Chapter C. Groundwater Flow Simulations of the Denver 

Basin Aquifer System, Colorado

By Edward R. Banta, Suzanne S. Paschke, and David W. Litke

the use of predictive sensitivity analysis to suggest monitoring locations; and (5) a discussion of appropriate model use 

and maintenance. Groundwater availability results from the 

Denver Basin model for predevelopment conditions are presented in Chapter A, and transient results describing temporal 

changes in recharge, discharge, aquifer storage, and groundwater flow directions are presented in Chapter B of this report.

The Denver Basin groundwater flow model includes 

several enhancements over previous modeling efforts because 

of the availability of additional data, improved modeling 

capabilities, and advanced computer technology. Additional 

data available for this study included updated geologic 

mapping of the extent of Denver Basin bedrock and alluvial 

aquifers (Chapter A); additional geophysical logs in the basin 

with which to better define the aquifer layering and geometry 

of the hydrogeologic framework for the model (Chapter A); 

additional water-level, streamflow, precipitation, and irrigation data collected since previous studies (Chapters A and B); 

and updated estimates of pumping from Denver Basin bedrock 

and alluvial aquifers (Chapter B). Modeling capabilities and 

computer technology also have advanced considerably since 

development of previous Denver Basin groundwater flow 

models such that additional features, hydrologic processes, 

and numerical techniques are included in the current model 

that were not possible in previous models. Updated modeling 

capabilities implemented by this study include:

• A fully three-dimensional representation of the 

aquifer system, which includes explicit definition of 

all Denver Basin aquifer and confining layers. Previous models used a quasi-three-dimensional approach, 

which represented confining layers by using a verticalconductance formulation.

• Explicit representation of the alluvial aquifer system 

as the uppermost layer in the model. Previous models 

simulated the alluvial aquifer as constant-head cells 

(Robson, 1987) or as head-dependent-flow boundaries using the MODFLOW River Package (Colorado 

Division of Water Resources, 1998).

• Use of streamflow-routing simulation capabilities 

(SFR2, Niswonger and Prudic, 2005), to represent 

stream systems. Previous models did not explicitly 

simulate streams.

Introduction

Groundwater flow in the Denver Basin bedrock aquifer system and overlying alluvial aquifer is simulated with 

the three-dimensional groundwater flow modeling program 

MODFLOW-2000 (Harbaugh and others, 2000; Hill and others, 2000). The calibrated Denver Basin model forms the basis 

for groundwater availability analysis presented in Chapters A 

and B of this report and provides a tool for analyzing temporal 

changes to the hydrologic system in response to changing climatic conditions and groundwater development. The Denver 

Basin groundwater flow model represents regional timevarying (transient) conditions prior to 1880 through 2003. A 

single steady-state model stress period represents predevelopment conditions prior to 1880. The 124-year transient modelcalibration period represents conditions from 1880 through 

2003 using 15 model stress periods ranging from 2 to 27 years 

in length. The model was calibrated by adjusting primarily 

hydraulic-conductivity and recharge parameters until a best 

fit was obtained between observed and simulated transient 

hydraulic heads and flows. The calibrated model represents 

a best fit of the numerical simulation to the observed data for 

the given model parameters and was attained using automated 

parameter-estimation techniques as implemented in PEST 

(Doherty, 2006). Sensitivity of the model results to estimated 

and assigned parameters was determined from PEST and 

UCODE_2005 (Poeter and others, 2005) sensitivity analysis, and the calibrated model was used in a predictive mode 

to estimate the hydrologic system response to two pumping 

scenarios for the period 2004 through 2053. Additional modelsensitivity calculations using Observation-Prediction (OPR) 

and Parameter-Prediction (PPR) statistics (Hill and Tiedeman, 

2007) were used to evaluate the benefits and locations of additional data collection.

This chapter, Chapter C, documents the groundwater 

flow model including model setup, calibration, and sensitivity analysis. Specifically this chapter includes information on 

the (1) development of input datasets for the transient threedimensional, finite-difference numerical model; (2) procedures 

and measures of model fit used to calibrate the flow model; 

(3) descriptions of the model sensitivity to estimated and 

assigned parameters; (4) descriptions of model predictions and 
182 Groundwater Availability of the Denver Basin Aquifer System, Colorado

• Inclusion of evapotranspiration as a boundary condition 

(ETS, Banta, 2000). Previous models did not explicitly 

include evapotranspiration as a hydrologic process.

• Use of recently developed software designed for 

parameter estimation and sensitivity analysis. In 

this report, the phrase “parameter estimation” refers 

to an automated inverse-modeling procedure such 

as those implemented in PEST (Doherty, 2006) or 

UCODE_2005 (Poeter and others, 2005). PEST 

was used to estimate model hydraulic parameters 

and guide transient model calibration. Model sensitivity to parameters was calculated with PEST and 

UCODE_2005 (Poeter and others, 2005). 

• A new MODFLOW numerical solver (GMG Package, 

Wilson and Naff, 2004; Banta, 2006). The Geometric 

MultiGrid (GMG) solver of MODFLOW-2000 provided improved model convergence for this highly 

nonlinear system.

• Parallel computing capabilities. Parameter estimation 

was accomplished with Parallel PEST (Doherty, 2006). 

Parallel simulations used multiple networked personal 

computers to simultaneously simulate various combinations of model parameters during model calibration.

Model Development

The three-dimensional, finite-difference, groundwater 

flow modeling program MODFLOW-2000 (Harbaugh and 

others, 2000; Hill and others, 2000) with modifications documented in McAda and Barroll (2002) and Banta (2006) was 

used to simulate the Denver Basin aquifer system. The summarized modifications are as follows:

1. The Layer Property Flow (LPF) Package was modified 

to eliminate the vertical flow correction (McAda and 

Barroll, 2002).

2. The Recharge (RCH) Package was modified to allow 

recharge to apply to the uppermost active cell connected 

by active cells to the lowermost active cell in a stack of 

cells (Banta, 2006).

3. The Evapotranspiration Segments (ETS) Package (Banta, 

2000) was modified to allow evapotranspiration to apply 

to the uppermost active cell connected by active cells to 

the lowermost active cell in a stack of cells (Banta, 2006).

4. The GMG solver was modified to support a new adaptivedamping option (Banta, 2006).

Geographic Information System (GIS) data containing 

the layer extent, layer top and base altitude values, geologic 

data, precipitation, and other hydrologic, geologic, and geographic data were stored and manipulated using ArcGIS version 9.0 (Environmental Systems Research Institute, 1999–

2004a). Input files for MODFLOW-2000 were generated 

from the GIS data by using ArcGIS (Environmental Systems 

Research Institute, 1999–2004a), ArcInfo (Environmental 

Systems Research Institute, 1982–2004b), and Argus Open 

Numerical Environments (Argus ONE, Argus Holdings, Ltd., 

1992–99) with the Graphical User Interface for MODFLOW 

(“MODFLOW-GUI”, Winston, 2000). The model-independent 

parameter-estimation program Parallel PEST (Doherty, 2006) 

was used for parameter estimation. Model results were processed using a series of utility computer programs (Banta and 

others, 2008) which translate the results into formats suitable 

for display as ArcGIS raster grids.

Model Conceptualization 

and Parameterization

Model parameterization consists of developing 

MODFLOW parameters and preparing model input files that 

represent various aspects of the conceptual hydrogeologic setting being simulated.

Model Area and Spatial Discretization

A model grid was defined to encompass the Denver 

Basin bedrock aquifer system and immediately adjacent areas 

of the alluvial aquifer of the South Platte River (fig. C1). The 

grid has 84 columns and 124 rows of square cells; each cell 

measures 1 mile by 1 mile (1-mi2). The grid was generated in 

the State Plane coordinate system (North American Datum 

of 1983, units: feet, zone: Colorado Central Zone). The grid 

origin is located at the northwest corner of the model area 

at easting 3,071,260 ft and northing 1,961,860 ft, such that 

row numbers increase from west to east and column numbers 

increase from north to south (fig. C1). The grid is aligned (not 

rotated) relative to the State Plane coordinate system.

MODFLOW-2000 provides two options for representation of confining units: “quasi-3D” and fully threedimensional. When a confining unit is represented as quasi3D, the confining unit does not occupy a layer in the model, 

vertical hydraulic connection across the confining unit is 

simulated by calculation or input of a vertical conductance, 

and lateral flow and storage changes in the confining unit are 

not simulated. In contrast, when the fully three-dimensional 

option is selected, the confining unit is explicitly represented as a model layer, lateral flow is simulated, and storage 

changes are simulated for transient stress periods. The fully 

three-dimensional approach was used in construction of the 

model described in this report primarily to allow simulation 

of storage changes in the confining units. Use of the fully 

three-dimensional approach also allows simulation of advective transport of particles. Table C1 lists each hydrogeologic 

unit and corresponding model layer; the section “Hydrologic 

Framework” in Chapter A presents detailed discussions of the 

aquifer-system stratigraphy.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 183

Figure C1. Extent of Denver Basin model grid, active model cells, and uppermost model layer.

PALMER

DIVIDE

PALMER

DIVIDE

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EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

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Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

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Denver

Greeley

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Bennett

Loveland

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Brighton

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COLUMN

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Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Model grid

Alluvial aquifer (model layer 1)

Upper Dawson aquifer (model layer 2)

Lower Dawson aquifer (model layer 4)

Denver aquifer (model layer 6)

Upper Arapahoe aquifer (model layer 8)

Lower Arapahoe aquifer (model layer 10)

Laramie–Fox Hills aquifer (model layer 12)

Confining units (model layers 3, 5, 7, 9, 11)
184 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C1. Vertical discretization of Denver Basin aquifers 

and confining units (see table A3 for detailed explanations of 

hydrologic units).

Model layer Hydrogeologic unit

1 Alluvial aquifer

2 Upper Dawson aquifer

3 Dawson confining unit

4 Lower Dawson aquifer

5 Denver upper confining unit

6 Denver aquifer

7 Denver lower confining unit

8 Upper Arapahoe aquifer

9 Arapahoe confining unit

10 Lower Arapahoe aquifer

11 Laramie confining unit

12 Laramie–Fox Hills aquifer

The extents of the seven aquifers and five confining 

units represented in the Denver Basin model, and described in 

Chapter A, were used to define the initial active/inactive status 

of cells for each model layer. In general, cells were initially 

specified as active where a hydrogeologic unit is present and 

inactive where it is absent. The bowl-shaped structure of the 

basin results in a ringed outcrop pattern, and the distribution 

of uppermost active model layers exhibits a similar distribution for model layers representing bedrock units (model 

layers 2 through 12; fig. C1). The alluvial aquifer (represented by model layer 1) overlies all of the bedrock model 

layers (fig. C1). In areas where the alluvial aquifer overlies a 

hydrogeologic unit stratigraphically below the upper Dawson 

aquifer and intervening bedrock units are missing from the 

simulated stratigraphic column, cells in the intervening layers were specified as active to simulate vertical hydraulic 

connection between the alluvial aquifer and the underlying 

bedrock unit. The activated cells were assigned a thickness of 

0.1 ft, a base altitude 0.1 ft below that of the overlying layer, 

and hydraulic properties of the overlying alluvial aquifer, to 

maintain lateral and vertical continuity among interconnected 

active model cells.

The top of the aquifer system was specified as the landsurface altitude. The raster datasets of the base altitude of 

hydrogeologic units (model layers) were used with ArcGIS 

(Environmental Systems Research Institute, 1999–2004a) 

tools to generate arrays of model-layer base altitude. In areas 

where a model cell represents a hydrogeologic unit that is 

absent, the base altitude of the layer was defined to be 0.1 ft 

lower than the base altitude of the overlying layer. The top 

altitude was set equal to land-surface altitude where the hydrogeologic unit crops out, or the base altitude of the overlying 

hydrogeologic unit, where the unit does not crop out.

Hydraulic properties of the hydrogeologic units were 

specified using the Layer Property Flow (LPF) Package of 

MODFLOW-2000 (Harbaugh and others, 2000). In the LPF 

Package, each layer may be specified as either confined or 

convertible. Cells in layers specified as confined are assumed 

to have an unvarying saturated thickness, regardless of the 

calculated head, and do not become inactive if the calculated 

head is below the cell bottom. Cells in layers specified as 

convertible are simulated as having head-dependent saturated 

thickness when the calculated head is below the cell top, and 

these cells are deactivated if the head is below the cell bottom.

Each of the aquifers is unconfined in at least part of 

its extent, primarily where the unit crops out at or near land 

surface. Because continued pumping from the aquifers is 

expected to increase the area of unconfined conditions, and to 

allow more realistic simulation of hydrologic conditions in the 

aquifers with changing saturated thickness, the model layers 

representing aquifers (layers 1, 2, 4, 6, 8, 10, and 12; table C1) 

were specified as convertible between confined and unconfined conditions. The model layers representing confining 

units, which are composed primarily of fine-grained materials 

that are not expected to drain substantially as heads decline, 

were specified as confined. The “wetting” option, which 

allows cells to return to active status after being deactivated, 

was disabled to enhance numerical stability.

Temporal Discretization

Simulated time periods in MODFLOW-2000 (Harbaugh 

and others, 2000) are subdivided into “model stress periods” 

during which recharge, pumping, and other stresses are held 

constant. Stress periods are further subdivided into “time 

steps” during the MODFLOW simulation to facilitate numerical calculations. For the Denver Basin model, 16 model stress 

periods are used to represent the time period from prior to 

1880 through 2003. Hydrologic stresses and groundwater 

flow rates are assumed to have been constant (steady state) 

prior to 1880, and a single steady-state stress period is used to 

represent pre-1880 (predevelopment) conditions. Groundwater 

development from 1880 through 2003 is simulated as timevarying (transient), and the model was calibrated to hydrologic 

data collected during this period. Fifteen transient stress periods are used to simulate variable stresses during the 124-year 

calibration period, January 1, 1880, through December 31, 

2003. The timing and duration of transient stress periods were 

selected to allow approximation of historical precipitation and 

pumping stresses (fig. C2). The stress-period durations for the 

calibration period ranged from 2 to 27 years (table C2).

Hydrogeologic-Unit Properties

Intrinsic hydraulic-conductivity and storage properties of 

the aquifers and confining units are required inputs for the LPF 

Package of MODFLOW-2000 (Harbaugh and others, 2000). 

The input defines horizontal and vertical hydraulic conductivity and specific storage for all model layers. For the convertible layers, additional input defines specific yield. The following sections describe parameterization of these properties.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 185

Figure C2. Temporal discretization of (A) annual precipitation from station data, and 

(B) simulated pumping.

5.0

10.0

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25.0

Basinwide mean annual preciptation, in inches

Basinwide mean annual precipitation

Simulated basinwide precipitation

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EXPLANATION

EXPLANATION

Transient stress-period number

Simulated total pumping

Simulated alluvial pumping

Simulated bedrock pumping

Estimated total pumping

Estimated alluvial pumping

Estimated bedrock pumping

4

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2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
186 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Hydraulic Conductivity

Horizontal hydraulic-conductivity values for the hydrogeologic units of the Denver Basin were parameterized using 

several different approaches summarized in table C3. Note 

that the conceptualization schemes described in the table 

incorporate simplifying assumptions. Vertical hydraulic conductivity was assumed to equal horizontal hydraulic conductivity in all model layers representing bedrock; this assumption is represented in the model input by assigning vertical 

anisotropy of bedrock aquifers (ratio of horizontal to vertical 

hydraulic conductivity, parameter VANI_BR) a value of 1.0. 

In this conceptualization, resistance to vertical flow among the 

bedrock aquifers is assumed to be primarily controlled by the 

confining units. The parameter VANI_QPlat was used in the 

model to represent vertical anisotropy of the alluvial aquifer 

along the South Platte River main stem and tributaries and was 

estimated by parameter estimation (calibrated value of 9.9). 

The parameter VANI_Qbas was used in the model to represent 

vertical anisotropy of the alluvial aquifer in the Big Sandy and 

Black Squirrel Creek basins and was assigned a value of 10.

Parameterization of the hydraulic-conductivity distributions of the Denver, upper and lower Arapahoe, and 

Laramie–Fox Hills aquifers used the pilot-point approach 

(de Marsily and others, 1984; Certes and de Marsily, 1991; 

Doherty, 2001) as implemented in PEST and associated 

utilities (Doherty, 2003, 2006). Pilot points are locations in 

the model where a parameter, hydraulic conductivity in this 

study, is estimated by the parameter estimation. The estimated 

parameter values at pilot points are then interpolated between 

locations within a model layer to assign a parameter distribution to the layer. The pilot-point approach allows the estimated 

parameter values to vary gradationally between the pilot 

points and contrasts with a MODFLOW zoned parameterization of hydraulic conductivity where hydraulic-conductivity 

parameters are used for various spatial zones of a simulated 

aquifer. For the Denver Basin, the pilot-point approach worked 

well because it allowed the model to represent gradational, 

rather than abrupt, hydraulic-conductivity distributions across 

the basin consistent with the sedimentary deposits that fine 

eastward from the mountain front.

Selection of the number of pilot points applied the 

principal of parsimony. A large number of model parameters 

increases the required number of parameter-estimation 

simulations, and a model parameter is required by PEST for 

each pilot point. The pilot-point locations were thus selected 

to provide reasonably uniform coverage over the aquifer 

domain, to provide a reasonable but least-complex representation of observed hydraulic-conductivity distributions, and to 

simplify the numerical calculations. To ensure that excessive 

extrapolation would not be required to populate the hydraulicconductivity arrays, some pilot points were located near the 

margins of the aquifers. The locations of pilot points used for 

the Denver, upper Arapahoe, lower Arapahoe, and Laramie–

Fox Hills aquifers are shown in figure C3.

Interpolation to populate the hydraulic-conductivity 

arrays from the pilot-point values implemented the geostatistical interpolation method ordinary kriging (Davis, 1986). For 

the kriging analysis, hydraulic-conductivity values (in ft/d) 

from aquifer pumping tests discussed in the section “Aquifer 

Hydraulic Properties” in Chapter A (table A4; Colorado 

Division of Water Resources, 2005) were transformed to 

base-10 logarithms to account for the tendency of hydraulic 

conductivity to have a log-normal distribution. Semivariograms of log hydraulic-conductivity data were prepared for 

the Denver, the upper and lower Arapahoe, and the Laramie–

Fox Hills aquifers. Records of aquifer tests of the Arapahoe 

aquifers generally did not distinguish between the upper and 

lower aquifers; therefore, the data were assumed to apply to 

both aquifers, and a single semivariogram was prepared for the 

Table C2. Temporal discretization for the Denver Basin model.

[--, not applicable]

Stress period Stress-period length

(days)

Stress-period length

(years) Time period simulated

1 -- -- Predevelopment through December 31, 1879

2 9,861 27 January 1, 1880 through December 31, 1906

3 4,748 13 January 1, 1907 through December 31, 1919

4 7,305 20 January 1, 1920 through December 31, 1939

5 5,114 14 January 1, 1940 through December 31, 1953

6 1,096 3 January 1, 1954 through December 31, 1956

7 1,826 5 January 1, 1957 through December 31, 1961

8 1,096 3 January 1, 1962 through December 31, 1964

9 2,556 7 January 1, 1965 through December 31, 1971

10 731 2 January 1, 1972 through December 31, 1973

11 1,826 5 January 1, 1974 through December 31, 1978

12 2,192 6 January 1, 1979 through December 31, 1984

13 730 2 January 1, 1985 through December 31, 1986

14 2,922 8 January 1, 1987 through December 31, 1994

15 1,826 5 January 1, 1995 through December 31, 1999

16 1,461 4 January 1, 2000 through December 31, 2003
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 187

Table C3. Hydraulic-conductivity conceptualization and parameterization.—Continued

[ft/d, feet per day]

Hydrogeologic unit Parameter names and definitions

(ft/d except where noted) Hydraulic-conductivity conceptualization

Alluvial aquifer K_Q_Platte—Hydraulic conductivity of alluvial aquifer 

adjacent to South Platte River and its tributaries.

Aquifer area is divided into zones. Assumption: 

Hydraulic conductivity within each zone is 

homogeneous and isotropic in the lateral dimensions. 

Parameters represent hydraulic conductivity of entire 

unit thickness or vertical anisotropy.

K_Q_bas—Hydraulic conductivity of alluvial aquifer 

in Big Sandy and Black Squirrel basins.

VANI_QPlat—Vertical anisotropy1 of alluvial aquifer 

adjacent to South Platte River and its tributaries. 

Unit: dimensionless.

VANI_Qbas—Vertical anisotropy1 of alluvial 

aquifer in Big Sandy and Black Squirrel basins. 

Unit: dimensionless.

Upper Dawson aquifer K_utdw—Hydraulic conductivity of the silt-plus-sand 

fraction of upper Dawson aquifer.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) hydraulic conductivity of silt-sized and coarser 

fraction is uniform. Parameter represents hydraulic 

conductivity of the silt-plus-sand fraction.

Dawson confining unit K_tdwc—Hydraulic conductivity of Dawson 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Lower Dawson aquifer K_ltdw—Hydraulic conductivity of the silt-plus-sand 

fraction of lower Dawson aquifer.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) hydraulic conductivity of silt-sized and coarser 

fraction is uniform. Parameter represents hydraulic 

conductivity of the silt-plus-sand fraction.

Denver upper confining unit K_tkduc—Hydraulic conductivity of Denver upper 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Denver aquifer p6_01, p6_02, p6_03, ... p6_08—Hydraulic conductivity 

of the silt-plus-sand fraction of Denver aquifer. Each 

parameter is associated with a pilot-point location 

(fig. C3; hydraulic-conductivity field is determined by 

interpolation from the point values.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) spatial variation of hydraulic conductivity of 

silt-sized and coarser fraction is represented by a 

small number of point values interpolated to aquifer 

domain. Parameters represent hydraulic conductivity 

of the silt-plus-sand fraction.

Denver lower confining unit K_tkdlc—Hydraulic conductivity of Denver lower 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Upper Arapahoe aquifer pKa_02, pKa_07, pKa_08, pKa_09, pKa_10, 

pKa_11, pKa_12, p8_01, p8_03, p8_04, p8_05, 

and p8_06—Hydraulic conductivity of the siltplus-sand fraction of upper Arapahoe aquifer. Each 

parameter is associated with a pilot-point location 

(fig. C3); hydraulic-conductivity field is determined 

by interpolation from the point values. Pilot points 

associated with parameters pKa_02, pKa_07, 

pKa_08, pKa_09, pKa_10, pKa_11, and pKa_12 are 

in locations where the Arapahoe confining unit is 

absent; these parameters accordingly apply to both 

upper and lower Arapahoe aquifers.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) spatial variation of hydraulic conductivity of 

silt-sized and coarser fraction is represented by a 

small number of point values interpolated to aquifer 

domain. Parameters represent hydraulic conductivity 

of the silt-plus-sand fraction.
188 Groundwater Availability of the Denver Basin Aquifer System, Colorado

undifferentiated Arapahoe aquifer. An exponential model was 

fitted to each semivariogram. The fitted model parameters are 

shown in table C4. These kriging models, in combination with 

parameter values for each of the pilot-point locations shown in 

figure C3, were then used with PEST utilities to generate, over 

the active domain of each aquifer, values of hydraulic conductivity of the silt-sized and coarser aquifer materials (siltplus-sand fraction). The hydraulic-conductivity values were 

multiplied by the fraction of silt-plus-sand materials to obtain 

an equivalent hydraulic conductivity for the overall aquifer 

thickness represented by each cell.

Specific Storage and Specific Yield

The capacity of each hydrogeologic unit to yield water was 

represented in the model by the parameters specific storage and 

specific yield. Hydrogeologic units represented as confined were 

assigned values of specific storage; units represented as convertible from confined to unconfined conditions were assigned 

values of both specific storage and specific yield. Specific-storage values were estimated separately for aquifers and confining units during model calibration. A specific-storage value of 

5.2 ×10–7/ft was estimated by PEST for aquifers (parameter 

SS_coarse in model input), and a value of 1.7 ×10–6 /ft was estimated by PEST for confining units (parameter SS_fine in model 

input). These aquifer specific-storage values are in the range of 

values computed by various methods for a well completed in the 

Arapahoe aquifer at Castle Pines, Colorado (Robson and Banta, 

1990), and the confining-unit specific-storage value is within 

the range of values reported for confining units by Konikow and 

Neuzil (2007).

Specific-yield values assigned to all aquifer units in the 

model (model layers 1, 2, 4, 6, 8, 10, and 12) allowed for the 

simulation of unconfined conditions and(or) conversion from 

confined to unconfined conditions. Mean specific-yield values 

for each aquifer unit were determined from laboratory and 

aquifer tests (see section “Storage Parameters” in Chapter A; 

table A6) and a spatial distribution of specific yield was 

determined for each bedrock aquifer model layer as described 

herein. For the bedrock aquifers, four specific-yield model 

parameters were defined for the bedrock aquifers (table C5), 

and a constant specific-yield value (equal to the mean values in table A6) was assigned to each model parameter. The 

silt-plus-sand fraction of aquifer materials for each grid 

cell (figs. A14, A20, A22, A27, A30, A34) were input to the 

model as multiplier arrays and multiplied by the constant 

Table C3. Hydraulic-conductivity conceptualization and parameterization.—Continued

[ft/d, feet per day]

Hydrogeologic unit Parameter names and definitions

(ft/d except where noted) Hydraulic-conductivity conceptualization

Arapahoe confining unit K_kac—Hydraulic conductivity of Arapahoe 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Lower Arapahoe aquifer pKa_02, pKa_07, pKa_08, pKa_09, pKa_10, 

pKa_11, pKa_12, p10_01, p10_03, p10_04, p10_05, 

and p10_06—Hydraulic conductivity of the siltplus-sand fraction of lower Arapahoe aquifer. Each 

parameter is associated with a pilot-point location 

(fig. C3); hydraulic-conductivity field is determined 

by interpolation from the point values. Pilot points 

associated with parameters pKa_02, pKa_07, pKa_08, 

pKa_09, pKa_10, pKa_11, and pKa_12 are in 

locations where the Arapahoe confining unit is absent; 

these parameters accordingly apply to both upper and 

lower Arapahoe aquifers.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; 

and (3) spatial variation of hydraulic conductivity 

of silt-sized and coarser fraction is represented 

by a small number of point values interpolated to 

aquifer domain. Parameters represent hydraulic 

conductivity of the silt-plus-sand fraction.

Laramie confining unit K_klc—Hydraulic conductivity of Laramie 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Laramie–Fox Hills aquifer p12_01, p12_02, p12_03, ... p12_11—Hydraulic 

conductivity of the silt-plus-sand fraction of 

Laramie–Fox Hills aquifer. Each parameter is 

associated with a pilot-point location (fig. C3); 

hydraulic-conductivity field is determined by 

interpolation from the point values.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; 

and (3) spatial variation of hydraulic conductivity 

of silt-sized and coarser fraction is represented 

by a small number of point values interpolated to 

aquifer domain. Parameters represent hydraulic 

conductivity of the silt-plus-sand fraction. 1

Vertical anisotropy is defined in Layer Property Flow Package as ratio of horizontal to vertical hydraulic conductivity.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 189

Figure C3. Location of pilot points for estimating hydraulic-conductivity distributions for model 

layers 6 (Denver aquifer), 8 and 10 (upper and lower Arapahoe aquifers undifferentiated), and 12 

(Laramie–Fox Hills aquifer).

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

South Platte River

Coal Creek

Big Dry Cr

Clear Creek

First Cree k

Sand Creek

West P ul m Creek

Running

Creek

Kiow a Creek

Comanche Creek

Muddy Creek

Bijou Creek

Middle Bijou Creek

Adobe Creek

West Bijou Creek Big Sandy Cree k

Cherry Cr

Cook Creek

Box Elder Creek

Lo st Creek

Boulder Creek

Indian Cr

Monument Cr

Crow Creek pKa_09

pKa_12

pKa_11

pKa_10

pKa_07

pKa_02

p10_01

p10_03

p10_04

p10_05

p10_06

p12_03

p12_08

p12_11

p12_10

p12_09

p12_06

p12_04

p12_05

p12_01 p12_02

p6_08

p6_04

p6_06

p6_07

p6_05

p6_03

p6_01

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Denver aquifer simulated extent Extent of active model cells

 (model layer 6)

Laramie–Fox Hills aquifer simulated 

 extent (model layer 12)

Lower Arapahoe aquifer simulated 

 extent (model layer 10)

Simulated streams

!( Layers 8 and 10 pilot points

!( Layer 12 pilot points

!( Layer 6 pilot points
190 Groundwater Availability of the Denver Basin Aquifer System, Colorado

specific-yield values during model execution to obtain an 

equivalent specific yield for the overall aquifer thickness 

represented by each cell (figs. A37, A38, A39, A40, A41, and 

A42). This calculation assumes that materials finer than silt 

sized provide minimal contribution to specific yield of the 

bedrock aquifers. A uniform mean specific yield of 0.165 was 

assigned to the alluvial aquifer (model layer 1; see table C13).

Hydrologic Stresses

Hydrologic stresses on the groundwater system include 

any processes that cause recharge to, or discharge from, the 

aquifers or confining units. Stresses simulated by the model 

include recharge from precipitation plus irrigation return 

flows, evapotranspiration, interaction with streams and reservoirs, spring discharge, and pumping from wells. Interaquifer 

flow in wells, many of which are no longer in use, also is simulated. The groundwater budget calculated by the flow model 

represents the hydrologic stresses discussed in this section.

Recharge

Two sources of water, infiltration of incident precipitation and irrigation in excess of consumptive use (irrigation 

return flow), are simulated as recharging the groundwater 

system. The entire groundwater system domain is assumed 

to be affected by recharge from precipitation. Recharge from 

irrigation return flow is simulated for areas affected by urban 

or agricultural irrigation as described in this section. Total 

recharge in irrigated areas is equal to precipitation recharge 

plus irrigation recharge.

Monthly precipitation data for the period 1931–2003 

for 129 climate-monitoring stations (National Oceanic and 

Atmospheric Administration, 2004) in and adjacent to the 

Denver Basin (fig. A4) were used to develop a series of data 

arrays representing the time-varying spatial distribution of 

precipitation in the model area. The number of active stations 

in a given year ranges from 27 in 1935 and 1936 to 54 in 1965 

and 1996 because of activation and deactivation of individual 

stations or periods of missing record. The interval 1957–2003 

was divided into eight 2- to 8-year stress periods (table C2, 

fig. C2), and the spatial distribution of precipitation, determined by cokriging precipitation data for the stress period 

with land-surface altitude, was held constant during each 

stress period. Stress periods were chosen on the basis of similarities in mean annual precipitation and to include data from 

a large number of climate-monitoring stations in each period. 

For each of the eight stress periods, the set of stations used to 

define the precipitation distribution included all stations with 

complete record for all years in the period.

A long-term mean annual precipitation distribution for 

1931–2003 was interpolated for stations with complete record 

for at least one year (fig. A4) and was applied to the model 

stress periods representing predevelopment through 1956. 

The method for developing the long-term distribution differed from the method used for the 2- to 8-year stress periods 

previously described. For the long-term distribution, a mean 

annual value was determined for each station, and those values 

were cokriged with land-surface altitude to generate a spatial 

precipitation distribution (fig. A4).

Recharge from agricultural irrigation return flows 

(agricultural recharge) was simulated during all stress periods. 

Because agricultural irrigation, primarily by surface-water 

diversions, began in the South Platte River valley prior to 

the 1880s (Nadler and Schumm, 1981), irrigation recharge 

is included in the predevelopment recharge estimates. The 

recharge rate attributed to agriculture, in terms of depth of 

water per unit time, was spatially uniform within an affected 

zone, but the area over which it applied was time varying. 

Irrigation ditch service areas delimited as part of the South 

Platte Decision Support System (Riverside Technology, Inc., 

2005) were used to define the maximum area for agricultural 

Table C4. Parameters of exponential models fitted to semivariograms of log hydraulic-conductivity data from aquifer tests.

Aquifer

Variogram

range

(feet)

Variogram

sill

Denver aquifer 40,416 0.21793

Upper and lower Arapahoe aquifers 118,530 0.31954

Laramie–Fox Hills aquifer 87,420 0.35665

Table C5. Specific-yield conceptualization and parameterization.

Aquifer Parameter name and definition

(units dimensionless) Specific-yield conceptualization

Alluvial aquifer SY_Qal—Specific yield of the alluvial aquifer. Assumption: Specific yield of aquifer is uniform.

Upper and lower Dawson aquifers SY_TDW—Specific yield of the silt-plussand fraction of the upper and lower 

Dawson aquifers.

Denver aquifer SY_TKD—Specific yield of the silt-plussand fraction of the Denver aquifer.Assumptions: (1) Specific yield of aquifer is attributable 

to materials with grain size reported as silt-sized or 

coarser; (2) contribution of finer grained material to 

specific yield is negligible; and (3) specific yield of 

silt-sized and coarser fraction is constant. Parameters 

represent specific yield of the silt-plus-sand fraction.

