Effectiveness of an Array of Porous Sand Fences to Reduce Sand Flux: Oceano Dunes, Oceano CA

John Gillies 1, Vicken Etyemezian2, George Nikolich2, Ronnie Glick3, Peter Rowland4, Tim Pesce4, Mark Skinner4
1Desert Research Institute, Reno, Nevada, USA, 2Desert Research Institute, Las Vegas, Nevada, USA, 3California State Parks, Pismo Beach, California, USA, 4Coastal San Luis Resource Conservation District, Morro Bay, California, USA

Fences of various construction materials and design have been used for some time to control the location and rate of erosion and deposition of sand and snow. By extension, the control of saltation of sand-sized particles will also affect the dust emission process that is driven by the ballistic impact of these grains as they move across sediments containing silt and clay-sized particles. The Oceano Dunes, part of a quaternary age coastal dune complex in California contains the Oceano Dunes State Vehicular Recreation Area (ODSVRA) California State Park, consisting of 508 hectares of dune environment where off-road recreational vehicle activity is allowed as well as 282 hectares of dune preserve where access is only allowed by pedestrians. Under conditions of elevated wind speed, typically >6 m s-1 with a dominant westerly component measured 10 m above ground level, the threshold for sand transport is exceeded and once this occurs it is accompanied by dust emissions. For periods of wind erosion within the dune system that last for greater than 6 hours, air quality measurement sites that are downwind of the eastern boundary of the park and that are operated by the San Luis Obispo County Air Pollution Control District (SLOCAPCD) have measured 24-hour mean PM10 concentrations (mass concentration of particulate matter less than or equal to 10 m aerodynamic diameter) that exceed both US EPA (150 g m-3) and California State air quality regulations (50 g m-3).

As part of an on-going effort to reduce dust emission impacts from the Oceano Dunes, control measures are being evaluated. In 2014, 20 parallel rows of sand fences 1.2 m high and ~300 m long separated by a distance of 10 fence heights (~12 m) encompassing ~12 hectares were established and left in place for 3 months. In 2015, 35 parallel rows of the same type of fence, with a separation distance of 7 fence heights (~8.5 m) were emplaced in a different area of the ODSVRA encompassing ~15 hectares and left in place for 4 months. We report here on the effectiveness of these arrays of sand fences to modulate sand flux over the area they covered. The expectation is that controlling sand flux will also reduce the emission of PM10 dust that contributes to the observed levels that breach the standards.