Data for static water-levels measured in about 730 wells during February through May 2008 by the U.S. Geological Survey (USGS), the Mojave Water Agency (MWA), and local water districts were used to construct a regional water-table map, which shows the altitude of the water table and general direction of groundwater movement in the Mojave River and Morongo groundwater basins. Water-level contours from the 2006 water-level map (Stamos and others, 2007) were used as a guide to interpret the 2008 water-level contours in areas where 2008 water-level data were not available. In addition to being available on the interactive map (2008 water-level contours from interactive map), the 2008 water-level data and contours are shown on a PDF formatted plate. Historical water-level data were used in conjunction with data collected for this study to construct 33 water-level hydrographs to show both long-term (as early as 1930) and short-term (beginning in 1990) water-level changes in the Mojave River and Morongo groundwater basins. Water-level changes between spring 2006 and spring 2008 (interactive map comparing 2006 and 2008), were determined by comparing water levels measured in the same well during both periods. Water-level changes between any of the water-level studies on this website can also be displayed on the interactive map.
Long-term (1930–2008) water-level changes are depicted by 24 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), and more than 100 ft in the Baja subarea since the late 1940s (wells 9N/2E-20Q1, and -20K1). The long-term hydrographs for the Morongo groundwater basin show little or no change in most of the subbasins, but water levels declined significantly in 5 of the 17 subbasins because of pumpage. Water levels have declined about 40 ft in the Joshua Tree subbasin since the early 1960s (well 1N/7E-32C1), about 60 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, -36K2). The rapid decline in some wells in the Warren subbasin has been reversed since 1994 because of artificial recharge to ponds at the Hi-Desert recharge sites.
Nine short-term hydrographs (unshaded) were constructed from data collected between 1992 and 2008 in the Mojave River groundwater basin (hydrographs) to record the effects of seasonal recharge and discharge along the river and the effects of evapotranspiration of 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, 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 2006 and February through May 2008 can be viewed by selecting those years on the water-level change map; 573 wells had water-level data for both years in the study area. About one quarter (151) of the water levels in 2008 were within 0.5 ft of the water levels in 2006. More than one half (338) of the wells had water-level declines greater than 0.5 ft, 114 wells had declines greater than 5 ft, and 16 wells had declines greater than 30 ft. Only 84 of the wells had a water-level increase of 0.5 ft or more.
Of the 392 wells compared within the Mojave River groundwater basin, about two thirds (258) had water-level declines greater than 0.5 ft; 93 of the wells had declines greater than 5 ft. The water-level change data show also that only 55 wells compared in the Mojave River groundwater basin had water-level increases of 0.5 ft or more; no wells in the Baja subarea had an increase in water levels. 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.
Of the 181 wells compared within the Morongo groundwater basin, slightly less than half (80) of the wells had water-level declines greater than 0.5 ft; 21 of the wells had declines greater than 5 ft. The water-level change data also show that only 29 of the wells compared had water-level increases of 0.5 ft or more. The greatest increases were mainly in the Warren subbasin, where artificial-recharge operations in Yucca Valley have caused water levels to rise more than 120 ft since 1994 (hydrographs, water-level change on interactive map).
Oro Grande Wash, Mojave Desert