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Mojave Water-Level Studies

Regional water-table maps of the Mojave River and Morongo groundwater basins have been published in reports by the U.S. Geological Survey (USGS) every two years since 1992. The water-level reports for the years 1992-2004 were published as USGS Water-Resources Investigations Reports or Scientific Investigations Reports and are available online as separate Portable Document Fomat (pdf) formatted reports, which can be accessed on the "References" page on this website; the water-level contours from most of the water-level maps are available also on this website: data page. Beginning in 2006, the biannually scheduled water-level reports and maps will be published on this interactive mapping website; any future water-level studies also will be available on this website..

The water-level studies include water-level contour maps drawn from data measured from wells during each study. Most of the studies demonstrate water-level changes by hydrographs that show long-term and short-term water-level changes, and by maps that compare water levels at individual wells between two consecutively published reports.

Water-Level Studies by Year:

2016 2014 2012 2010 2008 2006 2004 2002 2000 1998 1996 1994 1992

Water-Level Maps

Maps from the water-level reports show the altitude of the water table above mean sea level for a specific time period, and general direction of groundwater flow. The water table is the surface on which the fluid pressure in the pores of a porous medium is exactly atmospheric (Freeze and Cherry, 1979). The water table is defined by the levels at which water stands in wells that just penetrate the top of the water body (Lohman, 1972). The water-level measurements used for the water-level contour maps are from wells with various perforated intervals in the saturated zone of the groundwater basins. Although these wells may have different perforated zones, the measured water levels from the zones are within about 10 ft and, therefore, reasonably represent the water-table altitude. Water levels measured from the perched groundwater zones were not used to construct the water-level contours.

In areas where sufficient data exist, points of equal water-level altitude were connected by contour lines to show the general direction of groundwater flow. In areas where water-level data were unavailable for a particular year, the general shape of the contours was defined on the basis of the previously published water-table map, when available. In some areas of the maps, water-level measurements were affected by recent pumping, or nearby wells that were pumping, which resulted in steep water-level gradients and water-level contours that bend abruptly around wells.

As part of a groundwater observation network, the USGS, in cooperation with local water agencies, water districts, the military, and private landowners, has constructed many multiple-well monitoring sites. These sites consist of a cluster of two or more observation wells completed at different depths within a single borehole, each typically screened across a 20-foot interval (Huff and others, 2002). Data from the shallowest well of a multiple-well site were used for the regional water-table maps.

The water levels presented on the maps were measured using a steel tape or a calibrated electric tape; when neither of these methods was possible, an airline was used. Water-level data collected by other agencies were validated and deemed to adhere to USGS guidelines and were noted as "reported" in the USGS National Water Information System (NWIS) database. The water-level altitude was determined by subtracting the water-level measurement (depth to water, in feet below land surface) from the established land-surface referenced to the North American Vertical Datum 1988 (NAVD 88).

To access a file containing the USGS site and California State well numbers for the wells used to construct each of the maps, click on the button of the year of interest at the top of this page. These files can be used to retrieve water-level and water-quality data from the USGS NWIS database by going to http://waterdata.usgs.gov/ca/nwis. Water-level data from the USGS NWIS database can also be retrieved directly from the "Water Level Contours" and "Water Level Comparison Between 2 Years" data layers on the interactive map.

Groundwater Movement

Groundwater flows from areas of higher hydraulic head to areas of lower hydraulic head (downgradient), and perpendicular to the water-level contours. Inspection of water-table contours in the vicinity of faults indicates that some faults in the study area are barriers to groundwater flow. The barrier effect of the faults is probably caused by compaction and deformation of water-bearing deposits immediately adjacent to the faults and by cementation of the fault zone by mineral deposits from groundwater (Londquist and Martin, 1991).

The southern part of the Helendale Fault near the town of Lucerne is a very effective barrier to subsurface flow. Inspection of the water-table map indicates that the direction of groundwater movement on the east side of the Helendale Fault is toward Lucerne (dry) Lake. Therefore, groundwater east of the Helendale Fault in this area is considered to be in the Morongo groundwater basin. groundwater flow patterns in the Lucerne Lake area have changed little since 1916-17, the time of the first available data (Schaefer, 1979). West of the Helendale Fault, groundwater is considered to be in the Este subarea of the Mojave River groundwater basin, and the water table gradient is relatively flat.

Mojave River Groundwater Basin

In most subareas of the Mojave River groundwater basin, groundwater generally flows northward and eastward. However, in the Este subarea, the flow is northward and westward. The amount of subsurface flow across the boundary between the Alto and Este subareas was estimated by Stamos and Predmore (1995) using the following form of Darcy’ law:

Q = Tiw,

where Q is the quantity of subsurface flow [L3],

T is the transmissivity [L2/t],

i is the hydraupc gradient at the boundary [L/L], and

w is the width of the area through which the flow passes[L].

Hardt (1971) estimated that the transmissivity of the aquifer materials near the boundary of the Alto and Este subareas ranged from 5,000 to 10,000 (gal/d)/ft. The width of the boundary is about 4 mi and the hydraulic gradient was determined from the water-table map in 1992 (Stamos and Predmore, 1995) to be 0.0025 ft/ft. On the basis of these estimates, the approximate subsurface flow in 1992 from the Este subarea to the Alto subarea was 300 to 600 acre-ft/yr. Available data in the southwestern part of the Mojave River groundwater basin were insufficient to estimate the quantity of flow across the Oeste/Alto subarea boundary.

