepage) based on the water-table 

surface contours.

Groundwater Flow to and from Bedrock Units

Groundwater flow between the Canadian River alluvial 

aquifer and the adjoining bedrock units, or lateral flow, has 

been documented by previous studies. In central Oklahoma, 

Mogg and others (1960) reported lower groundwater levels in 

the Canadian River alluvial aquifer relative to the surrounding 

bedrock, particularly the Rush Springs Formation, where 

groundwater was determined to drain towards the Canadian 

River at an average water-table slope of 35 ft/mi. Seepage 

from topographically higher bedrock units generally located 

20–100 ft or more above the alluvial deposits in central 

Oklahoma was also reported by Wood and Burton (1968). 
Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. 

Date 2014 2015 

-4-2

02468

101214

Depth to water, in feet below land surface

Precipitation (Oklahoma Climatological Survey, 2015e)Water level recorded in Reach I well—Well name and number Crawford (355133099434901) Camargo (360110099215001) Taloga (360022098525501) Bridgeport (353211098191501)

EXPLANATION

Figure 11. Continuous water levels recorded in wells and precipitation in Reach I of the Canadian River alluvial aquifer, Oklahoma.
Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. 

Date 2014 2015 

-5

05

10152025303540

Depth to water, in feet below land surface

Precipitation (Oklahoma Climatological Survey, 2015e)Water level recorded in Reach II well—Well name and number

Purcell (345740097210801)Norman (Indian Hills) (351722097313601)Norman (NLF TS5) (351004097270101)Konawa (345302096412401)

EXPLANATION

Figure 12. Continuous water levels recorded in wells and precipitation in Reach II of the Canadian River alluvial aquifer, Oklahoma.
Hydrogeology of the Canadian River Alluvial Aquifer 17

Water Quality

Groundwater samples from 35 wells completed in the 

Canadian River alluvial aquifer were collected by the OWRB 

as part of the Groundwater Monitoring and Assessment 

Program (Oklahoma Water Resources Board, 2015b) in 

August and September 2013. Those groundwater samples 

were analyzed for physical properties (pH, temperature, 

dissolved oxygen, hardness, alkalinity, and specific 

conductance) in the field and for concentrations of major 

ions, trace metals, and nutrients in a laboratory (table 3). 

Data from 4 of the 35 samples were not included in the 

results in this report because of the greater than 10-percent 

discrepancies in cation-anion balances of those samples. Five 

of the remaining 31 groundwater samples contained nitratenitrogen concentrations (measured as nitrate plus nitrite 

concentrations) that exceeded the National Primary Drinking 

Water Regulation of 10 milligrams per liter (mg/L) (U.S. 

Environmental Protection Agency, 2016), with the maximum 

measured nitrate-nitrogen concentration for all of these 

samples being 16.1 mg/L. Twenty-one of 31 groundwater 

samples exceeded the National Secondary Drinking Water 

Regulation for dissolved solids concentration (500 mg/L), 

with the median dissolved solids concentration for all samples 

being 530 mg/L. Eleven of 31 groundwater samples exceeded 

the National Secondary Drinking Water Regulation for 

sulfate concentration (250 mg/L), with the median detected 

sulfate concentration for all samples being 103 mg/L. 

Twelve of 31 groundwater samples exceeded the National 

Secondary Drinking Water Regulation for iron concentration 

(300 micrograms per liter [μg/L]), with the median detected 

iron concentration for all samples being 1,429 μg/L. Fourteen 

of 31 groundwater samples exceeded the National Secondary 

Drinking Water Regulation for manganese concentrations 

(50 μg/L), with the median detected manganese concentration 

for all samples being 457.5 μg/L (table 3).

Concentrations of dissolved cations and anions were 

summarized by using Piper (1944) diagrams. Water type was 

determined by using methods from Back (1961). Water types 

in the Canadian River alluvial aquifer ranged from calciummagnesium-sulfate-chloride in the western part, transitioning 

into calcium-magnesium-bicarbonate towards the central 

part of the aquifer (fig. 13). Towards the eastern part of the 

aquifer, the water type was calcium magnesium-bicarbonate 

but increased in sodium-chloride concentrations (fig. 13). 

This transition in water type from calcium-magnesiumsulfate-chloride to calcium-magnesium-bicarbonate type 

water to more sodium chloride type water in the Canadian 

River alluvial aquifer can be explained by the exchange of 

groundwater containing dissolved constituents between the 

bedrock units and the alluvial aquifer. Concentrations of 

calcium, magnesium, and sulfate in the groundwater in the 

Cloud Chief Formation come from the dissolution of gypsum, 

dolomite, and calcite (Becker and Runkle, 1998). The calciummagnesium-sulfate chloride type water in the Canadian River 

alluvial aquifer in the western part of the study area was most 

likely caused by the inflow of groundwater from the Cloud 

Chief Formation. The central parts of the Canadian River 

alluvial aquifer in the study area overlie Permian sandstones, 

siltstones, and mudstones. Groundwater in the Rush Springs 

Formation is predominantly calcium-magnesium bicarbonate 

(Becker and Runkle, 1998). Groundwater in the shallow, 

unconfined part of the Central Oklahoma aquifer contained 

predominantly calcium, magnesium, and bicarbonate ions 

from the dissolution of dolomite. The calcium-magnesiumbicarbonate type water in the Canadian River alluvial aquifer 

in the central part of the study area is most likely from the 

inflow of groundwater from the Rush Springs Formation and 

Garber Sandstone (Parkhurst and others, 1996). In the eastern 

part of the Canadian River alluvial aquifer, the water type was 

calcium-magnesium-bicarbonate, which is associated with 

Pennsylvanian-age bedrock units (Hart, 1974). The eastern 

part of the Canadian River alluvial aquifer also contained 

greater concentrations of sodium and chloride, which may 

be due to seepage of naturally formed brines, disposal of 

industrial wastes, or solution of minerals (Hart, 1974). 

Surface Water

Streamflow in the Canadian River is described in this 

section to quantify estimates of streamflow magnitude, gaining 

and losing reaches, and contributions to streamflow from 

tributaries and groundwater. To estimate gaining and losing 

reaches in the Canadian River, a seepage run was conducted. 

To quantify stream base flow for the study period (1981–

2013), hydrograph-separation methods were performed on the 

basis of data from five USGS streamgages.

Streamflow Characteristics and Trends

Flow in the Canadian River has been regulated since 

1964 by the Sanford Dam in Texas (fig. 1) and influenced by 

five wastewater-treatment plants in Oklahoma (pl. 1). Dailyaveraged monthly streamflow data (U.S. Geological Survey, 

2013a) recorded at streamgages (fig. 1) are summarized in 

table 4. Streamflow data from streamgages were recorded 

during the entire study period (1981–2013), with the 

exception of the Norman streamgage (07229050) for which 

continuous streamflow data began in January 2007 and 

the Purcell streamgage (07229200) for which continuous 

streamflow data began in January 1986. Average streamflow 

ranged from 75 cubic feet per second (ft3/s) at the Canadian 

streamgage (07228000) to 1,937 ft3/s at the Calvin streamgage 

(07231500). Flows between each streamgage increased in 

the downstream direction (table 4). In the study area, the 

minimum streamflow typically occurred during August, and 

the maximum streamflow typically occurred during May 

at the streamgages. Streamflows in the Canadian River are 

sustained by groundwater discharge during most of the year; 

however, there are occurrences of zero flow in the Canadian 

River, as demonstrated by the minimum stream base flows at 

the Canadian streamgage (07228000), Bridgeport streamgage 

(07228500), and Calvin streamgage (07231500) (table 4). 
Table 3. Summary statistics of water-quality constituent values for groundwater samples collected August–September 2013 from the Canadian RiveOklahoma.—Continued [mg/L, milligrams per liter; μg/L, micrograms per liter; --, not available] Water-quality constituent Detection limit Number of samples analyzed Number of samples less than detection limit Minimum detected concen- trations Maximum detected concen- trations 25th percentile of detected concen- trations 50th percentile of detected concen- trations 75th percentile of detected concentrations 

Specific conductance -- 31 0 161.5 3,396.4 724.65 879.8 1,652.8 pH -- 31 0 6.25 7.45 6.865 7 7.105 Temperature -- 31 0 18.21 22.43 19.12 20.19 21.09 Dissolved oxygen, in mg/L -- 31 0 0.14 8.88 0.89 3.7 6.67 Hardness, in mg/L -- 31 0 46 1,484 293.5 386 811 Alkalinity, in mg/L -- 31 0 56 537 205.5 299 335 Dissolved solids, in mg/L 10 31 0 113 2,680 438 530 1,195 Calcium, in mg/L 5 31 0 16.7 445 80.6 111 207.5 Magnesium, in mg/L 5 31 0 5.3 180 16.75 39 65.55 Sodium, in mg/L 5 31 0 10.5 430 23 45.9 97.05 Potassium, in mg/L 0.5 31 3 0.5 5 1 2 2.725 Bicarbonate, in mg/L 12 31 0 68.8 661 253 368 412.5 Carbonate, in mg/L 6 31 31 -- -- -- -- -- Sulfate, in mg/L 10 31 2 16.6 1,750 74.7 103 650 Chloride, in mg/L 10 31 6 11.4 380 26.5 40.4 70.1 Fluoride, in mg/L 0.2 31 16 0.21 0.56 0.25 0.32 0.395 Bromide, in μg/L 100 31 3 127 966 241.75 331.5 459.25 Silica, in mg/L 50 31 0 11,000 54,200 20,050 21,700 24,750 Nitrate plus nitrite, in mg/L 0.05 31 8 0.07 16.1 0.925 3.79 6.92 Ammonia, in mg/L 0.1 31 24 0.2 0.97 0.235 0.26 0.405 Phosphorus, in mg/L 0.005 31 8 0.011 0.516 0.0285 0.042 0.0995 Aluminum, in μg/L 100 31 31 -- -- -- -- -- Antimony, in μg/L 1 31 31 -- -- -- -- -- Arsenic, in μg/L 10 31 29 12.2 19.9 Barium, in μg/L 10 31 1 10.5 987 26.05 92.15 230.75 

Table 3. Summary statistics of water-quality constituent values for groundwater samples collected August–September 2013 from the Canadian River Oklahoma. [mg/L, milligrams per liter; μg/L, micrograms per liter; --, not available]
Table 3. Summary statistics of water-quality constituent values for groundwater samples collected August–September 2013 from the Canadian RiveOklahoma.—Continued[mg/L, milligrams per liter; μg/L, micrograms per liter; --, not available]

Water-quality 

constituent

Detection 

limit

Number of 

samples 

analyzed

Number 

of samples 

less than 

detection 

limit

Minimum

detected 

concentrations

Maximum

detected 

concentrations

25th 

percentile

of detected 

concentrations

50th 

percentile

of detected 

concentrations

75th 

percentile

of detected 

concentrations

Beryllium, in μg/L 2 31 31 -- -- -- -- -- Boron, in μg/L 50 31 2 51.7 2,970 92.3 225 471 Cadmium, in μg/L 5 31 31 -- -- -- -- -- Chromium, in μg/L 5 31 29 6.1 6.4 -- -- -- Cobalt, in μg/L 10 31 31 -- -- -- Copper, in μg/L 5 31 29 6.7 13.1 -- -- -- Iron, in μg/L 50 31 15 59.6 4,940 507.5 1,429 2,237.5 Lead, in μg/L 10 31 31 -- -- -- -- -- Manganese, in μg/L 50 31 17 54 1,090 289 457.5 582.25 Mercury, in μg/L 0.05 31 30 0.73 0.73 -- -- -- Molybdenum, in μg/L 10 31 28 14.1 51.4 -- -- -- Nickel, in μg/L 10 31 31 -- -- -- -- -- Selenium, in μg/L 20 31 30 31.8 31.8 -- -- -- Silver, in μg/L 10 31 31 -- -- -- -- -- Thallium, in μg/L 1 31 31 -- -- -- -- -- Uranium, in μg/L 1 31 9 1.3 40.8 3 5.15 17.525 Vanadium, in μg/L 10 31 8 10.6 94.1 16.1 29.3 48.35 Zinc, in μg/L 10 31 13 10.2 424 11.675 25.45 67.9 
20 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Calcium + magnesium

Sulfate

Sodium + potassium

Bicarbonate + carbonate

Chloride + fluoride + sulfate

Magnesium

Calcium Chloride

PERCENT

PERCENT

PERCENT

0

20

40

60

80

100

100

20

40

60

80

0

0

20

40

60

80

100

100

80

60

40

20

0

100

80

60

40

20

0

100

20

40

60

80

0

0

20

40

60

80

100

0

20

40

60

80

100

100

20

40

60

80

0

0

80

60

40

20

100

EXPLANATION

Bedrock units adjoining or underlying the Canadian River

 alluvial aquifer and possibly contributing water types

 to the alluvial aquifer—Water type was determined by

 using methods from Back (1961)

 Ogallala Formation

 Rush Springs Formation

 Dog Creek Shale and Duncan Sandstone

 Garber Sandstone

 Pennsylvanian units (undifferentiated)

West East

Figure 13. Water types in wells completed in the Canadian River alluvial aquifer, Oklahoma, in 2013.
Hydrogeology of the Canadian River Alluvial Aquifer 21

Table 4. Summary statistics of daily-averaged monthly streamflow and Base-Flow Index (BFI) stream base flow at streamgages in the 

Canadian River alluvial aquifer study area.

[All units in cubic feet per second. ft3/s, cubic feet per second; TX, Texas; OK, Oklahoma]

Station 

number

Station 

name 

Analyzed period 

of record 

Average 

flow 

(ft3/s)

Minimum 

flow 

(ft3/s)

25th 

percentile flow 

(ft3/s)

Stream Base Stream Base Stream Base

07228000 Canadian River near Canadian, TX 1981–01–01 to 2013–12–31 75 46 0.0 0.0 31 21

07228500 Canadian River at Bridgeport, OK 1981–01–01 to 2013–12–31 326 142 0.3 0.0 88 30

07229050 Canadian River at Norman, OK 2007–01–01 to 2013–12–31 450 199 8.1 2.2 130 39

07229200 Canadian River at Purcell, OK 1986–01–01 to 2013–12–31 722 292 13.7 2.5 208 85

07231500 Canadian River at Calvin, OK 1981–01–01 to 2013–12–31 1,937 648 0.0 0.0 374 139

Station 

number

Station 

name 

Analyzed period 

of record 

Median 

flow 

(ft3/s)

75th 

percentile flow 

(ft3/s)

Maximum 

flow 

(ft3/s)

Stream Base Stream Base Stream Base

07228000 Canadian River near Canadian, TX 1981–01–01 to 2013–12–31 55 42 95 63 579 213

07228500 Canadian River at Bridgeport, OK 1981–01–01 to 2013–12–31 196 104 390 214 4,188 648

07229050 Canadian River at Norman, OK 2007–01–01 to 2013–12–31 319 155 517 294 2,988 1,060

07229200 Canadian River at Purcell, OK 1986–01–01 to 2013–12–31 426 229 825 424 7,717 1,329

07231500 Canadian River at Calvin, OK 1981–01–01 to 2013–12–31 970 393 2,421 778 20,643 4,941

Stream Base Flow

Stream base flow is defined for this report as the part 

of streamflow that is not from runoff and is discharged 

from aquifers adjoining a stream. Several methods can be 

used to quantify stream base flow. A seepage run consists 

of streamflow measurements at several places in a reach of 

a stream to determine if a section of the stream is receiving 

groundwater discharge or losing water to the underlying 

aquifer (Harvey and Wagner, 2000). A seepage run was 

done for this study in 2013. Base-flow separation techniques 

estimate the base-flow and runoff components of a streamflow 

record. The Base-Flow Index program (BFI) method (Wahl 

and Wahl, 2007) was used to estimate the average monthly and 

annual base-flow and runoff components of Canadian River 

daily streamflow records.

2013 Seepage Run

A seepage run was performed at 26 sites on the Canadian 

River during March 18–21, 2013, along a distance of 380 mi 

(fig. 14), beginning near the Texas-Oklahoma border. The 

seepage run was performed when ET and water use were 

considered to be minimal (during the winter and spring 

months in the study area) and when the runoff component of 

streamflow had dissipated. Streamflows measured in March 

2013 were analyzed from upstream near Durham, Okla., 

referred to as the “Durham site,” to downstream near Calvin, 

Okla. Generally, the streamflow increased from upstream to 

downstream sites. Downstream increases in stream base flow 

could be caused by increased inflows to the stream and alluvial 

aquifer from adjoining bedrock aquifers. Average stream 

base flow from four perennial tributaries (Deer Creek, Buggy 

Creek, Walnut Creek, and Little River) to the Canadian River 

was estimated on the basis of available data. These streamflow 

estimates were subtracted from the net streamflow difference 

between the upstream and downstream sites from which they 

were located. All other intermittent streamflows were assumed 

to be zero.

Stream base flows remained similar from the Durham 

site to the Canadian River near Aledo, Okla., site, referred 

to as the “Aledo site.” Stream base flows steadily increased 

from 70 to 150 ft3/s between the Aledo site and the Canadian 

River near Cogar, Okla., site, referred to as the “Cogar site” 

(fig. 14). Some of the increase in stream base flows between 

the Aledo and Cogar sites may have been caused from inflow 

from the local bedrock units (Rush Springs Formation). 

Stream base flows increased from 106 to 142 ft3/s between the 

Canadian River near Thomas, Okla., site, referred to as the 

“Thomas site,” and the Bridgeport streamgage (07228500) 

(fig. 14). Deer Creek is a tributary between the Thomas site 

and the Bridgeport streamgage (07228500) that contributed an 

estimated 8.2 ft3/s to the Canadian River in 2013, which would 
22 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

0 50 100 150 200 250 300

Downstream distance, in miles

350 400

0

50

100

150

200

250

300

350

Stream base flow, in cubic feet per second

Ogallala Formation Cloud Chief Formation Rush Springs Formation Marlow

Formation

Dog Creek

Shale

Duncan

Sandstone

Hennessey

Group

Garber

Sandstone

and

Wellington

Formation

Chase,

Council

Grove,

and 

Admire

Groups

Canadian River near Durham, Okla.

Canadian River near Arnett, Okla.

Canadian River near Roll, Okla.

Canadian River near Peek, Okla.

Canadian River near Angora, Okla.

