On the Geodetic Signature from Lake Mead Water Levels Fluctuations (1940-2016)

Debi Kilb, Adrian A. Borsa, & Duncan C. Agnew

Published August 13, 2017, SCEC Contribution #7544, 2017 SCEC Annual Meeting Poster #094

Large load changes due to fluctuations in surface water repositories (i.e., reservoirs and lakes) can result in a solid earth response that is observable in GPS surface displacements. The spatial distribution of the resulting earth response to these types of loads is proportional to the extent and magnitude of the water load. Here, we study the geodetic signature of fluctuations in water levels at Lake Mead, located southeast of Las Vegas on the border of Nevada and Arizona. Lake Mead can store up to 32 km3 of water at full capacity, making it the largest reservoir in the US. After the 1963 completion of the Glen Canyon Dam on the upriver side of the Grand Canyon, annual fluctuations in Lake Mead water levels stabilized (from annual 10s of meters peak-to-trough to a median of 4.13 m) while lake levels slowly increased. However, since 1998 long term drought and increased water demand has ensued a decline in lake levels, resulting in levels as low as those reported in 1937 when Lake Mead was initially being filled. We examine ~75 years (1940-2016) of lake level data recorded by the US Bureau of Reclamation (USBR), mapping the expected surface displacements across the southwestern US for seasonal and drought-induced lake level changes. We calculate elastic earth displacements resulting from lake level fluctuations at the location of 5 PBO GPS stations within ~150 km of Lake Mead (P006, P611,P621, P622 and P626) and compare these results to GPS-measured values. This study will serve as a pilot project for using the earth response to changing water loads to probe the rheology of the crust and upper mantle in the Lake Mead region.

Key Words
Lake Mead, Reservoirs, GPS, Geodetic, lake load, drought

Citation
Kilb, D., Borsa, A. A., & Agnew, D. C. (2017, 08). On the Geodetic Signature from Lake Mead Water Levels Fluctuations (1940-2016). Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy