WSPC12493 ‎(2)‎

• File Number: 8220.101.10
• Description: Colorado River Water Projects - Glen Canyon Dam-Lake Powell - Adaptive Management
• State: CO
• Basin: Colorado Mainstem
• Date: 4/1/1996
• Author: DOI-BOR
• Title: CRSSez - Annual Colorado River System Simulation Model - Overview-Users Manual - Update of 04-01-96 - With Revisions of 09-01-96 - 04-01-96
• Water Supply Pro - Doc Type: Report/Study

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user interface and defaults to 2000 kaf. The computed error is
added to the actual depleted and regulated runoff. The initial
random number seed is usually always the same so that 2 runs of
the same length can be compared without differences being due to
the forecast error. It is also optional to have a new starting
seed.

The effective system space is computed and includes gains and
uses in the Lower Basin and evaporation from Mead and Powell.
This space also includes bank storage between current and maximum
Powell and Mead contents. The space is computed as
pevap+(evap+mminr+meadpump-avglbgain} + (umaxc-uc+(trgt-
pmst}*1.075} where pevap is last years evaporation from Powell,
uevap is Upper reservoir evap, evap is evaporation from Mead,
mminr is objective Mead release computed above, avglbgain is
average gain above Hoover, umaxc is the Upper reservoir maximum
contents, uc is the computed new Upper reservoir contents, trgt
is the sum of Powell and Mead maximum contents read from the user
interface and defaults to contents at elevations 3685.5 and
1214.5 ft, pmst is beginning Powell and Mead contents minus
0.935*(bank-otherbank}. The 0.935 factor adjusts the water banks
for shoreline bank storage.

If the inflow forecast above Powell is greater than the effective
space then a surplus is declared in the Lower Basin if flood
control surplus is checked in the user interface.

Surplus Strategies:

Step 7. There are 4 surplus determination strategies in EZ other
than the flood control determination above that can be selected
from the user interface.

System Spill Avoidance: The basis for this method is to check an
assumed runoff for the year with the space computed above. A
runoff above Powell is selected from a normal distribution with
mean of 15077 kaf and standard deviation of 4379 kaf (fit a
normal distribution to NAT values in HYDRO.DAT). The selected
runoff is based on the degree of assurance of spill avoidance and
is read from the user interface. The default is 0.7. The runoff
is computed as 15077+4379*k where k is a computed standard normal
deviate for 0.7 probability. For 0.7 spill avoidance
probability, a runoff of 17,431 kaf is returned. A surplus is
declared if space computed above is less than the spill avoidance
probability runoff.

An option can be used to check space against a lagged forecast
instead of the assurance runoff. In this option, the 0.7 read
from the user interface is applied to the departure of the
previous years actual runoff from the average to give a forecast
of runoff. This adjusted departure forecast is checked against
space.

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