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<br />Office Report <br /> <br />On <br /> <br />The September 1970 Floods <br />in the <br /> <br />Upper Colorado River Basin, Four Corners Area <br /> <br />Chapter I - Introduction <br /> <br />1. Authori ty for and content of report. - This report covers the <br />rainfloods that occurred in the San Juan, Dolores and Uncompahgre <br />River Basins of the Colorado River Watershed above Lee Ferry during <br />September 1970. It was prepared pursuant to the provisions of <br />EM 500-1-1 and authority provided by 2nd Ind., ENGCW-OE 2 November <br />1970 (basic letter: SPKED-P 14 October 1970, Subject: "September <br />1970 Flood, Upper Colorado Basin, Post. Flood Report.") The report <br />presents information on precipitation, runoff, flood damage sus- <br />tained, and the effects of existing and authorized improvements <br />and structures on the floodwaters during the period September 4 <br />thru 15, 1970. Also included is infonnation on flood emergency <br />operations and rehabilitation work carried out by the Corps of <br />Engineers under continuing authorities. <br /> <br /> <br />2. Plate III shows the stream system of the area affected by the <br />flood, existing improvements which were instrumental in providing <br />flood control benefits, and the areas inundated during the floods. <br /> <br />3. Descriptive data. - Descriptive physiographic, climatological, <br />and economic data relative to the Upper Colorado Region and its <br />various subregionfJ ~e contained in the Upper Colorado Region <br />framework report.la) For purposes of this report, only the Upper <br />Main Stem and San Juan-Colorado Subregions are briefly described. <br /> <br />a. !!I:!per Main stem Subre~. - The Upper Main stem Subregion <br />includes the area drained by tliElCOlorado River and its tributaries <br />above the mouth of the Green River. The subregion includes 26,192 <br />square miles, which is about 23 percent of the area within the <br />Upper Colorado Region. About 85 percent of the subregion is in <br />Colorado and the remainder in Utah. <br /> <br />~. '. <br /> <br />The Colorado River within the Upper Main stem Subregion is <br />joined by numerous tributaries. The larger of these, all heading <br />in western Colorado, are Roaring Fork, Gunnison River, and Dolores <br />River. <br /> <br />(a) Refer to Bibliography item k. <br /> <br />1 <br />