WSP01414

• File Number: 8449.918
• Description: South Platte Projects
• State: CO
• Basin: South Platte
• Date: 8/1/1982
• Author: CWCB
• Title: South Platte River Basin Assessment Report
• Water Supply Pro - Doc Type: Publication

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Big Thompson River - This river flows into the South Platte River

approximately 3 miles south of laSalle, Colorado. It drains an area

of about 830 square miles, 70 percent of which is mountainous. The

Little Thompson River is its principal tributary. Mean annual runoff

for the Big Thompson at its mouth near laSalle, Colorado, for the 1928

through 1979 water year period was nearly 52,900 acre-feet

(Table 8). The Big Thompson River gage at laSalle is located

downstream of many water diversion structures in the sub-basin.

Consequently, the mean annual runoff at this point in the sub-basin is

considerably smaller than for the St. Vrain Creek at Platteville. II.

significant shift in mean annual flows from those recorded between the

1928 through 1952 water year period (36,600 acre-feet) and those

recorded between the 1953 through 1978 water year period (68,000 acre-

feet), is probably because of increased transbasin imports from the

Colorado-Big Thompson Project beginning about 1953.

Cache 18 poudre River - This is the largest of the mountain

tributaries. It drains an area of about 1,900 square miles, which

varies in elevation from over 13,000 feet at the Continental Divide to

4,600 feet in the plains where it joins the South Platte River near

Greeley, Colorado (Figure 1). Nearly all of the native surface water

supply of the river is derived from melting snowpack in the

mountains. Mean annual runoff at the gage located near Greeley was

73,200 acre-feet for the 1928 through 1979 water year period

(Table 8). The mean annual runoff of the Cache la poudre River near

Greeley is also smaller than would be expected for its drainage area

because of many water diversions and consumptive use upstream of the

gage. The flow of the Cache la Poudre near its mouth has increased

appreciably since 1952, from an average of 52,500 acre-feet per year

during the 1928 through 1952 water year period to 92,500 acre-feet

during the 1953 through 1979 water year period (Table 8). This shift

is due largely to increased transbasin imports of the Colorado-Big

Thompson Project during the latter period.

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