BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

generate observable changes in the shorezone. The shorezone is the settingwhere littoral sediment is entrained, transported, and deposited to the deeperportions of the lake. The lake’s physiography determines the fetch for windgeneratedwaves that dominate shaping much of the shorezone environment.Any interruption to the system, for instance by dredging or construction, mayresult in adjustments throughout the system; therefore, exercise diligence inidentifying unstable backshore areas and designing the proper shorezoneprotection that takes into account the dynamics associated with theshorezone’s energetic setting. In Lake Tahoe, the potential sources of sand andsediment include rivers, bluffs, dunes, and the inner nearshore shelves alongwith urban runoff. The potential sinks include bays, dunes, deeper offshoreareas, and dredging sites. Currently there is one detailed sediment budget forthe Lake Tahoe shorezone that was developed as part of source area analysisfor the Total Maximum Daily Load (TMDL). There is also current researchbeing conducted to examine and map the littoral cells and limited longshoredepositional patterns associated with Lake Tahoe.8.1.8.1 SHOREZONE TOLERANCE DISTRICTSAnalysis of the physical composition, incipient geometry, and dominantgeomorphic processes of Lake Tahoe’s shorezone has resulted in thedevelopment of a classification scheme that distinguishes eight separateShorezone Tolerance Districts, refer to Figure 8-b. 16 These ShorezoneTolerance Districts have been categorized using a scale, with an increasingresilience or decreasing sensitivity to development or disturbance as ratingsmove from 1 to 8 (Refer to Table 8-5). Shorezone Tolerance Districts aregeomorphic settings that vary in stability and sensitivity to physicalperturbation. Major factors influencing the shorezone geomorphic districts aregeological structure, regional tectonics, and quaternary (within the last 2million years) geomorphic processes such as, glaciation, hill-slope failure,patterns of nearshore sediment erosion, and deposition. Each of these factorsalone or in combination can affect shorezone stability. Multiple facets withineach of these elements combine to form complex and interrelated feedbackmechanisms that strongly determine the inherent sensitivity or stability foreach shorezone district. Figure 8-b presents the Shorezone Tolerance Districtsmapped around Lake Tahoe.16Orme, A.R., Department of Geography, UCLA,1972, Toward a Shorezone Plan for Lake Tahoe,p.52TRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 Page 8-11