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Hydrology of the Upper Colorado River Planning Area - Groundwater (Colorado River Basins)

The Upper Colorado River Planning Area is characterized by semi-arid to arid alluvial basins with few perennial streams.  Anderson, Freethey and Tucci (1992) divided the alluvial basins in south-central Arizona into categories based on similar hydrologic and geologic characteristics.  These categories are useful in describing general hydrologic characteristics.  Although their study area does not match the Department’s groundwater basins exactly, the Upper Colorado River Planning Area is included in their study area with the exception of the Peach Springs Basin.  Four basin categories identified by Anderson are represented in the planning area; West, Colorado River, Highland and Southeast.

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 Havasu Basin

The Lake Havasu Basin is a relatively small basin with its western boundary defined by the Colorado River. Extensive areas of the basin are covered by consolidated rock.  Basin fill, consisting of sand, silt and gravel, overlies the Bouse Formation (siltstone and fine-grained sandstone) and an underlying conglomerate unit.  These deposits decrease in thickness toward the basin margin. Most wells in the basin penetrate the upper 100-200 feet of the basin fill.  There is a direct hydraulic connection between the basin fill and the Colorado River, with groundwater occurrence and movement near the river controlled by the elevation of Lake Havasu. The lake elevation is relatively constant with a maximum fluctuation of approximately five feet during the period 1990-2008 (USBOR, 2009). 

Lake Havasu

London Bridge, Lake Havasu Basin.  The estimated volume of recoverable groundwater to a depth of 1,200 feet bls ranges from about 1.48 to 3.94 maf.  The median well yield in measured wells is generally 35 gpm or less.

Regional groundwater flow is north to south. Groundwater recharge is estimated at 35,000 AFA with an estimated 1.0 to 2.0 maf of groundwater in storage.  Water withdrawals from wells are primarily pursuant to Colorado River entitlements. Median well yields are relatively high at 1,500 gpm. Water level data for one public supply well showed a decline of 15 to 30 feet between 1990-91 and 2003-04.  Drinking water standard exceedences are primarily due to elevated concentrations of nitrate/nitrite and organics measured in the vicinity of Lake Havasu City.


Lake Mohave Basin

Colorado River, Lake Mohave Basin.  The principal water-bearing formations in this basin are alluvial sand, silt and gravel deposits adjacent to Lake Mohave and the Colorado River.

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.



For more information on groundwater in individual basins in the Upper Colorado River Planning Area see the menu to the right.


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