Upper and lower Arapahoe aquifers SY_KA— Specific yield of the silt-plussand fraction of the upper and lower 

Arapahoe aquifers

Laramie–Fox Hills aquifer SY_KLF—Specific yield of the silt-plus-sand 

fraction of the Laramie–Fox Hills aquifer.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 191

irrigation recharge from 1880 to 1953. The earliest available satellite imagery (U.S. Geological Survey, 1973–1979) 

was used to identify irrigated areas in the 1970s, and for the 

simulated period from pre-1880 to 1953 (model stress periods 

1 through 5), agricultural irrigation recharge was assumed 

to affect the 1973–1979 irrigated areas that also are within 

the ditch service areas (fig. B26). For the simulated period 

1954–1986 (model stress periods 6 though 13), polygons 

approximating the 1970s irrigated areas were used as zones 

of agricultural irrigation (fig. B27). For the simulation period 

1987–2003 (model stress periods 14 through 16), zones 

approximating irrigated areas were derived from satellite 

imagery from 2000 (U.S. Geological Survey, 1999–2000) 

(fig. B28).

Recharge from urban return flows was simulated starting in 1920. The recharge rate attributed to urban return 

flows, in terms of depth of water per unit time, was spatially 

uniform within an affected zone, but the area over which it 

was applied was time varying. Areas of urbanization were 

based on GIS datasets and satellite images. For the simulation 

period 1920–1939 (model stress period 4), the area for urban 

recharge application was delineated from “residential” land 

use in GIS data set LU30 (U.S. Geological Survey, 2001a). 

For the simulation period 1940–1953 (model stress period 5), 

the area for urban recharge application was delineated from 

residential land use in GIS data set LU50 (U.S. Geological 

Survey, 2001b) (fig. B26). Satellite images were used to identify areas affected by urban recharge for the simulation period 

1954-1986 (model stress periods 6 through 13; fig. B27) 

(U.S. Geological Survey, 1973–1979) and for the simulation 

period 1987–2003 (model stress periods 14–16; fig. B28) 

(U.S. Geological Survey, 1999–2000).

Model parameters representing recharge from precipitation and agricultural and urban irrigation return flows 

were defined as previously described and are summarized 

in table C6. Recharge was simulated using the NRCHOP=4 

option of the MODFLOW Recharge Package (Banta, 2006). 

This option specifies that recharge is applied to the uppermost 

active cell connected by active cells to the lowermost active 

cell in a stack of cells. The use of this option avoids unrealistic 

mounding of simulated heads in areas of thin, low-transmissivity cells in confined layers where cells in overlying and 

underlying convertible layers go dry during the simulation.

Evapotranspiration

To ensure that evapotranspiration (ET) was simulated 

at the same cells in which recharge was simulated, a new 

option for specifying the layer to which evapotranspiration 

applies was added to the Evapotranspiration Segments (ETS) 

Package (Banta, 2000). The modifications support a new 

NETSOP=4 option, which works identically to the NEVTOP=4 

option described by Banta (2006). The simulations described 

in this report use the MODFLOW ETS package with the 

NETSOP=4 option.

Land-surface altitude was used as the “evapotranspiration 

surface” of the ETS Package. When the calculated head in a 

cell affected by evapotranspiration is at or above the evapotranspiration surface altitude, simulated evapotranspiration 

is assigned as the maximum evapotranspiration flux. When 

the head is below the extinction depth, evapotranspiration 

is assigned as zero. When the calculated head is below the 

evapotranspiration surface altitude but above the extinction 

depth, the evapotranspiration rate is defined by a segmented 

Table C6. Recharge conceptualization and parameterization.

Water source Parameter name and definition Recharge conceptualization Areas affected

Precipitation RCH_Qal—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Assumptions: (1) Recharge (or 

recharge component, in areas 

also affected by irrigation) is a 

uniform fraction of precipitation; 

and (2) precipitation is accurately 

represented by interpolated distribution generated by cokriging 

observed precipation values for 

selected time intervals with landsurface elevation.

Areas where alluvial aquifer is the 

uppermost hydrogeologic unit.

RCH_Tdw—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where upper or lower Dawson 

aquifer or Dawson confining unit is 

the uppermost hydrogeologic unit.

RCH_TKd—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where Denver aquifer or upper 

or lower Denver confining unit is 

the uppermost hydrogeologic unit.

RCH_Ka—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where upper or lower Arapahoe 

aquifer or Arapahoe confining unit is 

the uppermost hydrogeologic unit.

RCH_Klf—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where Laramie confining unit 

or Laramie–Fox Hills aquifer is the 

uppermost hydrogeologic unit.

Agricultural irrigation RCH_AgIrr—Recharge from 

agricultural in affected area. 

Unit: inch per year, in/yr.

Recharge component is that part 

of applied irrigation water that 

reaches the water table. This 

component supplements recharge 

from precipitation.

Agricultural areas irrigated by flood, 

furrow, and sprinkler irrigation. 

The affected areas are time-varying.

Residential irrigation RCH_Resid—Recharge flux from 

residential irrigation in affected 

area. Unit: inch per year, in/yr.

Urban and suburban areas primarily in 

and adjacent to Denver and Colorado 

Springs. The affected areas are 

time-varying.
192 Groundwater Availability of the Denver Basin Aquifer System, Colorado

function of depth below the evapotranspiration surface. The 

segment ends are defined in terms of proportions of maximum 

evapotranspiration rate and of extinction depth. The maximum evapotranspiration rate used for the Denver Basin model 

was based on analysis described by David Groeneveld and 

Michael Prescott (HydroBio, Inc., written commun., 2006) 

who list 10-year average annual “grass-reference ET” rates for 

several stations in eastern Colorado; two of the stations are in 

the Denver Basin model area. The average of the rates for the 

two stations, 45 inches per year, was used as the maximum 

evapotranspiration rate (parameter ET_MAX in model input) 

for the Denver Basin model area. The function developed for 

the San Luis Valley of Colorado, which defines evapotranspiration rate for depths to water between land surface and an 

extinction depth of 30 ft (David Cooper, written commun., 

2005) was applied in the Denver Basin model (fig. C4).

Streams

Streams including the South Platte River, its tributaries, and streams in the Arkansas River Basin were simulated 

using the Streamflow Routing (SFR2) Package (Niswonger 

and Prudic, 2005, version 2.6, June 29, 2006). Locations of 

streams in the study area were obtained as Digital Line Graph 

(DLG) data (U.S. Geological Survey, 1989). This dataset was 

manually edited to convert streams represented as two lines to 

be represented instead as single lines. Ponds and small lakes 

were replaced with single lines, and lines were digitized to 

represent dry wash areas shown on 1:100,000 scale Digital 

Raster Graphic (DRG) images (Bailey, Castle Rock, Colorado 

Springs, Denver East, Denver West, Fort Morgan, Greeley, 

Karval, Last Chance, and Limon quadrangles, U.S. Geological 

Survey, 1999b). The digitized streams were divided into segments with segment lengths less than or equal to 25,000 ft. A 

raster dataset representing land-surface altitude at a horizontal resolution of 30 meters (U.S. Geological Survey, 1999a) 

was used to assign streambed top altitude of the upstream 

and downstream ends of each segment. The stream data 

were imported into the MODFLOW graphical user interface 

(Winston, 2000), which was then used to prepare model-input 

files in which streams were discretized as specified cells in the 

model grid (fig. C5). For all segments, the streambed thickness was assigned as 30 ft, and depth of water in the channel 

was assigned as 1.0 ft. Two streamflow routing parameters 

(table C7) were defined to represent the hydraulic conductivity 

of the streambed materials.

Streams simulated in the Denver Basin model include 

those that originate within the basin and those that originate 

outside the basin. Most of the basin is drained by streams 

that originate within the basin. Along the west and northwest 

margin of the basin, many of the streams originate in the Front 

Range west and outside of the basin.

To ensure that simulated leakage from streams that 

originate within the basin would not exceed the amount of 

water physically available, it was important to track simulated 

flows in those streams and allow them to behave in the model 

as many of them physically do, that is, as intermittent and 

ephemeral streams. Input to the SFR2 Package specified zero 

inflow at the headwaters of these streams. With inflow specified as zero, surface-water flow is limited to reaches where the 

simulated water table in the uppermost aquifer is above the top 

of the stream bed or surface-water flow from upstream reaches 

exceeds loss to groundwater. SFR2 was used to track streamflow rates, but it was not used to calculated stream stage; stage 

was assumed one foot above the streambed top wherever 

streamflow was simulated.

A number of perennial streams and rivers enter the 

Denver Basin from the west and north. Because these streams 

are perennial, tracking of streamflow was not important. 

However, for consistency with the streams originating within 

the basin, the streams originating outside the basin also were 

simulated with the SFR2 Package. Again, SFR2 was not used 

to calculate stream stage. To ensure that these streams behaved 

in the model as perennial streams, it was necessary to specify 

inflow at the upstream ends of the simulated reaches such that 

flow was great enough to supply downstream losses to groundwater as needed. Data from Boulder Creek (Murphy and 

others, 2003) indicated a base flow of 50 ft3/s would be typical 

and reasonable. This inflow rate was used for all streams and 

rivers originating outside the basin and was sufficient to maintain flow in the simulated streams. These assumptions and 

generalizations are suitable for the purpose of groundwater 

modeling, but the model-computed surface-water flow rates 

for these streams are not meaningful products of the model 

and were not included in the model calibration.

Reservoirs

Five reservoirs in the Denver Basin were simulated using 

the MODFLOW River (RIV) Package (Harbaugh and others, 

2000) (fig. C5). Table C8 lists the reservoirs and corresponding 

properties as simulated. One parameter (RIV_Lakes) was defined 

to control the hydraulic conductance of materials between the 

reservoirs and the underlying aquifer. The stress period chosen for 

the start of simulation of each reservoir was the one nearest the 

year of reservoir construction or filling. The purpose of reservoir 

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30

Evapotranspiration rate,

in inches per year

Depth to water,

in feet

Figure C4. Evapotranspiration as a function of depth to water 

used for the Denver Basin model.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 193

Figure C5. Locations of boundary condition cells for the Denver Basin model.

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Alluvial aquifer simulated extent Stream (SFR) cell

Spring (DRN) cell

Pre-1880 flowing well (DRN) cell

Reservoir (RIV) cell

General-head boundary (GHB) cell

Laramie–Fox Hills aquifer simulated extent Specified-flux (FHB) cell

Lower Arapahoe aquifer simulated extent

Denver aquifer simulated extent

Lower Dawson aquifer simulated extent

Simulated stream
194 Groundwater Availability of the Denver Basin Aquifer System, Colorado

simulation was to include the effects of the reservoirs on groundwater levels, and the RIV Package was used to simulate reservoirs 

as a simple head-dependent boundary.

Springs

All spring locations within the Denver Basin area that are 

shown on the 1:100,000 scale DRG images were digitized for 

representation in the model (fig. A11). The MODFLOW Drain 

(DRN) Package (Harbaugh and others, 2000) was used to 

simulate all springs (fig. C5). Drain cells were located at grid 

cells encompassing each spring location, and drain altitudes 

were assigned from land-surface altitudes (U.S. Geological 

Survey, 1999a). The hydrogeologic unit at land surface at each 

spring location determined the model layer for each drain feature. One DRN parameter, named DRN_COND, was defined 

to control the hydraulic conductance applied to all drains.

Groundwater Flow Across Basin Boundaries

The model domain approximately conforms to the extent 

of the Denver Basin bedrock units, and groundwater flow 

in the aquifer system is largely constrained to the extent of 

bedrock units. However, groundwater flow crosses the extent 

of bedrock units where saturated materials of the alluvial 

aquifer extend beyond the bedrock units, such as in the areas 

of the Black Squirrel Creek basin (Buckles and Watts, 1988) 

and the Nussbaum Alluvium (Paschke, 1992). These areas of 

alluvial aquifer overlap the southern and southeastern parts of 

the model boundary. Model cells in areas where groundwater 

flow crosses the model boundary were simulated as headdependent flow boundaries using the MODFLOW GeneralHead Boundary (GHB) Package (fig. C5).

Groundwater flow out of the model domain in the South 

Platte alluvial aquifer near Wiggins, Colorado, was simulated 

using specified flow boundaries with the MODFLOW Flow 

and Head Boundary (FHB) Package. Detailed information on 

water levels, transmissivity, and saturated thickness in this 

area (Hurr, Schneider, and others, 1972) was used to estimate 

groundwater flow parallel to the South Platte River in the 

alluvial aquifer. A 7-mile cross section of the alluvial aquifer — drawn approximately perpendicular to the South Platte 

River through the northeast corner of section 13 in Township 4 

North, Range 59 West and the northeast corner of section 8 

in Township 3 North, Range 59 West — was considered in 

intervals of 0.25 mile. Transmissivity, saturated thickness, 

and cross-sectional area for each interval were estimated from 

maps in Hurr, Schneider, and others (1972). Hydraulic gradient was estimated as 0.0014. Flow was computed for each 

interval and summed to obtain a total estimated underflow 

for the alluvial cross section of 14.1 ft3/s. Seven FHB cells 

were specified at the downgradient alluvial aquifer boundary 

(fig. C5) with a specified total withdrawal of 14.1 ft3/s.

Historical Flowing Wells

As discussed in Chapters A and B, many of the bedrock wells constructed in the late 19th century flowed at 

land surface upon installation. Emmons and others (1896, 

p. 422) inventoried 394 wells completed in the Arapahoe and 

Laramie–Fox Hills aquifers of the Platte Valley from 1883 to 

1890. A data table (Emmons and others, 1896, p. 433–447) 

explicitly lists 209 wells inventoried in Denver, and 185 wells 

were referenced as having locations in “the country” (Emmons 

and others, 1896). Well location information for the 209 wells 

was provided in the form of street addresses or major cross 

streets. To generate latitude and longitude coordinates and 

land-surface altitudes for the historical wells, well addresses 

were located on Sanborn Fire Insurance street maps from 

1887, 1890, 1893, 1897, 1903, and 1904 (accessed at the 

Denver Public Library), the locations were manually plotted 

on electronic street and topographic maps, and the latitude 

and longitude coordinates were generated by the map software (Garmin Ltd., 2004) (table C9). The wells were poorly 

constructed by modern-day standards, and many wells were 

Table C7. Properties assigned to Denver Basin model features representing the South Platte River and streams.

Stream or river Stream width

(feet)

Streambed

thickness

(feet)

Depth of water

in channel

(feet)

Parameter name

and definition

South Platte River 150 30 1 SFR_PLATTE—Hydraulic conductivity of riverbed 

materials, in feet per day.

All other streams 50 30 1 SFR_TRIBS—Hydraulic conductivity of streambed 

materials, in feet per day.

Table C8. Properties assigned to Denver Basin model features representing reservoirs.

Reservoir Year of reservoir

construction or filling

Stress period in

which reservoir is

first simulated

Model

layer

Bottom altitude

(feet)

Stage

(feet)

Area

(acres)

Barr Lake 1908 3 1 5,050 5,096 1,733

Milton Reservoir Prior to 1950 5 1 4,770 4,810 1,622

Cherry Creek Reservoir 1950 6 6 5,500 5,548 860

Chatfield Reservoir 1972 10 1 5,400 5,426 1,407

Aurora Reservoir 1990 14 3 5,810 5,930 638
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 195

constructed with multiple completion intervals (Emmons 

and others, 1896). For each well, the model layer or layers, 

row, and column were assigned on the basis of well location 

and depth. Locations could not be determined for 12 of the 

209 wells reported by Emmons and others (1896), resulting 

in 197 wells with estimated locations (table C9).

The 197 late-19th century (pre-1900) flowing wells for 

which locations could be determined were represented as 

drain features in 37 cells in model layers 6, 8, and 10 using 

the MODFLOW Drain Package (Harbaugh and others, 2000) 

(fig. C5). Most of the wells had stopped flowing by 1905 

(Darton, 1905), so they were simulated as drains only in stress 

period 2, which represents 1880 through 1906. Land-surface 

altitudes from the U.S. Geological Survey (1999a) at the well 

locations were assigned as the drain altitudes, and each drain 

feature was assigned hydraulic conductance based on the 

appropriate model layer or layers. The conductance of all drain 

cells representing flowing wells was controlled by a parameter 

named “FLWG_WELLS.”

Pumping

Pumping from wells completed in the alluvial and bedrock 

aquifers was simulated using the MODFLOW Well (WEL) 

Package (Harbaugh and others, 2000). No pumping was assigned 

to confining units. As described in the section “Denver Basin 

Pumping History” of Chapter B, the number and locations of 

domestic, irrigation, commercial/industrial, and municipal wells 

were tabulated for each year from 1880 to 2003 based on the 

CDWR well-permit database. Pumping rates were then assigned 

to each well type for each aquifer, and pumping was summed 

for each model grid cell (layer, row, and column) for each year. 

Annual pumping volumes for each grid cell were summed and 

averaged over each stress period for input to the WEL Package. 

Simulated pumping for 2003 for the alluvial aquifer (169 ft3/s) 

and the bedrock aquifers (111 ft3/s) was slightly less than the estimated pumping values of 187 ft3

/s for alluvial wells and 118 ft3/s 

for bedrock wells because some model cells representing pumping wells were deactivated during the iterative solution procedure 

of the simulation. In general, pumping increased in volume and 

geographic extent for each aquifer model layer through time. The 

spatial distribution of pumping is displayed along with simulated 

potentiometric surfaces for 1956, 1978, and 2003 for each aquifer 

model layer (layers 1, 2, 4, 6, 8, 10, and 12, respectively) in the 

section “Simulated Hydraulic Heads” of this chapter.

Multiaquifer Wells

Wells that allow hydraulic communication among 

geohydrologic units were simulated using the Multi-Node 

Well (MNW) Package (Halford and Hanson, 2002) for 

MODFLOW. The well-loss coefficient was assumed to be 

linear and was defined using the “skin” model of Halford and 

Hanson (2002, equation 3). The skin value was assigned a typical value of 2.0 (dimensionless) (Halford and Hansen, 2002).

Solver

The presence of seven convertible model layers and 

numerous nonlinear boundary conditions described in the 

previous sections produces a highly nonlinear system of finitedifference equations, which can be difficult to solve. Also, 

deactivation of cells due to approximations of hydraulic head 

being below cell-bottom altitudes during the iterative solution procedure was a common problem. The GMG Package 

(Wilson and Naff, 2004) for MODFLOW was selected to 

solve the system of equations because of its speed and efficiency. Damping of the head changes by specifying a constant 

damping value lessened the problem of cell deactivation, but 

at the expense of longer execution times. Use of Cooley’s 

adaptive damping method (Mehl and Hill, 2001) caused instability in the solution procedure. Use of an alternative adaptive 

damping method described by Banta (2006) was found to 

provide a solution in a reasonable execution time and with a 

relatively small number of deactivated cells.

Model Calibration

Model calibration is the process by which model parameter 

values are adjusted within reasonable limits to minimize the 

difference between model-computed and measured heads and 

flows. Calibration of the Denver Basin model used nonlinearregression methods implemented in PEST (Doherty, 2006) in 

combination with manual assignment of parameters that proved 

resistant to calibration by automated methods.

Model fit was evaluated by comparing model-simulated 

values to head or flow values observed in the field or derived 

by analysis of field data. For each observed value and corresponding model-simulated value, a residual was defined by 

subtracting the simulated value from the observed value. Each 

observation was assigned a weight based on an estimate of the 

standard deviation or coefficient of variation associated with 

the observation. For this study, the definition of weight follows 

the convention used in PEST, where weight is calculated as the 

inverse of the (estimated) standard deviation associated with 

an observation or item of prior information. A measurementobjective function (Sm) was defined as (Doherty, 2006):

S wr m i i

i

m

= =

∑( )2

1

(1)

where

wi is the weight associated with observation i,

ri is the residual for observation i,

and

m is the number of observations.

The value of Sm is an indicator of the fit of the model to observations; in general, a smaller value of Sm indicates a better 

fit than does a larger value of Sm. One of the goals of model 

calibration is to minimize Sm while maintaining physically 

reasonable parameter values.
196 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

1 1 Anderson -- -- 200,000 -- -- 0

2 2 Carico 50 ft 5,268 -- -- -- pumping

3 3 Collins -- -- 51,000 -- -- --

4 4 Ester 40 ft 5,260 40,000 –25 ft 5,195 24,000

5 5 Oakes -- -- 34,560 -- -- 0

6 6 Eckhart 32 psi 5,298 -- -- -- 0

7 7 The Rink -- -- -- -- -- 0

8 8 County Court House 50 ft 5,280 60,000 0 ft 5,230 pumping

9 9 Kinsey 30 ft 5,254 86,400 –25 ft 5,199 0

10 10 Albany Hotel 50 ft 5,273 50,000 –20 ft 5,203 pumping

11 11 Timerman -- -- -- –20 ft 5,201 0

12 12 Cowell -- -- 40,000 -- -- 0

13 13 Charles 80 psi 5,405 -- –20 ft 5,200 pumping

14 14 St. James Hotel -- -- 45,000 –27 ft 5,193 0

15 15 Tritch 25 ft 5,242 -- -- -- 0

16 16 Tabor Opera House 36 psi 5,301 -- –12 ft 5,206 pumping

17 17 Welker 50 ft 5,267 120,000 -- -- pumping

18 18 Daniels & Fisher 78 ft 5,290 40,000 -- -- pumping

19 19 McClelland 75 ft 5,287 -- –50 ft 5,162 pumping

20 20 Goode 75 ft 5,277 85,000 –25 ft 5,177 pumping

21 21 Metropolitan 70 psi 5,360 -- -- -- 0

22 22 Lothrop -- -- 21,600 -- -- 0

23 23 Barkley Block -- -- 76,320 –15 ft 5,195 pumping - 72,000

24 24 Windsor 50 psi 5,325 300,000 –92 ft 5,118 pumping

25 25 Stacy 35 psi 5,276 -- -- -- 0

26 26 Union Depot 20 psi 5,231 180,000 –200 ft 5,985 0

27 27 Mars, Middleton 

& Hunter

20 ft 5,205 -- -- -- 0

28 28 American House 25 psi 5,249 -- -- -- pumping

29 29 Columbus House 

(Watkins Bldg)

-- -- 17,280 -- -- 0

30 30 Tremont House 20 ft 5,215 -- –15 ft 5,180 pumping

31 31 Anheuser-Busch -- -- 100,000 -- -- 10,000

32 32 Mullen -- -- -- –15 ft 5,170 pumping

33 33 Mayer -- -- -- -- -- pumping

34 34 D&RG No. 1 38 ft 5,223 -- -- -- pumping - 20,000

35 35 Wagner 4 ft 5,199 -- –3 ft 5,192 pumping

36 36 Lindell Hotel 30 ft 5,225 86,400 –10 ft 5,185 pumping

37 37 Milwaukee Brewery 27 ft 5,222 -- –6 ft 5,189 pumping

38 38 Spitzer -- -- 43,200 -- -- 0

39 39 Western Hotel -- -- 150,000 –18 ft 5,180 pumping

40 40 Knight -- -- 60,000 -- -- 0

41 41 Denver Brewing Co -- -- 100,000 –28 ft 5,177 27,000

42 42 Lion Brewery 40 ft 5,235 26,448 –8 ft 5,187 pumping

43 43 Chase 8 ft 5,212 -- -- -- 0

44 44 Bomblitz 40 ft 5,235 -- –4 ft 5,191 0

45 45 Waterworks -- -- 40,000 -- -- 0

46 46 Waterworks -- -- 40,000 -- -- 0

47 47 Waterworks -- -- 40,000 -- -- 0

48 48 Waterworks -- -- 40,000 -- -- 0

49 49 Waterworks -- -- 40,000 -- -- 0

50 50 D&RG No. 2 30 ft 5,255 -- -- -- 0
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 197

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

1 1 375 1887 39.740 –104.998 8 51 14

2 2 375 1887 5,218 39.740 –104.995 8 51 14 S 12th St = Fox St south of Colfax

3 3 375 1887 39.742 –104.998 8 51 14

4 4 600 1887 5,220 39.737 –104.995 10 51 14 65 S 12th St = Fox St = approximate location south 

of 14th Ave

5 5 365 1887 39.744 –105.000 8 51 14

6 6 375 1887 5,224 39.745 –104.994 8 51 14

7 7 627 1887 39.745 –104.992 10 51 14

8 8 600 1887 sheet 22 5,230 39.743 –104.989 10 51 14 Arapahoe County Court House

9 9 615 1887 5,224 39.747 –104.990 10 51 14

10 10 700 1887 5,223 39.747 –104.992 10 51 14

11 11 600 1887 5,221 39.748 –104.993 10 51 14

12 12 580 1887 39.749 –104.992 10 50 14

13 13 564 1887 5,220 39.746 –104.996 8 51 14

14 14 670 1887 sheet 24 5,220 39.746 –104.995 10 51 14

15 15 650 1887 sheet 19 5,217 39.748 –104.994 10 50 14

16 16 375 1887 sheet 25 5,218 39.747 –104.995 8 51 14

17 17 650 1887 5,217 39.748 –104.994 10 51 14

18 18 669 1887 5,212 39.748 –104.996 10 50 14

19 19 607 1887 5,212 39.748 –104.997 10 51 14

20 20 680 1887 5,202 39.749 –104.998 10 50 14

21 21 545 1887 5,198 39.750 –104.998 8 50 14

22 22 473 1887 39.750 –104.994 8 50 14

23 23 602 1887 sheet 18 5,210 39.751 –104.995 10 50 14

24 24 530 1887 sheet 14 5,210 39.751 –104.995 8 50 14

25 25 600 1887 sheet 7 5,195 39.755 –104.992 10 50 14

26 26 506 1887 sheet17 5,185 39.753 –105.000 8 50 14

27 27 520 1887 sheet 18 5,185 39.753 –104.998 8 50 14

28 28 545 1887 sheet 18 5,191 39.751 –104.999 8 50 14

29 29 356 1887 sheet 27 39.751 –105.001 8 50 14

30 30 325 1887 sheet 32 5,195 39.748 –105.003 8 51 13

31 31 314 1887 sheet 36,

1890 volume 1

sheet 9a

39.748 –105.006 8 51 13

32 32 360 1887 sheet 35 5,185 39.746 –105.009 8 51 13

33 33 333 1887 sheet 35 39.746 –105.009 8 51 13

34 34 350 1887 sheet 36 5,185 39.745 –105.011 8 51 13

35 35 330 1887 sheet 33 5,195 39.744 –105.006 8 51 13

36 36 360 1887 sheet 33 5,195 39.745 –105.004 8 51 13 11th and Larimer

37 37 354 1887 sheet 33 5,195 39.745 –105.005 8 51 13

38 38 333 1887 sheet 32 39.746 –105.004 8 51 13

39 39 585 1887 sheet 32 5,198 39.746 –105.003 10 51 13

40 40 340 1887 sheet 28 5,198 39.746 –105.002 8 51 14

41 41 600 1887 sheet 31 5,205 39.743 –105.005 10 51 13 Artesian well shown on map

42 42 294 1887 sheet 34 5,195 39.744 –105.007 8 51 13

43 43 366 1887 sheet 31 5,204 39.744 –105.003 8 51 13

44 44 315 1887 sheet 1 5,195 39.740 –105.011 8 51 13 4th and Colfax

45 45 600 1887 sheet 1 39.735 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

46 46 600 1887 sheet 1 39.734 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

47 47 600 1887 sheet 1 39.734 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

48 48 600 1887 sheet 1 39.735 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

49 49 600 1887 sheet 1 39.734 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

50 50 800 1890 volume 1

sheet 24a

5,225 39.730 –105.006 10 52 13 Burnham shops at 9th Ave and S 7th (south of 

Lincoln Park)
198 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

51 51 A.E. Pierce 30 psi 5,335 100,000 -- -- 0

52 52 Brown -- -- -- -- -- 0

53 53 Fleming -- -- 165,375 -- -- 0

54 54 Miles -- -- -- -- -- 0

55 55 Bonesteel -- -- 21,600 -- -- 0

56 56 Buergy -- -- -- -- -- 0

57 57 Cemetery 35 psi 5,239 500,000 -- -- 0

58 58 Waverly -- -- 140,000 -- -- 0

59 59 Cowan -- -- 147,000 -- -- 0

60 60 Knox 24 psi 5,274 -- -- -- 0

61 61 Stevens -- -- 80,000 -- -- 0

62 62 Home Artesian Well -- -- 45,000 -- -- 0

63 63 Gas Works 20 ft 5,205 300,000 –25 ft 5,160 pumping

64 64 Germania House -- -- 36,000 –12 ft 5,173 0

65 65 Steam Heating Co 20 ft 5,203 200,000 –25 ft 5,158 0

66 66 Freund 25 ft 5,207 -- -- -- 0

67 67 Tierman -- -- 41,760 –55 ft 5,130 pumping

68 68 Jerome 15 ft 5,200 -- –8 ft 5,177 pumping

69 69 Nahring 25 ft 5,210 -- -- -- 0

70 70 Bareslaux -- -- 34,560 -- -- 0

71 71 McVeigh 20 ft -- -- –25 ft -- 0

72 72 Mazza -- -- -- -- -- 0

73 73 Electric Light Co. 30 psi 5,259 -- -- -- pumping

74 74 Schindelhotz 40 ft 5,225 -- -- -- 0

75 75 Belisle -- -- 14,400 -- -- pumping

76 76 City Laundry 19 psi 5,247 -- –27 ft 5,177 pumping

77 77 Universal 

Sampling Works

140 ft 5,335 547,200 –6 ft 5,189 pumping

78 78 Swift -- -- -- -- -- 0

79 79 Bennett -- -- 108,000 –20 ft 5,190 pumping

80 80 30th and 

Arapahoe Sts

-- -- 130,000 -- -- 0

81 81 Savage 50 ft 5,242 -- –25 ft 5,167 pumping

82 82 Walker -- -- 125,000 -- -- 0

83 83 Colorado

Iron Works

35 psi 5,266 -- –8 ft 5,177 pumping

84 84 Adair -- -- 72,000 –6 ft 5,189 pumping

85 85 Nichols 40 psi 5,287 -- -- -- pumping

86 86 Morrison Bros 30 ft 5,225 -- -- -- 0

87 87 U.P. Hospital 40 psi 5,287 90,000 -- -- 0

88 88 Grant Smelter 45 psi 5,289 500,000 -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 199

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

51 51 720 1890 volume 1

sheet 1

5,266 39.716 –104.986 10 53 14

52 52 995 1890 volume 1

sheet 1

5,268 39.716 –104.985 10 53 14

53 53 670 1890 volume 2 

sheet 56a

39.757 –105.005 10 50 13 Approx location Exposition bldg at Riverside Park?/

Text says southernmost of Denver wells south of 

old Exposition bldg

54 54 610 1893 volume 3 

sheet 111a

39.737 –104.989 10 51 14 Approx location, 1893 S 15th = 2006 Acoma south 

of Colfax—Deer and Moose still not found

55 55 850 1893 volume 3 

sheet 111a

39.737 –104.975 10 51 15 Approx location, 1893 Alta = 2006 Ogden south of 

Colfax—Deer and Moose still not found

56 56 550 1893 volume 3 

sheet 111b

39.736 –104.973 8 51 15 Approx location,1893 Hallett = 2006 Downing south 

of Colfax—Pine still not found

57 57 525 5,158 39.792 –104.962 10 48 16

58 58 860 1890 volume 1

sheet 8a

5,200 39.745 –105.005 10 51 13 Waverly Hotel—10th and Larimer

59 59 670 1887 sheet 9 5,220 39.751 –104.987 10 50 14 Not sure which corner

60 60 700 1887 sheet 1 5,219 39.753 –104.985 10 50 14

61 61 750 1887 sheet 1 39.755 –104.984 10 50 15

62 62 685 39.732 –104.967 10 52 15

63 63 610 1887 sheet 15 5,185 39.755 –104.998 10 50 14

64 64 341 1887 sheet 15 5,185 39.755 –104.998 8 50 14 On 19th south of gas works

65 65 325 1887 sheet 15 5,183 39.756 –104.999 8 50 14 On 19th north of gas works

66 66 309 1887 sheet 15 5,182 39.756 –104.998 8 50 14

67 67 535 1887 sheet 15 5,185 39.756 –104.997 8 50 14

68 68 325 5,185 39.756 –104.997 8 50 14 Approx location near Wewetta and 20th—can’t find 

Cottage Ln

69 69 300 1887 sheet 1 5,185 39.759 –104.997 8 50 14 Approx corner of Huron and 29th now

