WSP05057

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1983
• Title: Colorado River Water Quality Improvement Program - Status Report
• Water Supply Pro - Doc Type: Report/Study

through 1978 historical flows modified to reflect present depletions) as
had previous similar progress reports. Calculations were done by hand.

w
....
o
.",.

The CRSS (Colorado River Simulation System) computer model was also used
for future water Quality projections. A description of the model is given
in Part X. Speci al Studies. Progress Report No. 10. along with the projec-
tions. The model produces better water quality predictions because of
its ability to more accurately describe the river basin and its greater
degree of flexibility. Pro~r-ess Report No. 11 and all future progress
reports wi 11 shaw only the CR S resul ts. Figure 13 shows the various CRSS
projections presented in Progress Re~ort No. 11 to be released in January
1983 [2]. Figure 14 shows the CR S projections with CRWQIP projects
implemented.

The CRSS flow and salinity projections in Progress Report No. 10 are
considered pr-el iminary for several reasons. The hydrologlc data base for
the computer model was not completed beyond 1974. The intent was to use a
data base from 1906 to 1978. Also, time did not allow thorough checking of
the projections against the input data to ensure proper operation of the
model. The projections using "present modified method" based on annual
averages remain the best estimate at the time Pro~ress Report No. 10 was
published. However. the work on the data base has Slnce been completed and
an updated revision is available for future model operations. including
Proqress Report No. 11.

Projections made using CRSS will differ from those previously made in three
significant ways:

1. The model dynamically routes water and salt through the system usinq
a monthly time step. more accurately reflecting the time lags, changes
in reservoir storage. and related buffering of salinity as it travels
through the system. Previous techniques applied projected annual
changes in depletion and salt loading to a water and salt load accountw
ing wh ich assumed that the system was at a steady state of average
conditions for that point in time.

2. The data base used in CRSS utilizes the period beginning in 1906,
whi le previous analyses of future sal inily have been based upon the
period beginning 1n 1941. This change places the analyses of salinity
in the same context as water supply analyses conducted by the Department
of the Interior.

Traditionally, there has been some disagreement regarding the use of
water supply records from the first quarter of this century to determine
firm water supply. During hearings on the Colorado River Basin Project
Act (Public law 90-537) in the middle 1960's, experts testified that,
although the river has exhibited a long-term annual flow of 15 million
acre-feet. the safe usable volume needs to be based upon a lesser runoff
to r-eflect the impact of drought periods. Therefore. the water supply
studies prepar-ed by the Department of the Interior utilize:

31