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This dataset encompasses portions of California and Nevada surrounding Lake Tahoe. TRPA derived a new GIS data layer that outlines the nearshore littoral drift splash zone around Lake Tahoe. The purpose of this task is to inform the Littoral Sediment Loading standard that is a part of the Water Quality Threshold Evaluation. The adopted TRPA Threshold Standard aims to decrease sediment load as required to attain turbidity values not to exceed three Nephlometric Turbidity Units (NTU) and not exceed one NTU in shallow waters of Lake Tahoe not directly influenced by stream discharges. The littoral drift splash zone GIS layer was outlined based on the interpretation of 2012-2013 ortho-rectified aerial photographs (NAIP, USDA) and in comparison to other informative GIS datasets that were available. Basically, areas were delineated along the shoreline where sand was visible in the nearshore and then these areas were enclosed based on the presence of steep slopes. Aerial imagery issues related to glare and shade necessitated the incorporation of several aerial photograph sources such as the 2012-2013 NAIP USDA Aerials and other TRPA imagery resources. The nearshore bathymetry data from USGS proved useful for detecting steeply sloping bathymetry (http://tahoe.usgs.gov/bath.html). |