BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

Table 8-12: Overview of the Advantages and Disadvantages in using Beach Nourishment and Replenishmentas a BMPADVANTAGES• Protects an eroding foreshore and providesincreased protection to the backshore.• Can be used to restore an eroded beach toits prior dimensions.• Can provide a potential sediment sink forclean dredged material.• Designed to maintain or restore thedynamic equilibrium of a beach.• Often preferred to structural barriers thatcreate artificial boundary conditions andgenerate unwanted consequences.• Potentially provides a new supply ofmaterial to littoral transport system anddowndrift beaches.• Potentially assists in maintaining fish habitator spawning gravel sites.• Helps re-supply the natural geomorphicprotection against storms by absorbing anddissipating the energy of breaking waves.• Can provide additional recreational space byextending the beach area.DISADVANTAGES• Increased sediment loads could depositaround marina inlets or stream mouthsdowndrift of beach nourishment projects.• May increase turbidity if the materials are notwashed free of silts, clays, hydrocarbons, andnoxious invasive seeds, prior to placement inthe shorezone.• May increase environmental degradation ifnot completely free of hydrocarbons, othertoxics, and invasive non-native species.• May require frequent re-application(replenishment maintenance) if erosion ratesare higher than predicted.• May cause perturbation to the local vicinityor larger lake shore system if not properlydesigned and planned through programmaticcoordination.8.5.3 DESIGN CONSIDERATIONS AND PLANNINGThe beach nourishment project functions as an intentionally eroding buffer zone, modeled and designedto provide sufficient material to stabilize the dynamic adjustments of the beach. A nourishment projectusually involves widening the beach (i.e., translating it lake ward) to create a wider buffer for dissipatingstorm wave energy. The amount of additional width is determined based on the desired level of stormprotection, the persistent long-term erosional trends that characterize the project area, and the target renourishmentinterval (maintenance lifecycle).Answer the following design questions regarding project setting at the beginning of the design process:• In what type of littoral system, or littoral cell, will the project be constructed?• What is the extent of the littoral cell, and where within the cell is the project located?• What are the important nearshore processes that characterize the littoral cell and the project site?• How threatened are commercial and private structures and infrastructure such as roads and utilities bystorm waves and water level fluctuation?• Are there structures that protrude beyond the predominant shoreline position? If so, it may be difficultand not cost-effective to provide a lasting beach by maintaining the design width in front of thosestructures. Attempting to do so may result in persistent areas of erosion that could subject the projectto frequent maintenance, loss of protective function, and potentially poor public perception.The design berm width is determined through an iterative process that evaluates economic benefits as afunction of width. Because the beach nourishment berm will be subject to erosion, it has an inherent riskCHAPTER 8: Shorezone Protective Structures and BMPsTRPA BMP Handbook8.5 Beach Nourishment and Replenishment 2012Page 8-42