WSP00392

• File Number: 8276.150
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1992
• Title: 1991 Annual Report: Grand Valley Salinity Control Project Monitoring and Evaluation Program
• Water Supply Pro - Doc Type: Annual Report

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b. summary of Field Evaluations

The following is a brief summary of the 1991 monitoring field
evaluations:

1. Overuse of water is prevalent throughout the Grand Valley
because of abundant supply of inexpensive irrigation water.
Most producers are not concerned about irrigation water
management (IWM). Very few farmers practice a high degree
of IWM.

2. Poor irrigation efficiencies at some sites are due to over
irrigation, i.e. fields are irrigated too soon and too
long. All of the monitored surface irrigation systems are
capable of irrigating at 50% or greater efficiency with
proper management.

3. During pre-irrigation of annual crops and first irrigation
of perennial crops for stand establishment (e.g. alfalfa),
many farmers in the Grand Valley apply a large amount of
water to "black over" the soil so that seeds have adequate
moisture for germination and establishment. The
elimination of this practice would reduce deep percolation
substantially (see #5). However, farmer accepted
alternative cultural or management practice would be needed
to ensure stand establishment.

4. Excess pre-irrigation, or the first irrigation, is the
biggest contributor to seasonal deep percolation losses.
This is directly related to high infiltration rate during
these irrigations, which subsequently decreases after the
first irrigation. This is supported by the "advance time"
data obtained from some of the monitored sites. When
infiltration is high, it takes longer for water to reach
the end of the furrow. The "advance time" is less during
later irrigations because of the decrease in infiltration
rate due to sealing of the soil surface.

5. The 1991 data for surface irrigated monitored sites
indicate that, on the average, about 30% of the seasonal
deep percolation losses occurred during the first
irrigation event and about 45% by the end of second
irrigation. For annual crops (small grain and corn), 41%
of deep percolation occurred during the first irrigation
and about 59% by the completion of the second irrigation.

6. The 1991 data also show that surface irrigated perennial
crop sites had slightly more deep percolation than annual
crops. Normally, the reverse is true. Deep percolation
for perennial crops remained fairly uniform throughout the

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