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.,~ ./ Agenda Item lOb March 3, 1995 Page Two , - analysis that does not meet the Board's Rules and Regulations, it cannot be designated and approved by the Board. The possibility of floodplain information not being designated will place a hardship on local jurisdictions (cities, towns and counties). There are many stream reaches in Colorado for which approximate delineations have been prepared without hydrologic analyses, particularly delineations prepared by the Federal Emergency Management Agency (FEMA). To make those approximate delineations comply with state statutes, the Board staff embarked on a project to develop a methodology for computing peak flows for those stream reaches. DISCUSSION The CWCB staff has begun preparing a design manual which describes the methodology for computing approximate 100-year flows. The manual will be entitled: Guidelines for Determinin!!: Flood Peaks for Approximate IOO-Year Floodplains Preparation of the "Guidelines for Determining Flood Peaks for Approximate I Da- Year Floodplains" has been initiated by CWCB staff. These Guidelines will assist the staff in the determination of the lOa-year flood discharges for the approximate floodplains where . engineering is limited or unavailable. Many approximate delineations that are scheduled to be presented to the Board for designation and approval (Groups III and IV in the Floodplain Designation Plan) have no published hydrologic analyses to accompany them. The staff has prepared a Work Plan for the development of a procedure to relate the approximate delineations to hydrologic analyses for stream reaches that have already been designated and approved by the Board, The previously designated detailed' studies include hydrologic analyses. A mathematical methodology will be developed using the data from the detailed studies in order to compute peak flows for the approximate delineations. The staff anticipates the development of regression equations to define lOa-year flows and thereby assure that the approximate floodplains shown on the floodplain maps meet the basic technical requirements for designation and approval by the CWCR The Guidelines will provide a means for the floodplain maps (FIRMs prepared by FEMA and any other approximate floodplain maps) to meet statutory requirements. Technical Basis of the Guidelines for Approximate Floodplains The proposed methodology will develop a series of regression equations for various Colorado river basins. As proposed in the initial draft of the Guidelines, these regression equations will be prepared using a best-fit curve regression computer program. Equations/curves will relate peak flows to basin drainage areas. The staff has already grouped some data and run preliminary regression analyses as part of the initial work on the Guidelines. Because of the great . hydrologic diversity of Colorado's streams, the state had to divided into smaller regions of