FLOODC00270

• County: Jefferson
• County: Arapahoe
• Title: Chatfield Reallocation Study: Storage Use Patterns 2/1/2003
• Date: 2/1/2003
• Prepared For: Jefferson County / Arapahoe County
• Prepared By: US Army Corps of Engineers/CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Figure 14- E indicates that this scenario would result in a water surface elevation approximately
1.5 feet higher for approximately 50 percent of the days during the study period as compared to
the baseline condition with no reallocated storage

6.2.4.5 Scenario 5: Central and Greenway/Littleton. Scenario 5 consisted of the use of
junior water rights as inflow to Chatfield Reservoir and maximum demand from either Scenario
2 and 3 since water used to meet minimum streamflows in the Denver area could then be utilized
for augmentation purposes for Central. The desired demand was met 26.5 percent of the time
during the simulation and resulting in an average increase in lake elevation of 0.34 feet. During
the summer months the average lake increase was 0.68 feet. Figures 15-A, 15-B, l5-C and l5-D
show the detailed results of the simulation.

Figure 15- E indicates that this scenario would result in only relatively minor increases in
Chatfield Reservoir water surface elevations over the study period.

6.3 DISCUSSION

A comparison of the water surface elevations for the five scenarios is shown in Figure l6-A
(20,600 acre-foot pool), Figure l6-B (7,700 acre-foot pool) and Figure 16-C (2,900 acre-foot
pool). All scenarios under the three pool sizes show definite utilization of the reallocated storage
space to meet demand. Scenario 3, Greenway Foundation and City of Littleton, met demand
with releases from reallocated storage with the greatest reliability. In the case of the South
Metro Water Users, a strict comparison is not possible due to the derived nature of the demand
schedule presented to Brown and Caldwell for use in this investigation. The demand schedule
provided to Brown and Caldwell from Hydrosphere consisted of the estimated possible releases
from storage based on Hydrosphere's modeling study. The feasibility of making these releases
was confirmed in Brown and Caldwell's modeling by the very high reliability of meeting the
proposed release schedule. Scenario I, Denver Water, also showed a high rate of meeting
demand but did create the largest increases in surface water elevations. While Central Colorado
Water Conservancy District showed the lowest frequency of meeting demand there is a likely
possibility that Central could utilize water from Scenario 3 after it is used for supplementing
streamflows.

A copy of the model and data used in this investigation will be provided on CD-ROM to the
CWCB and Corps and will be available to others upon request.

P:\Data\GEN\CWCB\ChatfieJd\Report 12.02\RevisedChatReportl 03\Report2-03 .doc

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