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<br />of plains streams. Also, when the separate relations were combined by the <br />formul a, <br /> <br />P (Composite) = P (Snowmelt) + P (Rainfall) - P (Snowmelt x Rainfall), <br /> <br />where P = probability of occurrence, <br /> <br />the resulting composite relation fitted the larger flood peaks much better than <br />did the relation based on the annual flood array. Although much additional <br />detailed study is required, this technique appeared to yield acceptable results <br />for gaged sites, but the question of flood-information transfer to ungaged sites <br />was still unanswered. <br /> <br />.' <br /> <br />After an extensive literature search and tests of various methods, an interim <br />procedure was adopted which divided foothill flood areas into three subareas. The <br />basin area above a specified elevation was considered to be in the mountain flood <br />region, the area below another specified elevation to be in the plains or plateau <br />flood regions, and the area between the two elevations to be in a transition zone. <br />Although the method represents an improvement over earlier methods, it is <br />subjective, being iargely unverified because of the lack of flood records for <br />streams draining areas of intermediate elevation. <br /> <br />Following the publication of the report by McCain and Jarrett (1976), a <br />project proposal was circulated to several local, State, and Federal agencies for <br />their comments and expressions of interest in participating in a study of flood <br />hydrology of foothill streams. On July 31, 1976, the need for a study of this <br />type was dramatically reinforced by the occurrence of the devastating floods in <br />Larimer and Weld Counties. <br /> <br />AVAILABLE HYDROLOGIC DATA <br /> <br />Streamflow and precipitation data are available for many locations within <br />foothill areas of Colorado. Tabulations of existing information are given in the <br />following sections and site locations are shown on plate 1. <br /> <br />Streamflow Data <br /> <br />Active gaging stations.--During the 1978 water year, 81 gaging stations being <br />operated by several agencies provided streamflow data useful in attaining project <br />objectives. Of the 81 stations, 15 are located in the South Platte River basin, <br />19 in the Arkansas River basin, and 47 in the Colorado River basin. Only those <br />stations with 20 or more years of usable record are listed for the Colorado River <br />basin because of the limited scope of the project in that area. Information about <br />each active gaging station is listed in table 1 and the locations of the sites are <br />shown on piate 1. <br /> <br />Discontinued gaging stations.--A I isting of 43 discontinued gaging stations <br />that may provide pertinent streamflow data for the research phase of the project <br />is shown in table 2; locations are shown on plate 1. Several discontinued <br />stations ,will be reactivated as project stations where rainfall-runoff data will <br />be collected. Several others will be operated as crest-stage stations to extend <br />the annual flood record at the sites. <br /> <br />4 <br />