Prepared in cooperation with the BUREAU OF RECLAMATION Identifying Wells Downstream from Laguna Dam that Yield Water that will be Replaced by Water from the River, and The decree is specific about the returns, and consumptive use of water by This report summarizes a compre- responsibility of the Secretary of the individual water users is published hensive study and development of the Interior to account for consumptive use of annually by the Bureau of Reclamation method documented in Owen-Joyce water from the mainstream; consumptive (Bureau of Reclamation, 1965–2000). and others (2000). That report and one use is defined to include “water drawn The accounting-surface method is a tool for the area upstream from Laguna from the mainstream by underground the Bureau of Reclamation can use to Dam (Wilson and Owen-Joyce, 1994) pumping.” Accounting for the use of identify users of water Colorado River water is required by the and from which to build a policy to document the accounting-surface 1964 decree (U.S. Supreme Court, 1964); account for consumptive use of water method to identify wells that yield a report that contains records of diversions, from wells in the river aquifer. water that will be replaced by water from the Colorado River.

Downstream from Laguna Dam, the Colorado River is the source for nearly all recharge to the river aquifer. The complex surface-water and ground-water system that exists in the area is, in part, the result of more than 100 years of water- resources development. Agriculture is the principal economy and is possible only with irrigation. The construction and operation of canals provides the means to divert and distribute Colorado River water to irrigate agricultural lands on the flood plains and mesas along the Colorado and Gila Rivers, in Imperial and Coachella Valleys, and in the area upstream from Dome along the . Water is withdrawn from wells for irrigation, dewatering, and domestic use. The area downstream from Laguna Dam borders additional areas of agricultural development in where Colorado River water also is diverted for irrigation.

Why Identify Wells?

In the , water from the mainstream in the lower Colorado River is apportioned among the States of California, Arizona, and by the Boulder Canyon Project Act of False-color composite Landsat-7 thematic December 21, 1928, and confirmed by satellite image of the area downstream from the U.S. Supreme Court decree, 1964, in Arizona and California. Arizona v, California, in terms of Acquisition date: February 6, 2000, path 38, consumptive use (U.S. Congress, 1948). row 37, World Referencing System.

U.S. Department of the Interior USGS Fact Sheet 125-00 U.S. Geological Survey October 2000 River Aquifer 115°00' 45' 30' 15' 114°00' 33 00' ° C C A H A M O R C L O O I Z U L I F N A O The river and the underlying and T T A E O C I N A N R

IMPERIAL R S A adjacent river aquifer form a complex, M l G N

U a I

C O n A

COUNTY H a hydraulically connected ground-water M A Imperial Dam C O C U H n N i and surface-water flow system in the IM T O a P A M E I Laguna Dam Gila Gravity RI N AL S Main Canal Yuma area downstream from Laguna V A R LL Dam (fig. 1). The river aquifer consists EY E V al I A PILOT n N R of permeable sediments and sedimentary 45' m KNOB a I er C LA Dome G R l ic P il iv rocks that are hydraulically connected to Al an a e r n W i o Morelos Dam s G e the Colorado River so that water can n I ll e Main L t t o O A n x Yuma - Outlet M move between the river and the aquifer o a D C h w k E a YUMA n B a A Drain l

n R o i D in response to differences in water-level O a M u L r O D MESA O n O elevations between the river and the O U d t L a

e N C

l F r t T y

aquifer and withdrawal of water from u A o IN f

O s YUMA S t the aquifer. The subsurface limit of the u n d i y

a COUNTY a river aquifer is the nearly impermeable 30' r M e a bedrock of the bottom and sides of the Boundary of U NIT ED basins that underlie the Yuma area and flood plain ST AT ME ES adjacent valleys. Bedrock is a barrier to 124° XIC 122° 120° O T ground-water flow. 41° IN M A J 0 5 MILES O A The principal source of water to the U S N T A area downstream from Laguna Dam is 39° A L I T 0 5 KILOMETERS N A the Colorado River, although much of S S 118° the water does not arrive in the river 15' 37° 114° 112° 110° EXPLANATION channel. Water stored in upstream 116° SEDIMENTS AND SEDIMENTARY CALIFORNI surface reservoirs is delivered for use 35° A ROCKS downstream from Laguna Dam. Most of ARIZONA RIVER AQUIFER the water delivered at Imperial Dam is 33° Yuma OTHER THAN RIVER AQUIFER diverted from the river into the All- Area enlarged OR OUTSIDE STUDY AREA 0 100 MILES M American Canal on the California side E XICO BEDROCK of the river and into the Gila Gravity 0 100 KILOMETERS Main Canal on the Arizona side (fig. 2). 32°00' Millions of acre-feet of water are Figure 1. The lower Colorado River and the areal extent of the river aquifer diverted or pumped annually from the downstream from Laguna Dam, Arizona and California. river channel; most is transported for use in Imperial and Coachella Valleys use in the lower Gila River Valley The rest is used for irrigation of fields through the All-American Canal upstream from Dome through the Gila adjacent to the river and for municipal downstream from Pilot Knob and for Gravity Main and Wellton-Mohawk Canals. use in the Yuma area. Downstream from Laguna Dam, water also is stored T 18 E