Canadian River near Camargo, Okla.

Canadian River near Rhea, Okla.

Canadian River near Aledo, Okla.

Canadian River near Taloga, Okla.

Canadian River near Oakwood, Okla.

Canadian River near Thomas, Okla.

Canadian River at Bridgeport, Okla.

Canadian River near Cogar, Okla.

Canadian River west of Union City, Okla.

Canadian River near Union City, Okla.

Canadian River near Mustang, Okla.

Canadian River near Newcastle, Okla.

Canadian River at Norman, Okla.

Canadian River at Noble, Okla.

Canadian River near Noble, Okla.

Canadian River at Purcell, Okla.

Canadian River at Rosedale, Okla.

Canadian River near Wanette, Okla.

Canadian River near Asher, Okla.

Canadian River West of Konawa, Okla.

Canadian River at Calvin, Okla.

8.2 5.8

56.4

Underlying bedrock unit (pl. 1)

Deer Creek Buggy Creek

Walnut Creek 75.6

Little River

Canadian River near Aledo, Okla.

EXPLANATION

Estimated tributary inflow and name—Value

 indicates stream base flow

Canadian River base-flow measurement

 with error bars (plus or minus 8 percent

 of streamflow)

Station name 

56.4

Walnut Creek

Figure 14. Stream base-flow measurements from the March 2013 seepage run conducted for the Canadian River alluvial aquifer and 

underlying bedrock units.

account for approximately 23 percent of the net flow increase 

measured between the Thomas and the Bridgeport streamgage 

(07228500). Stream base flows decreased from 151 to 125 ft3/s 

between the Cogar site and the Canadian River west of Union 

City, Okla., referred to as the “Union City site” (fig. 14). No 

continuous water-table observations are available in this area; 

however, local differences in the water table between the 

Canadian River and the surrounding Rush Springs aquifer 

and Marlow Formation could result in a loss to the bedrock. 

Stream base flows increased from 125 to 197 ft3/s between 

the Union City site and the Purcell streamgage (07229200) 

(fig. 14). Some of the increase in discharge between the Union 

City site and the Purcell streamgage (07229200) could be from 

inflow from the local bedrock unit (Rush Springs and Marlow 

Formations). The seepage run indicates that the Canadian 

River is generally a gaining stream between the Texas border 

and the Purcell streamgage (07229200) and a losing stream 

between the Purcell streamgage (07229200) and the Calvin 

streamgage (07231500) (fig. 14).

Base-Flow Separation

The BFI (Base Flow Index) method used to determine 

base flows is based on procedures developed by the Institute 

of Hydrology (1980). The BFI method divides the daily 

streamflow record into n-day increments and identifies the 

minimum streamflow during each n-day period. Minimum 

streamflows are then compared to adjacent minimums to 

determine turning points on a base-flow hydrograph. Straight 

lines drawn between turning points define the base-flow 

hydrograph; the area beneath the base-flow hydrograph is 

an estimate of the base-flow volume. The ratio of the baseflow volume to the total streamflow volume for the period of 

analysis is the base-flow index. Although these procedures 

may not always yield the true base-flow volume of the stream, 

tests in Great Britain (Institute of Hydrology, 1980), Canada 

(Swan and Condie, 1983), and the United States (Wahl 

and Wahl, 1995) indicated that the results of this base-flow 

separation procedure were consistent and indicative of the true 

base-flow volume (Esralew and Lewis, 2010).
Hydrogeology of the Canadian River Alluvial Aquifer 23

For the five streamgages analyzed for this study along the 

Canadian River, the n-day partition length was tested over a 

range of values from zero to 10 days. A graph of the base-flow 

index compared to n was constructed to visually identify a 

slope change. The number of days where the slope no longer 

substantially changed, or the appropriate n-day value, was 

5 days for streamflow data collected at the Canadian River 

streamgages. 

The average annual BFI-computed base-flow index 

estimated by using the BFI method generally decreased from 

west to east at streamgages on the Canadian River (fig. 15); 

the average annual base-flow index was 63 percent at the 

Canadian streamgage (07228000) for 1981–2013, 45 percent 

at the Bridgeport streamgage (07228500) for 1981–2013, 

47 percent at the Norman streamgage (07229050) for 

2007–13, 41 percent at the Purcell streamgage (07229200) 

for 1986–2013, and 34 percent at the Calvin streamgage 

(07231500) for 1981–2013. This general decrease in base 

flow-index and increase in runoff may be due to the increased 

precipitation in Oklahoma from west to east (fig. 1, table 1), 

incised alluvial deposits in eastern Oklahoma (Tanner, 1956), 

and downstream decrease in horizontal hydraulic conductivity 

determined from this investigation. The base-flow index 

ranged from 33 percent in 1986 to 68 percent in 2003 (fig. 15). 

A higher than average base-flow index can be produced 

during extreme drought conditions (Institute of Hydrology, 

1980). Year 2003 has the lowest recorded annual precipitation 

during the period 1981–2013; therefore, the large annual 

base-flow index in 2003 is probably due to the severe drought 

conditions.

Substantial increases in the average stream base flow 

were observed from upstream to downstream, particularly 

between the Purcell streamgage (07229200) and Calvin 

streamgage (07231500) (table 4). Stream base flows, 

determined from the seepage measurements at the Norman 

(07229050), Purcell (07229200), and Calvin (07231500) 

streamgages, including tributary inflows, were 7, 27, and 

71 percent lower, respectively, than the average BFI-computed 

stream base flows for the period of record (1981–2013). This 

difference is likely due to the drought conditions during the 

2013 stream base-flow measurements or from error in the 

BFI method. Because of less recharge to the alluvial aquifer 

and surrounding bedrock, the drought conditions reduced the 

altitude of the water table. As a result, lateral flow decreased 

from the bedrock to the alluvial and terrace deposits, as well as 

from the alluvial deposits to the Canadian River, particularly 

between the Purcell streamgage (07229200) and Calvin 

streamgage (07231500). 

Streambed Hydraulic Properties

Estimated vertical saturated hydraulic conductivity 

of the streambed (Ksb) was measured by using falling-head 

permeameter tests with methods described in Fox and 

others (2011). These permeameter tests were completed 

at five streambed-hydraulic property sites near Konawa, 

Purcell, Crawford, Minco, and Thomas, Okla. (pl. 1). Each 

permeameter test was performed by driving a pipe into the 

streambed sediment to a depth of 20 centimeters (cm), adding 

a known amount of water in the pipe, and allowing the water 

level in the pipe to fall while measuring the head every 

30 seconds for at least 5 minutes. Three permeameter tests 

were repeated to average results for a site to reduce potential 

human-induced error in each test. Calculations of Ksb were 

derived by using an applied version of Darcy’s equation 

(Landon and others, 2001; Fox, 2004; Fox and others, 2011):

K d

t t

H

H t

sb = −





 



 ( )

ln

0 ( )

0 (2)

where

H(t) is the head above the streambed altitude at 

time (t),

H0 is the initial head in the pipe above the 

streambed altitude,

d is the streambed sediment depth (20 cm), and

t‐t

0 is the elapsed time.

Ksb values calculated from these five falling-head permeameter 

tests ranged from 15 ft/d at the Thomas site to 54 ft/d at the 

Minco site, with an average value of 37 ft/d.

Recharge

Groundwater recharge was defined for this study as the 

portion of precipitation that enters the groundwater system 

at the zone of saturation and represents the primary means 

of water inflow to the Canadian River alluvial aquifer. 

Recharge rates are controlled by a number of factors including 

precipitation, land-surface gradient, soil and sediment 

hydraulic conductivity, ET, and vegetation cover type. Though 

recharge rates are difficult to quantify because of high spatial 

and temporal variability, methods using environmental tracers, 

physical measurements, streamflow-hydrograph techniques, 

and computer codes have been used to estimate recharge rates. 

For this study, a hydrograph-based water-table fluctuation 

method was used to estimate localized recharge rates for 2014, 

and a code-based water-balance estimation technique was used 

to estimate spatially distributed recharge rates for the period 

1981–2013.
24 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

0

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

Base-flow index,

in percent

Base-flow index,

in percent

Base-flow index,

in percent

Base-flow index,

in percent

Base-flow index,

in percent

1981

19821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

2007200820092010201120122013

1986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

Year

Canadian River near Canadian, Tex. (07228000)

Canadian River at Bridgeport, Okla. (07228500)

Canadian River at Norman, Okla. (07229050)

Canadian River at Purcell, Okla. (07229200)

Canadian River at Calvin, Okla. (07231500)

Average base-flow index, in percent

EXPLANATION

[Base-flow index is defined as the part of streamflow that is not

from runoff and is discharged from aquifers adjoining a stream]

Figure 15. Average annual Base-Flow Index for streamgages along the Canadian River, Oklahoma, 1981–2013.
Hydrogeology of the Canadian River Alluvial Aquifer 25

Water-Table Fluctuation Method

The Water-Table Fluctuation (WTF) method (Healy 

and Cook, 2002) was used to estimate recharge to the 

Canadian River alluvial aquifer. The WTF method is based 

on the premise that short-term (hours to a few days) rises 

in groundwater levels in unconfined aquifers are due to 

recharge arriving at the zone of saturation following a period 

of precipitation. This method is most appropriately applied to 

groundwater wells with shallow water tables and hydrographs 

that display sharp rises in water levels after precipitation. The 

WTF method cannot account for a steady rate of recharge or 

recharge from sources other than precipitation. Recharge is 

calculated by using the WTF method as follows:

R S = ∆y h / ∆t (3)

where

Sy is the specific yield (dimensionless),

Δh is the change in water table, in inches, and 

Δt is the change in time of the water-level rise, in 

inches. 

A water-level hydrograph from the Crawford 

(355133099434901) well in Reach I (fig. 11) was analyzed 

by using the WTF method to estimate monthly recharge for 

2014. The water-level hydrographs from other wells did not 

display enough sharp water-level rises, or the water-level rises 

were so great that they indicated that recharge was coming 

from a source other than precipitation. Annual precipitation 

during 2014 was 17.0 in., measured at the nearby Camargo 

climate station (Oklahoma Climatological Survey, 2015e). The 

minimum estimated monthly recharge at this well was 0.0 in. 

for the month of January because only 0.02 in. of precipitation 

fell during this month. The maximum estimated monthly 

recharge at this site was 6.2 in. during June, calculated by 

using the specific-yield value of 22 percent described in the 

“Percent-Coarse Value and Hydraulic Properties” section. 

Estimated annual recharge at this site was 9.7 in. (57 percent 

of annual precipitation) during 2014. 

A portion of recharge estimated by using the WTF 

method at this alluvial site most likely flows through the 

sediments and discharges to the stream in days, so some of 

the estimated recharge is not accounted for on a monthly 

timescale. Additionally, a field-derived specific-yield value 

may be more appropriate for short-term changes in the water 

table (Scholl and others, 2005). As a result, the WTF method 

using the 22-percent specific yield may overstate recharge. 

Soil-Water-Balance Code

The soil-water-balance (SWB) code (Westenbroek and 

others, 2010) also was used to estimate the spatial distribution 

of groundwater recharge to the Canadian River alluvial 

aquifer. The SWB code is based on a modified ThornthwaiteMather method (Thornthwaite and Mather, 1957) and requires 

climatological and landscape characteristic data inputs 

including precipitation amount, temperature, soil-water storage 

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

land-cover type. These inputs are assigned to a user-specified 

grid (specified for this report as cell dimensions of 500 by 

500 ft), and the SWB code uses a mass-balance approach to 

compute gridded recharge as the difference between sources 

and sinks, accounting for the cumulative effects of the change 

in soil moisture.

R = (P + S + Ri) − (Int + Ro + ET) − ∆Sm (4)

where

R is recharge,

P is precipitation,

S is snowmelt,

Ri is surface runoff into a cell,

Int is plant interception,

Ro is surface runoff out of a cell,

ET is evapotranspiration, and

ΔSm is the soil moisture change.

Daily climate data were obtained for 39 climate stations 

(fig. 1; National Climatic Data Center, 2015) and interpolated 

to a grid by using the IDW method (Esri, 2015). Of the 39 

climate stations, 22 stations provided daily climate records 

throughout the study period of 1981–2013. In addition, 

these stations provided daily maximum and minimum air 

temperatures to allow for the SWB code to determine whether 

precipitation occurred as rain or snow.

Soil properties (soil-water storage capacity and 

hydrologic soil group) were derived from the Soil Survey 

Geographic database (Natural Resources Conservation 

Service, 2015). Surface runoff was calculated by using a 

flow-direction grid derived from a digital elevation model 

(DEM) (U.S. Geological Survey, 2013b), whereby values 

representing land-surface altitude were assigned to each SWB 

grid cell and runoff routed to downslope cells. In the SWB 

code, once water is routed to a closed surface, and the effects 

of ET from vegetation are accounted for, the only possible 

sink for the water is recharge, which can create situations 

where unreasonably high values are calculated. To ensure 

correct surface-water routing and to eliminate areas of internal 

drainage, depressions in the DEM were removed. 

Evapotranspiration in the SWB code is calculated 

as potential ET by using methods from Hargreaves and 

Samani (1985), whereby spatially variable ET estimates 

are produced by using user-supplied daily minimum and 

maximum temperatures. This potential ET represents the 

maximum amount of ET possible when given no limitation 

to soil moisture. The change in soil moisture is based on 

Thornthwaite and Mather (1957), where the potential ET is 

subtracted from daily precipitation. The resulting positive 

values represent water surplus, and negative values represent 

a cumulative deficiency calculated as a running total. For 

positive values, typically periods of high precipitation, actual 

ET equals potential ET. The SWB code does not compute ET 

from the groundwater table and therefore underestimates ET in 

areas where groundwater occurs near land surface.
26 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Scaling of vegetation root-zone values was necessary to 

allow for more recharge to the aquifer because stream base 

flow was otherwise substantially greater than inflows from 

recharge. Additionally, recharge obtained from the default 

root-zone values was 5.8 percent of precipitation, which was 

lower than the 7 to 11 percent range from literature describing 

recharge in Oklahoma (Barclay and Burton, 1953; Steele and 

Barclay, 1965) near the aquifer. Root-zone values represent 

the maximum depth to which various types of vegetation will 

grow and are classified on the basis of land use and soil type. 

Larger root-zone values result in the increased interception 

of soil moisture zone infiltration and thus decrease recharge, 

whereas smaller values increase recharge. For Reach I, the 

root-zone values for the forest and grass/pasture land-use types 

were scaled to 80 percent of the default root-zone values, and 

the crop land-use type was scaled to 50 percent of the default 

root-zone values. For Reach II, the root-zone values for the 

forest and grass/pasture land-use types were scaled to 50 

percent of the default root-zone values, and the crop land-use 

type was scaled to 30 percent of the default root-zone values.

The SWB code produced areally distributed monthly and 

annual recharge grids for the Canadian River alluvial aquifer. 

A prolonged period of less than average recharge occurred 

for 8 of the 10 years during 2003–12 (fig. 16), and 2011 was 

the ninth driest year in Oklahoma since 1925 (Shivers and 

Andrews, 2013). Additionally, 1981 was the last year of the 

1976–81 drought (Shivers and Andrews, 2013), and thus 

received less than average recharge. The SWB-estimated 

average annual recharge was 2.2 in/yr for Reach I (fig. 16A) 

and 4.2 in/yr for Reach II (fig. 16B). The SWB-estimated 

average annual recharge to the aquifer for both reaches was 

3.4 in/yr, or 8.7 percent of the average annual precipitation for 

the period 1981–2013 (fig. 16C). The highest SWB-estimated 

annual recharge for both reaches was 5.9 in/yr (173 percent of 

the average annual recharge [1981–2013]) in 1985 (fig. 16C). 

The lowest SWB-estimated annual recharge for both reaches 

was 0.6 in/yr (18 percent of the average annual recharge 

[1981–2013]) in 2003 (fig. 16C). 

A map of the spatially distributed average annual 

recharge in inches per year calculated by the SWB code is 

shown in plate 4. The decreased recharge in Reach I was 

expected to occur because of the lower precipitation from 

the semiarid climate versus the humid subtropical climate in 

Reach II. In Reach I, more precipitation occurred as recharge 

in the alluvial deposits than the terrace deposits because of 

a more sandy soil type that had a lower soil-water storage 

capacity. In Reach II, although the alluvial deposits were 

also of a more sandy soil type than the terrace deposits, less 

precipitation occurred as recharge in the alluvial deposits 

because of the lower infiltration rate from the assigned 

hydrogeologic soil group. Evapotranspiration was also higher 

in the Reach II alluvial deposits compared to the terrace 

deposits because of the predominance of the deeper-rooted 

grass/pasture land-cover type in the alluvial deposits, even 

after scaling of the root-zone values.

Compared to the WTF-estimated recharge, the SWBestimated average annual recharge for Reach I is substantially 

lower. Although recharge in 2014 was not estimated by using 

SWB, the high percentage of precipitation as recharge from 

the WTF method results in a much larger annual recharge for 

any given year. It is expected that the SWB-estimated recharge 

is a better estimate of recharge in this area based on previous 

reports that determined recharge as 12 percent of precipitation 

for the North Canadian River alluvial aquifer (Mogg and 

others, 1960) and 10 percent for the Rush Springs aquifer 

(Tanaka and Davis, 1963). 

Evapotranspiration from Groundwater

Evapotranspiration from groundwater was estimated 

by Scholl and others (2005) for the Canadian River alluvial 

aquifer in Norman, Okla., by using methods from White 

(1932). Uptake from plant transpiration was determined 

by using specific yield from soil columns and water-level 

measurements taken every hour from a continuous well for the 

following equation:

q S = ± y r ( ) 24 s (5) 

where

q is the daily-averaged ET in inches,

Sy is the specific yield (dimensionless),

24r is the average daily rise of the water table in 

inches per day (in/d), and

s is the decline in the water table during a 24-

hour period in inches.

By using this method, average, maximum, and minimum ET 

from groundwater values were estimated as 0.21, 0.51, and 

0.10 inches per day, respectively. 

The water table at the tested site was within 5.7 ft of 

land surface, which likely resulted in the relatively large 

contribution of evaporation and transpiration to water losses 

and may not characterize the alluvial deposits in other areas 

of the Canadian River alluvial aquifer where evaporative 

effects are minimal because of greater water-table depths. 