70 70 304 1887 sheet 1 5,185 39.760 –104.997 8 50 14 Approx Huron Ave

71 71 320 1887 sheet 1 39.759 –104.997 8 50 14 Approx Huron Ave

72 72 300 8

73 73 330 1887 sheet 39 5,190 39.758 –104.994 8 50 14

74 74 416 1887 sheet 5 5,185 39.759 –104.986 8 50 14 Schindelhotz Terrace

75 75 420 1887 sheet 5 -- 39.757 –104.985 8 50 14

76 76 406 1887 sheet 4 5,204 39.759 –104.984 8 50 15

77 77 400 1887 sheet 4 5,195 39.762 –104.985 8 50 14 Artesian well on map

78 78 457 1887 sheet 1 -- 39.758 –104.979 8 50 15

79 79 450 1887 sheet 1 5,210 39.759 –104.974 8 50 15

80 80 620 1887 sheet 1 -- 39.761 –104.979 10 50 15

81 81 400 1887 sheet 1 5,192 39.768 –104.975 8 49 15

82 82 587 1887 sheet 1 -- 39.763 –104.977 8 49 15

83 83 420 1887 sheet 38, 

1890 volume 2 

sheet 83a

5,185 39.768 –104.980 8 49 15 Well shown on map

84 84 392 1887 sheet 1 5,195 39.769 –104.976 8 49 15

85 85 366 1887 sheet 38 5,195 39.770 –104.976 8 49 15 Artesian well on map

86 86 400 1887 sheet 1 5,195 39.769 –104.974 8 49 15

87 87 675 1903 volume 2 

sheet 261, |

1903 volume 3 

sheet 112b

5,195 39.773 –104.967 10 49 15 North of 40th between Franklin and Gilpin

88 88 620 1903 volume 2 

sheet 261

5,185 39.778 –104.969 10 48 15
200 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[

1

, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

89 89 McNassor 23 ft -- -- -- -- 0

90 90 Morrison Bros -- -- -- –60 ft -- pumping

91 91 D.U and P.R.R. 25 ft 5,210 -- -- -- pumping

92 92 Smedley -- -- 216,000 –76 ft -- pumping

93 93 John Mullen -- -- 21,600 -- -- pumping

94 94 Doyle & White 20 ft 5,215 -- -- -- 0

95 95 Sanderson 30 psi 5,292 -- –25 ft 5,198 pumping

96 96 Green 30 ft 5,240 -- -- -- 0

97 97 Hanson -- -- -- -- -- --

98 98 Hecker 16 ft 5,219 -- –12 ft 5,191 pumping

99 99 Poole 35 ft 5,238 -- –28 ft 5,175 --

100 100 Granton 22.5 psi 5,227 -- –15 ft 5,160 0

101 101 Marquis 40 ft 5,218 -- -- -- pumping

102 102 Scanlon 20 ft 5,205 25,920 –8 ft 5,177 pumping

103 103 Oppenlander 31 psi 5,272 -- –8 ft 5,192 pumping

104 104 Frey & Hoelzle 25 ft 5,213 -- -- -- --

105 105 Spitzer -- -- 4,514,400 –20 ft 5,170 0

106 106 Highland House 70 ft 5,262 -- –12 ft 5,180 pumping

107 107 Crisman 40 ft 5,225 -- –5 ft 5,180 0

108 108 Shannon -- -- 86,400 –30 ft 5,258 0

109 109 Clark & Killison -- -- -- -- -- 0

110 110 Montague -8 ft 5,272 pumping –100 ft 5,180 --

111 111 Ashland

School House

-- -- pumping -- -- 0

112 112 Meanea 25 ft 5,225 -- –10 ft 5,190 0

113 113 Swenson 14 ft 5,224 8,640 –20 ft 5,190 pumping

114 114 Norton 30 ft 5,240 21,600 -- -- 0

115 115 Eckhart well No. 1 35 psi 5,384 -- -- -- 0

116 116 Eckhart well No. 2 -- -- -- -- -- 0

117 117 Quayle 35 ft 5,306 -- –50 ft 5,221 pumping

118 118 Zang No. 1 20 psi 5,246 -- -- -- 0

119 119 Zang No.2 25 psi 5,258 400,000 –40 ft 5,160 0

120 120 Gurley Bros 30 psi 5,264 -- -- -- 0

121 121 Weeber -- -- 1,800 -- -- 0

122 122 Myer 20 ft 5,280 -- –72 ft 5,188 pumping

123 123 Tegeler 32 ft 5,232 -- –2 ft 5,198 pumping

124 124 Higgins -- -- -- -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 201

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

89 89 300 -- 8

90 90 400 -- 8

91 91 306 1887 sheet 16 5,185 39.756 –104.999 8 50 14 South of Hartford btwn 19th and Division

92 92 647 -- 10 Approx location—Clear Creek = Pecos, can’t find 

Backus

93 93 300 1890 volume 2 

sheet 0

-- 39.764 –105.005 8 49 13 Osage between 33 and 34th

94 94 320 1887 sheet 1 5,195 39.761 –105.006 8 50 13

95 95 579 1887 sheet 1 5,223 39.761 –105.008 10 50 13

96 96 500 1887 sheet 1 5,210 39.761 –105.007 8 50 13

97 97 600 1887 sheet 1 5,210 39.761 –105.008 10 50 13

98 98 316 1887 sheet 1 5,203 39.760 –105.007 8 50 13

99 99 371 1887 sheet 1 5,203 39.761 –105.008 8 50 13

100 100 238 1887 sheet 1 5,175 39.759 –105.006 8 50 13

101 101 290 1887 sheet 37 5,178 39.758 –105.007 8 50 13 Marquis canned goods

102 102 251 1887 sheet 37 5,185 39.758 –105.008 8 50 13

103 103 515 1887 sheet 37 5,200 39.758 –105.009 8 50 13 Oppenlander City Brewery—artesian well shown 

on map

104 104 312 1887 sheet 37 5,187 39.757 –105.008 8 50 13

105 105 270 1887 sheet 37 5,190 39.756 –105.009 8 50 13

106 106 512 1887 sheet 37 5,192 39.756 –105.009 8 50 13

107 107 296 1887 sheet 37 5,185 39.756 –105.008 8 50 13

108 108 364 1890 volume 2 

sheet 91b

5,288 39.760 –105.013 8 50 13 Corner 30th and Vallejo

109 109 371 1890 volume 2 

sheet 91b

5,260 39.758 –105.013 8 50 13 Corner 29th and Vallejo

110 110 370 1890 volume 2 

sheet 91a

5,280 39.759 –105.016 8 50 13 Ashland = 29th, Gallup = Zuni

111 111 711 1890 volume 2 

sheet 91a

5,290 39.759 –105.017 10 50 13 29th and Zuni

112 112 185 1890 volume 2 

sheet 0

5,200 39.755 –105.011 6 50 13

113 113 293 1890 volume 2 

sheet 0

5,210 39.755 –105.013 8 50 13 Highland = 26th

114 114 509 1890 volume 2 

sheet 0

5,210 39.754 –105.014 8 50 13

115 115 665 1890 volume 2 

sheet 0

5,303 39.755 –105.021 10 50 13

116 116 840 1890 volume 2 

sheet 0

5,303 39.755 –105.022 10 50 12

117 117 565 1890 volume 2 

sheet 0

5,271 39.753 –105.018 8 50 13 Emerald = 25th

118 118 300 1887 sheet 35 5,200 39.752 –105.015 8 50 13 Rocky Mountain Brewery—artesian well on map

119 119 480 1887 sheet 35 5,200 39.752 –105.015 8 50 13 Rocky Mountain Brewery—artesian well on map

120 120 775 1890 volume 2 

sheet 0

5,195 39.748 –105.017 10 51 13

121 121 214 5,282 39.749 –105.025 6 50 12 Federal and 21st?

122 122 600 5,260 39.746 –104.980 10 51 15 St Lukes = 19th and Pearl

123 123 270 1890 volume 2 

sheet 0

5,200 39.746 –105.021 8 51 13 19th and Clay—under old Mile High Stadium

124 124 525 1893 volume 3 

index

5,200 39.740 –105.022 8 51 12 Morrison Rd and Colfax (Golden = Colfax)
202 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

125 125 Agerer 30 ft 5,230 -- –16 ft 5,184 pumping

126 126 Snively -- -- -- –15 ft 5,185 pumping

127 127 Heidrer 40 ft 5,240 -- –12 ft 5,188 pumping

128 128 Villa Park No. 1 -- -- -- –30 ft 5,230 pumping

129 129 Villa Park No. 2 -- -- -- –50 ft 5,210 pumping

130 130 Weir No. 1 -- -- 45,360 -- -- 0

131 131 Weir No. 2 55 psi 5,377 -- –12 ft 5,238 pumping

132 132 County Hospital -- -- 12,000 -- -- pumping

133 133 Sloan Lake -- -- 0 -- --

134 134 Reeves 18 psi 5,302 -- –60 ft 5,200 pumping

135 135 Alkire -- -- -- -- -- --

136 136 Standard

Bottling Works

30 ft 5,227 -- -- -- 0

137 137 United Oil Co -- -- -- –28 ft 5,157 0

138 138 Union Brewing Co -- -- -- –16 ft 5,171 pumping

139 139 Hungarian Mills -- -- -- –12 ft 5,173 pumping

140 140 United Oil Co -- -- -- –28 ft 5,157 0

141 141 Sanderson -- -- -- –25 ft 5,198 pumping

142 142 Highland House 70 ft 5,262 -- –12 ft 5,180 pumping

143 143 Denver Brick Co No. 1 -- -- -- 4 ft 5,184 flowing

144 144 Denver Brick Co No. 2 -- -- -- at land surface 5,220 flowing

145 145 Haverly -- -- -- –16 ft 5,181 pumping

146 E Evans -- -- -- -- -- --

147 401 Cliff -- -- 172,800 -- -- --

148 402 Symes -- -- 28,800 -- -- --

149 403 Smith -- -- 43,200 -- -- --

150 404 Segnor -- -- 25,920 -- -- --

151 405 Lightburn -- -- 57,600 -- -- --

152 406 Sanquinette -- -- -- -- -- --

153 301 A.J. Konzie -- -- -- -- -- pumping

154 302 Broadway Theatre -- -- 108,000 -- -- pumping

155 303 Wall & Purcell 12 ft 5,200 -- –4 ft 5,184 pumping

156 304 Armusson 35 ft 5,228 -- –12 ft 5,181 pumping

157 305 Haller -- -- -- -- -- pumping

158 306 Electric Light Co. 11 ft 5,208 72,000 -- -- pumping

159 307 Denver and South 

Park Shops

-1.5 ft 5,195 -- –14 ft 5,181 pumping

160 308 Tramway, Electric 

Power House

-12 ft 5,183 16,800 -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 203

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

125 125 280 1890 volume 1

sheet 41ab

5,200 39.740 –105.021 8 51 12 Morrison Rd and Colfax (Golden = Colfax)

126 126 280 1890 volume 1

sheet 41ab

5,200 39.740 –105.021 8 51 13

127 127 280 1890 volume 1

sheet 41ab

5,200 39.740 –105.020 8 51 13

128 128 100 1893 volume 3 

index

5,260 39.724 –105.026 6 52 12 Approx location, Barnum’s Sub

129 129 763 1893 volume 3 

index

5,260 39.724 –105.025 10 52 12 Approx location, Barnum’s Sub

130 130 365 1893 volume 3 

sheet 120a

5,250 39.727 –105.026 8 52 12 Approx location, Weir = 7th Ave west of 

S. Platte River

131 131 658 1893 volume 3 

sheet 120a

5,250 39.727 –105.025 10 52 12 Approx location, Weir = 7th Ave west of 

S. Platte River

132 132 635 1893 volume 1

sheet 30a

-- 39.726 –104.992 10 52 14 Arapahoe Co Hospital—Evans and W 6th Ave—

now 6th and Cherokee NE corner

133 133 400 1893 volume 3 

index

5,350 39.756 –105.048 8 50 11 Eckhart Place is north of Sloans Lake

134 134 541 5,260 39.746 –104.980 8 51 15 St Lukes = 19th and Pearl

135 135 700 1893 volume 1 

sheet 38

-- 39.717 –104.987 10 53 14

136 136 350 1887 sheet 33 5,197 39.746 –105.004 8 51 13 Standard Bottle Works next to Lindell Hotel (#36)

137 137 331 1887 sheet 1 5,185 39.757 –104.996 8 50 14

138 138 515 1887 sheet 1 5,187 39.757 –105.008 8 50 13

139 139 375 1887 sheet 35 5,185 39.746 –105.009 8 51 13

140 140 331 1887 sheet 1 5,185 8 Same as 137—assume this is a duplicate data entry 

and ignore

141 141 679 5,223 39.761 –105.008 10 50 13 Same as 95—no different depth 

142 142 516 1887 sheet 37 5,192 10 Same as 106—yes, assume this is a duplicate data 

entry and ignore

143 143 325 1890 volume 1

sheet 10a

5,180 39.748 –105.011 8 51 13 South side of Wewetta between 7th and 8th

144 144 325 1893 volume 3 

sheet 121a

5,220 39.714 –105.003 8 53 13 Shows Valverde location—never found brick co—

approx location = Valverde Park (near Bayaud 

and Osage (S 8th on old maps)

145 145 680 1887 sheet 33 5,197 39.745 –105.004 10 51 13

146 E 1140 1887 sheets 

25, 28

-- 39.746 –104.998 10 51 14

147 401 300 5,155 39.784 –104.981 8 48 15

148 402 300 5,155 39.783 –104.982 8 48 15

149 403 360 5,155 39.783 –104.982 8 48 15

150 404 340 5,155 39.784 –104.982 8 48 15

151 405 360 5,155 39.783 –104.982 8 48 15

152 406 -- 5,155 39.782 –104.982 8 48 15

153 301 605 1887 sheet 27 -- 39.751 –105.002 10 50 14

154 302 653 1890 volume 2 

sheet 60b

-- 39.744 –104.986 10 51 14 West of Lincoln and south of 18th

155 303 340 1887 sheet 27 5,188 39.751 –105.002 8 50 14

156 304 536 1887 sheet 36 5,193 39.748 –105.004 8 50 13

157 305 1100 1887 sheet 36 -- 39.746 –105.002 10 51 14

158 306 630 1887 sheet 34 5,197 39.742 –105.008 10 51 13 Check this 6th?

159 307 610.5 1890 volume 1

sheet 15a

5,195 39.741 –105.010 10 51 13 North side Colfax—DRG shops?

160 308 629 1890 volume 1

sheet 15a

5,195 39.740 –105.012 10 51 13 South side Colfax at 3rd
204 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

161 309 Harman 20 ft 5,215 -- –4 ft 5,191 pumping

162 310 McClelland 30 ft 5,225 -- –6 ft 5,189 pumping

163 311 Hanson 30 ft 5,225 -- –7 ft 5,188 pumping

164 312 Browne 11 ft 5,206 -- –4 ft 5,191 pumping

165 313 Artesian Ice Co at land surface 5,195 -- –5 ft 5,190 pumping

166 314 Crisman 4 ft 5,194 -- -- -- pumping

167 315 Excelsior Laundry 20 ft 5,222 -- –9 ft 5,193 pumping

168 316 West Denver

Gas Works

25 ft 5,205 -- -- -- pumping

169 317 Zang Brewery No. 3 4 ft 5,204 -- -- -- pumping

170 318 New Mining

Exchange

-- -- -- -- -- --

171 319 Denver City

Cable Co.

-- -- -- –60 ft 5,143 pumping

172 320 Mack Building -- -- -- –45 ft 5,180 --

173 321 Equitable Building -- -- -- –50 ft 5,173 pumping

174 322 McPhee Block -- -- -- –13 ft 5,215 pumping

175 323 Kittridge Block -- -- -- –20 ft 5,208 pumping

176 324 Railroad Building -- -- -- at land surface 5,206 pumping

177 325 Denver 

Tramway Co No. 1

-- -- -- –30 ft 5,210 pumping

178 326 Denver

Tramway Co No. 2

-- -- -- –10 ft 5,185 pumping

179 327 Stacy No. 2 30 ft 5,232 -- -- -- 0

180 328 Windsor Hotel No. 2 -- -- -- -- -- pumping

181 329 Crescent Mills -- -- -- –10 ft 5,170 pumping

182 330 United Oil Co No. 2 28 psi 5,250 129,600 –30 ft 5,155 pumping

183 331 Steam Heating Co -- -- -- –20 ft 5,163 pumping

184 332 Monat No. 1 -- -- -- –18 ft 5,167 pumping

185 333 Monat No. 2 -- -- -- –18 ft 5,167 pumping

186 334 Harris -- -- -- –12 ft 5,173 pumping

187 335 Welch -- -- -- –20 ft 5,183 pumping

188 336 Sewell -- -- -- –60 ft 5,205 pumping

189 337 Trowbridge -- -- -- –60 ft 5,200 pumping

190 338 Kountz –5 ft 5,195 -- –18 ft 5,182 pumping

191 339 Wightman –60 ft 5,170 -- –60 ft 5,170 pumping

192 340 Hurd -- -- -- –4 ft 5,201 pumping

193 341 Peabody -- -- -- –24 ft 5,191 pumping

194 342 Denver Brick Co No. 3 -- -- -- 1 ft 5,251 flowing

195 343 Denver Brick Co No. 4 -- -- -- –16 ft 5,204 pumping

196 344 Grand and 6th Ave 8 ft 5,208 -- -- -- pumping

197 345 Villa Park No. 3 -- -- -- –30 ft 5,230 pumping

198 346 Fletcher -- -- 945 12 ft 5,162 flowing

199 347 Boivier -- -- 472 12 ft 5,167 flowing

200 348 Morrison -- -- -- –60 ft -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 205

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

161 309 350 5,195 39.740 –105.011 8 51 13 Approx location—Grand Ave near Larimer

162 310 336 5,195 39.740 –105.012 8 51 13 Approx location—Grand Ave near Larimer

163 311 350 5,195 39.740 –105.012 8 51 13 Approx location—Grand Ave near Larimer

164 312 310 5,195 39.740 –105.013 8 51 13 Approx location—Grand Ave near Larimer

165 313 618 1890 volume 1

sheet 15

5,195 39.740 –105.010 10 51 13 South side Colfax between 3rd and Cottonwood

166 314 435 1887 sheet 1 5,190 39.753 –105.011 8 50 13

167 315 607 1890 volume 1

sheet 3a

5,202 39.745 –105.000 10 51 14 SW corner Arapahoe and 12th next to creek—

had 2 -315s need to recheck

168 316 650 1890 volume 1

sheet 10a

5,180 39.749 –105.011 10 50 13

169 317 660 1887 sheet 35 5,200 39.752 –105.015 10 50 13 Rocky Mountain Brewery—artesian well on map

170 318 608 1887 sheet 25 5,215 39.747 –104.997 10 51 14

171 319 650 5,203 39.751 –104.994 10 50 14

172 320 621 5,225 39.745 –104.992 10 51 14

173 321 610 5,223 39.747 –104.992 10 51 14

174 322 750 5,228 39.744 –104.990 10 51 14

175 323 650 5,228 39.744 –104.990 10 51 14

176 324 600 5,206 39.748 –104.999 10 51 14

177 325 600 5,240 39.740 –104.987 10 51 14

178 326 600 5,195 39.740 –105.012 10 51 13 2nd well at Tramway shop

179 327 600 5,202 39.754 –104.992 10 50 14

180 328 530 1887 sheet 14 -- 39.751 –104.995 8 50 14

181 329 393 1890 volume 2 

sheet 65a

5,180 39.759 –105.002 8 50 14 29th and 19th east of rr tracks

182 330 668 5,185 39.757 –104.996 10 50 14

183 331 340 5,183 39.756 –104.999 8 50 14 This well replaced Emmons65 and never flowed

184 332 400 5,185 39.760 –104.987 8 50 14

185 333 400 5,185 39.760 –104.987 8 50 14

186 334 100 1887 5,185 39.756 –104.999 6 50 14

187 335 463 5,203 39.760 –105.007 8 50 13

188 336 425 1893 volume 3 

index

5,265 39.764 –105.008 8 49 13

189 337 473 1893 volume 3 

index

5,260 39.764 –105.008 8 49 13 34th and Quivas

190 338 900 1890 volume 2 

sheet 0

5,200 39.766 –105.003 10 49 13 35th and Mariposa

191 339 340 1890 volume 2 

sheet 0

5,230 39.756 –105.013 8 50 13 27th and Vallejo

192 340 440 5,205 39.738 –105.022 8 51 12

193 341 530 5,215 39.738 –105.024 8 51 12

194 342 325 1893 volume 3 

sheet 117b

5,250 39.750 –105.019 8 50 13 Denver white lead just east of Cresent Dr and Zuni 

(Gallup)

195 343 480 1904 volume 4 

sheet 521

5,220 39.738 –105.024 8 51 12 AE Epleys brick yard not in operation 1904—well 

water noted on map

196 344 100 5,200 39.740 –105.008 6 51 13

197 345 300 1893 volume 3 

index

5,260 39.724 –105.026 8 52 12

198 346 500 5,150 39.777 –104.987 8 49 14

199 347 500 1893 volume 3 

index

5,155 39.778 –104.986 8 48 14 5th and Central in Argo = Lincoln and 45th

200 348 400 -- -- Look in 1890 v3
206 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Pilot-Point Approach to 

Hydraulic-Conductivity Estimation

Widely varying values of hydraulic conductivity for 

similar materials in different areas of a given aquifer can be 

considered unrealistic. Regularization, in combination with 

the pilot-point approach as applied to the parameterization of 

hydraulic conductivity of the Denver, Arapahoe, and Laramie–

Fox Hills aquifers, was used to impose a penalty on widely 

varying hydraulic-conductivity parameter values in a given 

aquifer. For each pair of points in a given aquifer, the penalty 

is formulated as prior information that the difference in parameter values is zero. The penalty takes the form of a regularization objective function (Sr

) (Doherty, 2006):

S F wr r r jj

j

p

= ⎛

⎝

⎜

⎞

⎠

⎟ =

∑( )2

1

(2)

where

rj is the difference in hydraulic-conductivity estimates 

for each pair of pilot points in a given aquifer,

wj is a weight applicable to the pair of pilot points,

p is the total number of pairs of pilot points for all 

layers,

and

Fr is a regularization weight factor.

During calibration, parameter values were adjusted in 

an attempt to minimize an objective function (Φ) defined as 

(Doherty, 2006):

Φ = Sm + Sr (3)

Adjustments to Fr (eq. 2) increase or decrease the effect of 

the regularization term of this objective function. When Fr is 

assigned a relatively large value, the penalty for widely varying estimates of parameters that control hydraulic conductivity of a particular aquifer (such as the set of pilot points that 

define the hydraulic conductivity of the Laramie–Fox Hills 

aquifer) is larger than when Fr (eq. 2) is assigned a relatively 

small value. By manipulating Fr, the regression algorithm 

attempts to find a set of parameters that achieves an acceptably small value of Sm while maintaining a reasonably uniform 

distribution of hydraulic conductivity in each aquifer where 

pilot points are used.

Calibration Targets

Two types of observations were used in calibrating the 

model: hydraulic heads and flows. The head observations 

were based on water-level measurements made in wells. The 

flow observations included estimates of base flow at select 

locations and estimates of the production rates of historical 

flowing wells based on information in Emmons and others 

(1896). The regression algorithm used for model calibration 

requires a weight be assigned to each observation, to allow 

inclusion of observations differing in type and units of measurement and to allow observations having different levels of 

uncertainty to be emphasized accordingly. The following sections include discussions of the calibration datasets and assignment of observation weights. The weights used in the regression are based on estimates of the errors associated with the 

observations. Use of estimated, reasonable weights is suitable 

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[

1

, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

201 349 Anderson -- -- -- –90 ft -- pumping

202 350 Norber Ice Co -- -- -- –60 ft -- pumping

203 351 Gunter -- -- -- –60 ft -- pumping

204 352 Boston and 

Colorado Smelting Co

-- -- -- -- -- pumping

205 353 Fisher -- -- -- –30 ft 5,248 pumping

206 354 Davis -- -- -- –80 ft 5,195 pumping

207 355 Richardson No. 1 -- -- -- –30 ft -- pumping

208 356 Richardson No. 2 -- -- -- –20 ft -- pumping

209 357 Globe Smelter -- -- -- -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 207

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

201 349 200 -- --

202 350 275 -- --

203 351 580 -- --

204 352 800 1887 sheet 40,

1890 volume 2 

sheet 93b,

1904 volume 4 

sheet 547

5,210 39.782 –104.995 10 48 14 47th and Fox (Argo on old maps) from 1904 

vol 4 index

205 353 700 1893 volume 3 

index

5,278 39.769 –105.011 10 49 13 38th and Tejon

206 354 557 1893 volume 3 

index

5,275 39.772 –105.011 8 49 13 40th and Tejon

207 355 540 --

208 356 540 --

209 357 505 5,180 39.794 –104.980 8 47 15

for calibration of the model because regression results generally are insensitive to moderate variation in the weighting (Hill 

and Tiedeman, 2007, p. 299).

Hydraulic Head

A total of 4,984 water-level measurements for 1,131 sites 

were used as observations of hydraulic head (Appendix C1, 

http://pubs.usgs.gov/pp/1770/). Water-level measurement 

dates ranged from 1883 through 2003. Because the earliest 

water-level measurements occurred during the calibration time 

period, model-simulated equivalents for all head observations 

were generated during transient-stress periods. No predevelopment water-level measurements were available. However, 

the long-term history of observations, which extends through 

nearly the entire period of development, provides useful information on stress conditions similar to those existing during the 

predevelopment period.

Head observations for the late 19th century were derived 

from the historical well inventory data (Emmons and others, 

1896; table C9). Initial head or pressure estimates at the 

time of well drilling were used as head observations for 91 

of the 197 wells for which locations were determined. Head 

or pressure estimates from 1890 were used as head observations for 103 of the 197 wells for which locations were 

determined (table C10). A total of 194 head observations at 

142 sites were derived from the 19th-century well inventory 

(Emmons and others, 1896).

Head observations for the alluvial and bedrock 

aquifer systems were primarily acquired from the USGS 

National Water Information System (NWIS) database 

(http://waterdata.usgs.gov/co/nwis/). A total of 4,672 waterlevel measurements for 875 sites were retrieved from the 

NWIS database. For the alluvial aquifer, 190 head observations were retrieved for 8 sites, and for the bedrock aquifers, 

4,482 head observations were retrieved for 867 sites. For 

the Nussbaum Alluvium, 113 head observations (one-time 

measurements at 113 sites) were obtained from CDWR 

well-permit records as compiled by Paschke (1992).

Water-level data for Denver Basin bedrock aquifers have 

been sparsely collected since the 1980s. The CDWR currently 

operates a water-level monitoring network of approximately 

278 wells (fig. B49), which was established in the 1980s, and 

water-level records for some wells date back to the 1950s and 

1960s (for example, Colorado Division of Water Resources, 

2003, 2004). Wells in the CDWR monitoring network are 

domestic, commercial, and municipal wells and are not solely 

dedicated monitoring wells. Water levels measured in these 

wells might not be representative of ambient water-level 

conditions because the completion intervals of some wells are 

unknown or not appropriate for monitoring water levels and 

because water levels in some wells appear affected by pumping at the time of the measurement (Courtney Hemenway, 

Hemenway Groundwater Consulting, written commun., 2008). 

Model calibration did not utilize the CDWR water-level data 

because of uncertainty related to well-completion intervals 

and pumping status. However, selected data from the CDWR 

water-level network are compared to simulation results in the 

section “Changes in Hydraulic Heads and Groundwater Flow 

Directions” in Chapter B.
208 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C10. Historical head observations derived from Emmons and others (1896).—Continued Well number Observation name Observation date Model layer Model row Model column Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Relative row offset used to locate the observation within a finite-difference cell (dimensionless) Relative column offset used to locate the observation within a finite-difference cell (dimensionless) Head altitude (feet)

2 E00218841115 11/15/1884 8 51 14 2 1,780 –0.082 –0.112 5,2682 E00218901215 12/15/1890 8 51 14 2 4,001 –0.082 –0.112 5,2184 E00418901215 12/15/1890 10 51 14 2 4,001 –0.300 –0.113 5,1956 E00618831115 11/15/1883 8 51 14 2 1,414 0.268 –0.061 5,2986 E00618901215 12/15/1890 8 51 14 2 4,001 0.268 –0.061 5,2248 E00818901215 12/15/1890 10 51 14 2 4,001 0.134 0.193 5,2309 E00918901215 12/15/1890 10 51 14 2 4,001 0.411 0.179 5,199

10 E01018901215 12/15/1890 10 51 14 2 4,001 0.391 0.078 5,203

11 E01118901215 12/15/1890 10 51 14 2 4,001 0.449 0.020 5,201

13 E01318831101 11/1/1883 8 51 14 2 1,400 0.340 –0.156 5,40513 E01318901215 12/15/1890 8 51 14 2 4,001 0.340 –0.156 5,20014 E01418901215 12/15/1890 10 51 14 2 4,001 0.371 –0.121 5,19315 E01518840515 5/15/1884 10 50 14 2 1,596 –0.498 –0.053 5,24216 E01618830701 7/1/1883 8 51 14 2 1,277 0.420 –0.110 5,30116 E01618901215 12/15/1890 8 51 14 2 4,001 0.420 –0.110 5,20617 E01718841101 11/1/1884 10 51 14 2 1,766 0.480 –0.046 5,26718 E01818840701 7/1/1884 10 50 14 2 1,643 –0.491 –0.166 5,29019 E01918840815 8/15/1884 10 51 14 2 1,688 0.448 –0.228 5,28719 E01918901215 12/15/1890 10 51 14 2 4,001 0.448 –0.228 5,16220 E02018850101 1/1/1885 10 50 14 2 1,827 –0.421 –0.243 5,27720 E02018901215 12/15/1890 10 50 14 2 4,001 –0.421 –0.243 5,17721 E02118831115 11/15/1883 8 50 14 2 1,414 –0.398 –0.267 5,35923 E02318901215 12/15/1890 10 50 14 2 4,001 –0.303 –0.120 5,19524 E02418830830 8/30/1883 8 50 14 2 1,337 –0.296 –0.098 5,32524 E02418901215 12/15/1890 8 50 14 2 4,001 –0.296 –0.098 5,11825 E02518840415 4/15/1884 10 50 14 2 1,566 –0.072 0.048 5,27626 E02618831215 12/15/1883 8 50 14 2 1,444 –0.182 –0.362 5,23126 E02618901215 12/15/1890 8 50 14 2 4,001 –0.182 –0.362 4,98527 E02718840715 7/15/1884 8 50 14 2 1,657 –0.211 –0.268 5,20528 E02818840815 8/15/1884 8 50 14 2 1,688 –0.339 –0.325 5,24930 E03018850215 2/15/1885 8 51 13 2 1,872 0.488 0.475 5,21530 E03018901215 12/15/1890 8 51 13 2 4,001 0.488 0.475 5,18032 E03218901215 12/15/1890 8 51 13 2 4,001 0.366 0.153 5,17034 E03418831101 11/1/1883 8 51 13 2 1,400 0.291 0.045 5,22335 E03518841007 10/7/1884 8 51 13 2 1,741 0.229 0.306 5,19935 E03518901215 12/15/1890 8 51 13 2 4,001 0.229 0.306 5,19236 E03618830915 9/15/1883 8 51 13 2 1,353 0.300 0.429 5,22036 E03618901215 12/15/1890 8 51 13 2 4,001 0.300 0.429 5,18537 E03718830915 9/15/1883 8 51 13 2 1,353 0.272 0.376 5,22237 E03718901215 12/15/1890 8 51 13 2 4,001 0.272 0.376 5,18939 E03918901215 12/15/1890 10 51 13 2 4,001 0.334 0.484 5,18041 E04118901215 12/15/1890 10 51 13 2 4,001 0.142 0.381 5,177
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 209

Table C10. Historical head observations derived from Emmons and others (1896).—Continued

Well

number

Observation

name

Observation

date

Model

layer

Model

row

Model

column

Reference stress

period to which

observation time

is referenced 

Time offset

from beginning

of reference stress 

period to time

of observation

(days)

Relative row

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Relative column

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Head

altitude

(feet)

