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<br />.., <br /> <br />D <br />U <br />U <br />D <br />U <br />D <br />D <br />D <br />ID <br />ID <br />m <br />~ <br />D <br />D <br />D <br />D <br />D <br />I <br />D <br /> <br />Executive Summary <br /> <br />This Riverine Erosion Hazard Area (REHA) mapping feasibility study addresses <br />requirements in the National Flood Insurance Reform Act (NFIRA) enacted in September <br />1994. Section 577 of NFIRA requires that FEMA submit a report to Congress that <br />evaluates the technological feasibility of mapping REHAs and assesses the eccnomic <br />impact of erosion and erosion mapping on the National Flood Insurance Program (NFIP). <br />The purpose of this study is to determine whether it is technologically feasible to map <br />riverine erosion hazard areas, <br /> <br />Section 577 of NFIRA has specifically defined an erosion hazard area as follows: <br /> <br />Erosion hazard area means. based on erosion rate information and other <br />historical data available, an area where erosion or avulsion is likely to <br />result in damage to or loss of buildings and infrastructure within a 50-year <br />period. <br /> <br />In the ccntext of this study, erosion is the removal of a volume of sediment from a stream <br />reach. However, in riverine areas, a stream reach can be stable and still migrate back and <br />forth. Channel instability occurs when natural or man-induced processes lead to <br />excessive erosion or deposition, Therefore, when a stream migrates laterally but <br />maintains its dimensions, pattern, and profile, stability is achieved even though the river is <br />"active" and moves across the fioodplain. 'For this study, a reach experiencing this type of <br />lateral migration is ccnsidered to be "eroding," and thus has an associated REHA. This is <br />because stream migration can threaten buildings and infrastructure, <br /> <br />,I <br /> <br /> <br />Collapsed house on eroding stream bank along the Cimarron River in Logan County, <br />Oklahoma in March 1998, Photograph courtesy of Kathy Schmidt. <br /> <br />4 <br />