Additionally, the 22 percent specific yield may result in an 

overstated amount of ET from groundwater. As a result, the 

minimum ET value of 0.10 in/d was used in the conceptual 

model, which may provide a more realistic estimate of ET 

from groundwater. 
Hydrogeology of the Canadian River Alluvial Aquifer 27

SS

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

SS

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

SS

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

Year

Annual precipitation, in inches Annual precipitation, in inches Annual precipitation, in inches

Annual recharge, in inches Annual recharge, in inches Annual recharge, in inches

Annual recharge, in acre-feet Annual recharge, in acre-feet Annual recharge, in acre-feet

0

6.5

13.0

19.5

26.0

32.5

39.0

45.5

52.0

58.5

0

6.5

13.0

19.5

26.0

32.5

39.0

45.5

52.0

58.5

0

6.5

13.0

19.5

26.0

32.5

39.0

45.5

52.0

58.5

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0

29.5

59.0

88.5

118.0

147.5

177.0

0

13.0

26.0

39.0

52.0

65.0

78.0

91.0

104.0

117.0

0

42.0

84.0

126.0

168.0

210.0

252.0

294.0

SS, Steady-state numerical groundwater-flow model

Total annual recharge

Average annual recharge, 1981–2013

Annual precipitation

EXPLANATION

B. Reach II

C. Reach I and Reach II

A. Reach I

Figure 16. Annual recharge from 1981 to 2013 by using the soil-water-balance (SWB) code for A, Reach I; B, Reach II; and C, Reaches I 

and II of the Canadian River alluvial aquifer, Oklahoma.
28 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Conceptual Flow Model of the 

Canadian River Alluvial Aquifer

A conceptual flow model is a simplified description of 

the movement of water in and out of an aquifer as defined by 

the hydrogeologic framework. Primary components of the 

conceptual flow model include the hydrogeologic boundaries, 

which describe the conditions for flow between the aquifer and 

surrounding units, and an aquifer conceptual water budget, 

which describes the amount of groundwater that moves 

between each hydrogeologic boundary. 

Hydrogeologic Boundaries

The land surface of the Canadian River alluvial aquifer 

is the most extensive hydrogeologic boundary through which 

precipitation is either evapotranspired or recharges the water 

table. The base of the Canadian River alluvial aquifer is the 

hydrogeologic boundary through which water can move to 

or from the underlying bedrock units. Stream boundaries 

allow flow to be exchanged between the Canadian River 

alluvial aquifer and the Canadian River (or tributaries). The 

lateral extent of the Canadian River alluvial aquifer is a 

hydrogeologic boundary in most areas where bedrock units 

adjoining the Canadian River alluvial aquifer yield water to 

this aquifer. Lateral inflow is expected on the basis of previous 

investigations (Mogg and others, 1960; Wood and Burton, 

1968) and on the distribution of water types described in the 

“Water Quality” section of this report. 

Conceptual Water Budget

A conceptual water budget was constructed for the 

Canadian River alluvial aquifer to quantify the addition 

and removal of water from the boundaries of the aquifer, 

with estimated fluxes listed in table 5. The conceptual water 

budget is a generalized average of water fluxes for the model 

period 1981–2013. The aquifer alluvial and terrace deposits 

are considered a single unit; thus, water that flows from the 

Canadian River alluvial aquifer to the Canadian River is an 

aquifer outflow, whereas the reverse constitutes an inflow to 

the aquifer. The same is true for lateral flow from and to the 

surrounding bedrock. Inflows to the Canadian River alluvial 

aquifer include recharge to the water table from precipitation, 

lateral flow from adjoining bedrock units, and flow, or leakage, 

from the Canadian River, whereas outflows include lateral 

flow to bedrock, water-table ET, flow to the Canadian River, 

and groundwater use. Wells associated with water-table 

observations, or observation wells (fig. 17), do not show any 

substantial long-term water-table trends; therefore, the net 

change in groundwater storage is assumed to be negligible. 

Table 5. Conceptual water budget for the Canadian River alluvial 

aquifer, Oklahoma, 1981–2013.

[All units are in acre-feet per year. See table 4 for station names. --, not 

applicable]

Groundwater 

budget category Reach I Reach II Total

Inflows

Recharge 28,919 82,006 110,925

Lateral flow1 43,803 164,849 208,652

Outflows

Evapotranspiration 34,123 32,061 66,184

Base-flow gain1 38,006 205,377 243,383

Texas border to 07228500 38,006 -- --

07228500 to 07229050 -- 44,849 --

07229050 to 07229200 -- 29,768 --

07229200 to 07231500 -- 130,759 --

Groundwater use 593 9,416 10,009

1

These terms represent net flows. Base-flow gain was calculated as the 

difference between flow to and from the Canadian River. Lateral flow was 

calculated as the difference between the aquifer inflows and the outflows.

Total annual recharge inflows estimated by the SWB 

code, averaging 2.2 in for Reach I and 4.2 in for Reach II, 

were multiplied by the area of the watershed in each reach, 

then averaged over the simulated period to produce an annual 

average of 28,919 acre-ft/yr for Reach I and 82,006 acre-ft/yr 

for Reach II (fig. 16, table 5). A more detailed description of 

the SWB-derived recharge is available in the “Soil-WaterBalance Code” section of this report. 

Net flow, or the difference between flow to and from the 

Canadian River, was predominantly towards the Canadian 

River from the aquifer. This flow is hereinafter referred to 

as “base-flow gain.” Flow from the Canadian River to the 

aquifer may occur during periods of low recharge, as shown 

by the 2013 seepage run measurements. However, the BFI 

analysis showed substantial downstream increases in average 

base flow for the period 1981–2013; therefore, the BFIcomputed base flow (see “Base-Flow Separation” section of 

the report) was used in the conceptual model. Average annual 

base-flow gain in Reach I and Reach II was determined as the 

difference between stream base flow at the most upstream and 

downstream gages. The effects of surface-water flows were 

removed from the average annual base-flow gain estimation, 

which included tributary and wastewater treatment plant flows 

(Vikki Southerland, Oklahoma Department of Environmental 

Quality, written commun., 2015). The base-flow gain estimate 

is a simplification of a more complex system that includes 
Conceptual Flow Model of the Canadian River Alluvial Aquifer 29

198119821983198419851986198719881989199019921993199319941995199619971998199920002001200220032004200520062007200820092010201120122013198119821983198419851986198719881989199019921993199319941995199619971998199920002001200220032004200520062007200820092010201120122013

Year Year

Depth to water, in feet below land surfaceDepth to water, in feet below land surface

0

5

10

15

20

25

30

35

40

10

12

14

16

18

20

0

2

4

6

8

Simulated

Observed

EXPLANATION

A. OWRB observation well 9666 B. OWRB observation well 9591

OWRB, Oklahoma Water Resources Board

Figure 17. Observed and simulated depth to water for water-table observations in Oklahoma Water Resources Board (OWRB) wells A, 

9666, and B, 9591, in the Canadian River alluvial aquifer, Oklahoma.

other factors that influence the base-flow gain, such as 

regulation from upstream reservoirs; however, no releases 

from Sanford Dam in Texas were recorded during the period 

1981–2013. Average annual base-flow gain during the period 

1981–2013 was estimated to be 38,006 acre-ft/yr for Reach I, 

and 205,377 acre-ft/yr for Reach II (table 5). Most of the baseflow gain in Reach II occurred between the Purcell streamgage 

(07229200) and the Calvin streamgage (07231500) (table 5). 

The Canadian River alluvial aquifer was determined to 

contribute base flow of 0.3–2.3 ft3/s per mile to the Canadian 

River. 

Water-table ET was estimated by using methods 

from Scholl and others (2005) previously described in the 

“Evapotranspiration from Groundwater” section of this report. 

Evapotranspiration was estimated by using the 0.10-in/d rate 

applied to areas of the alluvial deposits with a water-table 

elevation near land surface. Because the ET rate from Scholl 

and others (2005) was based on a single site, the estimated ET 

for the aquifer may differ from the actual ET.

Net lateral flow was calculated as the difference between 

the aquifer inflows (recharge) and the outflows (base-flow 

gain, water-table ET, and groundwater use). The substantial 

lateral flow into the aquifer was expected based on an analysis 

of the 2013 water-table surface and documentation from 

previous studies. The large base-flow gain in Reach II between 

the Purcell streamgage (07229200) and the Calvin streamgage 

(07231500) indicates that most of the lateral inflow in Reach 

II may occur in this area of the aquifer. In other areas of the 

Canadian River alluvial aquifer, lateral flows are expected to 

produce smaller amounts of inflow. Groundwater use accounts 

for a minor percentage of outflows from the Canadian 

River alluvial aquifer, totaling 593 acre-ft/yr in Reach I and 

9,416 acre-ft/yr in Reach II.
30 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Simulation of Groundwater Flow in the 

Canadian River Alluvial Aquifer

Numerical groundwater-flow models were constructed 

on the basis of the hydrogeologic framework and conceptual 

flow model. The groundwater-flow models used the Newton 

solver (Niswonger and others, 2011), which is based on the 

MODFLOW code (Harbaugh, 2005), to simulate groundwater 

levels, interactions with surface-water features, and changes in 

streamflow and aquifer storage. These models were calibrated 

to better reproduce observed characteristics; improve the 

accuracy of future-predictive scenarios run to evaluate the 

effects of groundwater use over 20-, 40-, and 50-year periods; 

and observe the effects of a hypothetical 10-year drought and 

of groundwater-use rates in 2013 extended 50 years into the 

future. 

Model Extents and Configuration

The Canadian River alluvial aquifer was split into two 

groundwater-flow models. Reach I extends from the Texas 

border to the Bridgeport streamgage (07228500); Reach 

II extends from the Bridgeport streamgage (07228500) to 

Eufaula Lake (pl. 1). This division was chosen because of the 

presence of the Bridgeport streamgage (07228500), which 

allows for surface-water inflow in the Reach II groundwaterflow model to be set to the stream base flow determined at 

this streamgage. The two models function independently and 

do not have linked flows. To aid groundwater-flow model 

assessment, individual water budgets are described in this 

report for Reaches I and II. 

Layer 1 of the models represented the undifferentiated 

Quaternary-age alluvial and terrace deposits, and layer 2 

represented undifferentiated bedrock units. The land-surface 

altitude of the models was represented by a DEM (U.S. 

Geological Survey, 2013b) and formed the top of layer 1, 

and the altitude of the bedrock surface formed the top of 

layer 2 for both reaches. The thickness of layer 1 included 

a maximum of 117 ft in Reach I near the Texas border and 

139 ft in Reach II near Eufaula Lake. Layer 2 was assigned an 

arbitrary and uniform thickness of 100 ft in both models. The 

bottom of layer 2 was a no-flow boundary. Bedrock outcrops 

in the aquifer areal extent were also simulated as no-flow 

boundaries. 

Initial values for horizontal hydraulic conductivity, 

specific yield, and specific storage for the Canadian River 

alluvial aquifer, represented by layer 1, are described in 

the “Percent-Coarse Value and Hydraulic Properties” section 

of this report. Vertical anisotropy was set to 3.0 for layer 1 

and 5.0 for layer 2, as described by Todd (1980). Specific 

storage was set to 0.0001 ft-1 and specific yield was set to 

20 percent for layer 2, as described by Domenico and Mifflin 

(1965). 

Discretization

A grid of 500-by-500-ft cells was used to represent the 

groundwater-flow model domains (pl. 5). This cell size was 

chosen to best capture variations in hydrogeologic parameters 

and boundary conditions without unduly slowing simulation 

speeds that arise from having large numbers of small cells 

in the model area. The Reach I model grid consisted of 

589 rows, 1,059 columns, and 2 layers, with 27,041 active 

cells in each layer. The Reach II model grid included 774 

rows, 1,958 columns, and 2 layers, with 41,120 active cells 

in each layer. In Reach II, the top altitude of the model was 

raised by 0.4 percent to prevent cells from flooding and thus 

converting to confined-flow conditions. The model grids were 

oriented approximately parallel to the hydraulic gradient of the 

Canadian River alluvial aquifer. The groundwater-flow model 

boundaries were adjusted to ensure that each active cell was in 

connection with at least one other active cell.

There are few long-term water-table-altitude observation 

wells completed in the Canadian River alluvial aquifer; 

therefore, predevelopment steady-state conditions could not 

be determined, and the steady-state period for Reach I and 

Reach II was simulated as the average of model stresses for 

the period 1981–2013 and used a single 365-day stress period. 

The first stress period in both Reach I and Reach II was the 

steady-state period. The transient simulations for Reach I 

and Reach II simulated the period 1981–2013 and used 396 

monthly stress periods, with 16 time steps per stress period to 

allow for temporal changes in the water table to be solved. The 

monthly stress periods implemented in the groundwater-flow 

models were used to capture seasonally variable processes, 

such as precipitation, water-table ET, and groundwater use.

Boundary Conditions

Boundary conditions for the Canadian River alluvial 

aquifer groundwater-flow models represent the locations 

where the inflow or outflow of water occurs (pl. 5). The 

selection of boundaries is important for development of an 

accurate groundwater-flow model (Franke and others, 1987). 

Boundary types are chosen that best represent hydrogeologic 

features on the basis of model objectives. Boundaries for the 

Canadian River alluvial aquifer were simulated by using two 

types of boundary conditions: specified-flux boundaries or 

head-dependent boundaries. For a specified-flux boundary, a 

user-specified discharge rate is set that allows for groundwater 

to move either in or out of the boundary. The no-flow 

boundaries established at the bottom of layer 2 and at some 

locations along the lateral boundary in both layer 1 and layer 2 

where bedrock units do not yield water to the Canadian River 

alluvial aquifer are also specified-flux boundaries. A headdependent boundary condition simulates flow on the basis 

of the difference between a user-specified altitude and the 

head in model cells. Unless otherwise specified, the boundary 

conditions described apply to both Reaches I and II.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 31

Groundwater Recharge

A specified-flux boundary condition representing areally 

distributed recharge was applied by using the Recharge 

package (Harbaugh, 2005), in which recharge was applied to 

the highest active model cell. Recharge rates were obtained 

from the SWB code, in which the steady-state simulations 

used an average recharge value calculated for the period 

1981–2013, and the transient simulations used recharge 

values calculated for each month. Time-varying adjustment 

of recharge during each stress period occurred during the 

calibration phase to obtain better matches between simulated 

and observed values. 

Water-Table Evapotranspiration

A head-dependent boundary condition was applied 

through use of the Evapotranspiration package (Harbaugh, 

2005). The Evapotranspiration package was used to simulate 

water-table ET processes that were not simulated by the SWB 

code, which only considers ET from vegetation on the basis 

of the soil moisture available. The maximum water-table ET 

rate for each stress period was set as the difference between 

the potential and actual ET computed from the SWB code. 

The water-table ET extinction depth, which is the depth at 

which water-table ET ceases to occur, was set equal to the 

SWB root-zone depth for each land-cover type. The watertable ET decreases linearly with decreases in the simulated 

water-table altitude, and no water-table ET occurs when the 

simulated water-table altitude is below the extinction depth. 

Water-table ET processes were limited to the alluvial deposits 

where the water table is most commonly near the land surface. 

The water-table ET rate was adjusted during groundwater-flow 

model calibration.

Streamflow

Stream base flow in the Canadian River alluvial aquifer 

was simulated by using the Streamflow-Routing package 

(SFR; Niswonger and Prudic, 2005) (plate 5), representing 

a head-dependent boundary condition. The SFR package 

routes flow between the aquifer and the stream by using 

Darcy’s Law The flow between the aquifer and the stream is 

the product of the streambed conductance and the difference 

between the water-table altitude 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 on the basis of the geometry 

of the stream channel. Where water-table altitudes are higher 

than stream stage, inflow to the stream occurs at a specified 

streambed conductance rate. Where water-table altitudes are 

lower than stream stage, streamflow discharge to the aquifer 

occurs. 

A stream-water balance provides the amount of water 

available for exchange between the stream and the aquifer 

in groundwater-flow model simulations. Inflows include 

specified inflows (such as simulated inflows from outside 

the active area), tributary stream segments, and base-flow 

gain from the groundwater table. Outflows include water 

routed downstream, diversions, ET, and base-flow to the 

aquifer. Flows are calculated for each part of the stream 

contained in a model cell, known as reaches, until the end of 

a segment, or group of cells with uniform or linear hydraulic 

properties, is reached during each time step. Calculation of 

flows for the next downstream segment repeats this process 

by using flows from the upstream segment until water is 

routed out of the active area at a groundwater-flow model 

boundary.

The spatial location and extent of the river were 

derived from the National Hydrography Dataset (NHDPlus; 

McKay and others, 2012), a 1:100,000-scale geospatial 

dataset of surface-water features. The groundwater-flow 

model active area was not extended to include surfacewater tributary channels, and inflow points were created 

to simulate monthly stream base-flow discharges from the 

perennial tributaries (Deer Creek, Buggy Creek, Walnut 

Creek, and Little River). Seven inflow points also were 

implemented that simulate smaller tributaries between the 

Norman streamgage (07229050) and the Purcell streamgage 

(07229200). 

All other stream features were considered to be 

intermittent or ephemeral and were assumed to have no 

base flow. In Reach I, stream base flow from the Canadian 

River in Texas that crossed the border into Oklahoma was 

simulated with an inflow point. In Reach II, stream base 

flow for the Canadian River estimated at the Bridgeport 

streamgage (07228500) was simulated with an inflow point. 

Additionally, inflow points were created for five wastewatertreatment plants in Reach II that discharge to the Canadian 

River, and discharge data were used as inputs for each stress 

period.

