Site Update: Due to extremely low flows the outfall site at SR431 has been removed from monitoring, however we are still monitoring for BMP effectiveness at this location.
Dominant Land Use:
This catchment is located in a rural area with moderate highway traffic density.
Percentage of Impervious Surface:
Approximately 95% of the catchment area is impervious.
Nevada Department of Transportation (NDOT)
The SR431 monitoring site is located on State Route 431 in Washoe County above Incline Village, Nevada. Ninety-five percent of the catchment area is primary road. The outfall pipe discharges directly into a perennial stream called Deer Creek which connects to Third Creek and discharges into Lake Tahoe, giving this site the distinction of being directly connected to the Lake despite being 2.5 miles from it.
The purpose of this monitoring site is to evaluate and compare the effectiveness of two adjacent stormwater treatment vaults containing different filter media. A Contech Jellyfish and a Contech MFS were installed as part of an environmental improvement project in 2013. Four monitoring stations collect data at this site and are located on the inflow and outflow pipes of the Jellyfish and on the inflow and outflow pipes of the MFS. Stormwater flow to the system is split approximately evenly and treated in one of the two vaults before being discharged to a short, steep swale that enters Deer Creek. Comparing inflow and outflow results allows researchers to determine how well the two different vaults remove the fine sediment particles (FSP) that impair Lake Tahoe’s clarity. Additional improvements include slope stabilization and the installation of permeable pavers on the shoulders of the highway.
SR431 is the only site in our monitoring network that isolates the characterization of runoff from primary roads. This is important because primary roads have been identified as the largest single generator of FSP in the Lake Tahoe basin (Lake Tahoe TMDL Technical Report, 2010). Though the catchment is of a size smaller than recommended for modeling using the Pollutant Load Reduction Model (PLRM), the monitoring data collected here provides a unique opportunity to evaluate whether PLRM can reasonably estimate pollutant loads in a small catchment. Because the catchment is comprised of only a single land-use that is almost entirely impervious, PLRM has the potential to be acceptably effective at predicting pollutant loads in this catchment. In addition, this is the only site currently available where a true side-by-side comparison of stormwater treatment vaults can be performed, allowing for a real-world comparison of two treatment technologies.