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<br />Economic Feasibility <br />Damage reduced through forecast, warning, and evacuation is particularly difficult to <br />measure because of the many variables, both in the types of actions which might be taken and <br />the affects of these actions. I n one study on economic feasibility it was found that damage <br />reduced exceeded costs by three to seven times, however, it is dangerous to generalize from <br />these data as each flood plain or river basin is unique (2). While the costs of preparedness occur <br />each year the flood events being prepared for are generally less frequent. When they become <br />quite infrequent it may be justified (economically, as well as practically) to invest in some other <br />means of protection even though the annual costs are low. The difficulty, of course, is that <br />floods are more or less random events and as such are not usually spaced evenly over time. <br /> <br />Advantages and Disadvantages <br />The principal advantages and disadvantages of forecast, warning, and evacuation as a means <br />of reducing flood damage are summarized in Table 8-1. <br /> <br />TABLE 8-1 <br /> <br />ADVANTAGES AND DISADVANTAGES <br />OF FLOOD FORECAST, WARNING, AND EVACUATION M~ASURES <br /> <br />Advantages <br /> <br />Preparedness. planning is almost always <br />economically feasible and desirable. Some- <br />thing can usually be done even in areas <br />where other flood loss reduction measures <br />are implemented. <br /> <br />A significant saving of lives may result in flash <br />flood or water related structural failure <br />situations. <br /> <br />Accurate forecasts and warnings may permit <br />sufficient time to implement temporary <br />protective measures which can significantly <br />reduce flood damage. <br /> <br />Disadvantages <br /> <br />The effectiveness of the warning system and <br />response of the community cannot be <br />accurately predetermined, consequently <br />neither can potential flood damage reduc- <br />tion. <br /> <br />Requires a continuous awareness and infor- <br />mation program, maintenance of equip- <br />ment, etc. <br /> <br />Effectiveness of preparedness plans tend to <br />diminish with increasing time between <br />floods. <br /> <br />References <br /> <br />1. Owen, H. James, "Guide for Flood and Flash Flood Preparedness Planning", National <br />Oceanic and Atmospheric Administration, National Weather Service, April 1976. <br /> <br />2. Day, Harold J., "Flood Warning Benefit Evaluation - Susquehanna River Basin (Urban <br />Residences)", Environmental Science Services Administration, Weather Bureau, U.S. Depart- <br />ment of Commerce, ESSA Technical Memorandum WBTM HYDRO 10, March 1970. <br /> <br />3. Susquehanna River Basin Commission, "Planning Guide, Self-Help Flood Forecast & <br />Warning System, Swatara Creek Watershed Penna.", Mechanicsburg, PA., November 1976 <br /> <br />4. Susquehanna River Basin Commission, "Neighborhood Flash Flood Warning Program <br />Manual", Mechanicsburg, PA, October 14, 1976. <br /> <br />61 <br />