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BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

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8.7 BREAKWATERS8.7.1 OVERVIEWBreakwaters are wave energy barriers aligned parallel or oblique to theshoreline. They are designed to protect the land and foreshore waters behindthem by dissipating the energy of approaching waves. They also serve toshelter boat moorings, marinas, and designated contact recreational areas.Breakwaters have been used mainly for mooring and navigational protection;this is in part because of the higher cost of these offshore structures ascompared to onshore structures (e.g., bulkheads and lake walls).Nearshore breakwaters are usually designed to be detached and positionedparallel to shore. However, in Lake <strong>Tahoe</strong>, breakwaters are more commonlyanchored in the backshore. Breakwaters are designed to attenuate the amountof wave energy reaching a foreshore and backshore area by interrupting thewater’s physical oscillation. They are similar in their hydraulic effect to naturalbars or reefs in that they dissipate wave energy as it approaches. This reductionin wave energy slows the littoral drift, produces sediment deposition and oftenresults in a salient deposition zone or feature in the sheltered area behind thestructure. Some offshore and longshore sediment transport may continuebehind a detached nearshore breakwater. On the other hand, the anchoredbackshore breakwater is positioned as a deflector and behaves more like a groinin that it often captures sediment behind it in the foreshore.Breakwaters are commonly applicable to marinas or commercial pier areaswhere calm waters are desired to aid in safe navigation and mooring. They canalso be constructed to protect a beach to provide for a safe recreationalswimming area.Overall, breakwaters are a permanent <strong>BMP</strong> that provide hydrologic control forstormwater.8.7.2 BREAKWATERS: ADVANTAGES AND DISADVANTAGESTable 8-15 lists some of the common advantages and disadvantages encounteredwhen installing breakwaters as a shorezone protection <strong>BMP</strong>.Table 8-15: Advantages and Disadvantages of Breakwaters as a <strong>BMP</strong>ADVANTAGES• Help dissipate wave energy and reduceerosion of the foreshore.• Can encourage the deposition of a widerbeach for accommodating contactrecreation like swimming• Provides calm waters desirable for boatmooring or marina activities.DISADVANTAGES• May disrupt the natural pattern of offshoreand longshore littoral drift, potentiallydepriving downdrift beaches of their normalsediment supply.• May reduce the ability of waves to transportsediment• May accumulate sediment behind thestructure.TRPA <strong>BMP</strong> HandbookCHAPTER 8: Shorezone Protective Structures and <strong>BMP</strong>s2012 8.7 BreakwatersPage 8-51

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