U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2013–3001

January 2013

Understanding and Managing the Effects of Groundwater 

Pumping on Streamflow

 roundwater is a critical resource 

 in the United States because it

provides drinking water, irrigates crops, 

supports industry, and is a source of water 

for rivers, streams, lakes, and springs. 

Wells that pump water out of aquifers 

can reduce the amount of groundwater 

that flows into rivers and streams, which 

can have detrimental impacts on aquatic 

ecosystems and the availability of surface 

water. Estimation of rates, locations, and 

timing of streamflow depletion due to 

groundwater pumping is needed for waterresource managers and users throughout 

the United States, but the complexity 

of groundwater and surface-water 

systems and their interactions presents 

a major challenge. The understanding 

of streamflow depletion and evaluation 

of water-management practices have 

improved during recent years through 

the use of computer models that simulate 

aquifer conditions and the effects of 

pumping groundwater on streams. 

Introduction

Groundwater is an important source 

of water for many human needs, including 

drinking water, agriculture, and industry. 

Groundwater and surface-water systems 

are connected, and groundwater discharge 

is often the primary source of streamflow, 

particularly during periods with no rainfall 

or snowmelt (fig. 1A). Pumping from 

wells reduces the amount of groundwater 

that flows to streams and, in some cases, 

can draw streamflow into the underlying 

aquifer. Streamflow reduction caused by 

pumping, also referred to as “depletion” 

or “capture,” has become an important 

water-resource management issue because 

of the negative effects that reduced 

flows can have on aquatic ecosystems, 

the availability of surface water, and the 

aesthetic value of streams and rivers.

Managing the effects of streamflow 

depletion by wells is one of the most 

common and often one of the most 

G

challenging aspects of conjunctively 

managing groundwater and surfacewater systems. Scientific research and 

practical applications of this research to 

real-world settings over the past seven 

decades have improved the understanding 

of the capture process by hydrologists, 

providing valuable insights to water 

administrators for improving groundwater 

and surface-water management. This 

Fact Sheet summarizes some of the basic 

information about how groundwater 

pumping affects streams, misconceptions 

that have developed around the process 

of streamflow depletion, and methods for 

understanding and managing streamflow 

depletion by wells. A more detailed 

description of these and other issues 

related to the effects of pumping on 

streams is provided in U.S. Geological 

Survey Circular 1376.

The Lower Colorado River and adjacent farmland near Yuma, Arizona. Court rulings on use of water 

in the river have recognized that water can be withdrawn from the Colorado River by “underground 

pumping.” (Photograph courtesy of Andy Pernick, Bureau of Reclamation)

A Vermilion Flycatcher in the riparian corridor 

of the San Pedro River, Arizona. (Photograph 

courtesy of Bob Herrmann, copyright 2011.)
Sources of Water to a Well

When a well begins to pump water 

from an aquifer, it first pulls water closest 

to the well from storage within the aquifer, 

forming a “cone of depression” in the 

water table around the well (fig. 1B). 

These water-level declines are largest 

Volume of cone of depression

refilled since pumping stoppedStream Stream Stream Stream Stream

Land surface

Water table

Unconfined aquifer

Confining unit

Water table

Unconfined aquifer

Confining unit

Water table

Unconfined aquifer

Confining unit

Water table

Unconfined aquifer

Confining unit

Water table

Unconfined aquifer

Confining unit

Land surface

Land surface

Land surface

Land surface

A. Under natural conditions,

recharge at the water table 

is equal to discharge at the 

stream.

Figure 1. Progressive changes to groundwater flow and streamflow before, during, and after

pumping at a hypothetical well site.

B. Pumping from a well

removes water from storage 

in a cone of depression and 

reduces discharge to the 

stream.

D. After pumping stops,

groundwater levels begin to 

recover, and water flows into 

aquifer storage to refill the 

cone of depression created by 

the previous pumping stress.

C. In some circumstances,

the pumping rate of the well 

may be large enough to cause 

water to flow from the stream 

to the aquifer, a process 

called induced infiltration of 

streamflow.

E. Eventually, the system 

may return to its prepumping 

condition with no additional 

changes in aquifer storage or 

streamflow depletion.

at the well and decrease with distance 

from the well. Over time, the cone of 

depression deepens and expands outward 

from the well. 

The release of water from aquifer 

storage continues to be the only source 

of water to the well until the cone of 

depression reaches one or more locations 

from which water can be captured—

commonly streams that are hydraulically 

connected to the aquifer.

