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..................I....._I.HI....... HB....HBII.I.I.I.IIIjI........................................................... II :::;:;:;::/ ::;:;:;:;::-:.;:; :::-:.:;. ::::;';:;"-" :,:;:;::: :-::. ,:;:::;: ::::::::::: ::-":;:;:::: ::," -.;:;:::::::;:;:;::::::- .;:::;:;:; ::::::: ::;:;:;:;:;:::::;:;:;:;:;:;:;:;:;:;:;:;:;:;:::;:;:;:::::;:;:;::::::;:..:::-:-:....... :?::.<.t <>{,:::.: ::.:{:; <::::.::;:::: :{:: ::<::tt: ::}}: ::;:./<: :::'_ "<<:::::\):-':::::-"\} ;::} <>::.((({:}::;::::::-:.:.:-....... ......... .... '-' . -....., ., ...-. -- . ....... .. .. . ". ..,....., ., ,.... .., .. . .., ...... -, .. - ..... '" . .... ......"...."." ............. .___ ______ - '.d __ ....... Participation in the National Flood Insurance Program is one way a community can protect new development from flood hazards and reduce potential flood damage to existing homes and businesses. It is not, however, the only way. In fact, overall reduction of flood damage is more iikely if local officials combine their floodplain development regulations with other activities that also reduce flood damages. This chapter briefly discusses a comprehensive approach local officials can take to effec- tively alleviate repetitive flood damage. Floodplain management can be defined as combined actions designed to reduce the damages from flood disasters. These actions may modify the flood itself, reduce susceptibility to flooding, prepare for an efficient response to and recovery from a flood disaster. Local officials may use a combination of these strategies to provide for the greatest amount of protection at the least expense. A. Modifying Floods Structural measures can modify floods and reduce flood damages. Large dams and reservoirs can control the flow of river systems. Smaller dams, dikes, floodwalls, and other structures can reduce local flooding. In some cases, channels may be altered to enlarge their capacity, to stabilize banks and prevent erosion, and to clear away vegetation, rocks, or other features that obstruct the flow of fioodwaters. Diversions and spillways employing natural or constructed channels can be installed to divert flood flows from developed areas. Land-treatment measures help increase absorption of rainfall into the soil and decrease runoff rates, which can result in reduced flood peaks. Such techniques include planting and maintaining vegetation to act as runoff interceptors and diversions, small detention and erosion control structures, and terraces. Detention measures, such as landscaped or paved holding areas, can be built into development sites to lower the runoff rate of rainfall and thereby reduce the flood peaks of collecting streams. While structural measures are often a popular answer to flooding problems, reliance on structures as the oniy solution to these problems has several disadvantages. Some of these are listed below. - Structural measures are generally expensive, which can make such solutions economically infeasible. - In many cases, structures encourage investment and development in flood-prone areas, thereby exposing more properties to the flood hazard. - Structures do not provide absolute protection. They offer a false sense of security. If a disaster does exceed the design for a struc- ture, damages are far greater than they may have been if fear of flooding had discourage development. - Gains in one area, such as protection for urban areas, may be offset by losses in other areas, such as inundation of agricultural or unique recreational areas. In other words, the structural measure Simply relocates the flood rather than reducing the hazard. - Structural techniques used alone often must be larger and exert a greater degree of man-made influence over the watercourse and other resources than would be necessary if land-use controls were used to direct future development away from flood-prone areas. 39