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BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

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Table 8-5: The General Geomorphic Characteristics of the Shorezone ToleranceDistrictsDISTRICTHAZARDCLASS1 H2 HCHARACTERISTICSYoung and old barrier beach and lakeshore dune deposits, composedof Beach (Be) sedimentsVolcanic and morainic shorezones with slopes over 30% and alluvialshorezones of 9-30% slope3 H Armored granite shorezones with slopes exceeding 30%4 MVolcanic and morainic shorezones with 15-30% slopes and alluvialshorezones with slopes of 0-9%5 M Armored granite shorezones with slopes of 15-30%6 M Shorezones of volcanic rock and morainic debris with 5-15% slopes7 L Shorezones of morainic and alluvial materials of 0-9% slope8 L Gently sloping (0-9%) armored granite shorezonesTolerance District 1 has been designated as the most sensitive in the Lake<strong>Tahoe</strong> Region; it includes barrier beaches and adjacent lakeshore dunes 17 .Barrier beach shorezones typically have a low sandy strand separating theforeshore from SEZs and wetlands on the inland side. Younger barrier beachsystems commonly have a shallow lagoon or inundated wetland behind them.The areas behind older barrier beach berms are usually filled with anaccumulation of sediment and are not generally as wet as those behind youngersystems. Regardless of age, the barrier beaches do experience periodic breachesas a result of strong wave action, especially if interference with littoral drift anddeposition disrupts the natural supply of sediment from updrift and offshoresources.Lake <strong>Tahoe</strong> dune lands have been traditionally included in Tolerance District 1protection standards. The montane dune lands that are associated with theLake <strong>Tahoe</strong> shorezone are highly erodible and as sensitive to disturbance asbarrier beaches. The aeolian (wind) deposits that comprise dune sedimentsmostly originate from the foreshore and nearshore. Littoral sediments areexposed, entrained, transported, and deposited by wind energy when lakewater surface elevations are low. Dune deposits generally lack cohesion and arequite susceptible to re-entrainment and transport by wind.Many dunes in Lake <strong>Tahoe</strong> are naturally mobile or geomorphically new andlack established vegetation. Surface stormwater and precipitation can rapidly17Orme, A.R., Department of Geography, UCLA, 1972, Toward a Shorezone Plan for Lake <strong>Tahoe</strong>p.52TRPA <strong>BMP</strong> HandbookCHAPTER 8: Shorezone Protective Structures and <strong>BMP</strong>s2012 Page 8-13

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