Water Supply in the Mojave River Ground-Water Basin, 1931-99, And

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Water Supply in the Mojave River Ground-Water Basin, 1931-99, and the Beneﬁts of Artiﬁcial Recharge The Mojave River and the associated aquifer system are important water supplies in the Mojave Desert of southern California. The river and aquifer system are in hydraulic connection in many areas, and when flow conditions change in one, the other usually is affected. The river is an unpredictable source of water; therefore, residents of the basin rely almost entirely on ground water for their water supply. This reliance on ground water has resulted in overdraft conditions that have caused water-level declines, changes in the quantity and spatial distribution of recharge from the Mojave River, and loss of riparian habitat. The U.S. Geo- logical Survey (USGS), in cooperation with the Mojave Water Agency (MWA), has completed several studies to determine the likely effects of overdraft on the ground-water and surface- water relations along the Mojave River. This report summarizes those studies, highlighting some of the simulation results from a ground-water flow model, and describes the ground- water and surface-water conditions of the Mojave River Basin.

117 30' 117 00' 116 30' Mojave River Ground-Water ° ° ° Mojave River 0 20 MILES Basin Surface-Water 0 20 KILOMETERS Kern Co Kern Drainage Basin Mojave River Regional aquifer The Mojave River ground-water San Bernardino Co Ground-Water Floodplain aquifer basin is in the western part of the Basin Mojave Desert and is about 80 Coyote miles northeast of Los Angeles, Lake California. The basin encompasses 35 Harper Baja ° Lake Afton about 1,400 square miles and is 00' 15 Canyon Centro subarea divided into six management sub- subarea Barstow areas: Oeste, Este, Alto, Transition

zone of the Alto (hereinafter refer- Mojave River Channel Troy Iron red to as the Transition zone sub- Mtn Lake Newberry 40 area), Centro, and Baja (fig. 1). The Springs major source of surface water and Mojave replenishment (recharge) to the Transition zone ground-water system in the basin is subarea El Mirage Desert the Mojave River, but the river is Lake LLowerower NarrowsNarrows unreliable for direct water supply Oeste Este sub- subarea because its 100 miles of streambed area Victorville Lucerne 34° Lake is dry—except for a short reach of 00' Alto subarea Mojave Water California Agency perennial flow and periods of flow Hesperia Rabbit management Aqueduct Lake San area after intense storms. Therefore, Francisco CALIFORNIA San Ga 15 Mojave Figure 1. Location of the study area and briel Desert subareas of the Mojave River ground- dino Mts Los Angeles water basin, southern California. Co San Diego San Bernardino Los Angeles Co Mts San Bernar

U.S. Geological Survey USGS Fact Sheet 122-01 U.S. Department of the Interior November 2001 residents of the basin rely almost plain aquifer ranges in width from areas away from the washes entirely on ground water for their 120 feet at the Upper Narrows to (Izbicki and others, 2000). water supply, which has resulted more than 5 miles in parts of the Mountain-front recharge moves in overdraft conditions. For the Baja subarea (Stamos and others, over long distances through the purposes of this report, overdraft 2001). The regional aquifer regional aquifer and eventually occurs when ground-water dis- extends throughout most of the discharges to the Mojave River charge (natural discharge plus study area and consists mainly of after thousands of years. Results pumpage) exceeds recharge, sand, silt, and clay; the permeabil- from isotopic analyses indicate resulting in a net reduction in ity of the aquifer decreases with that ground water sampled from ground water stored in the aquifer. depth. In general, the floodplain the regional aquifer beneath the The overdraft of the Mojave River aquifer is more permeable than Mojave River entered the ground- ground-water basin has led to the the regional aquifer. For a more water system more than 20,000 adjudication of the basin. The detailed description of the aquifer years ago (Izbicki and others, complaint that led to the adjudica- system, see Stamos and others 1995). tion alleged that the cumulative (2001) or visit http:// water production upstream of the water.usgs.gov/pubs/wri/ Hydraulic Connection between city of Barstow from 1931–90 wri014002. the Floodplain and Regional (referred to as the adjudication Aquifers period) had overdrafted the basin. Source, Movement, and Age of Ground Water The floodplain and regional Aquifer System aquifers have different hydrologic The primary source of natural properties but they are connected The aquifer system in the recharge to the basin is the hydraulically, that is, water and Mojave River ground-water basin Mojave River. The river contrib- fluid pressure responses are consists of two interconnected utes more than 80 percent of the transmitted between the aquifers. aquifers—a floodplain aquifer natural recharge to the basin and Pumpage and recharge cause and a regional aquifer underlying most of this contribution remains changes in fluid pressure within and surrounding the floodplain in the floodplain aquifer (Stamos one aquifer that can induce water aquifer (figs. 1 and 2). The flood- and others, 2001). Some natural to either move into, or out of, the plain aquifer, which is as much as recharge also is from precipitation other aquifer. The hydraulic 250 feet thick, is composed runoff that infiltrates the upper connection between aquifers is mainly of sand and gravel depos- reaches of normally dry washes, supported by chemical and ited by the Mojave River and and is referred to as mountain- isotopic data which indicate that extends beyond the recent flood- front recharge. Essentially no in areas near the river, the regional plain in some areas. The flood- mountain-front recharge occurs in aquifer contains water that was