42 E04218830701 7/1/1883 8 51 13 2 1,277 0.186 0.265 5,23542 E04218901215 12/15/1890 8 51 13 2 4,001 0.186 0.265 5,18743 E04218850115 1/15/1885 8 51 13 2 1,841 0.218 0.482 5,21244 E04318850215 2/15/1885 8 51 13 2 1,872 –0.096 0.072 5,23544 E04318901215 12/15/1890 8 51 13 2 4,001 –0.096 0.072 5,19150 E05018830701 7/1/1883 10 52 13 2 1,277 0.227 0.307 5,25551 E05118841101 11/1/1884 10 53 14 2 1,766 0.304 0.383 5,33552 E05218831101 11/1/1883 10 53 14 2 1,400 0.304 0.443 5,26857 E05718850615 6/15/1885 10 48 16 2 1,992 0.490 –0.366 5,23959 E05918840315 3/15/1884 10 50 14 2 1,535 –0.346 0.323 5,22060 E06018840815 8/15/1884 10 50 14 2 1,688 –0.172 0.406 5,27463 E06318840615 6/15/1884 10 50 14 2 1,627 –0.011 –0.287 5,20563 E06318901215 12/15/1890 10 50 14 2 4,001 –0.011 –0.287 5,16064 E06418901215 12/15/1890 8 50 14 2 4,001 –0.030 –0.272 5,17365 E06518831215 12/15/1883 8 50 14 2 1,444 0.006 –0.304 5,20365 E06518901215 12/15/1890 8 50 14 2 4,001 0.006 –0.304 5,15866 E06618831215 12/15/1883 8 50 14 2 1,444 0.037 –0.268 5,20767 E06718901215 12/15/1890 8 50 14 2 4,001 0.017 –0.230 5,13068 E06818851115 11/15/1885 8 50 14 2 2,145 0.040 –0.209 5,20068 E06818901215 12/15/1890 8 50 14 2 4,001 0.040 –0.209 5,17769 E06918830101 1/1/1883 8 50 14 2 1,096 0.206 –0.229 5,21073 E07318830715 7/15/1883 8 50 14 2 1,291 0.144 –0.057 5,25974 E07418831115 11/15/1883 8 50 14 2 1,414 0.242 0.364 5,22576 E07618841015 10/15/1884 8 50 15 2 1,749 0.253 –0.497 5,24876 E07618901215 12/15/1890 8 50 15 2 4,001 0.253 –0.497 5,17777 E07718830101 1/1/1883 8 50 14 2 1,096 0.442 0.445 5,33577 E07718901215 12/15/1890 8 50 14 2 4,001 0.442 0.445 5,18979 E07918901215 12/15/1890 8 50 15 2 4,001 0.256 0.007 5,19081 E08118840315 3/15/1884 8 49 15 2 1,535 –0.167 –0.064 5,24281 E08118901215 12/15/1890 8 49 15 2 4,001 –0.167 –0.064 5,16783 E08318831215 12/15/1883 8 49 15 2 1,444 –0.113 –0.293 5,26683 E08318901215 12/15/1890 8 49 15 2 4,001 –0.113 –0.293 5,17784 E08418901215 12/15/1890 8 49 15 2 4,001 –0.083 –0.082 5,18985 E08518840815 8/15/1884 8 49 15 2 1,688 –0.007 –0.116 5,28786 E08618840215 2/15/1884 8 49 15 2 1,506 –0.066 0.025 5,22587 E08718841101 11/1/1884 10 49 15 2 1,766 0.228 0.355 5,28788 E08818830701 7/1/1883 10 48 15 2 1,277 –0.422 0.271 5,28991 E09118851215 12/15/1885 8 50 14 2 2,175 0.040 –0.297 5,21094 E09418850915 9/15/1885 8 50 13 2 2,084 0.373 0.325 5,21595 E09518840215 2/15/1884 10 50 13 2 1,506 0.373 0.199 5,29295 E09518901215 12/15/1890 10 50 13 2 4,001 0.373 0.199 5,19896 E09618840115 1/15/1884 8 50 13 2 1,475 0.337 0.232 5,240
210 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C10. Historical head observations derived from Emmons and others (1896).—Continued Well number Observation name Observation date Model layer Model row Model column Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Relative row offset used to locate the observation within a finite-difference cell (dimensionless) Relative column offset used to locate the observation within a finite-difference cell (dimensionless) Head altitude (feet) 98 E09818850215 2/15/1885 8 50 13 2 1,872 0.318 0.270 5,219 98 E09818901215 12/15/1890 8 50 13 2 4,001 0.318 0.270 5,191 99 E09918831115 11/15/1883 8 50 13 2 1,414 0.363 0.206 5,238 99 E09918901215 12/15/1890 8 50 13 2 4,001 0.363 0.206 5,175 100 E10018840215 2/15/1884 8 50 13 2 1,506 0.224 0.291 5,227 100 E10018901215 12/15/1890 8 50 13 2 4,001 0.224 0.291 5,160 101 E10118840215 2/15/1884 8 50 13 2 1,506 0.173 0.262 5,218 102 E10218840315 3/15/1884 8 50 13 2 1,535 0.146 0.219 5,205 102 E10218901215 12/15/1890 8 50 13 2 4,001 0.146 0.219 5,177 103 E10318830701 7/1/1883 8 50 13 2 1,277 0.171 0.152 5,272 103 E10318901215 12/15/1890 8 50 13 2 4,001 0.171 0.152 5,192 104 E10418851115 11/15/1885 8 50 13 2 2,145 0.120 0.200 5,212 105 E10518901215 12/15/1890 8 50 13 2 4,001 0.053 0.128 5,170 106 E10618830615 6/15/1883 8 50 13 2 1,261 0.045 0.137 5,262 106 E10618901215 12/15/1890 8 50 13 2 4,001 0.045 0.137 5,180 107 E10718831015 10/15/1883 8 50 13 2 1,383 0.013 0.183 5,225 107 E10718901215 12/15/1890 8 50 13 2 4,001 0.013 0.183 5,180 108 E10818901215 12/15/1890 8 50 13 2 4,001 0.279 –0.075 5,258 110 E11018831101 11/1/1883 8 50 13 2 1,400 0.196 –0.225 5,272 110 E11018901215 12/15/1890 8 50 13 2 4,001 0.196 –0.225 5,180 112 E11218830815 8/15/1883 6 50 13 2 1,322 –0.057 0.049 5,225 112 E11218901215 12/15/1890 6 50 13 2 4,001 –0.057 0.049 5,190 113 E11318840515 5/15/1884 8 50 13 2 1,596 –0.080 –0.080 5,224

113 E11318901215 12/15/1890 8 50 13 2 4,001 –0.080 –0.080 5,190114 E11418840615 6/15/1884 8 50 13 2 1,627 –0.112 –0.141 5,240115 E11518830401 4/1/1883 10 50 13 2 1,186 –0.066 –0.485 5,384117 E11718840401 4/1/1884 8 50 13 2 1,552 –0.157 –0.332 5,306117 E11718901215 12/15/1890 8 50 13 2 4,001 –0.157 –0.332 5,221118 E11818830401 4/1/1883 8 50 13 2 1,186 –0.275 –0.164 5,246119 E11918830615 6/15/1883 8 50 13 2 1,261 –0.270 –0.157 5,258119 E11918901215 12/15/1890 8 50 13 2 4,001 –0.270 –0.157 5,160

120 E12018831101 11/1/1883 10 51 13 2 1,400 0.451 –0.275 5,264122 E12218901215 12/15/1890 10 51 15 2 4,001 0.362 –0.281 5,188123 E12318850101 1/1/1885 8 51 13 2 1,827 0.364 –0.462 5,232123 E12318901215 12/15/1890 8 51 13 2 4,001 0.364 –0.462 5,198125 E12518850215 2/15/1885 8 51 12 2 1,872 –0.083 0.500 5,230125 E12518901215 12/15/1890 8 51 12 2 4,001 –0.083 0.500 5,184126 E12618901215 12/15/1890 8 51 13 2 4,001 –0.084 –0.477 5,185127 E12718830815 8/15/1883 8 51 13 2 1,322 –0.085 –0.453 5,240127 E12718901215 12/15/1890 8 51 13 2 4,001 –0.085 –0.453 5,188128 E12818901215 12/15/1890 6 52 12 2 4,001 –0.196 0.281 5,230129 E12918901215 12/15/1890 10 52 12 2 4,001 –0.214 0.283 5,210
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 211

Table C10. Historical head observations derived from Emmons and others (1896).—Continued

Well

number

Observation

name

Observation

date

Model

layer

Model

row

Model

column

Reference stress

period to which

observation time

is referenced 

Time offset

from beginning

of reference stress 

period to time

of observation

(days)

Relative row

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Relative column

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Head

altitude

(feet)

131 E13118850215 2/15/1885 10 52 12 2 1,872 0.033 0.288 5,377131 E13118901215 12/15/1890 10 52 12 2 4,001 0.033 0.288 5,238134 E13418840701 7/1/1884 8 51 15 2 1,643 0.332 –0.303 5,302134 E13418901215 12/15/1890 8 51 15 2 4,001 0.332 –0.303 5,200136 E13618830701 7/1/1883 8 51 13 2 1,277 0.309 0.425 5,227137 E13718901215 12/15/1890 8 50 14 2 4,001 0.094 –0.156 5,157138 E13818901215 12/15/1890 8 50 13 2 4,001 0.109 0.198 5,171139 E13918901215 12/15/1890 8 51 13 2 4,001 0.363 0.157 5,173141 E14118901215 12/15/1890 10 50 13 2 4,001 0.370 0.192 5,198143 E14318901215 12/15/1890 8 51 13 2 4,001 0.476 0.062 5,184144 E14418901215 12/15/1890 8 53 13 2 4,001 0.146 0.472 5,220145 E14518901215 12/15/1890 10 51 13 2 4,001 0.281 0.406 5,181303 E30318880701 7/1/1888 8 50 14 2 3,104 –0.349 –0.459 5,200303 E30318901215 12/15/1890 8 50 14 2 4,001 –0.349 –0.459 5,184304 E30418870701 7/1/1887 8 50 13 2 2,738 –0.496 0.392 5,228304 E30418901215 12/15/1890 8 50 13 2 4,001 –0.496 0.392 5,181306 E30618891015 10/15/1889 10 51 13 2 3,575 0.048 0.183 5,208307 E30718900315 3/15/1890 10 51 13 2 3,726 –0.038 0.089 5,194307 E30718901215 12/15/1890 10 51 13 2 4,001 –0.038 0.089 5,181308 E30818900415 4/15/1890 10 51 13 2 3,757 –0.112 0.016 5,183309 E30918870701 7/1/1887 8 51 13 2 2,738 –0.098 0.037 5,215309 E30918901215 12/15/1890 8 51 13 2 4,001 –0.098 0.037 5,191310 E31018870315 3/15/1887 8 51 13 2 2,630 –0.098 0.005 5,225310 E31018901215 12/15/1890 8 51 13 2 4,001 –0.098 0.005 5,195

311 E31118870415 4/15/1887 8 51 13 2 2,661 –0.101 –0.017 5,225311 E31118901215 12/15/1890 8 51 13 2 4,001 –0.101 –0.017 5,188

312 E31218870701 7/1/1887 8 51 13 2 2,738 –0.101 –0.038 5,206312 E31218901215 12/15/1890 8 51 13 2 4,001 –0.101 –0.038 5,191313 E31318890215 2/15/1889 10 51 13 2 3,333 –0.114 0.087 5,195313 E31318901215 12/15/1890 10 51 13 2 4,001 –0.114 0.087 5,190314 E31418890715 7/15/1889 8 50 13 2 3,483 –0.157 0.031 5,194315 E31518860415 4/15/1886 10 51 14 2 2,296 0.267 –0.368 5,222315 E31518901215 12/15/1890 10 51 14 2 4,001 0.267 –0.368 5,193316 E31618860415 4/15/1886 10 50 13 2 2,296 –0.481 0.065 5,205317 E31718900815 8/15/1890 10 50 13 2 3,879 –0.272 –0.162 5,204319 E31918901215 12/15/1890 10 50 14 2 4,001 –0.349 –0.052 5,143320 E32018901215 12/15/1890 10 51 14 2 4,001 0.272 0.051 5,180321 E32118901215 12/15/1890 10 51 14 2 4,001 0.380 0.068 5,173322 E32218901215 12/15/1890 10 51 14 2 4,001 0.191 0.145 5,215323 E32318901215 12/15/1890 10 51 14 2 4,001 0.176 0.145 5,208324 E32418901215 12/15/1890 10 51 14 2 4,001 0.492 –0.295 5,206325 E32518901215 12/15/1890 10 51 14 2 4,001 –0.102 0.309 5,210
212 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C10. Historical head observations derived from Emmons and others (1896).—Continued Well number Observation name Observation date Model layer Model row Model column Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Relative row offset used to locate the observation within a finite-difference cell (dimensionless) Relative column offset used to locate the observation within a finite-difference cell (dimensionless) Head altitude (feet) 326 E32618901215 12/15/1890 10 51 13 2 4,001 –0.114 0.011 5,185 327 E32718870701 7/1/1887 10 50 14 2 2,738 –0.084 0.042 5,232 329 E32918901215 12/15/1890 8 50 14 2 4,001 0.204 –0.467 5,170 330 E33018870701 7/1/1887 10 50 14 2 2,738 0.083 –0.164 5,250 330 E33018901215 12/15/1890 10 50 14 2 4,001 0.083 –0.164 5,155 331 E33118901215 12/15/1890 8 50 14 2 4,001 0.002 –0.303 5,163 332 E33218901215 12/15/1890 8 50 14 2 4,001 0.300 0.313 5,167 333 E33318901215 12/15/1890 8 50 14 2 4,001 0.305 0.321 5,167 334 E33418901215 12/15/1890 6 50 14 2 4,001 0.021 –0.323 5,173 335 E33518901215 12/15/1890 8 50 13 2 4,001 0.308 0.260 5,183 336 E33618901215 12/15/1890 8 49 13 2 4,001 –0.402 0.186 5,205 337 E33718901215 12/15/1890 8 49 13 2 4,001 –0.399 0.214 5,200 338 E33818890701 7/1/1889 10 49 13 2 3,469 –0.316 0.467 5,195 338 E33818901215 12/15/1890 10 49 13 2 4,001 –0.316 0.467 5,182 339 E33918890701 7/1/1889 8 50 13 2 3,469 0.022 –0.076 5,170

339 E33918901215 12/15/1890 8 50 13 2 4,001 0.022 –0.076 5,170340 E34018901215 12/15/1890 8 51 12 2 4,001 –0.207 0.468 5,201341 E34118901215 12/15/1890 8 51 12 2 4,001 –0.215 0.381 5,191342 E34218901215 12/15/1890 8 50 13 2 4,001 –0.423 –0.360 5,251343 E34318901215 12/15/1890 8 51 12 2 4,001 –0.246 0.353 5,201344 E34418890701 7/1/1889 6 51 13 2 3,469 –0.056 0.216 5,208345 E34518901215 12/15/1890 8 52 12 2 4,001 –0.171 0.281 5,230346 E34618901215 12/15/1890 8 49 14 2 4,001 0.487 0.338 5,162347 E34718901215 12/15/1890 8 48 14 2 4,001 –0.417 0.378 5,167353 E35318901215 12/15/1890 10 49 13 2 4,001 –0.051 0.027 5,248354 E35418901215 12/15/1890 8 49 13 2 4,001 0.109 0.024 5,195
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 213

The weight for a head observation based on a depth to 

water relative to a measuring-point altitude was calculated as 

(Doherty, 2006):

Weight SD SD = + ( ) mst mp

− 2 2 0 5.

(4)

where

SDmst is the estimated standard deviation of the depthto-water measurement

and

SDmp is the estimated standard deviation of the 

measuring-point altitude.

The value of SDmst was assumed to equal 1.0 ft, and SDmp was 

assigned as the estimated measuring-point altitude accuracy 

from the source data base. For the water-level observations 

from Emmons and others (1896), the standard deviation of 

the measurement was assumed to be 25 ft, and the weight was 

assigned as 0.04 ft–1.

Stream Base Flow

Streamflow records for eight sites in the Denver Basin 

(fig. A6) were used to estimate base flow from groundwater. 

The base-flow analysis generated 153 observations for the 

eight sites (table C11), with observation dates ranging from 

1939 to 2003. Most of the stream base-flow observations 

(61 percent) are for Cherry Creek (63 observations for Cherry 

Creek near Franktown, 1939–2003, and 31 observations for 

Cherry Creek near Melvin, 1939–1969 and 1985). Twelve 

observations are for First Creek at Rocky Mountain Arsenal 

(1992–2003), 10 observations are for Kiowa Creek at Elbert 

(1955–1965), 10 observations are for Kiowa Creek at Kiowa 

(1955–1965), 4 observations are for Kiowa Creek at Bennett 

(1961–1964), 6 observations are for Bijou Creek near Wiggins 

(1950–1956), and 17 observations are for Cottonwood Creek 

at mouth, at Pikeview, CO (1985–2003). Observation weights 

for the base-flow observations were calculated for each mean 

annual observation from either the annual standard deviation 

or the coefficient of variation.

Historical Flowing Wells

Flow from model cells representing the 197 historical flowing wells for which locations were determined was 

estimated from information provided by Emmons and others (1896). Emmons and others (1896, p. 426) estimated 

a daily yield from the Denver wells of approximately 

1,500,000 gallons per day, which they reported is a “little 

more than one-seventh of the original rate of discharge.” 

Multiplying the estimate by 7, and assuming the original 

rate applied to the year 1883 when well installation began in 

Denver, results in a discharge estimate of 10,500,000 gallons 

per day for 1883. Emmons and others (1896) also stated that 

the flow in 1886 was approximately one-fourth of the original, 

which would be an estimated 2,625,000 gallons per day.

In the model, the historical flowing wells are represented using the Drain Package, which simulates continuous 

discharge when the head in a model cell is above the drain 

altitude. The drain altitude is assigned as the land-surface 

altitude at the well location. It is unknown to what extent 

discharge from these wells was controlled by valves. It is 

assumed that the reported discharge values (table C9) represent rates measured at a time when discharge from the well 

was not controlled and that the wells were shut in when not 

needed. Observations of flow for the drain cells representing the historical wells were included in the model to ensure 

that cumulative flows simulated from the drain cells were 

reasonable. For lack of information on well discharges, and 

based on initial model simulations that indicated flow rates 

less than those reported, the flow rates used as observations 

in calibration were assigned as one-half the reported flow rate 

(table C12). Weights for the flowing-well observations were 

based on a coefficient of variation of 0.5 to indicate a relatively large amount of uncertainty.

Model-Calibration Results

Parameters used in the simulation were adjusted within 

reasonable limits until the objective function and mean head 

residuals were minimized. Seventy-seven parameters were 

included in the model, 52 of which were adjusted during 

parameter estimation and 25 of which had assigned values. 

Estimated parameters included hydraulic conductivity and 

recharge parameters. The groundwater flow model was considered calibrated when the following criteria were satisfied:

1. Incremental changes in model parameters did not substantially reduce the objective function, root mean squared 

error (RMSE) (Hill and others, 2000), or other calibration 

statistics.

2. The RMSE of heads over the entire model was less than 

approximately 5 percent of the total head change in the 

study area.

3. Hydraulic-conductivity values and distributions provided 

reasonable representations of aquifer properties as compared to aquifer-testing results on a regional scale.

To evaluate the model-calibration process, model-estimated parameters (table C13) were compared to measured and 

estimated values, and model-computed heads and flows were 

compared to measured (observed) water levels and estimated 

discharges.
214 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C11. Summay of stream base-flow observations for eight surface-water gaging stations in the Denver Basin. [USGS site ID, U.S. Geological Survey site identification number; ft3/s, cubic feet per second] Site name USGS site ID Observation name prefix Period of record Number of annual observations Base flow (ft3/s) Total flow (ft3/s) Mean for period of record Standard deviation Coefficient of variation Mean for period of record Standard deviation Coefficient of variation Cherry Creek near Franktown 06712000 BF06712000 1939–2003 63 5.36 3.73 0.70 9.49 6.67 0.70 Cherry Creek near Melvin 06712500 BF06712500 1939–1969, 1985 31 3.40 4.83 1.42 12.33 12.13 0.98 First Creek below Buckley Road, at Rocky Mountain Arsenal 06720460 BF06720460 1992–2003 12 0.47 0.72 1.52 0.91 1.02 1.13 Kiowa Creek at Elbert 06758000 BF06758000 1955–1965 10 0.01 0.02 1.89 0.89 2.35 2.64 Kiowa Creek at Kiowa 06758200 BF06758200 1955–1965 10 0.74 0.61 0.82 3.81 3.29 0.86 Kiowa Creek at Bennett 06758300 BF06758300 1961–1964 4 0.52 0.45 0.87 3.23 0.96 0.30 Bijou Creek near Wiggins 06759000 BF06759000 1950–1956 6 0.01 0.03 2.45 9.21 12.01 1.30 Cottonwood Creek at mouth, at Pikeview 07103990 BF07103990 1985–2003 17 4.38 1.46 0.33 6.91 2.87 0.42 Table C12. Drain observations derived from historical data provided by Emmons and others (1896). [ft3/d, cubic feet per day] Observation name Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Model layer Model row Model column Estimated discharge (ft3/d) Observation, one-half of estimated discharge (ft3/d) Basis for estimated discharge E12118840701 2 1,643 6 50 12 241 120 Well 121 flow for 1884.

E40118851101 2 2,114 8 48 15 43,893 21,947 Sum of flow for wells 401, 402, 403, 404, and 405 for 1885.E34618891115 2 3,606 8 49 14 126 63 Well 346 flow for 1889.E09918831115 2 1,414 8 50 13 71,091 35,545 Sum of flow for wells 105, 108, and 119 for 1883.

E06918840101 2 1,461 8 50 14 172,535 86,267 Sum of flow for wells 22, 24, 26, 65, 67, and 77 for 1883.E07918830815 2 1,322 8 50 15 14,439 7,219 Well 79 flow for 1883.

E03418831101 2 1,400 8 51 13 34,231 17,116 Sum of flow for wells 31, 36, 38, and 42 for 1883.E13018831101 2 1,400 8 52 12 6,064 3,032 Well 130 flow for 1883.

E08818830701 2 1,277 10 48 15 66,845 33,422 Well 88 flow for 1883.E05718850615 2 1,992 10 48 16 66,845 33,422 Well 57 flow for 1885.

E08718841101 2 1,766 10 49 15 12,032 6,016 Well 87 flow for 1884.

E05318840315 2 1,535 10 50 13 22,109 11,054 Well 53 flow for 1884.E02318830804 2 1,311 10 50 14 10,203 5,102 Well 23 flow for 1883.E08018830804 2 1,657 10 50 15 17,380 8,690 Well 80 flow for 1884.E04618830701 2 1,277 10 51 13 40,107 20,053 Sum of flow for wells 41,45, 46, 47, 48, 49 for 1883.

E01718841101 2 1,766 10 51 14 41,631 20,816 Sum of flow for wells 8, 9, 14, and 19 for 1884.

E05518840615 2 1,627 10 51 15 2,888 1,444 Well 55 flow for 1884.E13218840315 2 1,535 10 52 14 1,604 802 Well 132 flow for 1884.E06218850515 2 1,961 10 52 15 6,016 3,008 Well 62 flow for 1885.

E05118841101 2 1,766 10 53 14 13,369 6,684 Well 51 flow for 1884.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 215

Table C13. Calibrated Denver Basin model parameter values.—Continued[ft/d, feet per day; in/yr, inches per year; ft–1, per foot; ft3/d, cubic feet per day; ft2/d, square feet per day]

Parameter

name Parameter description

Parameter

value

(units)

Composite scaled

sensitivity to

all head and flow

observations

(dimensionless)

Composite scaled

sensitivity to

flow observations

(dimensionless)

Composite scaled

sensitivity to

head observations

(dimensionless)

Estimated

using

automated

methods

Hydraulic-conductivity parameters

K_Q_Platte Hydraulic conductivity of alluvial aquifer adjacent to South Platte River 

and its tributaries.

200 (ft/d) 9.42 1.16 9.58 No

K_Q_bas Hydraulic conductivity of alluvial aquifer in Big Sandy and Black 

Squirrel basins.

5.0 (ft/d) 4.02 0.025 4.09 No

K_utdw Hydraulic conductivity of silt-plus-sand fraction of upper Dawson aquifer. 4.739 (ft/d) 1.35 3.89 1.17 YesK_tdwc Hydraulic conductivity of Dawson confining unit. 1.423×10–5 (ft/d) 1.69 0.057 1.72 YesK_ltdw Hydraulic conductivity of silt-plus-sand fraction of lower Dawson aquifer. 0.2662 (ft/d) 3.59 0.23 3.65 YesK_tkduc Hydraulic conductivity of Denver upper confining unit. 1.597×10–5 (ft/d) 3.94 0.09 4.01 Yesp6_01 Hydraulic conductivity of silt-plus-sand fraction of the Denver aquifer at a 

pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values.

3.943×10–4 (ft/d) 3.23 0.009 3.28 Yes

p6_02 6.317×10–5 (ft/d) 3.09 0.052 3.14 Yesp6_03 9.683×10–4 (ft/d) 4.57 0.022 4.65 Yesp6_04 8.815×10–5 (ft/d) 1.24 0.041 1.26 Yesp6_05 2.220×10–2 (ft/d) 4.59 0.019 4.67 Yesp6_06 8.396×10–5 (ft/d) 5.48 0.006 5.57 Yesp6_07 4.258×10–3 (ft/d) 1.25 0.027 1.27 Yesp6_08 2.618×10–5 (ft/d) 1.0 0.044 1.02 YesK_tkdlc Hydraulic conductivity of Denver lower confining unit. 9.731×10–5 (ft/d) 4.65 0.12 4.73 YespKa_02 Hydraulic conductivity of silt-plus-sand fraction of the upper Arapahoe 

aquifers at a pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values.

1.635×10–2 (ft/d) 0.86 0.013 0.88 Yes

pKa_07 21.83 (ft/d) 4.53 0.045 4.60 YespKa_08 3.172 (ft/d) 4.43 0.19 4.51 YespKa_09 2.387×10–4 (ft/d) 0.97 0.075 0.98 YespKa_10 0.8549 (ft/d) 5.32 0.030 5.41 YespKa_11 1.469×10–3 (ft/d) 1.23 0.017 1.25 YespKa_12 1.000×10–4 (ft/d) 3.69 0.029 3.75 Yesp8_01 95.90 (ft/d) 2.12 0.27 2.16 Yesp8_03 3.305 (ft/d) 2.67 0.14 2.71 Yesp8_04 619.7 (ft/d) 5.46 0.93 5.55 Yesp8_05 0.2236 (ft/d) 4.09 0.25 4.16 Yesp8_06 8.732 (ft/d) 6.76 0.22 6.88 YesK_kac Hydraulic conductivity of Arapahoe confining unit. 1.285×10–3 (ft/d) 3.03 0.044 3.08 Yesp10_01 Hydraulic conductivity of silt-plus-sand fraction of the lower Arapahoe 

aquifers at a pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values.

4.013×10–4 (ft/d) 1.19 1.21 Yes
216 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C13. Calibrated Denver Basin model parameter values.—Continued [ft/d, feet per day; in/yr, inches per year; ft–1, per foot; ft3/d, cubic feet per day; ft2/d, square feet per day] Parameter name Parameter description Parameter value (units) Composite scaled sensitivity to all head and flow observations (dimensionless) Composite scaled sensitivity to flow observations (dimensionless) Composite scaled sensitivity to head observations (dimensionless) Estimated using automated methods Hydraulic-conductivity parameters—Continued p10_03 7.698×10–3 (ft/d) 2.70 2.75 Yes p10_04 5.923 (ft/d) 0.98 1.00 Yes p10_05 5.434×10–4 (ft/d) 4.30 4.38 Yes p10_06 4.425 (ft/d) 5.56 5.65 Yes K_klc Hydraulic conductivity of Laramie confining unit. 1.314×10–5 (ft/d) 9.40 9.56 Yes p12_01 Hydraulic conductivity of silt-plus-sand fraction of the Laramie–Fox Hills aquifer at a pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values. 52.18 (ft/d) 0.94 0.007 0.96 Yes p12_02 44.60 (ft/d) 2.31 0.026 2.34 Yes p12_03 2.586 (ft/d) 3.01 0.033 3.06 Yes p12_04 3.054×10–4 (ft/d) 1.77 0.002 1.80 Yes p12_05 6.177×10–2 (ft/d) 10.4 0.011 10.6 Yes p12_06 9.489 (ft/d) 2.89 0.028 2.94 Yes p12_07 4.530×10–2 (ft/d) 4.62 0.038 4.70 Yes p12_08 9.480×10–5 (ft/d) 2.98 0.038 3.03 Yes p12_09 40.39 (ft/d) 0.99 0.017 1.00 Yes p12_10 1.150×10–5 (ft/d) 1.87 0.003 1.91 Yes p12_11 3.001×10–3 (ft/d) 6.67 0.001 6.79 Yes Vertical-anisotropy parameters VANI_QPlat Ratio of horizontal to vertical hydraulic conductivity for alluvial aquifer adjacent to the South Platte River and its tributaries. 9.927 (dimensionless) 0.50 0.0013 0.51 Yes

VANI_Qbas Ratio of horizontal to vertical hydraulic conductivity of alluvial aquifer in 

Black Squirrel and Big Sandy basins.

10.0 (dimensionless) 4.34 0.003 4.42 No

VANI_BR Ratio of horizontal to vertical hydraulic conductivity for bedrock aquifers 

and confining units.

1.0 (dimensionless) 19.8 0.58 20.2 No

Recharge parameters

RCH_Qal Fraction of precipitation in area overlying the alluvial aquifer that 

becomes recharge.

7.0 (percent) 14.9 0.84 15.1 No

RCH_Tdw Fraction of precipitation in area overlying the upper and lower Dawson 

aquifers that becomes recharge.

2.026 (percent) 21.8 7.55 22.1 Yes

RCH_TKd Fraction of precipitation in area overlying the Denver aquifer that 

becomes recharge.

1.086 (percent) 6.87 0.82 6.99 Yes

RCH_Ka Fraction of precipitation in area overlying the upper and lower Arapahoe 

aquifer that becomes recharge.

1.367 (percent) 1.60 0.097 1.63 Yes

RCH_Klf Fraction of precipitation in area overlying the Laramie–Fox Hills aquifer 

that becomes recharge.

1.367 (percent) 4.32 0.006 4.39 Yes
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 217

Table C13. Calibrated Denver Basin model parameter values.—Continued[ft/d, feet per day; in/yr, inches per year; ft–1, per foot; ft3/d, cubic feet per day; ft2/d, square feet per day]

Parameter

name Parameter description

Parameter

value

(units)

Composite scaled

sensitivity to

all head and flow

observations

(dimensionless)

Composite scaled

sensitivity to

flow observations

(dimensionless)

Composite scaled

sensitivity to

head observations

(dimensionless)

Estimated

using

automated

methods

Recharge parameters—Continued

RCH_Resid Recharge rate from urban irrigation in affected areas. 2.5 (in/yr) 0.57 0.30 0.58 NoRCH_AgIrr Recharge rate from agricultural irrigation in affected areas. 10.0 (in/yr) 4.58 0.076 4.66 No

Storage parameters

SY_Qal Specific yield of the alluvial aquifer. 16.5 (percent) 6.14 0.46 6.24 NoSY_TDW Specific yield of the upper and lower Dawson aquifers. 15.2 (percent) 0.50 0.030 0.51 NoSY_TKD Specific yield of the Denver aquifer. 13.3 (percent) 2.54 0.030 2.58 NoSY_KA Specific yield of the upper and lower Arapahoe aquifers. 17.8 (percent) 0.11 0.0004 0.11 NoSY_KLF Specific yield of the Laramie–Fox Hills aquifer. 18.6 (percent) 0.25 0.0006 0.25 NoSS_coarse Specific storage of bedrock aquifers. 5.2×10–7 (ft–1) 7.85 0.071 7.99 YesSS_fine Specific storage of bedrock confining units. 1.7×10–6 (ft–1) 3.14 0.028 3.19 Yes

Pumping parameters

Q_Qal_IR Pumping rate of alluvial irrigation well. (ft3/d) 9.97 0.85 10.1 NoQ_Qal_MU Pumping rate of alluvial municipal well. (ft3/d) 0.50 0.040 0.51 NoQ_QAL_CI Pumping rate of alluvial commercial/industrial well. (ft3/d) 0.098 0.004 0.10 NoQ_BR_IR Pumping rate of bedrock irrigation well. (ft3/d) 8.60 0.170 8.75 NoQ_BR_MU Pumping rate of bedrock municipal well. (ft3/d) 8.14 0.085 8.28 NoQ_BR_CI Pumping rate of bedrock commercial/irrigation well. (ft3/d) 7.77 0.048 7.91 No

Head-dependent boundary parameters

ET_MAX Maximum allowed evapotranspiration rate. 45.0 (in/yr) 2.44 1.05 2.47 NoDRN_COND Drain conductance for springs and flowing wells. 1500 (ft2/d) 2.90 0.040 2.95 NoRIV_LAKES Conductance for River cells. 2.25 (d–1) 0.008 0.0006 0.008 NoGHB_BS_CK General-head-boundary conductance along southern model boundary represents underflow out of basin through Black Squirrel Creek alluvial aquifer. 113 (ft/d) 4.54 0.0009 4.62 NoGHB_Nuss General-head-boundary conductance along southeastern model boundary 

represents underflow out of basin through Nussbaum Alluvium.

