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<br />e. An evaluation of flooding effects on other property <br /> <br />f. The specifications for building construction and <br />materials for flood proofing <br /> <br />For Planning Commission consideration of petitions and for rezoning <br />property deemed subject to flood hazard, the ordinance requires the <br />petitioner to submit the above information plus the specifications <br />for filling, dredging, grading, channel improvement, storage of <br />materials, water storage, and sanitary facilities. <br /> <br />3. 0 ~NC;Il:lE:I,:~IN~ METHOD~ <br /> <br />For flooding sources studied in detail in Steamboat Springs, standard <br />hydrologic and hydraulic study methods were used to determine the flood <br />hazard data required for this study. Floods having recurrence intervals <br />of 10, 50, 100, and 500 years have been selected as having special sig- <br />nificance for flood plain management and for flood insurance premium <br />rates. The analyses reported here reflect current conditions in the <br />watersheds of the streams. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for floods of the selected recurrence inter- <br />vals for each stream studied in detail in the community. The analyses <br />were based on rainfall-runoff computations and statistical analysis <br />of stage and discharge records by the log-Pearson Type III method <br />(Reference 2), with modifications for the standard project and other <br />rare flood events. The U.S. Army Corps of Engineers' standard <br />project rainfall and flood concept and the unit hydrograph method of <br />analysis were used in making rainfall-runoff computations. Snowmelt <br />flood data were derived from analysis of snowmelt flow records for <br />the Yampa River. <br /> <br />The unit hydrograph for the Yarnpa River was derived by utilizing an <br />S-graph for the Animas River and its tributaries at Durango. The <br />general mountain S-graph for Arizona, Colorado, Utah, and Wyoming was <br />used to produce unit hydrographs for the tributary creeks. <br /> <br />As noted earlier, general rainstorms that generate major floods in <br />western Colorado usually occur during September and October. On the <br />basis of available precipitation records, a standard project storm <br />for the Yampa River Basin was developed using a flood-producing storm <br />that occurred in September 1970 in the Four Corners Area (the area <br />around the intersection of Arizona, New Mexico, Utah, and Colorado) <br />as a model. The Steamboat Springs regional 24-hour probable maximum <br />precipitation is very similar to that of the San Juan Mountains and <br />the Grand Mesa area (Reference 3). Therefore, a standard project <br />storm centered over the Grand Mesa area east of Grand Junction was <br /> <br />17 <br />