WSP04853

• File Number: 8200.750
• Description: San Juan River General
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 6/1/1987
• Author: Wheeler and Assoc
• Title: Documentation for La Plata River Hydrology Analysis - Historic and Virgin Flow Conditions - June 1986
• Water Supply Pro - Doc Type: Report/Study

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were obtained and summarized. Diversion records were not available throughout

the study period for several of the small or infrequently used ditches. The com-

pleted summaries of the available ditch diversion records for the La Plata River

basin are presented in Appendix B of this report. For the purpose of analyzing

ditch diversions and irrigation depletions, a summation of the diversion records

in each of the three major irrigation areas was prepared, as shown in Tables

2 through 4. These areas are the La Plata River mainstem, the Cherry Creek

basin, and the Hay Gulch basin. A summation of all ditch diversions in the La

Plata River basin is presented in Table 5. As shown in Table 5, annual diversions

varied widely from year to year, reflecting the availability of water for irrigation.

A low of 6,300 acre-feet was diverted in 1977 and a high of 37,600 acre-feet

was diverted in 1965. The average annual diversion was 21,400 acre-feet.

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The summation of ditch diversions in Table 5 implicitly includes reuse

of return flows within the La Plata basin. As return flows accrue to the stream

from irrigation by upstream water users, these return flows become a part of

the streamflow that is available for downstream water users. During periods

of low streamflow in the La Plata River, most of the natural flow is successively

used for ilTigation in Colorado two or three times.

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Pioneer and Enterprise Ditches

The Pioneer and Enterprise ditches divert water from the La Plata River

at a location about one mile north of the Colorado-New Mexico state line. To

the extent that the ditches deliver water for irrigation across the state line

in New Mexico, the ditch diversions constitute a bypass of water around the

USGS gaging station at the state line. Because of the unique locations of the

Pioneer and Enterprise ditches near the state line, complete diversion records

for the 1951 through 1980 study period are not available. Diversion records

for the Pioneer Ditch have been maintained only for the period beginning in

1973 and the records do not indicate how much of the water was used in Colorado.

For the Enterprise Ditch, records for the entire study period are available for

the portion of the water used in Colorado, but records for the New Mexico portion

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