REGIONAL WATER TABLE (2016) IN THE MOJAVE RIVER AND MORONGO GROUNDWATER BASINS, SOUTHWESTERN MOJAVE DESERT, CALIFORNIA by Meghan C. Dick and Adam R. Kjos
Data for static groundwater-levels measured in about 645 wells during January-April 2016 by the United States 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. Previous hydrologic studies (Izbicki and others, 1995; Stamos and Predmore, 1995; Stamos and others, 2001) have modified the boundaries of El Mirage Valley, Upper Mojave River Valley, Middle Mojave River Valley, Lower Mojave River Valley, Harper Valley, Coyote Lake Valley and Caves Canyon Valley groundwater basins defined by the California Department of Water Resources (DWR) (California Department of Water Resources, 2003) and have referred to them collectively as the Mojave River groundwater basin. Similarly, the boundaries of Lucerne Valley, Johnson Valley, Means Valley, Bessemer Valley, Ames Valley, Deadman Valley, Twentynine Palms, Copper Mountain Valley, Warren Valley, and Joshua Tree groundwater basins (California Department of Water Resources, 2003) were modified and are collectively referred to as the Morongo groundwater basin. Groundwater levels recorded by the USGS and MWA staff were measured and compiled according to the procedures described in the Groundwater Technical Procedures of the USGS (Cunningham and Schalk, 2011). Groundwater-level measurements submitted by cooperating local water districts were collected using procedures established by the corresponding agency, and compiled according to the procedures described in the Groundwater Technical Procedures of the USGS (Cunningham and Schalk, 2011). Furnished groundwater-level measurements that did not meet USGS standards for inclusion in the USGS National Water Information System (NWIS) are available as an online data release at https://doi.org/10.5066/F7GB2291. All water-level records collected for the 2016 study were compared to historical data for quality-assurance purposes.
Groundwater-level contours from the 2014 groundwater-level map (Teague and others, 2016) were used as a guide to interpret and shape the 2016 groundwater-level contours. Contours are shown as dashed (approximate) on the water-table map where data were sparse. In addition to being available on the interactive map, 2016 groundwater-level data used in the map and the contours fitted to those data are shown for the entire area of the Mojave River and Morongo groundwater basins on Plate 1 (Dick and Kjos, 2017). Groundwater-level data for 2016 are accessible through this website's "Data Downloads" page (follow the Water-Level Sites link for 2016 Sites [2016 study]).
Historical groundwater-level data from the USGS National Water Information System (NWIS) database were used to construct 37 groundwater-level hydrographs to show long-term (1930-2016) and short-term (1990-2016) groundwater-level changes in the Mojave River and Morongo groundwater basins. Groundwater-level changes between the spring of 2014 and spring of 2016 were determined by comparing groundwater levels measured in the same well during both periods. Groundwater-level changes between any of the study years on this website can also be displayed on the interactive map by selecting the years of interest from the "Water-Level Changes between 2 Years" menu.
Long-term (1930–2016) groundwater-level changes are depicted by 25 groundwater-level hydrographs (shaded) for the Mojave River and the Morongo groundwater basins. Wells for three hydrographs (wells 5N/5W-22E6, 11N/4W-29R1, and 11N/4W-30N1) were destroyed or were unable to be measured in 2016, but the water levels from these wells are included to provide information that is discussed in previous water-level reports.
Data from more than one well were combined in some hydrographs to show groundwater-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, or could no longer be measured, and data from a well nearby could be used to continue the record. Data from the different wells are shown by using differently colored data points on the hydrographs.
The Morongo groundwater basin is divided into 17 subbasins. All of the long-term hydrographs for the Morongo groundwater basin showed declines in groundwater levels of variable magnitude since the wells were first measured. Groundwater levels have declined
Twelve short-term hydrographs (unshaded) were constructed from data collected between 1990 and 2016 in the Mojave River groundwater basin. Most hydrographs show data from wells that are located along the Mojave River. Hydrographs for these wells display the effects of seasonal recharge from streamflow, discharge along the Mojave River, artificial recharge, and evapotranspiration, which is minimal during winter months. These short-term hydrographs show that
Groundwater-level data exist for 505 wells in the Mojave River and Morongo groundwater basins for both spring 2014 and spring 2016. Groundwater-level changes between both years can be viewed by selecting those years on the groundwater-level change map (groundwater-level change maps can be created using the "Water-level Changes between 2 Years" menu). The groundwater-level data for 2016 represents the tail end of a 5-year drought in southern California and was marked by a relatively wet winter. Some wells had declines or increases in groundwater levels that were opposite of those in wells in the same area; these anomalies are likely a result of fluctuations in pumping and distance to artificial recharge areas. From 2014 to 2016,
Of the 345 wells assessed within the Mojave River groundwater basin, groundwater-level data shows
Approximately 60% of the wells in the Mojave River groundwater basin had groundwater-level declines greater than 0.5 ft and only 19% remained within 0.5 ft of 2014 groundwater-levels. The majority of groundwater levels in wells in the Alto subarea declined between 5 and 15 ft while levels in some wells north of the Amethyst Basin artificial recharge site have increased less than 2 ft. Recharge water had not been applied at the Amethyst Basin recharge site prior to spring 2016, therefore, increased groundwater levels in that area likely were a result of decreases in pumping volume. The majority of groundwater levels in the Alto Transition zone increased by less than 5 ft or remained unchanged because of infiltration from the treated wastewater discharged by the VVWRA and infiltration of surface water flow along the Mojave River at the Lower Narrows (10261500 Location). The majority of wells along the Mojave River in both the Centro and Baja subareas had declines in groundwater levels. A large region of decline between 5 and 15 ft occurred near the Mojave River at Lenwood. Groundwater-levels continue to decline in this area due to sustained pumping for agricultural and domestic uses. Southeast of Harper Lake, groundwater levels either increased or remained within 0.5 ft of measurements made in 2014. In the Baja subarea, wells south of the Mojave River had groundwater-level declines between 0.5 and 6 ft, but most wells north of the Mojave River near Coyote Lake had less than 0.5 ft of groundwater-level change. The declines in groundwater levels south of the Mojave River in Baja were likely due to continued pumping of groundwater for agricultural use (Mojave Water Agency Watermaster, 2016).
Of the 160 wells compared within the Morongo groundwater basin,
About 40% of wells had groundwater-level declines over 0.5 ft since 2014. Groundwater levels in the Fry, Johnson, and Deadman subbasins had groundwater-level changes within 0.5 ft between 2014 and 2016. The majority of the wells in the Surprise Spring subbasin had groundwater-level declines less than 5 ft. Groundwater levels in the Mainside subbasin were mostly unchanged, but two wells showed increased groundwater levels, and one well showed a decreased groundwater level. These groundwater-level increases can be attributed to a combination of recharge from irrigation of the Twentynine Palms Marine Corp golf course and effects from a possible reduction in pumpage (Li and Martin, 2011). Groundwater levels in wells northeast of the Ames-Reche recharge site increased while groundwater levels in the rest of the Reche subbasin declined. The increased groundwater levels are likely due to State Water Project deliveries to Pipes Wash at the Ames-Reche recharge site. The greatest groundwater-level increases continued to be observed in the Warren subbasin, where artificial-recharge operations in Yucca Valley, along with a reduction in groundwater pumpage (Stamos and others, 2013), have caused groundwater levels to rise more than 250 ft (well 1N/5E-36K2) since 1994.