BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

Table 8-11: Advantages and Disadvantages of Using Dynamic RevetmentsADVANTAGES• Stone size is smaller and is usually lessexpensive than the large armor stones usedin a conventional riprap revetment. Smallerequipment is required to place smallermaterial.• Placement of the material does not requirespecial care. As a result, the material may bedumped in place rather than the stonesbeing individually placed, making theconstruction process much simpler.• The final cross-sectional shape is morenatural looking than a typical staticrevetment.• The smaller stone size presents less of anobstruction to smaller organisms that needto enter or leave the shorezone.• The smaller material size may present lessof a hazard to foot traffic.• Movement does not constitute failure• Dynamic revetments are more aestheticallyacceptable.DISADVANTAGES• If smaller material is not less expensive thanconventional boulder riprap sizes, the greateruncertainty in the performance of dynamicrevetments over conventional ripraprevetments may serve to diminish itsattractiveness as an alternative design. Usemay be limited by suitable material source atacceptable costs (i.e., clean material ofadequate color, size, texture, amount, andacceptable transportation costs).• Larger volumes of material are required,which may also increase costs beyond thoseof conventional boulder riprap.• May need replenishment.• Foot traffic and other activities may damagethe equilibrium cross section obtained by therevetment.Although dynamic revetments require more material to construct than a ripraprevetment, construction is generally less expensive than comparable hardengineering structures. Nonetheless, it cannot be expected that a cobble bermwill provide the same level of shorezone protection as a conventional ripraprevetment or lake wall. 31 Therefore, dynamic revetments have more frequentmaintenance requirements than that of static revetments. The dynamicrevetment itself may sometimes pose a hazard to lakefront properties if thematerials are sized too small and are then moved by the waves of a severe eventup toward adjacent backshore structures and houses. Because of this potential,the use of dynamic revetments are safest if backed by a bluff or substantial sanddune, or if developments are sufficiently set back beyond the reach of highenergywaves.8.4.3 DESIGN CONSIDERATIONS AND PLANNINGThere is extensive literature of the study of natural gravel beaches. Of relevanceto the design of dynamic revetments are those addressing cobble movement bywaves, how the clasts are sorted by size and shape across the beach profile, andtransport off or along the shore 32 , also relevant are studies of beach response,how beach profiles change under varying wave conditions and at times of31Allan, et al., 2003, 2005, Remote Environmental Monitoring Units: An Autonomous Vehicle forCharacterizing Coastal Environments Journal of Atmospheric and. Oceanic Technology. 22, 1797–1808.32Carr A.P. (1971) Journal of Sedimentary Research; December 1971; Experiments on LongshoreTransport and Sorting of Pebbles; Chesil Beach, England. v. 41; no. 4; p. 1084-1104;TRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 8.4 Dynamic RevetmentsPage 8-37