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Hydrauli.cs The U.S. Army Engineers HEC-2 computer program was used to perform water surface profile computations. Numerous bridges and culverts exist along the channels through the study reach. Dimensions for these road crossings were determined from field investigations and the data was integrated into appropriate cross section data. Cross section data, and reach length information were obtained from 2 foot contour topographic maps. Maps were prepared especially for this study, at a scale of 1 inch = 200 ft. with 2.0 ft contour intervals. Hydraulic roughness coefficients (Mannings N-Values) were determined from field investigations and documented with photographs (in technical addendum). A tabulation of roughness coefficients is included in the FLOOD PLAIN MANAGEMENT Potential flood damages to existing development and possible loss of life can be alleviated or lessened through non-structural and structural flood hHard mitigation methods. (at map contour intervals) from plotted profiles (from HEC-2) to the maps, using stationing along the main channel as the location reference. These points were connected and smoothed to create the map flood lines. T~e Lower Cactus Valley Ditch, which passes through the Town of Silt, is a significant factor in the study. The ditch is near capacity during the summer months and therefore can contribute little in its present condition towards intercepting local runoff. Field surveys and water surface profile analyses show the carrying capacity of the ditch to be about 35-40 cfs (irrigation rights are for 50 cfs). The necessary hydraulic studies for possible enlargement of thedich,asa part of an altern ative treatment plan, were made and concluSions shown in the "Structur alFlood Control Measures" section of this report. Non-structural rrethods i~clude; local flood plain regulations, Ia~d treatment, flood warning and forecasting systems, flOOd insurance, fl~d proofing. flOOd fighting and emergency evacuations. Local Regulations The need to mfnimize property damage due to flooding has been recognized by planners and local community officials. Subdividers and developers are required to submit proposed storm drainage plans to the planningCOlOO1ission for approval. In the past, drainage plans have been prepared singularly or on aplat_by.plat basiS. Information contained in this reportwi11 Ileuseful in developing a master drainage plan for the study area. This report provides the outline of flood hazard areas on Jarge scale maps specifically for this purpose. The city may provide zoning regulations... ..."to establish, regulate:, restrict. and limH such uses on or along any storm or floodwater runoff channel or basin, as such storm or floodwater runoff channel or basin has been designated and approved by the ColoradO tlaterConservation Board, in order to 1 essenor avoid the hazards to persons and damage to property resulting from the accumulation of storm or floodwaters".., technical addendum. Water surface profiles, typical cross sections and maps showing the lOO-year flOOd boundaries are shown on included exhibits and flood plain maps. Table 1 shows computed flood elevations at specific cross sections. F'~d lines were located on the maps by transferring flood elevations as stated in Section 30-2B-lll for county governments and Sections 31-23-301 for municipal governments of the ColoradO Revised Statutes. -15- '" ..