Regional aquifer Floodplain aquifer

Desert 3,600 Wash Floodplain 3,200 aquifer Mojave River Water Table 2,800 Regional aquifer

2,400 05MILES

05KILOMETERS Fault

ELEVATION, IN FEET ABOVE SEA LEVEL ELEVATION, 2,000

Figure 2. Conceptualized geologic section of the aquifer system. View is to the south in the Alto subarea. recharged by the Mojave River AALTOLTO TTRANSITIONRANSITION ZZONEONE EXPLANATION less than 50 years ago (Izbicki subareasubarea ssubareaubarea Ground-water flow, in acre-feet and others, 1995). per year - Arrow indicates direction A ground-water flow model 2,250 Predevelopment developed for the basin (Stamos 9,950 1931-90 average and others, 2001) was used to 3,1103,110 34,29034,290 2,2502,250 9,9509,950 Floodplain aquifer evaluate how pumpage affected Regional aquifer the rate and direction of flow CCENTROENTRO BBAJAAJA between the floodplain and ssubareaubarea ssubareaubarea Figure 3. Simulated exchange regional aquifers. In the Alto, of water between the floodplain aquifer and the regional aquifer Transition zone, and Baja subar- for predevelopment and average eas, the ground-water flowed 1931−90 conditions. from the regional aquifer to the 3,9103,910 26,20026,200 1,0201,020 21,66221,662 floodplain aquifer during predevelopment conditions and from the floodplain aquifer to the Mojave River (Stamos and others, model was used to simulate the regional aquifer (a reversal in 2001), loss of riparian habitat (Lines, effects of two artificial recharge flow direction) during the adju- 1996; Lines and Bilhorn, 1996) and alternatives for the period of dication period of 1931–90 water-level declines in wells (Stamos 2000–2019 under drought condi- (fig. 3). In the Centro subarea, and others, 2001). Water levels have tions. Both alternatives assumed ground-water flowed from the declined between 50 and 75 feet in the that flow in the Mojave River was floodplain aquifer to the Alto subarea since the mid-1940s, equivalent to flow during the regional aquifer during both about 100 feet in the Centro subarea 20-year drought of 1945–64 and periods, but the rate of flow near Harper Lake since the early that annual pumpage was equiva- increased significantly during 1960s, and almost 100 feet in the Baja lent to the actual 1999 pumpage the adjudication period (fig. 3). subarea south of the river since the (166,000 acre-feet per year). The early 1930s (Stamos and others, 2001). first simulation evaluated the Pumpage and Changes in alternative in which no water was Ground-Water Storage Artificial Recharge available to artificially recharge Ground-water pumpage in To mitigate the effects of overdraft the ground-water system during the basin has increased with in the Mojave River ground-water the drought. The second simula- time, with a large increase start- basin, the MWA is using imported tion evaluated the potential bene- ing in the late 1940s (fig. 4). California State Water Project (SWP) fit of artificially recharging Results from the ground-water water for artificial recharge by surface 65,000 acre-feet per year of SWP flow model indicate that water spreading. The ground-water flow water at three existing and five was added to storage (storage accretion) from 1931 to the mid 400 260 1940s, and water was removed 240 from storage (storage depletion) 200 from the mid 1940s through 220 1999. The model results also 0 200 indicate that overdraft started in 180 the Centro and Baja subareas by -200 160 the early 1950s, and was present 140 in all subareas by 1960 (indi- -400 Simulated cated by negative numbers in overdraft 120 figure 4). By 1999, the cumula- -600 100 tive amount of overdraft for the 80 entire basin was about 2.5 mil- -800 EXPLANATION 60 lion acre-feet, most of which Alto Oeste Transition zone Este 40 occurred in the Centro (about -1,000 Centro Total 750,000 acre-feet) and Baja Baja pumpage 20 (about 1.1 million acre-feet) CUMULATIVE STORAGE, IN THOUSANDS OF ACRE-FEET -1,200 0 subareas (fig. 4). 1930 19401950 1960 1970 1980 1990 2000 TOTAL ANNUAL PUMPAGE, IN THOUSANDS OF ACRE-FEET Overdraft has caused changes YEAR in the quantity and spatial distri- Figure 4. Cumulative simulated aquifer storage by subarea and total pumpage bution of recharge from the for all subareas, 1931−99.

