Optimum Investment in Structural Flood Control

National flood damages have been increasing, despite extensive construction programs, due largely to economic encroachments on the flood plain. This situation calls for a reconsideration of flood control economics. Much of this encroachment occurs as a result of the areas being protected by flood control projects and may be described as project induced. Analysis of project-induced damages indicates that, contrary to the conclusions of certain academic critics, only quite high degrees of flood protection can be justified economically. As a result of this approach benefit-cost ratios as usually computed should be reduced. Basin-wide reservoir systems inherently involve extensive partial flood protection, due partly to the extension of effects downstream and partly to the continual economic development in flood plain areas lower than those to which adequate protection is afforded. Therefore, some way must be found to control project-induced growth downstream, as an adjunct of reservoir systems. This could be done by general reservation of floodways downstream of flood control reservoirs.