BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

inputs to the lake, plus nine groups of intervening zones, which are drainageareas between the mouths of streams that drain directly to the lake.The Watershed Model is more fully described in Lake Tahoe Total MaximumDaily Load Technical Report and Watershed Hydrologic Modeling and Sedimentand Nutrient Loading Estimation for the Lake Tahoe Total Maximum DailyLoad 11 .In addition to the Watershed Model, the TMDL program developed thePollutant Load Reduction Model (PLRM) through assistance from the U.S.Army Corps of Engineers (USACE). The PLRM is intended for application ata smaller scale than the Watershed Model and was specifically developed foranalysis of pollutant load reductions associated with typical Lake Tahoe Regionpublic water quality improvement projects 12 . A summary sheet with a link toPLRM executable files and model documentation is included in Section 1.3.3.6.1.4.2 SOILS, LAND USE, AND HYDROMETEOROLOGYThe Natural Resources Conservation Service (NRCS) completed acomprehensive soil survey for the Lake Tahoe Region in 2006 13 , which can bedownloaded from the NRCS for Soil Survey Symbol = CA693 at(http://soildatamart. nrcs.usda.gov/Survey.aspx?State=CA). The Web SoilSurvey is available at: (http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm).The TMDL program developed a GIS land use layer for the Lake TahoeRegion. This information is available as a downloadable zip file at:(http://www.swrcb.ca.gov/rwqcb6/water_issues/programs/tmdl/lake_tahoe/index.shtml)Hydrometeorology data for the Lake Tahoe Region was analyzed by theUSACE as part of development of guidance for the SWQIC and by hydrologicconsultants for development of the Watershed Model and PLRM for theTMDL program. The Watershed Model and PLRM models use similar longterm data sets developed from eight SnoTel gages around the Lake TahoeRegion. The SnoTel records were quality assured as part of modeldevelopment. These gages provide the best available short-interval (1-hour)meteorologic records for the Lake Tahoe Region, but are generally located athigher elevations and outside of urbanized areas. Both the Watershed Modeland PLRM use adjustments to this data set to develop synthetic meteorologicrecords for use in simulations. The data sets and extrapolations used in PLRMare described in model documentation at: http://www.tiims.org/TIIMS-Sub-Sites/PLRM/docs-down loads.aspx.11LRWQCB prepared by Tetra Tech, 2007. Watershed Hydrologic Modeling and Sediment andNutrient Loading Estimation for the Lake Tahoe Total Maximum Daily Load12USACE, Sacramento District prepared by Northwest Hydraulic Consultants, Geosyntec, and2NDNATURE, 2009, Pollutant Load Reduction Model (PLRM) Model Development Document13NRCS – U.S. Department of Agriculture, 2006, Soil Survey for the Lake Tahoe Basin, CA and NVCHAPTER 1: Urban HydrologyTRPA BMP HandbookPage 1-30 2012