FLOOD08374 - Laserfiche WebLink

Home Browse Search

-7- . planners and other land managers to forecast the effects of proposed development on flood hazards by means of readily identifiable and measurable parameters. The realization of these objectives will enable professionals involved in long-range planning to estimate the changes in discharge corresponding to relevant design frequencies accompanying projected changes in land use within a watershed. These estimates can then be applied in floodplain mapping to avoid jeopardizing new construction which otherwise might be- come situated in the expanded floodplain as urbanization proceeds. Fail- ure to account for this dynamic behavior of floodplains in certain set- tings may lead to a serious malfunction of the National Flood Insurance Program by charging rates which are inappropriate to the true hazards. It must be recognized that changes in the areal extent of floodplains cannot be directly evaluated in a general manner because of the complex hydraulic relationships among stream discharge, water surface elevation and area of inundation. Since discharge is essentially conservative along a stream reach regardless of the morphology, the discussions which follow will address the impact of urbanization on this parameter. Never- theless, the reader should be aware that changes in discharge correspond to definite, although unspecified changes in the extent of floodplains. Initial considerations for this research were made in the context of a process-response model (Smith and others, 1974). This is a useful de- vice for identifying relevant factors in a conceptual problem as well as describing their possible relations to one another. As shown in Figure 1, the process elements consist of both independent and semi-independent factors of which climate, bedrock geology and surficial geology affect morphometry and land use. Hydraulic flow parameters are dependent on ;