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<br />stabilize ground surface; ineffective against <br />other hazards. <br />In terraced su~divisions, where horizontal <br />house pads are separated by steep banks, drop <br />structures prevent headcutting and formation of <br />channels between structures. As shown in the <br />model tests (Part II. Section 5.4), the <br />reduction in scour hazard is substantial. <br />Where channels are used to convey floods down- <br />fan. drop structures can be used in the <br />channels to safely dissipate energy and prevent <br />channel erosion and failure. <br /> <br />Public Acceptance <br />While drop structures are <br />channels. no uses of <br />subdivisions were observed. <br />Acceptance is likely to be very good, since <br />they are inexpensive, can be installed by <br />developers. can be retrofitted to existing <br />communities. and can be covered completely by <br /> <br />commonly <br />them in <br /> <br />used <br /> <br />in <br /> <br />terraced <br /> <br />landscaping. <br /> <br />ReqUired Maintenance <br />None, except for inspection and repair. if <br />necessary. after floods. <br /> <br />Debris Fences <br /> <br />Susceptibility <br />Because they are designed to stop debris, such <br />fences will collect sediment and boulders until <br />they are buried. <br />Impact forces on the fences during mud or <br />debris flow events can be large. potentially <br /> <br />80 <br />