10.4 COASTAL HAZARDS ANDENGINEERING STRUCTURESEfforts to stabilize a beach can be generalized into threeapproaches:* Hard stabilization: Engineering structures to protect ashoreline from waves* Soft stabilization: Adding sand to a beach (beach nourishment)* Managed retreat: Living with beach erosion, with perhapsa mixture of hard and soft stabilizationHard StabilizationEngineering structures in the coastal environment, includingseawalls, groins, breakwaters, and jetties, are primarilydesigned to improve navigation or retard erosion. However,because they tend to interfere with the littoral transport ofsediment along the beach, these structures all too often causeundesirable deposition and erosion in their vicinity.Seawalls Seawalls are structures constructed parallel tothe coastline to help retard erosion. They may be constructedof concrete, large stones, wood, or other materials.Seawalls constructed at the base of a sea cliff may not be particularlyeffective; considerable erosion of the sea cliff resultsfrom mass-wasting processes on the cliff itself (see Figure10.8b), as well as wave erosion at the base. Seawall usehas been criticized because seawalls are often vertical structuresthat reflect incoming waves, or bounce them back fromthe shore. The reflection of waves enhances beach erosionand, over several decades, produces a narrower beach withless sand. Unless carefully designed to complement existingsử dụng đất, seawalls thường gây ra môi trường và thẩm Mỹsuy thoái.
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