BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

Adaptation and retreat requires the institutional elevation of structures, designrequisites for storm proofing and the imposition of zoning or developmentrestrictions through programmatic planning. Retreat is the permanentevacuation or abandonment of shorezone infrastructure; for specific settingssubject to chronically high erosion rates and storm damage, this is a plausiblealternative. Total costs and constraints of this alternative must include theenvironmental impact on the new site. In contrast to the implementation ofhard engineering solutions, many shorezone planning professionals advocateretreat as the most appropriate long-term answer.The combination of traditional engineering approaches with newer,nontraditional technologies should be pursued and implemented in manylocations. For example, proper existing conditions analysis should identify anappropriately elevated landscape position for siting and building structures. Acombination of this preplanning effort with minimal shoreline armoring andforeshore beach nourishment could be proposed to achieve a morecomprehensive, multi-pronged shorezone protection strategy for a littoralproperty.The “do nothing or no project” alternative is the option that allows forcontinued erosion and repeated storm damage until environmental equilibriumis reached (with the expected annual costs accrued for electing this choice).However, the “do nothing or no project” alternative also potentially providesthe basis or control for measuring the effectiveness of the other proposed activealternatives cited previously in this section. 118.1.5 PROTECTIVE STRUCTURES: ADVANTAGES AND DISADVANTAGESThis chapter will discuss, in detail, each of the protective structures that serveas shorezone protective BMPs. Consider the following general advantages anddisadvantages for protective structures (Table 8-2) before developing andimplementing specific designs.Table 8-2: General Advantages and Disadvantages of Protective StructuresADVANTAGES• Reduce erosion in the backshore andincrease the stability of unstable backshoreareas.• Protect backshore and foreshoredevelopment from adverse impacts bysevere littoral processes (e.g.,hydrodynamics, erosion, and sedimentation)• Reduce the severity of both catastrophicand gradual shoreline retreat.• Provide reasonable assurance of compliancewith federal, state, and regional waterquality discharge standards.DISADVANTAGES• May modify natural shorezone processes,especially littoral drift and beachsedimentation.• May decrease ecological and geomorphicfunction of SEZs and areas mapped as aBeach (Be) miscellaneous map unit (a nonsoilNRCS map unit) within the shorezonethrough direct or indirect alterations.• Can accelerate erosion in foreshore ordowndrift areas (static protective structures).• May require replenishment of the frontingbeach to maintain dynamic equilibrium and11USACE, 1989, EM 1110-2 -5025, Environmental Engineering for Coastal Shore ProtectionCHAPTER 8: Shorezone Protective Structures and BMPsTRPA BMP HandbookPage 8-6 2012