10 (ft/d) 0.88 0.011 0.89 No

SFR_PLATTE Hydraulic conductivity of streambed materials for the South Platte River. 0.76 (ft/d) 4.20 0.026 4.27 NoSFR_TRIBS Hydraulic conductivity of streambed materials. 2.06×10–2 (ft/d) 1.38 3.25 1.27 YesSkin Well-loss coefficient for multinode wells. 2.0 (dimensionless) 0.018 0.0007 0.018 NoFLWG_WELLS Conductance. 14.00 (ft2/d) 0.042 0.21 0.016 Yes
218 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Calibrated Hydraulic-Conductivity Distribution

The calibrated hydraulic-conductivity (K) values listed 

in table C13 provide reasonable representations of the alluvial and bedrock aquifers with values in relative proportion 

to each other that are consistent with the hydrogeologic 

conceptual model presented in Chapter A. The hydraulicconductivity parameters for the alluvial aquifer were assigned 

values of 200 ft/d in the main stem of the South Platte River 

(K_Q_Platte) and 5 ft/d in the Big Sandy and Black Squirrel 

Creek Basins, such that the alluvial aquifer is one of the most 

conductive parts of the model domain. Although hydraulicconductivity parameters of the alluvial aquifer were assigned 

during parameter estimation, their values were manually 

adjusted during model calibration to obtain the final values 

and resulted in an improved model fit.

Hydraulic conductivity for the bedrock confining units 

was systematically adjusted during parameter estimation, and 

the resulting values are representative of low-conductivity 

claystone bedrock of the Denver Basin. Calibrated hydraulicconductivity values for the Dawson (K_tdwc), upper Denver 

(K_tkduc), lower Denver (K_tkdlc), and Laramie (K_klc) 

confining units were 1.4×10–5, 1.6×10–5, 9.7×10–5, and 

1.3×10–5 ft/d, respectively. The largest calibrated hydraulicconductivity value for confining units was 1.3X10–3 ft/d for 

the Arapahoe (K_kac) confining unit. The calibrated confining unit hydraulic-conductivity values are in general, several 

orders of magnitude less than hydraulic-conductivity values 

for the aquifers (table C13).

For the bedrock aquifers, hydraulic conductivity also 

was systematically adjusted during parameter estimation, 

and the resulting calibrated hydraulic-conductivity values for 

the upper and lower Dawson aquifers (K_utdw and K_ltdw, 

respectively) fit within the hydraulic-conductivity values 

estimated from aquifer tests (fig. A36). The upper Dawson 

aquifer consists of coarse-grained arkosic sand and gravel 

deposits eroded from the nearby Rocky Mountain Front Range 

and forms the D2 depositional sequence of Raynolds (2004), 

while the lower Dawson aquifer is generally considered less 

conductive than the upper Dawson (Robson, 1987) and forms 

the upper part of the D1 sequence (Raynolds, 2004). The 

calibrated hydraulic-conductivity value for the upper Dawson 

aquifer (4.7 ft/d) is in the upper 90th percentile of hydraulicconductivity values estimated from aquifer tests for the Dawson aquifer (fig. A36) and is nearly equal to that of the tributary alluvial sediments. The calibrated hydraulic-conductivity 

value for the lower Dawson aquifer (0.27 ft/d) is in the lower 

25th percentile of hydraulic-conductivity values estimated for 

the Dawson aquifer (fig. A36). The calibrated hydraulic-conductivity values for the Dawson aquifers are within the range 

of the data and fit within the conceptual understanding that 

the lower Dawson aquifer is less conductive than the upper 

Dawson aquifer.

Parameter estimation of hydraulic conductivity for the 

Denver, upper Arapahoe, lower Arapahoe, and Laramie–Fox 

Hills aquifers used pilot points and regularization. 

For the Denver aquifer, calibrated hydraulicconductivity values at the pilot points ranged from 

2.6×10–5 ft/d (logK = –4.6) at pilot point p6_08 to 2.2×10–2 ft/d 

(logK = –1.7) at pilot point p6_05 (table C13), which is in the 

lower 10th percentile of hydraulic-conductivity values estimated from aquifer tests (fig. A36). The spatial distribution of 

hydraulic conductivity derived by kriging the estimated pilotpoint values for the Denver aquifer is generally consistent with 

the spatial distribution of hydraulic conductivity estimated 

from aquifer-test results and is a reasonable representation 

of hydraulic-conductivity distribution for the Denver aquifer 

(fig. C6). The locations of maximum simulated hydraulic 

conductivity values (logK = –2.3) for the Denver aquifer in the 

western and central parts of the basin correspond to the area 

with the greatest silt-plus-sand thickness (fig. A26) and with 

the location of the Wildcat Mountain fan in the D1 synorogenic deposition sequence (Raynolds, 2004).

Calibrated hydraulic-conductivity at the pilot points 

for the upper Arapahoe ranged from 0.2 ft/d (logK = –0.7) 

at pilot point p8_05 to about 620 ft/d (logK = 2.8) at pilot 

point p8_04 (table C13). For the lower Arapahoe, calibrated 

hydraulic conductivity at the pilot points ranged from 4.0×10–4

(logK = –3.4) at pilot point p10_01 to 5.9 ft/d (logK = 0.77 at 

pilot point p10_04, and the values generally encompass the 

full range of hydraulic-conductivity values estimated from 

aquifer tests for the Arapahoe aquifers (fig. A36). Spatially, the 

greatest hydraulic-conductivity values for the lower Arapahoe 

aquifer were for the south Denver metropolitan area (fig. C7) 

and correspond to the location of the Wildcat Mountain fan 

in the D1 sequence (Raynolds, 2004). There was close correspondence between the calibrated and estimated hydraulicconductivity values in the south Denver metropolitan area and 

the northern area, although in the Monument area, the calibrated hydraulic-conductivity values were less than the values 

estimated from aquifer tests (fig. C7). 

Calibrated hydraulic conductivity at the pilot points 

for the Laramie–Fox Hills aquifer ranged from 1.2×10–5

(logK = –4.9) at pilot point p12_10 to 52 ft/d (logK = 1.7) 

at pilot point p12_01 (table C13), and the values generally 

encompass the full range of values estimated from aquifer 

tests. Spatially, the greatest calibrated hydraulic-conductivity 

values were in the eastern part of the Laramie–Fox Hills 

aquifer where there was close correspondence between the 

calibrated and estimated values (fig. C8). The correspondence 

between calibrated hydraulic-conductivity values and values 

estimated from aquifer tests for the Laramie–Fox Hills aquifer 

in the south Denver metropolitan area was variable, but in 

general, the calibrated values in this area were less than the 

values estimated from aquifer tests.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 219

Figure C6. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values estimated 

from aquifer tests for the Denver aquifer.

DIVIDE

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Franktown

Elizabeth

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Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

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Limon

Simla

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Parker

Golden

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Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

p6_08

p6_04

p6_02

p6_06

p6_07

p6_05

p6_03

p6_01

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Logarithm of simulated hydraulic-conductivity 

 value, in feet per day

–5.3 to –5

–5 to –4.75

–4.75 to –4.5

–4.5 to –4.25

–4.25 to –4

–4 to –3.75

–3.75 to –3.5

–3.5 to –3.25

–3.25 to –3

–3 to –2.75

–2.75 to –2.5

–2.5 to –2.3

Denver aquifer simulated extent 

 (model layer 6)

Logarithm of hydraulic-conductivity 

 value from pumping, specific capacity 

 or laboratory test, in feet per day

–4 to –3

–3 to –2

–2 to –1

–1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 1

1. to 2

2 to 3

# Layer 6 pilot point
220 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C7. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values estimated 

from aquifer tests for the lower Arapahoe aquifer.

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Longmont

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Franktown

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Rock

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Ranch

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Springs

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Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

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Fort

Lupton

Fort

Morgan

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Rock

Highlands

Ranch

Colorado

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p10_03

p10_04

p10_05

p10_06

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Logarithm of simulated hydraulic-conductivity 

 value, in feet per day

–4.38 to –4

–4 to –3.5

–3.5 to –3

–3 to –2.5

–2.5 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 0.902

Lower Arapahoe aquifer simulated 

 extent (model layer 10)

Logarithm of hydraulic-conductivity 

 value from pumping, specific capacity 

 or laboratory test, in feet per day

–3.5 to –3

–2.7 to –2.5

–2.0

–2.0 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to 0

0.0 to 0.5

0.5 to 1

1 to 1.6

# Layer 10 pilot point
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 221

Figure C8. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values estimated 

from aquifer tests for the Laramie–Fox Hills aquifer.

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ADAMS

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105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Logarithm of simulated hydraulic-conductivity 

 value, in feet per day

–4.373 to –4

–4 to –3.5

–3.5 to –3

–3 to –2.5

–2.5 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 0.9

Laramie–Fox Hills aquifer simulated 

 extent (model layer 12)

Logarithm of hydraulic-conductivity 

 value from pumping, specific capacity 

 or laboratory test, in feet per day

–3.4 to –3 –3 to –2.5 –2.5 to –2 –2 to –1.5 –1.5 to –1 –1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 1

1. to 1.5

1.5 to 2.4

# Layer 12 pilot point
222 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Calibrated Recharge Parameters

Some recharge parameter values were assigned while others 

were determined by parameter estimation. Assigned recharge 

parameters included the percentage of precipitation that is 

recharged to alluvial aquifers (RCH_Qal, 7 percent), the agricultural irrigation recharge rate (RCH_AgIrr, 10 in/yr), and the urban 

recharge rate (RCH_Resid, 2.5 in/yr) (table C13). Four recharge 

parameters were estimated (RCH_Tdw, RCH_TKd, RCH_Ka, 

and RCH_Klf), representing the percentage of precipitation 

that is recharged to the surface-exposed areas of the Dawson, 

Denver, Arapahoe, and Laramie–Fox Hills aquifers, respectively. 

Parameter-estimation results indicate 2 percent of precipitation 

becomes recharge for the Dawson aquifers, 1.1 percent for the 

Denver aquifer, and 1.4 percent for the Arapahoe and Laramie–

Fox Hills aquifers. The relative percentages are consistent in that 

the upper and lower Dawson aquifers are believed to receive 

greater recharge than the other bedrock aquifers because they 

are exposed at higher altitudes in the basin where precipitation is 

greatest and because they are coarser grained than the underlying 

Denver aquifer.

The spatial distribution of simulated recharge rates changed 

through time, depending on the precipitation and irrigation 

distributions for the selected stress period. The predevelopment 

recharge distribution, which includes the effects of agricultural 

recharge, is shown in figure A47 and is discussed in the section 

“Recharge and Evapotranspiration” of “Groundwater-Budget 

Components” in Chapter A of this report. The recharge distribution for 2003 at the end of the model calibration period is shown 

in figure B28, and the changes in recharge through time are 

discussed in the section “Recharge and Evapotranspiration” of 

“Groundwater-Budget Components” in Chapter B of this report.

Comparison of Simulated and 

Observed Hydraulic Heads

The overall goodness of fit of the model-computed hydraulic heads to the observation data was evaluated using summary measures and graphical analyses. The root-mean-squared 

error (RMSE), the range of head and residuals, the mean and 

distribution of residuals, the standard deviation, and the spatial 

distribution of residuals were used to evaluate the model calibration. The RMSE is a measure of the variation of the residuals 

and was calculated as (Anderson and Woessner, 1992):

RMSE

h h

N

meas sim i

i

N

=

− =

∑( ) 2

1 (5)

where

hmeas is the measured (observed) hydraulic head,

hsim is the model-computed (simulated) hydraulic 

head,

(hmeas – hsim) is the head residual,

and

N is the number of observations used in the 

computation.

Positive head residual values indicate that the simulated heads 

are lower than the observed heads, and negative head residual 

values indicate that the simulated heads are higher than the 

observed heads. If the ratio of the RMSE to the total range of 

head observations in the modeled area is small, then the error 

in the head calculations is a small part of the overall model 

response (Anderson and Woessner, 1992).

The mean residual (Rmean) is computed as:

R

h h

N mean

meas sim i

i

n

=

− =

∑( )

1 (6)

and the positive or negative sign of the mean residual indicates 

whether simulated hydraulic heads were higher or lower than 

observed hydraulic heads, respectively.

The model-computed hydraulic heads in all model 

layers were in good agreement with groundwater flow directions indicated by previous regional investigations. A simple 

method of assessing model fit is to plot the model-computed 

hydraulic head values in relation to the measured observations. 

For a perfect fit, all points should fall on the 1:1 diagonal line. 

Figure C9 presents a graph of the head observations plotted 

in relation to simulated heads for the Denver Basin model 

area and indicates reasonable model fit. The mean residual 

for the entire model is –16 ft, the median residual is –13 ft, 

and residuals range from –477 ft to 399 ft (range of 875 ft) 

(fig. C10). The residuals are biased slightly low, which indicates that simulated heads are, on average, slightly higher than 

the head observations. The standard deviation of the residuals is 82 ft, and the standard error of the mean is 1.2 ft. The 

RMSE for the entire model is 85 ft, which is about 2.8 percent 

of the 3,024-ft range of head observations in the model, and 

the head residuals appear to be independent of head observations (fig. C11).

Weighted residuals also are considered when evaluating 

model fit. Observations are weighted to convert various types 

of observations (such as heads and flows) to consistent units 

Figure C9. Head observations in relation to simulated heads for 

the Denver Basin model.

1:1 line

R2

 = 0.993

4,000

4,500

5,000

5,500

6,000

6,500

7,000

7,500

8,000

Simulated head equivalent, in feet

4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 8,000

Observed head, in feet
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 223

Figure C10. Distribution of head residuals for the Denver Basin model.

Figure C11. Head observations in relation to head residuals for 

the Denver Basin model.

that can be squared and summed, to increase the influence of 

more accurate observations, and to decrease the influence of 

less accurate observations (Hill, 1998). For the Denver Basin 

model, head observations were weighted based on the accuracy of land-surface altitude as reported in the original data 

source. Similar to unweighted observations, when weighted 

observations are plotted in relation to weighted simulated 

values, the points should fall close to a line with slope equal to 

1.0, an intercept of zero, and a correlation coefficient near 1.0 

for a well-calibrated model (Hill, 1998). For the Denver Basin, 

a plot of weighted observations in relation to weighted-simulated equivalents (fig. C12) shows the points do fall close to 

the 1:1 line with an R-squared of 0.999. The correlation coefficient between the weighted head observations and normal 

order statistics is 0.993 (which is greater than the 5-percent 

significance level of 0.946), indicating the hypothesis that the 

weighted residuals are independent and normally distributed at 

the 5-percent significance level is valid (Hill, 1998).

The spatial distribution of head residuals for a given time 

can lend insight to any spatial bias in model calibration. In 

order to plot the spatial distribution of head residuals, head 

observations from a single time period need to be available 

for the entire modeled area. For the Denver Basin, 1978 is the 

Distribution of head residuals

–500

–400

–300

–200

–100

100

200

300

400

500

0 200 400 600 800 1,000 1,200

 Head residual, in feet

Number of residuals

–600

–500

–400

–300

–200

–100

0

100

200

300

400

500

600

Head residual, in feet

25 percent

75 percent

50 percent

90 percent

10 percent

Mean = –16 feet

Median = –13 feet

99 percent

1 percent

Minimum

Maximum

0

only time for which widespread and numerous water-level 

measurements are available, so a map of head residuals is plotted only for 1978 (fig. C13). The residual map for 1978 show 

that head residuals are randomly distributed across the study 

area with no apparent spatial bias.

100

200

300

400

500

600

4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 8,000

Head residual, in feet

Observed head, in feet

–500

–400

–300

–200

–100

0
224 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C12. Weighted head observations in relation to simulated head for the Denver 

Basin model.

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

5,500

6,000

6,500

7,000

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000

Weighted simulated head equivalent, in feet

Weighted observed head, in feet

1:1 line

R2

 = 0.999

Plots of simulated water levels over time (hydrographs) 

compared to observed values at specific sites can indicate 

how well the model represents temporal changes in hydraulic 

heads, and the results can guide future model refinements by 

identifying areas where the model did not achieve a good fit 

between simulated and observed values. Model calibration 

did not utilize water-level data from the CDWR water-level 

monitoring network (as described in the “Calibration Targets” 

section of this chapter). However, hydrographs of simulated 

and observed hydraulic heads are presented for selected wells 

in the CDWR network in the section “Changes in Hydraulic 

Heads and Groundwater Flow Directions” of Chapter B. 

There generally is good agreement between simulated and 

observed hydraulic heads for the lower Dawson (fig. B54), 

Denver (fig. B56), and Laramie–Fox Hills (fig. B64) There is 

opportunity for improvement in the match between transient 

simulated and observed hydraulic heads at selected sites for 

the lower Arapahoe aquifer (fig. B60). For the upper Dawson 

aquifer, simulation results indicate water-level declines of 

up to about 90 ft in the northern part of the aquifer and very 

little change in head for the southern part of the aquifer 

consistent with observed hydraulic-head changes. However, 

large simulated drawdown in the upper Dawson aquifer east 

of Parker was not observed in the CDWR water-level data 

(fig. B52). For the lower Arapahoe aquifer, comparisons 

between simulated and observed hydraulic heads for selected 

wells in the CDWR water-level monitoring network provide 

variable results with simulated heads being generally greater 

than measured water levels for several lower Arapahoe wells 

(fig. B60). The model appears to underestimate drawdown in 

the lower Arapahoe aquifer compared to the CDWR waterlevel data, indicating that further refinement of the hydraulicconductivity or pumping estimates might improve model 

fit for this aquifer. In an area south of Monument, observed 

water-level rise for wells completed in the Denver and lower 

Arapahoe aquifers, presumably in response to increased 

urban recharge, is not well represented in the model. Future 

modeling efforts should consider additional water-level 

data collection or refinement of model parameters in areas 

where the model did not achieve a good fit between transient simulated and observed hydraulic heads. For example, 

decreasing simulated hydraulic conductivity or increasing simulated pumping might improve the match between 

simulated and observed water-level measurements in the 

affected areas.

Comparison of Simulated and 

Observed Stream Base Flow

The simulated flows to streams and drains also were 

considered during model calibration, although the drain 

observations developed for the historical flowing wells are 

not considered accurate and were assigned small weights 

in the regression. In general, the Denver Basin simulated 

stream base-flow rates are less than those estimated from 

the streamflow data, and as with the flow estimates for 

historical flowing wells, low weights were assigned to 

the streamflow observations in the regression. A plot of 

flow observations in relation to simulated flow (fig. C14) 

indicates there is not a close 1:1 correspondence between 

observations and simulated flows. Weighted flow residuals 

are biased positively (fig. C15), the mean flow residual is 

2.83 ft3/s, and the median flow residual is 2.3 ft3/s, indicating that simulated flows are in general less than the estimated 

flow observations.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 225

Figure C13. Spatial distribution of head residuals for the Denver Basin model, 1978.

Parameter Sensitivity

Insight into the relations among model parameters and 

simulated equivalents of observed values can be gained by 

sensitivity analysis of a calibrated model. The sensitivity analysis 

included both estimated and assigned (nonestimated) parameters 

to investigate the degree to which the model results were sensitive to parameter values. Sensitivities were quantified by using 

UCODE_2005 (Poeter and others, 2005) to calculate composite 

scaled sensitivity (CSS) (Hill and Tiedeman, 2007, p. 50) of simulated values with respect to each estimated parameter. Values of 

CSS were computed for all observations (fig. C16A) and separately for head (fig. C16B) and flow (fig. C16C) observations 

(table C13). Prior information was not considered in calculation 

of the CSS values to eliminate the effect of the regularization 

scheme on parameter sensitivities. Composite scaled sensitivity values can be interpreted as indicating the relative degree to 

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

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!(

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!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Upper Dawson aquifer 

 head residuals, in feet

" –169 to –160.0

" –159.9 to –100.0

" –99.9 to –50.0

" –49.9 to –25.0

" –24.9 to 25.0

" 25.0 to 50.0

" 50.0 to 100.0

" 100.0 to 160.0

Lower Dawson aquifer 

 head residuals, in feet

X –332.0 to –100.0

X –99.9 to –25.0

X –24.99 to 25.0

X 25.01 to 100.0

X 100.01 to 200.0

X 200.000001 to 470.000000

Denver aquifer head 

 residuals, in feet

$ –476.6 to –300.0

$ –299.9 to –200.0

$ –199.9 to –100.0

$ –99.9 to –25.0

$ –24.9 to 25.0

$ 25.01 to 100.0

$ 100.01 to 200.0

$ 200.01 to 304.0

Lower Arapahoe aquifer 

 head residuals, in feet

# –315.0 to –200.0

# –199.9 to –100.0

# –99.9 to –25.0

# –24.9 to 25.0

# 25.01 to 100.0

# 100.01 to 226.0

Laramie–Fox Hills aquifer 

 head residuals, in feet

! –417 to –200.0

! –199.9 to –100.0

! –99.9 to –25.0

! –24.9 to 25.0

! 25.01 to 100.0

! 100.01 to 200.0

! 200.01 to 277.0
226 Groundwater Availability of the Denver Basin Aquifer System, Colorado

which information contained in the observations is useful in estimating values of individual parameters (Hill, 1998). Large CSS 

values indicate that the simulated equivalents of observations 

are sensitive to that parameter and that the observations contain 

much information for estimating a parameter. Small CSS values 

indicate that the simulated equivalents of observations are less 

sensitive to that parameter and that little information is available 

for estimating a parameter.

Simulation results are most sensitive to parameters 

representing the percentage of precipitation recharge to the 

Dawson aquifer (RCH_Tdw, estimated as 2 percent), the 

ratio of horizontal to vertical conductivity for bedrock units 

(VANI_BR, assigned a value of 1.0), and the percentage 

of precipitation recharge to the alluvial aquifer (RCH_Qal, 

assigned a value of 7 percent) on the basis of CSS values for 

all head and flow observations (fig. C16A, table C13). Other 

parameters to which the overall simulation results are sensitive, 

in decreasing order, include the hydraulic conductivity at pilot 

point p12_05 in the Laramie–Fox Hills aquifer (p12_05), irrigation pumping from the alluvial aquifer (Q_Qal_IR), hydraulic 

conductivity of the alluvial aquifer adjacent to the South Platte 

River and its tributaries (K_Q_Platte), hydraulic conductivity 

of the Laramie confining bed (K_klc), irrigation (Q_BR_IR) 

and municipal (Q_BR_MU) pumping rates for the bedrock 

aquifers, specific storage of the bedrock aquifers (SS_coarse), 

and the commercial/industrial pumping rate from the bedrock 

aquifers (Q_BR_CI) (fig. C16A, table C13). Simulation results 

are least sensitive to the urban recharge rate (RCH_Resid), 

specific yield of the Dawson aquifer (SY_TDW), the pumping 

rate for alluvial aquifer municipal wells (Q_Qal_MU), the ratio 

of horizontal to vertical hydraulic conductivity in the alluvial 

aquifer (VANI_QPlat), specific yield of the Laramie–Fox Hills 

(SY_KLF) and Arapahoe aquifers (SY_KA), the pumping rate 

for alluvial aquifer commercial/industrial wells (Q_Qal_CI), 

and conductance values for the historical flowing wells 

(FLWG_WELLS) and reservoirs (RIV_LAKES) (fig. C16A, 

table C13).

Sensitivity-analysis results indicate that simulated heads and 

flows are most sensitive to recharge rates to the Dawson and alluvial aquifers, vertical anisotropy within the bedrock units, specific 

storage of the bedrock aquifers, and pumping rates for wells with 

the greatest assigned production. Composite scaled sensitivity 

values computed from the head observations only (fig. C16B) 

exhibit a similar ranking to those computed from head and flow 

observations, reflecting the predominance of head observations 

used in model calibration. Composite scaled sensitivity values 

computed from the flow observations only (fig. C16C) indicate 

that the simulated flows are most sensitive to parameters representing the percentage of precipitation recharge to the Dawson 

aquifer (RCH_Tdw), hydraulic conductivity of the upper Dawson 

aquifer (K_utdw), and the hydraulic conductivity of streambed 

materials in tributaries (SFR_TRIBS). Additional data collection 

or refinement of these parameter values might improve the model 

fit to the observed flows.

The presence of large parameter correlation coefficients (values close to 1.0 or –1.0), generated by PEST or UCODE_2005 

for pairs of model parameters, generally indicates difficulty in 

estimating a unique set of parameter values (Hill and Tiedeman, 

2007, p. 51). Hill and Tiedeman (2007) indicate that if all correlation coefficients are less than 0.95, then it is likely that all parameter values can be estimated uniquely. The final PEST parameterestimation model execution, which involved only the estimated 

parameters values, showed that the largest parameter correlation 

coefficient is less than 0.90, which is well below the 0.95 value at 

which parameter correlation may result in nonuniqueness in the 

set of estimated parameters.

Simulated Groundwater Budgets

A groundwater flow model is a useful tool for quantifying water budgets in complex hydrologic systems such as the 

Denver Basin where hand calculations are intractable. A water 

budget calculated by any groundwater flow model that uses a 

discretized approximation of the aquifer system depends, to 

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

Observed flow,

in thousands of cubic feet per day

–20

20

40

60

80

100

120

140

160

180

200

Simulated flow equivalent, in thousands of cubic feet per day

0

Stream base-flow observations

Historical flowing well observations

EXPLANATION

Figure C14. Flow observations in relation to simulated flows for 

the Denver Basin model.

Figure C15. Simulated equivalents in relation to weighted flow 

residuals for the Denver Basin model.

–20

–15

–10

0

5

10

15

Weighted flow residual,

in cubic feet per day –5

–20 0 20 40 60 80 100 120 140 160 180

Simulated flow equivalent,

in thousands of cubic feet per day

Stream base-flow observations

Historical flowing well observations

EXPLANATION
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 227

a certain extent, on the resolution captured in the spatial and 

temporal discretization scheme used to represent the system 

and stresses. Flow processes that cycle water between the 

groundwater system and streams on a highly localized spatial 

scale (less than about 1 mile), for example, cannot be captured 

by a system discretized into 1-mi2 cells. Similarly, seasonal 

recharge and discharge processes cannot be fully captured by 

a temporal discretization scheme in which the shortest stress 

period is 2 years. Despite these limitations, useful inferences 

can be based on the simulated groundwater budget.

For the sake of model stability and accuracy, each transient 

stress period is subdivided into multiple time steps during model 

execution; simulated stresses are constant for all time steps in 

a given stress period. The initial steady-state stress period has 

a single time step. The model-calibration period uses a total of 

77 time steps in 16 stress periods. A water budget for the entire 

groundwater system is calculated for every time step in every 

stress period of the simulation. Simulated groundwater budgets at the end of each stress period were tabulated from model 

results using the programs ZONEBUDGET (Harbaugh, 1990) 

and GW_Chart (Winston, 2000). Table C14 lists the inflows, 

table C15 lists the outflows, and table C16 lists the net flows for 

the entire model (all model layers), the alluvial aquifer (model 

layer 1), and the bedrock aquifers and confining units combined 

(model layers 2–12 combined). The water budget for the initial 

steady-state stress period represents predevelopment (pre-1880) 

conditions as discussed in the section “Predevelopment Groundwater Budget” in Chapter A. Changes to the groundwater budget 

from predevelopment through 2003 are described in the section 

“Changes to the Groundwater Budget” in Chapter B.

Simulated Hydraulic Heads

MODFLOW calculates hydraulic head at the center of 

each active cell in the model grid, and the simulated heads can 

be contoured to prepare potentiometric-surface maps for each 

aquifer model layer. Potentiometric-surface maps illustrate 

the distribution of hydraulic heads in an aquifer using contour lines of equal hydraulic head. Groundwater flows from 

areas of high hydraulic head to areas of low hydraulic head, 

in a direction generally perpendicular to contours of equal 

hydraulic head on the potentiometric-surface maps. Potentiometric-surface maps for the Denver Basin were prepared 

0

5

10

15

20

RCH_Tdw

VANI_BR

RCH_Qal

p12_05

Q_Qal_IR

K_Q_Platte

K_klc

Q_BR_IR

Q_BR_MU

SS_coarse

Q_BR_CI

RCH_TKd

p8_06

p12_11

SY_Qal

p10_06

p6_06p8_04

pKa_10

K_tkdlc

p12_07

p6_05

RCH_AgIrr

p6_03

GHB_BS_CK

pKa_07pKa_08

VANI_Qbas

RCH_Klf

p10_05

SFR_PLATTE

p8_05

K_Q_bas

K_tkduc

pKa_12

K_ltdw

p6_01

SS_fine

p6_02

K_kac

p12_03p12_08

DRN_COND

p12_06p10_03

p8_03

SY_TKD

ET_MAX

p12_02

p8_01

p12_10p12_04

K_tdwc

RCH_Ka

SFR_TRIBS

K_utdw

p6_07p6_04

pKa_11

p10_01

p6_08

p12_09p10_04

pKa_09

p12_01

GHB_Nuss

pKa_02

RCH_Resid

SY_TDW

Q_Qal_MU

VANI_QPlat

SY_KLF

SY_KA

Q_Qal_CI

FLWG_WELLS

Skin

RIV_LAKES

Composite scaled sensitivity, dimensionless 25

A

Parameter name

Parameter groups

Storage properties

EXPLANATION

Recharge

Hydraulic conductivity

Vertical anisotropy 

Head-dependent boundaries

Pumping

Figure C16. Composite scaled sensitivities for the parameters of the final calibrated Denver Basin model for (A) all head and flow 

observations; (B) head observations only; and (C) flow observations only.
228 Groundwater Availability of the Denver Basin Aquifer System, Colorado

0

5

10

15

20

25

Composite scaled sensitivity, dimensionless

RCH_Tdw

VANI_BR

RCH_Qal

p12_05

Q_Qal_IR

K_Q_Platte

K_klc

Q_BR_IR

Q_BR_MU

SS_coarse

Q_BR_CI

RCH_TKd

p8_06

p12_11

SY_Qal

p10_06

p6_06p8_04

pKa_10

K_tkdlc

p12_07

p6_05

RCH_AgIrr

p6_03

GHB_BS_CK

pKa_07pKa_08

VANI_Qbas

RCH_Klf

p10_05

SFR_PLATTE

p8_05

K_Q_bas

K_tkduc

pKa_12

K_ltdw

p6_01

SS_fine

p6_02

K_kac

p12_03p12_08

DRN_COND

p12_06p10_03

p8_03

SY_TKD

ET_MAX

p12_02

p8_01

p12_10p12_04

K_tdwc

RCH_Ka

p6_07

SFR_TRIBS

p6_04

pKa_11

p10_01

K_utdw

p6_08

p12_09p10_04

pKa_09

p12_01

GHB_Nuss

pKa_02

RCH_Resid

SY_TDW

Q_Qal_MU

VANI_QPlat

SY_KLF

SY_KA

Q_Qal_CI

FLWG_WELLS

RIV_LAKES

Parameter name

B

Skin

Parameter groups

Storage properties

EXPLANATION

Recharge

Hydraulic conductivity

Vertical anisotropy 

Head-dependent boundaries

Pumping

Figure C16. Composite scaled sensitivities for the parameters of the final calibrated Denver Basin model for (A) all head and flow 

observations; (B) head observations only; and (C) flow observations only.—Continued

for each model aquifer layer (layers 1, 2, 4, 6, 8, 10, and 12) 

for predevelopment (pre-1880), 1956, 1978, and 2003 conditions. The predevelopment (pre-1880) potentiometric-surface 

maps are presented in the section “Predevelopment Hydraulic 

Heads and Groundwater Flow Directions” in Chapter A. 

Potentiometric-surface maps for each model layer are presented for 1956, 1978, and 2003 (figs. C17–C37) and include 

the distribution of simulated cell-by-cell pumping for the 

corresponding time. Drawdown of potentiometric surfaces and 

changes in groundwater flow directions caused by development are described in the section “Changes in Hydraulic 

Heads and Groundwater Flow Directions” in Chapter B.

Predictive Simulations

Two predictive scenarios were simulated with the 

calibrated Denver Basin model to calculate predictive model 

sensitivities and to demonstrate use of the model for predictive analysis. Predictive simulations were run 50 years 

into the future from the end of the model calibration period 

(December 31, 2003) to 2053 and were divided into ten 5-year 

stress periods (table C17). The predictive simulations lend 

insight to long-term effects of continued pumping on the 

groundwater system, although they are not considered definitive predictions of future conditions. Detailed discussion of the 

prediction results including water budget, hydraulic head, and 

predictive sensitivity are presented in the section “Simulated

Predictions of Future Conditions” in Chapter B.

