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<br />CHAPTER 3 <br />IDENTIFICATION OF <br />THE FLOODPLAIN <br /> <br />-_. <br /> <br />The starting point of any floodplain management program is identification of <br />the floodplain. This chapter discusses the reasons for identifying floodplain <br />areas, the engineering methods used for delineating the floodplain, and the <br />eWCB's designation process for floodplain studies performed in the state. It <br />was written for an administrator who needs to know the procedures and <br />language of the professionals who will assist in or actually perform the <br />technical work associated with identifying a floodplain. <br /> <br />The Role 0" Floodplain Identification in a <br /> <br />!Local Floodplain Management Program <br />The identification of floodpiains in a community begins with acknowledging <br />the hazard, describing the characteristics of the problem, and formulating <br />8olutions.- <br />ACknowledging the hazard <br />The extent of a community's drainage and flooding problems can be ascer- <br />tained through good documentation of historicai fiood events or through a <br />flood hazard anaiysis or both, <br />Describing the Flood Characteristics <br />The hydrologic and hydraulic parameters of each flood problem can be <br />quantified througtl engineerin\1 principles and procedures, A floodplain study <br />provides community officials with information to describe flooding and <br />drainage problems. Officiais will find out how high the water might rise, which <br />Htructures and dwellings might be damaged, and which areas would be safe. <br />Formulating Solutions <br />Basic engineering information is necessary to formulate solutions to com- <br />munity floodplain problems. Engineering information helps in three ways. <br />1) It can help a community select a regulatory or structural improvement <br />plan; the community's flood and drainage problems will be addressed <br />and expenditures prioritized. <br />2) It can show the limits of the reguiatory floodplains on the zoning map. <br />(Showing the floodplain limits and water surface elevations makes <br />implementation of regulations more feasible.) <br />3) It will heip the community to comply with Colorado Statutes, by deter- <br />mining a legally enforceable floodplain boundary delineated by: an <br />acceptable hydrologic and hydraulic investigation conforming to ewcs <br />standards and guidelines; and an official designation by the CWCB and <br />adoption by the local government. <br /> <br />Procedures and Methods <br />Those using floodplain information should be aware of the accuracy and the <br />limitations of "approximate" and "detailed" study methods. Many com. <br />munities have floodpiains which have been identified hy both methods. <br />Development preHSlJreS, study costs, and the community's adopted manage- <br />ment procedures for the floodpiain will determine an iclentification procedure <br />and method. <br /> <br />Approximate Studies <br />These studies are based on a minimal amount of technical data and should <br />be used only undE" the following conditions: <br />. for a limited rural area where only one or two single family residences or <br />other structures will be constructed; and <br />. for a river reach extending up to several miles where there is no imme- <br />diate need to delineate the detailed 1 OO-year floodplain hut where <br />the local government wishes to alert potential developers to the flood <br />hazard. <br />Approximate procedures allow the engineer to estimate the area that would <br />be affected by a 1 OO-year flood based solely on existing information. <br />l=tesearching the area's flood history, interpreting topographic features, using <br /> <br />15 <br />