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Securing Arizona's Water Future
Hydrology of the Lake Mohave Basin

Groundwater Hydrology

Colorado River Basins

The Colorado River Basins include the Lake Havasu and Lake Mohave basins and those portions of the Sacramento Valley and Bill Williams basins in the vicinity of the Colorado River. In these areas the direction and occurrence of groundwater are influenced by the amount of streamflow in the Colorado River.  Infiltration of river water is the main source of inflow to aquifers in this area.  The aquifers are composed primarily of recent stream alluvium deposits that is hydraulically connected to underlying basin fill.  Groundwater occurs under unconfined conditions in both the stream alluvium and basin fill.

Lake Mohave Basin

The Lake Mohave Basin is a long narrow basin located adjacent to the Colorado River.  The principal water-bearing formations are alluvial sand, silt and gravel deposits adjacent to Lake Mohave and the Colorado River.   The regional groundwater level is higher than it was prior to filling Lake Mohave upstream of Davis Dam. Groundwater flow direction is from north to south.  A granite ridge extends across the Colorado River near Davis Dam, restricting recharge from the lake to the south.  Groundwater is generally unconfined in the basin.  Compared to groundwater recharge from the lake, mountain front recharge is negligible. 

Groundwater recharge is estimated to total 183,000 AFA. Groundwater in storage estimates vary from 1.2 to 8.0 maf. Water withdrawals from wells in the basin are primarily pursuant to Colorado River entitlements. Median well yield is 1,000 gpm reported from 96 large (>10-inch) diameter wells (Table 4.6-6). Water level change data for the period 1990-91 to 2003-04 show slight declines south of Bullhead City and an increase north of the city.  The water level in these wells ranged between 337 and 427 feet bls. Elevated concentrations of total dissolved solids (TDS) and fluoride occur in welled completed along the mountain fronts. The drinking water standard for arsenic was the most frequently exceeded standard measured in the basin (Table 4.6-7). Springs, some of which are thermal, occur downstream of Hoover Dam and represent the only surface water in the basin other than the lake and the Colorado River.

Click to view Table 4.6-6

Click to view Table 4.6-6 Groundwater Data for the

Lake Mohave Basin

Click to view Figure 4.6-6

Click to view Figure 4.6-6 Lake Mohave Basin

Groundwater Conditions

Click to view Figure 4.0-5

Figure 4.0-5 Upper Colorado River USGS Watersheds

Surface Water Hydrology

The U.S. Geological Survey (USGS) divides and subdivides the United States into successively smaller hydrologic units based on hydrologic features.  These units are classified into four levels. From largest to smallest these are: regions, subregions, accounting units and cataloging units.  A hydrologic unit code (HUC) consisting of two digits for each level in the system is used to identify any hydrologic area (Seaber et al., 1987). A 6-digit unit code corresponds to accounting units, which are used by the USGS for designing and managing the National Water Data Network. 

Davis Dam

Davis Dam, Lake Mohave Basin.  Parker and Davis dams have created lakes that affect groundwater conditions along the Colorado River.

Lower Colorado below Lake Mead Watershed

This watershed covers parts of two planning areas.  The northern portion is within the Upper Colorado River Planning Area (north watershed) and the southern portion is located in the Lower Colorado River Planning Area.  Groundwater basins included in the north watershed are the Lake Havasu Basin and most of the Lake Mohave and Sacramento Valley basins.  A very small portion of Detrital Valley Basin also lies within the north watershed.  Sacramento Wash, an ephemeral wash in the Sacramento Valley Basin, is the only major contributing tributary to the Colorado River in the north watershed.  Sawmill Canyon, located at the northeastern edge of the Sacramento Valley Basin, is the only intermittent stream (Figure 4.9-5).

Parker and Davis dams have created lakes that also affect groundwater conditions along the Colorado River.  Parker Dam is located in the Lower Colorado River Planning area but the lake it creates, Havasu, extends into the Upper Colorado River Planning Area.  Davis Dam, north of Bullhead City, creates Lake Mohave.  There is outflow from the river and lakes into the surrounding aquifers.  Maximum storage in Lake Mohave is about 1.8 maf (including dead storage) and average storage from 1996 to 2005 was 1.65 maf.  Maximum storage in Lake Havasu is 651,000 acre-feet (including dead storage) and average storage from 1996-2005 was about 572,000 acre-feet.

The only streamgages in the north watershed are along the Colorado River.  Streamflow is largely subject to releases from upstream dams.  A gage at Topock reports median annual flow of 8.9 maf, a gage below Davis Dam reports median annual flow of 8.5 maf, and median annual flows below Hoover Dam are 9.2 maf.

Twenty-four major springs are found in the north watershed.  These springs are located in the northern half of the Sacramento Valley Basin and in the Lake Mohave Basin along the Colorado River immediately below Hoover Dam.  Only three of the major springs have had a measured discharge rate of 100 gpm or greater.  There are a relatively large number of minor springs (42) in the Sacramento Valley Basin.  The most recent spring measurements were taken in 1979 and some measurements date to the 1940s.

 

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Davis Dam Lake Havasu NWR