BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

8.4 DYNAMIC REVETMENTS8.4.1 OVERVIEWThe purpose of a dynamic revetment is to prevent backshore erosion, attenuatewave energy, and lessen wave scour at the base of bulkheads and lake walls.This intermediate type of structural design represents a soft, or geomorphicallyoriented, engineering alternative while also striving to achieve a more naturalaesthetic appearance.Less technical guidance is available for engineering dynamic revetments thanfor conventional riprap revetments. This soft engineering approach involvesthe construction of a gravel, cobble, or stone berm between the upper limits ofthe foreshore and backshore, in front of the property to be protected. Theconstructed cobble berm represents a transitional geomorphic engineeringstrategy between a conventional static riprap revetment made of large bouldersand a sandy beach nourishment project. As implied by the name, dynamicrevetments design incorporates wave shear stress and mass entrainmentcalculations to estimate the size of the material used. This structure is expectedto actively deform when encountering the larger waves (90 th percentile)without become structurally compromised. This contrasts with a conventionalstatic riprap revetment, where the boulders are calculated and sized so that theydo not move under the shear forces associated with the maximum design stormwave. 30Overall, dynamic revetments are a permanent BMP that apply both sourcecontrol and hydrologic control and are located on lakefronts.8.4.2 DYNAMIC REVETMENTS: ADVANTAGES AND DISADVANTAGESAs with static revetments, there exist advantages and disadvantages wheninstalling a dynamic revetment (Refer to Table 8-11). Conditions that arisefrom the disadvantages can lead to structural failure. One common reason forfailure of a dynamic revetment is that the material is sized too small to remaindynamically stable under the wave climate conditions.Further, the revetment is likely to fail if an insufficient volume of stone isplaced on the bank face. Another potential failure mode can occur if the stonesor cobbles are not constrained from moving laterally along the shoreline.30Ahrens, J.P., John Wiley and Sons, Ltd, 1995, Design Considerations for Dynamic Revetments inRiver, Coastal and Shoreline Protection: Erosion Control Using Riprap and Armourstone, pp264-280CHAPTER 8: Shorezone Protective Structures and BMPsTRPA BMP Handbook8.4 Dynamic Revetments 2012Page 8-36