The streambed hydraulic conductivity for Reach I and 

Reach II was set to 5 ft/d across all segments, representing 

a fine sand. This value increased the stability of the 

groundwater-flow models and is expected to reasonably 

represent the streambed hydraulic conductivity. Stream 

width was set to 150 ft in Reach I and 175 ft in Reach II on the 

basis of aerial photographs (U.S. Department of Agriculture, 

2015) from 2015. The streambed altitude for each stream 

reach was set between 3 and 5 ft below land surface in each 

model cell. Differences in stream channel spatial location 

occurred between the DEM and the NHDPlus flowline 

because of the averaging of DEM cells and migration of the 

stream channel in the alluvial valley over time. To ensure 

correct surface-water routing in the stream, the stream channel 

location was adjusted to ensure that the altitude decreased in 

a downstream direction to avoid the uphill routing of water in 

the model.
32 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Lateral Flow

Flow to and from bedrock aquifer units adjoining the 

Canadian River alluvial aquifer was represented by a headdependent boundary condition by using the General Head 

Boundary (GHB) package (Harbaugh, 2005) (pl. 5). The GHB 

package uses a linear relation between flux and the watertable altitude (or water head), and a user-specified reference 

water-table altitude and conductance. Similar to the SFR 

package, 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 condition and the model cell. When the simulated 

water-table altitude is lower than the reference water-table 

altitude, water flows into the groundwater-flow model at the 

specified conductance rate. When the simulated water table 

is higher than the reference water-table altitude, water is 

removed from the groundwater-flow model. 

GHB cells were implemented along the boundary of the 

aquifer in layer 1 to simulate lateral inflow from bedrock. 

GHB cells were implemented in layer 2 to simulate lateral 

inflow from adjoining bedrock units. Conductance values were 

estimated on the basis of the local hydraulic properties of the 

aquifer for each GHB cell. Higher values were used for layer 1 

when simulating the alluvial and terrace deposits, and lower 

values were used in layer 2 when simulating the bedrock. The 

reference water-table altitude for each GHB cell simulating 

flow from bedrock was determined from the nearest bedrock 

water-table measurement.

Flow to Eufaula Lake from the Canadian River alluvial 

aquifer was represented by a head-dependent boundary 

condition by using the Drain package (Harbaugh, 2005) 

(pl. 5). The function of these drain cells is similar to that of the 

GHB cells, except flow is only permitted in one direction.

Groundwater Use

Groundwater use representing a specified-flux boundary 

condition was simulated by using the Well package (Harbaugh, 

2005). Annual groundwater-use rates reported by the OWRB 

were tabulated from 1981 to 2013, and monthly water 

demand, or the percent of annual water use per month, was 

obtained for the three planning regions encompassed by the 

Canadian River alluvial aquifer. The monthly water demand 

for Reach I was obtained from the West Central Watershed 

Planning Region Report (Oklahoma Water Resources Board, 

2012b), whereas the monthly water demand for Reach II 

was obtained from the Central Watershed Planning Region 

Report (Oklahoma Water Resources Board, 2012c) and the 

Eufaula Watershed Planning Region Report (Oklahoma Water 

Resources Board, 2012d). This water demand quantifies the 

water use per month by each groundwater-well use type and 

watershed region. For the public-supply and irrigation well use 

types, annual groundwater-use rates were multiplied by the 

monthly public-supply water demand and the irrigation water 

demand, respectively. All other use types were multiplied 

by the monthly public-supply water demand. Groundwater 

use from self-supplied domestic wells was expected to be 

relatively small and was not simulated. 

Groundwater-use rates for the steady-state simulation 

were determined from the average annual groundwateruse rates of 1981–2013, whereas transient simulation 

groundwater-use rates were simulated for each stress period 

based on the respective water-demand use type. Pumping 

wells and the respective observations that were located in 

cells with steep water-level gradients were moved to a nearby 

cell with a lower water-level gradient to lessen the reduction 

of pumping rates because of lack of saturation in the cell. All 

pumping wells were located in layer 1 of the groundwaterflow models.

Model Calibration

Model calibration is the process by which the initial 

values for model inputs are adjusted to improve the fit between 

observed and simulated data. 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 on the basis of 

the reduction of this residual and the fit of the calibrated 

groundwater-flow model water-budget components to those of 

the conceptual flow model water budget.

The calibration process for the Reach I and Reach II 

groundwater-flow models included manual adjustment of 

model inputs, or parameters, by trial and error, followed 

by use of automated nonlinear regression techniques. 

Parameters were selected that represent important hydrologic 

processes, have a moderate uncertainty in their values, and 

have associated observations, or calibration targets, that are 

sensitive to adjustments in these parameters. Calibration 

targets included measurements of water-table altitude, 

estimated stream base flows, and base-flow gain to the 

Canadian River between streamgages. Manual parameter 

adjustment was conducted until minimal changes in the 

residuals occurred, and further adjustments did not yield 

improvements.

After the manual parameter adjustment, automated 

nonlinear regression techniques were performed by using 

parameter estimation (PEST) (Doherty, 2010), an open-source 

calibration and parameter uncertainty code. The PEST code 

uses the Gauss-Marquardt-Levenberg algorithm to adjust 

user-specified parameters to minimize the residual between 

the simulated data and the calibration targets (Doherty, 2010). 

PEST accomplishes this adjustment by running the model as 

many times as needed to determine the best parameter values 

(Doherty, 2010), while automatically updating the parameter 

values during each step of the process. This approach typically 

allows for the optimal values of a large number of parameters 

to be estimated together with greater speed than that of a 

traditional manual calibration approach.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 33

During the PEST calibration, the calibration targets were 

weighted to account for error in each type of observation. 

Weights were assigned by using an inverse relation to 

the standard deviation (Doherty, 2010), and the weighted 

calibration targets were placed in observation groups on the 

basis of observation type. The sum of the squared weighted 

residuals represented the objective function, which measured 

the fit between observed and simulated data. Weighting for 

each observation group was then adjusted to balance the 

contribution from each observation group to the objective 

function. Table 6 shows the water-table altitude, stream base 

flow, and base-flow gain standard deviations, observation 

counts, and group contributions to the objective function.

The calibration approach implemented hybrid 

regularization (Tonkin and Doherty, 2005), also known 

as singular value decomposition-assist (SVDA; Doherty, 

2010), to reduce the sustained run times associated with the 

calibration of a large number of parameters. SVDA computes 

a user-specified number of super parameters, or combinations 

of base parameters that are most responsive to the dataset 

(Doherty, 2010). The groundwater-flow model must be run 

one time for each adjustable parameter; thus, using fewer 

parameters greatly reduces the time required for calibration of 

the groundwater-flow models. Additionally, SVDA discards 

parameters with little to no sensitivity to the calibration 

targets, which produces a more stable calibration process.

Tikhonov regularization, whereby user-specified “soft” 

information pertaining to certain parameters is applied in the 

form of mathematical relations, was used to limit changes 

made to the calibrated values of certain parameters. This 

regularization is accomplished through use of a penalty 

applied to the objective function when the regularized 

parameters deviate from their original values (Doherty, 

2010). Tikhonov regularization was applied to the horizontal 

hydraulic conductivity array multiplier for layer 1 of the 

groundwater-flow models to minimize discrepancies between 

the average horizontal hydraulic conductivities for Reaches 

I and II. Additionally, by limiting the automated calibration 

adjustments to these arrays, the changes applied by using 

PEST are constrained to more realistic values.

Calibration Parameters

Five groups of parameters, representing 311 parameters 

in Reach I and 483 parameters in Reach II, were used in the 

groundwater-flow model calibration. Those groups included 

parameters representing horizontal hydraulic conductivity, 

water-table ET rate, recharge rate, specific yield, and GHB 

conductance. The recharge group consisted of a time-varying 

recharge-rate parameter as a multiplier for recharge in each 

stress period for both reaches. The remaining parameter 

groups were set as fixed parameters that did not change 

Table 6. Components of the objective function prior to calibration by using parameter estimation for Reach I and Reach II of the 

Canadian River alluvial aquifer, Oklahoma.

[USGS, U.S. Geological Survey; ft, feet; OWRB, Oklahoma Water Resources Board; ft3/s, cubic feet per second; <, less than]

Observation group Description Standard 

deviation

Group 

contribution

Number of 

observations

Objective function 

components

Reach I of the Canadian River alluvial aquifer

Water-table altitude USGS water-table measurements 1.5 ft 24 percent 101 10,916

Water-table altitude OWRB water-table measurements 1.2 ft 10 percent 82 4,621

Stream base flow Bridgeport streamgage (07228500) 25.0 ft3/s 56 percent 397 26,402

Base-flow gain Reach I base-flow gain 16.1 ft3/s 10 percent 1 4,218

Total 581 46,157

Reach II of the Canadian River alluvial aquifer

Water-table altitude USGS water-table measurements 2.0 ft 25 percent 762 26,386

Water-table altitude OWRB water-table measurements 4.0 ft 8 percent 244 8,779

Stream base flow Norman streamgage (07229050) 34.4 ft3/s <1 percent 85 517

Stream base flow Purcell streamgage (07229200) 55.3 ft3/s 4 percent 336 4,102

Stream base flow Calvin streamgage (07231500) 148.3 ft3/s 55 percent 397 57,653

Base-flow gain Bridgeport to Norman streamgages 23.7 ft3/s <1 percent 1 52

Base-flow gain Norman to Purcell streamgages 32.1 ft3/s <1 percent 1 458

Base-flow gain Purcell to Calvin streamgages 89.6 ft3/s 8 percent 1 8,617

Total 1,827 106,564
34 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

during the simulation. For areas where horizontal hydraulic 

conductivity was thought to be relatively uniform, horizontal 

hydraulic conductivity values were grouped into 25 parameter 

zones in Reach I, and 49 parameter zones in Reach II (pl. 6). 

The horizontal hydraulic conductivity was adjusted between 

5 and 100 percent where mixed bedrock and alluvial deposits 

were thought to be present. This range in multipliers represents 

the uncertainty inherent in the lithologic-log reclassification 

and interpolation methods used to obtain horizontal hydraulic 

conductivity. Temporal recharge array multipliers were applied 

to the monthly recharge arrays. The water-table ET rates were 

adjusted by using an array multiplier until an optimal rate was 

determined and then applied uniformly to all temporal ET 

arrays for both reaches. A multiplier of up to 30 percent was 

applied uniformly to the specific-yield arrays in both reaches. 

GHB conductance was adjusted until the water table in the 

simulated terrace locations approached observed data. 

Calibration Targets

Calibration targets included measurements of water-table 

altitude, estimated stream base flows, and base-flow gain to 

the Canadian River between streamgages, and were placed 

in an observation group of the same name (table 6). Watertable altitude observations were obtained from the National 

Water Information System (NWIS) database (U.S. Geological 

Survey, 2013a) and the OWRB database (Oklahoma Water 

Resources Board, 2015a). Screened intervals for observation 

wells were checked to ensure that the observations were 

made in the Canadian River alluvial aquifer. The landsurface altitude of the observations was compared to the 

altitude obtained from a DEM, and observation targets with 

large discrepancies were discarded. The water-table altitude 

observations in the alluvial and terrace deposits were spatially 

distributed, but only a few observations were available for 

each year of the model period. The Reach I groundwater-flow 

model used 64 observation wells. A total of 38 water-table 

altitude observations were used in the steady-state simulation, 

and 145 were used in the transient simulation. The Reach II 

groundwater-flow model used 363 observation wells. A total of 

77 water-table altitude observations were used in the steadystate simulation, and 929 were used in the transient simulation. 

Stream base flows at streamgages were used as 

primary calibration targets because of sparse water-table 

altitude observations in the simulated period. BFI-computed 

(estimated) stream base flows at the Bridgeport streamgage 

(07228500), the most downstream location in Reach I, were 

used as stream base-flow calibration targets in Reach I. 

BFI-computed stream base flows at the Norman streamgage 

(07229050), Purcell streamgage (07229200), and Calvin 

streamgage (07231500) were used as stream base-flow 

calibration targets in Reach II. Simulated stream base flows 

at streamgages were monitored by using the Gage package 

(Merritt and Konikow, 2000) in conjunction with the SFR 

package. For Reach I, 1 stream base-flow observation 

was used in the steady-state simulation, and 396 monthly 

stream base-flow observations (1 observation per stress 

period) were used in the transient simulation. For Reach II, 

1 stream base-flow observation was used in the steady-state 

simulation at the Purcell streamgage (07229200), and Calvin 

streamgage (07231500), and 816 monthly stream base-flow 

observations were used in the transient simulation between all 

3 streamgages.

Average annual base-flow gain to the Canadian River 

across the groundwater-flow model transient-simulation 

period was set as a calibration target (table 6). The simulated 

contribution was determined as the sum of the “Flow to 

Aquifer” column in the SFR flow file for the stream segments 

between each streamgage, divided by the 396 stress periods. 

In Reach I, the average annual base-flow gain to the Canadian 

River between the Texas border and the Bridgeport streamgage 

(07228500) was used as a single observation. In Reach II, each 

average annual base-flow gain to the Canadian River between 

successive streamgages was used as a single observation, for a 

total of three base-flow gain observations in Reach II. 

Calibration-Target Uncertainty and Weighting

The water-table altitude, stream base flow, and baseflow gain calibration targets in each observation group were 

weighted by using error-based weighting (Hill and Tiedeman, 

2007). Water-table weights were determined on the basis 

of three error components: (1) the location accuracy, or 

how precise the coordinates of the wells were known for 

observation wells; (2) the altitude accuracy, which is based on 

the method used to determine the land-surface altitude; and 

(3) the temporal variability of water levels at each observation 

well. Methods from Clark and Hart (2009) were used to 

determine the estimated uncertainty for the location accuracy. 

Stream base flow weights were determined on the basis of the 

accuracy of the streamflow data at each streamgage.

The location and altitude accuracy values recorded in 

the NWIS and OWRB databases are based on the method 

used to obtain each measurement, typically by using a Global 

Positioning System 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 arc-seconds. 

A radius equal to the location accuracy was created for each 

observation well, and the standard deviation associated with 

the land-surface altitude in the location-accuracy radius 

was then 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 water-table range was determined by using either the 

seasonal water-table range from the continuous recorder 

wells or directly from the water-table altitude observations. 

Though the continuous recorder wells had measurement 

periods of less than 2 years, those measurements show the 

effects of partial drought conditions prevalent in 2014 and 
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 35

unusually high precipitation in May 2015 (fig. 11, fig. 12). The 

minimum, maximum, and average range in water-table altitude 

observations for the period 2014–15 at the continuous recorder 

wells were 0.9 ft, 11 ft, and 4.4 ft, respectively (fig. 11, 

fig. 12). The standard deviation for the temporal variability 

was calculated as the water-table range divided by four (Hill 

and Tiedeman, 2007). 

By using methods from Hill and Tiedeman (2007), 

the standard deviations for the location accuracy, altitude 

accuracy, and temporal variability were converted to variances 

and summed for each observation well. The summed variance 

at each observation well was then converted to a standard 

deviation. The standard deviation of USGS water-table 

altitude observations was between 1.5 and 2.0 ft. The standard 

deviation for OWRB water-table altitude observations was 

between 1.2 and 4.0 ft (table 6). 

Most of the field streamflow measurements collected 

during the transient period at each of the four streamgages 

were rated as “fair” in NWIS, which corresponds to a 

95-percent confidence interval of ±15 percent of true 

streamflow (U.S. Geological Survey, 2013c). The standard 

deviation for the stream base-flow observations at each 

streamgage were then calculated as 15 percent of the stream 

base flow, divided by the critical value of a 95-percent 

confidence interval.

Weights for the base-flow gain were assigned by using 

methods from Hill and Tiedeman (2007) and were given a 

95-percent confidence interval of ±15 percent of actual flow. 

The standard deviations and variance of the stream base-flow 

at each streamgage during the transient period were calculated, 

and the upstream and downstream streamgage variances were 

summed and converted to produce a standard deviation for the 

base-flow gain. 

Prior to the automated calibration process using PEST, 

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 (table 6) was set through a series of PEST trial runs 

in which various combinations of observation-group weights 

were tested to determine the best weighting arrangement to 

reduce the objective function. Stream base-flow observations 

received the largest weighting in both Reach I and Reach 

II; at least one base-flow observation was available for each 

stress period. In Reach II, simulated stream base flows at 

the Norman streamgage (07229050) and Purcell streamgage 

(07229200) closely matched observed stream base flow; 

therefore, the group contribution for base-flow observations 

from those streamgages received minimal weighting (table 6). 

Calibration Results

Calibration outcomes were evaluated on the basis of 

the reduction of the residual between the calibration targets 

and simulated values, as well as the fit of the calibrated 

groundwater-flow model water-budget components to those 

of the conceptual flow model water budget. Additionally, the 

calibrated parameters were evaluated for unrealistic parameter 

values from the PEST calibration.

Comparison of Simulated and Observed Values

The water-table altitude, stream base flow, and base-flow 

gain residuals were determined as the difference between 

observed and simulated values; therefore, residuals with 

positive values indicate lower simulated values than observed 

values, whereas negative values indicate higher simulated 

values than observed values. The root-mean-square error 

(RMSE) was calculated for the water-table altitude by using 

the following equation:

RMSE

n

h hs

i

n

= − ( ) =

∑

1

0

2

1

(6)

where

n is the number of water-table altitude 

observations,

ho is the observed water-table altitude, in feet, 

and

hs is the simulated water-table altitude, in feet.

Reach I

For Reach I, a good agreement between the observed 

and simulated water-table altitudes was obtained (fig. 18A, 

table 7). The combined Reach I water-table altitude RMSE 

for both steady-state and transient simulations was 6.1 ft, 

and 75 percent of residuals were within ±6.7 ft of observed 

measurements (table 7). The simulated water-table relief in 

Reach I was 826 ft, and maximum and minimum water-table 

altitudes were 2,215 ft and 1,389 ft, respectively. The RMSE 

as a percentage of this water-table relief was 0.7 percent for 

the steady-state simulation and 0.8 percent for the transient 

simulation (table 7), which relates the RMSE to water-table 

variability.

The spatial distribution of the residuals was not random; 

a slight bias occurred in the simulated water-table altitude 

below the observed water-table altitude (fig. 18B), particularly 

at altitudes near 1,700 ft, 1,850 ft, and 2,100 ft (fig. 18A). 

