WSP03457

• File Number: 8276.100
• Description: Grand Valley Unit - Colorado River Basin Salinity Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1992
• Title: Grand Valley Salinity Project Monitoring and Evaluation Program -- 1990 Annual Report
• Water Supply Pro - Doc Type: Annual Report

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In 1990, the water budget program was updated to more accurately
estimate deep percolation for annual crops. In the past, deep
percolation for the first irrigation and or pre-irrigation was
considered to be any amount that was in excess of that required to
fill up the first foot of so i I; the fu II root prof i I e was not taken
into account. With this method, deep percolation estimates were
higher than what they should be. The updated program takes ful I
rooting profi Ie into consideration. All previous data from 1986 to
1989 have been re-processed using the updated program to get a better
estimate of deep percolation, soi I moisture and ETa etc.

ADDI ication Efficiency:

Appl ication efficiency is calculated as inflow minus outflow minus the
deep percolation divided by inflow, expressed as a percentage. As a
result, when there is under-irrigation, the application efficiency
wi II be very high and may not necessari Iy be an indication of good
i rr i gat ion. The seasona I app I i cat i on for a II sites (surface and
sprinkler) is provided in Table 2. The table shows appl ication
efficiency to be 39% for surface irrigation sites (22 sites) and 64%
for sprinklers (3 sites). When annual and perennial crops are taken
into account, the eff i c i ency is 33 and 53% respect i ve I y. App I i cat i on
efficiency for individual irrigation events are shown under site
summar i es in Append i x B.

The overall seasonal irrigation appl ication efficiency in 1990 was
42%, less than 1987, 1988, and 1989 <Table 4). This is considerably
better than 1985, which had an efficiency of 30%. A comparison of
irrigation monitoring data from 1985 to 1989 shows that during this
period irrigation efficiency increased progressively from year to year
wh i ch resu I ted in I ess water app I i cat ion, reduced runoff and deep
percolation <Table 4).

From 1985 to 1989, the average surface irrigation efficiencies were
28%, 39%, 41%, 46% and 46% respectively. For sprinkler/microspray
irrigation, the efficiencies were 52% for 1985, 61% in 1986, 80% in
1987, 70% in 1988, 79% in 1989 and 64% in 1990.

Iri-the past, the overall seasonal irrigation application efficiency
was computed erroneously; it was calculated as the average of all
individual site irrigation efficiencies. In 1989 and 1990, the
overal I average efficiency was calculated using the seasonal
irrigation efficiency formula shown on bottom of Table 2 and defined
on page 6. This formula is also used for calculating individual
irrigation efficiency as was done in the past. The overall irrigation
efficiency for the past five years has been recalculated and provided
in Table 4. These values are sl ightly lower than previously reported.

Of the 22 surface irrigated sites monitored in 1990, only five had
irrigation efficiency 50% or more, considerably less than 1989 and
1988 where half the sites had more than 50% efficiency. Six producers

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