Chapter B. Effects of Development on Groundwater 

Availability in the Denver Basin Aquifer System, Colorado

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

(Emmons and others, 1896; Darton, 1905), and most of the 

artesian wells were eventually abandoned. Since the 1950s, the 

Denver Basin bedrock aquifers have been used for domestic and 

municipal water supply, industrial and commercial uses, and to 

a lesser extent, for agricultural and urban irrigation. The Late 

Cretaceous- to Tertiary-age confined sandstone aquifers that 

compose the Denver Basin bedrock aquifer system are overlain 

by more permeable Quaternary sand and gravel alluvial deposits, primarily along present-day stream channels, that form a 

productive water-table aquifer where saturated. Since the 1950s, 

the alluvial aquifer has been used primarily for agricultural irrigation, while the bedrock aquifers have been used primarily for 

municipal and domestic water supplies in response to population growth as described in the section “Denver Basin Pumping 

History” in this chapter.

Changes in land use, water use, and climate have affected 

groundwater availability in the Denver Basin as described in the 

section “Effects of Development on Groundwater Availability 

in the Denver Basin” of this chapter. In areas of agricultural 

or urban land use, irrigation using local and imported surface 

water and pumped groundwater has increased water use on the 

landscape, which has generally increased recharge to, and thus 

groundwater availability in, the alluvial aquifer. Simultaneously, 

increased pumping from the bedrock aquifers has generally 

decreased discharge from the bedrock aquifers to the alluvial 

aquifer, increased downward interaquifer flow between bedrock 

units, decreased the amount of available groundwater in bedrock storage, and lowered hydraulic heads in bedrock aquifers. 

Climatic variation affects the amount of water available for 

precipitation recharge to the aquifer system, with less precipitation recharge in dry years and more precipitation recharge in 

wet years.

Land Use

Land use in the Denver Basin is changing from grasslands 

with sparse native shrubs and trees to land uses of agriculture, 

urbanized metropolitan areas, suburban residential housing, 

and rural residential. Present-day (2010) land use in the Denver 

Basin ranges from irrigated and nonirrigated agriculture along 

the South Platte River (fig. B1) to high-density urban development in downtown Denver (fig. B2). Based on year 2001 

National Land Cover data (U.S. Geological Survey, 2001a; 

Homer and others, 2004), 60 percent of the Denver Basin area 

is nonirrigated grassland and rangeland, 11 percent is irrigated 

agriculture, 16 percent is nonirrigated agriculture, 9 percent is 

Introduction

Population growth and associated land development for 

agricultural, commercial, and residential uses along the semiarid Colorado Front Range urban corridor have increased competition for limited water resources including Denver Basin 

groundwater. This study evaluated the effects of development 

and changing land use on the Denver Basin groundwater 

system by using a transient, three-dimensional groundwater 

flow model to represent conditions from predevelopment 

(pre-1880) through 2003 (Chapter C present details of the 

groundwater flow model). This Professional Paper chapter (Chapter B) describes the development of groundwater 

resources and the effects of that development on groundwater 

availability in the Denver Basin aquifer system on the basis of 

modeling results. This chapter presents the simulated spatial and temporal changes to the groundwater budget and its 

components including recharge, discharge, and aquifer storage 

for the entire aquifer system and separately for the alluvial 

and bedrock aquifers. The simulated effects of development 

on water levels and groundwater flow directions also are 

presented along with model predictions of future hypothetical 

conditions and a discussion of monitoring needs. The chapter 

concludes with implications for groundwater sustainability in 

the Denver Basin.

Development of the 

Denver Basin Aquifer System

The Denver Basin bedrock aquifers were discovered in the 

late 1800s when artesian groundwater conditions were encountered by exploration geologists drilling for coal near Denver 

in what are now recognized as sandstones of the Arapahoe 

and Laramie–Fox Hills aquifers (Cross and others, 1884; 

Emmons and others, 1896). At the time, downtown Denver 

was a bustling center of commerce and transportation for gold 

and silver mining in the Rocky Mountain Front Range and 

for agriculture (crops and cattle) along the South Platte River 

valley. The groundwater resource was heavily used in the city 

for steam baths, laundry facilities, public drinking fountains, 

public works, breweries, and even to power hotel elevators 

(Emmons and others, 1896). However, the large number and 

poor construction of wells during the late 1880s quickly dissipated the artesian pressure tapped by wells in downtown Denver 
96 Groundwater Availability of the Denver Basin Aquifer System, Colorado

developed urban and suburban land use, 3 percent is forested, 

and 1 percent is open water. Irrigated and nonirrigated agricultural land is primarily in the northern basin along the South 

Platte River valley with nonirrigated grassland covering much 

of the central and southern basin (fig. B3). Developed urban 

and suburban land use is primarily along the western side of the 

Denver Basin (fig. B3) and is associated with the metropolitan 

areas of Denver and Colorado Springs. The cities of Loveland 

and Fort Collins (about 50 miles north of Loveland) are considered part of the Front Range urban corridor, but they do not 

overlie the Denver Basin aquifer system or rely on the bedrock 

aquifers for water supply. Small towns, rural residences, and 

farms are spread across the less-populated parts of the basin, 

including forested areas at the higher elevations along the 

Palmer Divide northeast of Colorado Springs (fig. B3).

Population of the metropolitan areas over the Denver 

Basin aquifers has approximately doubled from 1.3 million 

in 1970 to about 2.7 million in 2005 (fig. B4) (T.L. Arnold, 

U.S. Geological Survey, written commun., 2009). Development has been especially rapid and extensive on the west side of 

the basin between Denver and Colorado Springs with Douglas 

County experiencing the fastest population and housing growth 

of any county in the United States in 2002 (Perry and Mackun, 

2002). Three general areas of recent development rely heavily 

on Denver Basin groundwater for municipal water supply. The 

area south of Littleton and encompassing Parker, Franktown, 

and Castle Rock (herein referred to as the south Denver metropolitan area; figs. B3 and B5) has undergone a transformation 

from rural residential land use to sprawling suburban land use 

(fig. B6) as part of this population increase. Land use for 2001 

in the southern half of the south Denver metropolitan area 

is largely shown as grassland and forest (fig. B3) rather than 

urban/suburban development because much of the development 

in this area occurred since compilation of the 2001 land-use 

datasets. Semiarid rangeland and rural-residential areas east 

of Monument and northeast of Colorado Springs have experienced similar rapid development (hereinafter referred to as the 

Monument area; fig. B3). A third area of suburban growth is 

developing north and northeast of Denver in Weld and Adams 

Counties (hereinafter referred to as the northern area; fig. B3). 

Rangeland and dryland farms in the northern area also are being 

converted to urban/suburban land use.

Water Use and Groundwater Administration

The State of Colorado and the Colorado Division of 

Water Resources (CDWR) administer State water law including groundwater withdrawal from the Denver Basin aquifers. 

Colorado water law is based on the prior-appropriation doctrine 

of first-in-time, first-in-right, which holds that older water rights 

are senior to more recent water rights (Graham and VanSlyke, 

2004). The doctrine applies to surface water and groundwater 

that is tributary to surface water (tributary groundwater), and, as 

a result of the administrative system, older municipalities such 

as Denver generally hold water rights senior to more recently 

established municipalities and suburbs. Public water supply is 

provided to Colorado residents by numerous local municipal 

utilities. For example, the Denver metropolitan area is serviced 

by the Denver Water Board, Colorado Springs is serviced by 

Colorado Springs Utilities, and Aurora is serviced by the City 

of Aurora. Smaller municipalities, suburbs, and rural towns are 

serviced by their respective municipal utilities. In rural areas, 

water is generally self-supplied from groundwater for domestic 

and irrigation purposes.

Public water suppliers rely on a combination of surface 

water from the mountains of the Front Range, groundwater 

from alluvial aquifers, and groundwater from Denver Basin 

bedrock aquifers (Colorado Water Conservation Board, 2004). 

Public water supply in the established municipal areas of 

Denver and Colorado Springs is primarily from surface-water 

sources. Much of the agricultural irrigation along the South 

Platte River and its tributaries also is supplied by surface water 

delivered through irrigation diversion ditches using water rights 

established as early as the 1860s (Colorado Water Conservation 

Board, 2004). Surface-water supplies are derived from inside 

and outside the basin. In-basin surface-water supplies, and 

the associated water rights, are derived from the South Platte 

River, the Arkansas River, and their tributaries. Transmountain 

diversions into the Denver Basin from drainages west of the 

Continental Divide are delivered to in-basin drainages by way 

of tunnels and pipelines through the Rocky Mountain Front 

Range. An estimated 480 ft3/s (345,000 acre-ft/yr) of water is 

transferred to the South Platte River basin, and an estimated 

Figure B1. An agricultural area in the South Platte River valley.

Figure B2. Urbanization along Cherry Creek in downtown Denver.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 97

Figure B3. Land use in the Denver Basin for 2001.

!

!

South Platte River

Lost Creek

Box Elder Creek

Cache la Poudre R

Big Thompson River Little ThompsonR

BoulderCr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Runn ni g Cre ek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger Creek

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 Creek

Saint Vrain Creek

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§ ̈¦70

§ ̈¦25

§ ̈¦76

Northern

area

South Denver

metropolitan area

Monument

area

Northern

area

South Denver

metropolitan area

Monument area

(

!(

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PALMER

DIVIDE

PALMER

DIVIDE

Barr

Lake

Aurora

Reservoir

Cherry Creek

Reservoir

Chatfield

Reservoir

Milton 

Reservoir

Barr

Lake

Aurora

Reservoir

Cherry Creek

Reservoir

Milton 

Reservoir

WELD

LARIMER

MORGAN

JEFFERSON

WASHINGTON

BROOMFIELD

LINCOLN

ADAMS

ARAPAHOE

TELLER

DOUGLAS

EL PASO

ELBERT

DENVER

BOULDER

WELD

LARIMER

MORGAN

JEFFERSON

WASHINGTON

BROOMFIELD

LINCOLN

ADAMS

ARAPAHOE

TELLER

DOUGLAS

EL PASO

ELBERT

DENVER

BOULDER

Greeley

Boulder

Loveland

Longmont

Brighton

Broomfield

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Aurora

Bennett

Parker

Morrison

Franktown

Elizabeth

Castle

Rock

Highlands 

Ranch

Littleton

Kiowa

Engelwood

Fort

Morgan

Wiggins

Deer

Trail

Limon

Simla

Calhan

Monument

Colorado

Springs

Greeley

Boulder

Loveland

Longmont

Brighton

Broomfield

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Aurora

Bennett

Parker

Morrison

Franktown

Elizabeth

Castle

Rock

Highlands 

Ranch

Littleton

Kiowa

Engelwood

Fort

Morgan

Wiggins

Deer

Trail

Limon

Simla

Calhan

Monument

Colorado

Springs

105°

40°

39°

104°

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

Land cover generalized from U.S. Geological Survey, 2001

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Land use category

Water

Urban/suburban development

Forest

Grassland

Irrigated pasture or row crops

Nonirrigated small grains or fallow

Urban recreational areas

Alluvial aquifer extent

Area of concentrated municipal pumping

Stream

Perennial

Ephemeral

# Bedrock municipal well
98 Groundwater Availability of the Denver Basin Aquifer System, Colorado

180 ft3/s (132,000 acre-ft/yr) of water is transferred to the 

Arkansas River basin from other basins, primarily from the 

Upper Colorado River Basin (Colorado Water Conservation 

Board, 2004).

Tributary groundwater pumped from the South Platte 

alluvial aquifer is mainly used for agricultural irrigation. Agricultural areas historically were located adjacent to streams, and 

thus also overlie alluvial aquifers. Both diverted surface water 

and pumped alluvial groundwater are sources of water for agricultural irrigation. Its large hydraulic conductivity and shallow 

depths to water compared to the bedrock aquifers also contribute to the beneficial use of the alluvial aquifer for agricultural 

irrigation (Hurr and others, 1975; Robson and Romero, 1981a, 

1981b; Robson, Romero, and Zawistowski, 1981, Robson, 

Wacinski, and others, 1981). The availability of South Platte 

River surface water made agriculture an important industry in 

the South Platte River valley beginning in the late 19th century 

(Nadler and Schumm, 1981). Crop irrigation from diversion 

ditches began in the 1880s, and by 1897, irrigation return flow 

had raised the alluvial-aquifer water table in late summer so that 

streamflow in the South Platte River changed from intermittent 

to perennial (Nadler and Schumm, 1981). Pumping from the 

alluvial aquifer for agricultural irrigation began and expanded 

in response to droughts of the 1930s and 1950s and the widespread availability of electricity (Hurr and others, 1975). By the 

1960s, State administration recognized the connection between 

groundwater and surface water, and regulation of pumping was 

considered necessary (Graham and VanSlyke, 2004). The Water 

Right Determination and Administration Act (Colorado Revised 

Statute (CRS) 37–92–101 to 37–92–602) recognized that prior 

appropriation also governs groundwater and regulated pumping 

Figure B4. Population for the areas overlying the Denver Basin aquifer system and for 

the fastest growing counties in the Denver Basin, 1970–2005.

of tributary groundwater, but application of the law was generally limited to the South Platte alluvial aquifer (Graham and 

VanSlyke, 2004).

Development of the bedrock aquifers began in the 1950s 

on the basis of well permits issued. In contrast to the alluvial 

aquifer, which is used mostly for agricultural irrigation, water 

from the bedrock aquifers is primarily used for municipal, 

commercial, industrial, and domestic purposes (Robson, 

1989; this study). In 1973, Senate Bill 73–113 (SB113, 

CRS 37–90–137(4)) was established to recognize the existence 

of nontributary groundwater in the Denver Basin and establish 

rules for its administration (Graham and VanSlyke, 2004). This 

law administers groundwater withdrawal based on ownership 

or control of the overlying land and limits annual withdrawal 

to 1 percent of the available water beneath the land in order 

to maintain a 100-year aquifer life for a given parcel of land 

(Graham and VanSlyke, 2004). By 1985, the continued increase 

in groundwater withdrawal from the Denver Basin prompted 

further study of the aquifers, and Colorado Senate Bill 85–5 

(SB85–5) was passed, which clarified nontributary groundwater 

definitions and established the Denver Basin Rules (Graham 

and Van Slyke, 2004). Senate Bill 85–5 adopted a 100-year 

aquifer life to administer pumping rates and accepted storage 

depletion by not protecting artesian head or aquifer water levels 

(Graham and VanSlyke, 2004). Because Denver Basin bedrock 

groundwater is considered mostly nontributary by SB85–5 and 

therefore is not subject to the prior-appropriation doctrine, it has 

been a readily available source of water to support growing and 

recently established municipalities in areas with limited surface 

water, limited tributary groundwater, or limited available water 

rights (Moore and others, 2007).

0

0.5

1.0

1.5

2.0

2.5

3.0

Population, in millions

El Paso County

Arapahoe County

Adams County

Weld County

DouglasCounty

Year

1970 1975 1980 1985 1990 1995 2000 2005

Weld County 69,500

AdamsCounty 177,057

Arapahoe County 151,424

El Paso County 168,602

DouglasCounty 5,881

DenverBasin total 1,299,860

84,446 96,072 102,270 102,596

208,516 234,385 252,581 254,425

205,458 273,905 344,629 365,632

209,992 221,083 264,561 283,667

10,353 17,595 27,173 42,244

1,498,537 1,661,830 1,864,405 1,899,595

115,187 140,822 176,572

287,777 346,756 381,023

417,390 455,712 492,423

332,082 369,346 405,918

69,870 122,948 172,383

2,145,263 2,468,846 2,669,768
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 99

Figure B5. Aerial photograph of suburban area in the south 

Denver metropolitan area.

Figure B6. A Denver Basin domestic well in a rural residential 

setting with new subdivision on the horizon.

Denver Basin Pumping History

In 1883, a well was drilled for coal exploration near 

downtown Denver but was abandoned because of the large, 

uncontrollable flow of water (Emmons and others, 1896). 

By 1884, about 80 wells had been drilled into what became 

later known as the Arapahoe and Laramie–Fox Hills aquifers, 

and by 1890, about 400 bedrock wells had been drilled in the 

downtown Denver area (fig. B7; Emmons and others, 1896; 

Robson, 1987). Flow from the uncapped wells was estimated at about 4.5 ft3

/s in 1884 (Cross and others, 1884), but 

decreasing heads in the aquifers and well interference caused 

the discharge to decrease to an estimated 2.3 ft3/s by 1894 

(Emmons and others, 1896; Robson, 1987).

Because pumping rates from the Denver Basin aquifer system are not monitored, various estimates of pumping have been 

made by previous work. In 1963, the U.S. Geological Survey 

compiled a preliminary tabulation of bedrock pumping in the 

Denver Basin, which included estimates of municipal, commercial, and industrial pumping (Robson, 1987). The 1963 pumping estimate indicated a total pumping rate of 12.5 ft3

/s from 

bedrock wells in the Denver Basin (Robson, 1987). Subsequent 

estimates indicated total pumping from bedrock aquifers ranged 

from about 15 ft3/s in 1958 to about 41 ft3/s in 1978 (Robson, 

1987). Previous pumping estimates indicated a substantial 

pumping increase between 1958 and 1962, relatively steady 

pumping from 1962 to 1975, and then another pumping increase 

between 1975 and 1978 (Robson, 1987). The 1975–78 pumping 

increase was attributed to the use of self-supplied groundwater 

for outdoor lawn watering in developing residential areas at a 

time when the Denver Water Department restricted the use of 

municipal water for lawn watering (Robson, 1987). In 1978, 

most of the pumping from bedrock aquifers was within a 30-mi 

radius of downtown Denver and had caused substantial waterlevel declines in the bedrock aquifers (Robson, 1987). Approximately one-half of the pumping from bedrock aquifers in 1978 

was from the Arapahoe aquifer (Robson, 1987).

Yield from bedrock wells is highly variable and can range 

from 2 to 700 gallons per minute (gal/min) depending on the 

transmissivity of the aquifer materials in which the well is 

completed (Robson, 1987). Large-capacity wells located in areas 

of high transmissivity can yield several hundred gallons per 

minute, but small discharges of only several gallons per minute 

are noted in areas of small transmissivity (Robson, 1987). More 

recently reported well yields exhibit similar variability because of 

aquifer heterogeneity, and well yields can decrease with time after 

well installation because of declining water levels in the bedrock 

aquifers (Frank Jaeger, City of Parker, oral commun., 2003). Well 

yields relate directly to hydraulic conductivity, such that wells 

in the Arapahoe aquifer generally have the greatest yields of the 

Denver Basin bedrock aquifers followed by wells in the Dawson, 

Laramie–Fox Hills, and Denver aquifers (Robson, 1987).

A well-permitting process through the CDWR administers installation of bedrock and alluvial wells in the Denver 

Basin, and permitted pumping rates for bedrock aquifers are 

determined based on SB85–5 requirements and the assumption 

of a 100-year aquifer life for a given parcel of land. However, 

systematic records of measured well pumping are not maintained for the entire basin. The most recent estimates of pumping from the Denver Basin aquifers were made by the CDWR 

(1998) in support of the SB96–74 groundwater flow model.

For this study, geographical information system (GIS) and 

database analysis were used to estimate pumping from a 2004 

version of the CDWR well-permit database (Brian Ahrens, 

Colorado Division of Water Resources, written commun., 

2004). Pumping from each of the alluvial and bedrock aquifers 

was estimated as the product of number of wells (derived from 

GIS and database analysis) and assigned pumping rates. For 

the period from 1880 to 2003, well locations and completioninterval depths listed in the well-permit database were compared 

to GIS files of aquifer extents and base altitude (presented in 

“Hydrogeologic Framework” section of Chapter A) and each 

well was assigned an aquifer designation. The analysis excluded 

nonproducing monitoring wells and wells with insufficient 

location or completion data. The previous well-permit database 

analysis by the CDWR assumed wells less 100 ft deep were 

completed in the alluvial aquifer, and these wells were excluded 

from the previous CDWR analysis because the alluvial aquifer 

was not explicitly represented in previous models (Colorado 
100 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B7. Locations of late 19th century artesian wells reported by Emmons and others (1896) in downtown Denver, Colorado.

76

6

70

6th

25

FEDERAL

8th

COLFAX

EVANS

38th

SHERIDAN

COLORADO

YORK

64TH

PECOS

ALAMEDA

70th

YALE

1st

26th

BROADWAY

VALLEY

FLORIDA

72nd

LOWELL

SANTA FE

44th

270

PARK

LINCOLN

58TH

UNIVERSITY

40th

32nd

DOWNING

SPEER

BRIGHTON

52nd

WASHINGTON

LARIMER

74TH

20th

IRVING

FOX

15th

IOWA

STEELE

LAWRENCE

KNOX

KALAMATH

ZUNI

TEJON

MORRISON

16th

JOSEPHINE

19th

E SPEER

29th

45th

VASQUEZ

23rd

AURARIA

22nd

48th

N SPEER

S PLATTE RIVER

BRYANT

47th

JEWELL

OSAGE

MARTIN LUTHER KING

AMHERST

WATER

RAMP

BLAKE

60th

8th AVENUE

SMITH

MARION

56th

OSCEOLA

25

KNOX

47th

FEDERAL

PARK

8th

WASHINGTON

6th

32nd

BLAKE

COLORADO

BRIGHTON

BROADWAY

44th

YORK

SPEER

SHERIDAN

COLORADO

SPEER

45th

YORK

SHERIDAN

44th

YALE

SPEER

26th

20th

SHERIDAN

IRVING

DENVER

DENVER BOULDER 76

6

70

6th

25

FEDERAL

8th

COLFAX

EVANS

38th

SHERIDAN

COLORADO

YORK

64TH

PECOS

ALAMEDA

70th

YALE

1st

26th

BROADWAY

VALLEY

FLORIDA

72nd

LOWELL

SANTA FE

44th

270

PARK

LINCOLN

58TH

UNIVERSITY

40th

32nd

DOWNING

SPEER

BRIGHTON

52nd

WASHINGTON

LARIMER

74TH

20th

IRVING

FOX

15th

IOWA

STEELE

LAWRENCE

KNOX

KALAMATH

ZUNI

TEJON

MORRISON

16th

JOSEPHINE

19th

E SPEER

29th

45th

VASQUEZ

23rd

AURARIA

22nd

48th

N SPEER

S PLATTE RIVER

BRYANT

47th

JEWELL

OSAGE

MARTIN LUTHER KING

AMHERST

WATER

RAMP

BLAKE

60th

8th AVENUE

SMITH

MARION

56th

OSCEOLA

25

KNOX

47th

FEDERAL

PARK

8th

WASHINGTON

6th

32nd

BLAKE

COLORADO

BRIGHTON

BROADWAY

44th

YORK

SPEER

SHERIDAN

COLORADO

SPEER

45th

YORK

SHERIDAN

44th

YALE

SPEER

26th

20th

SHERIDAN

IRVING

DENVER

DENVER BOULDER

Cherry Creek

South Platte River

Clear Cre ek

105°2' 105°00' 104°58'

39°48'

39°46'

39°44'

39°42'

39°40'

LARIMER

BOULDER

BROOMFIELD

DENVER

JEFFERSON

DOUGLAS

TELLER

FREMONT

EL PASO

ELBERT

ARAPAHOE

ADAMS

WELD

LOGAN

MORGANWASHINGTON

LINCOLN

105° 104°

40°

39°

EXPLANATION

Stream

Major street or highway

Estimated location of historical 

 flowing well from Emmons 

 and others (1896)

0 1 2 MILES

0 1 2 KILOMETERS

Division of Water Resources, 1998). For this study, alluvial 

wells were identified on the basis of their location within the 

limits of the simulated alluvial aquifer, well depth and yield 

criteria, or their classification as alluvial wells in the well-permit 

database. This study excluded alluvial wells if they were located 

outside the limits of the simulated alluvial aquifer. Uses of 

municipal, commercial/industrial, irrigation, or domestic and 

dates of use were assigned to each alluvial and bedrock well on 

the basis of information provided in the well-permit database. 

The number of wells was then totaled by aquifer of completion 

and water-use categories, and the results are described in the 

following discussion. The well-permit database analysis resulted 

in a count of about 52,000 pumped wells for the Denver Basin 

that were categorized by aquifer, use, and dates of use. Of the 

101,103 well records in the well-permit database, the analysis 

excluded about 23,340 records for non-producing monitoring 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 101

wells. The remaining excluded well records (25,763) were 

either duplicate records or contained insufficient information 

for inclusion.

Pumping rates were assigned to individual wells on the 

basis of aquifer of completion and water use consistent with 

previous methodology (Colorado Division of Water Resources, 

1998). The previous methodology developed average annual 

pumping factors on the basis of actual pumping rates reported 

by municipal providers for 1996. Average annual pumping 

rates of 72, 104, 158, and 64 acre-ft per well were indicated for 

1996 for municipal wells completed in the Dawson, Denver, 

Arapahoe, and Laramie–Fox Hills aquifers, respectively 

(Colorado Division of Water Resources, 1998). Weighting factors for each aquifer (table B1) were calculated as the ratio of 

the average pumping rate for the aquifer divided by the overall average annual pumping rate for all wells (120 acre-ft/yr; 

Colorado Division of Water Resources, 1998). Categorized 

by water use, the following average pumping rates were 

assigned to each well by the CDWR (1998) and this study 

for all time periods: 0.6 acre-ft/yr for domestic and livestock 

wells, 0.3 acre-ft/yr for household-use only wells (a subset of 

domestic wells with no outdoor water use), and 9.0 acre-ft/yr 

for commercial and industrial wells (Colorado Division of 

Water Resources, 1998). Assigned pumping rates for domestic 

and livestock wells assume 50-percent consumptive use and 

50-percent return flow; assigned pumping rates for householduse only, commercial, and industrial wells assume 10-percent 

consumptive use and 90-percent return flow (Colorado Division 

of Water Resources, 1998). The assigned pumping rate for 

irrigation wells (41 acre-ft/yr for all time periods) assumes 

90-percent consumptive use and 10-percent return flow, and the 

rate is multiplied by the appropriate aquifer weighting factor to 

compute a per-well pumping rate depending on the aquifer of 

completion (table B1). The assigned pumping rate for municipal 

wells (32 acre-ft/yr in 1979) assumes 50-percent consumptive use, and the rate is multiplied by the appropriate aquifer 

weighting factor to compute a per-well pumping rate depending on the aquifer of completion (table B1). In addition, the 

assigned municipal pumping rate for this study was increased 

linearly from 32 acre-ft/yr in 1979 to 45 acre-ft/yr in 1996 

consistent with methods used by the Colorado Division of Water 

Resources (1998). The assigned municipal pumping rate for this 

study was held constant at 45 acre-ft/yr from 1997 to 2003.

About 52,000 permitted pumping wells with sufficient 

well-location and completion data are included in this analysis. 

About 8,000 wells (15 percent) were completed in the alluvial 

aquifer and about 44,000 wells (85 percent) were completed 

in bedrock aquifers by 2003 (fig. B8). The number of alluvial 

aquifer wells initially exceeded that for the bedrock aquifers 

from the 1930s through the 1950s, reflecting the early groundwater development of the alluvial-aquifer system. After 1960, 

the number of bedrock wells exceeded the number of alluvial 

wells as development of the bedrock aquifers proceeded, and 

the number of bedrock wells increased most rapidly after 1990 

(fig. B8).

The number of alluvial wells increased rapidly during 

the 1950s and 1960s (fig. B9A) as irrigation and domestic 

supplies from the alluvial aquifer were developed (Hurr and 

others, 1975). The rate of alluvial-well installation decreased 

and stabilized after 1969 in response to imposed regulation, 

although the number of alluvial wells increased again in the 

1990s in response to municipal- and domestic-well installation (fig. B9A). Categorization of alluvial wells by water 

use for 2003 indicates most were used for domestic purposes 

(4,386 wells, 56 percent of alluvial wells) and irrigation 

(2,956 wells, 38 percent of alluvial wells) (fig. B9B). Alluvial 

wells are located throughout the alluvial aquifer with concentrations of pumping noted along the main stem of the South 

Platte River between Denver and Greeley and in tributary 

valleys of Lost, Kiowa, Bijou, and Black Squirrel Creeks 

(fig. B10). Municipal wells also are pumped from the tributary 

alluvial aquifer in upper basins of Cherry and Plum Creeks 

south of Denver.