The underfit of the simulated water-table altitudes compared 

to the observed water-table altitudes occurred in the terrace 

where simulated water-table gradients between 50 and 120 

ft/mi towards the Canadian River resulted in difficulties in 

maintaining a simulated saturated thickness. Most of the 

USGS observed water-table altitude data were from wells 

completed in the alluvial deposits and were above the 1:1 line, 

whereas many of the OWRB water-table altitudes were located 

in the terrace, and were below the 1:1 line (fig. 18A). The 

average simulated water-table altitude at OWRB observation 

well 9666 (fig. 17A) in the terrace was 3.3 ft below the average 

of the observed water-table altitudes. This observation well 

is located adjacent to multiple SFR stream cells, which may 

dampen fluctuations in the simulated water-table altitude. 
36 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Water-table residual (measured minus simulated), in feet

Water-table residual (measured minus simulated), in feet

Observed water-table altitude, in feet

Observed water-table altitude, in feet

1,300 1,500 1,700 1,900 2,100 2,300

500 700 900 1,100 1,300 1,500 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18

2,300

2,100

1,900

1,700

1,500

1,300

500

700

900

1,100

1,300

1,500 300

250

200

150

100

50

0

Count

Simulated water-table altitude, in feet

Count

Simulated water-table altitude, in feet

0

5

10

15

20

25

30

35

40

A. Reach l B. Reach l

C. Reach ll D. Reach ll

Simulated water table = 0.9962 (Observed water table) + 5.2739

Coefficient of determination (R2

) = 0.9995

Simulated water table = 0.9961 (Observed water table) + 5.8392

Coefficient of determination (R2

) = 0.9990

EXPLANATION

EXPLANATION

Water table, USGS

Water table, OWRB 

Water table, USGS

Water table, OWRB 

USGS, U.S. Geological Survey

OWRB, Oklahoma Water Resources Board 

Figure 18. Observed and simulated water-table altitudes for A, Reach I, and C, Reach II, and histograms showing water-table residuals 

for B, Reach I, and D, Reach II, of the Canadian River alluvial aquifer, Oklahoma.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 37

A total of 118 out of 145 observed water-table altitudes 

were measured between years 2001 and 2013; therefore, the 

temporal distribution of residuals was biased to this period. 

Fluctuations in the observed water-table altitude prior to 

this period were minimal, which simplified the water-table 

calibration, and resulted in a maximum water-table residual 

of less than 5 ft between 1980 and 2001. The largest residual 

of 18.8 ft (table 7) below the observed water table occurred in 

2013 at an observation well with a single measurement, which 

may poorly represent longer-term conditions. 

Observed (estimated) and simulated stream base flows 

at the Bridgeport streamgage (07228500) were comparable, 

though simulated average stream base flow was lower than 

the observed average stream base flow (fig. 19, table 8). This 

residual was due to stream base-flow differences of up to 

466 ft3/s that occurred between stress periods in the transient 

simulation, which also resulted in difficulties reproducing 

some stream base-flow peaks and valleys. Additionally, 

hydrograph separation techniques may not fully isolate baseflow conditions; therefore, it is possible that the peaks in the 

BFI-computed stream base flows represent a percentage of 

runoff. Moreover, bank storage effects (Chen, 2003), by which 

floodwater infiltrates the aquifer and is released days to weeks 

after floodwater recedes, may increase stream base flows 

during periods of no new recharge. The observed stream baseflow ranged from zero during summer months when watertable ET withdrawals were greatest to 648 ft3

/s during large 

precipitation events (table 4). The simulated average stream 

base flow in Reach I (table 8) was within the 95-percent 

confidence interval of the stream base-flow observations at the 

Bridgeport streamgage (07228500) (fig. 20). The variability 

in flow increases downstream at each successive streamgage 

because of the large increases in flows between streamgages. 

Streamflows at the Bridgeport streamgage (07228500) 

were typically the smallest and therefore had the narrowest 

confidence interval.

Simulated average base-flow gain from the border to the 

Bridgeport streamgage (07228500) was 8.8 ft3/s (17 percent) 

lower than estimated average base-flow gain (fig. 20). This 

difference is largely due to the stream base-flow peaks that 

were not matched at each streamgage in the groundwater-flow 

model. The simulated average base-flow gain is within the 

95-percent confidence interval of the estimated average baseflow gain (fig. 20).

Reach II

For Reach II, the observed and simulated water-table 

altitudes generally fit a 1:1 line (fig. 18C). The combined 

Reach II water-table altitude RMSE for both steady-state and 

transient simulations was 4.0 ft, and 75 percent of residuals 

were within ±4.3 ft of observed measurements (table 7). 

The water-table relief in Reach I was 759 ft, and maximum 

and minimum water-table altitudes were 1,362 ft and 602 

ft, respectively. The RMSE as a percentage of this watertable relief was 0.7 percent for the steady-state simulation 

and 0.5 percent for the transient simulation (table 7), which 

indicates the relation between RMSE and water-table 

variability. 

The residual distribution for Reach II was slightly above 

the 1:1 line, indicating a bias in the simulated water-table 

altitude above the observed water-table altitude (fig. 18D). 

Similar to Reach I, the large water-table gradients in the 

terrace—as large as 215 ft/mi towards the Canadian River in 

Reach II—resulted in lower simulated versus observed watertable altitudes compared to the alluvial deposits. This relation 

is shown on the 1:1 line for water-table altitudes below about 

650 ft. However, this increased hydraulic gradient in Reach 

II compared to Reach I, combined with greater GHB inflow 

to the terrace, resulted in increased groundwater flow to the 

alluvial deposits. As a result, higher water-table altitudes 

occurred in the alluvial deposits, which contained 75 percent 

Table 7. Comparison of observed and simulated water-table altitudes for the Canadian River alluvial aquifer, Oklahoma, 1981–2013.

[Residual is calculated as the measured value minus the simulated value; thus, a minimum residual indicates that simulated values are smaller than observed 

values, and a maximum residual indicates that simulated values are larger than observed values. All units except percentage of head relief are in feet. RMSE, 

root-mean-square error; ±, plus or minus]

Statistic

Reach I Reach II

Steady state Transient All Steady state Transient All

Observation count 38 145 183 77 929 1,006

Maximum residual -9.6 -15.2 -15.2 -14.4 -19.4 -19.4

Average residual -0.04 1.9 1.5 -2.8 -1.2 -1.3

Minimum residual 18.0 18.8 18.8 8.6 13.6 13.6

Mean absolute residual 0.04 1.9 1.5 2.8 1.2 1.3

RMSE 5.6 6.2 6.1 5.3 3.9 4.0

75 percentile residual range ±5.2 ±7.1 ±6.7 ±6.0 ±4.0 ±4.3

RMSE percentage of water-table relief 0.7 0.8 0.7 0.7 0.5 0.6
38 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer 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 2006 2007 2008 2009 2010 2011 2012 2013 2014

Stress period

Stream base flow, in cubic feet per second

0

100

200

300

400

500

600

700

800

900

1,000

Streamflow, in cubic 

feet per second

0

2,000

4,000

6,000

Observed stream base flow

Simulated stream base flow

EXPLANATION

Observed streamflow

Canadian River at Bridgeport, Okla. (07228500)

Figure 19. Observed streamflow, observed stream base flow, and simulated stream base flow at the Canadian River at Bridgeport, 

Oklahoma streamgage (07228500) for Reach I of the Canadian River alluvial aquifer, Oklahoma, 1981–2013.

Table 8. Comparison of observed and simulated average stream base flow for the Canadian River alluvial aquifer, Oklahoma, 1981–

2013.

[Residual is calculated as the measured value minus the simulated value; thus, a minimum residual indicates that simulated values are smaller than observed 

values, and a maximum residual indicates that simulated values are larger than observed values. All units are in cubic feet per second. ±, plus or minus]

Statistic

Streamgage

Bridgeport 

(07228500)

Norman 

(07229050)

Purcell 

(07229200)

Calvin 

(07231500)

Average observed stream base flow 142 199 292 648

Average simulated stream base flow 133 164 238 517

Average residual 8.8 35 54 132

Minimum residual 293 460 781 3,729

Maximum residual 170 55 191 497

75 percentile residual range ±30 ±52 ±112 ±235

Root-mean-square error 75 99 149 543
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 39

Base-flow observation location

Canadian River near Bridgeport, Okla.

Canadian River at Norman, Okla.

Canadian River at Purcell, Okla.

Canadian River at Calvin, Okla.

Base-flow gain from the

Texas-Oklahoma border to

Canadian River at Bridgeport, Okla.

Base-flow gain from

Canadian River at Bridgeport, Okla., to

Canadian River at Norman, Okla.

Base-flow gain from

Canadian River at Norman, Okla., to

Canadian River at Purcell, Okla.

Base-flow gain from

Canadian River at Purcell, Okla., to

Canadian River at Calvin, Okla.

0

200

400

600

800

1,000

1,200

Base flow, in cubic feet per second

61.1

17.0 8.8 11.3

Observed average stream base flow

Simulated average stream base flow

Estimated average base-flow gain

Simulated average base-flow gain

Upper and lower 95 percent

 confidence interval

Base-flow gain residual, in 

 cubic feet per second

EXPLANATION

8.8

Figure 20. Observed and simulated average stream base flow, estimated average base-flow gain, simulated average base-flow gain, 

and confidence intervals for Reach I and Reach II of the Canadian River alluvial aquifer, Oklahoma, 1981–2013.

of observed water-table altitudes. Most of the USGS observed 

water-table altitudes were located in the alluvial deposits and 

were above the 1:1 line, while most of the OWRB observed 

water-table altitudes were located in the terrace, and were 

below the 1:1 line (fig. 18C).

The average water-table residual at OWRB observation 

well 9591 was 3.6 ft above the observed values (fig. 17B). 

This observation well was completed in alluvial deposits near 

several agricultural and irrigation wells which may account for 

some of the fluctuations in the observed water table. A trend of 

increasing recharge occurred from 1981 to 1991 for Reach II 

(fig. 16B) which resulted in the simulated water table reaching 

land surface in 1987 and 1992. The water-table altitude 

observations were generally reproduced by the simulation, 

though the magnitude of the water-table changes was not fully 

simulated, particularly in 2007 and 2011.

A total of 588 out of 929 observed transient water-table 

altitudes were measured between 1995 and 2000, although 

the magnitude of the residuals during this period are smaller 

than during the remaining model period. The largest residual 

of 19.4 ft above the observed water table (table 7) occurred in 

1992, likely due to the generally increasing recharge between 

1981 and 1991 (fig. 16B). 

The simulated stream base flow in Reach II reproduced 

the majority of the observed stream base-flow trends at each 

of the three streamgages, though simulated average stream 

base flow was lower than the observed average stream base 

flow (fig. 21, table 8). The average simulated stream baseflow residual in Reach II was between 35 and 132 ft3

/s 

(table 8). The large fluctuations in stream base flow at the 

Calvin streamgage (07231500), ranging from nearly zero 

during summer months to as large as 4,941 ft3/s (table 4) 

during precipitation events, were difficult to simulate and thus 

resulted in the largest residuals of base flow at this streamgage 

compared to the other streamgages (fig. 21, table 8). 

Additionally, this large stream base-flow variability resulted 

in a wide 95-percent confidence interval (fig. 20). As in 

Reach I, stream base-flow peaks may contain a percentage of 

runoff, which results in additional uncertainty in the observed 

stream base flows. Most of the simulated stream base flow at 

each Reach II streamgage (table 8) is within the 95-percent 

confidence interval of the stream base-flow observations 

(fig. 20). The stream base flow at the Norman streamgage 

(07229050) exceeded the 95-percent confidence interval by 

less than 1 ft3/s.
40 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

0

200

400

600

800

1,000

1,200

1,400

1,600

200

0

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Stream base flow, in cubic feet per second Stream base flow, in cubic feet per second Stream base flow, in cubic feet per second

4,000

2,000

0

Streamflow, in cubic 

feet per second

10,000

5,000

0

Streamflow, in cubic 

feet per second

Streamflow, in cubic 

feet per second

0

10,000

20,000

Stress period

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013

Observed stream base flow

Simulated stream base flow

EXPLANATION

Observed streamflow

A. Canadian River at Norman, Okla. (07229050)

B. Canadian River at Purcell, Okla. (07229200)

C. Canadian River at Calvin, Okla. (07231500)

Figure 21. Observed streamflow, observed stream base flow, and simulated stream base flow at the Canadian River at A, Norman, 

Oklahoma (07229050); B, Canadian River at Purcell, Oklahoma (07229200); and C, Canadian River at Calvin, Oklahoma (07231500), 

streamgages for Reach II of the Canadian River alluvial aquifer, Oklahoma, 1981–2013.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 41

The average simulated base-flow gain residual in Reach 

II was between 11.3 and 61.1 ft3/s (fig. 20). Simulated average 

base-flow gain was lower than estimated average base-flow 

gain (fig. 20) because of the large stream base-flow peaks that 

were not matched at each streamgage in the groundwater-flow 

model. These peaks were substantially larger at the Calvin 

streamgage (07231500) (fig. 21) than at other streamgages, 

resulting in a wider 95-percent confidence interval for the 

base-flow gain at this streamgage. Although substantial 

tributaries were simulated in the groundwater-flow model, it 

is possible that other tributaries may contribute small amounts 

of continuous flow; thus, the lower simulated base-flow gain 

may be due in part to tributary flow that could not easily be 

quantified. The simulated average base-flow gain at each 

streamgage is within the 95-percent confidence interval of the 

estimated average base-flow gain (fig. 20). 

Water Budget

Water budgets list average annual inflows to and outflows 

from the groundwater-flow models (table 9). Average annual 

recharge was the largest inflow in both models, which 

accounted for 56 percent of total inflows in Reach I and 49 

percent of total inflows in Reach II. Average annual lateral 

inflow accounted for 26 percent of total inflows in Reach I 

and 41 percent of total inflows in Reach II. The increased 

percentage of lateral inflow in Reach II compared to Reach 

I may be due to the greater length of the aquifer, increased 

precipitation, or more incised alluvial deposits in eastern 

Oklahoma. Average annual flow to the Canadian River was the 

largest simulated outflow in both models, which accounted for 

65 percent of total outflows in Reach I and 77 percent of total 

outflows in Reach II.

The net change in groundwater storage is shown in 

the simulated groundwater levels, which rise when water 

enters storage, or leaves the groundwater-flow model, and 

decline when water flows from storage, or flows into the 

groundwater-flow model. The changes in storage in both 

reaches are primarily caused by recharge and water-table ET. 

Major precipitation events such as Tropical Storm Erin in 

2007 resulted in a large ratio of flows to storage compared to 

flows from storage, and a severe drought in 2003 resulted in a 

large ratio of flows from storage compared to flows to storage 

(tables 10–11). The changes in storage and water levels that 

result from these processes are shown in the changes in flows 

that rise after precipitation events and fall when water-table 

ET is greatest. 

Table 9. Average annual water budget for the Reach I and Reach II numerical groundwater-flow models of the Canadian River alluvial 

aquifer, Oklahoma, 1981–2013.

[All units acre-feet per year. Under the net budget totals, base-flow gain was calculated as the difference between flow to and from the Canadian River. Lateral 

flow was calculated as the difference between lateral inflows and outflows]

 Budget component Reach I Reach II Reach I and Reach II 

combined

Inflow

Recharge 38,584 116,068 154,652

Flow from the Canadian River 12,694 25,299 37,993

Lateral inflow 17,561 96,323 113,884

Total inflows 68,839 237,690 306,529

Outflow

Evapotranspiration 22,372 45,416 67,788

Flow to the Canadian River 44,243 180,607 224,850

Groundwater use 542 8,640 9,182

Lateral outflow 1,235 793 2,028

Total outflows 68,392 235,456 303,848

Net budget totals

Base-flow gain 31,549 155,309 186,858

Lateral flow 16,326 95,530 111,856

Change in storage 447 2,234 2,681
42 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Table 10. Numerical groundwater-flow model annual calibrated water budget for Reach I of the Canadian River alluvial aquifer, 

Oklahoma, 1981–2013.

[Annual fluxes in thousands of acre-feet per year. The average of each component, when converted to acre-feet per year, does not exactly match table 9 because 

of round-off errors after converting flow from model units. ET, water-table evapotranspiration; NA, not applicable]

Year

Inflow Outflow

Total

in

Total

out From 

storage

Lateral 

flow Recharge

Flow 

from the 

Canadian 

River

To 

storage Wells ET Lateral flow

Flow 

to the 

Canadian 

River

Steady state NA 18.5 23.1 6.1 NA 0.6 9.7 0.9 36.5 47.7 47.7

1981 17.3 19.0 33.8 12.9 27.3 0.9 19.1 0.9 34.6 82.9 82.7

1982 26.0 17.6 31.4 11.9 20.1 0.9 21.7 1.0 43.0 86.9 86.8

1983 22.8 17.1 51.2 10.8 29.9 0.8 21.5 1.2 48.3 101.9 101.7

1984 23.5 18.2 28.0 13.8 19.6 1.3 23.0 1.0 38.4 83.5 83.2

1985 14.3 19.1 9.6 13.5 8.2 0.8 17.2 0.9 29.4 56.4 56.3

1986 12.7 18.7 52.7 13.3 40.8 0.6 18.1 1.0 36.7 97.3 97.2

1987 34.6 15.6 66.9 11.1 35.4 0.5 28.9 1.5 61.7 128.2 127.9

1988 39.1 15.6 57.6 14.6 37.7 0.8 29.7 1.8 56.8 127.0 126.7

1989 30.5 16.7 57.7 10.4 35.2 0.6 25.6 1.4 52.4 115.3 115.1

1990 26.8 17.2 28.2 12.1 12.7 0.7 22.5 1.4 46.7 84.2 84.0

1991 14.4 18.9 25.1 14.2 20.7 0.5 19.1 0.9 31.3 72.6 72.5

1992 19.3 18.0 57.1 12.4 42.5 0.4 20.0 1.1 42.6 106.7 106.6

1993 40.4 14.7 71.6 10.1 35.5 0.5 28.4 1.9 70.3 136.9 136.6

1994 24.9 17.9 15.0 12.4 7.1 0.4 22.2 1.0 39.3 70.2 70.0

1995 20.5 17.8 38.7 11.5 21.8 0.4 22.2 1.1 42.7 88.5 88.3

1996 13.5 18.6 28.1 13.4 16.2 0.4 19.6 0.9 36.3 73.6 73.4

1997 18.4 17.5 53.6 11.6 33.6 0.2 19.5 1.1 46.7 101.2 101.1

1998 47.9 14.8 77.1 11.7 51.9 0.7 26.6 1.9 70.1 151.5 151.3

1999 38.9 15.6 65.9 12.9 41.2 0.4 30.1 1.6 59.8 133.4 133.1

2000 36.4 15.9 67.1 11.9 45.6 0.6 25.5 1.6 57.8 131.4 131.1

2001 60.4 12.5 122.0 9.3 81.0 0.4 23.9 3.4 95.3 204.2 204.0

2002 30.1 17.0 17.8 12.1 9.7 0.3 22.5 1.2 43.0 76.9 76.8

2003 23.0 18.5 2.1 14.3 2.0 0.3 22.0 1.0 32.4 57.9 57.7

2004 18.9 17.9 43.0 12.8 29.4 0.3 20.5 1.0 41.3 92.6 92.5

2005 25.5 17.6 20.7 13.8 12.7 0.3 23.6 1.1 39.9 77.7 77.6

2006 14.5 19.6 2.3 16.1 2.9 0.6 22.1 0.8 25.8 52.5 52.3

2007 19.5 16.4 79.6 8.6 44.5 0.2 21.0 1.7 56.7 124.2 124.1

2008 22.1 17.2 20.7 12.3 8.8 0.2 21.2 1.4 40.6 72.4 72.3

2009 15.2 19.2 3.4 15.2 3.2 0.2 20.8 0.9 27.8 53.0 52.9

2010 13.1 19.4 9.7 14.2 7.4 0.2 19.1 0.8 28.8 56.5 56.4

2011 12.4 20.3 2.2 16.2 4.7 0.9 20.8 0.8 24.0 51.2 51.0

2012 16.2 19.5 25.7 14.1 20.0 0.8 21.1 0.8 32.7 75.6 75.4

2013 12.7 19.8 14.3 12.4 12.6 0.8 16.6 0.8 28.2 59.1 59.0

Average flux 24.4 17.6 38.3 12.5 24.9 0.5 21.9 1.2 44.1 92.1 91.9
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 43

Table 11. Numerical groundwater-flow model annual calibrated water budget for Reach II of the Canadian River alluvial aquifer, 

Oklahoma, 1981–2013.

