BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

Table 8-9: Advantages and Disadvantages of using Concrete Block RevetmentsADVANTAGES• Provide open areas of 20 to 25 % toaccommodate vegetation.• Are cost effective.• Are known to be flexible, durable, and canconform to minor settlement.• Easy maintenance once established• Structural voids and hardened substrateprovide some cover and escape habitat forlocal biota.• Less tonnage required when compared toriprap. The thickness required is one-third toone-fifth that of riprap.DISADVANTAGES• Require cable-tied and geotextile bondedsystems, which are usually proprietary.• Can be expensive to apply in difficultsettings.• Susceptible to vandalism (non-cabledapplication).• Design and installation guidance is marginalfor some man-made concrete block systems.• May present an aesthetically unnaturalappearance unless vegetation is planted tobaffle visual impact.Table 8-10: Advantages and Disadvantages of using Riprap RevetmentsADVANTAGES• Self-adjusting to minor amounts of substrateconsolidation or movement.• May experience minor damage and continueto function adequately without furtherdamage.• The rough surface of riprap dissipates locallittoral cell currents and minimizes waverun-up more than a smooth revetment.• Material is readily available in manylocations and can be less expensive thanother structural alternatives.• Aquatic organisms can use the riprap asmarginally suitable habitat.• Can be repaired easily by placing additionalstone when needed.DISADVANTAGES• If material is not local, available, and easy totransport to the site, costs can becomeprohibitive.• May present a favorable habitat environmentfor certain aquatic invasive species.• May not be aesthetically acceptable withoutscenic mitigation.• May pose a hazard to people who mustaccess the revetment.• Can cover up a significant swath of beach.If properly designed and installed, static revetments prevent backshore erosion.However, static structures can contribute to the erosion of the downdriftshoreline by eliminating a source of sediment. Sloping rock revetments aremore cost effective than vertical barrier walls. Some researchers suggest thatstructures, which incorporate dynamic components into their design, arepreferred over most other methods where shorelines are eroding and thelittoral cells are lacking in an adequate sediment supply in order to maintain adynamic equilibrium.Take caution when designing a particular revetment type because not all areascan be effectively protected by a static revetment. The chosen revetment designmay not prevent erosion from unanticipated heavy wave action or othergeologic hazards.There are various reasons, or conditions, that may lead a concrete blockrevetment to fail. Toe scour can undermine manufactured concrete blockTRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 8.3 Static RevetmentsPage 8-31