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, 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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