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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Technological feasibility is defined as existence of. <br /> <br />Methodologies that are scientifically sound and implementable under the <br />NFIP. Scientific soundness means that the methodologies are based on <br />physical or statistical principles and are supported by the scientific <br />community. "Implementable" means that the approaches can be applied <br />by FEMA as part of a nationwide program under the NFIP and for an <br />acceptable cost. <br /> <br />In the present study, the project team conducted a search of existing methodologies used <br />to predict riverine erosion, with emphasis on case studies. In general, case studies were <br />categorized as: <br /> <br />1, Geomorphic methods - relying primarily on historic data and geomorphic <br />investigations; <br />2, Engineering methods - relying primarily on predictive equations based on engineering <br />and geomorphic principles; and <br />3, Mathematical modeling methods - relying primarily on computer modeling of fluvial <br />processes, <br /> <br />A Project Working Group (PWG) of experts in the field of riverine erosion was organized. <br />Their functions were to provide guidance to FEMA on technological feasibility of mapping <br />REHAs, to act as an information source to locate and select case studies, and to review <br />and comment on reports prepared during the study. The PWG included a nationwide mix <br />of individuals from academia; Federal. State. regional and local govemment; and the <br />private sector. <br /> <br />Based on the literature review, case study analysis, and input from the PWG, <br />methodologies for analyzing and mapping REHAs were identified. A determination on <br />technological feasibility was reached, <br /> <br />I <br />I <br /> <br />Using cost data associated with existing case studies, the study team estimated the <br />approximate unit cost (i.e., cost per river mile) of conducting riverine erosion hazard <br />studies and adding the areas to existing Flood Insurance Rate Maps (FIRMs). The study <br />team estimated the approximate overall costs for conducting studies and mapping the <br />riverine erosion hazard areas nationwide, <br /> <br />Riverine Erosion <br /> <br />I <br />I <br /> <br />Fluvial systems respond to perturbations that may be the result of naturally occurring <br />inputs, such as precipitation, or human intervention in the form of urban developmen~ <br />forestry, mining, flow diversions. flood regulation, navigation, and other activities. Complex <br />physical processes whose mathematical characterization is still imperfect govem the <br />response, although there is reasonable qualitative understanding of the nature of this <br />response. The basic premise is that streams are constantly attempting to attain a state of <br />balance involving their geometry (dimensions, pattem, profile), the properties of the bed <br />and bank material, and the extemal inputs imposed, The process to achieve this state of <br />equilibrium can span long periods and affect large areas. <br /> <br />I <br />I <br />II <br />I <br /> <br />In the context of riverine erosion hazard areas, engineers are mosijy concemed with <br />migration of the channel alignment and various forms of erosion and deposition. These <br />events can potentially occur in any stream environment but are often most dramatic in arid <br />and semi-arid regions where the large sediment yields and the flashy character of floods <br />can cause severe changes in channel configuration, <br /> <br />5 <br />