The total number of bedrock wells steadily increased 

after about 1955 (fig. B11A) with domestic wells (41,714 wells) 

accounting for the majority (94 percent) of bedrock wells 

in 2003 (fig. B11B). A count of bedrock wells by aquifer 

(figs. B12A, B12B) indicates that by 2003 most bedrock wells 

were completed in the Dawson aquifer (18,138 wells or 

41 percent of bedrock wells), followed by the Denver aquifer 

(11,488 wells or 26 percent of bedrock wells), the Arapahoe 

aquifer (9,118 wells or 21 percent of bedrock wells), and the 

Laramie–Fox Hills aquifer (5,405 wells or 12 percent of bedrock wells). Bedrock domestic wells are located throughout the 

basin and generally are completed in the bedrock aquifer nearest 

to the surface (fig. B13).

Bedrock municipal wells tend to be located on the west 

side of the basin near municipalities and are concentrated in the 

three identified areas of development (fig. B14). In the northern 

area, suburbs and municipalities in Boulder, Adams, and Weld 

Counties pump groundwater primarily from the Arapahoe and 

Laramie–Fox Hills aquifers. In the south Denver metropolitan 

Table B1. Estimated pumping rates assigned to wells in the Denver Basin model.

Aquifer in which well 

is completed

Aquifer

weighting

factor

Assigned pumping rate

(acre-feet per year)

Municipal Irrigation Commercial/ 

Industrial

Domestic

and livestock

Household

1880–1978 1979–1996 1997–2003 only

Alluvial aquifer 1.0 32.0 Linear increase to 45.0 45.0 41.0 9.0 0.6 0.3

Upper and lower Dawson aquifer 0.6 19.2 Linear increase to 27.0 27.0 24.6 9.0 0.6 0.3

Denver aquifer 0.87 27.8 Linear increase to 39.1 39.1 35.7 9.0 0.6 0.3

Upper and lower Arapahoe aquifer 1.32 42.2 Linear increase to 59.4 59.4 54.1 9.0 0.6 0.3

Laramie–Fox Hills aquifer 0.53 17.0 Linear increase to 23.8 23.8 21.7 9.0 0.6 0.3
102 Groundwater Availability of the Denver Basin Aquifer System, Colorado

area, a concentration of municipal wells supplies water to multiple municipalities and suburbs including Littleton, Parker, Castle Rock, Highlands Ranch, Castle Pines, Castle Pines North, 

Lone Tree, Stonegate, the Pinery, and other developments in 

Douglas and Arapahoe Counties. Municipal wells in the south 

Denver metropolitan area commonly are nested, with multiple 

wells at a given location, and each well completed in a different bedrock aquifer. Water pumped from various depths to meet 

demand commonly is blended to meet water-quality standards. 

Municipal water is used for lawn and garden irrigation in urban/

suburban areas, and water use peaks during the summer months 

to meet this irrigation demand. The extensive and conductive 

Cretaceous alluvial fans found in the Denver and Arapahoe 

aquifers provide a readily available source of nontributary 

water, and development in the south Denver metropolitan area 

relies on the availability of this water supply. In the Monument 

area, municipal wells completed in all of the bedrock aquifers 

are located near the southwestern margin of the basin, which 

is the regional discharge area of Monument Creek. Wells in 

the Monument area provide water supply to development east 

Figure B8. Total number of Denver Basin wells, 1880–2003.

Figure B9. Number of Denver Basin alluvial wells categorized by water use for (A) 1880–2003, and (B) 2003.

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

55,000

Number of wells

Alluvial wells

Total

Bedrock wells

EXPLANATION

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

A

Number of alluvial wells

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

EXPLANATION

Irrigation

Domestic/Household

Municipal

Commercial/Industrial

Total

Irrigation

2,956 wells

38 percent

Domestic

4,386 wells

56 percent

Municipal

189 wells

2 percent Commercial/Industrial

336 wells

4 percent

B
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 103

Figure B10. Locations of Denver Basin alluvial wells within limits of simulated alluvial aquifer, 2003.

South Platte

River

Lost Creek

Box Elder Creek

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 ree k

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

§ ̈¦70

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PALMER

DIVIDE

PALMER

DIVIDE

105° 104°

40°

39°

ADAMS

BOULDER

BROOMFIELD

JEFFERSON

DENVER

WELD

LARIMER

TELLER

DOUGLAS

ELBERT

ARAPAHOE

MORGAN

LINCOLN

EL PASO

WASHINGTON

ADAMS

BOULDER

BROOMFIELD

JEFFERSON

DENVER

WELD

LARIMER

TELLER

DOUGLAS

ELBERT

ARAPAHOE

MORGAN

LINCOLN

EL PASO

WASHINGTON

Golden

Denver

Brighton

Broomfield

Aurora

Engelwood

Littleton

Deer

Trail

Denver

Boulder

Lakewood

Longmont

Brighton

Broomfield

Fort

Lupton

Aurora

Lafayette

Engelwood

Morrison

Highlands 

Ranch

Littleton

Limon

Kiowa

Parker

Franktown

Elizabeth Castle

Rock

Deer

Trail

Simla

Monument Calhan

Colorado

Springs

Fort

Morgan

Greeley

Loveland

Bennett

Wiggins

Golden

Denver

Brighton

Broomfield

Aurora

Engelwood

Littleton

Deer

Trail

Denver

Boulder

Lakewood

Longmont

Brighton

Broomfield

Fort

Lupton

Aurora

Lafayette

Engelwood

Morrison

Highlands 

Ranch

Littleton

Limon

Kiowa

Parker

Franktown

Elizabeth Castle

Rock

Deer

Trail

Simla

Monument Calhan

Colorado

Springs

Fort

Morgan

Greeley

Loveland

Bennett

Wiggins

!(

!(

!(

!(

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!(

!(

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!(

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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

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Stream

Perennial

Ephemeral ! Alluvial aquifer well, 2003

EXPLANATION
104 Groundwater Availability of the Denver Basin Aquifer System, Colorado

of Monument, and the City of Colorado Springs supplements 

its municipal supply by pumping from satellite well fields in 

this area (Cortney Brand, Colorado Springs Utilities, written 

commun., 2005).

Using the well counts presented previously and the 

assigned pumping rates listed in table B1, total pumping from 

Denver Basin alluvial and bedrock wells was estimated at 

about 305 ft3/s (221,100 acre-ft/yr) in 2003 (fig. B15A). About 

62 percent of the pumping was from alluvial wells (187 ft3/s; 

135,400 acre-ft/yr), and 38 percent of the pumping was from 

bedrock wells (118 ft3/s; 85,400 acre-ft/yr) in 2003 (fig. B15B) 

although most of the 52,000 wells (85 percent) are completed 

in the bedrock aquifers. Categorized by water use, total pumping from Denver Basin alluvial and bedrock aquifers was about 

62 percent irrigation, 20 percent municipal, 12 percent domestic, and 6 percent commercial/industrial in 2003 (fig. B16).

Figure B11. Number of Denver Basin bedrock wells categorized by water use for (A) 1880–2003, and (B) 2003.

Figure B12. Number of Denver Basin bedrock wells categorized by aquifer for (A) 1880–2003, and (B) 2003.

A

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

Number of bedrock wells

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

UpperDawson

LowerDawson

Denver

UpperArapahoe

LowerArapahoe

Laramie–Fox Hills

EXPLANATION

Upper and lower

Dawson aquifer

18,138 wells

41 percent of 

bedrock wells

Denver aquifer

11,488 wells

26 percent of 

bedrock wells

Upper and lower

Arapahoe aquifer

9,118 wells

21 percent 

of bedrock 

wells

Laramie–Fox 

Hills aquifer

5,405 wells

12 percent 

of bedrock 

wells

B

A

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

Number of bedrock wells

Year 1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Domestic wells

Commercial/Industral wells

Municipal wells

Irrigation

Total bedrock wells

EXPLANATION Irrigation

458 wells

1 percent

Municipal

850 wells

2 percent

Commercial/Industrial

1,127 wells

3 percent

Domestic

41,714 wells

94 percent

B
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 105

Figure B13. Locations of Denver Basin bedrock domestic wells categorized by aquifer, 2003.

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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

PALMER DIVIDE

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

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

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

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

Lower Dawson aquifer simulated extent (model layer 4)

Denver aquifer simulated extent (model layer 6)

Lower Arapahoe aquifer simulated extent (model layer 10)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Extent of active model cells

! Upper or lower Dawson aquifer domestic well

! Denver aquifer domestic well

! Upper or lower Arapahoe aquifer domestic well

! Laramie–Fox Hills aquifer domestic well
106 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B14. Locations of Denver Basin bedrock municipal wells categorized by aquifer and areas 

of concentrated municipal pumping, 2003.

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

§ ̈¦70

§ ̈¦25

§ ̈¦76

Northern

area

South Denver

metropolitan area

Monument

area

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

105°

40°

39°

104°

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

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Area of concentrated municipal pumping

Extent of active model cells

# Laramie–Fox Hills aquifer municipal well

# Upper or lower Arapahoe aquifer municipal well

# Denver aquifer municipal well

# Upper or lower Dawson aquifer municipal well
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 107

Figure B15. Total estimated pumping from Denver Basin alluvial and bedrock wells for (A) 1880–2003, and 

(B) 2003.

Pumping from alluvial wells increased steadily from 

less than 5 ft3/s (about 3,600 acre-ft/yr) in the 1920s to about 

150 ft3/s (109,000 acre-ft/yr) in 1969 (fig. B17A). Pumping 

from alluvial wells continued to increase, but at a lesser rate, 

after 1969 because of State laws that regulated pumping from 

the alluvial aquifer. Groundwater pumped from the alluvial 

aquifer has been primarily used for agricultural irrigation; 

however, there was an increase in alluvial aquifer pumping for 

municipal and domestic purposes in the 1990s (fig. B17A). In 

2003, estimated alluvial aquifer pumping was 90 percent irrigation, 6 percent municipal, 2 percent commercial/industrial, 

and 2 percent domestic (fig. B17B).

Development of the bedrock aquifers began in the 1950s, 

and bedrock pumping increased steadily to about 118 ft3/s 

(85,400 acre-ft/yr) by 2003 (fig. B18A). Groundwater pumped 

from the bedrock aquifers is used for municipal, domestic, 

irrigation, and commercial/industrial purposes, although 

municipal supply was the primary use of bedrock groundwater 

A

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

EXPLANATION

0

50

100

150

200

250

300

350

Estimated pumping, in cubic feet per second

Total

Alluvial wells

Bedrock wells

B

Alluvial aquifer

187 cubic feet 

per second

62 percent of pumping

Upper Arapahoe

8 cubic feet per second

3 percent of pumping

Upper Dawson

7 cubic feet per second

2 percent of pumping

Lower Arapahoe

40 cubic feet per second

13 percent of pumping

Laramie–Fox Hills

18 cubic feet per second

6 percent of pumping

Denver

29 cubic feet per second

9 percent of pumping

Lower Dawson

15 cubic feet per second

5 percent of pumping

Bedrock aquifers

118 cubic feet per second

38 percent of pumping
108 Groundwater Availability of the Denver Basin Aquifer System, Colorado

since about 1985 (fig. B18A). In 2003, estimated bedrock 

pumping was 41 percent municipal, 28 percent domestic, 

19 percent irrigation, and 12 percent commercial/industrial 

(fig. B18B). The lower Arapahoe and Denver aquifers were 

the most heavily used of the four major bedrock aquifers since 

the 1950s (fig. B19A). In 2003, the Arapahoe aquifer was the 

most heavily pumped of the bedrock aquifers (41 percent of 

bedrock pumping), followed by the Denver aquifer (24 percent of bedrock pumping), the Dawson aquifer (19 percent of 

bedrock pumping), and the Laramie–Fox Hills aquifer (16 percent of bedrock pumping) (fig. B19B). The Arapahoe and 

Laramie–Fox Hills aquifers primarily were used for municipal 

purposes, while the Dawson primarily was used for domestic 

purposes in 2003 (fig. B20). The Denver aquifer water use was 

split relatively equally among municipal, domestic, and irrigation uses in 2003 (fig. B20).

Analysis of pumping from the Denver Basin aquifers 

indicates that the greatest irrigation pumping is from the 

alluvial aquifer along the South Platte River and that the greatest municipal pumping is from bedrock aquifers in populated 

areas on the west side of the basin. The results are consistent 

with the conceptual understanding of conditions in the basin 

and compare reasonably well to previous estimates of bedrock pumping. For example, the Colorado Division of Water 

Resources (1998) estimated pumping from bedrock aquifers 

at about 81 ft3/s for 1996, and this study estimated pumping from bedrock aquifers for 1996 at about 89 ft3

/s. Robson 

(1987) estimated pumping from bedrock aquifers at about 

15 ft3/s in 1958 and about 41 ft3/s for 1978, and this study 

estimated bedrock pumping as about 12 ft3/s in 1958 and 

about 49 ft3/s in 1978. Accuracy of the pumping estimates is 

considered in the range of plus or minus 30 percent (Robson, 

1987; Colorado Division of Water Resources, 1998), and all 

of these estimates are considered plausible values for bedrock 

pumping. Future studies and management of Denver Basin 

groundwater would benefit from implementation of a metering and reporting system for pumping information to decrease 

the uncertainty and increase confidence in pumping estimates. 

Further discussion of data needs, including pumping records, 

is presented in the section “Monitoring the Hydrologic 

System” of this chapter.

Figure B16. Estimated pumping from Denver Basin alluvial 

and bedrock wells categorized by water use, 2003.

Estimated alluvial pumping, in cubic feet per second

Year

0

20

40

60

80

100

120

140

160

180

200

A

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

EXPLANATION

Total

Irrigation

Municipal

Domestic

Commercial/Industrial

Municipal

11.7 cubic feet per second

6 percent of pumping

Domestic

3.6 cubic feet per second

2 percent of pumping

Commercial/Industrial

4.1 cubic feet per second

2 percent of pumping

Irrigation

167 cubic feet per second

90 percent of pumping

B

Figure B17. Estimated pumping from Denver Basin alluvial wells categorized by water use for (A) 1880–2003, and (B) 2003.

Irrigation

190 cubic feet per second

62 percent of pumping

Municipal

60 cubic feet per second

20 percent of pumping

Domestic

37 cubic feet per second

12 percent of pumping

Commercial/Industrial

18 cubic feet per second

6 percent of pumping
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 109

Effects of Development on Groundwater 

Availability in the Denver Basin

This groundwater-availability analysis describes changes 

to the water budget, aquifer storage, and potentiometric surfaces 

from predevelopment (pre-1880) conditions through 2053. 

Water-budgets and hydraulic heads simulated by the Denver 

Basin groundwater flow model (Chapter C) for the transient 

model-calibration period (1880–2003) and the predictive-simulation period (2004–2053) form the basis for this description of 

changes to groundwater availability in the Denver Basin. The 

transient-calibration period of the model represents changing 

aquifer conditions from 1880 to 2003, and the predictive simulation period of the model (2004–2053) represents hypothetical 

predictions of future conditions.

Overview

Development of groundwater resources in the Denver 

Basin has altered the groundwater budget and flow directions as 

compared to predevelopment conditions by increasing water use 

on the land surface while removing water from deep, confined, 

bedrock aquifer storage. The groundwater flow model simulates 

the expanding area of urban/suburban land use and irrigated 

agriculture since the 1950s, and the results indicate increases in 

recharge, evapotranspiration, and the overall quantity of water 

moving in and out of the groundwater system in response to 

expanded development. Simultaneously, groundwater pumping 

from the deep and confined bedrock aquifers also has increased 

steadily since the 1950s, primarily in response to increased 

municipal water-supply needs in urban/suburban areas. The 

simulated increased pumping from the bedrock aquifers generally decreased discharge from the bedrock aquifers to the 

alluvial aquifer, increased downward interaquifer flow between 

bedrock units, decreased the amount of available groundwater 

in bedrock storage, and lowered hydraulic heads in bedrock 

aquifers (fig. B21) compared to predevelopment conditions. The 

groundwater flow model simulates precipitation recharge as a 

percentage of time-varying precipitation to represent the effects 

of climate variability and recent drought. Results indicate 

storage-depletion rates have increased substantially since 1999 

in response to decreased precipitation recharge during recent 

drought years (2000–2003), continued increases in bedrock 

pumping, and conversion of parts of the basin to unconfined 

conditions. Two predictive simulations that represent conditions from 2004–2053 indicate continued storage depletion in 

response to pumping and that a reduction in pumping could 

slow storage depletion rates to extend the usable aquifer life.

Differences between the alluvial and bedrock aquifers have 

important implications for groundwater resource management 

in the Denver Basin. This study focused on evaluating groundwater flow conditions in the Denver Basin bedrock aquifers, 

although the alluvial aquifer is an important part of the overall 

aquifer system and was included in the groundwater flow model 

to represent water exchange between the bedrock aquifers and 

the surficial system of alluvial aquifers and streams on a basinwide scale. The unconsolidated and permeable alluvial aquifer 

occurs at the land surface in direct hydraulic connection with 

streams, with shallow depths to water, and has no overlying 

confining unit such that most of the water moving in and out 

of the system is moving through the alluvial aquifer. Simulated 

recharge, evapotranspiration, and groundwater/surface-water 

interaction for the alluvial aquifer are greater than for bedrock 

0

20

40

60

80

100

120

140

Estimated bedrock pumping, in cubic feet per second

Year

A

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

EXPLANATION

Municipal

Domestic/Household

Irrigation

Commercial/Industrial

Total

B

Irrigation

23 cubic feet 

per second

19 percent of pumping

Municipal

48 cubic feet per second

41 percent of pumping

Domestic

34 cubic feet per second

28 percent of pumping

Commercial/Industrial

14 cubic feet per second

12 percent of pumping

Figure B18. Estimated pumping from Denver Basin bedrock wells categorized by water use for (A) 1880–2003, and (B) 2003.
110 Groundwater Availability of the Denver Basin Aquifer System, Colorado

aquifers because, in the model, the alluvial aquifer receives 

more agricultural and urban irrigation recharge and it receives a 

greater percentage or precipitation recharge (7 percent of annual 

precipitation) than the bedrock aquifers (2–4 percent of annual 

precipitation). These factors, combined with the large hydraulic 

conductivity of the alluvial aquifer, result in minimal changes 

to the alluvial-aquifer storage and potentiometric surface in 

response to pumping. In contrast, the bedrock aquifers receive 

little precipitation recharge because of overlying confining 

units, low precipitation rates, and high evapotranspiration rates. 

These factors, combined with low hydraulic-conductivity values 

as compared to the alluvial aquifer, result in reduced flow to 

the alluvial aquifer, removal of water from storage, substantial 

drawdown to potentiometric surfaces, and increased areas of 

unconfined conditions in response to pumping from the bedrock 

aquifers (fig. B22).

EXPLANATION

0

10

20

30

40

50

60

70

80

90

100

110

120

Upper

Dawson

Lower

Dawson

Denver Upper

Arapahoe

Lower

Arapahoe

Laramie–

Fox Hills

Total

Estimated pumping for 2003, in cubic feet per second

Aquifer

Total

Municipal

Domestic

Irrigation

Commercial/Industrial

Figure B20. Estimated pumping from individual Denver Basin bedrock aquifers 

categorized by aquifer and by water use, 2003.

A

0

5

10

15

20

25

30

35

40

45

50

Estimated bedrock pumping, in cubic feet per second

Year 1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

EXPLANATION

UpperDawson aquifer

LowerDawson aquifer

Denver aquifer

UpperArapahoe aquifer

LowerArapahoe aquifer

Laramie–Fox Hills aquifer

upper Arapahoe

8.2 cubic feet 

per second

7 percent of 

bedrock pumping

Denver

28.8 cubic feet 

per second

24 percent of 

bedrock pumping

upper Dawson

7.4 cubic feet 

per second

6 percent of 

bedrock pumping

lower Dawson

15.4 cubic feet 

per second

13 percent of 

bedrock pumping

B

lower Arapahoe

40.4 cubic feet 

per second

34 percent of 

bedrock pumping

Laramie–Fox Hills

18.2 cubic feet 

per second

16 percent of 

bedrock pumping

Figure B19. Estimated pumping from Denver Basin bedrock wells categorized by aquifer for (A) 1880–2003, and (B) 2003.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 111

Figure B21. Conceptual block diagram of the Denver Basin aquifer system for developed conditions.

Figure B22. Groundwater budget for entire Denver Basin aquifer system, the alluvial aquifer, and bedrock units, 2003.

Groundwater flow 

out of basin

(19 cubic feet per second)

Precipitation plus 

irrigation recharge

(301 cubic feet 

per second)

ET

(218 cubic feet 

per second)

Stream and

spring

outflow

(21 cubic feet 

per second)

Stream and

reservoir inflow

(58 cubic feet 

per second)

Flow to 

alluvial aquifer

(27 cubic feet 

per second)

Flow from

alluvial aquifer

(12 cubic feet 

per second)

Bedrock

units

ET

(305 cubic feet 

per second)

Precipitation plus 

irrigation recharge

(593 cubic feet 

per second)

Stream and

reservoir inflow

(8 cubic feet 

per second)

Stream, 

reservoir,

and spring

outflow

(178 cubic feet 

per second)

Groundwater flow 

out of basin

(19 cubic feet per second)

Precipitation 

plus irrigation

recharge

(894 cubic feet 

per second)

Evapotranspiration (ET)

(523 cubic feet 

per second)

DENVER BASIN AQUIFER SYSTEM

Alluvial

aquifer

Stream and 

reservoir

inflow

(66 cubic feet 

per second) Stream, reservoir, 

spring outflow

(199 cubic feet 

per second)

Net storage loss 

(63 cubic feet per second)

Pumping 

(283 cubic feet 

per second)

Pumping 

(171 cubic feet 

per second)

Pumping 

(111 cubic feet 

per second)

Net storage loss 

(57 cubic feet per second)

Net storage loss 

(7 cubic feet per second)

Water

level

Denver aquifer

Dawson aquifer

Domestic well

Municipal wells

Laramie-Fox Hills aquifer

Arapahoe aquifer

Irrigation

well

South Platte River

Pierre Shale

Denver
112 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Changes to the Groundwater Budget

A groundwater budget accounts for all of the inflows and 

outflows for the hydrologic system. Inflow components of the 

developed Denver Basin groundwater budget are precipitation 

plus irrigation recharge, recharge from streams and reservoirs, 

interaquifer flow between hydrogeologic units, and changes in 

aquifer storage. Outflow components of the developed groundwater budget are evapotranspiration, discharge to springs, 

discharge to streams and reservoirs, pumping discharge to 

wells, interaquifer flow, and changes in aquifer storage. For 

some water-budget components, there are both inflows and 

outflows, and the difference between the inflow and outflow is 

herein referred to as the “net” inflow or outflow. For example, 

net recharge is calculated as the inflow from precipitation plus 

irrigation recharge minus evapotranspiration, and the net flow 

to streams and reservoirs is calculated as the inflow to aquifers 

from streams and reservoirs minus the outflow from aquifers 

to streams and reservoirs. For pumping, the MODFLOW Well 

(Harbaugh and others, 2000) and MNW Packages (Halford 

and Hanson, 2002) were used to simulate wells, and the net 

pumping presented in this water-budget discussion is the 

sum of outflow from the Well and MNW packages minus the 

interlayer inflow from MNW wells. For storage, MODFLOW 

assigns water removed from storage as an inflow and water 

returned to storage as an outflow. The groundwater budgets 

presented herein use the MODFLOW convention that positive 

values are inflows to the groundwater system and negative 

values are outflows from the groundwater system. Because 

MODFLOW simulates water removed from storage as an 

inflow to the groundwater flow system, positive net storage 

values indicate storage depletion (storage loss), and negative 

storage values indicate a return of water to storage (storage 

gain). Changes to aquifer storage are described in terms of 

storage-depletion rates and the cumulative volume of water 

removed from storage.

This discussion of transient groundwater budget results 

is based on the simulated, cell-by-cell water budget for the 

model-calibration period, which represents hydrologic conditions from predevelopment (pre-1880) to 2003. The predevelopment water budget, which is based on the initial (steadystate) model stress period, represents hydrologic conditions 

at the end of 1879 and is presented in section “Predevelopment 

Groundwater Budget” in Chapter A. Transient groundwater 

budgets are presented for the entire model (sum of all model 

layers), the alluvial aquifer (model layer 1), and the bedrock 

units (layers 2 through 12) and are discussed in terms of individual groundwater budget components.

Groundwater Budget for Entire Modeled Area

For the model-calibration period from pre-1880 (1879) to 

2003, recharge from precipitation plus irrigation was the largest inflow component (average of 90 percent of inflow) of the 

groundwater budget for the entire Denver Basin aquifer system 

(alluvial and bedrock units) (table B2; fig. B23A). The primary 

outflow components were to evapotranspiration, pumping, and 

streams. Stream inflow, spring outflow, and groundwater flow 

out of the basin though alluvial aquifers were minor components of the developed groundwater budget. Groundwater flow 

out of the basin includes underflow through the alluvial aquifer 

and specified flux to the South Platte alluvial aquifer. There is 

no groundwater flow out of the basin from bedrock aquifers.

Table B2. Simulated transient groundwater budget for the entire Denver Basin aquifer system during the model-calibration period, 

1879–2003.

