OCR Text |
Show or as a compliance by a local political subdivision with a condition of local cooperation imposed by the United States as a prerequisite to the provi- sion of the improvement. An alternative would be adequate plans for routing flood stages past existing developments. The United States, or the political subdivision, could acquire the lands in question and enforce the removal of existing improvements and pre- vent the erection of other improvements. In either case, the limitation in development of the flood plan would be attained at a cost to the acquiring agency. Enforced evacuation of areas subject to flood- ing is usually considered by the Army Engineers as a possible alternative for eliminating flood damage; it is usually found economically unjusti- fied or impracticable in comparison with other methods. Nevertheless, full possibilities of com- bined flood plain zoning with limited levee protection should be examined in connection with all proposed flood control projects, particularly where study reveals the feasibility of controlled utilization of flood waters to enrich alluvial bottom lands. Such flood plain zoning might, in the long run, save many lives and much property, for, in spite of all flood control works, the future always holds the possibility of unusual floods for which the maximum, of protection would prove inadequate. Flood Forecasting Flood forecasting should be considered as an integral part of any system whose function is to prevent or reduce the extent of damage caused by floods. It accomplishes its purpose by creating the opportunity for preparation. The United States Weather Bureau estimates that its flood forecasting service is preventing flood damage to the extent of approximately 30 million dollars a year. This means that flood damage to physical property, which the Bureau estimates to be running at the rate of about 150 million dollars a year, would be running at 180 million dollars a year if it were not for this fore- casting service. Today the Weather Bureau is spending about $870,000 a year on its over-all flood and water supply forecasting services. It estimates that about 2 million dollars a year would be required to provide the country with an adequate and thoroughly modern service of this kind, and that the result would be an estimated reduction of 66 million dollars in the current rate of flood damage. In the early 1930's, when the modern flood control program was in its early stages, the Army Engineers submitted to Congress a wide range of flood control possibilities supported by substantial benefit-cost ratios. But, as the program has gone forward, the proportion of projects with rela- tively low benefit-cost ratios has increased. In fact, there are flood situations in which the flood control possibilities involve costs which exceed benefits. It is in connection with the latter situa- tions especially that consideration should be given to increasing the effectiveness of flood forecasting. Flood forecasting can also serve a very im- portant part in making possible sound operation of flood control works and more effective use of reservoir storage to serve multiple-purpose objec- tives. Without forecasting there must be a rea- sonably rigid separation of the part of reservoir capacity reserved for flood control and the part utilized for conservation storage, for generation of power, maintenance of stream flow, and other purposes. Under such circumstances, the part of the reservoir reserved for flood control repre- sents the limit of the project's contribution to that purpose and must be emptied as rapidly as possible after a flood has passed in preparation for the next flood. If effective flood forecasting is available, how- ever, the use of the reservoir capacity can be placed on a truly multiple-purpose basis. In other words, to a measurable extent, each pur- pose can have the advantage of a portion of the other's storage, thus increasing the potentialities of the project for both purposes. This means that, pending a flood warning, the reservoirs can be held at a higher level for power or other purposes in the assurance that the warn- ing will come far enough in advance to permit the emptying of the reservoir in time to catch the advancing flood. Similarly, the draw-down in 146 |