Model-Based Statistical Evaluation 

of Potential Monitoring Locations

Model parameters, which can be readily adjusted during 

calibration, are subject to uncertainty that can be quantified 

with model statistics. These parameters include hydraulicconductivity values assigned to aquifers and pilot points, rates 

of recharge and discharge (precipitation, irrigation, withdrawal 

from wells), and degree of hydraulic connection between the 

groundwater system and surface water. Observed values used 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 229

0

1

2

3

4

5

6

7

8

RCH_Tdw

K_utdw

SFR_TRIBS

K_Q_Platte

ET_MAX

p8_04

Q_Qal_IR

RCH_Qal

RCH_TKd

VANI_BR

SY_Qal

RCH_Resid

p8_01p8_05

K_ltdw

p8_06

FLWG_WELLS

pKa_08

Q_BR_IR

p10_06

p8_03

K_tkdlc

RCH_Ka

K_tkduc

Q_BR_MU

RCH_AgIrr

pKa_09

SS_coarse

K_tdwc

p10_03

p6_02

Q_BR_CI

pKa_07

K_kac

p6_08p6_04

DRN_COND

Q_Qal_MU

p12_08p12_07p12_03

SY_TKD

SY_TDW

pKa_10pKa_12

p12_06

SS_fine

p6_07

SFR_PLATTE

p12_02

K_Q_bas

p6_03

p10_05

p6_05

p10_04

pKa_11

p12_09

K_klc

pKa_02

p12_05

GHB_Nuss

p6_01

p12_01

p6_06

RCH_Klf

Q_Qal_CI

p12_10p10_01

VANI_Qbas

p12_04p12_11

VANI_QPlat

GHB_BS_CK

Skin

SY_KLF

RIV_LAKES

SY_KA

Composite scaled sensitivity, dimensionless

Parameter name

C

Parameter groups

Storage properties

EXPLANATION

Recharge

Hydraulic conductivity

Vertical anisotropy 

Head-dependent boundaries

Pumping

Figure C16. Composite scaled sensitivities for the parameters of the final calibrated Denver Basin model for (A) all head and flow 

observations; (B) head observations only; and (C) flow observations only.—Continued

as calibration targets also have associated uncertainties, which 

are characterized by observation weights. Estimated uncertainties related to model parameters and observed values can be 

used to evaluate the part of prediction uncertainty not associated with the conceptual model and model discretization.

One benefit of the automated techniques used to calibrate 

the Denver Basin model is that the results can be used in an 

analysis of the relations among uncertainties in parameters, 

observations, and predictions. Hill and Tiedeman (2007) 

describe the Observation-Prediction (OPR) and ParameterPrediction (PPR) statistics, which quantify these relations. The 

OPR statistic quantifies the decrease in prediction uncertainty 

caused by addition or omission of an observation. The PPR 

statistic quantifies the decrease in prediction uncertainty 

caused by improved information for a parameter. The program 

OPR-PPR (Tonkin and others, 2007) is a model-analysis tool 

designed to calculate the OPR and PPR statistics. OPR-PPR 

also calculates the Observation-Parameter (OPA) statistic, which quantifies the relation of observations and their 

uncertainties to parameter uncertainty. OPR-PPR uses existing 

and potential additional observations and their assigned 

weights, sensitivities of simulated equivalents to observations 

with respect to parameters, sensitivities of predictions with 

respect to parameters, and other information to calculate 

these statistics.

When OPR-PPR calculates OPR statistics, it evaluates 

one potential observation at a time to determine its effect on 

reducing the uncertainty of each prediction or each group of 

predictions. The OPR statistic, which is calculated for each 

potential observation, is the percent reduction in uncertainty 

that would be expected due to the addition of the potential 

observation. The PPR statistic is an indicator of the value 

of improved information about a selected parameter with 

respect to a prediction or prediction group. PPR is defined as 

the percent change in prediction standard deviation resulting 

from decreasing the standard deviation of the parameter value 

by 10 percent. OPR-PPR calculates the PPR statistic for each 

prediction for each parameter. The OPA statistic is defined as 

the percent change in parameter standard deviation caused by 

omitting or adding an observation.
230 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Alluvial aquifer Inflows (ft3/s)

Stress period Time step Year Recharge Streams Reservoirs Multinode 

wells

Flow from 

bedrock units Storage Total inflow

1 1 1879 454.4 12.69 0.0 0.0 34.1 0.0 501.1

2 6 1906 454.4 12.69 0.0 0.0 34.1 0.0 501.1

3 5 1919 454.4 12.72 22.5 0.0 33.9 0.1 523.7

4 5 1939 454.4 12.59 22.6 0.0 33.8 0.6 523.9

5 5 1953 454.5 12.92 38.1 0.0 33.7 5.1 544.5

6 5 1956 511.4 12.47 38.3 0.0 33.8 17.1 613.1

7 5 1961 523.3 13.14 38.3 0.0 33.4 14.0 622.2

8 5 1964 476.6 13.41 38.9 0.0 32.5 42.6 604.0

9 5 1971 509.7 13.77 38.7 0.0 32.3 19.4 614.0

10 5 1973 509.6 19.79 41.5 0.0 31.8 21.3 623.9

11 5 1978 486.0 19.56 41.6 0.0 30.7 33.8 611.8

12 5 1984 528.7 19.86 41.5 0.0 29.9 8.9 628.8

13 5 1986 528.7 19.98 41.5 0.0 29.4 9.9 629.4

14 5 1994 604.7 20.09 37.9 0.0 29.4 6.9 699.1

15 5 1999 619.9 20.12 38.0 0.0 28.6 4.3 711.0

16 5 2003 592.7 20.05 38.1 0.0 27.2 11.4 689.6

Bedrock units Inflows (ft3/s)

Stress period Time step Year Recharge Streams Reservoirs Multinode

wells

Flow from 

alluvial aquifer Storage Total inflow

1 1 1879 176.0 3.49 0.0 0.0 7.8 0.0 187.3

2 6 1906 176.0 3.49 0.0 0.0 7.8 0.0 187.3

3 5 1919 176.0 3.50 0.0 0.0 8.0 0.7 188.2

4 5 1939 178.9 3.51 0.0 7.1E-6 7.9 0.8 191.2

5 5 1953 185.4 3.55 0.0 1.0E-5 7.7 1.7 198.4

6 5 1956 226.1 3.19 0.11 3.4E-4 7.8 2.5 239.6

7 5 1961 234.8 3.21 0.13 7.6E-3 7.9 3.1 249.2

8 5 1964 205.1 3.66 0.14 0.03 7.6 16.9 233.5

9 5 1971 231.7 3.48 0.15 0.08 8.5 7.9 251.8

10 5 1973 231.8 3.52 0.16 0.09 8.7 12.4 256.7

11 5 1978 214.6 3.78 0.20 0.14 8.9 24.8 252.4

12 5 1984 234.4 3.68 0.22 0.24 9.9 21.4 269.9

13 5 1986 234.4 3.73 0.23 0.26 10.3 27.7 276.6

14 5 1994 311.1 3.80 3.61 0.36 11.0 30.9 360.8

15 5 1999 319.5 3.96 3.62 0.45 11.8 39.6 378.9

16 5 2003 300.8 4.20 3.66 0.59 12.4 60.2 381.8

Table C14. Simulated transient inflows for the Denver Basin entire modeled area, alluvial aquifer, and bedrock units, 1879–2003.

[ft3/s, cubic feet per second]

Entire modeled area Inflows (ft3/s)

Stress period Time step Year Recharge Streams Reservoirs Multinode

wells Storage Total inflow

1 1 1879 630.3 16.18 0.0 0.0 0.0 646.5

2 6 1906 630.3 16.18 0.0 0.0 0.0 646.6

3 5 1919 630.3 16.22 22.5 0.0 0.9 670.0

4 5 1939 633.3 16.11 22.6 7.1E-6 1.5 673.4

5 5 1953 639.9 16.48 38.1 1.0E-5 6.9 701.4

6 5 1956 737.5 15.66 38.5 3.4E-4 19.6 811.1

7 5 1961 758.1 16.36 38.5 7.6E-3 17.1 830.1

8 5 1964 681.7 17.07 39.0 0.03 59.5 797.3

9 5 1971 741.4 17.25 38.9 0.08 27.3 824.9

10 5 1973 741.4 23.31 41.7 0.09 33.7 840.2

11 5 1978 700.6 23.34 41.8 0.14 58.7 824.6

12 5 1984 763.1 23.54 41.7 0.24 30.4 859.0

13 5 1986 763.1 23.71 41.7 0.26 37.6 866.3

14 5 1994 915.9 23.89 41.5 0.36 37.9 1019.5

15 5 1999 939.4 24.08 41.6 0.45 43.9 1049.5

16 5 2003 893.5 24.25 41.8 0.59 71.6 1031.7
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 231

Table C15. Simulated transient outflows for the Denver Basin entire modeled area, alluvial aquifer, and bedrock units, 1879–2003.

[ft3/s, cubic feet per second; ET, evapotranspiration]

Entire modeled area Outflows (ft3/s)

Stress

period

Time

step Year ET Streams Reservoirs Springs

Head

dependent

boundaries

Specified

flow Wells

Multinode

wells

Storage Total

outflow

1 1 1879 441.6 181.8 0.00 4.21 4.80 14.11 0.0 0.0 0.0 646.5

2 6 1906 441.5 181.8 0.00 4.23 4.80 14.11 0.1 0.0 0.0 646.6

3 5 1919 462.3 181.9 0.00 4.20 4.80 14.11 2.4 0.0 0.1 670.0

4 5 1939 459.9 180.3 0.00 4.19 4.80 14.11 9.9 3.8E-4 0.2 673.4

5 5 1953 457.3 175.0 1.88 4.17 4.80 14.11 43.9 2.2E-2 0.3 701.4

6 5 1956 470.4 179.1 1.85 4.32 4.80 14.11 94.4 6.6E-2 42.1 811.1

7 5 1961 469.5 183.0 1.80 4.41 4.83 14.11 120.8 0.50 31.1 830.1

8 5 1964 436.7 178.2 1.62 4.02 4.77 14.11 143.9 0.84 13.3 797.3

9 5 1971 440.5 179.8 1.48 4.13 4.71 14.11 171.0 1.10 8.0 824.9

10 5 1973 436.7 179.6 10.4 4.08 4.68 14.11 183.3 1.44 5.9 840.2

11 5 1978 416.1 176.1 10.1 3.82 4.57 14.11 195.7 2.13 1.9 824.6

12 5 1984 427.7 178.9 9.9 3.95 4.53 14.11 208.2 2.65 9.0 859.0

13 5 1986 426.1 178.4 9.9 3.93 4.52 14.11 219.0 3.06 7.4 866.3

14 5 1994 527.3 187.5 11.3 4.44 4.55 14.11 233.5 4.01 32.7 1019.5

15 5 1999 540.5 188.5 11.3 4.48 4.58 14.11 255.3 5.07 25.8 1049.5

16 5 2003 523.0 184.1 11.0 4.22 4.48 14.11 276.2 6.30 8.3 1031.7

Alluvial aquifer Outflows (ft3/s)

Stress

period

Time

step Year ET Streams Reservoirs Springs

Head

dependent

boundaries

Specified

flow Wells

Multinode

wells

Flow to

bedrock

units

Storage Total

outflow

1 1 1879 307.1 164.2 0.0 3.18 4.80 14.11 0.0 0.0 7.79 0.0 501.1

2 6 1906 307.0 164.2 0.0 3.18 4.80 14.11 4.9E-2 0.0 7.80 0.0 501.1

3 5 1919 328.1 164.3 0.0 3.18 4.80 14.11 1.1 0.0 7.96 0.1 523.7

4 5 1939 323.1 162.7 0.0 3.17 4.80 14.11 7.8 0.0 7.95 0.2 523.9

5 5 1953 315.5 157.1 1.9 3.15 4.80 14.11 39.9 0.0 7.75 0.2 544.5

6 5 1956 303.1 158.8 1.9 3.12 4.80 14.11 86.1 0.0 7.76 33.5 613.1

7 5 1961 296.8 162.1 1.8 3.12 4.83 14.11 106.8 6.7E-4 7.86 24.7 622.2

8 5 1964 279.2 159.2 1.6 3.02 4.77 14.11 123.7 8.3E-4 7.62 10.8 604.0

9 5 1971 273.3 159.4 1.5 2.95 4.71 14.11 143.6 8.3E-4 8.50 5.9 614.0

10 5 1973 270.9 159.2 10.4 2.94 4.68 14.11 148.5 8.3E-4 8.75 4.5 623.9

11 5 1978 260.3 157.1 10.1 2.87 4.57 14.11 152.4 3.5E-2 8.87 1.5 611.8

12 5 1984 265.3 159.3 9.9 2.91 4.53 14.11 155.9 4.5E-2 9.92 7.0 628.8

13 5 1986 264.4 158.9 9.9 2.91 4.52 14.11 158.7 4.8E-2 10.30 5.7 629.4

14 5 1994 303.2 166.1 11.3 2.96 4.55 14.11 162.1 5.1E-2 10.96 23.7 699.1

15 5 1999 311.9 167.0 11.2 3.00 4.58 14.11 168.1 5.6E-2 11.78 19.3 711.0

16 5 2003 304.9 164.3 11.0 2.95 4.48 14.11 170.8 6.0E-2 12.43 4.5 689.6

Bedrock units Outflows (ft3/s)

Stress

period

Time

step Year ET Streams Reservoirs Springs

Head

dependent

boundaries

Specified

flow Wells

Multinode

wells

Flow to

alluvial

aquifer

Storage Total

outflow

1 1 1879 134.5 17.65 0.0 1.03 0.0 0.00 0.0 0.0 34.1 0.0 187.3

2 6 1906 134.5 17.64 0.0 1.06 0.0 0.00 7.82E-2 0.0 34.1 0.0 187.3

3 5 1919 134.3 17.61 0.0 1.02 0.0 0.00 1.3 0.0 33.9 0.0 188.2

4 5 1939 136.8 17.57 0.0 1.02 0.0 0.00 2.0 3.8E-4 33.8 0.0 191.2

5 5 1953 141.8 17.88 0.0 1.02 0.0 0.00 4.0 2.2E-2 33.7 0.0 198.4

6 5 1956 167.3 20.24 0.0 1.20 0.0 0.00 8.4 6.6E-2 33.8 8.6 239.6

7 5 1961 172.7 20.82 0.0 1.28 0.0 0.00 14.0 0.50 33.4 6.4 249.2

8 5 1964 157.4 18.95 0.0 1.00 0.0 0.00 20.2 0.84 32.5 2.5 233.5

9 5 1971 167.2 20.41 0.0 1.18 0.0 0.00 27.4 1.10 32.3 2.1 251.8

10 5 1973 165.8 20.33 0.0 1.14 0.0 0.00 34.9 1.44 31.8 1.4 256.7

11 5 1978 155.8 19.06 0.0 0.95 0.0 0.00 43.3 2.09 30.7 0.4 252.4

12 5 1984 162.4 19.57 0.0 1.04 0.0 0.00 52.4 2.60 29.9 2.0 269.9

13 5 1986 161.7 19.47 0.0 1.02 0.0 0.00 60.3 3.01 29.4 1.7 276.6

14 5 1994 224.1 21.37 1.0E-2 1.48 0.0 0.00 71.4 3.96 29.4 9.1 360.8

15 5 1999 228.6 21.51 1.1E-2 1.48 0.0 0.00 87.2 5.02 28.6 6.5 378.9

16 5 2003 218.1 19.86 8.4E-3 1.28 0.0 0.00 105.4 6.24 27.2 3.7 381.8
232 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Alluvial aquifer Net flows (ft3/s)

Stress period Time step Year Net

recharge

Net

reservoir inflow

Net

stream outflow

Net

well outflow

Change

in storage

1 1 1879 147.3 0.0 –151.5 0.0 26.31 0.0

2 6 1906 147.4 0.0 –151.5 –0.0 26.28 0.0

3 5 1919 126.3 22.5 –151.6 –1.1 25.97 0.0

4 5 1939 131.2 22.6 –150.1 –7.8 25.89 0.4

5 5 1953 139.0 36.3 –144.2 –39.9 25.97 4.9

6 5 1956 208.3 36.5 –146.3 –86.1 26.02 –16.4

7 5 1961 226.5 36.5 –149.0 –106.8 25.56 –10.7

8 5 1964 197.3 37.3 –145.8 –123.7 24.92 31.8

9 5 1971 236.4 37.2 –145.7 –143.6 23.85 13.5

10 5 1973 238.8 31.1 –139.4 –148.5 23.01 16.8

11 5 1978 225.7 31.6 –137.5 –152.4 21.84 32.3

12 5 1984 263.4 31.6 –139.4 –155.9 19.94 2.0

13 5 1986 264.3 31.6 –138.9 –158.7 19.09 4.2

14 5 1994 301.5 26.6 –146.0 –162.2 18.44 –16.7

15 5 1999 308.0 26.8 –146.9 –168.1 16.85 –15.0

16 5 2003 287.8 27.1 –144.2 –170.9 14.80 6.9

Bedrock units Net flows (ft3/s)

Stress period Time step Year Net

recharge

Net

reservoir inflow

Net

stream outflow

Net

well outflow

Change

in storage

1 1 1880 41.5 0.0 –14.16 0.0 –26.31 0.0

2 6 1906 41.5 0.0 –14.15 –0.1 –26.28 0.0

3 5 1919 41.7 0.0 –14.11 –1.3 –25.97 0.7

4 5 1939 42.2 0.0 –14.05 –2.0 –25.89 0.8

5 5 1953 43.6 0.0 –14.33 –4.0 –25.97 1.7

6 5 1956 58.8 0.1 –17.05 –8.4 –26.02 –6.2

7 5 1961 62.1 0.1 –17.61 –14.5 –25.56 –3.3

8 5 1964 47.7 0.1 –15.29 –21.0 –24.92 14.4

9 5 1971 64.5 0.2 –16.93 –28.4 –23.85 5.8

10 5 1973 66.0 0.2 –16.81 –36.2 –23.01 11.0

11 5 1978 58.8 0.2 –15.28 –45.3 –21.84 24.4

12 5 1984 72.0 0.2 –15.89 –54.7 –19.94 19.4

13 5 1986 72.7 0.2 –15.73 –63.0 –19.09 25.9

14 5 1994 87.0 3.6 –17.57 –75.0 –18.44 21.9

15 5 1999 90.9 3.6 –17.55 –91.8 –16.85 33.1

16 5 2003 82.7 3.6 –15.66 –111.0 –14.80 56.5

Table C16. Simulated transient net water budget for the Denver Basin entire modeled area, alluvial aquifer, and bedrock units, 1879–2003.

[ft3/s, cubic feet per second]

Entire modeled area Net flows (ft3/s)

Stress period Time step Year Net

recharge

Net

reservoir inflow

Net

stream outflow

Net

well outflow

Change

in storage

1 1 1879 188.8 0.0 –165.7 0.0 0.0

2 6 1906 188.9 0.0 –165.6 –0.1 0.0

3 5 1919 168.0 22.5 –165.7 –2.4 0.7

4 5 1939 173.4 22.6 –164.2 –9.9 1.2

5 5 1953 182.6 36.3 –158.5 –43.9 6.6

6 5 1956 267.0 36.6 –163.4 –94.5 –22.5

7 5 1961 288.6 36.7 –166.6 –121.3 –14.0

8 5 1964 245.1 37.4 –161.1 –144.7 46.2

9 5 1971 300.9 37.4 –162.6 –172.0 19.3

10 5 1973 304.8 31.2 –156.2 –184.7 27.8

11 5 1978 284.4 31.8 –152.8 –197.7 56.7

12 5 1984 335.4 31.8 –155.3 –210.6 21.4

13 5 1986 337.0 31.8 –154.6 –221.7 30.1

14 5 1994 388.5 30.2 –163.6 –237.2 5.2

15 5 1999 399.0 30.4 –164.4 –259.9 18.2

16 5 2003 370.4 30.8 –159.9 –281.9 63.4
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 233

Figure C17. Simulated 1956 potentiometric surface and pumping rates for the alluvial aquifer 

(model layer 1).

South Platte River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand

Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

Middle Rush Creek

Mustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

Bi g Thompson River

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

5,900

6,200

6,000

6,300

6,400

6,500

5,800

5,700

6,000

5,900

6,300

6,100

5,900

6,200

6,000

6,300

6,400

6,500

5,800

4,700

4,800

4,400

5,000

4,900

4,600

4,700

4,800

4,700

4,800

4,400

5,000

5,700

4,900

4,600

5,100

5,200

4,900

4,800

4,900

4,600

4,900

4,600

5,000

4,700

5,000

5,000

4,900

5,100

5,200

4,600

5,700

5,800

6,000

6,300

6,200

4,900

6,000

4,800

4,900

5,900

4,600

6,000

4,900

4,600

4,700

6,300

5,000

4,800

6,300

4,700

5,000

5,000

4,900

6,200

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

Perennial

Ephemeral

Stream

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Alluvial aquifer simulated pumping, 

 1956, in cubic feet per second

EXPLANATION

–0.89 to –0.75

–0.75 to –0.5

–0.5 to –0.25

–0.25 to –0.1

0

<–0.1
234 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C18. Simulated 1978 potentiometric surface and pumping rates for the alluvial aquifer 

(model layer 1).

South Platte River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brackett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

Big Thompso n River

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

5,900

6,200

6,000

6,300 6,400

6,500

5,800

5,700

6,000

5,900

6,300

6,100

5,900

6,200

6,000

6,300 6,400

6,500

5,800

4,700

4,800

4,400

5,000

4,900

4,600

4,800

4,700

4,800

4,400

5,000

5,700

4,900

4,600

5,100

4,600

4,600

4,700

5,200

4,600

4,900

4,800

4,900 4,900

4,700

5,000

5,000

4,900

5,200

4,600

5,700

5,800

6,000

6,300

6,200

4,900

6,000

4,800

4,900

5,900

4,600

6,000

4,900

4,600

4,700

6,300

5,000 4,800

6,300

4,700

5,000

5,000

4,900

6,200

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

Perennial

Ephemeral

Stream

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Alluvial aquifer simulated pumping, 

 1978, in cubic feet per second

–1.2 to –1

–1 to –0.75

–0.75 to –0.5

–0.5 to –0.25

<–0.25

0
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 235

Figure C19. Simulated 2003 potentiometric surface and pumping rates for the alluvial aquifer 

(model layer 1).

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte River

Cac he la Poudre R

Big Thompson Riv er

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

Middle Rush Creek

Mustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

5,900

6,200

6,000

6,300

6,400

6,500

5,800

5,700

6,000

6,300

5,900

6,100

5,900

6,200

6,000

6,300

6,400

6,500

4,700

4,800

5,000

4,900

4,600

4,700

4,800

4,700

5,800

4,800

5,000

5,700

4,900

4,600

5,100

5,200

4,600

4,900 4,900

4,900

4,600

4,600

5,000

4,900

4,800

4,700

5,200

4,600

5,700

6,000

6,300

5,800

6,000

4,900

6,300

4,900

4,900

4,600

6,000

4,600

5,000

4,700

4,800

4,900

5,900

4,800

4,700

5,000

6,300

5,800

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Alluvial aquifer simulated pumping, 2003, 

 in cubic feet per second

EXPLANATION

–1.6 to –1.25

–1.25 to –1

–1.0 to –0.75

–0.75 to –0.5

–0.5 to –0.25

<–0.25

0
236 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C20. Simulated 1956 potentiometric surface and pumping rates for the upper Dawson aquifer 

(model layer 2).

PALMER

DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Clear Creek

West Sand Creek

First Cree

Sa

k

nd Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,700

6,600

6,800

6,500

6,900

6,400

6,100

6,300

7,000

6,200

6,000

7,100

5,900

6,700

6,600

6,800

6,500

6,900

6,400

6,100

6,300

7,000

6,200

6,000

7,100

5,900

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

Extent of active model cells

Layer 2 simulated pumping, Upper Dawson aquifer simulated extent (model layer 2)

 1956, in cubic feet per second

–0.035 to –0.025

–0.025 to –0.01

<–0.01

0

0 5 10 MILES

0 5 10 KILOMETERS
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 237

Figure C21. Simulated 1978 potentiometric surface and pumping rates for the upper Dawson aquifer 

(model layer 2).

PALMER

DIVIDE

PALMER

DIVIDE

Coal Creek

Clear Creek

West Sand Creek

First Cree

S

k

and Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Layer 2 simulated pumping, 

 1978, in cubic feet per second

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.17 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Upper Dawson aquifer simulated extent (model layer 2)

0 5 10 MILES

0 5 10 KILOMETERS
238 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C22. Simulated 2003 potentiometric surface and pumping rates for the upper Dawson aquifer 

(model layer 2).

DIVIDE

PALMERPALMER DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Creek

Sand Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.19 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 2 simulated pumping, Upper Dawson aquifer simulated extent (model layer 2)

 2003, in cubic feet per second

0 5 10 MILES

0 5 10 KILOMETERS
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 239

Figure C23. Simulated 1956 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).

PALMER DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Creek

Sand Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiowa Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,100

6,200

6,400

6,500

6,600

6,700

6,800

6,000

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,800

5,900

6,500

6,900

6,000

6,700

6,100

6,200

6,400

6,500

6,600

6,700

6,800

6,000

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,800

5,900

6,500

6,900

6,900

5,900

6,000

6,700

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.11 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)

Layer 4 simulated pumping, 

 1956, in cubic feet per second

Dawson confining unit simulated extent (model layer 3)
240 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C24. Simulated 1978 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).

PALMER DIVIDEPALMER DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Cree

S

k

and Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiowa Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25 6,100

6,200

6,400

6,500

6,000

6,600

6,800

6,700

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,900

6,500

6,600

6,700

6,100

6,200

6,400

6,500

6,000

6,600

6,800

6,700

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,900

6,500

6,600

6,700

6,900

6,700

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.25 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)

Layer 4 simulated pumping, 

 1978, in cubic feet per second 

Dawson confining unit simulated extent (model layer 3)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 241

Figure C25. Simulated 2003 potentiometric surface and pumping rates for the lower Dawson aquifer 

(model layer 4).

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Cree

S

k

and Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiowa Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,200

6,000

6,400

6,500

6,600

6,800

6,700

7,000

6,900

5,800

5,900

7,100

7,200

5,700

7,300

7,400

5,600

6,000

6,700

5,900

7,200

6,900

6,600

5,600

6,900

6,800

6,900

6,500

6,200

6,000

6,400

6,500

6,600

6,800

6,700

7,000

6,900

5,800

5,900

7,100

7,200

5,700

7,300

7,400

5,600

6,000

6,700

5,900

7,200

6,900

6,600

5,600

6,900

6,800

6,900

6,500

DIVIDE

PALMERPALMER

DIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.37 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)

Layer 4 simulated pumping, 

 2003, in cubic feet per second

Dawson confining unit simulated extent (model layer 3)
242 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C26. Simulated 1956 potentiometric surface and pumping rates for the Denver aquifer 

(model layer 6).

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

6,300

5,900

6,000

6,400

5,800

5,400

6,200

5,700 5,600

5,300

5,500

5,200

6,500 6,600

6,900

6,800

6,700

7,000

5,100

7,100

7,200

7,300

7,400

6,700

5,500

5,500

5,500

5,100

5,500

6,600

6,500

5,400

6,000

6,300

6,200

6,400

6,200

5,500

6,100

6,300

5,900

6,000

6,400

5,800

5,400

6,200

5,700 5,600

5,300

5,500

5,200

6,500 6,600

6,900

6,800

6,700

7,000

5,100

7,100

7,200

7,300

7,400

6,700

5,500

5,500

5,500

5,100

5,500

6,600

6,500

5,400

6,000

6,300

6,200

6,400

6,200

5,500

PALMER

DIVIDE

PALMER

DIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.25 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Layer 6 simulated pumping, 

 1956, in cubic feet per second

Denver upper confining unit simulated extent (model layer 5)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 243

Figure C27. Simulated 1978 potentiometric surface and pumping rates for the Denver aquifer 

(model layer 6).

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

6,300

5,900

6,400

6,000

5,800

5,400

5,700

6,200

5,600

5,500

5,300

6,500

5,200

6,600

5,100

6,900

6,800

6,700

7,000 7,100

7,200

7,300

7,400

5,100

6,700

5,200

6,800

5,500

5,500

5,500

6,300

6,200

6,200

5,300

6,500

6,800

6,700

6,000

6,400

5,500

6,000

5,400

5,500

6,100

6,300

5,900

6,400

6,000

5,800

5,400

5,700

6,200

5,600

5,500

5,300

6,500

5,200

6,600

5,100

6,900

6,800

6,700

7,000 7,100

7,200

7,300

7,400

5,100

6,700

5,200

6,800

5,500

5,500

5,500

6,300

6,200

6,200

5,300

6,500

6,800

6,700

6,000

6,400

5,500

6,000

5,400

5,500

PALMER

DIVIDE

PALMER

DIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Layer 6 simulated pumping, 

 1978, in cubic feet per second

Denver upper confining unit simulated extent (model layer 5)
244 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C28. Simulated 2003 potentiometric surface and pumping rates for the Denver aquifer 

(model layer 6).

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,300

6,100

5,900

6,000

5,800

6,400

5,700

6,200

5,600

5,400

5,500

5,300

5,200

6,500

5,100

6,900

6,600

7,000

6,800

6,700

7,100

7,200

6,200

6,700

6,600

5,500

5,600

7,000

6,300

6,500

6,200

6,400

6,700

6,200

6,900

6,700

6,000

5,200

6,700

5,500

5,400

6,500

6,700

6,300

6,100

5,900

6,000

5,800

6,400

5,700

6,200

5,600

5,400

5,500

5,300

5,200

6,500

5,100

6,900

6,600

7,000

6,800

6,700

7,100

7,200

6,200

6,700

6,600

5,500

5,600

7,000

6,300

6,500

6,200

6,400

6,700

6,200

6,900

6,700

6,000

5,200

6,700

5,500

5,400

6,500

6,700

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Layer 6 simulated pumping, 

 2003, in cubic feet per second

Denver upper confining unit simulated extent (model layer 5)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 245

Figure C29. Simulated 1956 potentiometric surface and pumping rates for the upper Arapahoe 

aquifer (model layer 8).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,200

5,100

5,400

5,000

5,600

5,000

5,400

5,000

5,300

5,200

5,100

5,400

5,000

5,600

5,000

5,400

5,000

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.175 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 8 simulated pumping, Upper Arapahoe aquifer simulated extent (model layer 8)

 1956, in cubic feet per second
246 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C30. Simulated 1978 potentiometric surface and pumping rates for the upper Arapahoe 

aquifer (model layer 8).

South Platte River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.24 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 8 simulated pumping, Upper Arapahoe aquifer simulated extent (model layer 8)

 1978, in cubic feet per second
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 247

Figure C31. Simulated 2003 potentiometric surface and pumping rates for the upper Arapahoe 

aquifer (model layer 8).