The water-table contours indicate that subsurface flow occurs across the northern part of the Helendale Fault from the Alto subarea to the Centro subarea along the Mojave River. Water-level data from multiple-well monitoring sites, as well as historical data, indicate that this fault restricts subsurface flow within the regional aquifer, but not within the overlying alluvial aquifer (Hardt 1971). Ground water passing into the Centro subarea flows either to the north, away from the Mojave River toward Harper (dry) Lake, or to the northeast through a narrow gap in the consolidated rocks on the south side of Iron Mountain. Steep water-level gradients between the Helendale Fault and Iron Mountain indicate the probable presence of subsurface faults or shallow geologic structures that impede subsurface flow to Harper Lake. On the east side of Iron Mountain, groundwater flows away from the Mojave river toward the northwest to Harper Lake and also northeast toward the city of Barstow.

Groundwater from the Centro subarea crosses the Camp rock-Harper Lake Fault zone and enters the Baja subarea east of Barstow. Within the fault zone, the water-table gradient is marked by abrupt, stairstep-like changes in the water-table gradient, decreasing in altitude as water flows eastward. Water-level data from multiple-well monitoring sites indicate that the fault zone impedes groundwater movement in both the shallow alluvial aquifer and underlying regional aquifer. East of the Camp Rock-Harper Lake Fault zone, the water-table gradient is relatively flat as groundwater flows northeastward through the Baja subarea. However, as groundwater enters the middle of the Baja subarea, it is impeded by the Calico-Newberry Fault, as indicated by more than 50-foot drop in the water table on the west side of the fault. Water-level data from multiple-well monitoring sites on both sides of the Calico-Newberry Fault indicate that, as in the Camp Rock-Harper Lake Fault zone, groundwater flow is impeded in both aquifers.

Subsurface flow through the Baja subarea is affected by low-permeability deposits present at shallow depths in two locations. Near Camp Cady, fine-grained unconsolidated deposits near the surface that are associated with ancient Manix Lake (California Department of Water Resources, 1967) cause an abrupt change in the water-table gradient as groundwater continues to flow toward Afton Canyon. At Afton Canyon, low-permeability deposits present at shallow depths below the Mojave River restrict subsurface flow, forcing groundwater to the surface before it exits the Mojave River groundwater basin.

Morongo Groundwater Basin

In the Morongo groundwater basin, groundwater generally flows eastward and northward from the San Bernardino Mountains. From Pipes Wash, flow is eastward toward the localized sinks in the water table at Deadman and Mesquite dry lakes. Ground water pumping by the U.S. Marine Corps Air/Ground Combat Center (USMCAGCC) in the Surprise Spring Basin has created a groundwater depression and has locally changed the direction of groundwater movement. From washes along the northern front of the San Bernardino Mountains, flow is northeastward to the pumping depression in the Lucerne Basin, and to the Soggy, Melville, and Means dry lakes. As groundwater moves eastward through the Morongo Basin, subsurface flow across faults is impeded, resulting in a steplike decrease in water levels. Ground water leaves the basin across the Mequite Fault in the southeastern part of the basin, and ultimately moves eastward toward.

Other patterns indicated by the contour lines and supported by previous findings are (1) northward flow from the Little San Bernardino Mountains to the Pinto Mountain Fault (Lewis, 1972), (2) minor flow southward from the San Bernardino Mountains into Warren Basin (Lewis, 1972), and (3) southward flow into Lucerne Basin from the Ord Mountains (Schaefer, 1979). Rates of groundwater movement in areas of the basin unaffected by pumping are low – generally a few feet per year (French, 1978).

Groundwater depressions are present in the areas of highest historical and current pumpage:  Warren, Lucerne, and Surprise Spring Basins. Construction of water-table contours in Warren Basin was difficult because water levels vary considerably. The variability might be due to (1) the presence of faults that separate the area into small isolated compartments, and (or) (2) incomplete recovery of the water table in the public-supply wells at the time of measurement – even though pumping had ceased 24 hours prior to measurement.

Perched water occurs in the Mainside Basin (under Mesquite Dry Lake) approximately 130 ft above the regional water table. Movement of this water seems to be southeastward, similar to that of the regional groundwater below. The probable source of this perched water is spreading ponds that are used for sewage-water treatment.

Water-Level Changes

Historical water-level data were used in conjunction with data collected for each map since 1994 to determine long-term (as early as 1930) water-level changes in the Mojave River and Morongo groundwater basins. Long-term water-level changes, shown by hydrographs, are depicted for approximately 20 wells, or groups of wells, on the maps. Some hydrographs combine data from more than one well to show water-level changes over a greater period of time for a particular area. Maps produced since 1996 also show as many as 14 short-term (beginning in 1990) water-level hydrographs from wells along the Mojave River to illustrate the effects of streamflow and evapotranspiration along the river.

The regional water-level map reports published by the USGS after 2000 also contained water-level change maps that were prepared by comparing water levels from wells that had water-level data from the same wells for two consecutively published reports. The interactive data map allows for comparison of the water-level changes in wells between any two years that have water-level data available for the same wells.