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. . . PREFACE This report is part of a program by the Colorado Water Conservation Board (CWCB) to make approximate floodplain maps prepared by the Federal Emergency Management Agency (FEMA) easier for local governments to use. This CWCB report provides limited engineering information to support the approximate delineations on the maps, and it provides floodplain management information to guide the local governments in the use of the maps. The official floodplain information for Rockvale is the Flood Insurance Rate Map (FIRM), dated October 15, 1985. The FIRM was prepared by FEMA, however this federal map does not have any published information accompanying it to describe either the engineering basis of the map or the manner in which the town could use it for floodplain management. The initial purpose of this report, therefore, is to provide the town with limited supporting information. The report includes a description of a hydrologic analysis that was performed for the town as part of the CWCB's technical assistance program. The hydrologic analysis is consistent with the map in this report. In addition, the report gives the town some basic information about floodplain management and it gives some alternatives that could be considered in formulating and implementing its floodplain management objectives. A second function of this report is to assure that the FIRM meets the basic technical requirements for designation and approval by the CWCB. Without a report and without a hydrologic analysis, a map like the FIRM for Rockvale cannot qualify for CWCB designation. Colorado statutes require that local governments obtain from the CWCB the designation and approval of floodplain information prior to its use for regulatory purposes. This report provides a means for the FIRM to meet that statutory objective. The FIRM was prepared prior to the completion of a CWCB document entitled Guidelines for Determining lOO-year Flood Flows for Approximate Floodplains (Guidelines). That document provides the necessary hydrologic information in support of the loo-year floodplain boundaries identified on the FIRM. The hydrologic information contained in the Guidelines was used in preparing this report and it supports the subsequent designation of the Rockvale FIRM.