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Inflow component

(ft3/s)

Precipitation plus

irrigation recharge Streams Reservoirleakage

Wells completed

in multiple aquifers Storage Total

1 1 1879 630.3 16.2 0.0 0.0 0.0 647

2 6 1906 630.3 16.2 0.0 0.0 0.0 647

3 5 1919 630.3 16.2 22.5 0.0 0.9 670

4 5 1939 633.3 16.1 22.6 0.0 1.5 673

5 5 1953 639.9 16.5 38.1 0.0 6.9 701

6 5 1956 737.5 15.7 38.5 0.0 19.6 811

7 5 1961 758.1 16.4 38.5 0.0 17.1 830

8 5 1964 681.7 17.1 39.0 0.0 59.5 797

9 5 1971 741.4 17.3 38.9 0.1 27.3 825

10 5 1973 741.4 23.3 41.7 0.1 33.7 840

11 5 1978 700.6 23.3 41.8 0.1 58.7 825

12 5 1984 763.1 23.5 41.7 0.2 30.4 859

13 5 1986 763.1 23.7 41.7 0.3 37.6 866

14 5 1994 915.9 23.9 41.5 0.4 37.9 1,020

15 5 1999 939.4 24.1 41.6 0.5 43.9 1,050

16 5 2003 893.5 24.3 41.8 0.6 71.6 1,032
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 113

Table B2. Simulated transient groundwater budget for the entire Denver Basin aquifer system during the model-calibration period, 

1879–2003.—Continued

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Outflow component 

(ft3/s)

Evapotranspiration

Streams Reservoir 

leakage Springs

Out of basin 

underflow 

through alluvial 

aquifers

Specified 

flux to South 

Platte alluvial 

aquifer

Wells 

completed 

in multiple 

aquifers

Wells Storage Total

1 1 1879 –441.6 –181.8 0.0 –4.2 –4.8 –14.1 0.0 0.0 0.0 –647

2 6 1906 –441.5 –181.8 0.0 –4.2 –4.8 –14.1 0.0 –0.1 –0.0 –647

3 5 1919 –462.3 –181.9 0.0 –4.2 –4.8 –14.1 0.0 –2.4 –0.1 –670

4 5 1939 –459.9 –180.3 0.0 –4.2 –4.8 –14.1 –0.0 –9.9 –0.2 –673

5 5 1953 –457.3 –175.0 –1.9 –4.2 –4.8 –14.1 –0.0 –43.9 –0.3 –701

6 5 1956 –470.4 –179.1 –1.9 –4.3 –4.8 –14.1 –0.1 –94.4 –42.1 –811

7 5 1961 –469.5 –183.0 –1.8 –4.4 –4.8 –14.1 –0.5 –120.8 –31.1 –830

8 5 1964 –436.7 –178.2 –1.6 –4.0 –4.8 –14.1 –0.8 –143.9 –13.3 –797

9 5 1971 –440.5 –179.8 –1.5 –4.1 –4.7 –14.1 –1.1 –171.0 –8.0 –825

10 5 1973 –436.7 –179.6 –10.4 –4.1 –4.7 –14.1 –1.4 –183.3 –5.9 –840

11 5 1978 –416.1 –176.1 –10.1 –3.8 –4.6 –14.1 –2.1 –195.7 –1.9 –825

12 5 1984 –427.7 –178.9 –9.9 –4.0 –4.5 –14.1 –2.6 –208.2 –9.0 –859

13 5 1986 –426.1 –178.4 –9.9 –3.9 –4.5 –14.1 –3.1 –219.0 –7.4 –866

14 5 1994 –527.3 –187.5 –11.3 –4.4 –4.6 –14.1 –4.0 –233.5 –32.7 –1,020

15 5 1999 –540.5 –188.5 –11.3 –4.5 –4.6 –14.1 –5.1 –255.3 –25.8 –1,050

16 5 2003 –523.0 –184.1 –11.0 –4.2 –4.5 –14.1 –6.3 –276.2 –8.3 –1,032

Stress 

period

Time 

step Year

Net flow for selected components

(ft3/s)

Net recharge (recharge 

plus evapotranspiration)

Net to streams 

(stream inflow plus 

stream outflow)

Net reservoir leakage 

(reservoir inflow plus 

reservoir outflow)

Wells

Change in storage

(positive value indicates loss, 

negative value indicates gain)

1 1 1879 188.8 –165.7 0.0 0.0 0.0

2 6 1906 188.9 –165.6 0.0 0.1 0.0

3 5 1919 168.0 –165.7 22.5 2.4 0.7

4 5 1939 173.4 –164.2 22.6 9.9 1.2

5 5 1953 182.6 –158.5 36.3 43.9 6.6

6 5 1956 267.0 –163.4 36.6 94.5 –22.5

7 5 1961 288.6 –166.6 36.7 121.4 –14.0

8 5 1964 245.1 –161.1 37.4 144.7 46.2

9 5 1971 300.9 –162.6 37.4 172.2 19.3

10 5 1973 304.8 –156.2 31.2 184.8 27.8

11 5 1978 284.4 –152.8 31.8 198.0 56.7

12 5 1984 335.4 –155.3 31.8 211.1 21.4

13 5 1986 337.0 –154.6 31.8 222.3 30.1

14 5 1994 388.5 –163.6 30.2 237.9 5.2

15 5 1999 399.0 –164.4 30.4 260.8 18.2

16 5 2003 370.4 –159.9 30.8 283.1 63.4

All of the groundwater budget components remained 

relatively constant until the 1950s when irrigated agriculture, urban development, and associated water use began 

increasing. After 1953, irrigation recharge and pumping both 

increased in response to development, causing the total inflow 

and outflow from the system to increase by about 60 percent from 650 ft3

/s for predevelopment (1879) conditions to 

1,030 ft3/s by 2003 (fig. B23A). Increases in the spatial extent 

of urban recharge are simulated for the periods 1954–1986 

and 1987–2003, and the additional water application results 

in step increases for simulated recharge and evapotranspiration in 1956 and 1994. Net recharge (recharge minus 

evapotranspiration) increased from about 190 ft3/s in 1953 to 

about 400 ft3/s in 1999 then decreased to about 370 ft3/s in 

2003 because of the less than average precipitation simulated 

from 2000 to 2003 to represent drought conditions (table B2). 

Inflow from streams to groundwater increased from about 

16 ft3/s for 1879 conditions to about 24 ft3/s in 2003, while 

outflow to streams for the entire modeled area remained 

relatively constant at about 180 ft3/s over the simulation period 

(table B2). Simulated total pumping steadily increased about 

sixfold from 44 ft3/s in 1953 to about 280 ft3/s in 2003 and was 

accompanied by a net storage-depletion rate of about 63 ft3/s 

in 2003 (table B2; fig. B23A).
114 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B23. Simulated transient groundwater budget for (A) the entire Denver Basin modeled area, 

(B) the alluvial aquifer, and (C) the bedrock aquifers and confining units, 1879–2003.

The water budget for the entire Denver Basin aquifer 

system at the end of the model-calibration period (2003) 

reflects the transient changes to recharge rates and pumping 

since the predevelopment condition. Precipitation plus irrigation recharge increased compared to predevelopment conditions because of an increase in the area of urban recharge, 

and recharge was the largest inflow component (894 ft3/s or 

87 percent of inflow) of the developed budget for the entire 

Denver Basin aquifer system (fig. B24). Inflow from streams 

and reservoirs (66 ft3/s or 6 percent of inflow) and storage 

(72 ft3/s or 7 percent of inflow) were other sources of inflow 

to the entire aquifer system in 2003 (fig. B24). Outflow from 

the entire aquifer system in 2003 was primarily to evapotranspiration (523 ft3

/s or 51 percent of outflow), wells (282 ft3/s 

or 27 percent of outflow), and streams (184 ft3/s or 18 percent 

of outflow). Net inflow was from precipitation and irrigation 

recharge (370 ft3/s or 85 percent of net inflow) and storage 

(63 ft3/s or 15 percent of net inflow). Most of the net outflow 

was to wells (282 ft3/s or 65 percent of net outflow) and 

streams (129 ft3/s or 30 percent of net outflow, fig. B24).

–1,200

–1,000

–800

–600

–400

–200

0

200

400

600

800

1,000

1,200

Flow rate, in cubic feet per second

Year

A

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

–1,200

–1,000

–800

–600

–400

–200

0

200

400

600

800

1,000

1,200

Flow rate, in cubic feet per second

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

B
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 115

–1,200

–1,000

–800

–600

–400

–200

0

200

400

600

800

1,000

1,200

Flow rate, in cubic feet per second

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

C

EXPLANATION

Storage change

Netflow from bedrock to alluvial aquifer

Stream and reservoir outflow

Evapotranspiration

Pumping

Springs and flow out of basin

Stream and reservoir inflow

Recharge

Figure B23. Simulated transient groundwater budget for (A) the entire Denver Basin modeled area, 

(B) the alluvial aquifer, and (C) the bedrock aquifers and confining units, 1879–2003.—Continued

Groundwater Budget for Alluvial 

and Bedrock Aquifers

Separating the water budget for the alluvial aquifer 

(table B3; fig. B23B) from that of the bedrock aquifers and 

confining units (herein referred to collectively as bedrock 

units) (table B4; fig. B23C) indicates that in 2003, about twothirds of the water moved in and out of the system through the 

alluvial aquifer (690 ft3/s), and about one-third of the water 

moved in and out of the system through the bedrock units 

(382 ft3/s). The fraction of total flow through the bedrock aquifers relative to flow through the alluvial aquifer increased from 

about one-quarter under predevelopment conditions to about 

one-third in 2003, reflecting the transient increase in bedrock 

aquifer water use relative to the alluvial aquifer. On average from 1879 to 2003, about 80 percent of the simulated net 

recharge was directly to the alluvial aquifer, while 20 percent 

of net recharge was directly to the bedrock aquifers. In 1956, 

simulated pumping from the alluvial aquifer (86 ft3/s) represented about 90 percent of the total pumping (about 95 ft3

/s), 

and pumping from bedrock aquifers (8 ft3/s) represented about 

10 percent of the total pumping. By 2003, pumping from the 

alluvial aquifer (about 170 ft3/s) represented about 60 percent 

of the total pumping (282 ft3/s), and pumping the bedrock 

aquifers (111 ft3/s) represented about 40 percent of the total 

pumping. The majority of net outflow to streams (90 percent 

on average) also was from the alluvial aquifer, while about 

10 percent of net outflow to streams was directly from bedrock 

aquifers from 1879 to 2003. The majority of net storage loss 

in 2003 (about 57 ft3/s or 90 percent) was from the bedrock 

aquifers (table B4).

Alluvial Aquifer Groundwater Budget

Inflow components of the developed alluvial aquifer 

water budget are recharge from infiltration of precipitation 

plus irrigation, inflow from underlying bedrock aquifers, 

and inflow from streams (table B3, fig. B25). Major outflow 

components from the alluvial aquifer are discharge to evapotranspiration, wells, and streams (table B3; fig. B23B, B25). 

Net recharge (recharge minus evapotranspiration) to the 

alluvial aquifer nearly doubled from a predevelopment (1879) 

flow rate of about 150 ft3/s to about 290 ft3/s in 2003 because 

of increases in the area of urban recharge. The maximum net 

recharge to the alluvial aquifer of about 308 ft3/s occurred in 

1999 before the onset of recent drought conditions (table B3). 

Simulated pumping from the alluvial aquifer increased 

approximately fourfold from about 40 ft3/s in 1953 to about 

144 ft3/s in 1971 and then more gradually to about 170 ft3/s in 

2003 (table B3). Outflow from the alluvial aquifer to streams 

remained relatively constant during the model-calibration 

period, but inflow to the alluvial aquifer from streams 

increased from a predevelopment flow rate of about 13 ft3/s 
116 Groundwater Availability of the Denver Basin Aquifer System, Colorado

to about 20 ft3/s in 2003 (table B3) and is attributed to the net 

increase in pumping through time. Recharge, evapotranspiration, and groundwater/surface-water interaction to and from 

the alluvial aquifer all increased from 1879 through 2003 

because of the increase in area of irrigation recharge overlying 

the alluvial aquifer and because of the increase in pumping 

from the alluvial aquifer. The alluvial aquifer is in hydraulic 

connection with the bedrock aquifers where bedrock sandstones are in direct contact with alluvial materials, and inflow 

from bedrock aquifers is a source of water to the alluvial aquifer. Net inflow from bedrock aquifers to the alluvial aquifer 

decreased from a predevelopment flow rate of about 26 ft3/s 

to a rate of about 15 ft3/s in 2003 (table B3), presumably in 

response to bedrock pumping, which has lowered hydraulic 

heads in the bedrock aquifers. Reservoir leakage also became 

a source of recharge to the alluvial aquifer through the modelcalibration period. Alluvial-aquifer storage gains and losses 

are related to net recharge rate and reflect climate variability. 

Storage loss (positive values of “net from storage”) is simulated during dry periods from 1964 through 1978 and from 

2000 through 2003, and storage gain (negative values of “net 

from storage”) is simulated during wet years from 1956 to 

1961 and from 1984 to 1999 (fig. B23B).

Bedrock Groundwater Budget

Recharge from precipitation plus irrigation is the primary 

inflow component of the bedrock water budget with inflow 

from streams and the overlying alluvial aquifer comprising 

minor inflow components (table B4; fig. B25). Inflow from 

storage became a contributing component of the bedrock 

water budget as pumping increased through time (table B4; 

fig. B23C). Primary outflow components from the bedrock 

aquifers and confining units are discharge to evapotranspiration, 

wells, the alluvial aquifer, and streams (table B4; fig. B23C, 

B25). Net recharge to the bedrock units approximately doubled 

from about 42 ft3/s in 1956 to about 83 ft3/s in 2003 because 

of increases in the area of urban recharge, and the maximum 

net recharge to the bedrock units of about 90 ft3/s occurred in 

1999 before the onset of recent drought conditions (table B4). 

Simulated pumping from the bedrock aquifers increased 

steadily from about 8 ft3/s in the 1956 to about 111 ft3/s in 

2003 (table B4). Net outflow to streams from the bedrock units 

increased slightly from a predevelopment flow rate of about 

14 ft3/s to about 16 ft3/s in 2003 (table B4). Net discharge 

from the bedrock units to the alluvial aquifer decreased from 

a predevelopment flow rate of about 26 ft3/s to about 15 ft3/s 

in 2003 (table B4), and the bedrock net storage-depletion rate 

increased from zero during predevelopment to about 57 ft3/s 

in 2003 (table B4, fig. B25) in response to pumping from the 

bedrock units.

Groundwater Budget Components

This discussion presents in-depth discussion of the changes 

to each groundwater budget component from 1879 to 2003. Simulated inflows were precipitation plus irrigation recharge, streams, 

reservoirs, interaquifer flow, and groundwater storage. Simulated 

outflows were evapotranspiration, wells, springs, interaquifer 

flow, groundwater storage, and model boundaries. The model 

represents streams, reservoirs, interaquifer flow, and groundwater 

storage such that they are both sources and sinks of groundwater.

INFLOW

NETFLOW

OUTFLOW

Inflow

Outflow

ALLUVIAL AQUIFER AND BEDROCK UNITS

Streams

24 cubic feet 

per second

(2 percent 

of inflow)

Recharge

894 cubic feet per second

(87 percent of inflow)

Reservoirs

42 cubic feet 

per second

(4 percent 

of inflow)

Storage loss

72 cubic feet per second

(7 percent of inflow)

Springs 

4 cubic feet 

per second

(<1 percent 

of outflow)

Groundwater 

flow out of basin

19 cubic feet 

per second

(2 percent 

of outflow)

Storage gain

8 cubic feet 

per second

(<1 percent 

of outflow)

Wells

282 cubic feet 

per second

(27 percent 

of outflow)

Streams

184 cubic feet 

per second

(18 percent 

of outflow)

Evapotranspiration

523 cubic feet per second 

(51 percent of outflow)

Reservoirs

11 cubic feet 

per second

(1 percent 

of inflow)

Groundwater flow

out of basin

19 cubic feet 

per second

(4 percent 

of net outflow)

Springs 

4 cubic feet 

per second

(1 percent 

of net outflow)

Wells

282 cubic feet 

per second

(65 percent of 

net outflow)

Net recharge

370 cubic feet per second

(85 percent of 

net inflow)

Net storage loss

63 cubic feet per second

(15 percent of net inflow)

Net to streams

129 cubic feet 

per second

(30 percent 

of net outflow)

Figure B24. Groundwater budget inflow and outflow components 

for the entire Denver Basin aquifer system at the end of the model 

calibration period, 2003.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 117

Recharge and Evapotranspiration

Sources of recharge to the developed Denver Basin aquifer 

system include infiltration of incident precipitation and return 

flows in excess of consumptive use from agricultural irrigation and from urban applications (lawn irrigation and general 

water use). Simulated recharge from incident precipitation was 

applied to the land surface of the entire modeled area as a percentage of time-varying precipitation, and model stress periods 

were chosen so that climate variability, including recent drought 

conditions from 2000–2003, is represented in the model. 

Precipitation for a given model stress period was assigned as a 

spatial distribution (two-dimensional array) of average precipitation values for the given time period, and the percentage 

of incident precipitation assigned as recharge was estimated 

during model calibration. Model representation of precipitation 

recharge is described in section “Model-Calibration Results,” 

“Calibrated Recharge Parameters” in Chapter C.

Irrigated agricultural areas in the Denver Basin tend to 

overlie the alluvial aquifer along the South Platte River and 

its tributaries where surface water and alluvial groundwater 

Table B3. Simulated transient groundwater budget for the Denver Basin alluvial aquifer during the model-calibration period, 

1879–2003.

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress

period

Time

step Year

Inflow component

(ft3/s)

Precipitation plus

irrigation recharge Streams Reservoirleakage

Total from bedrock 

aquifers and 

confining units

Storage Total

1 1 1879 454.4 12.7 0.0 34.1 0.0 501

2 6 1906 454.4 12.7 0.0 34.1 0.0 501

3 5 1919 454.4 12.7 22.5 33.9 0.1 524

4 5 1939 454.4 12.6 22.6 33.8 0.6 524

5 5 1953 454.5 12.9 38.1 33.7 5.1 544

6 5 1956 511.4 12.5 38.3 33.8 17.1 613

7 5 1961 523.3 13.1 38.3 33.4 14.0 622

8 5 1964 476.6 13.4 38.9 32.5 42.6 604

9 5 1971 509.7 13.8 38.7 32.3 19.4 614

10 5 1973 509.6 19.8 41.5 31.8 21.3 624

11 5 1978 486.0 19.6 41.6 30.7 33.8 612

12 5 1984 528.7 19.9 41.5 29.9 8.9 629

13 5 1986 528.7 20.0 41.5 29.4 9.9 629

14 5 1994 604.7 20.1 37.9 29.4 6.9 699

15 5 1999 619.9 20.1 38.0 28.6 4.3 711

16 5 2003 592.7 20.1 38.1 27.2 11.4 690

Stress 

period

Time 

step Year

Outflow component

(ft3/s)

Evapotranspiration

Streams Reservoir 

leakage Springs

Out of basin 

underflow 

through 

alluvial 

aquifers

Specified 

flux to 

South Platte

alluvial 

aquifer

Wells 

completed 

in multiple 

aquifers

Wells

Total to 

bedrock 

aquifers and 

confining 

units

Storage Total

1 1 1879 –307.1 –164.2 0.0 –3.2 –4.8 –14.1 0.0 0.0 –7.8 0.0 –501

2 6 1906 –307.0 –164.2 0.0 –3.2 –4.8 –14.1 0.0 –0.0 –7.8 –0.0 –501

3 5 1919 –328.1 –164.3 0.0 –3.2 –4.8 –14.1 0.0 –1.1 –8.0 –0.1 –524

4 5 1939 –323.1 –162.7 0.0 –3.2 –4.8 –14.1 0.0 –7.8 –7.9 –0.2 –524

5 5 1953 –315.5 –157.1 –1.9 –3.1 –4.8 –14.1 0.0 –39.9 –7.7 –0.2 –544

6 5 1956 –303.1 –158.8 –1.9 –3.1 –4.8 –14.1 0.0 –86.1 –7.8 –33.5 –613

7 5 1961 –296.8 –162.1 –1.8 –3.1 –4.8 –14.1 –0.0 –106.8 –7.9 –24.7 –622

8 5 1964 –279.2 –159.2 –1.6 –3.0 –4.8 –14.1 –0.0 –123.7 –7.6 –10.8 –604

9 5 1971 –273.3 –159.4 –1.5 –2.9 –4.7 –14.1 –0.0 –143.6 –8.5 –5.9 –614

10 5 1973 –270.9 –159.2 –10.4 –2.9 –4.7 –14.1 –0.0 –148.5 –8.7 –4.5 –624

11 5 1978 –260.3 –157.1 –10.1 –2.9 –4.6 –14.1 –0.0 –152.4 –8.9 –1.5 –612

12 5 1984 –265.3 –159.3 –9.9 –2.9 –4.5 –14.1 –0.0 –155.9 –9.9 –7.0 –629

13 5 1986 –264.4 –158.9 –9.9 –2.9 –4.5 –14.1 –0.0 –158.7 –10.3 –5.7 –629

14 5 1994 –303.2 –166.1 –11.3 –3.0 –4.6 –14.1 –0.1 –162.1 –11.0 –23.7 –699

15 5 1999 –311.9 –167.0 –11.2 –3.0 –4.6 –14.1 –0.1 –168.1 –11.8 –19.3 –711

16 5 2003 –304.9 –164.3 –11.0 –2.9 –4.5 –14.1 –0.1 –170.8 –12.4 –4.5 –690
118 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table B3. Simulated transient groundwater budget for the Denver Basin alluvial aquifer during the model-calibration period, 

1879–2003.—Continued

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress

period

Time

step Year

Net flow for selected components

(ft3

/s)

Net from recharge 

(recharge plus 

evapotranspiration)

Net to streams 

(stream inflow plus 

stream outflow)

Net to 

reservoir leakage

(reservoir inflow plus 

reservoir outflow)

Wells

Total to bedrock 

aquifers and 

confining units

Change in storage

(positive value indicates 

loss, negative value

indicates gain)

1 1 1879 147.3 –151.5 0.0 0.0 26.3 0.00

2 6 1906 147.4 –151.5 0.0 –0.0 26.3 0.01

3 5 1919 126.3 –151.6 22.5 –1.1 26.0 0.01

4 5 1939 131.2 –150.1 22.6 –7.8 25.9 0.38

5 5 1953 139.0 –144.2 36.3 –39.9 26.0 4.88

6 5 1956 208.3 –146.3 36.5 –86.1 26.0 –16.35

7 5 1961 226.5 –149.0 36.5 –106.8 25.6 –10.69

8 5 1964 197.3 –145.8 37.3 –123.7 24.9 31.84

9 5 1971 236.4 –145.7 37.2 –143.6 23.8 13.53

10 5 1973 238.8 –139.4 31.1 –148.5 23.0 16.80

11 5 1978 225.7 –137.5 31.6 –152.4 21.8 32.35

12 5 1984 263.4 –139.4 31.6 –155.9 19.9 1.97

13 5 1986 264.3 –138.9 31.6 –158.7 19.1 4.19

14 5 1994 301.5 –146.0 26.6 –162.2 18.4 –16.71

15 5 1999 308.0 –146.9 26.8 –168.1 16.8 –14.96

16 5 2003 287.8 –144.2 27.1 –170.9 14.8 6.93

Table B4. Simulated transient groundwater budget for the Denver Basin bedrock aquifers and confining units during the model-calibration

period, 1879–2003.

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Inflow component

(ft3

/s)

Precipitation plus

irrigation recharge Streams Reservoir leakage

Wells completed

in multiple aquifers

Total from

alluvial aquifer Storage Total

1 1 1879 176.0 3.5 0.0 0.0 7.8 0.0 187

2 6 1906 176.0 3.5 0.0 0.0 7.8 0.0 187

3 5 1919 176.0 3.5 0.0 0.0 8.0 0.7 188

4 5 1939 178.9 3.5 0.0 0.0 7.9 0.8 191

5 5 1953 185.4 3.6 0.0 0.0 7.7 1.7 198

6 5 1956 226.1 3.2 0.1 0.0 7.8 2.5 240

7 5 1961 234.8 3.2 0.1 0.0 7.9 3.1 249

8 5 1964 205.1 3.7 0.1 0.0 7.6 16.9 233

9 5 1971 231.7 3.5 0.2 0.1 8.5 7.9 252

10 5 1973 231.8 3.5 0.2 0.1 8.7 12.4 257

11 5 1978 214.6 3.8 0.2 0.1 8.9 24.8 252

12 5 1984 234.4 3.7 0.2 0.2 9.9 21.4 270

13 5 1986 234.4 3.7 0.2 0.3 10.3 27.7 277

14 5 1994 311.1 3.8 3.6 0.4 11.0 30.9 361

15 5 1999 319.5 4.0 3.6 0.5 11.8 39.6 379

16 5 2003 300.8 4.2 3.7 0.6 12.4 60.2 382

are used as sources of irrigation water supply. Recharge from 

agricultural irrigation was applied as a constant rate to timevarying areas of irrigated agriculture determined from available 

GIS datasets and satellite images. Surface water used for irrigation is diverted from the South Platte River and its tributaries 

through irrigation ditches. Agricultural recharge in irrigation 

ditch service areas downstream from Denver was assigned 

a constant recharge rate of 10 in/yr on the basis of preliminary results from irrigation return-flow studies (L.R. Arnold, 

U.S. Geological Survey, oral commun., 2005). 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 irrigation recharge. 

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 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 119

Table B4. Simulated transient groundwater budget for the Denver Basin bedrock aquifers and confining units during the modelcalibration period, 1879–2003.—Continued

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Outflow component

(ft3/s)

Evapotranspiration

Streams Reservoir 

leakage Springs Wells completed in multiple aquifers Wells Total toalluvial aquifer Storage Total

1 1 1879 –134.5 –17.6 0.0 –1.0 0.0 0.0 –34.1 0.0 –187

2 6 1906 –134.5 –17.6 0.0 –1.1 0.0 –0.1 –34.1 –0.0 –187

3 5 1919 –134.3 –17.6 0.0 –1.0 0.0 –1.3 –33.9 –0.0 –188

4 5 1939 –136.8 –17.6 0.0 –1.0 –0.0 –2.0 –33.8 –0.0 –191

5 5 1953 –141.8 –17.9 0.0 –1.0 –0.0 –4.0 –33.7 –0.0 –198

6 5 1956 –167.3 –20.2 0.0 –1.2 –0.1 –8.4 –33.8 –8.6 –240

7 5 1961 –172.7 –20.8 0.0 –1.3 –0.5 –14.0 –33.4 –6.4 –249

8 5 1964 –157.4 –18.9 0.0 –1.0 –0.8 –20.2 –32.5 –2.5 –233

9 5 1971 –167.2 –20.4 0.0 –1.2 –1.1 –27.4 –32.3 –2.1 –252

10 5 1973 –165.8 –20.3 0.0 –1.1 –1.4 –34.9 –31.8 –1.4 –257

11 5 1978 –155.8 –19.1 0.0 –1.0 –2.1 –43.3 –30.7 –0.4 –252

12 5 1984 –162.4 –19.6 0.0 –1.0 –2.6 –52.4 –29.9 –2.0 –270

13 5 1986 –161.7 –19.5 0.0 –1.0 –3.0 –60.3 –29.4 –1.7 –277

14 5 1994 –224.1 –21.4 –0.010 –1.5 –4.0 –71.4 –29.4 –9.1 –361

15 5 1999 –228.6 –21.5 –0.011 –1.5 –5.0 –87.2 –28.6 –6.5 –379

16 5 2003 –218.1 –19.9 –0.008 –1.3 –6.2 –105.4 –27.2 –3.7 –382

Stress 

period

Time 

step Year

Net flow for selected components

(ft3/s)

Net from recharge 

(recharge plus 

evapotranspiration)

Net to streams 

(stream inflow plus 

stream outflow)

Net to reservoir leakage 

(reservoir inflow plus 

reservoir outflow)

Wells

Total to bedrock 

aquifers and

confining units

Change in storage

(positive value indicates 

loss, negative value 

indicates gain)

1 1 1879 41.5 –14.2 0.0 0 –26.3 0

2 6 1906 41.5 –14.2 0.0 –0.08 –26.3 0.04

3 5 1919 41.7 –14.1 0.0 –1.3 –26.0 0.7

4 5 1939 42.2 –14.1 0.0 –2.0 –25.9 0.8

5 5 1953 43.6 –14.3 0.0 –4.0 –26.0 1.7

6 5 1956 58.8 –17.1 0.1 –8.4 –26.0 –6.2

7 5 1961 62.1 –17.6 0.1 –14.5 –25.6 –3.3

8 5 1964 47.7 –15.3 0.1 –21.0 –24.9 14.4

9 5 1971 64.5 –16.9 0.2 –28.4 –23.8 5.8

10 5 1973 66.0 –16.8 0.2 –36.2 –23.0 11.0

11 5 1978 58.8 –15.3 0.2 –45.3 –21.8 24.4

12 5 1984 72.0 –15.9 0.2 –54.7 –19.9 19.4

13 5 1986 72.7 –15.7 0.2 –63.0 –19.1 25.9

14 5 1994 87.0 –17.6 3.6 –75.0 –18.4 21.9

15 5 1999 90.9 –17.5 3.6 –91.8 –16.8 33.1

16 5 2003 82.7 –15.7 3.7 –111.0 –14.8 56.5

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).

For urban recharge, a constant recharge rate was applied 

to time-varying urban areas also determined from available 

GIS datasets and satellite images. On the basis of recent lawnirrigation return-flow studies (Kevin Lusk, Colorado Springs 

Utilities, written commun., 2005), a constant water-application 

rate of 2.5 in/yr was applied to the mapped areas of urban 

recharge. While the urban recharge rate remained constant, 

the area over which urban recharge occurred increased 

through time on the basis of land-use mapping. Urban recharge 

is simulated beginning in 1920. 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 dataset LU50 (U.S. Geological Survey, 2001b) 

(fig. B26). Satellite images were used to identify areas affected 
120 Groundwater Availability of the Denver Basin Aquifer System, Colorado

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). The Denver aquifer underlies much of the area 

affected by urban recharge (fig. B28).

Simulated precipitation plus irrigation recharge to the 

entire aquifer system increased from a predevelopment 

(1879) flow rate of about 630 ft3/s to about 894 ft3/s in 2003 

(table B2). For the alluvial aquifer, simulated precipitation 

plus irrigation recharge increased from the 1879 flow rate of 

about 454 ft3/s to about 593 ft3/s in 2003, and for the bedrock 

aquifers, simulated precipitation plus irrigation recharge 

increased from the 1879 flow rate of about 176 ft3/s to about 

300 ft3/s in 2003 (fig. B29). Maximum recharge to the alluvial aquifer (about 620 ft3

/s) and to the bedrock aquifers 

(about 320 ft3/s) occurred in 1999 before the onset of recent 

drought conditions simulated from 2000–2003 (tables B2, 

B3; fig. B29). Recharge to the alluvial and bedrock aquifers 

showed step increases in 1956 and 1994 in response to the 

increase in the area of urban recharge simulated for the periods 

1954–1986 and 1987–2003 (fig. B29).