[Annual fluxes in thousands of acre-feet per year. The average of each component, when converted to acre-feet per year, does not exactly match table 9 because 

of round-off errors after converting flow from model units. ET, water-table evapotranspiration; NA, not applicable]

Year

Inflow Outflow

Total 

in

Total 

out From 

storage

Lateral 

flow Recharge

Flow 

from the 

Canadian 

River

To 

storage Wells Drains ET Lateral flow

Flow 

to the 

Canadian 

River

Steady state NA 97.9 49.2 33.0 NA 9.5 0.1 30.6 0.4 139.3 180.1 180.1

1981 34.4 101.5 12.5 20.3 10.3 8.2 0.1 21.3 0.3 128.4 168.6 168.6

1982 44.6 98.8 88.9 22.9 63.8 8.3 0.1 32.0 0.5 150.6 255.2 255.3

1983 29.7 100.3 28.6 28.8 24.1 6.8 0.1 28.2 0.4 127.9 187.5 187.5

1984 31.7 101.2 23.3 22.4 19.2 7.1 0.1 23.7 0.4 128.2 178.6 178.7

1985 78.0 91.9 288.2 24.7 189.1 8.3 0.1 55.6 1.1 228.6 482.8 482.9

1986 50.9 96.8 137.0 24.2 96.0 6.6 0.1 33.5 0.7 172.1 308.9 308.8

1987 104.1 91.3 173.9 32.1 89.7 5.5 0.1 77.0 1.3 227.8 401.4 401.4

1988 64.6 98.5 27.8 27.2 14.3 8.1 0.1 40.8 0.6 154.2 218.0 218.0

1989 62.5 96.7 120.5 26.0 77.0 7.0 0.1 47.4 0.7 173.6 305.7 305.7

1990 96.4 90.0 294.8 24.0 158.5 7.4 0.1 72.3 1.6 265.3 505.2 505.2

1991 89.9 92.0 308.7 22.7 198.3 6.4 0.1 54.0 1.3 253.2 513.2 513.3

1992 106.4 90.2 178.9 24.4 64.1 4.8 0.1 73.8 1.5 255.8 399.9 400.1

1993 102.9 92.8 120.4 24.9 50.7 7.1 0.1 63.7 1.3 218.1 341.0 341.0

1994 69.8 96.8 66.7 21.6 25.0 6.3 0.1 45.9 0.9 176.6 254.9 254.7

1995 68.7 93.2 202.1 25.1 101.5 6.9 0.1 65.9 1.0 213.6 389.0 389.1

1996 68.7 96.0 107.8 26.5 68.8 6.8 0.1 40.5 0.8 181.9 299.0 299.0

1997 60.8 95.4 101.4 26.3 45.6 6.2 0.1 48.8 0.8 182.5 283.9 284.0

1998 96.3 92.9 144.4 27.8 84.7 8.9 0.1 57.8 1.1 208.9 361.5 361.6

1999 61.1 96.9 76.9 30.1 47.4 7.5 0.1 44.0 0.7 165.4 265.0 265.1

2000 54.2 95.1 210.6 23.7 122.5 9.3 0.1 45.3 0.9 205.8 383.7 383.8

2001 87.8 95.2 54.8 27.2 19.8 9.1 0.1 53.1 0.9 182.0 264.9 265.0

2002 60.1 95.8 142.7 23.7 82.1 9.3 0.1 44.6 0.8 185.6 322.5 322.5

2003 63.3 99.0 17.4 24.3 11.2 9.0 0.1 34.6 0.6 148.2 203.9 203.7

2004 36.0 98.5 136.1 25.6 106.7 8.1 0.1 24.7 0.6 155.9 296.1 296.2

2005 73.9 98.2 7.3 26.7 6.6 8.1 0.1 41.4 0.6 149.1 206.0 206.0

2006 36.5 102.2 9.4 22.0 9.8 9.8 0.1 25.9 0.4 124.1 170.0 170.1

2007 69.8 89.9 343.9 27.7 200.5 9.3 0.1 74.5 1.2 245.4 531.2 531.1

2008 80.0 95.9 75.9 27.8 30.5 11.8 0.1 57.2 0.8 179.2 279.6 279.6

2009 69.3 96.0 118.9 25.7 63.9 11.7 0.1 47.0 0.7 186.3 309.8 309.8

2010 83.6 95.1 131.1 26.4 77.5 11.3 0.1 49.0 0.9 197.5 336.2 336.3

2011 50.6 101.6 8.6 23.1 10.6 14.5 0.1 26.3 0.5 131.9 183.9 183.9

2012 40.0 102.2 7.6 24.5 12.6 16.4 0.1 23.3 0.4 121.6 174.3 174.4

2013 27.8 100.4 79.2 24.6 60.0 11.5 0.1 22.3 0.4 137.9 232.1 232.1

Average flux 65.3 96.4 114.6 25.5 68.0 8.6 0.1 44.9 0.8 179.5 299.8 299.8
44 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Monthly inflows, including recharge and lateral flows, 

tended to be greatest between December and March in 

both reaches (fig. 22). Outflows, including flow to streams, 

water-table ET, and groundwater use, were greatest between 

March and August for both reaches (fig. 22). During this 

time, water-table ET was the largest outflow component and 

sometimes greatly exceeded the sum of recharge and lateral 

flow. Groundwater use, most of which is done by irrigation 

wells, peaked between June and September. The simulated 

groundwater use was 9 percent lower in Reach I and 8 percent 

lower than the specified input pumping rate in Reach II 

because of a lack of saturation in some areas of the terrace due 

to steep water-level gradients. Although the specified input 

pumping rates were checked for unrealistic values, it could not 

easily be determined if screened intervals extended into the 

bedrock units below the Canadian River alluvial aquifer for 

some wells with large pumping rates. Thus, the entire volume 

of groundwater pumped from each well occurred in this 

aquifer, resulting in a lack of saturation in some well locations 

regardless of any combination of parameter changes. 

The temporal offset between maximum monthly inflows 

and outflows results in large storage changes that occur 

primarily in January–March, when inflows are greater than 

outflows, and July–October, when outflows are greater than 

inflows (fig. 22). Those large changes in groundwater storage 

limited the calibration that could be applied without causing 

numerical instability, despite using the Newton solver and 16 

time steps per stress period. As a result, one monthly stress 

period exceeded a mass-balance error of 1 percent in Reach I. 

The maximum monthly stress period mass-balance error was 

0.4 percent in Reach II. 

Calibrated Parameters

The calibrated recharge was 33 percent greater in Reach I 

and 42 percent greater in Reach II than the recharge estimated 

in the conceptual flow model. The increase in calibrated 

recharge, particularly in January–April, and decrease in 

recharge during June–October (fig. 23) was primarily used to 

match the stream base-flow observations at each streamgage. 

The increased recharge also improved the simulated watertable observation residuals in the terrace, which were typically 

below the observed values. The average Reach I recharge 

temporal array multiplier was 1.05 (5 percent increase), and 

the average Reach II recharge temporal array multiplier was 

1.22 (22 percent increase) (fig. 23). 

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

Month

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

Month

200

100

0

-100

-200

0

50

100

150

200

250

300

350

400

450

50 500

25

0

-25

-50

-75

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

Aquifer inflow or outflow, in thousands of acre-feetAquifer inflow or outflow, in thousands of acre-feet

Change in aquifer storage

(inflows minus outflows),

in thousands of acre-feet

Change in aquifer storage

(inflows minus outflows),

in thousands of acre-feet

A. Reach I B. Reach II

Aquifer inflow

Aquifer outflow

Change in aquifer storage

 (inflow minus outflow)

EXPLANATION

Figure 22. Average monthly aquifer inflow, outflow, and change in storage for A, Reach I, and B, Reach II, of the Canadian River 

alluvial aquifer, Oklahoma, 1981–2013.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 45

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

Month Month

0

50

100

150

200

250

300

350

400

450

500

Average recharge 

multiplier

Average recharge 

multiplier

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

Recharge, in thousands of acre-feetRecharge, in thousands of acre-feet

0

1

2

3

0

1

2

3

Precalibration average monthly recharge multiplied by 12

Calibrated average monthly recharge multiplied by 12

Average recharge multiplier

Precalibration average annual recharge, 1981–2013

Calibrated average annual recharge, 1981–2013

EXPLANATION

Calibrated average recharge multiplier, 1981–2013

A. Reach I B. Reach II

Figure 23. Precalibration recharge, calibrated recharge, and average recharge multipliers for A, Reach I, and B, Reach II, of the 

Canadian River alluvial aquifer, Oklahoma, 1981–2013.

In Reach I and Reach II, the calibrated water-table ET 

rate was increased by 60 percent in each stress period to match 

low base-flow (sometimes zero base-flow) conditions during 

summer months. Water-table ET in Reach I was 34 percent 

lower than the conceptual model, and water-table ET in Reach 

II was 42 percent greater. This change is due to the variability 

in the simulated water table, whereas the conceptual model ET 

withdrawals are based on a single site with a static depth to 

water.

The calibrated net lateral flow was 63 percent lower in 

Reach I and 42 percent lower in Reach II than the net lateral 

flow estimated in the conceptual flow model (table 5). In 

Reach I, average and maximum calibrated GHB conductances 

of 486 square feet per day (ft2/d) and 1,320 ft2/d, respectively, 

were used to simulate lateral inflow from bedrock. In Reach II, 

average and maximum calibrated GHB conductances of 260 

ft2/d and 924 ft2/d, respectively, were used to simulate lateral 

inflow from bedrock. Increases in the lateral flow beyond 

the calibrated values resulted in smaller residuals for the 

base-flow gain. However, these increases also resulted in 

larger stream base-flow residuals during summer months, 

when the simulated base flow could not match the lower 

estimated base flow. As a result, no improvement in the model 

calibration occurred due to the greater group weight assigned 

to the stream base flow versus the base-flow gain (table 6). 

Increases in the water-table ET rate, combined with increases 

in the lateral flow, may have improved the model calibration; 

however, no increases in the water-table ET rate were possible, 

as they lead to model instability. 

In Reach I, calibrated horizontal hydraulic conductivity 

ranged from 0.1 to 176 ft/d (pl. 6, fig. 24), with an average 

of 45 ft/d. A total of 95 percent of the calibrated horizontal 

hydraulic conductivity values in Reach I ranged from 0.1 to 93 

ft/d; thus, the multiplier range resulted in the majority of these 

conductivities remaining near the originally defined range 

of 0.1–90 ft/d. In Reach II, calibrated horizontal hydraulic 

conductivity ranged from 0.15 to 158 ft/d (pl. 6, fig. 24), with 

an average of 75 ft/d. A total of 95 percent of the calibrated 
KH1

KH2

KH3

KH4

KH5

KH6

KH7

KH8

KH9

KH11

KH13

KH14

KH51*

KH52*

KH53*

KH54*

KH55*

KH56

KH58

KH59

KH61*

KH63*

KH68*

KH69

KH70*

KH1

KH2

KH3

KH4

KH5

KH6

KH7

KH8

KH9

KH10

KH11

KH12

KH13

KH14

KH15

KH16

KH17

KH18

KH19

KH20

KH21

KH22

KH23

KH24

KH25

KH26

KH27

KH28

KH29

KH30

KH51

KH52

KH54

KH55

KH56*

KH57*

KH58

KH59*

KH61*

KH62*

KH63*

KH67*

KH71

KH72

KH73*

Parameter zone name

Horizontal hydraulic conductivity, in feet per day Horizontal hydraulic conductivity, in feet per day 0.1

1

10

100

1,000

0.1

1

10

100

1,000

A. Reach IB. Reach II

EXPLANATION

Calibrated parameter zone value rangeCalibrated average parameter zone value

* Considered a semi-confining parameter z

Figure 24. Calibrated average parameter zone values and ranges for 

A, Reach I, and 

B, Reach II of the Canadian River alluvial aquifer, 1981–2013. 
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 47

horizontal hydraulic conductivity values in Reach II ranged 

from 0.1 to 115 ft/d. The increased horizontal hydraulic 

conductivity in Reach II compared to Reach I resulted in a 

lower water table, which improved the water-table observation 

residuals. 

Specific yield was adjusted by an array multiplier to a 

final average value of 16 percent for Reach I and 15.2 percent 

for Reach II from an initial value of 22 percent for both 

reaches. Because specific yields from laboratory analyses 

are often larger than the specific yields obtained from well 

pumping tests in the field, laboratory-derived specific yields 

may be more useful for evaluating groundwater reserves 

over a long period of time versus the evaluation of more 

short-term groundwater-level responses to well pumping 

(Neuman, 1987). The determination of the aquifer response to 

well pumping and determination of a sustainable yield were 

investigated by this study; therefore, the average of 22 percent 

determined from previously published literature may overstate 

the specific yield of the Canadian River alluvial aquifer, thus 

the calibrated specific yield may provide a better estimation of 

specific yield for this groundwater study.

Sensitivity Analysis

A sensitivity analysis was performed by using the 

PEST sensitivity process (Doherty, 2010) to ensure that the 

parameters used during the calibration process were effective 

in reducing the objective function and the groundwater-flow 

model error. During calibration, PEST records the sensitivity 

of each calibration target to changes in parameters. These 

sensitivities are a measure of the change in residuals affected 

by adjustments to a parameter; thus, calibration target 

residuals are more easily reduced by larger sensitivities. 

Sensitivities were calculated by using the Jacobian matrix 

output from PEST and summed for each parameter group, 

listed in figure 25.

In both reaches, all three observation groups were most 

sensitive to changes in recharge, hydraulic conductivity, and 

GHB conductance. Spatially-distributed recharge to the water 

table was the largest inflow (table 9), which, when combined 

with the high hydraulic conductivity of the sandy alluvial and 

terrace deposits, directly affected the water table and stream 

base flows. In Reach II, the greater percentage of water-table 

observations located in the alluvial deposits versus the terrace 

may contribute to an increased water-table group sensitivity to 

recharge in Reach II compared to Reach I. 

The observation groups were sensitive to changes in the 

GHB conductance because of the moderate to steep hydraulic 

gradient from the terrace to the alluvial deposits that resulted 

in a rapid decline of the water table in terrace areas without 

continuous lateral inflow. Additionally, lateral inflow provided 

flow downgradient from the alluvial and terrace deposits to the 

Canadian River, particularly in areas where the river channel 

was near areas of lateral inflow.

The evapotranspiration area of both reaches (pl. 5) 

included nearly all segments of the Canadian River alluvial 

deposits; therefore, the base-flow observation group was 

more sensitive to changes in evapotranspiration compared to 

the water-table observation group, which had observations 

upgradient in the terrace. The water-table observation group in 

Reach II was more sensitive to changes in evapotranspiration 

due to the greater number of observations in Reach II than in 

Reach I. 

The observation groups were least sensitive to changes in 

specific yield. Decreases in specific yield magnified changes 

in stream base flow and the water-table altitude, particularly 

for stream base flow in Reach I, and for the water table in 

Reach II. 

In both reaches, the smallest sensitivities were greater 

than 1 percent of the largest sensitivities, thus reducing 

the likelihood of convergence issues during the nonlinear 

regression using PEST (Hill and Tiedeman, 2007). The 

reduction in small sensitivities was accomplished by the 

removal of parameters that had no sensitivity.

Equal Proportionate Share Scenarios

The EPS for the alluvial and terrace aquifers is defined by 

the OWRB as the amount of fresh water that each landowner 

is allowed per year per acre of owned land to maintain a 

saturated thickness of at least 5 ft in at least 50 percent of the 

total overlying land of the groundwater basin for a minimum 

of 20 years (82 OK Stat § 82-1020.5). For the Canadian River 

alluvial aquifer, the EPS was computed for time periods of 20, 

40, and 50 years into the future. 

A hypothetical well was placed in each active cell in layer 

1 of the calibrated groundwater-flow models, with all wells set 

to the same pumping rate for the duration of the EPS scenario. 

At the conclusion of each scenario, the number of cells with at 

least 5 ft of saturated thickness was compared to the number 

of active cells. If more than 50 percent of the cells had a 

saturated thickness of 5 ft or more, the pumping rate for each 

cell was increased by 5 cubic feet per day and the scenario was 

repeated until 50 percent of the cells had a saturated thickness 

of 5 ft or less. To provide a range of EPS pumping rates, the 

process was repeated with recharge increased and decreased 

by 10 percent. Additional 20-, 40-, and 50-year EPS scenarios 

were run without the GHB package simulating lateral flow. 

These scenarios simulated the effects of substantial reductions 

in the water-table altitude of the surrounding bedrock units on 

the EPS pumping rate for the Canadian River alluvial aquifer.

