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u " FLOOD PLAIN MANAGEMENT Hvdraulics Hydraulic analyses conducted in this study were done using U.S. Army Corp of Engineers computer model HEC-2. The general land slope in the study reach is greater than 4 percent, therefore supercritical flow conditions prevail through almost all study reaches. It was determined by representatives of the Colorado Water Conservation Board Soil Conservation Service, GMS Inc., and FEMA in a . . meeting on June 11, 1992 that a backwater analYSIS would be cOmputed and used in preparing flood elevations for this study in lieu of using supercritical drawndown analysis. This is in compliance with FENA's 1985 guidelines and specifications which state that flood hazard areas of natural streams with supercritical flow should be based upon the critical flow profile. Discharge values were discussed in the hydrology section of this report. Most of the cross section data were digitized from topographic maps with a scale of 1 inch _ 200 ft with 5-ft contour intervals. Some supplemental field surveys were made at specific sites and a number of additional cross sections needed at road crossings were developed from the topographic maps. Dimensions of bridges and hydraulic roughness coeficients (n- values) were determined from field investigations and from the "Orainage Master Plan for The city of Cripple Creek". Potential flood damages to existing development and possible 1055 of life can be alleviated or lessened through non-structural and structural flood ha~ard mitigation methods. Non-structural methods inClude: local flood plain regulations, land treatment, flood warning and forecasting systems, flood insurance, flood proofing, flood fighting and emergency evacuations. Local Regulations The need to minimi~e property damage due to flooding has been recogni~ed by planners and local community officials. Subdividers and developers are required to submit proposed storm drainage plans to the planning commission for approval. In the past, drainage plans have been prepared singularly or on a plat-by-plat basis. Information contained in this report will be useful in developing a master drainage plan for the study area. This report provides the outline of flood ha~ard areas on large scale maps specifically for this purpose. The city may provide ~oning regulations ".. .to establish, regulate, restrict, and limit suoh uses on or along any storm or floodwater runoff channel or basin, as such storm or floodwater runoff channel or basin has designated and approved by the Colorado water Conservation Board in order to lessen or avoid the hazards to persons and dam~ge . to property resulting from the accumulation of storm or floodwaters..." as stated in Section 30-28-111 for county governments and Seotions 31-23-302 for municipal governments of the Colorado Revised Statutes. Water surface profiles, typical cross sections, and maps showing the lOO-year flood boundaries are shown on included exhibits and flood plain maps. Table 3 shows computed flood elevations at specific cross sections. Flood boundaries were located on the set of topographic maps, previously referred to, by transferring flood elevations (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 tlood boundaries. Colorado Natural Hdzard Area RegulationH Changes are being made almost daily in Cripple Creek, Some have an influence on the watershed hydraulic characteristics therefore the follo~ing ~ssumptions are m~de pert~ining to recent constructions projects: 1. A new double-cell culvert is in place on Cripple Creek at Fourth Street and Meyers Avenue. 2. A new pipeline system is in place along Second Street between Warren Avenue and Carr Avenue Which will essentially eliminate the flood plain through that reach. 3. A project near the Cripple Creek/Victor school at the intersection of "A" Street and West Avenue will prevent any trans-basin diversion of flood waters between Pony Gulch and Second street tributary. In 1974 the Colorado General Assembly passed House Bill 1041, a bill . . "concerning land use, and providing for identification, designatIon, and administration of areas and activities of State interest,..." (H.B. 1041, Title 24, Article 65.1, CRS, as amended). Areas of State interest include natural hazard areas, or those areas that are "so adverse to past, current, or foreseeable construction or land use as to constitute a significant hazard to public health and safety or to property". Flood plains are natural hazard areas.