proposed recharge sites during some of the artificial sites than if can help mitigate the effects of the drought. no artificial recharge was available overdraft, particularly when natu- Simulation results indicate that (fig. 6). The increases in the water- ral recharge to the ground-water when no SWP water was available levels extended several miles into system is limited. the regional aquifer from the point for artificial recharge (the first To better understand the effects alternative), water levels declined of recharge. For example, in the Alto subarea, water levels were of the artificial recharge, the by as much as 60 feet after 20 USGS has produced an animation years (fig. 5). However, when more than 5 feet higher in the 65,000 acre-feet per year of SWP regional aquifer as far as 10 miles that shows the spatial and temporal water was available for artificial from the recharge site. These distribution of these water-level recharge for 20 years (the second results show that artificial recharge changes. The animation can be alternative), water levels were can benefit the ground-water viewed at http://water.usgs.gov/ more than 100 feet higher near basin, and that artificial recharge pubs/FS/fs-122-01.

Baja Baja subarea subarea Barstow Barstow

Centro Centro subarea subarea

Transtion Transtion zone zone subarea subarea Mojave Mojave River River 0 10 20 MILES Oeste 0 10 20 MILES Oeste subarea subarea Victorville 0 10 20 KILOMETERS Victorville 0 10 20 KILOMETERS Alto Este Alto Este subarea subarea subarea subarea EXPLANATION Hesperia Hesperia Artificial recharge site

SIMULATED CHANGE IN WATER LEVEL, IN FEET SIMULATED CHANGE IN WATER LEVEL, IN FEET -60 -50 -30 -10 -5 5 10 30 40 -5 5 10 30 50 90 130 200 800

Figure 6. Difference between simulated 2019 water levels with Figure 5. Simulated water-level change between 1999 and 2019 artificial recharge, and 2019 simulated water levels without without artificial recharge. artificial recharge.

− C.L. Stamos, Tracy Nishikawa, and Peter Martin

REFERENCES CITED: TECHNICAL CONTACT Izbicki, J.A., Martin, Peter, and Michel, R.L., 1995, Source, movement and age of groundwater in the upper part of the Mojave River basin, California, U.S.A., in Adar, E.M., and Christina L. Stamos Leibundgut, Christian, eds., Application of tracers in arid zone hydrology: U.S. Geological Survey International Association of Hydrological Sciences, no. 232, p. 43−56. 5735 Kearny Villa Road, Suite O Izbicki, J.A., Radyk, J.C., and Michel, R.L., 2000, Water movement through a thick unsaturated zone underlying an intermittent stream in western Mojave Desert, southern California, San Diego, CA 92123-1135 USA: Journal of Hydrology, v. 238, p. 194−217. e-mail: [email protected] Lines, G.C., 1996, Ground-water and surface-water relations along the Mojave River, southern Voice: (858) 637-9005 California: U.S. Geological Survey Water-Resources Investigations Report 95-4189, 43 p. Fax: (858) 637-9201 Lines, G.C., and Bilhorn, T.W., 1996, Riparian vegetation and its water use during 1995 along the Mojave River, southern California: U.S. Geological Survey Water-Resources Califorina District activities website: Investigations Report 96-4241, 10 p., 1 pl. http://ca.water.usgs.gov Stamos, C.L., Martin, Peter, Nishikawa, Tracy, and Cox, B.F., 2001, Simulation of ground-water flow in the Mojave River Basin, California: U.S. Geological Survey Water-Resources Investigations Report 01-4002, 129 p. Cover photo courtesy J.A. Izbicki, USGS