WSP06126

• 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 Animas River Hydrology Analysis - Historic and Virgin Flow Conditions - June 1987
• Water Supply Pro - Doc Type: Report/Study

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0011S97

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PART VI. IllSTORIC STREAMFLOW DEPLETIONS

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The depletion to the Animas River resulting from historic irrigation prac-

tices was estimated by analyzing the historic ditch diversions, irrigated acreage,

and the estimated irrigation requirement for the crops grown in the area. For

the purposes of this analysis, depletion is defined as the reduction in streamflow

that occurs as a result of inigation practices, taking into account stream diver-

sions, consumptive use of water, and return flows. Consumptive use is that

portion of the irrigation water that is consumed through evaporation or crop

evapotranspiration.

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Crop Ccmsumptive Use

Based on field inspections of the area and on interviews with the Division

Engineer and Water Commissioner, it was determined that the principal crops

grown in the Animas River basin, excluding the Florida River and Florida Mesa

area, include pasture grass and alfalfa. The consumptive use of irrigation water

was estimated through use of the modified Blaney-Criddle procedure, calibrated

to the area through use of data obtained from lysimeter studies at the Navajo

Indian hrigation Project (NIIP). Monthly precipitation data were obtained from

the Durango weather station (elev. 6550), where the mean annual precipitation

is 18.61 inches. Average monthly precipitation and mean monthly temperatures

for the irrigation season are summarized as follows:

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Precipitation (in.)
Mean Temperature

APR
1.20
45.1

MAY

1.02
52.9

JUN
0.63
60.2

JUL
1. 73
67.5

AUG

2.38
66.0

SEP

1.58
58.6

OCT
2.04
48.8

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A portion of the precipitation occUIring during the irrigation season was

estimated to be effective in reducing irrigation requirements, based on use

of the modified Blaney-Criddle procedure for calculating effective precipitation.

Using these data, the average annual potential consumptive use of irrigation

water was estimated to be 2.10 acre-feet per acre. A summary of potential

consumptive use for the 1951 through 1980 study period is shown in Table 2.

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