E in the river aquifer and is pumped

F Colorado River below Imperial Dam - 16 from wells for irrigation, municipal, E Gila Gravity Main Canal R

C All-American Canal and domestic use. Much of the

A 14 irrigation water is transpired by F O 12 vegetation or evaporates, and the S

N remainder percolates below the root O 10 I

L zone into the river aquifer. Some of L I 8 M

the water in the unlined canals and in N I

the river channel and marshes during , 6

W high flows percolates through the O

L 4

F underlying soils and sediments and

L

A 2 recharges the river aquifer. Small U

N quantities of runoff that originate from

N 0 A 1930 1940 1950 1960 1970 1980 1990 2000 precipitation infiltrate the beds of washes and intermittent tributary Figure 2. Annual flow in the Colorado River above Imperial Dam. This flow streams; most of the infiltrated water is the sum of flow diverted from the Colorado River into the All-American Canal near Imperial Dam, 1938 – 98, flow diverted into the Gila Gravity later evaporates or is transpired Main Canal, 1944 – 98, and flow in the Colorado River below Imperial leaving little to recharge the river Dam, 1961– 98. aquifer. Ground water flows downgradient wells that are presumed to yield water Wells that have a static water-level through the river aquifer and discharges that will be replaced by river water elevation equal to or below the accounting as seepage into drainage ditches or stored above river level. The identi- surface are presumed to yield water that through the river banks into the river. fication is made by determining the static will be replaced by water from the Water moves back and forth between water-level elevation in the well and Colorado River (fig. 3, wells labeled R). the surface-water and ground-water comparing it to the elevation of the The water-table elevation in the river systems in response to application of accounting surface at the well. The aquifer near a well or well field is assumed water to irrigated fields and annual accounting surface represents the to be the same as the elevation of static changes in the water-level elevation of elevation and slope of the unconfined water levels in the wells. Pumping water the river. In addition to drainage ditches, static water table in the river aquifer from a well completed in the river aquifer dewatering wells also are used to outside the flood plain of the Colorado where the elevation of the static water manage ground-water levels beneath River that would exist if the river were level in the well is below the elevation of irrigated areas by withdrawing ground the only source of water to the river the accounting surface eventually will water for discharge to the Colorado aquifer. The accounting surface was cause the slope of the hydraulic gradient River. Water is pumped from thousands generated by using water-surface profiles between the river and the well to be of wells completed in the river aquifer of the Colorado River from Laguna Dam downward toward the well. This, in turn, on the flood plain, on alluvial slopes, to about the downstream limit of will result in the movement of water from and in tributary valleys. Agricultural perennial flow at Morelos Dam and the Colorado River into the river aquifer. development, degradation of the river without consideration of the time The modification to the accounting- channel because of reduced sediment required for water to travel from the river surface method for use downstream load, and diversions upstream have to any point of withdrawal from the river from Laguna Dam is in the designation caused the Colorado River to become a aquifer. River discharges selected for the of the source of the water in wells where drain in the Yuma area. The river computation of water-surface profiles are the static water level is above the channel from Laguna Dam to Pilot based on flow for 1998-99, which accounting surface. Wells that have a Knob wasteway normally conveys reflects average cropping patterns and static water-level elevation above the seepage and flow from drainage ditches. agricultural drainage, neither flood nor accounting surface are presumed to Except for occasional discharge of drought conditions, and no operational yield river water stored above river level water past Morelos Dam as a result of activities. The accounting surface (fig. 3, wells labeled S). In an area deliveries to Mexico in excess of treaty extends outward from the edges of the underlain by a ground-water mound, the requirements, the channel downstream flood plain to the subsurface boundary of water-level elevation in a well can from Morelos Dam normally conveys the river aquifer (fig. 3). Water pumped remain above the accounting surface as seepage and discharge from the Main from wells on the flood plain, including long as river water stored above river Outlet Drain Extension or is dry. the area downstream from Morelos Dam, level can move to the well to replace is presumed to be Colorado River water. river water removed from storage. Accounting-Surface Method

