Large Scale Modification of the Salton Sea Shoreline to Reduce the Potential for Dust Emissions

The Salton Sea in California’s Imperial and Riverside counties is a large endorheic lake with significant areas of exposed shoreline.  The exposed shoreline and surrounding desert are potential sources of wind-blown dust that can contribute to degraded air quality as the emissions create high concentrations of particulate matter ≤10 µm in aerodynamic diameter (i.e., PM10), which is a federally regulated pollutant in the USA.  The Salton Sea’s water surface height is lowering at an accelerating rate.  The decreasing volume of water leads to increased shoreline exposure with the potential for high wind speed events to cause dust emissions. This increases the potential for degradation of air quality with respect to PM10 mass concentrations within the basin potentially elevating the health risk to the surrounding population.  The State of California has implemented the Salton Sea Management Plan that has several phases of development to protect air quality and ecosystem values at the Salton Sea.  California Department of Water Resources (DWR) began a series of projects at the Salton Sea designed to limit dust emissions from shoreline areas deemed vulnerable to wind erosion and dust emissions based on evaluation of soil textural properties and in situ measurements of PM10 emissivity.  To protect sandy surfaces vulnerable to wind erosion, surface roughening based on the super-positioning of non-erodible roughness elements onto the exposed sediments of the shoreline has been implemented.  The non-erodible elements are bales of straw sourced from agricultural producers in the vicinity.  They are rectangular prisms of dimensions 0.41 m high, 1.12 m long, and 0.55 m wide. 

To evaluate the effectiveness of the roughness arrays, designed initially to offer 95% reduction in sand transport and dust emissions compared to the unprotected surface, computational fluid dynamics modeling was carried out to quantify the reduction in surface shear stress and dust emission potential due to the presence of the roughness.  In addition, in situ measurements of sand flux and PM10 concentrations were collected to corroborate the simulation results.  Air flow across the roughness array for three freestream wind speeds and three wind direction angles was simulated using CFD in OpenFOAM.  The mean shear stress reduction compared to the surface without roughness for the three freestream wind speeds and wind directions was 62% (±1%), 66% (±0.2%), and 79% (±1%), for 225°, 270°, and 315° wind directions, respectively.  The greatest probability for high wind speed events is expected from the wind direction range 225° to 315°. The mean reduction in total PM10 emission for these three conditions were: 73% (±4%), 85% (±2%), and 80% (±2%).  In situ measurements suggest control effectiveness is even greater as saltation has not been recorded within the roughness for the range of observed wind speed, and there is no indication that PM10 has been emitted from the protected surfaces.  This suggests that large size superposed roughness has effectively modified the dust emission potential of these susceptible surfaces and provides the protection needed to ensure that the exposed shoreline does not contribute to the regional PM10 burden.