WSP08978

• File Number: 8276.110
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 10/1/1980
• Title: Monitoring Plan: Stage One Development - Grand Valley Unit
• Water Supply Pro - Doc Type: Report/Study

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W Table 5 depicts tailwater runoff for the predominant soils under row

'-
c:. crop production as determined by ARS.
c:.

Soil
Billings
Fruita
Hinman
Ravola
Mack
Weighted

Number
of
sites
2
2
2
9
1

TABLE 5
Tailwater runoff in Grand
1975
Number
of irri-
gations
16
15
19
58
7

Valley

Mean

Mean frac-
tion of
runoff
0.321
.141
.255
.400
.319
.327

Number
of
sites
3
2
1
5

1976
Number
of irri-
gations
50
29
9
84

Mean frac-
t ion 0 f
runoff
0.288
.123
.220
.365

.296

Deep percolation

The Agricultural Research Service (ARS, 1977) undertook studies to

measure deep percolation in Grand Valley by using vacuum extractor and

chloride ratio techniques. These methods were checked by correlation with

on-farm annual water balance. Vacuum extractors were instaUed on 6 fields

in Grand Valley during the years 1974 to 1976; one of these fields is in the

Reed Wash study area. Results show deep percolation ranginll from 0.6 to 4.1

inches and averaging 2.2 inches. The highest value measured in 1976 measure-

ments was 3.09 inches. The chloride ratio technique showed an irrigation

season rate for deep percolation of 14.2 inches.

In studying the annual water balance as computed by ARS in 1977, the

data from the vacuum extractors appear low and the chloride ratio values

appear high. The correct deep percolation is believed to be about 5.42

inches or 8 percent of effective farm delivery (5.2 acre-feet per acre),

This corresponds to a leaching percentage (ET x 100) of about 13 percent or

nearly 25,000 acre-feet per season for the entire Grand VaHey; this was

derived as follows:

18