WSP12351

• File Number: 8273.300
• Description: Colorado River Basin Salinity Control - Federal Agencies - USGS
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 9/1/1988
• Author: USGS
• Title: Estimation of Natural Dissolved Solids Discharge in the Upper Colorado River Basin - Western United States
• Water Supply Pro - Doc Type: Report/Study

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4.

Separate the annual mass-balance discharge of dissolved solids
(computed in step 1) based on the distribution of mean monthly
discharge (water years 1914-57) from the model results in step 3.
Add the values of monthly dissolved-solids discharge computed in step 4
to the data set. These values represent predevelopment conditions at
the site, They are paired with values of mean monthly natural stream-
flow from the same period (water years 1914-57). All development
variables for these predevelopment "observations" are set to zero.
Calibrate the model using the predevelopment and historical data.
Adjust the values of monthly predevelopment dissolved-solids discharge
based on the mean monthly distribution for water years 1914-57 from the
model results in step 6.
Recalibrate the model.
Compute ~eighting factors using the monthly residual variances.
Recalibrate the model using weighted regression.
Repeat steps 9 and 10, if necessary, until there are no significant
differences among the monthly weighted-residual variances,
Adjust the values of monthly predevelopment dissolved-solids discharge
based on the' mean monthly distribution of dissolved-solids discharge
for water years 1914-57 obtained from the model results in step 10.
Recalibrate the weighted-regression model.
Compute the monthly coefficients a using equation 21, with time
(t) as given by equation 12. m
Compute monthly natural dissolved-solids discharge using equation 20, the
regression parameters estimated in steps 13 and 14, and monthly values
of natural streamflow.

5.

6,
7.

8,
9.
10.
11.

12.

13,
14.

15.

ESTIMATION OF NATURAL DISSOLVED-SOLIDS DISCHARGE USING
THE STATISTICAL METHOD

The results of applying the outlined statistical method to data from
16 selected sites in the Upper Colorado River Basin are reported in tables
8 and 9. The coefficient and exponent values used to estimate natural
dissolved-solids discharge for each site are listed in table 8. Estimates
of monthly mean natural dissolved-solids discharge for each site are listed
in table 9.

The development variables that were included in the model for each site
and the sign (positive or negative) of the associated regression coefficients
are listed in table 10, The R2, standard errors of estimation, and compari-
sons between the mean annual (water years 1914-57) natural dissolved-solids
discharge estimated by the statistical method and by mass balance also are
listed. The development variables expected to indicate an increase in
dissolved-solids discharge were: irrigated area, net reservoir releases,
consumptive use in preceding months, and total adjustments to streamflow, if
the predominant adjustments were reservoir releases, Net diversions, consump-
tive use, and total adjustments to streamflow, if predominantly diversions,
were expected to indicate a decrease in dissolved-solids discharge, The
development variables included in the model for each site generally had the

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