BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

8.6 JETTIES8.6.1 OVERVIEWIn Lake Tahoe, jetties primarily protect marina channel entrances fromclogging with excessive sediment due to offshore and longshore transport anddeposition.A jetty is a backshore-connected structure, generally built perpendicular to theshoreline, extending into a body of water to direct and confine a stream orflow through a selected channel in order to prevent or reduce the shoaling orsedimentation of that channel.Jetties are most often designed as paired structures installed on either side of anentrance to stabilize the width and depth of the navigation channel by raisingflow velocities and providing adequate sediment flushing. They are used tocontrol the movement of sand migrating from offshore, along the adjacentbeaches, and into the channel where it interferes with navigation.The impoundment of sand at the updrift side of the jetty can create significantmaintenance dredging requirements. When in place for a long time, a jetty cancause an updrift depositional plume to form which could extend far updrift ofthe structure and outward toward the tip of the jetty.Although jetties have a different function than breakwaters, jetty structuraldesign is similar to a breakwater in that most jetties are built as boulder riprapstructures. Jetties can be built from a variety of materials but the few that existin Lake Tahoe are constructed from native field and quarry stone. Jetties inLake Tahoe are found associated with the anchored breakwaters that protectsmall private residential moorings. Jetties can also act as breakwaters,protecting the landward mooring from wave action.Fixed impermeable jetties are not permitted in locations where beach erosionor loss of sediment from the shorezone is likely to occur. Jetties must bedesigned to be permeable, allowing free circulation of water and sedimentaround the structure. The TRPA Code of Ordinances requires that new publicor private jetties shall be permitted only if part of a marina project or boatramp. In addition, private jetties shall not be permitted for expansion but maybe repaired or modified to improve function and environmental benefit.Overall, jetties are a permanent BMP that apply source and hydrologic controlfor stormwater.8.6.2 JETTIES: ADVANTAGES AND DISADVANTAGESAs with previously discussed BMPs, there are advantages and disadvantages inusing jetties for shorezone protection (Refer to Table 8-14).CHAPTER 8: Shorezone Protective Structures and BMPsTRPA BMP Handbook8.6 Jetties 2012Page 8-48