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floodplains. The operations of Paonia Reservoir have been reflected in the approximate floodplains shown on the North Fork of the Gunnison downstream of the Reservoir. Community response: The CWCB staff transmitted a letter dated December 17, 2001 to the Gunnison County floodplain administrator as notification of the proposed designation action for the subject Flood Insurance Study. The County was also contacted by Montgomery Watson Harza (CWCB's engineering consultant) via telephone to further discuss the proposed Board action. The County was receptive to the designation process and verbally consented to the Board! action. The County indicated that it would transmit a letter to the CWCB staff in the near future requesting designation of the subject floodplain information. Staff findings: A new hydrology addendum is being produced by Montgomery Watson Harass (CWCB' s engineering consultant) to provide regulatory information and additional technical information to supplement the September 1989 Flood Insurance Study for Gunnison County. New hydrology data (100- year peak flow values) ,are being developed by Montgomery Watson for the approximate (Zone A) , floodplains shown on the FEMA map panels. (Detailed lQO-year flood hydrology values are required for each stream in order to be in conformance with the dWCB's rules and regulations for floodplain designation)~ CWCB staff has determined that the subject floodplain information for Gunnison County is in conformance with the CWCB' s rules and regulations for floodplain designation and approval. Staff recommendation: Staff recommends that the Board: 1) designate and approve the 100-year detailed and approximate floodplain information containedin said report within unincorporated Gunnison County, and 2) authorize staff to prepare a floodplain resolution to be signed by the Director and transmitted to Gunnison County and FEMA. This action is recommended in order to meet statutory requirements. 3) Ae:enda Item 2.c Floodplain Resolution Number: FPR 01-558 Affected Community: Douglas County Name of study to be formally acted on: "Flood Hazard Area Delineation, Plum Creek Watershed, Douglas County, Colorado" dated November 2001 - prepared by the Urban Drainage & Flood Control District. ' Studied Streams: The report includes detailed 100-year :floodplain information for Plum Creek and a number of its tributaries within the County. The studied stream reaches are in the South Platte River watershed. Technical Issues: Topographic base mapping for this project was prepared by Landmark Mapping and were compiled at a scale of 1"=200' with 2-foot contour intervals. The topographic maps were based on aerial photographs taken in May 1999. Culvert and bridge structures were measured in the field. The computer model CUHP was used to determine runoff chatacteristics from the studied watersheds as the first step in the hydrologic analysis for this study. ~he computer model UDFCD SWMM was subsequently used to route the CUHP generated runoff hydro graphs to finalize the hydrologic analysis. Hydraulic analyses were carried out to determine the hydraulic conditions and associated capacities of the studied channel reaches and structures. For this study, ,the u.s. Army Corps of Engineers computer program HECRAS was used to determine water surface profiles for various flood frequencies and to . compute channel and structure capacities. Water surface profiles were computed for the 10-, 50-, 100-, and 500-year storm events. Floodways were also generateq. In summary, all of the technical information is consistent with accepted engineering practices and With the CWCB's rules and regulations for floodplain designation. ' Flood Protection. Water Project Planning and Financing. Stream and Lak~ Protection Water Supply Protection. Conservation Planning . . . 4