WATERSHED-BASED SCIENCE: INTEGRATING IMPERVIOUS COVER INTO ANALYSES FOR THE LAKE TAHOE BASIN, CA

Impervious cover is recognized as an environmental indicator for watersheds undergoing development but acquiring accurate impervious cover measurements is difficult and expensive. Nonetheless, it is a critical variable in the broader context of watershed processes and is often poorly represented. The Tahoe Regional Planning Agency (TRPA) in Lake Tahoe, California/Nevada, is responsible for drafting regulations on land development and land use as well as for evaluating the effects of consequential regulatory choices based on these land use models. For this reason, improved methods for calculating impervious surface cover estimates are needed for the Lake Tahoe Basin. Accurate estimation of impervious cover is relevant to all TRPA thresholds including recreation and scenic resources, air and water quality, wildlife and fish habitat, soils, noise, and vegetative cover. In particular, accurate estimates of impervious cover are required for predicting surface water runoff, for refining existing sediment loading models, and for improving data quality for the USGS Center for Science Policy's land market hedonic model. From a regulation perspective, TRPA needs an objective assessment of the extent of the impervious coverage in the Basin for their internal monitoring and permitting program. Academically, establishing a land use benchmark using a scientifically rigorous, objective, and repeatable technique will prove invaluable to future environmental research. All of these applications are integral to the protection of the Lake Tahoe Basin from continued degradation of its natural resources, and specifically the improvement of water quality and clarity of both the lake and its tributaries. We present the results from a pilot analysis to assess the use of satellite imagery to derive accurate estimates of impervious cover using a combination of image processing methods for a 25km² urban area. The methodology produced very accurate identification of both commercial and residential impervious cover in an area dominated by dense conifer canopy. Results from this analysis will be used to better understand the impacts of urban development on the ecology of the Lake Tahoe Basin. We discuss the importance and future integration of the impervious cover layer for better understanding the ecology of the Lake Tahoe Basin.