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Tuesday, May 19 1:30 - 3 :00 PM Track 2 - CoastalII - Moderator: Mark Mauriello DEVELOPING SHORELINE RECESSION RATES LAKE MICffi(aN COAST Mark Riebau, PE, Jack Cox, PE, and Chris Jones, PE Recession of the Wisconsin shoreline of Lake Michigan is related to both lake dynamics and upland processes, Wave action in the lake works to move sediment along the shoreline, Vwying lake levels expose bluffed areas to direct wave attack during limes of high water level while low lake levels uncover and widen beaches so that bluff erosion is temporarily halted, Geology and development of the shoreline also influence the shoreline recession process, Swface runoff rates, exacerbated by development, can cause bluff edge failures. Erosion control measures placed at the toe of a bluff slope can decrease the recession rate locally while accelerating the rate on adjacent shorelines. The approach used fur this effort was to rely on the historical recession rate evidence and ignore variable f.ctors such as type of failure, variable water level, and geologic formations, Reference and control lines for measuring the r_ssion, and the calculation method employed to detennine the rate were selected to be insensitive to these measures, This study employed automated photogrammetric analysis of stereographic pairs to develop mid-bluff elevation contours to determine recession rates of the Lake Michigan coast in three Wisconsin counties; Manitowoc, Ozaukee, and Racine, After the toe-of-bluff was projected 30- and 60-years into the future, using the recession rates from mid-bluff contours, the stable bluff angle was used to calculate the location of the "top-of-bluff" for each future condition, Shoreline recession, particularly on bluffed shorelines, or shoreline which experience large long term variations in water level, tend to occur in discrete steps, rather than a smooth continuous process. This is due, in part, to geotechnical considerations and episocidic storm events. To develop a reliable recession rate requires a sufficiently long sampling interval, and a number of recession measurements to encompass and incorporate these episodic events into an equivalent continuous rate, ASSESSING LIKELY U.S, COASTAL EROSION HAZARD AREAS Darryl 1. Hatheway, Robert Hallermeier, PhD, and Mark Crowell The Phase I results for the FEMA evaluation of coastal erosion hazards along the Atlantic and Pacjjk Oceans, Gulf of Mexico, and Great Lakes shorelines in the United States are completed for the selected 27 counties. The Congressional mandate of the study, addressed in Section 577 of the National Flood Insurance Reform Act of 1994, requires that FEMA conduct the study and mapping of a statistically valid sample of coastal counties before proceeding with the Phase II structure Inventory and Economic Impact Analysis, Each of the coastal counties were allowed to select the period of record for analyzing historical shoreline change rates, select a specific method for detennining long-term (60-year) erosion rates, select form a number of unique erosion reference features applicable to their county, and select their own recent aerial imagery for the mapping and projection of erosion hazard areas, The completed erosion hazard studies have provided detailed historical results and demonstrat,:d that some uncertainties exist in the available methodologies utilized to establish mean erosion rates over vastly different shoreline types, Selection of base map imagery and erosion reference feann-es proved to be problematic as well, However, a programmatic strategy can be developed based on an assessment of the study similarities and conceptual understanding of the use and intent of implementing an erosion hazard mapping and actuarial tool for the National Flood Insurance Program, Regional applications of mean erosion rates and erosion reference features will be reviewed in this paper, as well as an assessment of the shoreline recession analyticallools and methods which may prove to be most useful in establishing somewhat unifonn treatments of erosion and r_ssion ofU,S. shorelines over periods of 60 years or more, REVISIONS TO THE COASTAL mCR HAZARD AREA SROWN ON NFIP MAPS Doug Bellomo P .E" Federal Emergency Management Agency The coastal environment is dynamic, and the hazards associated with coastal flooding are very diff,:rent from those associated with rivers and streams. These differences were realized at the inception of the National Flood Insurance Program (NFIP) in 1 968, and beginning in the early 1970's, coastal high hazard areas (or V Zones) have been identified on Flood Insurance Rat" Maps (FIRMs). How these areas are identiJied and mapped, however, has evolved considerably since that time, and continues to do so. Land along major U,s, coasts is generally more valuable than that in other parts of the counlly, and for communities participating in the NFIP, the location of the V zone has a significant impact on the type of construction permitted in this area. Furthermore, insuring structures constructed in the V zone can be as much as three times more expensive than in other flood hazard areas. The combination of these factors makes accurate delineation of the V zone important to property owners, planners, and local officials, Engineering analyses are perfonned when determining the inland limit of the V zone, and computing regulatory Base (1 % annual chance) Flood Elevations (BFEs) within it These analyses involve determining storm surge elevations (I % 'rulUal chance stillwater elevation) and deepwater wave conditions, assessing stonn induced erosion and scour, perfonning wave runup and overtopping analyses, computing wave heights, and locating the inland limit of the primary frontal dune. Therefore, any requests to revise existing V zone boundaries or BFEs must address each of these factors, This paper will describe in more detail what is required to revise the aerial extent of the V zone and the BFEs within it.