South Platte

River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 8 simulated pumping, Upper Arapahoe aquifer simulated extent (model layer 8)

 2003, in cubic feet per second
248 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C32. Simulated 1956 potentiometric surface and pumping rates for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

5,400

6,000

5,300

5,900

5,600

5,800

5,200

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

6,900

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

6,200

4,900

6,000

5,000

6,000

5,900

5,000

6,100

5,500

5,900

5,500

5,900

5,700

5,000

5,400

6,000

5,300

5,900

5,600

5,800

5,200

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

6,900

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

6,200

4,900

6,000

5,000

6,000

5,900

5,000

6,100

5,500

5,900

5,500

5,900

5,700

5,000

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 8)

Layer 8 simulated pumping, 

 1956, in cubic feet per second

Overlying confining units simulated extent (model layers 7 and 9)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 249

Figure C33. Simulated 1978 potentiometric surface and pumping rates for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

6,000

5,400

5,600

5,900

5,200

5,800

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

7,000

6,900

4,900

7,100

7,200

7,300

4,800

5,700

5,900

5,700

6,200

5,500

5,500

6,000

5,900

4,900

6,000

5,000

5,000

5,900

6,100

5,000

5,300

6,000

5,400

5,600

5,900

5,200

5,800

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

7,000

6,900

4,900

7,100

7,200

7,300

4,800

5,700

5,900

5,700

6,200

5,500

5,500

6,000

5,900

4,900

6,000

5,000

5,000

5,900

6,100

5,000

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.25 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Arapahoe aquifer (model layer 10) simulated extent

Layer 10 simulated pumping, Overlying confining units (model layers 7 and 9) simulated extent

 1978, in cubic feet per second
250 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C34. Simulated 2003 potentiometric surface and pumping rates for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,400

6,000

5,600

5,900

5,200

5,500

5,800

6,100

5,700

6,200

5,100

6,300

6,400

5,000

6,500

6,600

6,700

6,900

6,800

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

5,500

4,900

5,000

5,400

5,900

6,900

6,200

5,700

5,900

6,000

5,000

5,900

6,100

5,900

5,300

5,400

6,000

5,600

5,900

5,200

5,500

5,800

6,100

5,700

6,200

5,100

6,300

6,400

5,000

6,500

6,600

6,700

6,900

6,800

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

5,500

4,900

5,000

5,400

5,900

6,900

6,200

5,700

5,900

6,000

5,000

5,900

6,100

5,900

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.41 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Layer 10 simulated pumping, Overlying confining units simulated extent (model layers 7 and 9)

 2003, in cubic feet per second
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 251

Figure C35. Simulated 1956 potentiometric surface and pumping rates for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,400

5,300

5,200

5,100

5,600

5,700

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,200

6,400

6,300

6,500 6,600

6,700

6,800

6,900

7,000 7,100

4,500

7,200

7,300

7,400

4,400

5,600

5,700

6,000

4,900

5,600

6,300

5,800

4,400

5,400

4,600

5,000

5,700

5,700

5,900

5,500

4,600

5,500

5,900

5,400

5,300

5,200

5,100

5,600

5,700

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,200

6,400

6,300

6,500 6,600

6,700

6,800

6,900

7,000 7,100

4,500

7,200

7,300

7,400

4,400

5,600

5,700

6,000

4,900

5,600

6,300

5,800

4,400

5,400

4,600

5,000

5,700

5,700

5,900

5,500

4,600

5,500

5,900

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.06 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Layer 12 simulated pumping, Laramie confining units simulated extent (model layer 11)

 1956, in cubic feet per second
252 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C36. Simulated 1978 potentiometric surface and pumping rates for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

Broomfield

Lafayette

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,200

5,100

5,600

5,700

5,400

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,300

6,200

6,400

6,500

6,600

6,700

6,800

6,900

7,000

7,100

4,500

7,200

7,300

7,400

5,800

4,600

5,900

5,000

5,000

5,600

6,000

4,800

4,900

5,900

5,800

5,700

5,500

5,500

5,000

6,200

6,600

5,800 5,700

5,700

4,600

5,300

5,200

5,100

5,600

5,700

5,400

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,300

6,200

6,400

6,500

6,600

6,700

6,800

6,900

7,000

7,100

4,500

7,200

7,300

7,400

5,800

4,600

5,900

5,000

5,000

5,600

6,000

4,800

4,900

5,900

5,800

5,700

5,500

5,500

5,000

6,200

6,600

5,800 5,700

5,700

4,600

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.14 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Layer 12 simulated pumping, Laramie confining units simulated extent (model layer 11)

 1978, in cubic feet per second
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 253

Figure C37. Simulated 2003 potentiometric surface and pumping rates for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Lafayette

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,100

5,200

5,600

5,700

5,800

5,900

5,300

5,000

5,400

4,800

4,900

5,500

4,700

6,000

4,600

6,200 6,100

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

4,500

7,100

7,200

7,300

7,400

4,800

4,900

5,400

6,000

4,900

6,800

4,600

5,000

7,000

6,600

5,400

5,900

5,800

5,700

5,600

4,600

4,600

5,100

5,000

6,700

5,500

5,200

5,900

5,700

5,100

5,200

5,600

5,700

5,800

5,900

5,300

5,000

5,400

4,800

4,900

5,500

4,700

6,000

4,600

6,200 6,100

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

4,500

7,100

7,200

7,300

7,400

4,800

4,900

5,400

6,000

4,900

6,800

4,600

5,000

7,000

6,600

5,400

5,900

5,800

5,700

5,600

4,600

4,600

5,100

5,000

6,700

5,500

5,200

5,900

5,700

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.18 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Layer 12 simulated pumping, Laramie confining units simulated extent (model layer 11)

 2003, in cubic feet per second
254 Groundwater Availability of the Denver Basin Aquifer System, Colorado

For the Denver Basin model, the potentiometric surface 

for the lower Arapahoe aquifer at the end of the prediction 

period (2053) was identified as being of predictive interest. To 

characterize the simulated potentiometric surface, a subset of 

the model layer representing the lower Arapahoe aquifer was 

selected for analysis (layer 10). A uniformly distributed subset 

of cells was established by selecting all cells for which row and 

column indices are evenly divisible by 5. Head predictions at 

the resulting 184 cells were defined as a prediction group in 

OPR-PPR. Potential head observations were defined for the end 

of the calibration period at all active cells in the seven layers 

representing aquifers (layers 1, 2, 4, 6, 8, 10, and 12). Maps of 

the PPR statistic values for a selected parameter can be used 

to identify areas where prediction uncertainty would be most 

effectively decreased as a result of improved information about 

the parameter. The PPR values for all parameters in the Denver 

Basin model were averaged over all 184 predictions, and the 

resulting averages were used to rank the parameters. The 10 

parameters with the highest PPR statistic values (out of a total 

of 75 parameters) are listed in table C18, and maps of PPR 

statistic values for the four highest-ranked parameters (p12_10, 

p12_09, and pKa_11 ) are presented in figures C38–C40. The 

darkest colors on the maps of PPR statistics identify areas where 

additional information about the indicated parameter would 

most effectively decrease prediction uncertainty for hydraulic 

heads in the lower Arapahoe aquifer. Additional information about parameter p12_10 (hydraulic conductivity of the 

Laramie–Fox Hills aquifer at pilot point p12_10) would most 

reduce uncertainty of predicted heads in the lower Arapahoe 

aquifer in the eastern and southern parts of the basin (fig. C38). 

Additional information about parameter p12_09 (hydraulic 

conductivity of the Laramie–Fox Hills aquifer at pilot point 

p12_09) would most reduce uncertainty of predicted heads in 

the lower Arapahoe aquifer in the south-central part of the basin 

(fig. C39). Additional information about parameter pKa_11 

(hydraulic conductivity of the lower Arapahoe aquifer at pilot 

point pKa_11) would most reduce uncertainty of predicted 

heads in the lower Arapahoe aquifer in the eastern and northern 

parts of the basin (fig. C40).

Maps of the OPA statistic values for a selected parameter 

can be used to identify areas where parameter uncertainty 

would be most effectively decreased by adding an observation 

(in this case, a head observation). Figures C41–C44 illustrate 

OPA statistic values for the four highest-ranked parameters for 

potential additional head observations in the lower Arapahoe 

aquifer. The darkest colors on these maps identify areas where 

the standard deviation of the specified parameter would be most 

effectively decreased by an additional head observation. Results 

indicate additional head observations in the northern part of the 

basin would decrease parameter uncertainty for all four of the 

highest-ranked parameters. Additional observations in the lower 

Arapahoe aquifer in the south Denver metropolitan area and the 

Monument area, where future development and drawdown are 

anticipated, also would reduce parameter uncertainty.

Table C17. Denver Basin model predictive simulation stress periods.

Predictive

stress period

number

Beginning of 

stress period

End of 

stress period

Stress period 

length

(days)

1 January 1, 2004 December 31, 2008 1,826

2 January 1, 2009 December 31, 2013 1,826

3 January 1, 2014 December 31, 2018 1,826

4 January 1, 2019 December 31, 2023 1,826

5 January 1, 2024 December 31, 2028 1,826

6 January 1, 2029 December 31, 2033 1,826

7 January 1, 2034 December 31, 2038 1,826

8 January 1, 2039 December 31, 2043 1,826

9 January 1, 2044 December 31, 2048 1,826

10 January 1, 2049 December 31, 2053 1,826

Table C18. Parameters with the highest ranking parameter-prediction (PPR) statistic values from the Denver Basin model.

Rank Parameter 

name Parameter description

 Parameter-prediction 

statistic average value

(percent)

1 p12_10 Hydraulic conductivity of silt-plus-sand sized fraction of the Laramie–Fox Hills aquifer 

(model layer 12) at pilot point 10.

2.99

2 p12_11 Hydraulic conductivity of silt-plus-sand sized fraction of the Laramie–Fox Hills aquifer 

(model layer 12) at pilot point 9.

2.44

3 p12_09 Hydraulic conductivity of silt-plus-sand sized fraction of the Laramie–Fox Hills aquifer 

(model layer 12) at pilot point 11.

1.86

4 pKa_11 Hydraulic conductivity of silt-plus-sand sized fraction of the upper and lower Arapahoe 

aquifer (model layers 8 and 10) at pilot point 11.

1.74

5 SS_all Specific storage of bedrock aquifers. 1.03

6 Q_BR_MU Pumping-rate factor for bedrock municipal wells. 0.93

7 RCH_Qal Fraction of precipitation in areas where alluvial aquifer is the uppermost hydrogeologic 

unit that becomes recharge.

0.81

8 p6_04 Hydraulic conductivity of silt-sized and coarser fraction of Denver aquifer (model layer 6) 

at pilot point 4.

0.81

9 RCH_Resid Recharge rate applied for urban/suburban irrigation return flow. 0.51

10 p10_03 Hydraulic conductivity of silt-sized and coarser fraction of lower Arapahoe aquifer (model 

layer 10) at pilot point 3.

0.49
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 255

Figure C38. Parameter-prediction statistic (PPR) distribution for parameter p12_10.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

6 8

4

2

0

10

0

2

0

2 8

0

8

6

4

2

0

0

4

0

4

2

0 2

2

6

4

0

0

6 8

4

2

0

10

0

2

0

2 8

0

8

6

4

2

0

0

4

0

4

2

0 2

2

6

4

0

0

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Line of equal Prediction-Parameter (PPR) statistic for pilot 

 point P_12_10, in percent. Contour interval 2 percent

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)
256 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C39. Parameter-prediction statistic (PPR) distribution for parameter p12_09.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

4

2

8

6

0

-2

10

–2

0

6

0

2 0

8 4

0

0

2

0

–2

4

2

8

6

0

-2

10

–2

0

6

0

2 0

8 4

0

0

2

0

–2

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Line of equal Prediction-Parameter (PPR) statistic for pilot 

 point P12_09, in percent. Contour interval 2 percent

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 257

Figure C40. Parameter-prediction statistic (PPR) distribution for parameter pKa_11.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

2

4

0

0

2

0

0

0

2

0

2

4

0

0

2

4

0

0

2

0

0

0

2

0

2

4

0

0

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Line of equal Prediction-Parameter (PPR) statistic for pilot 

 point pKa_11, in percent. Contour interval 2 percent

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)
258 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C41. Observation-parameter (OPA) statistic distribution for parameter p12_10.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–2.4 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to –0.2

–0.2 to –0.1

–0.1 to –0.05

–0.05 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10) 

Observation parameter (OPA) statistic

 in model layer 10 for pilot point P12_10,

 in percent
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 259

Figure C42. Observation-parameter (OPA) statistic distribution for parameter p12_09.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–11.5 to –10

–10 to –8

–8 to –6

–6 to –4

–4 to –2

–2 to –1

–1 to –0.5

–0.5 to –0.2

–0.2 to –0.1

–0.1 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Observation parameter (OPA) statistic

 in model layer 10 for pilot point P12_09,

 in percent
260 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C43. Observation-parameter (OPA) statistic distribution for parameter pKa_11.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–2.2 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to –0.1

–0.1 to –0.05

–0.05 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Observation parameter (OPA) statistic

 in model layer 10 for pilot point pKa_11,

 in percent
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 261

Figure C44. Observation-parameter (OPA) statistic distribution for parameter p10_03.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–38 to –20

–20 to –10

–10 to –5

–5 to –2.5

–2.5 to –1

–1 to –0.5

–0.5 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Observation parameter (OPA) statistic

 in model layer 10 for pilot point P10_03,

 in percent
262 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Maps of the OPR statistic values can be used to identify 

areas where additional head observations likely would be most 

beneficial in reducing the uncertainty in the simulated potentiometric surface and drawdown. The OPR statistic values 

in the analysis were averaged over all 184 predictions, and a 

map of the values was prepared on a cell-by-cell basis for each 

model layer. Maps of the OPR statistic for the lower Arapahoe 

aquifer (fig. C45) and the Laramie–Fox Hills aquifer (fig. C46) 

indicate two general areas where additional head observations 

in the respective aquifer likely would reduce the uncertainty 

of the simulated potentiometric surface of the lower Arapahoe 

aquifer. One area is in the north-central part of the basin near 

the Adams and Weld County boundary, and the second area 

is in the south-central part of the basin where future development and drawdown are expected. Maps of OPR statistics for 

layers overlying the lower Arapahoe aquifer tend to have areas 

of high and low values in the same locations as for the lower 

Arapahoe (fig. C45).

Interpretation of the OPR statistic maps is aided by considering maps of the other statistics calculated by OPR-PPR. 

The OPR statistic combines uncertainty information about all 

parameters and all existing and potential observations. Reduction of uncertainty for a parameter with large areas of large 

PPR values (for example, fig. C38) will reduce the uncertainty 

of the predictions more than will reduction of uncertainty for 

a parameter with smaller PPR values. If comparing the OPA 

and PPR maps for a given parameter, no spatial correlation 

between areas of large OPA statistic and areas of large PPR 

statistic is apparent. However, the PPR maps do provide an 

indication of the degree to which the corresponding OPA distribution contributes to the OPR map; that is, parameters with 

large areas of large PPR values will cause the corresponding 

OPA distributions to be represented more prominently in the 

OPR distribution. For example, the area of large OPA values along the border between Adams and Weld Counties in 

figures C41–C44 is important to several parameters that rank 

high in PPR statistic value; as a result, this area shows up as 

the most prominent feature on the OPR map for the lower 

Arapahoe aquifer (fig. C45).

The maps resulting from the OPR analysis (figs. C45, 

C46) can be interpreted as showing areas where additional 

data would be most valuable in terms of reducing uncertainty 

of predicted heads in the Arapahoe aquifer; to use a common 

term, these are “data gap” areas. The largest and most prominent of these features is along the border between Adams and 

Weld Counties; less prominent features are in central Adams 

and north-central Elbert Counties. Each of these features of 

elevated OPR statistics is in or immediately adjacent to an 

area overlain by the alluvial aquifer. The elevated-OPR feature 

along the Adams-Weld border is closely associated with the 

alluvium of Box Elder Creek. The feature in central Adams 

County is at a location where the alluvium of the Lost Creek 

Basin connects with the alluvium of the Kiowa Creek Basin. 

The feature in north-central Elbert County is in and adjacent 

to the alluvium of West Bijou Creek. The association of large 

OPR statistic values with the alluvial aquifer in these areas is 

interpreted as an indication of uncertainty in the simulation of 

conditions at and adjacent to the bedrock/alluvium interface in 

these areas. Future modeling efforts likely would benefit from 

additional hydraulic-head data collection and more detailed 

characterization of hydraulic connection between alluvial and 

bedrock aquifers in these areas.

Comparisons Between Current 

and Previous Models

Differences in methods used to represent the hydrogeologic framework and hydrologic stresses complicate 

comparisons between the current Denver Basin model and 

previous models. However, some comparisons of the methods and results are warranted as general measures of how 

well the model fits the current conceptual understanding of 

the hydrologic system. Major refinements used in the current model compared to previous models included (1) a fully 

three-dimensional representation of the aquifer system, which 

includes explicit definition of all Denver Basin aquifer and 

confining layers; (2) explicit representation of the alluvial 

aquifer system as the uppermost layer in the model; (3) use of 

streamflow-routing simulation capabilities (SFR2, Niswonger 

and Prudic, 2005) to represent streams; (4) inclusion of 

evapotranspiration as a boundary condition (ETS, Banta, 

2000); and (5) updated pumping estimates to include pumping 

from the alluvial aquifer. In addition, recharge from urban and 

agricultural irrigation return flows is included in the current 

model, whereas previous models simulated only precipitation 

recharge.

The current 12-layer model explicitly represents the 

alluvial aquifer (model layer 1) and each of bedrock aquifers 

(6 model layers) and confining units (5 model layers). Previous models used a quasi-three-dimensional approach, which 

represented confining layers by using a vertical-conductance 

formulation. The current model assumes no vertical anisotropy 

within bedrock model layers, such that hydraulic conductivity of confining units controls vertical flow between model 

layers. Previous models used vertical-conductance variables 

to control vertical flow between bedrock aquifers. For the 

current study, the geometric mean of calibrated horizontal 

hydraulic-conductivity values (equal to vertical hydraulicconductivity values) for the Dawson and Denver confining 

units is about 3×10–5 ft/d (about 1.0×10–8 cm/s), and the 

values are in the range of values used by previous models 

(Robson, 1987; Colorado Division of Water Resources, 1998; 

table C19). The confining-unit hydraulic-conductivity values used in the present study also are in the range of vertical 

hydraulic conductivities reported by Barkmann (2004) and 

are considered reasonable values of low-conductivity materials for the current model. For the Laramie confining unit, 

Robson (1987) assumed zero vertical flow from the Arapahoe 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 263

Figure C45. Observation-prediction (OPR) statistic distribution for the lower Arapahoe aquifer.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Cree

L

k

ittle DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

0 to 0.005

0.005 to 0.01

0.01 to 0.02

0.02 to 0.05

0.05 to 0.075

0.075 to 0.1

0.1 to 0.125

0.125 to 0.145

Extent of active model cells

Observation prediction (OPR) statistic for

 model layer 10, in percent

Lower Arapahoe aquifer simulated extent 

 (model layer 10)
264 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C46. Observation-prediction (OPR) statistic distribution for the Laramie–Fox Hills aquifer.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

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!(

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

0 to 0.001

0.001 to 0.0025

0.0025 to 0.005

0.005 to 0.01

0.01 to 0.025

0.025 to 0.05

0.05 to 0.075

0.075 to 0.1

Laramie–Fox Hills aquifer simulated extent

 (model layer 12)

Extent of active model cells

Observation prediction (OPR) statistic for model

 layer 12, in percent
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 265

Table C19. Comparison of vertical hydraulic-conductivity values between the current and previous Denver Basin models.

[NA, not applicable – parameter not included in model; ft/d, feet per day; CDWR, Colorado Division of Water Resources]

Between aquifers

(confining unit in current model)

Current model 

calibrated values

(ft/d)

Robson (1987)

(ft/d)

Banta (1989)

(ft/d)

CDWR (1998)

(ft/d)

Upper Dawson–lower Dawson (Dawson confining unit) 1.4×10–5 NA NA 5.0×10–3

Dawson–Denver (Denver upper confining unit) 1.6×10–5 3.5×10–5 4.1×10–5 5.0×10–5

Denver–upper Arapahoe (Denver lower confining unit) 9.7×10–5 2.6×10–5 1.3×10–5 5.0×10–5

Upper Arapahoe–lower Arapahoe (Arapahoe confining unit) 1.3×10–3 NA NA 5.0×10–4

Arapahoe–Laramie–Fox Hills (Laramie confining unit 1.3×10–5 0 6.2×10–7 6.2×10–8

to the underlying Laramie–Fox Hills aquifer, while the 

CDWR SB96–74 model used a small, but non-zero, vertical 

hydraulic conductivity of 6.2×10–8 ft/d (Colorado Division of 

Water Resources, 1998). The calibrated hydraulic conductivity for the Laramie confining unit in the current model was 

1.3×10–5 ft/d, which allows a reasonable amount of downward 

flow of downward flow from the Laramie confining bed to the 

Laramie–Fox Hills aquifer (about 7 ft3/s for predevelopment 

conditions; fig. A54).

The differences among vertical hydraulic-conductivity 

values used by the various models, combined with variation 

in the methods used to simulate predevelopment recharge 

and evapotranspiration, affect the groundwater budget and 

interaquifer flow calculated by each model (table C20). For 

the Dawson aquifers and confining units, predevelopment 

inflow from the surficial system (precipitation recharge, 

streams, and the alluvial aquifer) recharge simulated by the 

current study (35.3 ft3/s) was about 14 percent less than the 

value of 40.6 ft3/s simulated by the Robson (1987) model and 

about 30 percent less than the values of 47.7 ft3/s simulated by 

the CDWR SB96–74 model; table C20). However, a revised 

model calibration of the CDWR SB96–74 model resulted in 

an inflow rate to the Dawson aquifers of 37 ft3/s (Colorado 

Division of Water Resources, 1998), which is within 5 percent 

of the current calibrated model. Predevelopment interaquifer 

flow from the Dawson aquifers and confining unit to the 

underlying Denver units computed by the current model was 

5.8 ft3/s, which is about 20 percent less than the value computed by the Robson model (7.2 ft3

/s) and about 50 percent 

less than the value computed by the CDWR SB96–74 model 

(9.4 ft3/s) (table C20). The water budget and interaquifer flow 

simulated by the current model for the Denver aquifer and 

confining units are about five times greater than the water budget and interaquifer flow simulated by previous models (table 

C20) because the current model simulates recharge from precipitation and historical agricultural irrigation return flows to 

the Denver aquifer and confining units. Previous models simulated only precipitation recharge. The increased recharge in the 

current model results in increased outflow to the surficial system and increased downward interaquifer flow from the Denver aquifer as compared to previous models. Unlike previous 

models, the current model also simulates evapotranspiration 

from the water table. The combination of increased recharge 

in historically irrigated areas and the associated increased discharge to evapotranspiration simulated by the current model 

results in a much larger total water budget for the current study 

(187 ft3/s) compared to the range for previous models (54.7 

to 60.9 ft3/s) (Colorado Division of Water Resources, 1998) 

(table C20). Furthermore, the increased recharge to the Denver 

aquifer simulated by the current model, in addition to the differences in vertical hydraulic conductivities, results in greater 

simulated downward interaquifer flow from the Denver to the 

Arapahoe aquifers in the current model than previous models 

for predevelopment conditions (table C20).

The representation and simulated interaction between 

bedrock groundwater, streams, and the alluvial aquifer is 

another substantial difference between the current and previous models. Previous models represented the alluvial aquifer 

as constant-head cells (Robson, 1987) or as head-dependentflow boundaries using the MODFLOW River Package 

(Harbaugh and others, 2000; Colorado Division of Water 

Resources, 1998); streams were not represented in previous 

models. The current model simulates the alluvial aquifer as the 

uppermost layer in the model and simulates streams using the 

MODFLOW Streamflow-Routing Package SFR2 (Niswonger 

and Prudic, 2005). The current model thus represents the 

surficial system of streams and the alluvial aquifer in a more 

detailed manner than previous bedrock-modeling studies. 

The current model simulates outflow to the surficial system 

of 52.8 ft3/s compared to outflow values of 54.7 ft3/s (Robson, 

1987) and 60.9 ft3/s (Colorado Division of Water Resources, 

1998) from previous models (table C21). Results from a 

second calibration of the CDWR SB96–74 model indicated 

outflow as low as 36.6 ft3/s (table C21). In addition to simulating a predevelopment outflow about 14 percent less than that 

by the CDWR SB96–74 first calibration model, the current 

model also simulates a different spatial distribution of outflow 

than previous models. The current model simulates about 

70 percent less outflow from the Dawson aquifers and confining unit and 70–75 percent more outflow from the Arapahoe 

and Laramie–Fox Hills aquifers and confining units than was 

simulated by the CDWR SB96–74 first calibration model 

(table C21).
266 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C20. Comparison of predevelopment groundwater budget for current and previous Denver Basin models. [For the current model, inflow equals flow from precipitation plus irrigation recharge, streams, and the alluvial aquifer; outflow equals flow to evapotranspiration, streams, springs, and the alluvial aquifer; see table A7 for the current model results. For previous models, inflow equals flow from precipitation recharge and the alluvial aquifer; outflow equals flow to the alluvial aquifer; ft3/s, cubic feet per second; CDWR, Colorado Division of Water Resources; negative interaquifer flow indicates outflow to underlying units; positive interaquifer flow indicates inflow from overlying units] Dawson aquifers and confining units Denver aquifer and confining units Arapahoe aquifers and confining units Laramie confining unit and Laramie–Fox Hills aquifer Total Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Inflow (ft3/s) 35.3 40.6 47.7 32.5 5.5 6.9 24.3 2.8 3.3 90.0 5.8 3.1 187 54.7 60.9 Outflow (ft3/s) 29.4 33.4 38.3 22.2 7.4 9.8 37.9 8.1 9.4 97.7 5.8 3.5 187 54.7 60.9 Outflow minus Inflow = Interaquifer flow (ft3/s) –5.8 –7.2 –9.4 –10.3 1.9 2.9 13.6 5.3 6.1 7.7 0 0.4 0 0 0
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 267

Model Uncertainty and Limitations 

The Denver Basin groundwater flow model simulates a 

reasonable conceptual understanding of regional hydrogeologic conditions to calculate temporal changes in groundwater 

availability since predevelopment. The present model represents the salient features of the Denver Basin aquifer system 

and provides an updated understanding of the flow system at 

a regional scale that is relevant to regional water-management 

decisions. However, as with any groundwater model, the 

Denver Basin simulations are subject to sources of uncertainty, 

which can include the temporal and spatial discretization of 

the model domain, representation of aquifer heterogeneity, and 

uncertainty in the data used to develop boundary conditions 

and calibration targets. Though the Denver Basin model used 

current modeling methods and software available at the time 

of the study, limitations of modeling software, data limitations, 

and assumptions made during model development and calibrations are all factors that may constrain appropriate use of this 

and all models (Bredehoeft, 2005).

The Denver Basin groundwater flow model simulates 

transient flow in the Denver Basin bedrock and alluvial 

aquifers using a temporal discretization designed to represent 

large-scale changes in hydrologic stresses from predevelopment (pre-1880) to 2003. Model stress periods range from 

2 to 27 years in length and were defined so as to represent 

large-scale temporal changes in precipitation, land use, and 

total pumping. The longer stress periods at the beginning 

of the simulation are considered adequate to represent early 

withdrawals because temporal changes in pumping were 

small. However, the model may not accurately represent 

detailed changes in precipitation before 1957 because the average annual precipitation distribution from 1930 to 2003 was 

applied to all pre-1957 stress periods. The model uses average 

annual rates for recharge, evapotranspiration, and well pumping and provides a reasonable representation of groundwater 

flows through time consistent with the current conceptual 

understanding of groundwater flow and with previous groundwater flow models of the basin. However, the use of multiyear 

stress periods does not allow simulation of seasonal changes in 

water use. Future model applications addressing issues related 

to seasonal groundwater flow conditions in the Denver Basin 

should consider more detailed temporal discretization because 

recharge, evapotranspiration, and well pumping do exhibit 

seasonality, reaching peak values during the summer irrigation 

season and minimal values during the winter.

Modeled areas are discretized into finite-difference grid 

cells for solution of the three-dimensional groundwater flow 

equation. For the Denver Basin model, the modeled area was 

divided into 1-mi2 grid cells in the horizontal direction. The 

1-mile grid spacing is consistent with previous modeling 

studies in the basin and was deemed necessary to expedite 

model computations. The 1-mile grid provides sufficient detail 

over most of the study area for this regional study but may 

not accurately represent the steep bedrock dip along some 

parts of the western basin margin or may not provide adequate 

spatial resolution for future site-specific modeling efforts. A 

finer spatial discretization using local grid-refinement (LGR) 

techniques (Mehl and Hill, 2005) could be used in areas where 

finer resolution of the model domain is needed.

The Denver Basin was subdivided into 11 bedrock layers 

and 1 overlying alluvial aquifer layer. The vertical discretization used by the current model is more detailed than previous 

models and is considered a substantial improvement over 

previous efforts because the entire volume of the groundwater system is explicitly represented in the model. The base 

altitude and thickness of each model layer were determined 

from an existing database of geophysical logs (Brian Ahrens, 

Colorado Division of Water Resources, written commun., 

2003). Sources of error in the geophysical log database include 

inaccurate land-surface altitudes, anomalous aquifer base 

altitudes, and variation in aquifer base altitude “picks” from 

the geophysical logs by the original interpretation. Geophysical logs were not reinterpreted for this study, although entries 

in the geophysical log database were examined for anomalies 

through geographic analysis. Aquifer-base altitudes were plotted and contoured using an inverse-distance-weighted method, 

which highlighted anomalous values. Altitudes considered 

anomalous were removed from the dataset before final contouring of the surfaces. The contoured aquifer-base altitudes 

were subsequently converted to a raster dataset, which was 

then processed using an area-weighted averaging scheme to 

derive a value for each 1-mi2 grid cell. While the methods used 

do not guarantee an error-free dataset, the resulting aquiferbase-altitude maps provide reasonable representations of the 

aquifer layering in the Denver Basin consistent with the conceptual understanding of geologic structure and stratigraphy.

The Denver Basin bedrock aquifers consist of a sequence 

of heterogeneous sandstones, siltstones, and claystones. The 

layering used in the present groundwater flow model represents some, but not all, of the heterogeneity inherent in the 

Denver Basin. Heterogeneity within each bedrock aquifer is 

represented by a varying hydraulic conductivity within the 

corresponding model layer. Hydraulic conductivity is varied 

in two ways for the bedrock aquifers. For the upper and lower 

Dawson aquifers, a constant value of hydraulic conductivity, 

Table C21. Comparison of predevelopment outflow to the surficial 

system (streams, springs, and the alluvial aquifer) from bedrock 

aquifers and confining units for the current and previous Denver 

Basin models.

[For the current model, outflow is the sum of outflow to streams, springs, and 

the alluvial aquifer. For previous models, outflow is to the alluvial aquifer; 

CDWR, Colorado Division of Water Resources; ft3/s, cubic feet per second]

Aquifer

Current

model

(ft3/s)

Robson

(1987)

(ft3/s)

CDWR

(1998), first 

calibration

(ft3/s)

CDWR

(1998), second

calibration

(ft3/s)

Dawson 11.1 33.4 38.3 20.7

Denver 6.8 7.4 9.8 5.2

Arapahoe 17.7 8.1 9.4 7.9

Laramie–Fox Hills 17.1 5.8 3.5 2.8

Total 52.8 54.7 60.9 36.6
268 Groundwater Availability of the Denver Basin Aquifer System, Colorado

derived from model calibration, is multiplied by an array of 

the silt-plus-sand fraction for the layer. The resulting distribution of hydraulic conductivity represents the conductive part 

of each bedrock aquifer (silt-plus-sand fraction). The silt-plussand fraction was calculated as the silt-plus-sand thickness 

values taken from the geophysical log database divided by 

aquifer thickness from the same geophysical log. Silt-plussand fractions were contoured, converted to a raster grid, and 

averaged onto the 1-mi2 grid cells to form a multiplier array in 

the groundwater flow model. For the Denver, Arapahoe, and 

Laramie–Fox Hills aquifers, a spatial distribution of hydraulic 

conductivity was developed by kriging hydraulic-conductivity 

values at pilot points that were derived from model calibration. 

The spatially variable hydraulic-conductivity distribution was 

then multiplied by the silt-plus-sand fraction for the layer to 

represent the conductive parts of the aquifers. Bedrock confining units were each assigned a single hydraulic-conductivity 

value based on model calibration and were assumed 

homogeneous.

While there are many possible ways to represent heterogeneity in the Denver Basin groundwater flow model, the 

methods used in this effort utilize the available lithologic 

and aquifer-testing data to the extent possible and provide a 

more detailed representation of aquifer properties than previous efforts. The current groundwater flow model in general 

provides reasonable representations of Denver Basin aquifer 

properties and stratigraphic features. For example, the Arapahoe aquifer in the south Denver metropolitan area has a greater 

thickness and hydraulic conductivity than in other parts of the 

basin owing to the presence of the subsurface Wildcat Mountain alluvial fan (Raynolds, 2002, 2004). The features representing the Wildcat Mountain alluvial fan are evident on maps 

of the Denver and lower Arapahoe aquifers, and the current 

model represents the fan as areas of high hydraulic conductivity in the Denver and lower Arapahoe aquifers consistent with 

the conceptual understanding of the system. Similarly, the 

model appropriately represents high hydraulic-conductivity 

zones in the Laramie–Fox Hills aquifer observed on the 

eastern edge of the basin. Future modeling efforts should 

consider additional data collection or refinement of model 

parameters in areas where the model did not achieve a good 

fit between transient simulated and observed hydraulic heads. 

For example, large simulated drawdown in the upper Dawson 

aquifer east of Parker was not observed in the CDWR waterlevel data, and the model appears to underestimate drawdown 

in the lower Arapahoe aquifer compared to the CDWR waterlevel data. South of Monument, observed water-level rise for 

wells completed in the Denver and lower Arapahoe aquifers, 

presumably in response to increased urban recharge, is not 

well represented in the model. These discrepancies between 

simulated and observed hydraulic heads indicate the need 

for additional water-level data collection or refinement of the 

hydraulic-conductivity distribution and pumping estimates for 

the affected areas.

