BOARD01350

• Board Meeting Date: 1/24/2006
• Description: WSP Section - Colorado River Issues - Development of Opearations for Lakes Powell and Mead under Low Reservoir Conditions, including the Development of Lower Basin Shortage Criteria
• Board Meetings - Doc Type: Memo

.

.

.

Modeling of Reservoir Management Strategies
for Lakes Powell and Mead

Figure .t.22
I)fobahilit)'" ur I.ake ~Iead E:J{'\'ation BrIo\\" 1000

""".

___NctmaI.S,lepSl-oorlage",.,
--f+,tt'>d~.S1~S>'o'tage,....,
_Hyllnd","'.Sl",,~nl'\I'
l-~re..r.!.Sl""srataoo_'
_~!'f!\03_Slep~r....'
! 70%

"" ,

""

.!-----=

I""
!

~,

..
~
:0 40'>\.
.
~

~,

"'" +

10% - -+

'"
''''''

.~
"'''

"'''

2015
C,l@nda,Year

"''''

Figure 4-22 shows the probability of Lake ~1cad going below 1000 tt. Because Lake Powell releases
7.48 for an extended elevation range. Hyhrid rev2 and rev3 introduce a chance of going below 1000 It
one year carlier Lhan Hybrid Original and rev\. For this same reason, under Hybrid rc\'2 and rev3 the
probability is higher compared to the Nannal for all years after 2015.

4.3.3 Summary of Findings
The plots presented show that both Lakes Powell and Mead arc more sensitive to incrcas1I1g the
elevation range .It which Lake PO\\'ell releases 7A8 MAF than increasing the l.ake Mead balancing
elevation.. This is the same finding that resulted from the Hybrid Step Shortage Original sensitivity
analysis. presented in Section 4.1. Increasing the Lake Mead elevation to trigger a shortage so that
balancing releases from Lake Powell do not occur before a Lower Basin shortage does not change the
relative effects of the parameter adjustments made to fonn the Hybrid revisions. As shO\\'n in Section
4.2. the effect of increasing the shortage trigger elevation from 1075 n to 1100 n is higher 10th
percentile elevations at Lakes Powell and ~kad.

4.4 Extending the Interim Surplus Guidelines (ISG)

In addition to the sensitivity analyses for the Hybrid and Step Shortage strategies. two other sensitivity
analyses were perfomled that revealed significant findings. The first analysis involved extending the
Interim Surplus Guidelines from 2016 through 2025. with all other parameters remaining unchanged.

lake Powell was operated according to the Hybrid Original strategy. Lake i\.lcad's shortage strategy \vas
Step Shortage Original.

"
.,

Working. Draft. \'ersion 1. January. 2006