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. " . , " ~ " . " . " . o o . . " o ------j , , 1M o , I --+---- o . . , , , " ~-~- W .. tf} ;; :.~\\ <'3 <;... , . ..--- '''J~ . " o z < u " m ~ ~ w ~ . . o 'L ^ w ~ < " ~ .- ~ w > ~ , I , I , , o I ",""'l' o :i< ~., 00 '" '" , , , I :::; d . . , 1 . < . w '0 Z < ~ ~ z ~ < m , 1:;!rZ t-t-W- a:<2::~ IZre::-m , o ~ . o , I , '4--, ~II ,i!' : " (i ,! 'l.. r-L:::":(' _'\1-__ ~ < "", 0-' "'_ . > ^ o . < ~Z",m . < ., W D. t!~~- Y " "'{ /'-"-"'J __~_;~'W>J ------ - . ~ , W > ~ o . , , , , , 'W"'Y'l~ o o o . o . o " . . " 2.3 Ba~in Characteristics The Colorado River ha:> its origination upstream of Lake Granby in north central Colorado_ The headwaters originate in the Continental Divide to the north and east. in the Sawatch Range to the southeast. in the Elk and West Elk Mountain~ to the south and in the northern and western slopes of the San Juan Mounlains. . ~ ~ u ~ ~ m ! ~ 8 o u ~ o z o - ~ g ~ ~. ~ ~ Most drainages in western Colorado are either direct or indirect tributaries of the Colorado River. This report, Volume 4, focuses on the Colorado River mainstem. The other three volumes uflhe study address three major tributary streams. Volumes I and 2 provide infonnation for the Yampa River and the White River, which are tributaries of the Green River. The Green River joins the Colorado River mainsrem dovmstream of the study reach in Utah. Volume 3 provides infonnarion for the Gunnison River, which joins the Colorado River at Orand Junction, within the study reach. There are other western Colorado streams, not included in this study, which join the Colomdo River in Utah, downstream of the study reach for Volume 4. . . o The watershed area at the downstream limit of the study near the Utah statcHne is approximately 17,843 square miles. Approximately half of that watershed area is in the Gunnison River watershed. The elevation within the watershed ranges from more than 14,000 feet above Mean Sea Level at the headwaters to 4330 feet at the stateHne. The average slope within the study reach is approximately 11 feet per mile, with a maximum of 16 feet per mile in the upper reach and a minimum of 7 fcet per mile near the suteHne. , I The climate in the Colorado River basin is directly influenced by the varying topography. lbe area w~"lofPalisade to the ~"tateline is classified as arid to semi-arid and is characterized by moderate temperatures, low precipitation, low humidity, and frequent \,..ind. The higher mesa areas are subject to more moderate to heavy precipitation. The mowrtains to the north, east and south are subject to lower temperatures and greater precipitation. The primary sources of moisture are air masses originating in the Pacific <kean from <ktober through April, and airmasscs from the Gulf of Me>:ico during the late spring and summer. Normal annual precipitation is less than lOinches in the Grand Valley near Orand Junction, from 10 to 20 inches in thc higher mcsas, and more than 40 inches in the mountain regions. <kcurrence of precipitations is highly variable, with a large part of the total concentrated in a few months. Much of the annual precipitation occurs as snow from October to April. Rainfall can occur as convective-type thunderstorms during the late spring and summer months generally over the lower elevations of the basin, making August, September and October nonnally the wenest months of the year. The Colorado River basin, from its headwaters to the Utah stateline. is shown in Figure J. is 2.4 Summarv of Draina2e Areas Thc drainagc areas for sclected b)'drologic points were determined through published r-':pOrlS, planimetering, and established values at USGS gage locations. The results of the planimctering wcre compared to the values in the published reports and at the USGS gages Thedrainagearea, at the selc<:tcd hydrologic points are shov."ll in Table 1_ . ffi ,< 5