Figure B25. Groundwater budget inflow and outflow components for the Denver Basin alluvial aquifer 

and bedrock units at the end of the model calibration period, 2003.

Streams

4 cubic feet per second

(1 percent of inflow)

Flow from 

alluvial aquifer

12 cubic feet per second

(3 percent of inflow)

Recharge

301 cubic feet per second

(79 percent 

of inflow)

Storage loss

60 cubic feet per second

(16 percent of inflow)

Reservoirs

4 cubic feet per second

(1 percent of inflow)

ALLUVIAL AQUIFER BEDROCK UNITS

INFLOW

NETFLOW

OUTFLOW

Inflow

Outflow

Recharge

592 cubic feet per second

(86 percent of inflow)

Streams

20 cubic feet per second

(3 percent of inflow)

Flow from 

bedrock units

27 cubic feet per second

(4 percent of inflow)

Reservoirs

38 cubic feet per second

(6 percent 

of inflow)

Storage loss

12 cubic feet per second

(2 percent of inflow)

Net recharge

288 cubic feet per second

(93 percent of net inflow)

Springs

3 cubic feet per second

(1 percent of net outflow)

Groundwater flow

out of basin

19 cubic feet per second

(6 percent of net outflow)

Flow from bedrock units

15 cubic feet per second

(5 percent of net inflow)

Wells

171 cubic feet 

per second

(61 percent 

of net outflow)

Storage loss

7 cubic feet per second

(2 percent of net inflow)

Streams

117 cubic feet 

per second

(91 percent of 

net outflow)

Evapotranspiration

304 cubic feet per second

(44 percent of outflow)

Streams

164 cubic feet

per second

(24 percent 

of outflow)

Wells

171 cubic feet 

per second

(25 percent 

of outflow)

Flow to bedrock units

12 cubic feet per second

(2 percent of outflow)

Storage gain

5 cubic feet per second

(1 percent of outflow)

Reservoirs

11 cubic feet per second

(1 percent of outflow)

Springs

3 cubic feet 

per second

(<1 percent of

 outflow)

Groundwater flow out of basin

19 cubic feet per second

(3 percent of outflow)

Streams

20 cubic feet 

per second

(5 percent 

of outflow)

Evapotranspiration

218 cubic feet per second

(57 percent of outflow)

Flow to alluvial aquifer

27 cubic feet per second

(7 percent of outflow)

Wells

111 cubic feet per second

(29 percent of outflow)

Storage gain

4 cubic feet per second

(1 percent of outflow)

Streams

12 cubic feet per second

(9 percent of net outflow)

Net recharge

83 cubic feet per second

(59 percent of net inflow)

Flow to alluvial aquifer

15 cubic feet per second

(11 percent of net outflow)

Storage loss

57 cubic feet per second

(41 percent of net inflow)

Wells

111 cubic feet per second

(80 percent of net outflow)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 121

Figure B26. Estimated areas of agricultural and urban irrigation as simulated by the Denver Basin 

model, 1940–1953.

South

Platte River

Lost Creek

Cache la Poudre R

Big Thompson R

Little ThompsonR

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek WestP ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek

S aint Vrain Creek

Box Elder Creek

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

Greeley

Boulder

Bennett

Loveland

Morrison

Monument

Longmont

Brighton

Franktown

Elizabeth

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Colorado

Springs

Wiggins

Lafayette

Lakewood Denver

Broomfield

Highlands 

Ranch

Aurora

Littleton

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Greeley

Boulder

Bennett

Loveland

Morrison

Monument

Longmont

Brighton

Franktown

Elizabeth

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Colorado

Springs

Wiggins

Lafayette

Lakewood Denver

Broomfield

Highlands 

Ranch

Aurora

Littleton

Engelwood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

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

Agricultural irrigation recharge, 1880–1953

Urban irrigation recharge, 1940–1953 Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1) Stream

Perennial

Ephemeral
122 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B27. Estimated areas of agricultural and urban irrigation as simulated by the Denver Basin 

model, 1954–1986.

South

Platte River

Lost Creek

Box Elder Creek

Cache la Poudre R

Big Thompson Riv er

Little ThompsonR

Boulder Cr

Coal Creek

BigDry 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 Creek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squir rel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek Saint Vrain Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

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

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

105°

40°

39°

104°

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

Agricultural irrigation recharge, 1954–1986

Urban irrigation recharge, 1954–1986

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1) Stream

Perennial

Ephemeral
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 123

Figure B28. Estimated areas of agricultural and urban irrigation as simulated by the Denver Basin 

model, 1987–2003.

South

Platte

River

Lost Creek

Box Elder Creek

Cache la Poudre R

Big Thompson River Little Thompson R

BoulderCr

Coal Creek

Big Dry 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

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek

Saint Vrain Creek

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

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

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

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

Agricultural irrigation recharge, 1987–2003

Urban irrigation recharge, 1987–2003

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1) Stream

Perennial

Ephemeral
124 Groundwater Availability of the Denver Basin Aquifer System, Colorado

The simulated spatial distribution of recharge for 2003 

shows that recharge rates were greatest (10 to 11.2 in/yr) in areas 

of agricultural irrigation overlying the alluvial aquifer (fig. B30). 

The effects of urban recharge in the Denver and Monument 

areas also are apparent in the 2003 recharge distribution map, 

where precipitation plus urban recharge rates ranged from 2.5 to 

3.8 in/yr (fig. B30). In areas not affected by agricultural or urban 

recharge, simulated precipitation recharge rates were greatest 

over the Dawson aquifers and confining unit, where recharge 

was estimated by model calibration as 2 percent of annual 

precipitation and ranged from 0.2 to 0.4 in/yr. The effects of 

recent drought are evident in the simulated recharge distribution 

for 2000–2003 (model stress period 16; fig. B30) which shows 

lower recharge rates to the northern part of the Dawson aquifer 

as compared to predevelopment conditions (fig. A47).

Of the bedrock units, the Denver aquifer received the 

greatest amount of precipitation plus irrigation recharge after 

1954 (table B5; fig. B31). The Denver aquifer underlies both 

of the areas receiving urban recharge (Denver and Monument) 

and therefore received greater amounts of recharge as 

urbanization proceeded. A large step increase in recharge to 

the Denver aquifer occurred in 1956, and step increases in 

recharge to all bedrock aquifers and confining units occurred 

in 1994 in response to increases in the area of urban recharge 

(fig. B31). Estimated precipitation recharge rates for the 

Dawson units are greater than to the other bedrock aquifers. 

However, simulation results indicate that the Laramie–Fox 

Hills aquifer and the Laramie confining unit received more 

Flow, in cubic feet per second

Year

–700

–500

–300

–100

100

300

500

700

EXPLANATION

Recharge to (positive flow) and evapotranspiration 

 from (negative flow) alluvial aquifer

Recharge to (positive flow) and evapotranspiration 

 from (negative flow) bedrock units

Recharge minus evapotranspiration for alluvial aquifer

Recharge minus evapotranspiration for bedrock units

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

Figure B29. Simulated transient recharge, evapotranspiration, and recharge minus 

evapotranspiration for the alluvial aquifer and bedrock units in the Denver Basin, 1879–2003.

total recharge than the combined Dawson units since predevelopment, likely because they receive agricultural irrigation 

recharge in the northern part of the basin.

The temporal distribution of recharge reflects climate variability and represents recent drought conditions. Dry conditions 

in the early 1960s resulted in decreased recharge rates to all bedrock aquifers and confining units in 1964 (fig. B31), and wetter 

conditions in the early 1970s resulted in increased recharge rates 

to all bedrock aquifers and confining units in 1971 and 1974 

(fig. B31). Recharge to almost all of the bedrock units increased 

substantially around 1990 in response to increased precipitation, and maximum recharge rates occurred in 1999 prior to the 

recent drought. The simulated decrease in precipitation recharge 

for the period 2000–2003 (fig. B31) represents the effects of 

recent drought conditions which began in 2000.

Evapotranspiration from groundwater is the primary 

process for natural discharge in the Denver Basin and was a 

simulated value based on a piecewise linear relation of evapotranspiration rate compared to depth to water as discussed 

in the sections “Hydrologic Stresses,” “Evapotranspiration” 

in Chapter C. A map of the predevelopment evapotranspiration distribution indicates small evapotranspiration rates (less 

than 0.5 in/yr) over much of the Denver Basin with greater 

evapotranspiration rates along stream channels and in areas 

of irrigated agriculture (fig. A49). The spatial distribution of 

evapotranspiration in 2003 (fig. B32) is similar to that for 

predevelopment conditions in that evapotranspiration rates 

are greatest from areas underlain by the alluvial aquifer along 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 125

Figure B30. Spatial distribution of simulated precipitation plus irrigation recharge for the Denver 

Basin modeled area, 2003.

South Platte River

Cache la Poudre R

Big Thompson Riv er

Little ThompsonR

Boulder Cr

Coal Creek

BigDry Cr Clear Cre ek

West Sand Creek

First Cree k

Sand Cree

L

k

ittle Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Creek

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

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

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

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 precipitation plus irrigation

 recharge, 2003, in inches per year

0.13 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.75

0.75 to 1.3

1.3 to 2.5

2.5 to 4

10.0 to 11.1 Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)
126 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table B5. Simulated groundwater budget for individual bedrock aquifers and confining units in the Denver Basin, 2003. [In some cases values do not sum because of rounding; all flow rates are in cubic feet per second (ft3/s); <, less than; blank, not applicable] Groundwater-budget component Upper Dawson aquifer Dawson confining unit Lower Dawson aquifer Denver upper confining unit Denver aquifer Denver lower confining unit Upper Arapahoe aquifer Arapahoe confining unit Lower Arapahoe aquifer Laramie confining unit Laramie–Fox Hills aquifer Inflow Recharge (precipitation + irrigation) 19.3 2.7 24.1 5.5 69.3 18.1 16.5 10.3 19.4 56.8 58.9 Streams 0.25 0.0 1.1 0.06 1.9 0.06 0.20 0.0 0.33 0.26 0.05 Reservoir leakage 0.0 3.4 0.0 0.0 0.27 0.0 0.0 0.0 0.0 0.0 0.0 From alluvial aquifer 0.04 0.008 0.28 0.0005 3.1 0.47 2.3 0.007 0.62 1.2 4.3 From overlying bedrock 0.0 6.8 7.4 12.5 13.6 41.6 53.3 36.9 38.0 4.1 15.1 From wells completed in multiple aquifers 0.0 0.0 0.36 0.0 0.44 0.0 0.04 0.0 0.12 0.0 0.03 Storage 4.3 0.11 10.3 0.25 26.1 0.64 2.6 0.17 1.6 6.2 8.0 Total inflow 24.3 13.4 44.2 19.0 116.9 63.9 78.1 50.5 63.0 69.6 86.4 Outflow Evapotranspiration –6.4 –5.1 –13.7 –3.9 –42.6 –6.9 –10.9 –9.3 –17.7 –50.0 –51.5 Streams –3.1 –0.39 –2.9 –0.59 –5.1 –0.31 –2.2 –0.10 –0.66 –1.2 –3.4 Reservoir leakage 0.0 0.008 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Springs –0.19 –0.07 –0.007 –0.17 –0.11 –0.22 –0.05 0.0 0.0 –0.003 –0.41 To alluvial aquifer –0.9 <–0.001 –0.35 –0.007 –1.1 –0.48 –10.4 –0.005 –0.58 –0.31 –13.2 To underlying bedrock –6.8 –7.4 –12.5 –13.6 –41.6 –53.3 –36.9 –38.0 –4.1 –15.1 0.0

To wells completed in multiple aquifers –0.5 0.0 –0.6 0.0 –0.04 0.0 –4.1 0.0 –0.96 0.0 –0.008Wells –6.5 0.0 –13.5 0.0 –25.3 0.0 –7.7 0.0 –35.7 0.0 –16.7Storage 0.0 –0.01 –0.05 0.0 –0.31 –0.003 –3.0 –0.003 –0.17 –0.004 –0.22

Total outflow

–24.3 –13.4 –44.2 –19.0 –116.9 –63.9 –78.1 –50.5 –63.0 –69.6 –86.4

Net flows

Net recharge (recharge + evapotranspiration) 12.9 –2.4 10.3 1.6 26.7 11.1 5.6 1.0 1.7 6.8 7.4Net stream discharge (stream inflow + stream outflow) –3.3 –0.40 –4.0 –0.65 –6.9 –0.37 –2.4 –0.1 –0.10 –1.4 –3.5Net from reservoirs 0.0 3.4 0.0 0.0 0.27 0.0 0.0 0.0 0.0 0.0 0.0Net to alluvial aquifer –0.9 0.008 –0.08 –0.002 2.0 –0.01 –8.0 0.06 0.04 –0.93 –8.8Net to wells –7.0 0.0 –13.8 0.0 –25.3 0.0 –11.7 0.0 –36.5 0.0 –16.7Net from storage 4.2 0.10 10.2 0.25 25.8 0.63 –0.41 0.17 1.5 6.2 7.8
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 127

stream channels and in areas of irrigated agriculture. However, 

in 2003, increased evapotranspiration is also evident in the areas 

of urban recharge near Denver and Monument (fig. B32).

Evapotranspiration from all of the bedrock units except the 

Denver aquifer remained relatively constant from predevelopment until the 1990s (fig. B33). Similar to recharge, a large step 

increase in evapotranspiration from the Denver aquifer occurred 

in 1956, and step increases in evapotranspiration from all bedrock 

aquifers and confining units occurred in 1994 in response to 

increases in the area of urban recharge (figs. B31, B33). Evapotranspiration from the bedrock units was greatest for the Laramie–

Fox Hills aquifer for the entire simulation period (table B5; 

fig. B33) likely because it crops out in the area of agricultural 

irrigation recharge in the northern part of the basin.

Net recharge is calculated as the difference between recharge 

and evapotranspiration. The simulated net recharge rates over 

undeveloped and nonirrigated areas of the Denver Basin represent 

recharge from precipitation only and were less than 0.5 in/yr for 

the entire model-calibration period changing only in response to 

climatic variations in precipitation recharge. Net recharge rates 

in the range of 0.5 to 2 in/yr were calculated for urban recharge 

areas overlying alluvial aquifers as 7 percent of precipitation plus 

2.5 in/yr for urban recharge minus model-calculated evapotranspiration. Net recharge rates in the range of 10 to 11.2 in/yr 

were calculated for agricultural recharge areas overlying alluvial 

aquifers for 2003 (fig. B34). In some areas of the basin, primarily in agricultural recharge areas overlying the alluvial aquifer 

in the South Platte River valley, simulated evapotranspiration 

exceeds recharge from precipitation plus irrigation such that a 

negative net recharge, or net discharge, results (fig. B34).

Of the bedrock units, the Denver aquifer received the 

greatest net recharge since predevelopment (table B5; fig. B35). 

Application of urban recharge near Denver and Monument 

accounts for the increase in net recharge to the Denver aquifer 

from the 1879 value of about 10 ft3/s to a 2003 value of about 

27 ft3/s. The upper Dawson aquifer received the second-greatest 

quantity of net recharge, which ranged from about 5 ft3/s in the 

1950s to about 13 ft3/s in 2003 (fig. B35). The Laramie–Fox Hills 

aquifer and Laramie confining units received large amounts of 

precipitation recharge (fig. B29), but evapotranspiration from 

these units also was large (fig. B33), which resulted in less net 

recharge to these units than to the Dawson and Denver units 

(fig. B35). From the mid-1980s to 1999, net recharge to all of 

the bedrock units increased in response to increased precipitation 

and urban recharge. However, net recharge to the bedrock units 

decreased after 1999 (figs. B29, B35) in response to regional 

drought, which is simulated by the model as reduced precipitation 

recharge from 2000 to 2003. These results indicate that variations 

in climate and thus precipitation directly affect recharge rates in 

the Denver Basin.

Increase in area of

urban recharge

Increase in area of

urban recharge

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Flow, in cubic feet per second 0

10

20

30

40

50

60

70

80

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upperconfining unit

Denver lowerconfining unit

EXPLANATION

Figure B31. Simulated transient precipitation plus irrigation recharge for individual Denver Basin bedrock 

units, 1879–2003.
128 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B32. Spatial distribution of simulated evapotranspiration for the Denver Basin modeled 

area, 2003.

South Platte River

Cache la Poudre R

Big Thompson Rive r

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr Clear Cre ek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestP ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Creek

Lost Creek

Box Elder Creek

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

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

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 evapotranspiration, 2003, 

 in inches per year

–45 to –25

–25 to –10

–10 to –5

–5 to –2

–2 to –1

–1 to –0.5

<–0.5

0 Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 129

Discharge to Wells

Simulated pumping increased steadily for the alluvial 

and bedrock aquifers since the 1950s consistent with assigned 

pumping rates and locations developed by this study (fig. B36). 

Simulated pumping for 2003 for the alluvial aquifer (170 ft3/s) 

was greater than that for the bedrock aquifers (111 ft3/s) consistent with the conceptual understanding that the alluvial aquifer 

is more conductive and more heavily pumped than the bedrock 

aquifers. Simulated pumping was slightly less than 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 when simulated heads calculated during 

the iterative solution procedure dropped below the bottom of the 

model cell (dry model cells).

Simulated pumping also increased steadily since the 1950s 

for individual bedrock aquifers (fig. B37). The lower Arapahoe 

aquifer is considered the most transmissive and productive of 

the bedrock aquifers because of its relatively high hydraulic 

conductivity, large thickness, and extensive sandstones, and, of 

the bedrock aquifers, the greatest simulated pumping is from 

the lower Arapahoe aquifer (about 30 ft3/s in 2003, 31 percent 

of bedrock pumping). The remaining bedrock aquifers and their 

simulated pumping rates in 2003, in order of decreasing pumping, are the Denver aquifer (about 25 ft3

/s, 22 percent of bedrock 

pumping), the Laramie–Fox Hills aquifer (about 17 ft3/s, 14 percent of bedrock pumping), the lower Dawson aquifer (about 

14 ft3/s, 13 percent of bedrock pumping), the upper Arapahoe 

aquifer (about 12 ft3/s, 11 percent of bedrock pumping), and 

the upper Dawson aquifer (about 7 ft3/s, 6 percent of bedrock 

pumping) (table B5). The spatial distribution and quantities of 

simulated pumping are displayed on maps of simulated hydraulic heads for each model aquifer layer for 1956, 1978, and 

2003 in the section “Model Calibration Results,” “Simulated 

Hydraulic Heads” in Chapter C.

Groundwater/Surface-Water Interaction

Groundwater from the alluvial aquifer, bedrock aquifers, and confining units interacts with streams. There also is 

hydraulic connection between the bedrock units and the alluvial 

aquifer. Where alluvium is thin or absent, such as in higher 

altitude parts of the basin near the Palmer Divide, bedrock units 

discharge directly to streams that originate in the Denver Basin 

(as indicated by negative groundwater flow to streams) both for 

simulated predevelopment (fig. A52) and 2003 (fig. B38) conditions. In downstream parts of the basin where the topographic 

gradient flattens and the alluvial aquifer is present, flow is from 

streams to groundwater (as indicated by positive groundwater 

flow to streams on fig. B38) and streambeds can be dry for 

both predevelopment (fig. A52) and 2003 (fig. B38) conditions. 

Negative changes in groundwater flow to streams are simulated 

from 1880 to 2003 in the Denver and Monument areas affected 

by urban development (fig. B39) and indicate a transient 

increase in groundwater discharge to streams in urbanized areas 

resulting from the increase in urban recharge. Positive changes 

in groundwater flow to and from streams flow from 1880 to 

2003 represent a reduction in groundwater flow to streams and 

Figure B33. Simulated transient evapotranspiration for individual Denver Basin bedrock units, 1879–2003.

Increase in area 

of urban recharge

Increase in area 

of urban recharge

0

10

20

30

40

50

60

Flow, in cubic feet per second

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upper confining unit

Denver lower confining unit

EXPLANATION
130 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B34. Spatial distribution of simulated recharge minus evapotranspiration for the Denver 

Basin modeled area, 2003.

South

Platte River

Cache la Poudre R

Big Thompson R

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr Clear Cre ek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestP ul m

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Creek

Big Sandy Cre ek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek Saint Vrain Creek Lost Creek

Box Elder Creek

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

105°

40°

39°

104°

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 recharge minus evapotranspiration, 

 2003, in inches per year

–45 to –25

–25 to –10

–10 to –3

–3 to 0

0

0 to 0.5

0.5 to 1

1.0 to 2.5

2.5 to 4

4.0 to 10

10.0 to 11.1

Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 131

Flow, in cubic feet per second

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

–5

0

5

10

15

20

25

30

Increase in area of

urban recharge

Increase in area of

urban recharge

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upper confining unit

Denver lower confining unit

EXPLANATION

Figure B35. Simulated transient recharge minus evapotranspiration for individual Denver Basin 

bedrock units, 1879–2003.

Figure B36. Simulated transient pumping from Denver Basin alluvial and bedrock aquifers, 1879–2003.

Simulated pumping, in cubic feet per second 20

40

60

80

100

120

140

160

180

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

0

Alluvial aquifer

Bedrock aquifers

EXPLANATION
132 Groundwater Availability of the Denver Basin Aquifer System, Colorado

are simulated in upland areas near the Palmer Divide (fig. B39) 

in response to decreased precipitation recharge and increased 

pumping for the bedrock aquifers. The overall transient pattern 

of increased groundwater discharge to streams in urbanized 

areas is consistent with the conceptual understanding of changes 

to the hydrologic system and previous studies that indicate 

increased irrigation in developed parts of the basin contributes 

to perennial surface-water flow in naturally ephemeral streams 

(Nadler and Schumm, 1981).

Groundwater/surface-water interaction is predominantly 

between the alluvial aquifer and streams on the basis of simulation results and is about 10 times greater than direct groundwater/surface-water interaction between the bedrock units and 

streams (fig. B40). Transient groundwater outflow to streams 

from the alluvial aquifer showed little variation ranging from a 

predevelopment value of about –164 ft3/s to a minimum value 

of about –157 ft3/s in 1953 and 1978, and to a maximum value 

of about –167 ft3/s in 1999 before recent drought conditions 

(table B2; fig. B40). Transient groundwater inflow (recharge) 

from streams to the alluvial aquifer increased from about 

13 ft3/s in 1956 to about 20 ft3/s in 2003 (table B3; fig. B40). 

The resulting transient net flow to streams from the alluvial 

aquifer decreased from about –150 ft3/s for predevelopment 

conditions to about –144 ft3/s for 2003 (table B2; fig. B40). For 

the bedrock aquifers and confining units, transient groundwater 

outflow to streams varied between about –18 and –20 ft3/s for 

the period 1879–2003, and the transient groundwater inflow 

from streams varied between about –3.5 and –4.2 ft3/s with a 

slight increase over time (table B3; fig. B40). The transient net 

flow to streams from bedrock units varied between –14 and 

–18 ft3/s with a slight increase over time (fig. B40).

For the individual bedrock units (fig. B41), net flow to 

streams before the 1950s was greatest from the upper and lower 

Dawson aquifers, which crop out beneath the Palmer Divide in 

the headwaters area of streams draining the Denver Basin. However, there was an overall decrease in net flow to streams for 

the upper and lower Dawson aquifers from 1880 through 2003. 

There was a substantial decrease in net flow to streams from 

both the upper and lower Dawson aquifers from 2000 to 2003 

(fig. B41) caused by a corresponding decrease in net recharge 

during recent drought conditions. Net flow to streams from the 

Denver aquifer increased over the model-calibration period in 

response to the increase in urban recharge. Simulated net flow 

to streams from the Denver aquifer increased from about –1 ft3/s 

prior to 1953 to about –3.3 ft3/s by 2003 (fig. B41).

The net flow to the alluvial aquifer from bedrock units 

decreased through time (fig. B42). Simulated flow from bedrock 

units to the alluvial aquifer decreased from about 34 ft3/s in 

1879 to 27 ft3/s in 2003, and simulated flow from the alluvial 

aquifer to the bedrock aquifer increased from about 8 ft3/s in 

1879 to 12 ft3/s in 2003 (table B3; fig. B42). The difference 

between bedrock flow to the alluvial aquifer and alluvial aquifer 

flow to the bedrock is the net flow from bedrock to alluvium, 

which has decreased from about 26 ft3/s in 1879 to about 15 ft3/s 

in 2003 (table B3; fig. B42). These flows translate to equivalent 

flux rates of 0.16 and 0.10 in/yr, for predevelopment and 2003, 

respectively, when the flow rates are divided by the alluvial 

aquifer area (2,121 mi2).

For individual bedrock units, net flow to the alluvial 

aquifer is greatest from the upper Arapahoe and Laramie–Fox 

Hills aquifers (fig. B43), which crop out in the northern parts 

of the Denver Basin where the alluvial aquifer is extensive. Net 

flow to the alluvial aquifer from the upper Arapahoe aquifer 

decreased from about 13 ft3/s before 1953 to about 8 ft3/s in 

2003, while there was little variation in the net flow to the 

alluvial aquifer from the Laramie–Fox Hills aquifer (table B5; 

fig. B43). Net flow to the alluvial aquifer from other bedrock 

aquifers was generally less than 2 ft3/s, and net flow to the 

Figure B37. Simulated transient pumping from individual Denver Basin bedrock aquifers, 1879–2003.

18801885

1890

1895

1900

1905

1910191519201925

193019351940

1945

1950

1955

19601965

1970

19751980

198519901995

2000

2005

Year

0

5

10

15

20

25

30

35

Flow, in cubic feet per second

Upper Dawson aquifer

Lower Dawson aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Denver aquifer

EXPLANATION
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 133

Figure B38. Spatial distribution of simulated groundwater flow to and from streams for the Denver 

Basin modeled area, 2003.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thompson R

Boulder Cr

Coal Creek

BigDry Cr

Clear Cre ek

West Sand Creek

First Creek

Sand Cree

L

k

ittle Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Creek

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Cre ek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Creek

L ost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦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

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

105°

40°

39°

104°

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

Groundwater flow to and from streams, 

 2003, in cubic feet per second

–5.9 to –4

–4 to –2

–2 to –1

–1 to –0.25

–0.25 to 0

0

0 to 2

2 to 4

4 to 5.5

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
134 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B39. Spatial distribution of change in sumulated groundwater flow to and from streams 

for the Denver Basin modeled area, 1880–2003.

Sout h Platte River

Cache la PoudreR

Big Thompson R

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestPlu m

Bear Creek

Running Creek

Dry Creek Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Creek

Middle Bijou Creek

East BijouCreek

Middle R ush Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Creek

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦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

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

105°

40°

39°

104°

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

Change in groundwater flow to and 

 from streams, 1880–2003, in cubic 

 feet per second

–2.8 to –1

–1 to –0.25

–0.25 to 0

0

0 to 0.25

0.25 to 2

2 to 5 Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 135

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

0

50

–50

–100

–150

–200

Flow , in cubic feet per second

EXPLANATION

Net flow to streams from alluvial aquifer Net flow to streams from bedrock units

Inflow from streams to the alluvial aquifer 

(positive) or outflow to streams from 

the alluvial aquifer (negative)

Inflow from streams to the bedrock units 

(positive) or outflow to streams from 

the bedrock units (negative)

Figure B40. Simulated transient groundwater flow to and from streams from the alluvial aquifer and bedrock units 

for the Denver Basin modeled area, 1879–2003.

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Flow, in cubic feet per second –5.0

–4.5

–4.0

–3.5

–3.0

–2.5

–2.0

–1.5

–1.0

–0.5

0

0.5

Increase in area

of urban recharge

Increase in area

of urban recharge

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upper confining unit

Denver lower confining unit

EXPLANATION

Figure B41. Simulated transient net groundwater flow to streams from individual bedrock aquifers in 

the Denver Basin modeled area, 1879–2003.
136 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B42. Simulated transient flow between the alluvial aquifer and bedrock units for the Denver Basin 

modeled area, 1879–2003.

Figure B43. Simulated transient net flow between the alluvial aquifer and individual bedrock aquifers 

for the Denver Basin modeled area, 1879–2003.

