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<br />. <br /> <br />Memorandum/Issues/Rules <br />September 22. 1987 <br /> <br />l. <br />. <br />2. <br />3 . <br />4. <br />5. <br />6. <br /> <br />. <br /> <br />understood as relating to the level of detail used to draw <br />a floodplain boundary on a map. All floodplain designated <br />by the Board will fall into one of these two categories. <br />The rules. therefore. define the limit between these two <br />categories. However. approximate floodplain information <br />may not be suitable for making accurate (and therefore <br />reasonable) land use decisions under statutorily <br />authorized zoning powers. <br /> <br />At its November. 1984. meeting. the Board formally adopted <br />a pOlicy regarding designation and approval of approximate <br />floodplain information. All elements of that pOlicy <br />statement have been incorporated into the proposed rules. <br />(See RUles 6.B.l. 6.B.2. 6.D.l. 6.E. and 9.C.) <br /> <br />Another important concept to make clear in adopting the <br />rules is the engineering process for delineating <br />floodplains by detailed methods. This process involves <br />several steps in the following logical order: <br /> <br />Topographic base mapping. or the determination of the <br />ground surface geometry of the floodplain on a work <br />map (definition 30) and in a series of cross sections <br />at intervals along the stream. <br /> <br />Hydrologic Analysis. or the determination of the peak <br />rule of flow (definition 19). <br /> <br />Hydraulic Analysis. or determining how deep and how <br />fast the water will flow (definition 20). <br /> <br />Water Surface Profile. similar to a side view or <br />cut-away view of the flood (definition 29). <br /> <br />Flooded Area Map. an interpretation of the water <br />surface profile in plan view (definition l5). and <br /> <br />PUblished Report and Map. where the information in the <br />computer output and work map is typically reformated <br />and made available for use by the pUblic. <br /> <br />The engineering standards provided by these rules have <br />been organized in the same order. first for the <br />delineation of detailed floodplain information (Rule 5) <br />followed by delineation of approximate floodplain <br />information (Rule 6). As you are aware. Rules 7 and 8 <br />relate to additional criteria for evaluating dams and <br />levees. respectively. <br /> <br />-3- <br /> <br />" --.... <br />