REGIONAL WATER TABLE (2012) IN THE MOJAVE RIVER AND MORONGO GROUNDWATER BASINS, SOUTHWESTERN MOJAVE DESERT, CALIFORNIA by Nick F. Teague, Christina L. Stamos, Sally F. House, and Dennis A. Clark
Data for static water-levels measured in about 580 wells during March-May 2012 by the U.S. Geological Survey (USGS), the Mojave Water Agency (MWA), and other local water districts were compiled to construct a regional water-table map. This map shows the elevation of the water table and general direction of groundwater movement in and around the Mojave River and Morongo groundwater basins. Water-level measurements recorded by the USGS and MWA staff were compiled according to the procedures described in the Groundwater Technical Procedures of the U.S. Geological Survey (Cunningham and Schalk, 2011). Water-level data submitted by cooperating local water districts were collected by using procedures established by the corresponding agency. All data were compared to historical data for quality-assurance purposes. Water-level contours from the 2010 water-level map (Smith and others, 2011) were used as a guide to interpret the 2012 water-level contours in areas where 2012 water-level data were not available. In addition to being available on the interactive map, 2012 water-level data and contours are shown for the entire area of the Mojave River and Morongo groundwater basins on plate 1; greater detail of the Warren subbasin in the Morongo groundwater basin is shown on plate 2. Water-level data for 2012 are accessible through the website by clicking on the 2012 button above the title on the Water Levels page. Historical water-level data from the National Water Information System (NWIS) database were used in conjunction with data collected for this study to construct 36 water-level hydrographs to show long-term (1930-2012) and short-term (1990-2012) water-level changes in the Mojave River and Morongo groundwater basins. Water-level changes between the spring of 2010 and spring of 2012 were determined by comparing water levels measured in the same well during both periods. Water-level changes between the studies on this website can also be displayed on the interactive map by selecting the years of interest from the Groundwater Data menu.
Long-term (1930–2012) water-level changes are depicted by 27 water-level hydrographs (shaded) for the Mojave River and the Morongo groundwater basins.
The Mojave River groundwater basin is divided into five subareas. Data from more than one well were combined in hydrographs to show water-level changes over long periods in particular subareas. Combining data from multiple wells onto a single hydrograph was done when a well went dry due to a decline in the water table and data from a well in close approximation could be used to continue the record. Data from the different wells are shown using different colored data points on the hydrographs. The long-term hydrographs for the Mojave River groundwater basin show that water levels have declined more than 70 feet (ft) in part of the Alto subarea since the mid-1940s (wells 5N/5W-22E1, -22E2, and -22E6), about 55 ft in the eastern part of the Harper Lake region of the Centro subarea since the 1960s (wells 11N/3W-28R1, -28R2), and more than 100 ft in part of the Baja subarea since the late 1940s (wells 9N/2E-20Q1, -20K1, and -20G3).
The Morongo groundwater basin is divided into 16 subbasins. Data from multiple wells were combined in hydrographs to show water-level changes over long periods for particular subbasins. Five of the six long-term hydrographs for the Morongo groundwater basin showed declines in water levels of variable magnitude; these changes may be in response to groundwater pumping. Water levels have declined about 45 ft in part of the Joshua Tree subbasin since the early 1960s (well 1N/7E-32C1), about 60 ft in part of the Reche subbasin since the early 1960s (well 2N/6E-18B1), about 100 ft in part of the Lucerne subbasin since the early 1950s (well 5N/1W-25G1), about 150 ft in part of the Surprise Spring subbasin since the early 1950s (well 2N/7E-2C1), and more than 300 ft in part of the Warren subbasin between the early 1950s and 1994 (wells 1N/5E-36K1 and -36K2). Water levels in the Warren subbasin have risen substantially since 1994 in response to artificial recharge of imported water using ponds at the Hi-Desert recharge sites (wells 1N/5E-36K1 and -36K2).
Nine short-term hydrographs (unshaded) were constructed from data collected between 1992 and 2012 in the Mojave River groundwater basin to record the effects of seasonal recharge and discharge along the river, and evapotranspiration, which is minimal during winter months. These short-term hydrographs showed that there has been some recharge to the floodplain aquifer from stormflows in the Mojave River in the Alto and Centro subareas since 1992, but recharge from stormflows in the Baja subarea has been minimal. In the Alto Transition zone, the groundwater levels near well 7N/5W-23R3 remained stable as a result of recharge from treated wastewater that is discharged about 4 miles upstream by the Victor Valley Wastewater Reclamation Authority (location map).
Water-level changes between spring of 2010 and the spring of 2012 can be viewed by selecting those years on the water-level change map (directions to access the water-level change map can be found under the "Layer Descriptions" menu). Water-level data exist for 516 wells in the Mojave River and Morongo groundwater basins for both years. In 2012, about 25 percent of the wells (131) had water levels within 0.5 ft of those in 2010. About 30 percent (157) of the wells had water-level declines between 0.5 and 5 ft, about 3 percent (18) of the wells had declines between 5 and 30 ft, and 1 percent (5) of the wells had declines greater than 30 ft. About 39 percent of the wells (200) had water-level increases between 0.5 and 30 ft or more, and about 1 percent of the wells (5) had water-level increases of 30 ft or more.
Of the 343 wells assessed within the Mojave River groundwater basin, about 18 percent of the wells (61) had water levels within 0.5 ft of those in 2010. About 31 percent of the wells (107) had water-level declines greater than 0.5 ft, and about 4 percent (14) of the wells had declines greater than 5 ft. The water-level data also showed that about 47 percent (161) of the wells compared in the Mojave River groundwater basin had water-level increases of 0.5 ft or more. Only one well had a water-level increase of 30 ft or more.
Overall, water levels in wells along the Mojave River in the Alto subarea and the Alto Transition zone increased because of the infiltration of high surface flow during the winter of 2010 and spring of 2011, as recorded at gage stations at Lower Narrows (10261500) and Barstow (10262500). Data from the Centro subarea showed an overall increase in groundwater levels, whereas data from the Baja subarea showed an overall decline in groundwater levels. Groundwater-level increases downstream of the artificial recharge operations in the Centro subarea could be attributed, at least in part, to an increase in water storage at those operations. Water levels southwest of Harper Lake (dry) in the Centro subarea increased (well 11N/4W-29R1) from 1998 to 2010 because of a sustained reduction in groundwater pumping since the early 1990s (Stamos and others, 2001); however, the magnitude of water-level increases leveled in 2012. In the Baja subarea, most wells had water-level declines between 0.5 and 5 ft, but most wells north of the Mojave River had water-level increases between 0.5 and 5 ft.
Of the 173 wells compared within the Morongo groundwater basin, about 40 percent of the wells (70) had water levels within 0.5 ft of those in 2010. About 29 percent (50) of the wells had water-level declines between 0.5 and 5 ft, and about 5 percent (9) of the wells had declines greater than 5 ft. The water-level data also showed that about 23 percent (40) of the wells had water-level increases between 0.5 and 30 ft, and about 2 percent (4) of the wells had water-level increases of 30 ft or more. The greatest increases were in the Warren subbasin, where artificial-recharge operations in Yucca Valley (Plate 2) and a reduction in groundwater pumping have caused water levels to rise more than 230 ft (well 1N/5E-36K2) since 1994 (Stamos and others, 2013).
Palm Canyon, Mojave Desert