18801885

1890

1895

1900

1905

1910

19151920

1925

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

Flow, in cubic feet per second 0

5

10

15

20

25

30

35

40

1930

EXPLANATION

Flow to alluvial aquifer from bedrock units

Flow to bedrock units from alluvial aquifer

Net flow to alluvial aquifer from bedrock units

Increase in area 

of urban recharge

Increase in area 

of urban recharge

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Flow, in cubic feet per second

Upper Dawson aquifer

Lower Dawson aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Denver aquifer

EXPLANATION

Variable to dry conditions

Variable to wet conditions
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 137

alluvial aquifer from the bedrock confining units was less than 

1 ft3/s and is not shown in figure B43. Net flow to the alluvial 

aquifer from all bedrock aquifers decreased through time owing 

to increased pumping with the greatest capture of alluvial water 

occurring in the upper Arapahoe and Denver aquifers. Simulated net flow to the alluvial aquifer from the Denver aquifer 

before 1953 was about 1.0 ft3/s. By the mid-1970s, the Denver 

aquifer no longer discharged to the alluvial aquifer, and by 

2003, the Denver aquifer received about –2 ft3/s of net inflow 

(negative net flow) from the alluvial aquifer (fig. B43).

Flow to streams and the alluvial aquifer was a small 

percentage of the overall water budget for the Denver Basin 

bedrock aquifers (table B4). However, the simulated decrease 

in bedrock flow to streams and the alluvial aquifer, and in 

the case of the Denver aquifer, reversal of flow between the 

bedrock and alluvial aquifers, indicate pumping from the 

bedrock aquifers has reduced flow to the alluvial aquifer and 

streams that compose the surficial hydrologic system. The 

simulated increases in streamflow from the alluvial, Denver, 

and Laramie–Fox Hills aquifers represent the increase in nearsurface water use for urban and agricultural applications.

Discharge to springs was less than 1 percent of the overall 

groundwater budget for the Denver Basin bedrock aquifers, and 

similar to stream and alluvial aquifer discharge, simulated flow 

to springs has changed through time in response to changes in 

recharge and pumping rates. Flow to springs from the Laramie–

Fox Hills aquifer was greater than from other bedrock units and 

was relatively constant (about 0.4 ft3/s) for the entire modelcalibration period (table B5). Before 1953, flow to springs from 

the lower Dawson aquifer was about 0.33 ft3/s, but by 2003, 

flow to springs from the lower Dawson aquifer had decreased 

to less than 0.01 ft3/s, presumably because of a decrease in 

recharge and an increase in pumping. Flow to springs for the 

lower Denver confining unit was relatively constant before 1953 

(0.05 ft3/s) but then increased after 1953 to a relatively constant 

rate of 0.22 ft3/s in response to development and the associated 

increase in recharge. Flow to springs from the remaining hydrologic units (upper Dawson aquifer, upper Denver confining unit, 

Denver aquifer, and upper Arapahoe aquifer) was negligible 

(less than 0.2 ft3/s).

Interaquifer Flow

Interaquifer flow is flow between aquifers. For bedrock 

units with limited outcrop at the land surface and therefore limited recharge, interaquifer flow is an important source of water 

to wells. Similar to other water-budget components, interaquifer 

flow was relatively constant before 1953, and the net interaquifer flow between all bedrock units was downward as indicated 

by positive inflow values from overlying bedrock units in table 

B5. After 1953, as pumping and recharge increased, interaquifer 

flow also substantially increased from (1) the Denver aquifer to 

the lower Denver confining unit (from about 17 ft3/s in 1953 to 

about 42 ft3/s in 2003); (2) the lower Denver confining unit to 

the upper Arapahoe aquifer (from about 20 ft3/s in 1953 to about 

53 ft3/s in 2003); (3) the upper Arapahoe to the Arapahoe confining unit (from about 7 ft3

/s in 1953 to about 37 ft3/s in 2003); 

and (4) from the Arapahoe confining unit to the lower Arapahoe 

Figure B44. Simulated transient net flow between bedrock units in the Denver Basin modeled area, 

1879–2003.

–50

–45

–40

–35

–30

–25

–20

–15

–10

–5

0

Flow, in cubic feet per second

1880

–55

Year

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Upper Dawson aquifer

Lower Dawson aquifer

Denver aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Denver upper confining unit

Denver lower confining unit

Arapahoe confining unit

Dawson confining unit Laramie confining unit

EXPLANATION
138 Groundwater Availability of the Denver Basin Aquifer System, Colorado

aquifer (from about 7 ft3/s in 1953 to about 38 ft3/s in 2003) 

(tables A7, B5; figs. B44, B45). From predevelopment to 2003 

conditions, there was a substantial increase of downward interaquifer flow from the Denver aquifer (about 24 ft3

/s), Denver 

lower confining unit (about 34 ft3/s), the upper Arapahoe aquifer 

(about 32 ft3/s) and the Arapahoe confining unit (about 33 ft3/s) 

to underlying bedrock units (fig. B45). These results indicate 

substantial simulated vertical connection between these layers 

and downward flow induced by the increase in pumping in the 

Arapahoe aquifers. Downward interaquifer flow from the lower 

Arapahoe aquifer to the Laramie confining unit was relatively 

constant and negligible (about 2 ft3/s) for the entire modelcalibration period of 1879–2003, indicating a lack of downward 

flow from the lower Arapahoe to the Laramie confining unit 

consistent with previous modeling results (Robson, 1987).

Change in Aquifer Storage

The simulated change in aquifer storage is the water 

removed from storage (storage inflow to the model) minus the 

water returned to storage (storage outflow from the model) so 

that a positive change in the storage value indicates removal 

of water from storage (storage depletion or storage loss). 

Simulated storage by MODFLOW is the total of confined 

aquifer storage from compressibility of the water and the rocks 

and unconfined aquifer storage from drainable porosity. Storage properties of an aquifer are commonly described in terms 

of specific storage for confined aquifers and specific yield 

for unconfined aquifers, and the volume of water released 

from or taken into aquifer storage as hydraulic head changes 

can vary substantially depending on whether the aquifer is 

under confined or unconfined conditions (Lohman, 1979). As 

the confined aquifer experiences drawdown and converts to 

unconfined conditions, the storage-depletion rate will theoretically increase because more water is released from drainable 

storage than from confined storage for a unit decrease in 

hydraulic head (Robson, 1987).

On the basis of simulation results for the model-calibration 

period 1879–2003, storage changes for the alluvial aquifer have 

varied depending on precipitation and pumping with storage 

being gained in wet years and depleted in dry years, while 

bedrock aquifer storage-depletion rates have increased since 

predevelopment (1879) because of pumping (fig. B46). In the 

1950s and early 1960s, simulated recharge increased in the 

Denver Basin as areas of urban recharge expanded, but pumping 

Figure B45. Change in simulated net flow between bedrock units in the Denver Basin modeled area, 

1880–2003.

Flow, in cubic feet per second –55

–50

–45

–40

–35

–30

–25

–20

–15

–10

–5

0

5

10

15

–1.3

–3.4 –3.7 –5.8 –6.4

–14.2

–3.2

–5.9 –6.5

–24.8

–6.3 –6.9

–11.7 –12.9

–38.9

–16.1

–1.9 –2.3

–34.1

–31.8 –32.5

–50.2

–33.7

–7.2

–7.0

–1.2

Hydrogeologic unit

Upper

Dawson

aquifer 

Dawson

confining

unit 

Lower

Dawson

aquifer 

Denver

upper

confining

unit 

Denver

aquifer

Denver

lower

confining

unit 

Upper

Arapahoe

aquifer 

Arapahoe

confining

unit 

Lower

Arapahoe

aquifer 

Laramie

confining

unit 

Change in net flow to underlying layer, 1880–2003

Predevelopment (pre-1880) net flow to underlying unit

Net flow to underlying layer, 2003

EXPLANATION

–2.9

–14.2

–34.8

–2.5
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 139

was not yet great enough to remove water from storage, so 

recharge contributed to alluvial and bedrock aquifer storage. As 

dry conditions ensued in the mid-1960s and pumping continued 

to increase, storage loss occurred in both the alluvial and bedrock aquifers (fig. B46). Wetter climatic conditions in the 1990s 

provided recharge that contributed storage to the alluvial aquifer, but in the bedrock aquifers, continued increases in pumping 

resulted in continued storage depletion (fig. B46). By 2003, dry 

climatic conditions, coupled with continued pumping, resulted 

in a storage-depletion rate for the alluvial aquifer of about 7 ft3/s 

(5,100 acre-ft/yr) (table B3) and a storage-depletion rate for the 

bedrock aquifers of about 57 ft3/s (41,300 acre-ft/yr) (table B4).

For individual Denver Basin bedrock aquifers, there 

was little change in storage inflow or outflow before 1953 

(fig. B47). From 1953 to 1961, storage was gained for the 

Denver and upper Arapahoe aquifers in response to the 

increase in area of urban recharge. There was a similar contribution to storage of the upper Arapahoe aquifer in response 

to increased urban recharge in the 1990s (fig. B47). However, 

except for the two mentioned increases, water was removed 

from storage for all of the bedrock aquifers after 1953. The 

greatest net storage-depletion rate was for the Denver aquifer, 

which reached a maximum of about 26 ft3/s in 2003 at the simulation end (table B5; fig. B47). Net storage-depletion rates for 

the lower Dawson and Laramie–Fox Hills aquifers were about 

10 and 8 ft3/s, respectively, by 2003. The net storage-depletion 

rate for all bedrock units increased exponentially after 1999 in 

response to drought conditions and the associated reduction in 

precipitation recharge combined with pumping increases.

The cumulative volumes of water removed from alluvial 

and bedrock aquifer storage reflect climatic and pumping 

conditions from 1880 to 2003 (fig. B48). Note that cumulative 

storage loss is plotted as a negative value in figure B48. The 

cumulative storage loss from the alluvial aquifer increased 

in response to pumping during the 1960s through the 1980s 

and reached a maximum cumulative storage loss of about 

326,000 acre-ft in 1986. After 1986, the simulated area of 

urban recharge increased in areas overlying the alluvial 

aquifer, which resulted in additional simulated recharge to 

the alluvial aquifer and about 200,000 acre-ft of storage gain 

(fig. B48). An estimated 25,000 acre-ft of cumulative storage was lost from the alluvial aquifer from 1999 to 2003 in 

response to drought conditions. The cumulative volume of 

water removed from bedrock units increased from zero under 

predevelopment (1879) conditions to about 690,000 acre-ft 

in 2003 (fig. B48). For context, Dillon Reservoir, a surface 

impoundment operated by Denver Water in the mountains 

west of Denver, has a storage volume of about 200,000 acre-ft 

(Robson, 1987). The amount of water removed from storage 

by pumping of the bedrock aquifers is thus about 3.5 times the 

volume of Dillon Reservoir. The simulated cumulative storage 

loss is about 0.28 percent of the total estimated amount of 

water in storage (247 million acre-ft). However, there is large 

uncertainty associated with estimates of total water in storage 

(Alley, 2006, 2007), especially in the Denver Basin where the 

fine-grained and heterogeneous aquifers exhibit spatially variable storage parameters.

Simulated flow, in cubic feet per second

Year

–40

–50

–60

–70

–30

–20

–10

0

10

20

30

EXPLANATION

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

Alluvial aquifer

Bedrock units

Figure B46. Simulated transient net storage loss (positive) and gain (negative) rates for the alluvial 

aquifer and bedrock units in the Denver Basin modeled area, 1879–2003.
140 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Flow, in cubic feet per second

Year 1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Increase in area

of urban recharge

Increase in area

of urban recharge

–30

–25

–20

–15

–10

–5

0

5

10

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upperconfining unit

Denver lowerconfining unit

EXPLANATION

Figure B47. Simulated transient net storage-depletion rates for individual bedrock units in the Denver 

Basin modeled area, 1879–2003.

Figure B48. Simulated transient cumulative volume of water removed from storage for bedrock units in the 

Denver Basin modeled area, 1880–2003.

Increase in area

of urban recharge

–800

–700

–600

–500

–400

–300

–200

–100

0

100

Cumulative change in bedrock groundwater storage,

in thousands of acre-feet 

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

Increase in area

of urban recharge

Variable to dry conditions

Variable to wet conditions

Total for alluvial aquifer

Total for bedrock units

Bedrock units in south Denver

 metropolitan area

Bedrock units in all other areas

EXPLANATION
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 141

While the overall percentage of storage loss is small 

compared to the estimated total water in storage, the temporal 

trend and spatial distribution of the storage loss lend insight to 

hydrologic processes controlling storage and warrant further 

consideration. Drought conditions, simulated in the model as 

reduced recharge from 2000 to 2003, coupled with continued 

pumping increases, caused an exponential increase in simulated cumulative storage loss from the bedrock aquifers since 

1999 (fig. B48). During dry years, less recharge is available 

than in wet years so that climate variability and the resulting recharge variability can directly affect aquifer storage. 

Because recharge and storage are the two primary sources of 

water to wells, a reduction in available recharge causes more 

storage loss during dry years. Storage-depletion rates also are 

expected to increase substantially as the confined aquifers 

experience drawdown and convert to unconfined conditions 

because more water is released from unconfined drainable storage than from confined storage for a unit decrease 

in hydraulic head (Robson, 1987). The increased storagedepletion rate simulated after 1999 is likely caused by a combination of factors including increased pumping, decreased 

recharge, and conversion to unconfined conditions. Spatially, 

50 percent of the 2003 storage loss from the bedrock units was 

from the 20 percent of the basin volume encompassed by the 

south Denver metropolitan area (fig. B48). The other 50 percent of storage loss was from remaining parts of the basin.

Changes in Hydraulic Heads 

and Groundwater Flow Directions

Changes in storage and hydraulic head in the alluvial 

aquifer are much less pronounced than those in bedrock 

aquifers because aquifer hydraulic conductivity and recharge 

rates for the alluvial aquifer are greater than those for the bedrock aquifers. Pumping and the removal of groundwater from 

storage have affected potentiometric conditions and regional 

groundwater flow directions in all of the Denver Basin bedrock aquifers.

Potentiometric-surface maps illustrate the distribution of hydraulic heads in an aquifer for a given time period. 

Groundwater flow directions are interpreted from potentiometric conditions with groundwater flow 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 

can be generated from field measurements of depth to water or 

from groundwater flow simulations. Plots of water levels over 

time (hydrographs) also are useful for interpreting temporal changes in water levels. This section describes transient 

changes to hydraulic heads and groundwater flow directions 

in the Denver Basin aquifer system on the basis of existing 

water-level data and modeling results.

Water levels were routinely measured in a large number of Denver Basin wells during the 1970s and early 1980s, 

and potentiometric-surface maps developed from the data 

were published as a series of hydrologic atlases (Robson and 

Romero, 1981a, 1981b; Robson, Romero, and Zawistowski, 

1981; Robson, Wacinski, and others, 1981). 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 about 278 wells 

(fig. B49), which was established in the 1980s and includes 

some wells with water levels dating back to the 1950s and 

1960s (Colorado Division of Water Resources, 2003; 2004). 

The number of water levels measured annually in the CDWR 

network does not provide sufficient geographic coverage to 

prepare potentiometric-surface maps, and there are questions as to whether water levels measured in these wells are 

representative of ambient water-level conditions because of 

well-construction issues (issues associated with the CDWR 

water-level monitoring network are discussed in the section 

“Future Hydrologic Monitoring” in this chapter). Because 

of the limitations associated with the existing monitoring 

network, model calibration did not use water-level data from 

the CDWR network. However, hydrographs of simulated and 

observed hydraulic heads for selected wells in the CDWR 

network presented herein are useful for describing temporal 

water-level changes in the basin. The observed hydraulic 

heads are generally consistent with simulation results.

The Denver Basin groundwater flow model calculates 

heads at the center of every active model cell, and the head 

represents the average altitude of the potentiometric surface 

in the cell. The simulated heads from each cell were contoured 

to prepare a potentiometric-surface map for each aquifer layer 

in the Denver Basin model. Simulated potentiometric surfaces 

for the seven aquifer layers for 1956, 1978, and 2003 are presented in the section “Model-Calibration Results,” “Simulated 

Hydraulic Heads” in Chapter C and, when compared to each 

other, represent changes to the potentiometric surfaces over 

time as described in the following sections.

Alluvial Aquifer

For the alluvial aquifer, the water-level change between 

the simulated predevelopment potentiometric surface (fig. A55) 

and the simulated 2003 potentiometric surface (fig. B50) was 

less than plus or minus 10 ft over most of the affected area 

(fig. B50). The model simulated small drawdowns for the 

alluvial aquifer, despite increased groundwater development, 

because of large hydraulic conductivity values and recharge 

rates simulated for the alluvial aquifer relative to the bedrock 

aquifers. The greatest drawdowns in the alluvial aquifer were on 

the order of 40 ft in Black Squirrel Creek, which is not connected to a perennial stream, and in the upper reaches of Plum, 

Cherry, Box Elder, and Kiowa Creeks, where municipal and irrigation wells are active. Water-level rise on the order of 40 ft is 

noted in the northeast corner of the modeled area near Wiggins 

(fig. B50). These results are consistent with results from the 

CWCB and current modeling efforts of the SPDSS, which 

concluded that, despite local variation in water levels caused by 

pumping and irrigation return flows, the regional water table in 

the South Platte alluvial aquifer has remained relatively stable 

from 1968 to 2005 (Colorado Water Conservation Board, 2006).
142 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B49. Location of wells in the Colorado Division of Water Resources Denver Basin water-level 

monitoring network.

South

Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleD ry C

P

r

lum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Creek

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDEDIVIDE

!(

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§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

ELBERT

ADAMS

MORGAN

BOULDER

Golden

Greeley

Boulder

Loveland

Morrison

Longmont

Deer

Trail

Fort

Lupton

Fort

Morgan

Lafayette

WELD

EL PASO

LINCOLN

TELLER

Calhan

Colorado

Springs

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Limon

Simla

Parker

Denver

Bennett

Lakewood

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Englewood

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

Kiowa

105°

40°

39°

104°

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

Laramie–Fox Hills aquifer simulated extent

Lower Arapahoe aquifer simulated extent

Denver aquifer simulated extent

Lower Dawson aquifer simulated extent

Stream

Perennial

Ephemeral

Colorado Division of Water Resources 

 water-level monitoring site

! Laramie–Fox Hills aquifer

! Arapahoe aquifer undifferentiated

! Lower Arapahoe aquifer

! Upper Arapahoe aquifer

! Denver aquifer

! Dawson aquifer undifferentiated

! Lower Dawson aquifer

! Upper Dawson aquifer
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 143

Figure B50. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 

for the alluvial aquifer (model layer 1).

South Platt e River

Cac he la Poudre R

Big Thompson R

Little Thomps onR

Bould er Cr

Coal Creek

BigDryCr Clear Creek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestP ul m Creek

Bear Creek

Running Creek

Dry Creek Kiowa Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCre ek

Bijou Creek

Antelope Creek

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr 

Lake

Milton 

Reservoir

WELD

LARIMER

BOULDER

WASHINGTON

Golden

Greeley

Boulder

Loveland

Lakewood

Longmont

Lafayette

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir Aurora

Reservoir

Cherry Creek

Reservoir

ADAMS

MORGAN

Parker

Bennett

Morrison

Deer

Trail

Highlands

Ranch

Aurora

Reservoir

Cherry Creek

Reservoir

WELD

EL PASO

LINCOLN

TELLER

DOUGLAS

Colorado

Springs

EL PASO

ELBERT

ARAPAHOE

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

Denver

Brighton

Broomfield

Fort

Lupton

Aurora

Littleton

Englewood

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Calhan

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth Castle

Rock

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Wiggins

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

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105°

40°

39°

104°

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

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Simulated potentiometric contour; shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Stream

Perennial

Ephemeral

Simulated change in hydraulic head, 

 1880–2003, in feet

–44 to –20

–20 to –10

–10 to 0

Dry model cell

0 to 10

10 to 20

20 to 50

50 to 62
144 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Upper Dawson Aquifer

The changing potentiometric conditions in the upper 

Dawson aquifer reflect the increase in domestic and municipal pumping from the aquifer since 1956. Pumping from the 

upper Dawson aquifer in the south Denver metropolitan area 

increased between 1956 and 1978, lowering the potentiometric 

surface in the upper Dawson along Cherry Creek and shifting groundwater flow toward Cherry Creek. The area and rate 

of pumping from the upper Dawson continued to increase 

through 2003, which caused continued lowering of the potentiometric surface along Cherry Creek (fig. B51). By 2003, simulated drawdown in the upper Dawson potentiometric surface 

was as much as 277 ft in the northern part of the aquifer near 

Castle Rock and Parker, and a pattern indicative of regional 

discharge toward Cherry Creek developed (fig. B51) that was 

not present in the predevelopment potentiometric surface 

(fig. A56). Consistent with simulation results, water-level measurements from the CDWR network exhibit up to 89 feet of 

water-level declines in the northern part of the upper Dawson 

aquifer and very little change in hydraulic head in the southern 

part of the aquifer (fig. B52). The large simulated drawdown 

east of Parker was not observed in the CDWR water-level data 

(fig. B52) indicating additional refinement of the hydraulicconductivity distribution or pumping estimates might improve 

model fit in this area.

Lower Dawson Aquifer

Simulated hydraulic heads in the lower Dawson aquifer also decreased in response to pumping since 1956. The 

predevelopment potentiometric contours for the lower Dawson 

aquifer indicate discharge to Plum, Cherry, Kiowa, Bijou, 

Big Sandy, and Monument Creeks (fig. A57). In 1956, there 

was groundwater development near the northern and southern limits of the upper Dawson aquifer, but changes to the 

potentiometric surface from predevelopment conditions were 

limited in extent. By 1978, groundwater development had 

spread over much of the northwest part of the lower Dawson 

aquifer in the south Denver metropolitan area resulting in as 

much as 100 feet of drawdown since 1880. The potentiometric surface was further lowered by 2003 as the area and rate 

of pumping from the lower Dawson continued to increase. 

Drawdown in the potentiometric surface for 2003 as compared to predevelopment conditions was in the range of 100 

to 250 ft in the confined parts of lower Dawson aquifer in 

the Cherry Creek basin (fig. B53). The greatest drawdown 

was on the unconfined southwest margin of the aquifer in the 

Monument area (500 to 984 ft below the predevelopment surface, fig. B53). The extent of drawdown in the south Denver 

metropolitan area is more widespread than in the Monument 

area because of spatial variation in hydraulic conductivity. 

In the Monument area hydraulic conductivity is less than in 

the south Denver metropolitan area, which results in steeper 

and more isolated drawdown cones than in the south Denver 

metropolitan area. Urban recharge in the unconfined northwest 

part of the lower Dawson aquifer resulted in as much as 62 ft 

water-level rise in 2003 compared to predevelopment conditions (fig. B53).

Water-level data for the lower Dawson aquifer from the 

CDWR network in the Castle Rock area are consistent with the 

simulation results. In the Parker area, about 50 ft of water-level 

decline was measured and simulated at wells C119 and C145, 

while as much as 150 ft of water-level decline was measured 

at well C147 near Castle Rock since 1988 (water-level decline 

rate of as much as 23 ft/yr) (fig. B54). In the Monument area, 

CDWR water-level data indicate water-level decline of about 

215 ft since 1967 at well C200 with a water-level decline rate 

of about 6 ft/yr.

Denver Aquifer

Early groundwater development of the Denver aquifer took 

place in and around Denver during development of its western 

suburbs in the 1950s. By 1956, there was substantial drawdown 

in the Denver aquifer potentiometric surface in the Denver area 

compared to predevelopment conditions (fig. A58) (Robson, 

1987). In 1978, pumping from the Denver aquifer was more 

widespread with pumping increases in the south Denver metropolitan area and in the Monument area that resulted in substantial lowering of the simulated potentiometric surface along 

Cherry and Monument Creeks and shifting of groundwater flow 

toward these discharge areas. Pumping from the Denver aquifer 

in the Denver area decreased from 1956 to 1978, which resulted 

in aquifer recovery and contributed to the observed and simulated water-level rise on the northwest and southwest margins of 

the aquifer (Robson, 1987). From 1978 to 2003, pumping from 

the Denver aquifer increased, particularly in the south Denver 

metropolitan area around Castle Rock. In 2003, drawdown from 

predevelopment conditions was between 200 and 500 ft in the 

south Denver metropolitan area (fig. B55). In the Monument 

area, 2003 drawdown from predevelopment conditions was in 

the range of 500 to 924 ft (fig. B55). There was up to 442 ft 

of simulated water-level rise in the Denver aquifer on the 

unconfined northwest and southwest aquifer margins where the 

aquifer occurs near land surface and receives simulated urban 

recharge (fig. B55).

Hydrographs of water-level data from the CDWR are 

generally consistent with simulation results for the Denver 

aquifer. In the northern part of the aquifer near Bennett, 

measured water-level decline is about 40 ft at well C044 from 

1965 to 2003 (fig. B56). In the Castle Rock area, about 190 ft 

of water-level decline was observed at well C184 since 1991 

(fig. B56) where a water-level decline rate of about 16 ft/yr was 

observed since 1999. In the Monument area at well C217, about 

150 ft of water-level decline was observed since 1976 (waterlevel-decline rate of 35 ft/yr since 1999). East of Monument 

Creek water-level rise is observed at well C241 (fig. B56), and 

although there is not a good match between observed and simulated heads at this well, the model does simulate urban recharge 

and water-level rise south of Monument consistent with the 

observations (fig. B55).
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 145

Figure B51. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the upper Dawson aquifer (model 

layer 2).

Coal Creek

Clear Creek

Bear Creek

Little DryCreek

Plum Creek

West Plum

Creek

Cook Cree k

Dry Creek

Black Squirrel Creek

Brackett Creek

CherryCreek

Kettle Cre ek

We st K oi wa Creek

RunningCreek

Dry Creek

KiowaCreek

Sand Creek

Wolf Creek

West Sand Creek

Commanche Creek

Antelo peCreek

Rock Cr

First Creek

West Bijou Creek

Big Sandy Cree k

Horse Creek

Steals Fork

M di dl e Bijou Cr

6,600

6,500

6,900

6,400

6,300

7,000

6,700

6,800

6,600

6,500

6,900

6,200

6,100

5,900

6,400

6,300

7,000

6,000

5,800

6,100

7,100

7,200

6,800

5,900

5,800

6,700

6,800

§ ̈¦25

PALMER

DIVIDE

PALMER

DIVIDE

Barr 

Lake

Aurora

Reservoir

Cherry Creek

Reservoir

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

DOUGLAS

Kiowa

Golden

Calhan

Denver

Bennett

Lakewood

Monument

Broomfield

Highlands 

Ranch

Colorado

Springs

Barr 

Lake

Chatfield

Reservoir

Morrison

Aurora

Englewood

Aurora

Reservoir

Cherry Creek

Reservoir

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Franktown

Elizabeth

Castle

Rock

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

39°30'

39°

104°30'

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

Simulated change in hydraulic head,

 1880–2003, in feet

South Denver metropolitan area

Upper Dawson aquifer simulated extent (model layer 2)

Extent of active model cells

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased well, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Stream

Perennial

Ephemeral

–38 to –25 

–25 to 0

Dry model cell

0 to 25 

25 to 50 

50 to 100 

100 to 200

200 to 277

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)
146 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B52. Hydrographs of measured and simulated hydraulic head for selected wells completed in the upper Dawson aquifer.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Cree

L

k

i ttleDry Cr

Plum Creek

West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Creek

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

!(

!(

!(

!(

!(

!( !(

!( !(

Limon

Kiowa

Parker

Golden

Calhan

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Deer

Trail

Castle

Rock

Highlands

Ranch

Aurora

Limon

Simla

Denver

Greeley

Boulder

Bennett

Loveland

Longmont

Brighton

Fort

Lupton

Fort

Morgan

Colorado

Springs

Wiggins

Lafayette

Englewood

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

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

0 10 20 MILES

0 10 20 KILOMETERS

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

Upper Dawson aquifer simulated extent (model layer 2)

Extent of active model cells

Stream

Perennial

Ephemeral

! Colorado Division of Water Resources water-level monitoring 

 site, upper Dawson aquifer

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

6,520

6,540

6,560

6,580

6,600

6,620

6,640

6,660

Summary for 'SiteID' C190 (17 detail records)

Identifier SC00906308BBD Layer 2 Simulated Observed

11/1/1973

11/1/1975

11/1/1977

11/1/1979

11/1/1981

11/1/1983

11/1/1985

11/1/1987

11/1/1989

11/1/1991

11/1/1993

11/1/1995

11/1/1997

11/1/1999

11/1/2001

8/1/1965

8/1/1968

8/1/1971

8/1/1974

8/1/1977

8/1/1980

8/1/1983

8/1/1986

8/1/1989

8/1/1992

8/1/1995

8/1/1998

8/1/2001

6,760

6,780

6,800

6,820

6,840

6,860

6,880

6,900

Summary for 'SiteID' = C193 (17 detail records)

Identifier SC00906525DBB Layer 2 Simulated Observed

5,700

5,750

5,800

5,850

5,900

5,950

Summary for 'SiteID' = C130 (3 detail records)

Identifier SC00606711CC Layer 2 Simulated Observed

8/1/1994

8/1/1995

8/1/1996

8/1/1997

8/1/19988/1/1999

8/1/2000

8/1/2001

8/1/2002

6,120

6,140

6,160

6,180

6,200

6,220

6,240

6,260

6,280

9/1/1971

9/1/1973

9/1/1975

9/1/1977

9/1/1979

9/1/1981

9/1/1983

9/1/1985

9/1/1987

9/1/1989

9/1/1991

9/1/1993

9/1/1995

9/1/1997

9/1/1999

9/1/2001

Identifier SC00706512AAA Layer 3 Simulated Observed

Summary for SiteID = C143 (18 detail records)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 147

Figure B53. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the lower Dawson aquifer (model 

layer 4).

