REGIONAL WATER TABLE (2010) IN THE MOJAVE RIVER AND MORONGO GROUNDWATER BASINS, SOUTHWESTERN MOJAVE DESERT, CALIFORNIA by Gregory A. Smith, Christina L. Stamos, Carolyn S. Glockhoff, Sally F. House, and Dennis A. Clark
Data for static water-levels measured in about 610 wells during January through June 2010 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, which shows the altitude of the water table and general direction of groundwater movement in and around the Mojave River and Morongo groundwater basins. Water-level contours from the 2008 water-level map (Stamos and others, 2009) were used as a guide to interpret the 2010 water-level contours in areas where 2010 water-level data were not available. In addition to being available on the interactive map,the 2010 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. Historical water-level data from the National Water Information System (NWIS) database were used in conjunction with data collected for this study to construct 37 water-level hydrographs to show both long-term (1930 - 2010) and short-term (1990 - 2010) water-level changes in the Mojave River and Morongo groundwater basins. Water-level changes between spring 2008 and spring 2010 were determined by comparing water levels measured in the same well during both periods. Water-level changes between the studies on this website can be displayed on the interactive map by entering the years of interest.
Long-term (1930–2010) water-level changes are depicted by 28 water-level hydrographs (shaded). Some hydrographs combine data from more than one well to show water-level changes over a greater period of time in a particular area. The long-term hydrographs for the Mojave River groundwater basin show that water levels have declined more than 80 ft in the Alto subarea (location map, water-level hydrographs) 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 (well 11N/3W-28R1, -28R2), and more than 100 ft in the Baja subarea since the late 1940s (wells 9N/2E-20Q1, -20K1, and -20G3). The long-term hydrographs for the Morongo groundwater basin show little or no change in most of the subbasins, but water levels declined in 5 of the 17 subbasins in response to pumpage. Water levels have declined about 40 ft in the Joshua Tree subbasin since the early 1960s (well 1N/7E-32C1), about 55 ft in the Reche subbasin since the early 1960s (well 2N/6E-18B1), about 100 ft in the Lucerne subbasin since the early 1950s (well 5N/1W-25G1), about 140 ft in the Surprise Spring subbasin since the early 1950s (well 2N/7E-2C1), and more than 300 ft in the Warren subbasin between the mid 1940s and 1994 (wells 1N/5E-36K1 and -36K2). Water levels in the Warren subbasin have risen substantially since 1994 in response to the application of imported water to ponds at the Hi-Desert Water District recharge sites.
Nine short-term hydrographs (unshaded) were constructed from data collected between 1992 and 2010 in the Mojave River groundwater basin (hydrographs) to record the effects of seasonal recharge and discharge along the river and the effects of evapotranspiration from riparian vegetation, which is minimal during winter. These short-term hydrographs show that since 1992, there has been some recharge to the floodplain aquifer from stormflows in the Mojave River in the Alto and Centro subareas, but recharge from stormflows in the Baja subarea has been minimal. In the Transition zone of the Alto subarea, the groundwater levels near well 7N/5W-23R3 remained stable owing to recharge from treated wastewater that is discharged about 4 mi upstream by the Victor Valley Wastewater Reclamation Authority (location map).
Water-level changes between spring of 2008 and January through June 2010 can be viewed by selecting those years on the water-level change map; 513 wells in the study area had water-level data for both years. In 2010, about 25 percent (126) had water levels that were within 0.5 ft of those in 2008. About 44 percent (225) of the wells had water-level declines greater than 0.5 ft, about 11 percent (54) of the wells had declines greater than 5 ft, and less than 1 percent (4) of the wells had declines greater than 30 ft. About 32 percent of wells (162) had a water-level increase of 0.5 ft or more.
Of the 340 wells compared within the Mojave River groundwater basin, about 46 percent of the wells (156) had water-level declines greater than 0.5 ft, and about 14 percent (47) of the wells had declines greater than 5 ft. The water-level data also show that about 35 percent (118) of the wells compared in the Mojave River groundwater basin had water-level increases of 0.5 ft or more (water-level change on interactive map).
Overall, water levels in wells along the Mojave River in the Alto subarea (location map) and the Alto Transition zone increased because of the infiltration of surface flow during the early months of 2010. Data from the Centro and Baja subareas showed an overall decline in water levels (water-level change on interactive map). Water-level declines downstream of the artificial recharge operations in the Centro subarea could be attributed, at least in part, to the suspension of artificial recharge applied to ponds since 2008 (www.mojavewater.org/regionalInformation/WaterDeliveries.aspx). Water levels southwest of Harper Lake (dry) in the Centro subarea continued to increase because of the sustained reduction in pumpage since the early 1990s. In the Baja subarea, most wells had water-level declines between 0.5 and 5 ft.
Of the 173 wells compared within the Morongo groundwater basin, about 39 percent (68) of the wells had water-level declines greater than 0.5 ft, and about 4 percent (7) of the wells had declines greater than 5 ft. The water-level data also show that about 25 percent (44) of the wells had water-level increases of 0.5 ft or more. The greatest increases were in the Warren subbasin, where artificial-recharge operations in Yucca Valley (Plate 2) and a reduction in pumpage (Hi-Desert Water District, written commun., 2010) have caused water levels to rise more than 120 ft since 1994 (hydrographs, water-level change on interactive map). A reduction of pumpage in the Lucerne, Surprise Spring, and Twentynine Springs subbasins also resulted in water-level rises.
Palm Canyon, Mojave Desert