After the completion of Hoover Dam in 1935, sediment began accumulating in the new reservoir as the flow of the Colorado River was captured by the rising waters of Lake Mead. Initial estimates were that the new reservoir would last a little over 200 years as it filled with fine silt and sand from the high sediment load carried by the Colorado River. However, revised estimates in 1948 based on new data increased the life expectancy of the reservoir to more than four centuries.
With the completion of Glen Canyon Dam in 1963 upstream of Hoover Dam, sediment volume entering Lake Mead from the Colorado River was reduced to only about a tenth of its previous volume. Much of the sediment is now trapped within Lake Powell behind Glen Canyon Dam. With the reduced sediment input into Lake Mead, the lifetime of the reservoir has been extended to potentially more than a thousand years.
Post-impoundment sediment in Lake Mead is generally distributed along the floors of the deepest parts of the lake, mainly following the paths of the former Colorado River and the tributary valleys that fed into it, rather than being deposited as a drape across the entire lake floor. These sediments are thickest in the deltas that formed at the mouths of the Colorado River and its tributaries, including the Virgin and Muddy Rivers. Maximum sediment thickness exceeds 250 ft where the Colorado River enters Lake Mead, thinning to 50 - 100 feet in thickness along the remainder of the drowned Colorado River channel to Hoover Dam.
Tributary valleys have a thinner sediment cover indicating the Colorado River has been the primary sediment source. Sediments are composed of between 12 and 45 percent sand with the remainder being a mix of clay and silt. Most of the clay and silt has been transported to the deepest parts of the lake by the dense, sediment-laden currents flowing into Lake Mead from the Colorado River. Over time, sediment in the deeper parts of the lake has been compacted as additional sediment has accumulated.
*Increase in reservoir capacity and decrease in sediment volume due to significant compaction of sediments in lower elevation portions of the reservoir.
**Decreased rate of sedimentation due to closure of Glen Canyon Dam in 1963.
References & Resources
2001 Lake Mead Sedimentation Survey Bureau of Reclamation, February 2008
Comprehensive Survey of Sedimentation in Lake Mead, 1948-49 Geological Survey Professional Paper 295 https://pubs.usgs.gov/pp/0295/report.pdf
Mapping the Floor of Lake Mead (Nevada and Arizona): Preliminary Discussion and GIS Data Release U.S. Geological Survey Open File Report 03-320, 2003 https://pubs.usgs.gov/of/2003/of03-320/
Mapping Lake Mead Geophysical Review, Vol. 31, No. 3, pp. 385-405, July 1941
Surficial Geology of the Floor of Lake Mead (Arizona and Nevada) as Defined by Sidescan-sonar Imagery, Lake Floor Topography and Post-impoundment Sediment Thickness U.S. Geological Survey Open File Report 2009-1150 https://pubs.usgs.gov/of/2009/1150/
The 1963-64 Lake Mead Survey Bureau of Reclamation REC-OCE-70-21 http://www.usbr.gov/pmts/sediment/projects/ReservoirSurveys/Reports/The 1963-64 Lake Mead Survey.pdf
*Note: Calculations and mapping are based on a lake elevation of 1100’.
Surveys were conducted between 1999 and 2001 by the U.S. Geolgocial Survey in collaboration with the Bureau of Reclamation, University of Nevada Las Vegas, and the National Park Service.
Last updated: October 4, 2019