WSPC00659

• File Number: 8283.100
• Description: Colorado River Basin-Colorado River Computer Models-Colorado River Simulation System Reclamation
• State: CO
• Water Division: 5
• Date: 6/1/1985
• Author: John Burke
• Title: CR Colorado River Simulation System CRSS-Corres Reports etc-1984-1985-CRSS vs CRSP-Analysis of Data and Results from Two CAP Water Supply Studies
• Water Supply Pro - Doc Type: Report/Study

:

"'

'u0289{

.

.

Summary of Differences CRSS vs, CRSP

The following are the major sources of additional water in CRSS:

1. Undepleted inflow above Lees Ferry--about 227,000 af per year.

2. Scheduled demands which go unsatisfied in CRSS--about 200,000 af per
year.

3. Differences in the Parker to the Imperial reach losses or gains
attributable to unidentified and unmeasured return flows as assigned in the
CRSP model--about 130,000 af per year.

4. Differences in the Parker to the Imperial reach losses or gains
attributable to both past and future reductions in phreatophyte consumptive
_ ~e in the CRSS model--260,OOO af.

~ ~~e following are differences in simulation model mechanisms that result in
_~, more water being delivered to CAP in CRSS:

\ ~(Y}.}.JV 1. The "602a" storage rule curve in CRSS required equalization releases
..y'WY'r;.' X- more frequently than did CRSP' s,
,. fo01J ?-
vJ'~
~

2. A water shortage determination in CRSS only occurred when Lake Mead
was below 1095 feet. CRSP imposed shortages when Lake Mead fell below
1124 feet. CRSS also delivered 50,000 af per year more when shortages did

occur.

There are numerous other minor differences; however, these are relatively
insignificant in comparison with the major differences. Under the heading
of minor differences, for purposes of this comparison, would be factors
such as: reservoir contents at the beginning of the study, flood control
criteriaJ surplus water supply decision criteria, and CAP delivery
capability in the early project' stages. Also, it should be noted that
since the data and assumptions change routinely, some of the differences
noted in this comparison would vary somewhat if other studies were used for
comparison. The demand data base is frequently updated, for example.
Future changes to either the data or operating assumptions could
significantly affect the projections of CAP water supply. Nevertheless,
much of the increase in yield to CAP produced by CRSS can be attributed to
the characteristics of the model and its hydrology data base. These are
not so subject to change. Two future changes to the hydrology data base
will probably further increase CRSS estimates of CAP yield: (1) the
addition of hydrology data below Imperial Dam and (2) the addition of water
years 1984 and 1985 to the data set. On the other hand, the identification
and accounting of unmeasured return flows in the Lower Basin could tend to
reduce projections of CAP yield.

In summary, the difference in CAP yield, as estimated by CRSS versus the
old CRSP model estimates, is explained by differences in the data bases and
simulation methodologies. However, because CAP yield is the most sensitive
operational parameter, it can be expected that future modifications to the
models and data base will continue to affect CAP's water supply.

5