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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planned and (2) that the overall result is a significant
decrease in dissolved-solids load.

Verifying the function of project features needs to be
tailored to the specific feature being studied. Interception
of a point source can be verified by monitoring water
levels in observation wells or discharge from a spring. The
effectiveness of canal lining can be verified by observing a
decrease in the water-table levels downgradient from the
canal. Water table declines also can be used to verify
reductions in onfarm seepage or deep percolation. .If
several of these features are implemented concurrently, in-
dividual impacts may not be separable. Because most
verification of project -feature effectiveness is qualitative, it
is useful in confirming assumptions, but is of limited value
in dete,rmining the actu,a1 change in dissolved-solids load-
ing,

Theoretically, the' overall effect of a salinity control project
may be verified by testing the change in salt load reduc-
tions downstream from the project area, using at-test
(Snedecor and Cochran, 1980, p. 89) of the difference be-
tween mean annual loads for preproject and ste;ldy-state
postproject conditions. This requires at least 3 years each
of preproject and postproject data to estimate the stand-
ard deviations, In actual practice, however, even in a small
controlled area such as Reed Wash in the Grand Valley,
Colorado, it is not possible to apply these statistical proce-
diJres since short-term natural hydrologic variability usual-
ly prevents direct measurements of project effects, Conse'
quently, additional years of data would probably be neces-
sary to find a statistically significant change if the dissolved-
solids reduction is a small percentage of lI!e total dissolved-
soli,ds load. If other hydrologic conditions have changed
between the preproject and postproject periods, it also
may be necessary to test for a difference in the salt-pickup
component of the hydrosalinity budget,

The annual salt pickup is computed using measured inflow
and outflow for both preproject and postproject years.
The difference between mean salt pickup values is then

tested using a t-test. If this budget method is used, data
should be collected to verify the assumptions made in the
budget. Stiff diagrams based on chemical analysis of the
water can test the assumption that concentrations of IDS
(total dissolved solids) and the individual constituents have
not changed, ,Aerial photographs or ground surveys could
be used to verify changes in phreatophytedensity or COver
which might indicate changes in phreatophyte consumptiv;
use,

Consequently, for most projects, verifying a reduction in
dissolved-solids loading is made by testing for a change in
salt pickup at sampling sites upstream and downstream of
the project. Salt pickup is the difference between the total
inflow load and the outflow load, Samples used to com-
pute s~t pickup should be taken at approximately the
same time or averaged over a common time period, Mean
salt pickup is then computed for preproject and
postproject samples, and their difference tested using a
t-test. Salt pickup testing works best where'the dissolved-
solids reduction is constant throughout the year. An
example of this type of analysis is given in the concluding
report on the Bureau of Reclamation's Meeker Dome
Unit (U.S, Bureau of Reclamation, 1985a).

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