Coal Creek

Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleDry Cr

Plum Creek

West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Antelope Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

§ ̈¦25

PALMER

DIVIDE

!(

!(

!( !( !(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

Simla

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

5,700

6,200

5,900

6,000

5,800

6,500

6,600

6,900

6,200

6,000

7,100

7,200

6,900

6,900

7,000

7,300

7,400

6,900

6,600

6,800

6,700

7,000

6,500

6,700

6,300

6,400

5,900

6,200

6,600

6,700

5,700

6,200

5,900

6,000

5,800

6,500

6,600

6,900

6,200

6,000

7,100

7,200

6,900

6,900

7,000

7,300

7,400

6,900

6,600

6,800

6,700

7,000

6,500

6,700

6,500

6,300

6,400

5,900

6,200

6,600

6,700

105°

39°30'

39°

104°30'

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

–62 to –25

–25 to 0

Simulated change in hydraulic head, 

 1880–2003, in feet

dry model cell

0 to 50

50 to 100

100 to 250

250 to 500

500 to 984

South Denver metropolitan area

Lower Dawson aquifer simulated extent

 (model layer 4)

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Stream

Perennial

Ephemeral

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent 

 (model layer 6)

Dawson confining unit simulated extent

 (model layer 3)

EXPLANATION
148 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B54. Hydrographs of measured and simulated hydraulic head for selected wells completed in the lower Dawson aquifer.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleDryC

P

r

lum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Creek

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe

S

Creek

teels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

105°

40°

39°

104°

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

Lower Dawson aquifer simulated extent (model layer 4)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Extent of active model cells

Stream

Perennial

Ephemeral

! Colorado Division of Water Resources water-

 level monitoring site, lower Dawson aquifer

6,800

6,850

6,900

6,950

7,000

7,050

7,100

7,150

7,200

7,250

7,300

7,350

Summary for 'SiteID' = C200 (18 detail records)

Identifier SC01006736ADB Layer 4 Simulated Observed

3/1/19673/1/19703/1/19733/1/19763/1/19793/1/19823/1/19853/1/19883/1/19913/1/19943/1/19973/1/20003/1/2003

Summary for 'SiteID' = C171 (17 detail records)

5,700

5,750

5,800

5,850

5,900

5,950

6,000

6,050

6,100

Identifier SC00806606ACC2 Layer 4 Simulated Observed

7/1/19847/1/19867/1/19887/1/19907/1/19927/1/19947/1/19967/1/19987/1/20007/1/2002

5,650

5,700

5,750

5,800

5,850

5,900

5,950

Identifier SC00606626CAD Layer 4 Simulated Observed

3/1/19633/1/19663/1/19693/1/19723/1/19753/1/19783/1/19813/1/19843/1/19873/1/19903/1/19933/1/19963/1/19993/1/2002

Summary for 'SiteID' = C119 (17 detail records)

5,830

5,840

5,850

5,860

5,870

5,880

5,890

5,900

5,910

5,920

Summary for 'SiteID' = C145 (17 detail records)

Identifier SC00706617BAB Layer 4 Simulated Observed

4/1/19844/1/19864/1/19884/1/19904/1/19924/1/19944/1/19964/1/19984/1/20004/1/2002

5,700

5,750

5,800

5,850

5,900

5,950

6,000

 Summary for 'SiteID' = C147 (16 detail records)

Identifier SC00706629AAC Layer 4 Simulated Observed

4/1/19884/1/19894/1/19904/1/19914/1/19924/1/19934/1/19944/1/19954/1/19964/1/19974/1/19984/1/19994/1/20004/1/20014/1/20024/1/2003
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 149

Figure B55. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the Denver aquifer (model layer 6).

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleD ry Cr

Plum Creek

West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Cr

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir Cherry Creek

Reservoir

Barr

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir Cherry Creek

Reservoir

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

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

5,800

6,400

6,000 5,600

5,400

5,200

6,800

6,600

7,000

5,600

5,200

5,400

6,200

7,200

7,400

6,400

6,000

6,200

6,800

6,200

6,600

6,800

6,400

6,400

6,600

5,800

6,400

6,000 5,600

5,400

5,200

6,800

6,600

7,000

5,600

5,200

5,400

6,200

7,200

7,400

6,400

6,000

6,200

6,800

6,200

6,600

6,800

6,400

6,400

6,600

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

–442 to –100

–100 to 0

Simulated change in hydraulic head, 

 1880–2003, in feet

Dry model cell

0 to 50

50 to 100

100 to 250

250 to 500

500 to 924

South Denver metropolitan area

Denver aquifer simulated extent (model layer 6) Simulated potentiometric contour, shows altitude at which

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet

Generalized groundwater flow direction

Extent of active model cells

Stream Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)
150 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B56. Hydrographs of measured and simulated hydraulic head for selected wells completed in the Denver aquifer.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

BigDry C r

Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleD ry Cr

Plum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

BadgerCr eek

Bijou Creek

Antelope Cr

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett C

B

r

lack Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDEDIVIDE

§ ̈¦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

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

105°

40°

39°

104°

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

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Extent of active model cells

Stream

Perennial

Ephemeral

! Colorado Division of Water Resources water-

 level monitoring site, Denver aquifer

Summary for 'SiteID' = C044 (18 detail records)

Identifier SC00306328ADA Simulated Observed

6/1/19656/1/19686/1/19716/1/19746/1/19776/1/19806/1/19836/1/19866/1/19896/1/19926/1/19956/1/19986/1/2001

Layer 6

5,310

5,320

5,330

5,340

5,350

5,360

5,370

5,380

5,390

5,400

Summary for 'SiteID' = C184 (8 detail records)

5,500

5,600

5,700

5,800

5,900

6,000

6,100

6,200

Identifier SC00806714DB2 Layer 6 Simulated Observed

4/1/19914/1/19924/1/19934/1/19944/1/19954/1/19964/1/19974/1/19984/1/19994/1/20004/1/20014/1/2002

6,200

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

Summary for 'SiteID' = C217 (15 detail records)

Identifier SC01106723AA1 Layer 6 Simulated Observed

11/1/197611/1/197811/1/198011/1/198211/1/198411/1/198611/1/198811/1/199011/1/199211/1/199411/1/199611/1/199811/1/200011/1/2002

Summary for 'SiteID' = C241 (11 detail records) 

5,900

6,000

6,100

6,200

6,300

6,400

6,500

6,600

6,700

Identifier SC01206701CCB Layer 6 Simulated Observed

2/1/19872/1/19892/1/19912/1/19932/1/19952/1/19972/1/19992/1/20012/1/2003
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 151

The area of unconfined conditions in the Denver aquifer for 2003 (fig. B57) increased substantially in the northern, western, and southern parts of the aquifer compared to 

predevelopment conditions (fig. A58). Drawdown in response 

to pumping converted confined parts of the Denver aquifer 

to unconfined conditions, which resulted in the accelerating storage-depletion rate simulated for the Denver aquifer 

since 1999 (fig. B47). As the confined aquifer experiences 

drawdown and converts to unconfined conditions, the storagedepletion rate increases because more water is released 

from drainable storage than from confined storage for a unit 

decrease in hydraulic head (Robson, 1987).

Arapahoe Aquifer

The Arapahoe aquifer is divided into upper and lower 

aquifers in the northern part of its extent by a recognizable 

claystone confining unit (Chapter A). The predevelopment 

potentiometric surface for the upper Arapahoe aquifer (model 

layer 8) depicts groundwater flow from the south and west 

toward a regional discharge area along the South Platte River 

(fig. A59). The 2003 drawdown from predevelopment conditions in the upper Arapahoe aquifer ranged from about 100 

to 400 ft south of Denver and Aurora (fig. B58). Drawdown 

in the northern parts of the upper Arapahoe along the South 

Platte River was generally less than 50 ft (fig. B58) because 

the aquifer is near land surface and receives direct recharge 

from the surface. As much as 105 ft of water-level rise was 

simulated in the upper Arapahoe aquifer on the northwest 

margin of the aquifer where it is near land surface, receives 

recharge from the land surface, and where pumping has 

decreased since 1956 (Robson, 1987; Colorado Division of 

Water Resources, 1998).

Development of the lower Arapahoe aquifer followed a 

pattern similar to that of the Denver aquifer. Initial development in the 1950s was in the northwest part of the aquifer 

and in the Monument area. By 1978, pumping from the 

lower Arapahoe had expanded in the northern area along the 

South Platte River, in the south Denver metropolitan area, 

and in the Monument area. In the northern area of development, drawdown from 1880 to 1978 was generally less than 

50 ft because the aquifer is near land surface in this area and 

receives recharge from the surface and overlying alluvial 

aquifer. In the south Denver metropolitan area, drawdown 

as much as 300 ft is simulated over a widespread area, and 

in the Monument area, steep drawdown cones as much as 

675 ft deep are simulated for 1978. Pumping from the lower 

Arapahoe aquifer continued to expand through 2003 to 

provide municipal water supply for continuing urban development. In the south Denver metropolitan area, where the 

aquifer is thickest and exhibits large transmissivity, a large 

coalescing area of drawdown (as much as 400 ft) is simulated for 2003 (fig. B59). In the Monument area, simulated 

drawdown was about 800 to 1,690 ft by 2003 (fig. B59). 

The difference in drawdown patterns between the two areas 

is caused by the contrast in simulated hydraulic conductivity. 

Hydraulic conductivity and thickness, the product of which 

is transmissivity, in the lower Arapahoe in the south Denver 

metropolitan area is simulated as greater than that in the 

Monument area to represent the Wildcat Mountain alluvial 

fan. Because hydraulic conductivity, and thus transmissivity, are less in the Monument area than in the south Denver 

metropolitan area, smaller, steeper, and more isolated cones 

of drawdown are simulated in the Monument area. Future 

studies should consider additional data collection, compilation, and model refinement of the hydraulic-conductivity 

contrast between the south Denver metropolitan area and the 

Monument area.

Comparisons between simulated and observed hydraulic 

heads for selected wells in the CDWR water-level monitoring network provide variable results with simulated heads 

being greater than measured water levels for several lower 

Arapahoe wells. In the northern area near Brighton, where the 

lower Arapahoe aquifer is unconfined, water-level data from 

well C018 indicate a total water-level decline of about 95 ft 

since 1973, whereas simulation results indicate less than 50 ft 

of water-level decline (fig. B60). Near Aurora, water-level 

data from well C050 indicate a total water-level decline of 

about 475 ft since 1964 and a water-level decline rate of about 

23 ft/yr since 1999 (fig. B60), whereas simulation results indicate about 200 ft of water-level decline since 1880 (fig. B59, 

B60). Similarly, in the south Denver metropolitan area, 

water-level data indicate water-level decline of about 540 ft 

since 1986 at well C088 (water-level decline rate of about 

28 ft since 1999) and about 420 ft since 1987 at well C157 

(water-level decline rate of 31 ft/yr), while simulated waterlevel decline was on the order of about 100 ft for the same 

time period (fig. B60). In the Monument area, simulated heads 

were again greater than measured water levels at well C214, 

although the simulated and measured water-level decline 

(about 530 ft since 1986) and water-level decline rates (about 

72 ft/yr) were similar (fig. B60). South of Monument waterlevel rise is observed at well well C239, and although there 

is not a good match between observed and simulated heads at 

this well, the model does simulate urban recharge and waterlevel rise south of Monument consistent with the observations 

(fig. B59).

The extent of unconfined conditions in the lower Arapahoe 

aquifer for 2003 (fig. B61) increased slightly in the northwestern and southern parts of the aquifer extent compared to 

predevelopment conditions (fig. A60). The area of simulated 

unconfined conditions for the lower Arapahoe aquifer did not 

increase substantially since 1880 as it did for the Denver aquifer, indicating storage removal from the lower Arapahoe aquifer 

was primarily from confined storage in 2003.

Laramie–Fox Hills Aquifer

As with the other bedrock aquifers, the potentiometric 

surface of the Laramie–Fox Hills aquifer has been lowered on 

the western margin of its extent where groundwater development was greatest. Numerous potentiometric-surface cones of 
152 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B57. Calculated areas of confined and unconfined conditions for the Denver aquifer (model 

layer 6), 2003.

South

Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleDry Cr

Plum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Cr

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

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

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

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 extent of confined conditions

Simulated extent of unconfined conditions

Simulated extent of change from confined to unconfined 

 conditions, 1880–2003

South Denver metropolitan area

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Lower Arapahoe aquifer simulated extent (model layer 10)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Denver upper confining unit simulated extent (model layer 5)

Stream

Perennial

Ephemeral
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 153

Figure B58. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the upper Arapahoe aquifer 

(model layer 8).

South Platte

River

Box Elder Creek

Cache la Poudre R

Big Thompson River

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek Saint Vrain Cr

Lost Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

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

5,100

5,200

5,300

5,400

5,000

5,000

5,300

5,000

5,100

5,200

5,300

5,400

5,000

5,000

5,300

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

105°

40°

39°

104°

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

–105 to –50

–50 to 0

Simulated change in hydraulic head, 

 1880–2003, in feet

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 300

300 to 403

Upper Arapahoe aquifer simulated extent (model layer 8) Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Extent of active model cells

Stream Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

EXPLANATION

Denver aquifer simulated extent (model layer 6)
154 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B59. Simulated 2003 potentiometric surface and hydraulic-head change from 1879 to 2003 

for the lower Arapahoe aquifer (model layer 10).

South Platte

River

Box Elder Creek

Cache la Poudre R

Big Thompson River

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek Saint Vrain Cr

Lost Creek

6,000 6,200

6,400

6,600

6,800

7,000

7,200

7,400

6,800

7,000

6,400

6,800

7,200

6,600

6,400

6,200

6,200

6,800

6,000

6,000

6,4007,000

6,200

6,200

5,800

5,600

5,400

5,200

5,000

5,000

5,000

4,800

5,800

6,000 6,200

6,400

6,600

6,800

7,000

7,200

7,400

6,800

7,000

6,400

6,800

7,200

6,600

6,400

6,200

6,200

6,800

6,000

6,000

6,4007,000

6,200

6,200

5,800

5,600

5,400

5,200

5,000

5,000

5,000

4,800

5,800

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

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

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°

40°

39°

104°

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

–104 to –50

–50 to 0

Simulated change in hydraulic head,

 1880–2003, in feet

Dry model cell

50 to 100

100 to 200

200 to 400

400 to 800

800 to 1,690

South Denver metropolitan area

Upper Arapahoe aquifer simulated extent (model layer 8)

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

0 to 50

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 155

Figure B60. Hydrographs of measured and simulated hydraulic head for selected wells completed in 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 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

Lost Creek

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

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(!(!(

!(

!(

!(

!

!((!(!(

!(!(!( !(

!( !( !(

!(

!(!(

!(

!(

!( !(

!(

!(!(!( !( !(!( !(!(!(

!(!(!(

!(

!(

!(

!( !(

!(

!(!(!( !(!(

!(

!(!(

!(

!(

!(!(!(!(

!(!(

!(

!( !(!(!( !(

!(

!( !(

!(

!(!(

!(!(

!(

!(

!(

!( !(

!(

!(

!( !(!(!(!(!(!(!(!(

!(

!( !( !(

!(

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

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

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

!( Colorado Division of Water Resources water-level 

 monitoring site, Araphaoe aquifer undifferentiated

Stream

Perennial

Ephemeral

Summary for 'SiteID' = C018 (18 detail records)

4,800

4,850

4,900

4,950

5,000

5,050

5,100

Identifier SC00106732DDA Layer 10 Simulated Observed

12/1/197312/1/197512/1/197712/1/197912/1/198112/1/198312/1/198512/1/198712/1/198912/1/199112/1/199312/1/199512/1/199712/1/199912/1/2001

4,300

4,400

4,500

4,600

4,700

4,800

4,900

5,000

5,100

5,200

5,300

Identifier SC00306631DCD Layer 10 Simulated Observed

6/1/19646/1/19676/1/19706/1/19736/1/19766/1/19796/1/19826/1/19856/1/19986/1/19916/1/19946/1/19976/1/2000

Summary for 'SiteID' = C050 (17 detail records)

Summary for 'SiteID' = C238 (12 detail records)

6,150

6,200

6,250

6,300

6,350

6,400

6,450

6,500

6,550

Identifier SC01206618DC Layer 10 Simulated Observed

2/1/19872/1/19892/1/1991

2/1/19932/1/19952/1/19972/1/19992/1/20012/1/2003

Summary for 'SiteID' = C157 (9 detail records)

4,400

4,600

4,800

5,000

5,200

5,400

5,600

5,800

6,000

Identifier SC00706709CA Layer 10 Simulated Observed

9/1/19879/1/19889/1/19899/1/19909/1/19919/1/19929/1/1993

9/1/1994

9/1/19959/1/19969/1/19979/1/1998

9/1/19999/1/20009/1/2001

Identifier SC00506709CDA Layer 10 Simulated Observed

4,200

4,300

4,400

4,500

4,600

4,700 4,800

4,900

5,000

5,100

5,200

5,300

Summary for 'SiteID' = C088 (18 detail records)

4/1/19864/1/1988

4/1/1990

4/1/19924/1/19944/1/19964/1/19984/1/2000

4/1/2002

Identified SC01106701DC Layer 10 Simulated

5/1/19865/1/19885/1/19905/1/19925/1/19945/1/19965/1/19985/1/20005/1/2002

Observed

Summary for 'SiteID' = C214 (14 detail records)

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

5,550

5,560

5,570

5,580

5,590

5,600

5,610

5,620

Summary for 'SiteID' = C138 (17 detail records)

Identifier SC00706009DBC Layer 10 Simulated Observed

8/1/19608/1/1963

8/1/19668/1/19698/1/19728/1/19758/1/1978

8/1/19818/1/19848/1/19878/1/19908/1/19938/1/1996

8/1/1999

8/1/2002
156 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B61. Calculated areas of confined and unconfined conditions for the lower Arapahoe 

aquifer (model layer 10), 2003.

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 Cre

M

ek

ustang 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

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

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

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

Simulated extent of confined conditions

Stream

Perennial

Ephemeral

Simulated extent of unconfined conditions

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Arapahoe and Denver lower confining units combined 

 simulated extent (model layers 7 and 9)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 157

depression developed along the western one-third of the aquifer 

in response to pumping from 1956 to 2003 (Colorado Division 

of Water Resources, 1998). In 1978, numerous drawdown cones 

are simulated in the northern area of development, in the south 

Denver metropolitan area, and in the Monument area. By 2003, 

simulated drawdown in the northern and south Denver metropolitan area had expanded over a larger area and had deepened 

to about 1,000 ft (fig. B62). The extent of simulated unconfined 

conditions in the Laramie–Fox Hills aquifer increased slightly, 

primarily along the northwestern and southern margins of the 

aquifer, from predevelopment conditions (fig. A61) to 2003 

(fig. B63).

There was relatively good agreement between simulated 

heads and measured water levels from the CDWR network 

for the Laramie–Fox Hills aquifer. In the northern area near 

Brighton and Broomfield, measured water-level decline 

ranged from about 220 ft since 1969 at well C001 (waterlevel decline rate of 7.5 ft/yr since 1999) to about 340 ft since 

1971 at well C004 (water-level decline rate of about 6.6 ft/yr 

since 1999) (fig. B64). Measured water-level decline was less 

east of 186 ft at well C043 (water-level decline rate of about 

33 ft/yr), and near Byers, a water-level decline of about 40 was 

measured since 1978 at well C081 (water-level decline rate of 

about 2 ft/yr) (fig. B64). In the south Denver metropolitan area, 

water-level decline of about 70 ft was measured from 1989 to 

1998 at well C072, and water-level decline of about 370 ft was 

measured from 1988 to 1996 at well C083 (fig. B64). Simulated water-level decline and water-level decline rates for the 

Laramie–Fox Hills aquifer at these locations were well represented in the model.

Simulated Predictions of Future Conditions

Predictive simulations use the calibrated Denver Basin 

model to calculate predictive model sensitivities and to demonstrate the possible effects of future pumping and precipitation 

variability on groundwater conditions. Predictive simulations 

were run 50 years into the future from the end of the modelcalibration period (December 31, 2003) to 2053. The predictive 

simulations demonstrate the effects of drought conditions and 

hypothetical temporal changes to pumping on bedrock flow to 

the alluvial aquifer, storage-depletion rates, aquifer drawdown, 

and conversion to unconfined conditions. 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.

The first predictive simulation was used to calculate predictive sensitivities and examines the effects of future pumping 

on the water budget and hydraulic heads in a simple fashion 

by continuing recharge and pumping conditions from 2003 

through 2053. This simulation addresses the effects of drought 

on recharge to the Denver Basin aquifers because precipitation 

recharge is assigned using the precipitation distribution from 

2000 to 2003, which represents recent drought conditions. The 

simulation assumes pumping and recharge are held constant, 

using the 2003 rates and spatial distributions, from 2004 to 

2053. All other model boundary conditions for simulation such 

as springs, reservoirs, and streams (head-dependent flux boundaries) are the same as in the calibrated model.

A second predictive simulation demonstrates the use of 

the model to evaluate possible future management strategies. 

The simulation predicts the effects of reducing pumping from 

the Denver Basin aquifers. This simulation uses continued 

2000–2003 drought conditions for precipitation recharge, as in 

the first predictive simulation, but without pumping from the 

lower Arapahoe aquifer (layer 10) in the south Denver metropolitan area (model cells in rows 57–81 and columns 9–35) 

beginning in 2009. The simulation is somewhat unrealistic 

in that pumping from the lower Arapahoe likely will not 

completely cease in the near future; however, the simulation was intended to demonstrate the potential for aquifer 

water-level recovery should storage depletion be reduced 

because of surface-water importation, reductions in pumping, 

or aquifer-storage-and-recovery projects.

Predictive Simulation Results

Predictive simulations can lend insight to the effects of 

varying input parameters such as recharge and pumping on 

other components of the water budget. Many different predictive simulations are possible, and future work should examine 

additional scenarios. For this study, the effects of pumping from 

the bedrock aquifer on discharge to streams, the alluvial aquifer, 

storage, and potentiometric surfaces were examined for the 

predictive simulations.

Discharge to Streams and the Alluvial Aquifer

Based on simulation results for the model-calibration 

period 1879–2003, discharge to streams was variable depending on precipitation recharge. Discharge from bedrock aquifers 

to the alluvial aquifer decreased, and storage loss increased 

because of pumping during the model-calibration period. 

Results from the first predictive simulation indicate continued 

pumping from the bedrock aquifers will continue to capture 

water discharging to the surficial system, reducing bedrock 

discharge to streams and the alluvial aquifer (fig. B65). The 

simulated net discharge to streams, reservoirs, and springs (all 

surface-water inflows minus all surface-water outflows) was 

reduced about 10 percent from 15.7 ft3/s in 2003 to 14.5 ft3/s in 

2053 for the first predictive simulation. As pumping continued 

at the 2003 rate, simulated inflow from the alluvial aquifer to the 

bedrock units increased from 12.4 ft3/s in 2003 to 14.0 ft3/s in 

2053 for the first predictive simulation, while discharge from the 

bedrock units to the alluvial aquifer decreased from 27.2 ft3/s in 

2003 to 26.1 ft3/s in 2053 (fig. B65). The result was a decrease 

in the net flow from bedrock units to the alluvial aquifer (inflow 

minus outflow) from 14.8 ft3/s in 2003 to 12.1 ft3/s in 2053 

for the first predictive simulation (fig. B65). Decreased pumping from the lower Arapahoe aquifer in the second predictive 

simulation resulted in a net discharge from bedrock units to the 

alluvial aquifer of 12.9 ft3/s (fig. B65).
158 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B62. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 

for the Laramie–Fox Hills aquifer (model layer 12).

South

Platte

River

Cac he la Poudre R

Big Thompson River

Little Thompson R

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 Cre

M

ek

ustang Creek

Adobe Cree

Ste

k

els 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

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,600

5,800

5,000

5,200

5,400

4,800

4,600

4,400

4,600

5,000

4,600

5,400

4,600

5,600

5,000

4,800

5,400

5,400

5,000

4,600

6,000

6,200

6,400

6,600

6,800

7,000

7,200

7,400

5,800

5,600

5,600

5,800

5,000

5,200

5,400

4,800

4,600

4,400

4,600

5,000

4,600

5,400

4,600

5,600

5,000

4,800

5,400

5,400

5,000

4,600

6,000

6,200

6,400

6,600

6,800

7,000

7,200

7,400

5,800

5,600

DIVIDE

PALMERPALMER DIVIDE

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

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

–70 to –25

–25 to 0

Simulated change in hydraulic head,

 1880–2003, in feet

Dry model cell

100 to 200

200 to 400

800 to 1,000

1,000 to 1,200

1,200 to 1,975

South Denver metropolitan area

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

0 to 100

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 159

Figure B63. Calculated areas of confined and unconfined conditions for the Laramie–Fox Hills 

aquifer (model layer 12), 2003.

