Vegetation, hydrology, and sand movement interactions on the Slate Canyon alluvial fan-Keeler Dunes Complex, Owens Valley, California

Abstract

Relationships among hydrology, sand movement, and vegetation community dynamics within the Slate Canyon alluvial fan and Keeler Dunes Complex, Owens (dry) Lake, California, were characterized. Construction of flood control berms (1954, 1967) cut off surface overflow events on the alluvial fan, resulting in subsequent very low plant cover and significant sand movement. Hydrologic modeling and analysis of plant cover and sand movement from aerial photos were combined to document and explain changes in plant cover in the study area for upland vegetation and groundwater-dependent vegetation. Where hydrologic factors dominated, upland vegetation was observed to have much lower cover (median 6%) than groundwater-dependent vegetation (median 41%) and much higher variability throughout the 1944 to 2012 study period. For upland vegetation, simulated potential plant cover was 9.2% and this declined to 4.4% when channel flow inputs were eliminated due to berm construction. Areas with minimal sand movement over the study period expressed actual plant cover similar to simulated levels. Areas with significant sand movement, however, had much lower plant cover than simulated potential values and areas with flood flow inputs had much higher cover. The decline in plant cover from 9.2 to 4.4% resulted in an estimated 4.4-fold greater sand movement (normalized sand flux increased from 14% to 62% relative to 100% for bare soil). The sensitivity of surface stability at low vegetation cover and the potential for hydrologic changes to reduce vegetation cover in this range illustrates how hydrology and sand movement interactions can destabilize sensitive sand dunes.