The accounting-surface method was River aquifer boundary developed for the area upstream from A lluv ial slo h C Laguna Dam and is based on the concept pe c a it n l d R al of a river aquifer and an accounting a e VE ca n g RI D Irrigated a O N

I

n

surface within the river aquifer (Wilson i

O field

r

d a A D e O

n L L and Owen-Joyce, 1994). This method i D F l P n

S D A S was modified for use downstream from U O D S R R O IN A L A R O ter table Laguna Dam to identify wells outside the F L O L Wa P L O flood plain of the lower Colorado River River water CO C River that yield water that will be replaced by stored above Accounting Accounting water river level surface River aquifer surface stored water from the river. Use of the same above method provides a uniform criterion of river level identification for all users pumping Sediments and sedimentary rocks water from wells by determining if the static water-level elevation in the well is EXPLANATION above or below the elevation of the accounting surface. SEDIMENTS AND SEDIMENTARY WELL—The symbol "R" denotes a well that has a static ROCKS water-level elevation equal to or below the accounting The accounting-surface method can surface and is presumed to yield water that will be be used in the area downstream from BEDROCK replaced by water from the Colorado River. The symbol "S" denotes a well that has a static water-level Laguna Dam outside the flood plain of elevation above the accounting surface and is presumed the Colorado River to identify wells that to yield river water stored above river level. are presumed to yield water that will be Figure 3. Schematic diagram showing the river aquifer and accounting replaced by water from the river, and surface. If more water is pumped from a well than can be replaced by river water stored above river level, the static water- level elevation in the well will decline below the accounting surface and water will eventually move from the Colorado River into the river aquifer toward the well. In an area where a well has a static water level below the accounting surface but where a ground-water mound exists between that well and the river upstream from Morelos Dam, water pumped from that well is presumed to be replaced by river water stored above river level until the mound is depleted. When the mound of river water stored above river level no longer exists, water eventually will move from the Colorado River into the river aquifer toward the well and the well will be presumed to yield water that Selected References will be replaced by water from the Colorado River. Bureau of Reclamation, 1965–2000, Owen-Joyce, S.J., Wilson, R.P., Compilations of records in accord- Carpenter, M.C., and Fink, J.B., Applying the Method ance with Article V of the Decree 2000, Method to identify wells that of the Supreme Court of the United yield water that will be replaced by Application of the accounting-surface States in Arizona v, California water from the Colorado River method will require identification of all dated March 9, 1964, calendar year downstream from Laguna Dam in wells within the river aquifer from which 1965–99: Bureau of Reclamation Arizona and California: U.S. water is pumped for consumptive use. duplicated report [published Geological Survey Water- Static water levels need to be measured annually]. Resources Investigations Report and compared to the accounting surface 00–4085, 3 plates, 31 p. for the method to be applied. The Loeltz, O.J., Irelan, Burdge, Robison, inventory of each well will include J.H., and Olmsted, F.H., 1975, Wilson, R.P., and Owen-Joyce, S.J., interviewing the well owner or operator to Geohydrologic reconnaissance of 1993, Determining the source of collect current ownership and historical the , California: U.S. water pumped from wells along the information to enable the tracking of the Geological Survey Professional lower Colorado River: U.S. driller’s log. Other data to be collected Paper 486–K, 54 p. Geological Survey Open-File during an inventory include precise Report 93–405, 2 p. locations and elevations determined by Loeltz, O.J., and Leake, S.A., 1983, A use of a Global Positioning System, and method for estimating ground-water —- 1994, Method to identify wells that photographs of the wells to help with return flow to the lower Colorado yield water that will be replaced by identification for future monitoring of River in the Yuma area, Arizona and Colorado River water in Arizona, static water levels. Bureau of Reclamation California: U.S. Geological Survey California, Nevada, and : U.S. management responsibilities include a Water-Resources Investigations Geological Survey Water- legal mandate to ensure that all diversions Report 83–4220, 86 p. Resources Investigations Report of Colorado River water, including those 94–4005, 19 plates, 36 p. by wells, are authorized. Olmsted, F.H., Loeltz, O.J., and Irelan, Burdge, 1973, Geohydrology of the U.S. Congress, 1948, The — Sandra J. Owen-Joyce Yuma area, Arizona and California: documents: U.S. Congress, 80th, 2d U.S. Geological Survey Profes- session, House Document No. 717, sional Paper 486–H, 227 p. 936 p.

For further information, contact: Sandra J. Owen-Joyce U.S. Geological Survey, WRD 520 North Park Avenue, Suite 221 E-mail: [email protected] or visit Tucson, Arizona 85719-5035 home page http://az.water.usgs.gov