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

§ ̈¦70

§ ̈¦25

§ ̈¦76

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

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

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

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

Simulated extent of confined conditions

Simulated extent of unconfined conditions

Simulated extent of change from confined to unconfined conditions, 

 1880–2003

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Laramie confining unit simulated extent (model layer 11)

Stream

Perennial

Ephemeral

EXPLANATION
160 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B64. Hydrographs of measured and simulated hydraulic head for selected wells completed in the Laramie–Fox Hills 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 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

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!( !(

!(!( !( !( !(!( !(

!(

!(!(

!(

!(!( !( !(!(

!( !( !(!( !(

!(

!( !(

!(

!( !(!(

!( !(

!( !( !(

!(

!(

!(

!(!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

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

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

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Stream

Perennial

Ephemeral

!( Colorado Division of Water Resources water-level monitoring 

 site, Laramie–Fox Hills aquifer

4,940

4,960

4,980

5,000

5,020

5,040

5,060

5,080

5,100

Identifier SC00406718BCA Layer 12 Simulated Observed

Summary for 'SiteID' = C072 (8 detail records)

5/1/19895/1/1990

5/1/19915/1/19925/1/1993

5/1/1994

5/1/19955/1/19965/1/19975/1/1998

Identifier SC00106935BBA Layer 12 Simulated Observed

4,600

4,700

4,800

4,900

5,000

5,100

5,200

5,300 Summary for 'SiteID' = C020 (17 detail records)

6/1/19586/1/1961

6/1/1964

6/1/19676/1/19706/1/19736/1/19766/1/19796/1/19826/1/19856/1/19886/1/19916/1/19946/1/19976/1/2000

Summary for 'SiteID' = C083 (11 detail records)

Identifier SC00506603AD Layer 12 Simulated Observed

4,200

4,400

4,600

4,800

5,000

5,200

5,400

1/1/19881/1/19891/1/19901/1/19911/1/19921/1/1993

1/1/19941/1/1995

1/1/19961/1/19971/1/19981/1/1999

Summary for 'SiteID' = C004 (18 detail records)

Identifier SB00106617DCC Layer 12 Simulated Observed

4,200

4,300

4,400

4,500

4,600

4,700

4,800

4,900

5,000

4/1/19714/1/19744/1/19774/1/19804/1/19834/1/19864/1/1989

4/1/19924/1/1995

4/1/1998

4/1/2001

Summary for 'SiteID' = C042 (16 detail records)

5,000

5,050

5,100

5,150

5,200

5,250

5,300

5,350

Identifier SC00306327BD Layer 12 Simulated Observed

4/1/19884/1/19894/1/19904/1/19914/1/19924/1/19934/1/19944/1/19954/1/19964/1/19974/1/1998

4/1/19994/1/20004/1/20014/1/2002

4/1/2003

Identifier SC00506123ABB Layer 12 Simulated Observed

5,160

5,170

5,180

5,190

5,200

5,210

5,220

5,230

Summary for 'SiteID' = C081 (17 detail records)

7/1/19787/1/19807/1/19827/1/1984

7/1/19867/1/19887/1/19907/1/19927/1/19947/1/19967/1/19987/1/20007/1/2002

Identifier SB00106529AAD Layer 12

4,600

4,650

4,700

4,750

4,800

4,850

4,900

4,950

5,000 Summary for 'SiteID' = C001 (18 detail records)

Simulated Observed

10/1/196910/1/197210/1/197510/1/197810/1/198110/1/198410/1/198710/1/199010/1/199310/1/1996

10/1/199910/1/2002
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 161

Figure B65. Simulated transient flow between the Denver Basin alluvial aquifer and bedrock units for 

model-calibration period and predictive simulations, 1879–2053.

0

5

10

15

20

25

30

35

40

Flow, in cubic feet per second

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

2008

2013

2018

2023

2028

2033

2038

2043

2048

2053

Flow to alluvial aquifer from bedrock units for first

 predictive simulation 

Flow to bedrock units from alluvial aquiferfor first

 predictive simulation 

Net flow to alluvial aquife frombedrock units for

 first predictive simulation

Net flow to alluvial aquifer from bedrock units for

 second (reduced pumping) predictive simulation 

EXPLANATION

Storage

Predictive simulations to 2053 indicate continued storage 

loss as pumping continues. The rate of storage removal may be 

reduced by reducing pumping, but storage depletion will continue 

consistent with 100-year predictions simulated by the CDWR 

SB96–74 model (Colorado Division of Water Resources, 1998). 

The cumulative volume of water removed from bedrock storage 

was simulated to reach about 2.5 million acre-ft by 2053 with no 

increase in pumping over 2003 rates (fig. B66). About 50 percent 

of the storage loss for the first predictive simulation was from the 

south Denver metropolitan area, and about 50 percent of the storage loss was from the remaining areas of the basin. If pumping 

from the Arapahoe aquifer in the south Denver metropolitan area 

were reduced, as represented in the second predictive simulation, 

about 350,000 acre-ft of water would remain in storage for later 

use. These results demonstrate the relation between pumping and 

storage-depletion and indicate that reduction of pumping could 

slow the rate of storage depletion, at least while the aquifers are 

confined, to extend the usable aquifer life.

Changes in Predicted Hydraulic Heads

Model-simulation results for the calibration period 

1879–2003 indicate substantial drawdown in all of the Denver 

Basin bedrock aquifers compared to predevelopment conditions because of pumping from the confined aquifers. Pumping 

at the 2003 rate through 2053, as simulated in the first predictive simulation, shows continued drawdown of potentiometric 

surfaces in all model aquifer layers. Results from the second 

predictive simulation indicate some water-level recovery 

would occur in the Denver and lower Arapahoe aquifers if 

pumping from the lower Arapahoe aquifer was reduced.

Some cells became inactive during the predictive simulations. Inactive cells (shown in white on the drawdown figures) 

are considered artifacts of the model and do not indicate complete dewatering of the aquifer at the cell locations. Because of 

limitations of the model-solution procedure, model cells may 

become inactive when calculated heads are near the defined cell 

bottom. This problem typically arises when ambient hydraulic 

heads are near cell bottoms and the saturated thickness in the 

vicinity of the well cell is insufficient to support continued 

pumping at the specified withdrawal rate. Under actual field 

conditions, the well pumping rate would be limited by locally 

small transmissivity as the head approaches the aquifer bottom. 

However, the WEL Package does not adjust withdrawal rates 

as head approaches the cell bottom, and continued simulated 

pumping can result in cell deactivation. If a cell in which pumping is simulated by the WEL package deactivates, simulation of 

pumping at that cell ceases when the cell is made inactive.

For the upper Dawson aquifer, an additional 85 ft of 

drawdown is predicted from 2004 through 2053 with the maximum drawdown occurring in the Monument area and east of 
162 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Franktown (fig. B67). As pumping in the simulation lowered the 

upper Dawson potentiometric surface, groundwater flow directions shifted toward the Cherry Creek discharge area. An area 

of up to 28 ft of water-level rise was simulated in downgradient 

areas where urban recharge is applied (fig. B67).

For the lower Dawson aquifer, the first prediction simulates 

drawdown of less than 50 ft in much of the aquifer area, although 

as much as 200 ft of additional drawdown is simulated south 

and east of Franktown from 2004 to 2053 (fig. B68). Maximum 

predicted drawdown in the lower Dawson aquifer for the period 

2004–2053 is as much as 340 ft in the Monument area (fig. B68). 

Total predicted drawdown in the lower Dawson 2053 potentiometric surface from predevelopment conditions was about 100 

to 400 ft in the south Denver metropolitan area and about 400 to 

800 ft near the aquifer margin east of Monument.

Continued pumping in the Denver aquifer also will 

result in additional drawdown. Maximum drawdown from 

the first predictive simulation in the Denver aquifer for the 

period 2004–2053 will again occur east of Monument near the 

basin margin with simulated drawdowns of as much as 630 ft 

(fig. B69). In the south Denver metropolitan area as much as 

200 ft of drawdown was simulated south and east of Franktown 

for the predictive period 2004–2053 (fig. B69). Maximum 

predicted drawdown in the Denver aquifer 2053 potentiometric surface compared to predevelopment conditions was more 

than 800 ft in some parts of the south Denver metropolitan 

area and east of Monument, although less than 50 ft of regional 

drawdown is calculated for much of the aquifer. The extent of 

unconfined conditions in the Denver aquifer also increased from 

2004 to 2053 in response to pumping, primarily in the center of 

the basin (fig. B70).

Model-predicted heads for 2053 in the lower Arapahoe aquifer for the first predictive simulation reflect continued pumping in 

the south Denver metropolitan and Monument areas (fig. B71). 

An additional 100 to 200 ft of drawdown is predicted in the 

south Denver metropolitan area, and an additional 400 to 1,200 ft 

of drawdown is predicted in the area east of Monument from 

2004 to 2053 (fig. B71). Total predicted drawdown in the lower 

Arapahoe aquifer from predevelopment to 2053 was about 400 to 

800 in the south Denver metropolitan area and locally was about 

1,150 ft in the Monument area. The lower Arapahoe aquifer in the 

south Denver metropolitan area is heavily pumped for municipal 

purposes and has a large simulated transmissivity so that drawdown cones from individual wells have coalesced into a large 

area of regional drawdown. Drawdown in the lower Arapahoe 

aquifer in the Monument area was restricted to individual cones 

of depression with steep gradients surrounding pumping centers 

because the aquifer has a lower transmissivity. Some areas of 

water-level rise were simulated along the margins of the aquifer 

where it is unconfined and in hydrologic connection with the alluvial aquifer (fig. B71). The extent of unconfined conditions for 

the lower Arapahoe aquifer increased slightly in the northwestern 

and southern parts of the aquifer extent from predevelopment to 

2003, and additional conversion to unconfined conditions in the 

lower Arapahoe aquifer by 2053 is predicted for only a few model 

cells along the southern aquifer margin.

Figure B66. Simulated cumulative volume of water removed from storage for Denver Basin 

bedrock units, 1880–2053.

–3.0

–2.5

–2.0

–1.5

–1.0

0.5

0

0.5

Cumulative change in bedrock groundwater storage, 

In millions of acre-feet 

Year 1880

1890

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

2010

2020

2030

2040

2050

2060

All bedrock units, calibration period

All bedrock units, first predictive simulation

All bedrock units, second (reduced pumping) 

 predictive simulation 

South Denver metropolitan area, 

 calibration period

South Denver metropolitan area, first 

 predictive simulation

South Denver metropolitan area, second 

 (reduced pumping) predictive simulation

Bedrock all other areas, calibration period

Bedrock other areas, first predictive simulation

Bedrock other areas, second (reduced pumping) 

predictive simulation 

EXPLANATION
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 163

Figure B67. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 for the upper Dawson aquifer (model 

layer 2) for predictive simulation 1.

Coal Creek

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

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

DIVIDE

PALMER

DIVIDE

!

!

! ! !

! !

!

!

!

!

!( ! !

!

!

!

!

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

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦25

6,700

6,600

6,500

6,800

6,900

6,400

6,300

6,200

7,000

6,100

6,000

7,100

5,900

6,700

6,600

6,500

6,800

6,900

6,400

6,300

6,200

7,000

6,100

6,000

7,100

5,900

6,000

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

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated change in hydraulic head, 

 2004–2053, in feet

South Denver metropolitan area

Upper Dawson aquifer simulated extent (model layer 2) 

 

Generalized groundwater flow direction Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2053. 

 Datum NAVD88. Contour interval 100 feet –28 to –10

–10 to 0

Dry model cell

0 to 10

10 to 20

20 to 40

40 to 60

60 to 85
164 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B68. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 for the lower Dawson 

aquifer (model layer 4) for predictive simulation 1.

Coal Creek

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

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

DIVIDE

PALMERPALMER DIVIDE

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

!

!

! ! !

! !

!

!

!

!

! !

!

!

!

!

!

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

6,100

6,200

6,300

6,000

6,400 6,500

6,600

6,800

6,700

6,900

5,900

5,800

7,000

7100

5,700

7,200

7,300

6,800

6,700

5,900

6,900

6,800

6,500

7,000

7,000

6,100

6,700

6,900

6,100

6,200

6,300

6,000

6,400 6,500

6,600

6,800

6,700

6,900

5,900

5,800

7,000

7100

5,700

7,200

7,300

6,800

6,700

5,900

6,900

6,800

6,500

7,000

7,000

6,100

6,700

6,900

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

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated change in hydraulic head, 

 2004–2053, in feet

South Denver metropolitan area

Lower Dawson aquifer simulated extent 

 (model layer 4)

Generalized groundwater flow direction

Extent of active model cells

Lower Arapahoe aquifer simulated extent

 (model layer 10)

Denver aquifer simulated extent 

 (model layer 6)

Laramie–Fox Hills aquifer simulated extent

 (model layer 12)

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

–110 to –50 Datum NAVD88. Contour interval 100 feet

–50 to 0

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 300

300 to 328
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 165

Figure B69. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 for the Denver aquifer 

(model layer 6) for predictive simulation 1.

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 Cre

M

ek

ustang Creek

Adobe Cree

Ste

k

els 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

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

PALMER

DIVIDE

PALMER

DIVIDE

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

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

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 change in hydraulic head,

 2004–2053, in feet

South Denver metropolitan area

Denver aquifer simulated extent (model 

 layer 6) 

Generalized groundwater flow direction

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent

 (model layer 12)

Lower Arapahoe aquifer simulated extent

 (model layer 10) Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2053. 

–354 to –150 Datum NAVD88. Contour interval 200 feet

–150 to 0

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 400

400 to 628

5,800

6,400 6,000

6,200

5,600

5,400

5,200

6,800

6,600

7,000

7,200

5,600

5,600

5,200

5,200

6,000

6,400

6,600

7,000

5,400

6,200

6,600

6,800

6,600

6,200 6,400

6,800

5,400

5,800

6,400 6,000

6,200

5,600

5,400

5,200

6,800

6,600

7,000

7,200

5,600

5,600

5,200

5,200

6,000

6,400

6,600

7,000

5,400

6,200

6,600

6,800

6,600

6,200 6,400

6,800

5,400
166 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B70. Calculated areas of confined and unconfined conditions for the Denver aquifer (model 

layer 6) in 2053 for predictive simulation 1.

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 Bijou Creek

Middle Rush Cre

M

ek

ustang 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

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

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

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

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

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 extent of confined conditions

Stream

Perennial

Ephemeral

Simulated extent of unconfined conditions

Simulated extent of change from confined

 to unconfined conditions, 2004–2053

Simulated extent of change from confined

 to unconfined conditions, 1880–2003 South Denver metropolitan area

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Denver upper confining unit simulated extent (model layer 5)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 167

Figure B71. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 

for the lower Arapahoe aquifer (model layer 10) for predictive simulation 1.

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

5,400

6,000

5,200

5,600

5,800

6,200

6,400

5,000

6,600

6,800

7,000

7,200

4,800

7,000

6,200

5,000

6,600

6,200

6,200

5,800

6,400

6,600

6,000

5,000

6,600

5,000

5,400

6,000

5,200

5,600

5,800

6,200

6,400

5,000

6,600

6,800

7,000

7,200

4,800

7,000

6,200

5,000

6,600

6,200

6,200

5,800

6,400

6,600

6,000

5,000

6,600

5,000

PALMER DIVIDE

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

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

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

Simulated change in hydraulic head,

 2004–2053, in feet South Denver metropolitan area

Lower Arapahoe aquifer simulated extent (model layer 10) 

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2053. 

 Datum NAVD88. Contour interval 200 feet

–167 to –100

–100 to 0

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 400

400 to 800

800 to 1,210
168 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Results for the Laramie–Fox Hills aquifer from the first 

predictive simulation indicate continued lowering of the potentiometric surface. From 2004 to 2053, as much as about 1,900 ft 

of drawdown is calculated for the south Denver metropolitan and 

Monument areas, while predicted regional drawdown over much 

of the aquifer extent is about 100 ft (fig. B72). Maximum predicted drawdown from predevelopment conditions was more than 

2,000 ft in the south Denver metropolitan and Monument areas. 

The area of unconfined conditions in the Laramie–Fox Hills 

aquifer expanded primarily along the northwestern and southern 

margins of the aquifer from predevelopment to 2003 (fig. B73). 

Some additional conversion to unconfined conditions is predicted 

near the northwestern and southern basin margins by the first 

predictive simulation, and a new area of unconfined conditions is 

predicted just north of Parker (fig. B73).

Results from the second predictive simulation indicate less 

drawdown of the lower Arapahoe potentiometric surface and less 

storage loss from 2004 to 2053 compared to the first predictive 

simulation, if pumping from the lower Arapahoe aquifer was 

ceased in south Denver metropolitan area (fig. B74). The predictive simulation of reduced pumping also indicates less drawdown 

of the Denver aquifer potentiometric surface by 2053 if pumping 

from the lower Arapahoe aquifer in the south Denver metropolitan area is ceased in 2009 (fig. B75) because of the hydraulic 

connection between the Denver and Arapahoe aquifers. In the 

south Denver metropolitan area, the second prediction simulated 

as much as 400 ft less drawdown for the lower Arapahoe aquifer 

(fig. B74) and as much as 100 ft less drawdown for the Denver 

aquifer (fig. B75) than for the first predictive simulation. Because 

of the large hydraulic-conductivity values simulated for the 

Denver and lower Arapahoe aquifers in this region, a difference in 

drawdown between the two predictive simulations of about 10 ft 

extends over a large area north toward the South Platte River, east 

to Bennett, and south toward the Palmer Divide (figs. B74, B75). 

These results indicate that pumping from the lower Arapahoe 

aquifer is affecting hydraulic heads and storage depletion in the 

northern two-thirds of the basin in the overlying Denver aquifer.

Monitoring the Hydrologic System

Sources of uncertainty related to hydrogeologic understanding and simulations of the Denver Basin aquifer system 

include system conceptualization and geologic framework, datameasurement uncertainty, and estimation or generalization uncertainty. Some sources of uncertainty, such as data-measurement 

and parameter estimation, can be quantified through statistical 

model analysis, and the results can be used to guide future data 

collection that could reduce model uncertainty as described in the 

section “Model-Based Statistical Analysis of Potential Monitoring 

Locations” in Chapter C. This ability to perform statistical 

analysis on model results is an important outcome from model 

construction. Other aspects of the model, such as spatial (cell 

size) and temporal discretization, aquifer top and bottom configurations, and values and distribution of sand-plus-silt fractions, 

are assigned (fixed) in the model input, and are not amenable to 

automated parameter estimation and sensitivity analysis. Errors 

associated with assigned parameters are more difficult to quantify, 

and suggestions for data collection related to assigned (fixed) 

parameters are thus more qualitative than the prediction sensitivity analysis presented in Chapter C for adjustable parameters.

Additional data-collection efforts are often appropriate to 

address sources of uncertainty and further future hydrogeologic 

analysis. The conceptual model and corresponding numerical 

simulations presented herein provide one realization of groundwater conditions in the Denver Basin. A reasonable and unique 

set of model parameters was developed by this study, although 

other conceptualizations of the flow system and different numerical results are possible. Future data-collection efforts are suggested to further improve the understanding of hydrogeologic 

conditions and the groundwater flow model. Future continued 

monitoring and refinements to the groundwater flow model also 

are needed to document future storage depletion in response to 

climate variability and continued groundwater pumping in the 

Denver Basin.

Geologic Framework and Aquifer Properties

The conceptualization of geologic layering used by this 

study is reasonable and provides model layering consistent with 

previous studies in the basin. Definitions of geologic layering 

implemented by the present model follow the Denver Basin Rules 

and Regulations (2CCR 410–1), which are defined on the basis of 

a combination of administrative and geologic factors. However, 

the Arapahoe, Denver, and lower Dawson aquifers are quite heterogeneous, and other conceptualizations of bedrock layering are 

possible. Aquifer-base altitudes in the geophysical database were 

assigned from geophysical logs by several workers over the years, 

and while a conscientious effort was made to pick geologic layers 

with consistency, aquifer heterogeneity causes inherent variability 

in the geologic database. Efforts are currently (2010) underway 

to reevaluate the continuity of well-defined sandstone layers 

and the layering definitions being applied to the Denver Basin 

(Peter Barkmann, Colorado Geological Survey, oral commun., 

2009). The groundwater flow model is constructed such that different base-altitude configurations could be substituted into the 

model framework and related to changes in model output.

The Parameter-Prediction statistical analysis in Chapter C 

indicates areas in the Denver Basin where additional hydraulicconductivity values 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 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 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 reduce uncertainty of predicted heads in the 

lower Arapahoe aquifer most in the eastern and northern parts of 

the basin (fig. C40).
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 169

Figure B72. Simulated 2053 potentiometric surface and hyraulic-head change from 2004 to 2053 

for the Laramie–Fox Hills aquifer (model layer 12) for predictive simulation 1.

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

5,600

5,000

5,800

5,200

5,400

4,800

6,000

4,600

6,200

6,400

6,600

6,800

7,000

7,200

4,400

4,200

4,600

5,200

4,600

4,800

6,000

5,400

5,800

5,000

5,400

4,800

4,800

7,000

6,400

5,000

6,600

6,000

6,800

6,400

5,600

5,400

5,600

4,800

4,600

4,600

4,800

4,600

4,400

5,600

4,800

6,200

5,600

5,000

5,800

5,200

5,400

4,800

6,000

4,600

6,200

6,400

6,600

6,800

7,000

7,200

4,400

4,200

4,600

5,200

4,600

4,800

6,000

5,400

5,800

5,000

5,400

4,800

4,800

7,000

6,400

5,000

6,600

6,000

6,800

6,400

5,600

5,400

5,600

4,800

4,600

4,600

4,800

4,600

4,400

5,600

4,800

6,200

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

DIVIDE

PALMERPALMER

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

!(

!

!

!(

!(

!

!(

! ! !(

!

!

!

!

!( !

!

!

!

!

!

!

!

!

!

!

!(

!

!

!

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

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 change in hydraulic head, 

 2004–2053, in feet South Denver metropolitan area

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet

–164 to –100

–100 to 0

Dry model cell

0 to 100

100 to 250

250 to 500

500 to 1,000

1,000 to 1,500

1,500 to 1,875
170 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B73. Calculated areas of confined and unconfined conditions for the Laramie–Fox Hills 

aquifer (model layer 12) in 2053 for predictive simulation 1.

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 Cre

M

ek

ustang 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

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

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

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

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 extent of confined conditions

Stream

Perennial

Ephemeral

Simulated extent of unconfined conditions

Simulated extent of change from confined to 

 unconfined conditions, 1880–2003

Simulated extent of change from confined to 

 unconfined conditions, 2004–2053

South Denver metropolitan area

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Laramie confining unit simulated extent (model layer 11)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 171

Figure B74. Simulated 2053 potentiometric surface for reduced pumping conditions and hydraulichead difference between predictive simulations 1 and 2 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 Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

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

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

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

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

Simulated difference in hydraulic head

 between first and second predictive 

 simulations, 2053, in feet South Denver metropolitan area

Lower Arapahoe aquifer simulated extent 

 (model layer 10) 

Extent of active model cells

Stream

Perennial

Ephemeral

–400 to –200

–200 to –100

–100 to –50

–50 to –25

–25 to –10

–10 to 0

0
172 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B75. Simulated 2053 potentiometric surface for reduced pumping conditions and 

hydraulic-head difference between predictive simulations 1 and 2 for the Denver aquifer (model 

layer 6).

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 Cre

M

ek

ustang 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

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

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

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

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

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 difference in hydraulic head

 between first and second predictive 

 simulations, 2053, in feet South Denver metropolitan area

Denver aquifer simulated extent (model layer 6)

Extent of active model cells

Stream

Perennial

Ephemeral

Lower Arapahoe aquifer simulated extent (model layer 10)

–156 to –100

–100 to –50

–50 to –25

–25 to –10

–10 to –5

–5 to 0

0
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 173

Aquifer storage properties were fixed parameters in 

the groundwater flow model because there were insufficient 

measured values with which to compare an estimated spatial 

variation. However, the Denver Basin bedrock aquifers are 

heterogeneous, and there is spatial variability in storagecoefficient and specific-yield values. As drawdown continues 

and parts of the aquifer convert from confined to unconfined 

conditions, information on the spatial distribution of specific 

yield will become important to evaluating storage depletion especially for the Denver aquifer, which was simulated 

as having the most area converted to unconfined conditions. 

Continued collection of storage-coefficient and specific-yield 

estimates determined from aquifer testing or core analysis 

is encouraged, whenever the opportunity arises, to enhance 

the understanding of storage in the Denver Basin. Additional 

model realizations using expanded pilot-point configurations 

may improve the ability of the groundwater flow model to represent aquifer-property distributions in more detail (see section 

“Pilot-Point Approach to Hydraulic-Conductivity Estimation” 

in Chapter C for a description of the pilot-point methodology 

used to represent hydraulic-conductivity distributions for the 

present model).

Recharge and Discharge 

Recharge parameters were estimated in model calibration, 

and sensitivity analysis indicates model results are sensitive to 

recharge parameters, especially the percentage of precipitation 

that becomes recharge to the Dawson aquifer. Because recharge 

to the Dawson and to the Denver aquifers are two model 

parameters to which results are most sensitive (as discussed in 

the section “Parameter Sensitivity” in Chapter C), field efforts 

to better quantify precipitation recharge to these units would 

improve model and water-budget accuracy. More accurate 

estimates of agricultural and urban irrigation return flows also 

would increase model and water-budget accuracy. Unsaturatedzone monitoring of water content in both developed and undeveloped areas of the Dawson and Denver aquifers could provide 

estimates of recharge under varying land-use conditions that 

would be useful to estimating recharge.

Long-term streamflow records are sparse in undeveloped parts of the basin where they would be most useful 

for estimating base flow from groundwater. The site Cherry 

Creek near Franktown (06712000; fig. A6) is the only Denver 

Basin gaging station with a long-term record and minimal 

effects from upstream diversion and development. Monitoring 

streamflow in the headwaters of other tributaries in the basin 

could provide additional base-flow estimates of groundwater 

discharge from Denver Basin aquifers.

Pumping from the Denver Basin aquifers was estimated 

in this study by following methods used in previous studies. 

The resulting estimates are reasonable and consistent with the 

conceptual understanding of conditions in the basin, indicating 

that the greatest irrigation pumping is from the alluvial aquifer 

along the South Platte River and that the greatest municipal 

pumping is from bedrock aquifers in populated areas on 

the west side of the basin. However, because pumping is a 

large part of the water budget, model results for drawdown 

and storage depletion are sensitive to simulated pumping 

rates. Specifically, of the pumping parameters, the model 

was most sensitive to pumping rates from alluvial irrigation 

wells and pumping rates from irrigation, municipal and commercial/industrial bedrock wells as discussed in the section 

“Parameter Sensitivity” in Chapter C. If pumping information 

was collected from municipal water providers for irrigation, 

municipal, and commercial/industrial wells, simulated pumping estimates could be improved and thus model-prediction 

uncertainty would be reduced. Currently (2010), no centralized database or reporting system exists for pumping rates 

from the Denver Basin aquifers. Many individual municipal 

water providers meter and record pumping as part of daily 

operations, but these data are not compiled on a regional 

basis. Implementation of a metering and reporting system for 

pumping information would provide discharge information for 

the basin with which to better evaluate aquifer drawdown and 

storage depletion rates.

Water-Level Data

Water levels were periodically measured by the 

U.S. Geological Survey at more than 1,000 wells in the 

Denver Basin prior to the 1980s. Since the 1980s, the 

CDWR has operated a water-level monitoring network of 

about 278 wells (fig. B49). The network includes some wells 

with water levels dating back to the 1950s and 1960s (for 

example, Colorado Division of Water Resources, 2003, 2004). 

While the current network provides useful information, there 

are issues and concerns related to the present water-level 

monitoring network. Most of the wells in the present waterlevel monitoring network are active municipal, commercial, or 

domestic production wells, and, thus, are not solely dedicated 

to monitoring water levels. The network wells are constructed 

of various materials, some of which are not resistant to corrosion and plugging, and the screened intervals are not necessarily designed to appropriately monitor selected aquifer layers. 

For example, one domestic well in the network was logged 

with a televiewer tool, and substantial deterioration of the 

well screen was observed such that water levels measured in 

the well may not be representative of the static water level in 

the aquifer at this location (Courtney Hemenway, Hemenway 

Groundwater Engineering, oral commun., 2008). Water levels 

measured in wells with poor hydraulic connection to the 

aquifer likely do not reflect ambient water levels in the aquifer 

and should be considered for replacement or elimination from 

the network.

Questions also exist as to the pumping status of wells 

associated with the monitoring network at the time of waterlevel measurement. Because the water-level network wells are 

used for production, the water level recorded in the database 

may represent a pumping water level in the well, which would 
174 Groundwater Availability of the Denver Basin Aquifer System, Colorado

be lower than the ambient head in the aquifer. The pumping 

status of a well also is influenced by seasonal pumping variations. Many Denver Basin wells are more heavily pumped 

during the summer when lawn and garden watering occurs 

in urban and suburban areas. If water levels are measured 

during the summer and fall, the measurement is likely representative of pumping conditions and may indicate drawdown 

greater than what would be indicated by a winter water-level 

measurement. Water-level measurements in the CDWR 

Denver Basin network historically have been measured in 

the spring. In 2003, the CWCB and CDWR began collecting 

Denver Basin water-level data in the fall after the summer 

irrigation season and in the spring before irrigation season. 

Analysis of the data indicates summer and fall water-level 

measurements are substantially lower than spring water-level 

measurements, and measurements taken in the spring are 

considered most representative of ambient aquifer conditions 

(Brian Ahrens, Colorado Division of Water Resources, written 

commun., 2008).

