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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sites that have low deep percolation, about 15% to 20% of ETa, e.g.
13, and 16 tend to be under-irrigated during the second through
fourth irrigation events (refer to individual irrigation data in
Appendix D). Surge sites such as 39 and 41 also tend to be under-
irrigated. Some sites with fairly high overall deep percolation
for the season were under-irrigated at times. site 33 with
sprinkler had low deep percolation and was under-irrigated most of
the season.

g. Infiltration Estimates:

Figure 2 shows the application infiltration rates (by irrigation
event) for the various sites monitored in 1991. The infiltration
rates were extrapolated from the individual site summary data
provided in Appendix D. For each irrigation, the infiltrated depth
was divided by the number of hours per set to determine an
application infiltration rate in inches per hour. From these data,
the average infiltration rates for the different soils monitored in
the Grand Valley were determined (surface irrigated sites only) and
provided below:

soil Type

Average
Infiltration Rates
(in/hr)

Billings silty clay loam
Fruita clay loam
Genola clay loam
Hanksville silty clay loam
Mesa clay loam
Ravola clay loam/fine sandy loam

0.16
0.27
0.23
0.21
0.52
0.18

In the above calculation, the wetted perimeter was not taken into
consideration and the data shown is based on 100% wetted acreage.
In the Grand Valley, it can be safely assumed that with furrow
irrigation the wetted perimeter is actually less then 50%. This
means that the application infiltration rates provided above may be
doubled for sites with every row irrigation to get an estimate of
average soil intake rate (a conservative estimate based upon having
only half, 50%, of the soil surface actually wetted and the
application infiltration rate based upon total, 100%, wetted
surface area). Alternate row irrigation is also fairly common in
the Valley and with this method the wetted perimeter may be assumed
to be about 25%. The application infiltration rates provided above
may be multiplied by a factor of four when dealing with alternate
row irrigation in order to estimate soil intake rate.

Infiltration rate for the first irrigation is generally higher for
annual row crops, but not necessarily so for perennial crops

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