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<br />~. <br /> <br />i <br />, . <br /> <br />LEfTIIANlJ CREEK HYDROLOGY <br />BOULDER CDUNTY, COLORADO <br /> <br />1. GENERAL. This report is the hydrologic portion of a special study <br /> <br />that is being"made for the &olorado Water Conservation Board and Boulder '_ <br /> <br />County. Discharges for the lO~, 50-, 100-, and 500-year floods are given <br />c <br /> <br />for Lefthand Creek from Ward, ~olorado, to the mouth. <br /> <br />A map of the Left- <br /> <br />, <: <br /> <br />7' <br /> <br />hand Creek basin is shown on attachment 1. <br /> <br />2. BASIN DESCRIPTION. Lefthand Creek, a right bank tributary to St. Vrain <br /> <br />Creek, has its,source in the Rocky Mountains southwest of Longmon~,'Colorado. <br /> <br />Draining approximately 56 square miles of mountain area and 12 square miles <br /> <br />of plains area, Lef~hand Creek enters St. Vrain Creek south of Longmont. <br /> <br />James Creek, a 19 sGuare mile mountain stream, is the major Lefthand Creek <br /> <br />tributary_ The plaiJ.s basin is long and narrow with no significant 'cribu- <br /> <br />taries. Structures )n Lefthand Creek consist of 12 ditch diversions. <br /> <br />Elevations in the ba3in range from 4,920 to 11,640 feet above mean sea <br /> <br />level. <br /> <br />3. PRELIMINARY DISC lARGE PROBABILITY AT GAGE SITES. <br /> <br />a. General. Tw) former gaging stations were .located on Lefthand <br /> <br />Creek. One was in t.1e foothills north of Boulder, and the other was. down-' <br /> <br />stream from the U.S. Highway 287 bridge, approximately one mile above the ,..' <br /> <br />mouth. A preliminarf discharge probability analysis was made at the gage <br /> <br />sites. The analytic,] methods presented in Bulletin No. 17 published by <br /> <br />the Water Resources :ouncil ~WRC) were used for each analysis. The <br /> <br />results of these stulies arc discussed in the following paragraphs. <br /> <br />_.._'----'--~....._,_.. <br /> <br />: ':":~.~.;. _~ .....~~':::__A~.~:~'::_ <br /> <br />~..h;~\. <br />~,-, <br />m~k-:. <br />~~: <br />....,~ <br /> <br />~~ <br />>._~,' . . <br /> <br />~.," <br /> <br />'--=-- <br /> <br />,.' <br />'w."_, <br /> <br />..".... <br /> <br />"::';:,~:, <br /> <br /> <br />~:. ~~.~~ <br />K.;o.~, <br />"......... <br /> <br />!?i:~': <br /> <br />~.; ." '. <br /> <br />,;".,. <br />..,.-. <br /> <br />'i...i.',., <br /> <br />....F.... <br />..--.... <br />t:::.~~:' <br /> <br />'r'".'" <br />~\. ":'. .:~ ," <br />~'.'.'.'.' <br /> <br />~.,:..~". . <br />.: ..," <br />~':;';:;.o.'" <br /> <br />'-';"".,' <br />