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BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

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A detailed natural and humanhistory of the Basin is providedin the Lake <strong>Tahoe</strong> WatershedAssessment.Source: USDA (United StatesDepartment of Agriculture).2000. Lake <strong>Tahoe</strong> WatershedAssessment. Volume 1. PacificSouthwest Research Station,USDA Forest Service.IMPERVIOUS COVER AFFECTS ON HYDROLOGYWhile the Lake <strong>Tahoe</strong> Region has experienced human use for thousands ofyears, the period of rapid urban development following the winter Olympics atSquaw Valley in 1960 prompted the today’s water quality protectionregulations <strong>BMP</strong>s.Impervious land coverage is a fundamental characteristic of urban andsuburban landscapes. Rooftops, roadways, parking areas, and other impervioussurfaces cover the soil that, before development, allowed rainwater andsnowmelt to infiltrate. Infiltration is the process by which surface water entersthe soil and is influenced by many factors including soil structure, porosity,texture, moisture content, and vegetation among other attributes. Impervioussurfaces such as asphalt, concrete, and compacted soils, prevent or reduceinfiltration of water into the soil.In a naturally functioning watershed, rain and snowmelt slowly infiltrates closeto where it drops, or is captured through evapotranspiration. In contrast,impervious surfaces cause rainfall to run off quickly, taking with it pollutantsthat have collected over time on the surface. While roads and rooftops are themost prevalent types of impervious surface, other types include sidewalks,patios, bedrock outcrops, and compacted soil. As development increases andalters a natural landscape, the percentage of the land covered by impervioussurfaces also increases.IntroductionTRPA <strong>BMP</strong> HandbookPage 8 2012

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