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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precipitation) is important because it represents that volume of water

which will not be available to the downstream users. The total net

consumptive use was estimated for the 1978 crop mix. Using an average net

consumptive use value of 1.15 acre-feet per acre for irrigating

793,000 acres (Table 4), the total net consumptive use is 914,000 acre-feet

of water for the 1978 crop mix (Table 7). When compared to the mean annual

irrigation diversions of 1.4 million acre-feet annually for the 1947-

through-1970 period, this consumptive use total compared well to an assumed

net consumptive use value of 67 percent of applied water for irrigated

agriculture (U.S. Department of Agriculture Soil Conservation Service,

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1970).

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The volume of water diverted for irrigation relative to return flows also

is related to conveyance losses and farm efficiency. Existing surface

water diversions in the basin are basically gravity systems that require

canals and laterals for conveyance. These canals and laterals are unlined

and conveyance losses vary seasonally, with the largest losses occurring

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during the summer months. Moreover, for storage projects, conveyance

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losses may occur in cases where natural stream channels are used to

transport water from an impoundment to a point of diversion. An overall

conveyance loss factor of 67 percent was assumed for proposed projects that

developed agricultural water utilizing existing unlined canals. This

compares well to estimated conveyance losses for the Bijou and Riverside

Irrigation District canal systems (Bob Samples, personal communication,

Colorado State Engineer's Office, Water Division 1, June 1981).

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The municipalities in the study area are located primarily along the Front

Range of the Rocky Mountains. As was previously discussed, these cities

and towns have been growing at phenomenal rates in recent years, and this

growth is expected to continue. Potential sources of water supply for new

urban growth may include increased transbasin imports, greater efficiency

or reuse of existing supplies, development of nontributary ground water,

and conversion of water from agricultural to municipal use.

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