Thesis

Aeolian sand transport and deposition along the northeast margin of Owens Lake, California

The behavior of dune fields along lake margins, as along open coasts, depends on the availability of sand and of winds of sufficient velocity to entrain, transport, and deposit sediment. This study addresses the question of aeolian sand transport and deposition along the northeast margin of Owens Lake following the forced increase of water flows to the formerly dry lake basin starting in 2005. The reintroduction of water was an attempt to minimize the entrainment and transport of dust particles from the dry-lake surface, by modifying the surface wind environment both on and marginal to the lake. Prior studies had suggested that a shallow water cover would reduce surface roughness and increase local surface wind velocities while at the same time reducing the availability of sediment for aeolian transport. This study reveals that, in contrast, average wind velocities have decreased since 2000 while sand transport and deposition within the dune field have increased. Using eighty two sand traps and weekly topographic surveys of the Keeler dunes located along the lake's northeast margin, this study shows that sand transport and deposition within the dune field have occurred at a rapid rate over a short period of time (July 1 - August 2, 2009). Significant sand transport occurred in response to a shift in dominant wind direction, initially from the south-southwest during the first two weeks of the study, then to strong winds from the northwest during the third week of the study. During this latter period, nearly 70% of the sand traps collected up to 600 cm3 of sediment. Sieve analysis of the sediment reveals the dominance of fine-medium sand, with a silt component of up to 2.5%-a relatively low percentage compared with other dune systems in arid regions. In the broader context, the dune field appears to be migrating southeastwards with the segregation of the field into a northern component-characterized by long, transverse ridges and a southern component characterized by smaller independent dunes. However, the relationship between broader synoptic wind patterns and continued sand transport remains unclear. Wind data demonstrate rapid shifts in direction and velocity superimposed on the broader pattern of bi-directional and seasonal winds in the region. These factors are reflected in the nature and distribution of dunes within the Keeler dune field.

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