EPS estimates were provided for two subregions in Reach 

II, noted as Reach IIa and Reach IIb. Reach IIa includes the 

Canadian River alluvial aquifer extent between the Bridgeport 

streamgage (07228500) and the eastern border of Cleveland 

County (pl. 1). Reach IIb includes the remaining aquifer 

extent between the eastern border of Cleveland County and 

Eufaula Lake (pl. 1). For Reach IIa and Reach IIb, the EPS 

was calculated on the basis of the number of active cells in 

each subregion. The Reach I and Reach II groundwater-flow 

models are not coupled, and streamflow entering Reach II is 

the stream base flow observed at the Bridgeport streamgage 
48 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

EXPLANATION

Observation group

 Base flow

 Base-flow gain

 Water table

Recharge Hydraulic conductivity General Head Boundary

conductance

Evapotranspiration Specific yield

Recharge Hydraulic conductivity General Head Boundary

conductance

Evapotranspiration Specific yield

Parameter group

1

10

100

1,000

10,000

100,000

1

10

100

1,000

10,000

100,000

Dimensionless sensitivities for observation group

by parameter group

Dimensionless sensitivities for observation group

by parameter group

A. Reach I

B. Reach II

Figure 25. Observation group sensitivity by parameter group in the numerical groundwater-flow models for A, Reach I, and B, Reach II, 

of the Canadian River alluvial aquifer, Oklahoma.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 49

(07228500); therefore, if stream base flow in Reach I at 

the Bridgeport streamgage (07228500) is decreased, a 

corresponding decrease in the Reach II EPS would be 

expected.

The EPS scenarios were configured to step backward 

through the transient simulation, starting with 2013, and the 

monthly stress periods were configured to step forward in 

each year. The EPS scenarios were stepped backward until 

1981 and then stepped forward through the remaining scenario 

period; therefore, the 20-year EPS scenario included years 

2013–1994, the 40-year EPS scenario included years 2013–

1981 and 1982–88, and the 50-year EPS scenario included 

years 2013–1981 and 1982–98. The 2013 simulated water 

table was used as the starting water table in each EPS scenario. 

Model stresses for recharge, water-table ET, and tributary 

inflows were configured as the average of each stress period 

used in the calibrated groundwater-flow models. In some 

areas of the terrace, water levels are below the base of the 

Canadian River alluvial aquifer or are unsaturated through the 

calibrated transient simulation. As a result, only saturated cells 

were included in the total cell count for the EPS scenarios. The 

EPS rate was based on 5.74 acres in each 500-by-500-ft model 

cell.

During the EPS scenarios, the drawdown caused by 

the pumping wells placed in each cell would be expected to 

affect the water table in nearby areas. Lateral inflow of water 

from GHB cells reduced rebound effects at the boundary 

from pumping-well propagated stresses where the radius 

of influence may exceed the width of the active area of the 

model. Because of the linear relation between flux and watertable altitudes in the GHB package, continually increasing 

lateral inflows could result in an overestimated EPS pumping 

rate; however, the GHB conductance was limited in the 

calibrated models such that lateral inflows were not large 

enough to prevent dewatering from the pumping wells located 

in most areas of the alluvial and terrace deposits.

Estimated Reach I Equal Proportionate Share

For Reach I, the 20-year EPS pumping rate was 1.35 

(acre-ft/acre)/yr (fig. 26A, table 12). Decreasing recharge 

by 10 percent resulted in a 20-year EPS pumping rate of 

1.32 (acre-ft/acre)/yr, and increasing recharge by 10 percent 

resulted in a 20-year EPS pumping rate of 1.38 (acre-ft/acre)/

yr. For the 40-year EPS scenario, the 40-year EPS pumping 

rate was 1.34 (acre-ft/acre)/yr (table 12). Decreasing recharge 

by 10 percent resulted in a 40-year EPS pumping rate of 

1.31 (acre-ft/acre)/yr, and increasing recharge by 10 percent 

resulted in a 40-year EPS pumping rate of 1.37 (acre-ft/acre)/

yr. The results for the 50-year EPS scenario were the same as 

the 40-year EPS scenario. For the 20-year scenario without 

lateral flow, the EPS rate was 0.94 (acre-ft/acre)/yr. For the 40- 

and 50-year scenarios without lateral flow, the EPS rate was 

0.91 (acre-ft/acre)/yr. 

Substantial spatial variability in the aquifer saturation 

was present at the end of the EPS scenarios (pl. 7). During 

each scenario, water-table declines from groundwater pumping 

resulted in outflows from the Canadian River to the alluvial 

deposits in most of the aquifer. The majority of the terrace 

material upland of the alluvial deposits was unsaturated except 

for areas where a shallow hydraulic gradient occurred. For 

the EPS scenarios without lateral flow, this dewatering of the 

terrace was more rapid, which resulted in a larger reduction 

in groundwater flow from the terrace to the alluvial deposits. 

Flow in the Canadian River for the EPS scenarios was then 

sustained mostly from the inflows from the Canadian River 

in Texas. As a result, the western half of the Reach I alluvial 

deposits near the Canadian River remained saturated, whereas 

most other alluvial deposits had minimal or no saturation at 

the end of the EPS scenarios. The part of the alluvial deposits 

adjacent to the Rush Springs Formation also remained mostly 

saturated because of bedrock lateral inflow coupled with the 

narrow areal extent of the alluvial deposits in this area. Water 

availability under the maximum EPS pumping rates was 

primarily from the alluvial deposits. 

The EPS pumping rates for the 40- and 50-year periods 

were similar for each scenario type (table 12). In the first 

15 simulated years of each scenario, substantial amounts of 

water were removed from storage by the wells in each model 

cell in Reach I (fig. 27A). During this time, total groundwater 

pumping decreased as the thinner alluvial and terrace 

areas were dewatered and dropped below 5 ft of saturated 

thickness or went dry. Storage changes decreased in tandem 

with groundwater pumping, and approximate steady-state 

conditions were reached in as little as 15 simulated years; 

thus, storage changes were then only caused by the averaged 

stresses in each stress period. These stresses were averaged 

across each month (e.g. all model period stresses for January), 

and thus reflect seasonal stresses, which are shown by the 

oscillations in storage (fig. 27A). 

Estimated Reach II Equal Proportionate Share

For Reach II, the 20-year EPS pumping rate was 3.08 

(acre-ft/acre)/yr (fig. 26B, table 12). Decreasing recharge 

by 10 percent resulted in a 20-year EPS pumping rate of 

3.04 (acre-ft/acre)/yr, and increasing recharge by 10 percent 

resulted in a 20-year EPS pumping rate of 3.13 (acre-ft/acre)/

yr (fig. 26B, table 12). The results for the 40- and 50-year 

EPS scenarios were the same as the 20-year EPS scenario 

(table 12).

For Reach IIa, the 20-year EPS pumping rate was 2.75 

(acre-ft/acre)/yr (fig. 28A). Decreasing recharge by 10 percent 

resulted in a 20-year EPS pumping rate of 2.71 (acre-ft/acre)/

yr, and increasing recharge by 10 percent resulted in a 20-year 

EPS pumping rate of 2.79 (acre-ft/acre)/yr (fig. 28A). For the 

20-, 40-, and 50-year scenarios without lateral flow, the EPS 

rate was 2.28 (acre-ft/acre)/yr (table 12).
50 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Continuous equal-proportionate-share groundwater-pumping rate, in acre-feet per acre per year

Continuous equal-proportionate-share groundwater-pumping rate, in acre-feet per acre per year

1.25 1.28 1.31 1.34 1.37 1.40 1.43

2.90 2.95 3.00 3.05 3.10 3.15 3.20

3.04 3.08 3.13

1.32 1.35 1.38

Percentage of basin with less than 5 feet of saturated thickness Percentage of basin with less than 5 feet of saturated thickness

47

48

49

50

51

47

48

49

50

51

20-year equal proportionate share

Recharge decrease 10 percent

Recharge increase 10 percent

EXPLANATION

B. Reach ll

A. Reach l

Note: The dashed lines represent the final equal-proportionate-share groundwater-pumping rate.

 The pumping rates above the graphs are rounded values.

50 percent of basin with less than

5 feet of saturated thickness

50 percent of basin with less than

5 feet of saturated thickness

Figure 26. Percentage of A, Reach I, and B, Reach II, of the Canadian River alluvial aquifer, Oklahoma, with less than 5 feet of 

saturated thickness after 20 years of continuous equal-proportionate-share groundwater pumping.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 51

Table 12. Equal-proportionate-share pumping for Reach I and Reach II of the Canadian River alluvial aquifer, Oklahoma.

[All units of pumping are in acre-feet per acre per year. no lateral flow, describes the results of the equal-proportionate-share scenario with no change in recharge 

and lateral flow removed]

Period 

in years

Reach I Reach II Reach IIa Reach IIb

Recharge 

reduced 

10 percent

No change 

in recharge

Recharge 

increased 

10 percent

No lateral 

flow

Recharge 

reduced 

10 percent

No change 

in recharge

Recharge 

increased 

10 percent

No lateral 

flow

No lateral 

flow

20 1.32 1.35 1.38 0.94 3.04 3.08 3.13 2.28 1.93

40 1.31 1.34 1.37 0.91 3.04 3.08 3.13 2.28 1.93

50 1.31 1.34 1.37 0.91 3.04 3.08 3.13 2.28 1.93

For Reach IIb, the 20-year EPS pumping rate was 4.30 

(acre-ft/acre)/yr (fig. 28B). Decreasing recharge by 10 percent 

resulted in a 20-year EPS pumping rate of 4.23 (acre-ft/acre)/

yr, and increasing recharge by 10 percent resulted in a 20-year 

EPS pumping rate of 4.36 (acre-ft/acre)/yr (fig. 28B). For the 

20-, 40-, and 50-year scenarios without lateral flow, the EPS 

rate was 1.93 (acre-ft/acre)/yr (table 12).

Stream base flow from upstream and the multiple 

tributaries sustained saturation in the alluvial deposits for the 

majority of the groundwater-flow model area, particularly 

Reach IIa (pl. 7). Water-table declines from groundwater 

pumping resulted in outflows from the Canadian River and 

tributaries to the nearby alluvial deposits. As a result, stream 

base flow decreased downstream to nearly zero flow between 

the Union City site and the Purcell streamgage (07229200). 

Below the Purcell streamgage (07229200), inflow from 

Walnut Creek sustained streamflow in the most downstream 

section of Reach IIa and the upstream area of Reach IIb. 

Inflow from Little River sustained streamflow downstream to 

Eufaula Lake.

Lateral flow primarily sustained saturation in Reach 

IIb because of the large base-flow gain and narrow alluvial 

deposit extent. As a result, the alluvial deposits remained 

mostly saturated in Reach IIb even when stream base flow was 

minimal. When lateral flow was removed, the EPS pumping 

rate substantially decreased from 4.30 to 1.93 (acre-ft/acre)/

yr in Reach IIb, compared to a decrease from 2.75 to 2.28 

(acre-ft/acre)/yr in Reach IIa (fig. 28, table 12). The majority 

of the terrace material was unsaturated for each EPS scenario. 

Water availability under the maximum EPS pumping rates was 

primarily in the alluvial deposits.

The EPS pumping rate results for the 20-, 40-, and 

50-year periods were largely the same for each scenario type. 

In the first 8 simulated years of each scenario, substantial 

amounts of water were removed from storage by the wells 

in each model cell in Reach II (fig. 27B) as the system 

approached steady-state conditions. During this time, 

groundwater pumping decreased (fig. 27B) as the thinner 

alluvial and terrace areas were dewatered and dropped below 

5 ft of saturated thickness or went dry. This time period was 

shorter because of an average calibrated-model saturated 

thickness of 26.2 ft in Reach II versus 33.2 ft in Reach I, thus 

providing less available water from storage. Additionally, 

the increased stream base flow in Reach II compared to 

that in Reach I sustained more saturation for cells near the 

stream channel; thus, other cells upgradient to the stream 

channel were dewatered more rapidly, and the remaining cells 

remained saturated through the end of the scenarios.

Projected Water Use

The calibrated groundwater-flow models were used to 

determine the water available for groundwater use on the 

basis of the effects of current groundwater use projected 

over a 50-year period and a sustained drought. Future water 

availability was determined on the basis of the simulated 

amount of groundwater in storage and the simulated 

streamflow in the Canadian River. Groundwater storage is 

defined as the amount of water that can be pumped on the 

basis of the saturated thickness and specific yield.

Fifty-Year Water Use

A 50-year water-use scenario was used to evaluate the 

effects of water use on the groundwater resources of the 

Canadian River alluvial aquifer. The scenario used pumping 

rates from 2013, the last year of the calibrated transient 

groundwater-flow models, repeated over a 50-year period. 

The projected water-use scenario was configured the same 

as the 50-year EPS scenario, starting in year 2013, stepping 

backward to 1980, and then stepping forward to 1998. Model 

stresses for recharge, water-table ET, and tributary inflows 

were configured as the average of each stress period used 

in the calibrated groundwater-flow models. The effects of 

2013 pumping rates were evaluated by comparing changes 

in groundwater storage between a 50-year scenario by 

using 2013 pumping rates and a 50-year scenario with no 

groundwater pumping. Groundwater storage at the end of the 

50-year period was calculated by multiplying the calibrated 

specific yield by the saturated thickness for each active model 

cell in the groundwater-flow models.
52 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Figure 27. Net change in groundwater in storage and groundwater pumping for A, Reach I, and B, Reach II, of the Canadian River 

alluvial aquifer, Oklahoma, during 20 years of continuous equal-proportionate-share groundwater pumping.

0

25

50

75

100

125

150

175

200

225

0

25

50

75

100

125

150

175

200

225

-100

0

100

200

300

400

500

Net storage change, in thousands of acre-feet

Groundwater pumping, in thousands of acre-feet Groundwater pumping, in thousands of acre-feet

Net storage change, in thousands of acre-feet

-20

0

20

40

60

80

100

120

140

Years

Years

0 2 4 6 8 10 12 14 16 18 20

0 2 4 6 8 10 12 14 16 18 20

A. Reach I

B. Reach II

Net storage change, 12-month

moving average

Net storage change, 24-month

moving average

Equal-proportionate-share pumping rate

EXPLANATION
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 53

50 percent of basin with less than 5 feet

 of saturated thickness

50 percent of basin with less than 5 feet

 of saturated thickness

2.71 2.75 2.79

4.23 4.30 4.36

2.55 2.60 2.65 2.70 2.75 2.80 2.85

3.90 4.00 4.10 4.20 4.30 4.40 4.50

Continuous equal-proportionate-share groundwater-pumping rate, in acre-feet per acre per year

Continuous equal-proportionate-share groundwater-pumping rate, in acre-feet per acre per year

47

48

49

50

51

47

48

49

50

51

Percentage of basin with less than 5 feet of saturated thickness Percentage of basin with less than 5 feet of saturated thickness

B. Reach llb

A. Reach lla

Recharge decrease 10 percent

Recharge increase 10 percent

EXPLANATION

20-year equal proportionate share

Figure 28. Percentage of A, Reach IIa, and B, Reach IIb, of the Canadian River alluvial aquifer, Oklahoma, with less than 5 feet of 

saturated thickness after 20 years of continuous equal-proportionate-share groundwater pumping.
54 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

Based on the results of the 50-year groundwater-use 

scenarios, the 2013 pumping rates can be sustained with only 

small decreases in groundwater storage. For Reach I, the 

groundwater-storage totals at the end of the 50-year period 

with and without groundwater pumping were 885 thousand 

acre-ft and 887 thousand acre-ft, respectively (table 13). The 

decrease in groundwater storage (0.2 percent) was small 

because groundwater pumping in Reach I was only a small 

percentage of the calibrated groundwater-flow model budget. 

For Reach II, the groundwater-storage totals at the end of the 

50-year period with and without groundwater pumping were 

1,343 thousand acre-ft and 1,351 thousand acre-ft, respectively 

(table 13). As in Reach I, the decrease in groundwater storage 

(0.6 percent) was small because groundwater pumping in 

Reach II was a relatively small percentage of the groundwaterflow model budget. 

Some assumptions underlie these groundwater-storage 

projections. This scenario provides for no additional growth in 

the demand for groundwater use, which is primarily used for 

public supply and irrigation. Groundwater use has decreased 

17 percent in Reach I but has increased 44 percent in Reach II 

over the model period (1981–2013). Additionally, the scenario 

assumes that future climate conditions are similar to those 

of the model period (1981–2013). Future changes in climate 

variability and duration, such as the drought conditions 

observed during years 2010–15, may affect the amount 

of available water and storage and the usefulness of these 

projected water-use scenarios.

Sustained Drought

Sustained drought scenarios were used to evaluate the 

effects of a hypothetical 10-year drought on water availability. 

A 10-year period starting in January 1984 and ending 

December 1993 was chosen where the effects of drought 

conditions would be simulated. This time period was chosen 

because of the similarity of stream base flows between these 

dates and the average annual stream base flow for the entire 

transient model period. One scenario was used to calculate the 

effects of a drought on stream base flow, and the second was 

used to calculate effects of drought on groundwater storage. 

Both scenarios compared conditions during the hypothetical 

10-year drought to the calibrated groundwater-flow models.

To simulate the effects of a sustained drought on stream 

base flow, recharge was reduced by 75 percent in the Reaches 

I and II groundwater-flow models for the duration of the 

simulated drought period. This reduction in average annual 

recharge for both reaches was estimated on the basis of the 

average recharge of the years with lowest recharge during the 

model period. To approximate stream base-flow conditions 

during an extended drought, tributary inflows were reduced 

by 60 percent in Reach I and by 77 percent in Reach II. This 

decrease represents the average decrease in annual stream 

base flow during the drought of years 1976–81 (Shivers and 

Andrews, 2013) at the Bridgeport streamgage (07228500) and 

Calvin streamgage (07231500) compared to the model period. 

The reduction in tributary inflows includes the estimated 

stream base flow that crosses the border into Oklahoma from 

Texas in Reach I and the Canadian River inflow into Reach 

II, as well as the Deer Creek, Buggy Creek, Walnut Creek, 

and Little River tributaries. Changes in the stream base flow 

were evaluated at the Bridgeport streamgage (07228500) in 

Reach I and at the Purcell streamgage (07229200) and Calvin 

streamgage (07231500) in Reach II.

Stream Base Flow

In Reach I, average simulated stream base flow at the 

Bridgeport streamgage (07228500) decreased by 58 percent 

during the 1984–93 hypothetical 10-year drought compared 

to average simulated stream base flow during the nondrought 

period (fig. 29). The decrease in stream base flows during 

these drought conditions was greatest during simulated periods 

of higher flow, in which stream base flow decreased by as 

much as 70 percent (fig. 29). In Reach II, average simulated 

stream base flows at the Purcell streamgage (07229200) and 

Calvin streamgage (07231500) decreased by 64 percent and 54 

percent, respectively (fig. 30A, fig. 30B). During higher flow 

conditions in 1989, stream base flow at the Purcell streamgage 

(07229200) and Calvin streamgage (07231500) decreased 

by a maximum of 84 percent and 74 percent, respectively. 

Simulated low-flow conditions in some months may be 

underestimated during the drought scenario because periods 

of nearly zero flow periodically occur in the transient period 

for both reaches that could not be reproduced in the calibrated 

groundwater-flow model.

Groundwater in Storage

To simulate the effects of a sustained drought on 

groundwater in storage, drought conditions from 2003 were 

used for both reaches, which represent the year in which the 

most severe drought conditions were observed during the 

model period. The monthly recharge, ET, and stream baseflow values from that year were repeated over the hypothetical 

10-year drought period, and the resulting changes on storage 

were then compared to initial water in storage. Changes in 

groundwater storage for both reaches were measured by 

Table 13. Changes in groundwater storage after 50 years of 

groundwater pumping at the 2013 rate for the Canadian River 

alluvial aquifer, Oklahoma.

[All units are in thousands of acre-feet unless specified]

Reach 

Water in storage 

with pumping 

at 2013 rate 

(percent decrease)

Water in 

storage 

without 

pumping

Water-table 

decline

(in feet)

Reach I 885 (0.2) 887 0.1

Reach II 1,343 (0.6) 1,351 0.2
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 55

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Year

Percentage decrease in

simulated stream base flow

40

50

60

70

Simulated stream base flow, in cubic feet per second

0

100

200

300

400

500

600

700

800

Simulated stream base flow with drought (1984–93)

Simulated stream base flow without drought

Percentage decrease in simulated stream base flow

Average percentage decrease in simulated stream base flow

EXPLANATION

Hypothetical drought period, 1984–93

Note: Decreases in simulated stream base flow during the drought period are based on a reduction of recharge by 75 percent.

Figure 29. Changes in stream base flow in Reach I of the Canadian River at the Bridgeport, Oklahoma streamgage (07228500) during a 

hypothetical 10-year drought for the Canadian River alluvial aquifer, Oklahoma.

using an annual moving average of stress-period groundwater 

volumes. In Reach I, groundwater in storage declined 

from 872 thousand acre-ft to 842 thousand acre-ft, a total 

groundwater-storage decline of 30 thousand acre-ft (fig. 31), 

or an average decline in the water table of 1.2 ft. In Reach 

II, groundwater in storage declined from 1,260 thousand 

acre-ft to 1,189 thousand acre-ft, a total groundwater-storage 

decline of 71 thousand acre-ft (fig. 31), or an average decline 

in the water table of 2.0 ft. This scenario uses 1 drought year 

repeated for each of the 10 years of drought conditions, and 

therefore the results may understate the severity of a sustained 

drought on the groundwater in storage for the Canadian 

River; however, this scenario does provide a generalized 

representation of changes to groundwater in response to 

sustained drought conditions.

Assumptions and Limitations

Some assumptions and simplifications were necessary 

in the simulation of groundwater flow. The use of the 

MODFLOW code to simulate groundwater flow in an 

aquifer assumed that groundwater flows are governed 

by Darcy’s Law, water is incompressible and of uniform 

density, and the aquifer hydrogeology can be simulated 

appropriately by the cell size and number of layers present. 

The hydrogeologic characteristics of the aquifer vary at a 

scale smaller than that of the model cell size. Computing 

limitations prevented the use of cell sizes that could better 

represent these heterogeneities, assuming such variability 

could be reproduced. As a result, the response of the calibrated 

groundwater-flow models may vary compared to actual 

conditions, and results generated by the model may be more 

applicable to a regional, rather than local area.

Spatial and temporal data gaps in the water-table altitude 

observations occurred because of the uneven distribution of 

these observations. Although the simulated water table in 

these areas is in an expected water-table altitude range, more 

site-specific and local calibration target data would facilitate 

a more detailed characterization of water-table conditions. 

Additionally, base-flow gain to the Canadian River is based on 

the simulated water table and may not be well represented in 

locations where observation data were relatively sparse. 
56 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Year

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Year

20

40

60

80

100

0

20

40

60

80

100

Percentage decrease in

simulated stream base flow

Percentage decrease in

simulated stream base flow

0

400

800

1,200

1,600

2,000

2,400

2,800

3,200

3,600

4,000

1,800

1,600

1,400

1,200

1,000

800

600

400

200

0

Simulated stream base flow, in cubic feet per second Simulated stream base flow, in cubic feet per second

Simulated stream base flow with drought (1984–93)

Simulated stream base flow without drought

Percentage decrease in simulated stream base flow

EXPLANATION

Average percentage decrease in simulated stream base flow

A. Canadian River at Purcell, Okla. (07229200)

B. Canadian River at Calvin, Okla. (07231500)

Hypothetical drought period, 1984–93

Hypothetical drought period, 1984–93

Note: Decreases in simulated stream base flow during the drought period are based on a reduction of recharge by 75 percent.

Figure 30. Changes in stream base flow in Reach II of the Canadian River at A, Purcell, Oklahoma (07229200), and B, Calvin, Oklahoma 

(07231500), streamgages during a hypothetical 10-year drought for the Canadian River alluvial aquifer, Oklahoma.
Simulation of Groundwater Flow in the Canadian River Alluvial Aquifer 57

0 1 2 3 4 5 6 7 8 9 10

Years

0 1 2 3 4 5 6 7 8 9 10

Years

A. Reach I

B. Reach II

12-month moving average

Groundwater storage

EXPLANATION

12-month moving average

Groundwater storage

EXPLANATION

Simulated groundwater in storage, in thousands of acre-feet Simulated groundwater in storage, in thousands of acre-feet

835

840

845

850

855

860

865

870

875

880

1,180

1,190

1,200

1,210

1,220

1,230

1,240

1,250

1,260

1,270

1,280

Figure 31. Change in groundwater storage during a hypothetical 10-year drought in A, Reach I, and B, Reach II, for the Canadian River 

alluvial aquifer, Oklahoma.
58 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

The stream network used in the groundwater-flow models 

is a simplification of the actual stream geometry and hydraulic 

properties. More work could be done to refine the stream 

channel width, streambed hydraulic conductance, and water 

exchange with the aquifer, all which can vary substantially at 

the local scale. The groundwater-flow models are calibrated 

primarily to stream base-flow estimates; therefore, collection 

of more streamflow data would further reduce uncertainty in 

local-scale simulation results. 

Exact amounts of reported groundwater use are unknown 

because groundwater wells are not metered, and wateruse data are based on self-reported estimates submitted to 

the OWRB by permit holders. Reported groundwater use 

declined substantially after 1980, which may be have been 

caused by changes in reporting requirements; thus, the actual 

groundwater available for permitted use may differ than was 

simulated in the groundwater-flow models. Additionally, 

domestic wells are not included in the permitted groundwater 

use, although they are not expected to have substantial effects 

on the water budget because of the relatively small amount of 

groundwater use by domestic wells in the study area. 

Summary

This report describes a study of the hydrogeology and 

simulation of groundwater flow for the Canadian River 

alluvial aquifer in western and central Oklahoma. The report 

(1) quantifies the groundwater resources of the Canadian 

River alluvial aquifer by developing a conceptual model; 

(2) summarizes the general water quality of the Canadian 

River alluvial aquifer groundwater by using data collected 

during August and September 2013; (3) evaluates the effects 

of estimated equal proportionate share (EPS) on aquifer 

storage and streamflow for time periods of 20, 40, and 

50 years into the future by using numerical groundwaterflow models; and (4) evaluates the effects of present-day 

groundwater pumping over a 50-year period and sustained 

hypothetical drought conditions over a 10-year period on 

stream base flow and groundwater in storage by using 

numerical flow models. The Canadian River alluvial aquifer 

is an unconfined alluvial aquifer consisting of beds of clay, 

silt, sand, and fine gravel sediments in western and central 

Oklahoma. Groundwater in approximately 606 square miles of 

the aquifer extent is used for irrigation, municipal use, mining 

(oil and gas), livestock, and domestic supply. For the study 

described in this report, the Canadian River alluvial aquifer 

was divided into two sections: Reach I, with an extent of 242 

square miles from the Texas border to the Canadian River at 

the Bridgeport, Okla., streamgage (07228500); and Reach II, 

with an extent of 364 square miles from the Canadian River 

at the Bridgeport, Okla., streamgage (07228500) to Eufaula 

Lake.

Land cover on the Canadian River alluvial aquifer was 

composed of mostly grass/pasture, crops, and forest in 2015. 

The average annual precipitation in the study area from 

1896 to 2014 was 34.4 inches per year (in/yr). On average, 

the greatest amounts of precipitation occur in May, and the 

least amounts occur in January. Precipitation trends indicate 

(1) below-average precipitation from the late 1890s through 

the early 1920s, (2) above-average precipitation from the late 

1920s to the late 1940s, (3) variable precipitation between 

1950 and the early 1980s, (4) above-average precipitation 

from the mid-1980s to 2010, and (5) below-average 

precipitation from 2010 to 2014.

The average annual groundwater use from this aquifer 

from 1967 to 2013 was 11,887 acre-feet per year (acre-ft/yr). 

The annual groundwater-use data indicate a period of greater 

use from 1967 to 1979, followed by a period of lower use from 

1980 to 1999. From 2000 to 2013, groundwater use increased, 

with a peak of 23,380 acre-ft/yr in 2012. The greatest 

use of groundwater from 1967 to 2013 was for irrigation, 

8,476 acre-ft/yr, or about 71.3 percent of groundwater use. 

The aquifer extent was determined primarily by using 

1:100,000-scale geologic maps, approximately 1,400 driller’s 

lithologic logs, and 6 sediment cores. The aquifer areal extent 

ranged from less than 0.2 to 8.5 miles wide. The maximum 

aquifer thickness was 120 feet (ft), and the average aquifer 

thickness was 50 ft. Average horizontal hydraulic conductivity 

for the aquifer was estimated at 39 feet per day, with a 

maximum of 100 feet per day and a minimum of 0.1 foot per 

day.

Water quality in the Canadian River alluvial aquifer was 

evaluated through summary of data from samples collected 

for the Oklahoma Water Resources Board Groundwater 

Monitoring and Assessment Program at 31 sites during 2013. 

Most of the samples met primary drinking-water standards 

established by the U.S. Environmental Protection Agency, but 

5 of the 31 samples contained nitrate-nitrogen concentrations 

(measured as nitrate plus nitrite concentrations) that exceeded 

the standard of 10 milligrams per liter. Changes in water types 

from the western portion to the eastern portion of the Canadian 

River alluvial aquifer indicate interaction of groundwater 

between local bedrock units and the alluvial aquifer.

Stream base flow in both reaches was analyzed by using 

one seepage run and a base-flow separation method. Increases 

in the average stream base flow were observed from upstream 

to downstream, although drought conditions affected the 2013 

seepage-run measurements. The average annual base-flow 

index (1981–2013), estimated by using the Base-Flow Index 

method, generally decreased from west to east at streamgages 

on the Canadian River. This general decrease in base flowindex and increase in runoff may be due to the increased 

precipitation in Oklahoma from west to east, incised alluvial 

deposits in eastern Oklahoma, and downstream decrease in 

horizontal hydraulic conductivity.

Recharge rates to the Canadian River alluvial aquifer 

were estimated by using a soil-water-balance code to estimate 

the spatial distribution of groundwater recharge and a watertable fluctuation method to estimate localized recharge 
Summary 59

rates. By using daily precipitation and temperature data 

from 39 climate stations, recharge was estimated to average 

3.4 in/yr, which corresponds to 8.7 percent of precipitation 

as recharge for the Canadian River alluvial aquifer from 

1981 to 2013. The highest estimated annual recharge of 

5.9 in/yr occurred in 1985, and the lowest estimated annual 

recharge of 0.6 in/yr occurred in 2003. The water-table 

fluctuation method was used at one site where continuous 

water-level observation data were available to estimate 

the percentage of precipitation that becomes groundwater 

recharge. Estimated annual recharge at that site was 9.7 in/yr 

during 2014. 

Groundwater flow in the Canadian River alluvial aquifer 

was identified and quantified by a conceptual flow model for 

the model period 1981–2013. Groundwater inflows to the 

Canadian River alluvial aquifer included recharge to the water 

table from precipitation, lateral flow from the surrounding 

bedrock, and flow from the Canadian River. Total annual 

recharge inflows estimated by the soil-water-balance code 

were multiplied by the area of each reach and then averaged 

over the simulated period to produce an annual average of 

28,919 acre-ft/yr for Reach I and 82,006 acre-ft/yr for Reach 

II. Average annual lateral inflow during the model period was 

43,803 acre-ft/yr for Reach I and 164,849 acre-ft/yr for Reach 

II. Outflows include flow to the Canadian River (base-flow 

gain), evapotranspiration, and groundwater use. Average 

base-flow gain was determined to be the largest outflow at 

38,006 acre-ft/yr for Reach I and 205,377 acre-ft/yr for Reach 

II. Base-flow gain rates ranged from 0.3–2.3 cubic feet per 

second (ft3/s) per mile. Groundwater use accounts for a minor 

percentage of outflows from the Canadian River alluvial 

aquifer, totaling 593 acre-ft/yr in Reach I and 9,416 acre-ft/yr 

in Reach II.

Objectives for the numerical groundwater-flow models 

included simulating groundwater flow in the Canadian River 

alluvial aquifer from 1981 to 2013 to address groundwater 

use and drought scenarios, including calculation of the EPS 

pumping rates. The EPS for the alluvial and terrace aquifers 

is defined by the Oklahoma Water Resources Board as the 

amount of fresh water that each landowner is allowed per year 

per acre of owned land to maintain a saturated thickness of 

at least 5 ft in at least 50 percent of the overlying land of the 

groundwater basin for a minimum of 20 years. 

The groundwater-flow models were calibrated to watertable altitude observations, streamgage base flows, and 

base-flow gain to the Canadian River. Both models were first 

calibrated manually by trial and error, followed by automated 

nonlinear regression techniques by using the parameter 

estimation code. The Reach I water-table altitude observation 

root-mean-square error was 6.1 ft, and 75 percent of watertable altitude residuals were within ±6.7 ft of observed 

measurements. The average simulated stream base-flow 

residual at the Bridgeport, Okla. streamgage (07228500) 

was 8.8 ft3/s, and 75 percent of stream base-flow residuals 

were within ±30 ft3/s of observed measurements. Simulated 

base-flow gain in Reach I was 8.8 ft3/s lower than estimated 

base-flow gain. The Reach II water-table altitude observation 

root-mean-square error was 4 ft, and 75 percent of water-table 

altitude residuals were within ±4.3 ft of the observations. The 

average simulated stream base-flow residual in Reach II was 

between 35 and 132 ft3/s. The average simulated base-flow 

gain residual in Reach II was between 11.3 and 61.1 ft3/s.

Several future predictive scenarios were run, including 

estimating the EPS pumping rate, determining the effects of 

current groundwater use over a 50-year period into the future, 

and evaluating the effects of a sustained drought on water 

availability for both reaches. The EPS pumping rate was 

determined to be 1.35 acre-feet per acre per year ([acre-ft/

acre]/yr) in Reach I and 3.08 (acre-ft/acre)/yr in Reach II for 

a 20-year period. For the 40- and 50-year periods, the EPS 

pumping rate was determined to be 1.34 (acre-ft/acre)/yr in 

Reach I and 3.08 (acre-ft/acre)/yr in Reach II. 

A 50-year water-use scenario was used to evaluate the 

effects of recent groundwater use rates on future groundwater 

resources of the Canadian River alluvial aquifer. The scenario 

used groundwater-pumping rates from 2013, the last year 

of the calibrated groundwater-flow models, repeated over a 

50-year period. For Reach I, the groundwater-storage totals at 

the end of the 50-year period with and without groundwater 

pumping were 885 thousand acre-feet (acre-ft) and 887 

thousand acre-ft, respectively. For Reach II, the groundwaterstorage totals at the end of the 50-year period with and without 

groundwater pumping were 1,343 thousand acre-ft, and 

1,351 thousand acre-ft, respectively. The small changes in 

storage are due to groundwater use by pumping composing a 

small percentage of the total groundwater-flow model budgets 

for Reaches I and II.

Two scenarios were run to estimate the effects of a 

hypothetical 10-year drought on water availability. One 

scenario was used to calculate the effects of a drought on 

stream base flow by decreasing recharge by 75 percent, and 

the second was used to calculate effects of that drought on 

groundwater storage, which is the amount of water that can be 

extracted on the basis of the saturated thickness and specific 

yield. A 10-year period starting in January 1984 and ending 

December 1993 was chosen where the effects of drought 

conditions would be simulated.

In Reach I, average simulated stream base flow at the 

Bridgeport streamgage (07228500) decreased by 58 percent 

during the hypothetical 10-year drought compared to average 

simulated stream base flow during the nondrought period. In 

Reach II, average simulated stream base flows at the Purcell 

(07229200) and Calvin (07231500) streamgages decreased 

by 64 percent and 54 percent, respectively. In Reach I, the 

groundwater-storage drought scenario resulted in a storage 

decline from 872 thousand acre-ft to 842 thousand acre-ft, a 

total groundwater-storage decline of 30 thousand acre-ft, or 

an average decline in the water table of 1.2 ft. In Reach II, the 

groundwater-storage drought scenario resulted in a storage 

decline from 1,260 thousand acre-ft to 1,189 thousand acre-ft, 

a total groundwater-storage decline of 71 thousand acre-ft, or 

an average decline in the water table of 2.0 ft.
60 Hydrogeology and Simulation of Groundwater Flow and Analysis of Projected Water Use, Canadian River Alluvial Aquifer

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