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

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2,1

Lower Basin Shortage

2.1.1 Step Shortage
The original Step Shortage strategy (Step Shortage Original) was developed as part ofa collaborative in.
state process in Arizona to provide a recommendation for Colorado River shortage guidelines. The basic
concept of Step Shortage is to specify the occurrence and ma!:,'l1itude of Lower Basin shortages based on
Lake Mead's elevation at the beginning of each calendar year (similar to the Interim Surplus Guidelines
currelllly in elTect to detemline surpluses). The shortage amount is the reduction in consumptive use and
annual release from lake Mead.

Three revisions to Step Shortage were also studied. These revisions and the Step Shortage Original
strategy are illustrated in Figure 2.1. There is no absolute protection of specific elevations in Lake Mead
under these strategies; therefore, the maximum shortage amount in any year is 600 thousand acre. feet
(KAF) regardless of how low the water surface elevation of Lake "-kad is projected to be. Results of
modeling these strategies sho\".,cd that Lake Mead does drop below elevation 1000 feet, but never
reaches dead pool storage through 2025.

Figure 2.1
Lake ~Il'ad Slep Shortage

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Mud - Mud
-
ele~.lIon SI....~.OOVk>al S1....Sf>"".y.,_3 el.~al;on
s.....sr-uogoo,_, SI....Sf>o<u ,.v2
'220 .m
"00 ------------- ------------- ------------ "00
'00 '00 .,,,
1075 ------------ ------------- ------------- ------------ 1075
'00 ~ '00 ~
""00 ------------ ------------- ------------- ------------ ""00
~ ~ ~ ~
10'5 ------------ ------------- ------------ 10'5
~ ~ ~
'00' ""00
'" '"

If~_"_. ~o/u...."''''ou._~..oq

Step Shortage re\' I. incorporated an additional shortage step at Lake Mead elevation 1100 ft and
modified the shortage pattern from the original. It \....as the most aggressive stcp shortage strategy
studied. Step Shortage rc\'2 had an additional shortage step at Lake "1ead elevation 1100 11 with the
sallle shortage pattern as the original below 1075 feet. Step Shortage rev3 had an additional shortage
step at Lake "1ead elevation 1100 with a slightly more aggressi\'e shortage pattern than the original
below 1075 fl. A comparison of these shortage strategies is presentcd in Section 4.

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2

Working Drat1. Version 2. January. 2006