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<br />The first step in this study task is to identify records of gaging stations <br />affected by floods in foothill areas. Available records for gaging stations in <br />the project area are being studied and a list is being prepared of those stations <br />having foothill-flood characteristics. In addition to annual flood arrays, which <br />are already accessible, annual arrays of snowmelt and rainfall floods are being <br />developed for each station. These annual flood arrays will provide the required <br />data base for statistical research. <br /> <br />Statistical research will consist of testing probability distributions for <br />adequacy in fitting snowmelt, rainfall, and combined flood arrays and <br />investigating statistical techniques for combining snowmelt, rainfall, and <br />combined flood-frequency relations into a composite relation. An evaluation of <br />relative accuracy between the individual and composite flood-frequency relations <br />will be made with particular emphasis placed on fitting of large peak discharges. <br /> <br />Flood-Information Transfer Techniques <br /> <br />Standard regression techniques for estimating flood characteristics at <br />ungaged sites from gaging-station data yield unusable results for foothill basins. <br />Total basin area has been found to be an inadequate indicator of flood potential <br />and there is no verified method for using other basin and climatic parameters. <br />The report by McCain and Jarrett (1976) contains an interim procedure for <br />computing flood characteristics at ungaged sites in foothill areas of Colorado, <br />but the method is unverified and yields questionable results for small basins near <br />the transition zone. Also, the decision to set the lower limit of the Mountain <br />Region at 7,500 or 9,000 feet was largely based on subjective information because <br />of the lack of flood data for basins draining intermediate elevations along the <br />foothills. A problem of equal importance is that of using synthetic hydrologic <br />models where design rainfalls are placed over entire foothill basins to generate <br />flood hydrographs. If total basin area yields inadequate results in regression <br />analysis, then it is questionable that the total area should be used in modeling. <br /> <br />This research effort is based on the premise that certain physical and <br />climatic features of foothill basins have an identifiable relationship with type <br />and, possibly, magnitude of flooding that produced the features. Therefore, a <br />study of selected physical features should provide valuable evidence relating to <br />areal extent of rainfall flooding and should lead to improvement in flood- <br />information transfer techniques. Several physical features of foothill basins <br />being studied are: <br /> <br />1. <br />streams <br />vat ion, <br />tion. <br /> <br />Measurement and analysis of hydraul ic and geometric properties of main- <br />and their tributaries; also other basin characteristics, such as mean ele- <br />mean annual precipitation, soil types, forest cover, aspect, and urbaniza- <br /> <br />2. Geomorphic studies across flood plains, along outside valley limits, and <br />on alluvial fans where steep tributaries flow onto flatter valley floors. <br /> <br />3. Studies of the feasibil ity of using botanic evidence of floods, such as <br />tree scars, vegetation modification, and lichen-growth rates. <br /> <br />18 <br />