BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

ADVANTAGES• Provides wave protection to backshorewetlands and SEZs.• Can augment restoration by increasing thelife cycle (longevity) of a beach nourishmentproject.• Can provide protection to backshoreproperties and development from severewave climates and the associated stormdamage.DISADVANTAGES• Increase in costs as water depth and waveclimate intensity increase.• May degrade scenic quality.• May inhibit navigation.Breakwaters can be very effective in dissipating the energy of approachingwaves. The commonly used backshore anchored breakwaters of Lake Tahoe dosignificantly affect the natural pattern of littoral drift and deposition; as aresult, their effectiveness must be balanced with the ongoing periodic costsassociated with their maintenance dredging requirements.8.7.3 DESIGN CONSIDERATIONS AND PLANNINGIn contrast to bulkheads, lake walls, and static revetments, breakwaters areinstalled in the waters of the foreshore and nearshore rather than directly inthe backshore. They dissipate the energy of approaching waves and form a lowhydraulic energy zone on their landward side. Any decrease in wave heightreduces the ability of waves to entrain and transport sediment. Sand moving offand along the shore will be deposited, accumulate, and be temporarily bankedbehind the structure. As a result, downdrift beaches are usually deprived oftheir normal sediment supply and may suffer increased erosion.Permanent breakwaters can be fixed to the substrate or floating; they can besolid or permeable. Floating breakwaters in Lake Tahoe are consideredtemporary structures designed to provide backshore construction operationsprotection during barge based activities. Floating breakwaters may beparticularly advantageous where offshore slopes are steep and water depthscaused fixed breakwaters to be undesirable and too expensive. Fixedbreakwaters are most economical when the slope is gentle and the high waterlevel at the proposed site is less than about 4 feet deep. 43Similar to jetties, breakwaters must be designed by licensed professional civilengineers who regularly design in-water structures of this type. The designmust demonstrate the following:• Design should not adversely affect erosion or deposition in the lee of thebreakwater or in the downdrift areas.• The breakwater must be structurally stable enough to resist wave action andthe scour hydraulics caused by incoming waves.43USACE, 1995, Engineer Manual EM 1110-2-1810, Engineering and Design: Coastal Geology andUSACE, 2008, Coastal Engineering Manual - Parts I-6CHAPTER 8: Shorezone Protective Structures and BMPsTRPA BMP Handbook8.7 Breakwaters 2012Page 8-52