Captured streamflow consists of 

two possible components: groundwater 

that would otherwise have discharged to 

a stream or river (“captured groundwater 

discharge”) and streamflow that is drawn 

into an aquifer because of pumping 

(“induced infiltration” of streamflow; 

fig. 1C). Streamflow depletion, therefore, 

is the sum of captured groundwater 

discharge and induced infiltration. 

Captured groundwater discharge is often 

the primary component of streamflow 

depletion, but if pumping rates are 

relatively large or the locations of 

withdrawal are relatively close to a stream, 

then induced infiltration may become an 

important component of depletion.

Other hydrologic features also 

can be affected by pumping wells. 

Groundwater withdrawals can decrease 

groundwater discharge rates to lakes 

and springs and reduce the amount of 

water that would otherwise be available 

to groundwater-dependent plants in 

riparian areas.

Time Response of Streamflow 

Depletion

The timing of streamflow depletion 

from pumping at a particular well is 

affected by many factors, includingthe 

geologic structure, dimensions, 

and hydraulic properties of the 

groundwater system and streambeds, 

and—importantly—the distance from 

the pumping location to the streams 

connected to the aquifer. Substantial 

streamflow depletion by a well that is 

tens of feet from a stream may occur in a 

matter of days, whereas depletion from a 

well that is tens of miles from the nearest 

stream may occur over decades or even 

centuries. 

An example of the transition 

from aquifer storage to streamflow 

depletion as a source of pumped water 

is illustrated in figure 2. At any given 

time, the sum of aquifer storage change 

and streamflow depletion account for 

100 percent of the pumping rate of the 

well, with a trend toward the condition 

in which all of the pumping rate is from 

depletion. The pumping time at which 

50 percent of the pumping rate is from 

depletion is referred to as the “time to 

depletion-dominated supply.”
of streamflow depletion will equal the 

volume of water pumped.

Misconception 4: Pumping 

groundwater exclusively below a clay layer 

or other confining layer will eliminate the 

possibility of depletion of surface water 

connected to the overlying groundwater 

system. Even though clay or other 

confining layers canslow the progression 

of depletion in comparison to equivalent 

aquifer systems without confining layers, 

it is not reasonable to expect that pumping 

beneath an extensive confining layer will 

entirely eliminate depletion. Furthermore, 

pumping below discontinuous confining 

beds may actually increase the speed 

of the depletion process relative to a 

condition in which the beds are absent.

Managing Streamflow Depletion by 

Wells

Managing streamflow depletion by 

wells is challenging because of the natural 

complexity of groundwater systems, 

the often-difficult task of identifying 

streamflow depletion from data collected 

at gaging stations, and the time delays that 

may occur between the onset of pumping 

until significant (that is, measurable) 

effects occur in nearby streams. Therefore, 

effective management of streamflow 

depletion requires both a long-term 

planning perspective and a basinwide 

understanding of how streamflow depletion 

responds to pumping each well individually 

and at all wells simultaneously. Many 

groundwater basins have hundreds or 

thousands of pumped wells. Individually, 

these wells may have little effect on 

streamflow depletion, but small effects of 

many wells within a basin can combine to 

produce substantial effects on streamflow 

and aquatic habitats. Moreover, basinwide 

groundwater development typically occurs 

over a period of several decades, and the 

resulting cumulative effects on streamflow 

depletion may not be fully realized for 

many years. 

Although monitoring of streamflow 

depletion at gaging stations can be 

effective for determining both short-term 

and long-term changes in streamflow in 

response to groundwater pumping, the 

most robust approach for determining the 

rates, locations, and timing of streamflow 

depletion is numerical modeling.

Numerical models have been 

used across the United States to 

better understand and improve watermanagement options and practices 

because they can account for the effects 

of complex aquifer settings, stream 

geometries, and pumping histories from 

large numbers of wells on all types of 

hydrologic features, including streams. 

(See case study on the next page.)

Further Information

A fuller exposition of the effects of 

groundwater pumping on streamflow can 

be found in:

Barlow, P.M., and Leake, S.A., 2012, 

Streamflow depletion by wells—

Understanding and managing the 

effects of groundwater pumping on 

streamflow: U.S. Geological Survey 

Circular 1376, 84 p. (Available at 

http://pubs.usgs.gov/circ/1376/.)

Common Misconceptions 

Regarding Streamflow Depletion 

by Wells 

Despite the many advances that have 

been made in our understanding of the 

processes that affect streamflow depletion 

by wells, several misconceptions related to 

the effects of pumping on streamflow have 

developed over the years. These include 

the following:

Misconception 1: Total 

development of groundwater resources 

from an aquifer is “sustainable” or “safe” 

when the overall rate of groundwater 

extraction does not exceed the long-term 

average rate of recharge to the aquifer.

