Conjunctive Use Model S-1

• Description: Conjunctive Use Model S-1
• State: CO
• Title: Conjunctive Use Model S-1
• Water Supply Pro - Doc Type: Report/Study

Conjunctive Use Model H -1
At the request of the Basin States Technical Team, model H -1 has been developed in
CRSS/Riverware. The rule set in H -I follows the logic used by the Central Arizona
Project (Henning et al) in their Interim Lake Powell Release Trigger spreadsheet model.
There are three adjustable parameters in the H -1 model:
• Lake Powell Trigger (LPT)
• Reduced Objective Minimum (ROM) from Lake Powell
• Water Supply Trigger (WST) at Lake Mead
The rules in RiverWare in H -1 allow these parameters to be adjusted to accommodate
investigation of the impacts on the Colorado River System under various combinations of
values for these parameters. Two model runs have been made using H -1. For these first
implementations of the H -1 model, the following values were assigned to the three
parameters.
LPT — elevation 3,560 feet at Lake Powell (for both model runs)
ROM — 6.5 million acre -feet of annual release from Lake Powell — Run 1
- 7.48 million acre -feet of annual release from Lake Powell — Run 2
WST — elevation 1,050 feet at Lake Mead (for both model runs)
In H -1, releases from Lake Powell are 8.23 million acre -feet unless Lake Powell is below
the LPT elevation. The LPT is evaluated against the September 30 (end of the water
year) water surface elevation at Lake Powell. When Lake Powell ends the water year
below the LPT, releases the subsequent water year are the ROM.
If storage equalization releases have a higher priority than maintaining the ROM in H -1.
If a very wet year occurs when the ROM is in place, releases from Lake Powell are
increased above the ROM, if necessary, to achieve the appropriate level of equalization.
The equalization methods used in H -1 is the same 602(a) storage algorithm (in
combination with the interim 602(a) storage guideline) used in the conventional CRSS
model'.
Once Lake Powell drops below the LPT, water year releases from Lake Powell remain at
the ROM until, (1) The water surface elevation of Lake Powell rebounds above the LPT
elevation on September 30, or (2) Lake Mead drops below the WST. If either of these
two events occur, releases from Lake Powell revert to 8.23 million acre- feet2.
The MST is evaluated against the December 31 (end of calendar year) water surface
elevation at Lake Mead. If Lake Mead is below the WST at the end of the calendar year,
1 It should also be noted that in the first two model runs of H -1, there was no instance of the event
described in this paragraph occurring.
2 Equalization releases as described in the previous paragraph could also result in releases going above the
ROM.