The density and locations of wells in the current 

water-level monitoring network are insufficient to draw 

aquiferwide potentiometric-surface contours for the Denver 

Basin bedrock aquifers. An increased density of monitoring wells and additional measurements in areas identified by 

the model-sensitivity analysis would help evaluate regional 

water-level changes and reduce model uncertainty. For 

example, as discussed in the section “Model-Based Statistical 

Evaluation of Potential Monitoring Locations” in Chapter C, 

model-prediction statistical analysis indicates that additional 

observations in aquifer layers in the north-central and southcentral parts of the basin would likely reduce uncertainty 

in the model-calculated potentiometric surface of the lower 

Arapahoe aquifer.

Long-term water-level data from the CDWR database indicate water-level declines of as much as 500 ft and 

maximum water-level decline rates of 20 to 30 ft/yr for 

the Arapahoe and Laramie–Fox Hills aquifer in the south 

Denver metropolitan area (Colorado Division of Water 

Resources, 2004). Water-level decline in the Arapahoe and 

Laramie–Fox Hills aquifers is much less north of Denver in 

Adams County where the aquifers are near land surface and 

thus receive more recharge than areas near the center of the 

basin where confined conditions exist and there is little to 

no recharge. Recent review of well and pumping conditions 

for the network indicates regional drawdown for the Arapahoe aquifer in the south Denver metropolitan area is perhaps 

less than indicated by the CDWR network because of poor 

well construction in the network and the seasonal changes 

in pumping (Courtney Hemenway, Hemenway Groundwater 

Engineering, oral commun., 2008). Hydrographs of simulated 

heads generated by this study compared to observed heads 

for the CDWR water-level network wells indicate observed 

values were less than simulated values for wells completed 

in the lower Arapahoe aquifer. However, agreement between 

simulated heads and water levels measured in the CDWR 

water-level network was reasonable for the Dawson, Denver, 

and Laramie–Fox Hills aquifers.

The Observation-Parameter statistic discussed in 

Chapter C can be used to identify areas where parameter 

uncertainty would be decreased by adding head observations. 

Results indicate additional head observations in the northern 

part of the basin would decrease parameter uncertainty for 

all four of the highest ranked parameters (figs. C41–C44). 

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. Maps of the ObservationPrediction statistic discussed in Chapter C 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. 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.

Future water-level monitoring efforts in the Denver Basin 

would benefit from dedicated monitoring wells constructed 

of material resistant to corrosion, such as polyvinylchloride 

(PVC) with screened intervals appropriately placed to monitor selected bedrock units. Because costs to install a dedicated 

monitoring-well network may be prohibitive, domestic and 

production wells will likely continue to be used for water-level 

measurements. The construction integrity of existing wells 

should be considered as additional wells are selected for a 

monitoring network. An ideal network would include wells 

located throughout the basin, perhaps with a concentration of 

monitoring wells on the west side of the basin where pumping 

is greatest. Based on analysis of the present network, waterlevel measurements collected in the spring represent ambient 

heads in the nonirrigation season while fall measurements are 

useful to evaluate the effects of summer irrigation pumping. 

Retaining existing wells in a long-term network should be 

considered if a long-term water-level record exists for the well 

and if the well condition and completion interval are appropriate for the inclusion in the network. Because model-sensitivity 

results indicate that the simulation results are sensitive to 

vertical hydraulic conductivity, vertical nesting of monitoring 

wells in the various bedrock aquifers also should be considered so that vertical head gradients between aquifers can be 

monitored. Vertical well nests also would facilitate field-scale 

aquifer testing from which vertical hydraulic-conductivity 

could be estimated.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 175

Groundwater Sustainability 

and Management

Groundwater sustainability can be defined as the achievement of an acceptable tradeoff between groundwater use and 

the long-term effects of that use (Alley, 2006). In order to be 

sustainable, groundwater resources must be used and managed 

in a manner that can be maintained for an indefinite amount of 

time (Faunt, 2009). Sustainability requires iterations of monitoring, analysis, and application of management practices and 

is affected by physical, chemical, economic, environmental, 

legal, philosophical, and institutional factors (Faunt, 2009). 

The Denver Basin aquifer system is administrated as nonrenewable and nonsustainable because the aquifers are primarily 

confined and receive little precipitation recharge (Graham and 

VanSlyke, 2004). Groundwater storage is being depleted in the 

Denver Basin, and the present level of pumping is not considered sustainable over the next 50 years, especially in the south 

Denver metropolitan area (South Metro Water Supply Study 

Board, written commun., 2004). Recurring monitoring and 

analysis of groundwater availability is thus especially important to guide groundwater management and evaluate alternatives in areas such as the Denver Basin, where groundwater 

storage depletion is occurring.

This study developed a groundwater flow model to 

evaluate past and present groundwater availability in the 

Denver Basin, which could be useful for evaluating different 

management options in the future. Simulation results indicate 

changes in land and water use have altered the groundwater 

flow system compared to predevelopment conditions. The 

expansion of urban/suburban land use and irrigated agriculture since the 1950s has increased water use on the landscape, 

which has increased recharge, evapotranspiration, streamflow, 

and the overall groundwater budget in this semiarid region. 

Groundwater pumping from the bedrock aquifers also has 

increased steadily since the 1950s, primarily in response to 

increased municipal water-supply needs. The combination of 

these changing land- and water-use distributions has generally increased groundwater availability in the alluvial aquifer 

and shallow parts of the hydrologic system while removing 

water from storage and decreasing groundwater availability 

in the bedrock aquifers. Pumping from the bedrock aquifers 

also is capturing groundwater that would have discharged to 

evapotranspiration, streams and alluvial aquifers. This capture 

can result in a decline in groundwater discharge from bedrock 

aquifers to the surficial system, which could affect storage 

and groundwater availability in the overlying alluvial aquifer 

(Watts, 1995; Banta, 1989). Ecology of streams, wetlands, or 

riparian zones in discharge areas also could be affected.

While the estimated cumulative storage loss in the 

Denver Basin through 2003 is only a small percentage 

(0.3 percent) of the total estimated water in storage, the temporal trend and spatial distribution lend insight to hydrologic 

processes controlling storage. Drought conditions, simulated 

in the model as reduced recharge from 2000 to 2003, coupled 

with continued pumping increases, caused an exponential 

increase in simulated cumulative storage loss from the bedrock 

aquifers since 1999 (fig. B48). During drought years, less 

recharge is available and more water is removed from storage 

than in years with plentiful precipitation recharge such that climate variability and the resulting recharge variability directly 

affect aquifer storage.

Theoretically, storage loss would be expected to increase 

substantially as the confined aquifers experience drawdown 

and convert to unconfined conditions because more water is 

released from drainable (unconfined) storage than from confined storage for a unit decrease in hydraulic head (Robson, 

1987). The increased storage-depletion rate simulated after 

1999 is likely a combination of factors including increased 

pumping, decreased recharge, and conversion to unconfined 

conditions. Spatially, 50 percent of the 2003 storage loss 

from the bedrock units was from the south Denver metropolitan area where groundwater provides most of the municipal 

water supply. The other 50 percent of the loss was from 

remaining parts of the basin (fig. B48). These results suggest that storage depletion is most severe in the south Denver 

metropolitan area.

Water providers in the south Denver metropolitan area 

recognize the need to import additional renewable water supplies and are actively seeking alternative water supplies as the 

population continues to increase (South Metro Water Supply 

Board, written commun., 2004). After defeat of the Colorado 

and South Platte River Storage Agreement in 1989, which 

would have provided renewable water to the area from the 

proposed Two Forks reservoir along the upper South Platte 

River, growth in the south Denver metropolitan area developed limited surface-water and tributary groundwater rights on 

the South Platte River and Plum and Cherry Creeks in addition 

to nontributary Denver Basin bedrock groundwater (South 

Metro Water Supply Study Board, written commun., 2004). 

The Denver Basin aquifers provide an excellent source of 

water; however, well production rates from the Denver Basin 

aquifers vary widely and can be as low as 50 to 100 gallons 

per minute, requiring many wells to meet peak water demand 

(South Metro Water Supply Study Board, written commun., 

2004). Over the past 20 years, pumping from the confined 

aquifers has lowered hydraulic heads at rates of as much as 

30 ft/yr. As the head in the aquifer is lowered, larger pumps 

are needed to move water to the surface, increasing energy use 

and pumping costs (South Metro Water Supply Study Board, 

written commun., 2004). In 2004, a group of south Denver 

metropolitan area providers, partnered with State agencies and 

water-rights administrators from the Colorado River Basin and 

completed a study investigating alternatives for meeting watersupply needs of the South Denver Metropolitan area through 

2050 (South Metro Water Supply Study Board, written 

commun., 2004). Alternatives considered were the continued 
176 Groundwater Availability of the Denver Basin Aquifer System, Colorado

use of Denver Basin groundwater, importation of additional 

renewable water supplies, and better management of existing 

resources including conservation, reuse of nonpotable water, 

and aquifer-storage-and-recovery (ASR) (South Metro Water 

Supply Study Board, written commun., 2004). Providers 

continue to pursue renewable water supplies maximizing the 

development of available in-basin surface water and developing water-conservation and reuse programs.

Some providers, such as Centennial Water and Sanitation 

District, which serves the Highlands Ranch community, are 

successfully pursuing conjunctive-use projects that use excess 

surface water during spring runoff and other wet periods to 

artificially recharge the bedrock aquifer through injection 

wells (aquifer-storage-and-recovery, ASR). The stored water is 

later pumped from the bedrock aquifers to meet peak demands 

(Swithen Dick, Centennial Water and Sanitation District, oral 

commun., 2008). The City of Colorado Springs also has developed a conjunctive-use bedrock ASR project in the Monument 

area (Cortney Brand, Colorado Springs Utilities, oral commun., 2005), and the Consolidated Mutual Water Company 

in Lakewood has implemented a successful conjunctive-use 

bedrock ASR project injecting surface water into the Arapahoe 

aquifer west of Denver (Courtney Hemenway, Hemenway 

Groundwater Engineering, oral commun., 2005). The success of these projects may vary from year to year depending 

on available surface water for injection. In 2009, the Front 

Range experienced recordbreaking spring snowmelt runoff 

in addition to above-average summer precipitation, allowing 

the Centennial Water and Sanitation to inject up to 5 million gallons of water per day into the bedrock aquifers with 

no withdrawals needed for the year (Courtney Hemenway, 

Hemenway Groundwater Engineering, written commun., 

2009). Conjunctive-use and ASR projects such as these are 

promising solutions to storage depletion in the Denver Basin. 

Drawdown and unconfined conditions in the Denver and 

Arapahoe aquifers in particular may provide opportunity for 

additional ASR projects where sufficient surface water is 

available for injection.

There are other ongoing and planned water projects for 

municipalities and suburbs south of Denver to import surface 

water and to reduce the reliance on nonrenewable Denver 

Basin groundwater. For example, several municipal water 

suppliers including Parker Water and Sanitation, Castle Pines 

North, Town of Castle Rock, and Stonegate are partnering 

to store water in the Reuter-Hess Reservoir near Parker, 

Colorado (http://www.pwsd.org/rueter_hess_reservoir.php, 

accessed April 3, 2008). In addition, the East Cherry Creek 

Valley Water and Sanitation District in 2006 completed a 

new pipeline from the South Platte River to deliver surface 

water to its service area. The Chatfield reallocation project 

is a third effort to import surface water to the south Denver metropolitan area. Chatfield Reservoir, located at the 

mouth of Waterton Canyon on the South Platte River, was 

constructed beginning in 1967 as a flood-control reservoir. 

The reservoir also is used for water-supply storage by the 

Denver Water Board. In 2004, the CWCB began a process 

of reallocating water rights for 20,600 acre-ft of floodcontrol water storage in Chatfield Reservoir. The Chatfield 

Reservoir reallocation process is intended to provide additional surface water to several water providers in the south 

Denver metropolitan area who currently (2010) rely on 

groundwater for public water supply (http://cwcb.state.co.us/

WatershedProtectionFloodMitigation/ProgramsProjects/

ChatfieldReservoirReallocationProject/SiteInformation/, 

accessed April 3, 2008; http://www.douglas.co.us/community/

planning/documents/WorkSessiononWaterDCPC.pdf, accessed 

April 3, 2008). A Feasibility Study and Environmental Impact 

Statement (EIS) addressing engineering and environmental concerns was submitted to the U.S. Corps of Engineers 

in 2010, and public comment on the reallocation process 

will begin in 2011 (http://www.chatfieldstudy.org/faq.html, 

accessed January 14, 2011).

Like other natural resources, groundwater in storage 

(groundwater reserves) can be depleted (Alley, 2006). Water 

providers in the Denver Basin recognize that concentrated 

development and depletion of groundwater storage limits 

the ability to pump the aquifers in the future (South Metro 

Water Supply Study Board, written commun., 2004). While 

the length of time over which this resource may be available 

is uncertain, the conclusions of this and other studies indicate that pumping from the Denver Basin bedrock aquifers is 

not indefinitely sustainable and that renewable water supplies will be needed in the future. Conjunctive-use projects, 

conservation, water reuse, and importation of renewable 

water will enhance the prudent management of Denver Basin 

groundwater resources and can likely extend the practical 

usable life of the aquifers.

Summary

Groundwater development to support agriculture and 

urbanization in the Denver metropolitan area has affected 

groundwater availability in the Denver Basin aquifer system. 

This chapter discusses groundwater availability of the Denver 

Basin in terms of temporal changes to the groundwater budget, 

storage, and groundwater flow directions. Temporal changes 

are presented for the entire aquifer system and separately 

for the bedrock and alluvial systems on the basis of previous 

studies and results from the transient groundwater flow model 

developed by this study. Predictive simulations for hypothetical conditions from 2004 through 2053 were used to calculate 

model sensitivity, and results were used to evaluate which 

geographic areas of the system are most sensitive to additional 

data collection. Predictive simulations also demonstrate the 

utility of the model for evaluating future system response to 

continued pumping. Finally, the chapter presents a discussion 

of future monitoring needed to improve model calibration and 

to provide the necessary data for future and recurring hydrologic analysis.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 177

Land-use data for the Denver Basin (2001) indicates the 

basin is 60 percent nonirrigated grassland and rangeland, 11 percent irrigated agriculture, 16 percent nonirrigated agriculture, 

9 percent developed urban and suburban land use, 3 percent 

forested, and 1 percent open water. Irrigated and nonirrigated 

agricultural land is located primarily along the South Platte 

River valley, and nonirrigated grassland and rangeland cover 

much of the central and southern basin. Developed urban and 

suburban land use is primarily along the western side of the 

basin along the Front Range urban corridor. Small towns, rural 

residences, and farms are spread across the less-populated parts 

of the basin including the forested areas at the higher elevations 

along the Palmer Divide. Population of the metropolitan areas 

overlying the Denver Basin aquifer system has approximately 

doubled from 1.3 million in 1970 to about 2.7 million in 2005. 

Development has been especially rapid and extensive on the 

west side of the basin between Denver and Colorado Springs. 

Three primary areas of development are identified that rely 

on groundwater for water supply: (1) the area north of Denver 

in Weld and Adams Counties; (2) the south Denver metropolitan area encompassing Littleton, Parker, Franktown, and 

Castle Rock; and (3) the Monument area northeast of Colorado 

Springs. Because groundwater in the Denver Basin bedrock 

aquifers is mostly considered nontributary and is not subject to 

the prior-appropriation doctrine, it has been a readily available 

source of water to support growing and recently established 

municipalities in areas with limited surface water, limited tributary alluvial groundwater, limited available water rights, or all 

of the above.

Because actual pumping in the Denver Basin is not monitored, this study estimated pumping from 1880 through 2003 

from the Colorado Division of Water Resources well-permit 

database following methods implemented in previous studies. Analysis results compare favorably to previous pumping 

estimates and were used as input to the groundwater flow 

model. About 52,000 permitted pumping wells with sufficient 

well-location and completion data were included in the analysis. About 8,000 wells (15 percent) were completed in the 

alluvial aquifer, and the remaining 44,000 wells (85 percent) 

were completed in the bedrock aquifers by 2003. Total pumping from the Denver Basin alluvial and bedrock wells was 

estimated at about 305 ft3/s (221,000 acre-ft/yr) in 2003. About 

62 percent of the pumping was from alluvial wells (187 ft3/s), 

and about 38 percent of the pumping was from bedrock wells 

(118 ft3/s). While most of the wells (85 percent) are completed in the bedrock aquifers, most of the estimated pumping (62 percent) is from the alluvial aquifer. These results are 

consistent with the conceptual understanding of the system 

and reflect the inherent difference in hydraulic conductivity 

between the more transmissive alluvial aquifer and the less 

transmissive bedrock aquifers.

Categorized by water use, total pumping from the entire 

system (alluvial plus bedrock aquifers) was about 62 percent 

irrigation, 20 percent municipal, 12 percent domestic, and 

6 percent commercial/industrial in 2003. For the alluvial aquifer, most of the wells were used for domestic (56 percent) and 

irrigation (38 percent) purposes, although most of the pumping 

(90 percent) was used for irrigation purposes in 2003. For the 

bedrock aquifers, most of wells also were used for domestic 

purposes (94 percent), and only 2 percent of the bedrock wells 

were used for municipal purposes in 2003. However, because 

assumed pumping rates for municipal wells are greater than 

those for domestic wells, estimated municipal pumping 

accounted for 41 percent and domestic pumping accounted 

for 28 percent of the bedrock pumping in 2003. The upper and 

lower Arapahoe aquifers were the most heavily pumped of the 

bedrock aquifers (41 percent of bedrock pumping) in 2003. 

Bedrock domestic wells are located throughout the basin and 

are generally completed in the bedrock aquifer nearest to the 

surface, while bedrock municipal wells are associated with 

development on the west side of the basin.

Changes in land and water use have altered the groundwater flow system compared to predevelopment conditions. 

The expansion of urban/suburban land use and(or) irrigated 

agriculture since the 1950s has increased water use on the 

landscape, which has increased recharge, evapotranspiration, 

streamflow, and the overall groundwater budget in this semiarid region. Groundwater pumping from the bedrock aquifers also has increased steadily since the 1950s, primarily in 

response to increased municipal water-supply needs. The combination of these changing land- and water-use distributions 

has increased groundwater availability in the alluvial aquifer 

and shallow parts of the hydrologic system while removing 

water from storage and decreasing groundwater availability in 

the bedrock aquifers.

The majority of water moving in and out of the groundwater system is moving through the alluvial aquifer. On 

average from 1880 through 2003, 80 percent of net recharge 

was directly to the alluvial aquifer, while 20 percent of net 

recharge was directly to the bedrock aquifers. The majority of 

net outflow to streams (90 percent on average) also was from 

the alluvial aquifer, while about 10 percent of net outflow to 

streams was directly from bedrock aquifers. Simulated pumping from the alluvial aquifer increased more than threefold 

from 40 ft3/s in 1953 to about 143 ft3/s in 1971 and then more 

gradually to about 170 ft3/s in 2003. Simulated pumping from 

the bedrock aquifers increased steadily from about 10 ft3/s in 

the 1950s to about 111 ft3/s in 2003. Flow from bedrock units 

to the alluvial aquifer decreased from about 34 ft3/s for predevelopment (1879) conditions to about 28 ft3

/s in 2003, and 

flow from the alluvial aquifer to the bedrock aquifer increased 

from about 8 ft3/s for predevelopment conditions to about 

12 ft3/s in 2003, indicating the net flux to the alluvial aquifer 

from bedrock units has decreased through time from about 

26 ft3/s to about 16 ft3/s from 1880 through 2003. Downward 

interaquifer flow between bedrock units increased substantially from the Denver aquifer and lower Denver confining 

unit into the upper and lower Arapahoe aquifer, indicating 

that vertical connection exists between these layers and that 

downward flow is induced by the increased pumping from the 

Arapahoe aquifers.
178 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Simulated bedrock aquifer storage responds to changes in 

pumping and net recharge. Based on simulation results for the 

model-calibration period 1879–2003, bedrock aquifer storagedepletion rates have increased since predevelopment because 

of pumping. Storage changes for the alluvial aquifer have 

varied depending on recharge and pumping with storage being 

gained in wet years and removed in dry years. In the 1950s 

and early 1960s, simulated recharge increased in the Denver 

Basin as urban areas expanded, but pumping was not yet sufficient to remove water from storage, so recharge contributed to 

alluvial and bedrock aquifer storage. As dry conditions ensued 

in the mid-1960s and pumping continued to increase, storage 

loss occurred in both the alluvial and bedrock aquifers. Wetter climatic conditions in the 1990s contributed precipitation 

recharge to storage in the alluvial aquifer, but in the bedrock 

aquifers, continued increases in pumping resulted in continued 

storage loss. By 2003, dry climatic conditions, coupled with 

continued pumping, resulted in a storage-depletion rate from 

the alluvial aquifer of about 7 ft3/s and a storage-depletion rate 

from the bedrock aquifers of about 57 ft3/s. All of the bedrock 

aquifers are experiencing storage depletion, although depletion 

is most severe in the Denver aquifer.

The cumulative storage loss from the alluvial aquifer 

increased in response to pumping during the 1960s through 

1980s and reached a maximum cumulative storage loss of 

about 326,000 acre-ft in 1986. After 1986, the simulated area 

of urban recharge increased in areas overlying the alluvial 

aquifer, which resulted in additional simulated recharge to the 

alluvial aquifer and about 200,000 acre-ft of storage recovery. There were about 25,000 acre-ft of cumulative storage 

loss from the alluvial aquifer simulated from 2000 to 2003 

in response to drought conditions. The simulated cumulative volume of water removed from bedrock aquifer storage 

increased from zero under predevelopment conditions to about 

690,000 acre-ft in 2003. While the overall amount of storage 

depletion is small compared to the estimated total water in 

storage, the spatial distribution and temporal trend of the storage loss warrant further consideration. Spatially, 50 percent 

of the 2003 storage loss from the bedrock units was from the 

south Denver metropolitan area where groundwater provides 

most of the municipal water supply to a growing population. 

The other 50 percent of the loss was from remaining parts of 

the basin. These results suggest that storage depletion is most 

severe in the south Denver metropolitan area. Drought conditions, simulated in the model from 2000 to 2003, coupled with 

continued pumping increases, caused an exponential increase 

in simulated cumulative storage loss from the bedrock aquifers 

since 1999. Storage depletion is expected to increase substantially as the confined aquifers experience drawdown and convert to unconfined conditions because more water is released 

from drainable storage than from confined storage for a unit 

decrease in hydraulic head.

The change in recharge patterns caused by development 

as well as pumping and the removal of groundwater from 

storage have lowered the potentiometric heads and altered 

groundwater flow directions in the Denver Basin aquifer 

system. Changes in hydraulic head in the alluvial aquifer 

are much less pronounced than those in the bedrock aquifers 

because of the alluvial aquifer’s connection to surface water 

and large hydraulic conductivity and recharge rates compared 

to the bedrock aquifers. Pumping from each of the bedrock 

aquifers resulted in substantial drawdown of their respective 

predevelopment potentiometric surfaces and an increase in 

unconfined conditions for some layers. For the upper Dawson 

aquifer, pumping south of the Denver metropolitan area near 

Castle Rock and Parker has lowered the potentiometric head 

up to 100 ft below predevelopment conditions in the Cherry 

Creek basin, creating a regional discharge area that was not 

present under predevelopment conditions. The greatest concentration of pumping wells in the Arapahoe aquifer occurs 

in the south Denver metropolitan area where the aquifer is 

thickest and most conductive. Simulated drawdown from 1880 

through 2003 for the lower Arapahoe aquifer is in the range of 

200–400 ft in the south Denver metropolitan area and in the 

range of 750–1,000 ft in the Monument area. In the northern 

part of the basin, drawdown in the Arapahoe aquifer was 

limited because the unit occurs near land surface and receives 

direct recharge from the surface and alluvial aquifer. Drawdown through 2003 was greatest in all bedrock aquifer model 

layers in the south Denver metropolitan and Monument areas, 

but the drawdown patterns were somewhat different between 

the two areas because of contrasts in hydraulic conductivity. In the south Denver metropolitan area, drawdown cones 

for individual wells in the lower Arapahoe aquifer coalesced 

into a large area of regional drawdown within an extensive 

lobe of transmissive sandstone. However, drawdown in the 

lower Arapahoe aquifer in the Monument area was restricted 

to individual cones of depression with steep hydraulic gradients surrounding pumping centers because the aquifer has a 

lower hydraulic conductivity. The spatial distribution of 1880 

through 2003 drawdown for the Laramie–Fox Hills aquifer is 

slightly different than that of the other bedrock aquifers with 

the greatest drawdown occurring in the northern Denver suburbs in addition to the south Denver metropolitan area.

Predictive simulations were used to calculate model 

predictive sensitivities and to demonstrate use of the model to 

evaluate future groundwater conditions. Predictive simulations 

were run 50 years into the future from the end of the model 

calibration period (December 31, 2003) to 2053. The first 

predictive simulation to 2053 assumes dry climatic conditions and that pumping continues at the 2003 rate. The second 

predictive simulation to 2053 demonstrates the use of the 

model to evaluate future conditions and simulates the effects 

of reducing pumping from municipal wells completed in the 

lower Arapahoe aquifer in the south Denver metropolitan area. 

As expected, results from the first predictive simulation indicate continued drawdown, an increase in unconfined areas, and 

continued storage loss in all bedrock aquifer layers. Results 

from the second predictive simulation indicate about 400 ft 

less drawdown for the lower Arapahoe potentiometric surface 

from 2009 to 2053 as compared to the first predictive simulation if pumping from the lower Arapahoe aquifer were to cease 

in the south Denver metropolitan area. Because of the hydraulic connection between the Denver and Arapahoe aquifers, 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 179

results from the second predictive simulation also predict as 

much as 150 ft less drawdown in the Denver aquifer potentiometric surface by 2053 if pumping were to cease in the lower 

Arapahoe aquifer. Results from predictive simulations indicate 

bedrock discharge to the alluvial aquifer will continue to 

decrease and storage loss will continue through 2053 if pumping is maintained at the 2003 rates. The storage-depletion rate 

may be reduced and the useful aquifer life extended by reducing pumping from the lower Arapahoe aquifer.

Further studies of the Denver Basin aquifers would benefit 

from additional and continued data collection and interpretation. 

The Colorado Division of Water Resources maintains centralized databases of well-permit records (with drilling logs) and 

geophysical logs. Maintenance and updating of these databases 

in a consistent manner is essential to further the availability of 

well and geologic data in the Denver Basin. As drilling and construction of water-supply wells continues in the basin, continued 

compilation of hydrogeologic data, such as geologic layering 

information, aquifer tests, and water levels, into a centralized 

database would allow more effective sharing of data among 

Federal, State, and local governments and scientists. Currently 

(2010) no centralized database exists for pumping records from 

the Denver Basin aquifers. Individual water providers meter and 

record pumping as part of daily operations, but these data are 

not compiled on a regional basis. Implementation of a metering 

and reporting system for pumping information would provide 

discharge information for the basin with which to better evaluate aquifer drawdown and storage depletion and reduce model 

uncertainty. Future water-level monitoring efforts in the Denver 

Basin would benefit from an expanded network of dedicated 

monitoring wells constructed of material resistant to corrosion 

with screened intervals placed to monitor selected bedrock 

units. Based on analysis of the present network, water-level 

measurements collected in the spring represent ambient heads 

in the nonirrigation season while fall measurements are useful 

to evaluate the effects of summer irrigation pumping. Retaining 

existing wells in a long-term network should be considered if 

there already is a long-term water-level record for the well and 

if the well condition and completion interval are appropriate for 

the inclusion in the network.

Bedrock groundwater storage is being depleted in the 

Denver Basin. While the length of time over which this resource 

may be available is uncertain, the conclusions of this and other 

studies indicate that pumping from the Denver Basin bedrock 

aquifers is not indefinitely sustainable and that renewable water 

supplies will be needed in the future. Water providers and 

administrators in the Denver Basin are working to develop and 

promote conservation, conjunctive-use projects, water reuse, 

and importation of renewable water to enhance the prudent 

management of Denver Basin groundwater resources, which 

can likely extend the practical usable life of the aquifers. Recurring monitoring and analysis of groundwater availability is 

especially important to guide groundwater management in areas 

such as the Denver Basin, where a growing population presently 

relies on this important and limited resource.

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