A jetty is any of a variety of structures used in river, dock, and maritime works that are generally carried out in pairs from river banks, or in continuation of river channels at their outlets into deep water; or out into docks, and outside their entrances; or for forming basins along the coast for ports in tideless seas. The forms and construction of these jetties are as varied as their uses (directing currents or accommodating vessels), for they are formed sometimes of high open timber-work, sometimes of low solid projections, and occasionally only differ from breakwaters in their object. The term derived from the French word jetée, "thrown", and signifies something thrown out. Jetties at the coast that have been raised and extended, help prevent long shore drift, so therefore slowing down beach erosion.
Read more about Jetty: For Regulating Rivers, For Berthing At Docks, At Entrances To Jetty Harbors, At Lagoon Outlets