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<br />DEPLETION OF SURFACE WATER SUPPLIES
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<br />It is therefore evident that large reservoirs must be provided for
<br />. cyclic storage as well as se~sonal regulatio~ in order tJ;tat full use ma;y
<br />: be made of those waters of Colorado RIver to whICh Colorado IS
<br />. entitled.
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<br />ORIGIN OF SUPPLY
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<br />. While very long periods of carryover will be necessary in some reser-
<br />:voirs for other purposes, it is unlikely that more than lO years of carry-
<br />over would be justified to satisfy future demands for water in Colorado.
<br />The lO-year period ending September 30, 1950, was reasonably typical
<br />and more records of runoff were available for these years than for any.
<br />'earlier period; hence, it has been used as a basis for comparison.
<br />; The quantity of water originating in the Colorado River Basin
<br />within Colorado and which passed out of Colorado during these 10
<br />:years averaged 9,347,000 acre-feet per year. The total drainage area
<br />:includes 38,932 square miles in Colorado, so that the average runoff'
<br />:was 240 acre-feet pel' year pel' square mile. A little more than 19 per-
<br />;Cent of this total was contributed by Yampa River, White River, and
<br />.certain smaller tributaries of Green River; the contribution from the
<br />main stem of Colorado River was 31.7 percent, Gunnison Riveradded
<br />21.4 percent, and Dolores River only 7.5 percent; and San Juan River
<br />contributed the balance of 20.1 percent.
<br />: Yampa River and small streams directly tributary to Green River
<br />drain the northwesterly portion of Colorado. The combined drain-
<br />iJ,ge area includes 6,820 square miles in Colorado and 2,000 square
<br />miles in Wyoming. The average discharge of Yampa River during
<br />the lO-year period ending September 30, 1950, was about 1,500,000
<br />acre-feet, of which about 1,290,000 acre-feet originated in Colorado.
<br />The latter quantity is equivalent to 189 acre-feet pel' square mile.
<br />White River drains an area in Colorado just south of Yampa River,.
<br />containing 3,863 square miles, but its headwaters do not extend back
<br />to the Continental Divide. The average runoff at the westerly
<br />boundary of the State for the same lO-year period was about 510,000
<br />!tcre-feet per year, equivalent to 132 acre-feet per square mile. .
<br />: Next in order from north to south is the drainage basin ofthe main
<br />stem of Colorado RiVer. The total drainage area, excluding the.
<br />Gunnison River Basin, is 10,180 square miles, of which 8,055 square
<br />miles are above the point of diversion to lands in the vicinity of
<br />~rand Junction. The average runoff at the State line for the 10-year
<br />period ending September 30, 1950, was about 2,960;000 acre-feet per
<br />year (exclusive of the contribution from Gunnison River), equivalent
<br />to 291 acre-feet per square mile.
<br />: Gunnison River actually enters Colorado River at Grand Junction
<br />but may properly be treated separately because little use is now, or
<br />is expected to be, made in Colorado of water diverted below the'
<br /><jonfluence of these rivers. Gunnison River drains 8,020 square miles
<br />l!>nd has its origin along the Continental Divide opposite the head-
<br />waters of Arkansas River. The average runoff for the 10 years ending
<br />September 30, 1950, was 2,007,000 acre-feet, equivalent to 250 acre-
<br />fj:letper square mile.
<br />Dolores River drains that portion of Colorado lying west of the
<br />Gunnison River Basin, and north of the San Juan River Basin, The
<br />drainage area of Dolores River includes 4,160 square miles in Colorado.
<br />'the runoff originating in Colorado during the lO-year period ending
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