In many aquifers, however, the level of 

groundwater development may be limited 

by the amount of reduced streamflow that 

a community or regulatory authority is 

willing to accept.

Misconception 2: Streamflow

depletion is dependent on the rate and 

direction of water movement in an aquifer.

Actually, for all butthe most extreme 

pumping conditions, the rates, locations, 

and timing of streamflow depletion 

caused by pumping are independent of 

the prepumping rates and directions of 

flow within an aquifer—including the 

recharge rates to an aquifer. Moreover, 

depletion is unlikely to be affected by 

transient events such as changes in 

aquifer recharge rates or variations in 

river stage from flood flows in streams.

Misconception 3: Depletion 

stops immediately after pumping ceases. 

Streamflow depletion continues after 

pumping stops because it takes time 

for groundwater levels in the cone of 

depression to recover from the previous 

pumping stress and for the aquifer to be 

refilled (fig. 1D). During the time that the 

aquifer is being replenished, groundwater 

that otherwise would have flowed to 

streams instead goes into aquifer storage; 

thus, streamflow depletion is ongoing, 

even though pumping has ceased. In 

many cases, the time of maximum 

streamflow depletion actually occurs 

after pumping has stopped. Eventually, 

the aquifer and stream may return to their 

prepumping conditions (fig. 1E), but the 

time required for full recovery may be 

quite long, possibly much longer than the 

total time that the well was pumped. Over 

the time interval from when pumping 

starts until the system fully recovers 

to its prepumping levels, the volume 

Figure 2. Relation of storage change and streamflow depletion as sources of pumped 

groundwater through time for a hypothetical well. The variable tdds is the time to reach the 

condition of depletion-dominated supply for a particular pumping location. In some settings, the 

transition from storage-dominated to depletion-dominated supply can occur in a matter of days to 

months, whereas for others depletion-dominated supply may not occur for decades.

Water from storage depletion

Water from streamflow depletion

0

50

100

Percentage of groundwater pumping rate

Pumping time

t

dds

Storagedominated 

supply Depletion-dominated supply
The upper San Pedro River 

Basin spans the international 

boundary between the United 

States and Mexico, covering an 

area of about 1,700 square miles. 

Groundwater discharge sustains 

perennial reaches in the San Pedro 

River and its tributaries, as well 

as the adjacent riparian area. The 

riparian area provides year-round 

habitat for wildlife species and 

is an important corridor for birds 

migrating between Mexico and the 

United States.

A numerical groundwater 

model was used by USGS 

hydrologists to study the timing 

of depletion from pumping in 

the aquifer of the upper San 

Pedro River Basin. Model runs 

were completed for about 1,500 

hypothetical well locations 

throughout the aquifer. The 

pumping time required to reach 

depletion-dominated supply was 

determined for each of the potential 

well locations and the results 

plotted on a map. Maps such as 

these—which have been referred 

to as “capture maps”—provide 

a visual tool for scientists and 

water-resource managers to better 

understand the effects of pumping at 

individual locations within a larger 

set of possible pumping locations 

within the aquifer. In the resulting 

map, the lightest color, generally 

adjacent to connected rivers, 

indicates that depletion-dominated 

supply would occur within 10 years 

of pumping. In contrast, the darkest 

color indicates that depletiondominated supply would not be 

reached within 100 years.

Case Study: Use of Numerical Modeling for Analysis of Streamflow Depletion in the Upper San Pedro River Basin

Stanley A. Leake and Paul M. Barlow

Edited by Claire Landowski

and Lara Schmit

Graphic design by Jeanne S. DiLeo

Banner photograph by Michael Collier

Pumping time required to reach depletion-dominated supply as a function of well location in 

the primary aquifer underlying the upper San Pedro River Basin.

For more information contact:

U.S. Geological Survey

Arizona Water Science Center

Tucson, Arizona

520-670-6671

Mule Mountains

Huachuca Mountains

San

Pedro

River

Fort

Huachuca

Tombstone

Charleston

Bisbee

Sierra

Vista

Palominas ARIZONA,

UNITED STATES

SONORA, 

MEXICO

0

0

5

5

10 KILOMETERS

10 MILES

30’

31o45’

110o30’

15’

31o

15’ 110o

EXPLANATION

Major roads Pumping time to reach depletion-dominated supply, in years

0 10 20 30 40 50 60 70 80 90 100

Perennial and intermittent streams

ARIZONA

Model

area

Tucson

San Pedro

River Basin

Babocomari River

©2010 B. HERRMANN This Fact Sheet and any updates to it are 

available online at:

http://pubs.usgs.gov/fs/2013/3001