WSP05034

• File Number: 8273.100
• Description: Colorado River Basin Salinity Control - Federal Agencies - Bureau of Reclamation
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 7/1/1987
• Author: BOR
• Title: Monitoring and Evaluation of Salinity Control Projects - Interim Guide for the Colorado River Basin Salinity Control Program
• Water Supply Pro - Doc Type: Report/Study

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necessary, the ponding test method is recommended for
use in measuring ditch seepage. When onfarm earthem
ditches are lined or replaced by pipe, seepage losses may
be estimated by assuming conveyance losses of 05 percent
per 1,000 linear feet for pipeline and 1 percent per 1,000
linear feet for concrete lining,

should be made before planting and following harvest 01' at
the beginning and end of the growing season if the crop is
a perennial Soil moisture-holding capacity has been
generalized by soil texture by the U ,S. Department of
Agriculture and is available in soil survey reports for most
areas,

Onfarm Reduction of Deep Percolation
Onfarm deep percolation cannot be directly measured
under field conditions. However, it may be calculated
from irrigation delivery, drain flow, and irrigation,water
management data. The evaluation process requires data
on total inflow, outflow, crop evapotranspiration (ET), and
soil moisture,

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Because outflow from large areas is not well correlated
with irrigation delivery, obtaining reliable estimates of
deep percolation is possible only at the farm or field level.
Therefore, farm or field monitoring sites should be estab-
lished on a representative sampling basis, and results
should be extrapolated to reflect conditions for the larger
area. Irrigation should be monitored throughout the
season. Soils tend to be more permeable after the winter
season and following cultivation, therefore, it is important
, that first irrigations following these events be monitored.

At the end nf tile irrigation season, water budgets should
be summarized by monitoring site and irrigation event.
The accumulation of irrigation events will become the an-
nual water budget for each site. The annual water budgets
for these sites can be classified according to soil type,
crop, method of irrigation, and existence of sa1inity-control
features. These characteristics are used to extrapolate
deep percolation estimates to unmonitored areas,

Total inflow is the sUm of natural precipitation on the field
and irrigation deliveries to the field. Precipitation can be
estimated using data from local climatological stations.
Distribution system inflow measurements usually are
available. However, the precision and frequency of
measurement progressively decreases from the canal diver-
sion to the lateral, sublateral, farm turnout, and the field.
Primary outflows other than deep percolation are taiIwater
runoff and drift loss. Tailwater runoff should be measured
directly, Drift loss can be estimated as a percentage of
delivery,

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Off-farm Wildlife Habitat

Implementing salinity control projects may impact wildlife
habitat through: (1) disturbance or elimination due to con-
struction, (2) changes in ground-water or surface-water
regime, and (3) changes in salinity levels in the root zones,
For off-farm projects, monitoring of existing vegetation
and establishment of experimental vegetation plots can
provide data to assess impacts and management options.

To monitor existing vegetation, aerial imagery obtained for
the years preceding, during, and after project implementa-
tion can be used to determine changes in the extent of
vegetation types within the project area. False-color
infrared photography is usually preferred, because the

The difference between inflow and outflow is given as the
volume of water evaporating from the surface plus water
infIltrating into the soil. Deep percOlation is the amount
of infiltration in excess of the soil-moisture deficit, which is
defined as the water needed to bring soil moisture content
up to field capacity. The soil-moisture deficit can be deter-
mined by measuring soil moisture immediately before and
comparing it to the field capacity or it can be estimated by
calculating the crop ET since the previous irrigation. ET
is derived from climatological data collected and available
in many locations. If crop ET is used to determine the ~oil
moisture deficit, several field measurements of actual soil
moisture should be made during the irrigation season to
verify the calculations. Soil-moisture measurements

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