Various data types were used to develop boundary 

conditions for the Denver Basin model and some uncertainty 

is inherent in these data. Estimates of recharge are based on 

precipitation data, land-use data, and recharge estimates from 

previous studies. Estimates of recharge from precipitation 

are reasonable and consistent with previous studies. However, additional field studies on agricultural and urban irrigation return-flow rates could improve estimates of irrigation 

recharge. Evapotranspiration is a simulated value based on 

a piecewise linear function relating evapotranspiration rate 

to depth to the water table, and while the simulation results 

are considered reasonable. Estimates of discharge from wells 

are made on the basis of well permits on file in the Colorado 

Division of Water Resources well-permit database. The location, depth, type, and dates of use for each well in the database 

were used to locate the well within the model grid, and pumping rates were assigned using methods from previous studies. 

This study followed methodology used by previous Denver 

Basin modeling studies to develop the pumping estimates, and 

the results are considered accurate to plus or minus 30 percent 

(Colorado Division of Water Resources, 1998). Sources of 

error in the pumping estimates include inadequacies in the 

well-permit database as well as assumptions regarding perwell pumping rates.

The data used to develop model-calibration targets are 

another source of uncertainty in the Denver Basin model. Two 

data types were used as calibration targets—water-level measurements and flow estimates from stream base-flow determinations and historical flowing wells. The water-level data are, 

in general, accurate to the accuracy level of the land-surface 

altitude determination and were most heavily relied upon in 

model calibration. All flow observations are estimated values, 

and are not considered accurate. In order to maximize the 

influence of head observations and minimize the influence of 

flow observations on parameter values, assigned observation 

weights were greater for the head observations than for the 

flow observations.

The Denver Basin model was designed to primarily 

evaluate groundwater availability in the bedrock aquifer system. The alluvial aquifer system was included as the uppermost model boundary to represent interaction between the 

bedrock system and the surficial hydrologic system. While this 

representation provides more detailed analysis of groundwater/

surface-water interaction than previous models, representation of the alluvial aquifer is generalized in the Denver Basin 

model, and the model may not be suitable for detailed modeling investigations of the alluvial aquifer. For example, because 

a 1-mile grid spacing was used in the model, the area of the 

alluvial aquifer included in the model was limited to the extent 

of alluvium in present-day stream channels where the alluvium width is greater than one-half mile. In addition, detailed 

representations of surficial water features and flow such as 

streamflow routing, wastewater discharge, irrigation return 

flows, and irrigation ditches were not explicitly included in the 

Denver Basin model. Instead, estimates of water derived from 

these surficial sources were included as urban and agricultural 

recharge to the model. A detailed groundwater flow model of 

the South Platte alluvial aquifer and its tributaries is currently 

(2010) being developed by the CWCB as part of the South 

Platte Decision Support System, which does include detailed 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 269

groundwater/surface-water interaction between the alluvial 

aquifer and surface-water delivery systems (Colorado Water 

Conservation Board, 2008).

The Denver Basin groundwater flow model provides 

an updated representation of groundwater flow conditions in 

the study area from predevelopment through 2003 by using 

justifiable aquifer properties and boundary conditions. The 

current model is considered an improvement over previous 

models because, unlike previous models, it explicitly represents confining layers and the alluvial aquifer. The current 

model also represents temporal changes in pumping, recharge, 

and evapotranspiration in a more detailed manner and includes 

more calibration targets than previous models. A good model 

fit was achieved to the head observations, although the fit to 

estimates of stream base flow and historical flowing wells was 

less satisfactory. The Denver Basin model is a data-analysis 

tool well suited for evaluating temporal changes to regional 

groundwater flow conditions and directions, making predictions of changing conditions into the near future, and guiding 

future detailed investigations in the study area. The use of 

parameter-estimation techniques facilitated statistical evaluation of the model calibration and predictions.

Future Model Maintenance 

and Applications

The refinements of the present Denver Basin model over 

previous models and areas for improvement in the current 

model highlight the need for recurring model maintenance and 

updates. As additional data, modeling techniques, and conceptual understanding develop, the Denver Basin model and the 

groundwater availability conclusions made from the results 

will require updates and revision. The underlying data and 

supporting computer programs can be refreshed on a regular 

basis to update groundwater availability results with sufficient 

frequency so that water-management decisions can respond to 

changing climatic and anthropogenic conditions.

The ability of the Denver Basin model to represent 

realistic hydrologic conditions could be improved upon in 

several ways related to the model calibration and the availability of modeling tools. As additional geologic, hydrologic, and 

aquifer property data are compiled, further refinement of the 

model layering, parameterization of aquifer properties, and the 

resulting effects on model calibration may need reconsideration. For example, additional parameter estimation techniques 

such as more detailed pilot-point analysis might be useful to 

further refine hydraulic-conductivity distributions and improve 

model fit between transient simulated and observed hydraulic 

heads in parts of the aquifer system. Refined pumping estimates from measured discharge would produce more accurate 

model results, and additional monitoring observations could 

be used to refine the model calibration. While the match 

between simulated and observed hydraulic heads was quite 

good, the match between simulated and observed flows was 

less satisfactory. Parameter sensitivity results indicate that the 

simulated flows are most sensitive to parameters representing 

the percentage of precipitation recharge to the Dawson aquifer 

(RCH_Tdw), hydraulic conductivity of the upper Dawson 

aquifer (K_utdw), and the hydraulic conductivity of streambed materials in tributaries (SFR_TRIBS). Because the flow 

observations were derived from a limited set of streamflow 

measurements, additional streamflow data and(or) refinement 

of the parameters affecting streamflow calculations might 

improve the model fit to the observed flows.

Improved modeling tools, which could separate individual water-budget components, would be beneficial to refine 

interpretations of modeling results. For example, the ability 

to separate recharge sources in model input and output would 

support calculations separating precipitation and irrigation 

return-flow recharge in the water budget. Similarly, the ability 

to separate calculations of confined and unconfined storage 

depletion in model output would further the understanding of 

storage depletion rates in the basin. Further temporal discretization could be used to examine seasonal patterns of pumping, 

precipitation, and irrigation, and a finer spatial discretization 

using local grid-refinement (LGR) techniques (Mehl and Hill, 

2005) could be used in areas where finer resolution of the 

model domain is needed.

The Denver Basin model is designed to evaluate longterm regional changes in groundwater availability and thus is 

well suited for future regional applications such as optimization modeling, particle-tracking simulations of groundwater 

age, and coupling with more detailed models of the surficial 

system. Optimization modeling involves evaluating watermanagement strategies to meet optimization criteria such as 

maximizing pumping while minimizing drawdown or storage 

depletion (Ahlfeld and others, 2005). Optimization modeling 

is an appropriate use of the Denver Basin model because the 

effects of changing pumping conditions can be evaluated on 

a regional scale. Optimization modeling also can incorporate 

the effects of conjunctive-use projects such as aquifer-storageand-recovery (ASR) efforts. Particle-tracking simulations using 

MODPATH (Pollack, 1994) and related tools could be used for 

calculating advective traveltimes from recharge to discharge 

areas and for delineating zones of capture for wells of interest 

(for example, Paschke, 2007). Coupling of the Denver Basin 

model with a surface-water or watershed model such as the 

Precipitation-Runoff Modeling System (Leavesley and others, 

1983) could allow more detailed analysis of groundwater/surface-water interaction and precipitation recharge. The Colorado 

Water Conservation Board is currently (2010) calibrating a 

groundwater flow model of the alluvial aquifer of the South 

Platte River and its tributaries (Colorado Water Conservation Board, 2008). Software utilities were developed for this 

study (Banta and others, 2008), which allow flows for bedrock 

discharge to alluvial aquifers calculated by the Denver Basin 

model to be imported to the South Platte alluvial-aquifer model. 

However, formal linking of the Denver Basin model with a 

detailed model of the South Platte alluvial aquifer and streams 

could provide a more refined representation of groundwater/

surface-water interaction in the basin.
270 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Summary

Groundwater flow in the Denver Basin bedrock aquifers and overlying alluvial aquifer is simulated with a threedimensional groundwater flow model to provide a framework 

for analysis of aquifer and confining bed materials, hydrologic 

stresses, field observations of past hydrologic conditions, and 

predictions of future hydrologic conditions. The model uses 

the U.S. Geological Survey (USGS) modular finite-difference 

groundwater flow modeling program MODFLOW-2000 and 

includes several enhancements over previous modeling efforts 

because of additional data availability, improved modeling 

capabilities, and improved computer technology.

The Denver Basin model grid encompasses the Denver Basin bedrock aquifer system and immediately adjacent 

areas of the alluvial aquifer of the South Platte River with 

84 columns and 124 rows of square cells; each cell measures 

1 mile by 1 mile. A fully three-dimensional approach was used 

to simulate lateral and vertical flow and storage changes in 

all hydrogeologic units of the aquifer system. Each of the six 

bedrock aquifers, five bedrock confining units, and the alluvial 

aquifer are explicitly represented in the model with aquifer 

base altitudes defined from geophysical logs and geologic 

mapping from previous work. The alluvial aquifer is simulated 

as unconfined, the bedrock aquifers are simulated as convertible from confined to unconfined, and the bedrock confining 

units are simulated as confined. The model simulates steadystate conditions prior to 1880 and transient groundwater 

conditions from 1880 through 2003 using 16 stress periods of 

durations ranging from 2 to 27 years.

Horizontal hydraulic conductivity for the bedrock units is 

represented in the model by using several adjustable parameters whose values were calibrated through parameter estimation. Vertical hydraulic conductivity was assumed equal to 

horizontal hydraulic conductivity in the bedrock units, such 

that resistance to vertical flow among the bedrock aquifers is 

primarily controlled by the hydraulic conductivity of the confining units. For model layers representing the Denver, Arapahoe, and Laramie–Fox Hills aquifers, hydraulic-conductivity 

parameterization used the pilot-point approach. Pilot points are 

locations in the model where a parameter, hydraulic conductivity in this study, is calibrated by parameter estimation. The 

estimated parameter values at pilot points are then interpolated 

between locations within a model layer to assign a parameter 

(hydraulic conductivity) distribution to the layer. Finally, the 

calibrated hydraulic-conductivity values for each layer were 

multiplied by the percent of coarse-grained materials (siltplus-sand fraction) for each model cell to obtain an equivalent hydraulic conductivity for the overall aquifer thickness 

represented by each cell. For the Denver Basin, the pilot-point 

approach worked well because it allowed the model to represent gradational, rather than abrupt hydraulic-conductivity 

distributions across the basin consistent with basin stratigraphy. For the alluvial aquifer, horizontal hydraulic conductivity 

was assigned a value of 200 ft/d for the alluvial aquifer in the 

South Platte River Basin and a value of 5 ft/d for the alluvial 

aquifer in the Big Sandy and Black Squirrel Creek Basins. 

The ratio of horizontal to vertical hydraulic conductivity 

for the alluvial aquifer in the South Platte River Basin was 

represented by an adjustable parameter whose final value (9.9) 

was determined through model calibration. A fixed parameter 

value of 10 was assigned to the ratio of horizontal to vertical 

hydraulic conductivity for the alluvial aquifer in the Big Sandy 

and Black Squirrel Creek Basins.

Aquifer storage properties of specific storage for confined 

units and specific yield for unconfined units were represented 

in the model by using several estimated and assigned 

parameters. Specific storage was represented by using two 

adjustable parameters. One specific-storage parameter was 

estimated for the model layers representing aquifers, and one 

specific-storage parameter was estimated for the model layers 

representing confining units. The final calibrated specificstorage values of 5.2×10–7/ft for aquifers and 1.7×10–6/ft for 

confining units are in the range of reasonable values for materials in the Denver Basin. Specific-yield values were assigned 

for each aquifer unit based on previous field studies in the 

basin and were multiplied by the percentage of coarse-grained 

materials (silt-plus-sand fraction) for each model cell to obtain 

an equivalent specific yield for the overall aquifer thickness 

represented by each cell.

Hydrologic stresses simulated by the model include 

recharge from precipitation plus irrigation return flows, evapotranspiration, streams, springs, reservoirs, pumping wells, 

interaquifer flow, flow across basin boundaries, and storage. 

The percentage of precipitation becoming recharge was represented in the model by using several adjustable parameters 

whose values were calibrated through parameter estimation. 

Model-calibration results indicate about 1 to 2 percent of 

precipitation becomes recharge to the bedrock aquifers, and 

an estimated 7 percent of precipitation becomes recharge to 

the alluvial aquifer. Recharge rates in irrigated areas were 

assigned values of 2.5 in/yr for urban irrigation return flows 

(urban recharge) and 10 in/yr for agricultural irrigation return 

flows. The recharge rates attributed to urban and agricultural 

return flows were uniformly applied within an affected zone, 

but the areas of urbanization and irrigated agriculture over 

which they were applied increased over time, as defined by 

satellite imagery and land-use maps. Evapotranspiration was 

simulated using a piecewise linear function in which evapotranspiration decreased as depth to groundwater increased 

over the entire modeled area. Streamflow was simulated using 

the SFR2 Package, reservoirs were represented using the RIV 

Package, and springs were simulated with the DRN Package. 

Flow across the southern basin boundary was simulated using 

the GHB Package and across the northeast basin boundary 

using the FHB Package. Pumping was simulated using the 

WEL and MNW Packages and was estimated for each aquifer 

model layer on the basis of well locations, depths, and water 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 271

use taken from the Colorado Division of Water Resources 

well-permit database as described in Chapter B. The GMG 

Package and an alternative adaptive damping method were 

used to solve the highly nonlinear system of finite-difference 

equations, which provided a solution in a reasonable execution 

time and with a relatively small number of deactivated cells.

The Denver Basin model was calibrated using nonlinear 

regression methods as implemented in the parameter estimation program PEST in combination with manual adjustments 

to parameters that proved resistant to calibration by automated 

methods. Seventy-seven parameters were included in the 

model, 52 of which were adjusted during parameter estimation 

and 25 of which had assigned values. Estimated parameters 

included hydraulic conductivity and recharge parameters. The 

model-calibrated distributions of aquifer hydraulic conductivity and recharge are consistent with previous data, previous 

modeling efforts, and the hydrogeologic conceptual model. 

Calibrated hydraulic-conductivity values for various model 

layers also are in appropriate relative proportion to each 

other, which is consistent with the hydrogeologic conceptual 

understanding.

Model fit was evaluated by comparing model-computed 

heads and flows to observed values. A total of 4,984 transient 

head observations from 1883 through 2003, 147 base-flow 

observations from 1941 through 2003, and 20 flow observations from historical flowing wells were used to calibrate the 

model. The model is well calibrated to the transient heads 

with a mean head residual of –16 ft and a RMSE of 85 ft, 

which is approximately 3 percent of the 3,024-ft range of 

head observations in the model. The head residuals appear 

to be independent of measured head and do not appear to be 

spatially correlated across the study area. Plots of simulated 

water levels over time (hydrographs) compared to observed 

values from the CDWR water-level network indicate a good 

match between transient simulated hydraulic heads for the 

lower Dawson, Denver, and Laramie–Fox Hills aquifer. The 

poor match between transient simulated hydraulic heads 

and observed heads for CDWR water-level monitoring sites 

in the northeastern part of the upper Dawson aquifer, the 

lower Arapahoe aquifer, and the Denver and lower Arapahoe 

aquifers south of Monument indicates areas where additional 

water-level data collection and(or) model parameter refinement might improve model fit. The weighted-flow residuals are biased positively, indicating simulated flows are, in 

general, less than the observations. Flow observations were 

assigned small weights in the nonlinear regression to minimize the effects of inaccurate flow observations on estimated 

model parameters.

Composite scaled sensitivities indicate simulated 

equivalents of observations were most sensitive to estimated 

parameters that control percent precipitation recharged to the 

Dawson and alluvial aquifers, vertical anisotropy within the 

bedrock units, specific storage of the bedrock aquifers, and 

pumping rates for wells with the greatest assigned production. 

Composite scaled sensitivity values computed from the flow 

observations indicate that the simulated flows are most sensitive to parameters representing the percentage of precipitation 

recharge to the Dawson aquifer, hydraulic conductivity of 

the upper Dawson aquifer, and the hydraulic conductivity of 

streambed materials in tributaries. Additional data collection 

or refinement of these parameter values might improve the 

model fit to the observed flows.

Two predictive scenarios were simulated with the 

calibrated Denver Basin model to calculate predictive model 

sensitivities and to demonstrate use of the model for predictive analysis. Predictive simulations were run 50 years 

into the future from the end of the model calibration period 

(December 31, 2003) to 2053 and were divided into ten 5-year 

stress periods. The predictive simulations lend insight to longterm effects of continued pumping on the groundwater system, 

although they are not considered definitive predictions of 

future conditions.

One benefit of the automated techniques used to calibrate 

the Denver Basin model is that the results can be used in an 

analysis of the relations among uncertainties in parameters, 

observations, and predictions. For the Denver Basin model, 

the potentiometric surface for the lower Arapahoe aquifer at 

the end of the prediction period (2053) is of particular predictive interest because of its importance as a water supply. 

The Observation-Prediction (OPR) and Parameter-Prediction 

(PPR) statistics were calculated for a subset of cells in this 

model layer (10) to identify prediction uncertainty and the 

effects of additional observations on predictions. Maps of 

the PPR statistic values for a selected parameter were used 

to identify areas where prediction uncertainty would be most 

effectively decreased as a result of improved information 

about the parameter. Maps of the OPA statistic values for a 

selected parameter were used to identify areas where parameter uncertainty would be most effectively decreased by adding 

observations (in this case, head observation). Maps of the OPR 

statistic values were used to identify areas where additional 

head observations likely would be most beneficial in reducing 

the uncertainty in the model-calculated potentiometric surface 

and drawdown. An OPR statistic map for the lower Arapahoe 

aquifer indicates additional observations in aquifer layers in 

the north-central and south-central parts of the basin would 

likely reduce uncertainty in the model-calculated potentiometric surface of the lower Arapahoe aquifer.

Comparisons between the current and previous Denver 

Basin models highlight the differences and similarities among 

the models. Major refinements used in the present model 

compared to previous models included (1) a fully threedimensional representation of the aquifer system, (2) explicit 

representation of the alluvial aquifer, (3) use of streamflowrouting capabilities, (4) inclusion of evapotranspiration as a 

boundary condition, (5) updated pumping estimates to include 

pumping from the alluvial aquifer, and (6) recharge from 

urban and agricultural irrigation. The current model is considered an improvement over previous models because it includes 

these model refinements.
272 Groundwater Availability of the Denver Basin Aquifer System, Colorado

The Denver Basin groundwater flow model developed for 

this study provides an updated representation of groundwater 

flow conditions from 1880 through 2003 by using reasonable 

aquifer properties and boundary conditions. The current model 

also represents temporal changes in recharge, evapotranspiration, and well pumping in a more detailed manner and 

includes more calibration targets than previous models. The 

model is well suited for evaluating changing regional groundwater flow directions and water budgets through time in the 

Denver Basin, making predictions of changing conditions into 

the near future, and guiding future detailed investigations in 

the study area. The refinements of the present Denver Basin 

model over previous models highlight the need for recurring 

model maintenance and updates. As additional data, modeling techniques, and conceptual understanding develop, the 

Denver Basin model and the groundwater availability conclusions made from the results will require updates and revision 

to support water-management decisions made in response to 

changing climatic and anthropogenic conditions.

References

Ahlfeld, D.P., Barlow, P.M., and Mulligan, A.E., 2005, GWM—

A ground-water management process for the U.S. Geological 

Survey modular ground-water model (MODFLOW-2000): 

U.S. Geological Survey Open-File Report 2005–1072, 124 p.

Anderson, M.P., and Woessner, W.W., 1992, Applied groundwater modeling: San Diego, Calif., Academic Press, Inc., 

381 p.

Argus Holdings, Ltd., 1992–99, Argus One user’s guide, 

Argus Open Numerical Environments—A GIS modeling 

system, version 4.0: Jericho, New York, Argues Interware, 

Inc., variously paginated.

Banta, E.R., 2000, MODFLOW-2000, the U.S. Geological 

Survey modular ground-water model—Documentation 

of packages for simulating evapotranspiration with a segmented function (ETS1) and drains with return flow (DRT1): 

U.S. Geological Survey Open-File Report 2000–466, 127 p.

Banta, E.R., 2006, Modifications to MODFLOW boundary conditions and an adaptive-damping scheme for 

Picard iterations for a highly nonlinear regional model, 

in Poeter, Eileen, Hill, Mary, and Zheng, Chunmiao, eds., 

MODFLOW and more, 2006—Managing ground-water 

systems: International Groundwater Modeling Center and 

Colorado School of Mines, 2006 [Proceedings, Golden, 

Colo.], p. 596–600.

Banta, E.R., Paschke, S.S., and Litke, D.W., 2008, User guide 

and documentation for five MODFLOW ground-water modeling utility programs: U.S. Geological Survey Techniques 

and Methods 6–A28, 24 p.

Barkmann, P.E., 2004, Vertical hydraulic conductivity measurements in the Denver Basin, Colorado: The Mountain 

Geologist, v. 41, no. 4, p. 169–183.

Bredehoeft, John, 2005, The conceptualization model problem 

– surprise: Hydrogeology Journal, v. 13, p. 37–46.

Buckles, D.R., and Watts, K.R., 1988, Geohydrology, water 

quality, and preliminary simulations of ground-water flow 

of the alluvial aquifer in the upper Black Squirrel Creek 

basin, El Paso County, Colorado: U.S. Geological Survey 

Water-Resources Investigations Report 88–4017, 49 p.

Certes, Catherine, and deMarsily, G., 1991, Application of the 

pilot point method to the identification of aquifer transmissivities: Advances in Water Resources, v. 14, no. 5. p. 

284–300.

Colorado Division of Water Resources, 1998, Denver Basin 

and South Platte River Basin Technical Study, Final Report, 

Colorado Senate Bill 96–074, variously paged.

Colorado Division of Water Resources, 2003, Ground water 

levels in the Denver Basin bedrock aquifers: Colorado Division of Water Resources 2003 annual report, 132 p.

Colorado Division of Water Resources, 2004, Ground water 

levels in the Denver Basin bedrock aquifers: Colorado Division of Water Resources 2004 annual report, 132 p.

Colorado Division of Water Resources, 2005, Hydrobase data 

set: Analysis/query tools, Statewide, 07/01/2005: 1 DVD.

Colorado Water Conservation Board, 2008, SPDSS Phase 4, 

Task 48.2 Development of calibration targets and criteria 

– final, 31 p., accessed September 20, 2009, at ftp://dwrftp.

state.co.us/cdss/gwm/tm/SPDSS_48_2_20081008.pdf.

Darton, N.H., 1905, Preliminary report on geology and underground water resources of the central Great Plains: U.S. 

Geological Survey Professional Paper 32, 433 p.

Davis, J.C., 1986, Statistics and data analysis in geology: New 

York, John Wiley and Sons, Inc., 646 p.

de Marsily, G., Lavedan, G., Boucher, M., and Fasanino, G., 

1984, Interpretation of interference tests in a well field using 

geostatistical techniques to fit the permeability distribution 

in a reservoir model, in Verly, G., and others, eds., Geostatistics for natural resources characterization, part 2: Dordrecht, Holland, Reidel Publishing Company, p. 831–849.

Doherty, John, 2001, Using pilot points and regularization in ground-water model calibration, in Seo, H.S., 

Poeter, Eileen, Zheng, Chunmiao, and Poeter, Onna, eds., 

MODFLOW 2001 and other modeling odysseys, 2001, 

Proceedings: [Golden, Colo.], International Groundwater 

Modeling Center, Colorado School of Mines, and 

U.S. Geological Survey, p. 181–187.

Doherty, John, 2003, Ground-water model calibration using 

pilot points and regularization: Groundwater, v. 41, no. 2, 

p. 170–177.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 273

Doherty, John, 2006, PEST—Model-independent parameter 

estimation user manual, 5th ed.: Corinda, Australia, Watermark Numerical Computing, variously paginated, accessed 

September 17, 2010, at http://www.pesthomepage.org/.

Emmons, S.F., Cross, Whitman, and Eldridge, G.H., 1896, 

Geology of the Denver Basin: U.S. Geological Survey 

Monograph 27, 556 p., 31 pls.

Environmental Systems Research Institute, Inc., 1999–2004a, 

ArcGIS 9.2, accessed January 1, 2004, at http://www.esri.com/.

Environmental Systems Research Institute, Inc., 1999–2004b, 

ArcInfo 9.0, accessed January 1, 2004, at http://www.esri.com/.

Garmin Ltd., 2004, MapSource trip and waypoint manager, version 6.0: Olathe, Kansas, Garmin Ltd., accessed January 1, 

2004, at http://www.garmin.com/garmin/cms/site/us.

Halford, K.J., and Hanson, R.T., 2002, User guide for the 

drawdown-limited, Multi-Node Well (MNW) package for the 

U.S. Geological Survey’s modular three-dimensional finitedifference ground-water flow model, versions MODFLOW-96 

and MODFLOW-2000: U.S. Geological Survey OpenFile Report 2002–293, 33 p., accessed August 31, 2009, 

at http://pubs.er.usgs.gov/usgspubs/ofr/ofr02293.

Harbaugh, A.W., 1990, A computer program for calculating subregional water budgets using results from the 

U.S. Geological Survey modular three-dimensional groundwater flow model: U.S. Geological Survey Open-File 

Report 90–392, 46 p.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to modularization concepts and the groundwater flow process: U.S. Geological Survey Open-File Report 2000–92, 121 p.

Hill, M.C., 1998, Methods and guidelines for effective model 

calibration: U.S. Geological Survey Water-Resources Investigations Report 98–4005, 90 p.

Hill, M.C., Banta, E.R., Harbaugh, A.W., and Anderman, 

E.R., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to the observation, sensitivity, and parameter-estimation processes and 

three post-processing programs: U.S. Geological Survey 

Open-File Report 2000–184, 209 p. 

Hill, M.C., and Tiedeman, C.R., 2007, Effective groundwater model calibration, with analysis of data, sensitivities, 

predictions, and uncertainty: Hoboken, New Jersey, Wiley, 

455 p.

Hurr, R.T., Schneider, P.A., and others, 1972, Hydrogeologic 

characteristics of the valley-fill aquifer in the Greeley reach 

of the South Platte River Valley, Colorado: U.S. Geological 

Survey Open-File Report 73–124, 2 p.

Konikow, L.F., and Neuzil, C.E., 2007, A method to estimate groundwater depletion from confining layers: Water 

Resources Research, v. 43, W07417, 15 p.

Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, 

L.G., 1983, Precipitation-Runoff Modeling System—User’s 

manual: U.S. Geological Survey Water-Resources Investigations 83–4238, 207 p.

McAda, D.P., and Barroll, Peggy, 2002, Simulation of groundwater flow in the middle Rio Grande basin between Cochiti 

and San Acacia, New Mexico: U.S. Geological Survey 

Water-Resources Investigations Report 2002–4200, 81 p.

Mehl, S.W., and Hill, M.C., 2001, MODFLOW-2000, The 

U.S. Geological Survey modular ground-water model—

User guide to the Link-AMG (LMG) package for solving 

matrix equations using an algebraic multigrid solver: 

U.S. Geological Survey Open-File Report 2001–177, 33 p.

Mehl, S.W., and Hill, M.C., 2005, MODFLOW-2005, the 

U.S. Geological Survey modular ground-water model—

Documentation of shared node Local Grid Refinement 

(LGR) and the Boundary Flow and Head (BFH) Package: 

U.S. Geological Survey Techniques and Methods 6–A12, 

68 p.

Murphy, S.F., Barber, L.B., Verplanck, P.L., and Kinner, D.A., 

2003, Chapter 1 – Environmental setting and hydrology of 

the Boulder Creek watershed, Colorado, in Murphy, S.F., 

Verplanck, P.L., and Barber. L.B., eds., Comprehensive water 

quality of the Boulder Creek watershed, Colorado, during 

high-flow and low-flow conditions, 2000: U.S. Geological 

Survey Water-Resources Investigations Report 2003–4045, 

p. 5–26.

Nadler, C.T., and Schumm, S.A., 1981, Metamorphosis of 

South Platte and Arkansas Rivers, eastern Colorado: Physical Geology, v. 2, no. 22, p. 95–115.

National Oceanic and Atmospheric Administration, 2004, 

1931–2003, Monthly surface data for Colorado, accessed 

October 29, 2004, at http://www.ncdc.noaa.gov/oa/ncdc.html.

Niswonger, R.G., and Prudic, D.E., 2005, Documentation 

of the Streamflow-Routing (SFR2) package to include 

unsaturated flow beneath streams—A modification to SFR1: 

U.S. Geological Survey Techniques and Methods 6–A13, 

48 p.

Paschke, S.S., 1992, Evaluating the hydrogeology of the 

Pleistocene Nussbaum Alluvium, Colorado, using vertical 

variability analysis and numerical modeling: Golden, Colorado School of Mines, Unpublished Master of Engineering 

Report, 152 p.

Paschke, S.S., ed., 2007, Hydrogeologic settings and groundwater flow simulations for regional studies of the transport 

of anthropogenic and natural contaminants to public-supply 

wells—Studies begun in 2001: U.S. Geological Survey 

Professional Paper 1737–A, 244 p.
274 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Poeter, E.P., Hill, M.C., Banta, E.R., Mehl, Steffen, and 

Christensen, Steen, 2005, UCODE_2005 and six other 

computer codes for universal sensitivity analysis, calibration, and uncertainty evaluation: U.S. Geological Survey 

Techniques and Methods 6–A11, 283 p.

Pollock, D.W., 1994, User’s guide for MODPATH/MODPATHPLOT, version 3—A particle tracking post-processing package 

for MODFLOW, the U.S. Geological Survey finite-difference 

ground-water flow model: U.S. Geological Survey Open-File 

Report 94–464, 6 chaps.

Raynolds, R.G., 2002, Upper Cretaceous and Tertiary stratigraphy of the Denver Basin, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 111–134.

Raynolds, R.G., 2004, Stratigraphy and water levels in the 

Arapahoe aquifer, Douglas County area, Denver Basin, Colorado: Rocky Mountain Geologist, v. 41, no. 4, p. 195–210.

Riverside Technology, Inc., 2005, SPDSS 2001 Division 1 

ditch service areas: Online data accessed October 11, 2006, 

at http://cdss.state.co.us/DNN/GIS/tabid/67/Default.aspx.

Robson, S.G., 1987, Bedrock aquifers in the Denver Basin, 

Colorado—A quantitative water-resources appraisal: 

U.S. Geological Survey Professional Paper 1257, 73 p.

Robson, S.G., and Banta, E.R., 1990, Determination of specific storage by measurement of aquifer compression near a 

pumping well: Groundwater, v. 28, no. 6, p. 868–874.

Tonkin, M.J., Tiedeman, C.R., Ely, D.M., and Hill, M.C., 2007, 

OPR–PPR, a computer program for assessing data importance to model predictions using linear statistics: U.S. Geological Survey Techniques and Methods 6–E2, 115 p.

U.S. Geological Survey, 1973–1979, Landsat MSS scenes, 

WRS-1, P35R32, P35R33, P36R32, P36R33: Sioux Falls, 

South Dakota.

U.S. Geological Survey, 1989, Digital line graphs from 

1:100,000 scale maps: Data Users Guide #2, Reston, Va.

U.S. Geological Survey, 1999a, National altitude dataset: 

U.S. Geological Survey Fact Sheet 148–99, http://erg.usgs.gov/

isb/pubs/factsheets/fs14899.html.

U.S. Geological Survey, 1999b, USGS digital raster graphics: 

accessed November 23, 2004, at http://topomaps.usgs.gov/drg/.

U.S. Geological Survey, 1999–2000, Enhanced Landsat 

mosaic of Colorado: Sioux Falls, South Dakota.

U.S. Geological Survey, 2001a, Coverage LU30—Highresolution land use and land cover 1937/1938 Front Range 

Infrastructure Resources Project Demonstration Area, 

Version 1.0, April 5, 2001: U.S. Geological Survey Rocky 

Mountain Mapping Center, Lakewood, Colo., accessed 

November 23, 2004, http://rockyweb.cr.usgs.gov/frontrange/

NMD/data/lu30.html.

U.S. Geological Survey, 2001b, Coverage LU50—Highresolution land use and land cover 1953–1958 Front Range 

Infrastructure Resources Project Demonstration Area, 

Version 1.0, April 5, 2001: U.S. Geological Survey Rocky 

Mountain Mapping Center, Lakewood, Colo., accessed 

November 23, 2004, http://rockyweb.cr.usgs.gov/frontrange/

NMD/data/lu50.html.

Wilson, J.D., and Naff, R.L., 2004, The U.S. Geological Survey modular ground-water model—GMG Linear Equation 

Solver package documentation: U.S. Geological Survey 

Open-File Report 2004–1261, 47 p.

Winston, R.B., 2000, Graphical User Interface for 

MODFLOW, version 4: U.S. Geological Survey OpenFile Report 2000–315, 27 p., accessed June 1, 2004, 

at http://water.usgs.gov/nrp/gwsoftware/mfgui4/

modflow-gui.html.

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