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<br />DODES reviews current research in the area of disaster pre- <br />paredness and recovery to assure that the state is informed on <br />recent trends. On a broader scale, they have prepared a report <br />entitled Colorado's Vulnerability to Very High Risk Natural <br />Hazards to provide a $tatewide perspective of hazards and <br />preparedness. <br /> <br />2.5.9 Division of Highways <br /> <br />The Highway Department is involved in the des ign and con- <br />struction of highways throughout the state, frequently in river <br />valleys, so it is one state agency that is familiar with flood- <br />plain issues. Additionally, federal requirements tied to federal <br />funding of highway projects have dictated that floodplain consid- <br />erations enter into the highway design process.' <br /> <br />Most highways in the state fall into two categories: <br /> <br />(a) Federally fundeq highways, and <br /> <br />(b) Federal aid designated highways. <br /> <br />Criteria, policies, and methodolog ies used by the Highway <br />Department to design l1ighways in floodplains are discussed below: <br /> <br />For Interstate Highways, U.S. Highways, and Colorado High- <br />ways in urban areas, the 100-year flood is the design standard. <br />For Interstate Highways outside of urban areas, the 50-year flood <br />is the design standard. For U.S. Highways and Colorado Highways <br />in rural areas, design is based on the 25-year flood or less. <br />what discharge is used depends on a benefit/cost analysis which <br />considers two major factors: <br /> <br />(a) Interruption of highway service, and <br /> <br />(b) Safety to users during a flood event. <br /> <br />In addition, the consequences of the 100-year flood are <br />analyzed. All of the above enter into the design 'of bridges, <br />culverts, and the highways themselves. The methodologies, <br />including computer models, used to calculate flows are all <br />described in the Department's Design Standards. These include <br />S.C.S. methodology, CUHP, USGS methodology for small basins, and <br />others. The Highway Department uses flood histories as avail- <br />able. When floods occur, photographs are taken and report forms <br />are filled out. <br /> <br />A couple of the older interstate highway segments in <br />Colorado were built before these design standards were used, <br />including I-25 through the City of Pueblo. If that segment were <br />built now, it would be built to allow for the 100-year flow plus <br />a calculated freeboard. The freeboard would be based on the <br /> <br />62 <br />