Water Quality Relative To Groundcover Treatments Under Simulated Rainfall

摘要

Vegetation decreases soil detachment and transport from project sites. Past research has shown rolled erosion control products in conjunction with native vegetation placed in strips at the toe slope effectively reduce total sediment loss. However, in urban settings the common vegetation is ground cover. How effective is the ground cover as a BMP to improve water quality in the urban setting? This research study utilized a rainfall simulator to compare ground cover effectiveness at reducing sediment loss and improving overall water quality. The design was to compare whether ground cover cultivars grown in a toe strip with an jute netting on the upper slopes was as effective at reducing sediment production as a total vegetation cover of 70% or greater on the entire slope. The project was conducted at the Erosion Research Facility at California Polytechnic State University (Cal Poly), San Luis Obispo in conjunction with the Offices of Landscape Architecture and Stormwater of the California Department of Transportation (Caltrans), and the Office of Water Programs (OWP) at Sacramento State University. A sandy clay loam subsoil was collected from a California highway construction site. Test boxes were then filled with soil to 90% compaction and positioned at a 2H:1V slope. The control boxes were left bare while remaining half of the test boxes received applications of the four ground cover cultivars covering 20% of the slope on the toe with jute netting above and the other half of the test boxes were totally covered with a minimum of 70% ground cover. Storm water runoff was monitored for total water runoff, total sediment, sediment concentration, NTUs, pH, electrical conductivity, nutrients, and selected metals over a series of simulated storm events. In terms of water quality, all combinations of toe strips with jute on the upper slopes and total ground cover in the test boxes performed better than the control. Different ground cover cultivars varied in ability to decrease soil detachment and decrease sediment loads. Total runoff was highest with bare soil and lowest with total ground cover. The lowest NTUs were with total ground cover. Total ground cover did have the highest concentration of sediment, but with low runoff means low total sediment. Results indicate water quality significantly improves with use of ground cover cultivars. The use of total ground cover appears to be the overall best treatment followed closely by just jute and vegetation toe strip.