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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Figures l-C through l5-C for each scenario present a comparison of Chatfield
Reservoir water surface elevation for baseline conditions (no reallocation of
Chatfield Storage) with Chatfield Reservoir water surface elevation with storage
reallocation.

Figures I-D through l5-D for each scenario show the difference in Chatfield
Reservoir water surface elevations with and without reallocated storage.

Figures l-E through l5-E present the cumulative frequency distributions of water
surface elevations in Chatfield Rcservoir with and without storage reallocation
scenarios. This figure should prove helpful to the Colorado Division of State
Parks and the Colorado Division of Wildlife in determining the effect of the
various reallocated storage pools on recreation and wildlife habitat at Chatfield
Reservoir.

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6.2.2 20,600 Acre-Foot Pool

6.2.2.1 Scenario 1: Denver Water. Scenario I consisted of the use of junior water rights as
inflow to Chatfield Rcservoir and the Denver Water drought contingency demand with a
20,600 acre-foot allocation pool. The desired demand was met 88.6 percent of the time during
the simulation and resulting in an average increase in lake elevation of8.97 feet. During the
summer months the average lake increase was 9.38 feet. Figures I-A, l-B, l-C and l-D show
the detailed results of the simulation.

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

6.2.2.2 Scenario 2: Central Colorado Water Conservancy District. Scenario 2 consisted of
the use of junior water rights as inflow to Chatfield Reservoir and the Central Colorado Water
Conservancy District's augmentation requirements with a 20,600 acre-foot allocation pool. The
desired demand was met 78.0 percent of the time during the simulation and resulted in an
average increase in lake elevation of 6.28 feet. During the summer months the average lake
increase was 6.84 feet. Figures 2-A, 2-B, 2-C and 2-D show the detailed results of the
simulation.

Figure 2-E indicates that this scenario would result in a water surface elevation approximately
6 feet higher for approximately 50 percent of the days during the study period as compared to the
baseline condition with no reallocated storage.

6.2.2.3 Scenario 3: Greenway Foundation and Littleton. Scenario 3 consisted of the use of
junior water rights as inflow to Chatfield Reservoir and the release of stored water to meet
minimum streamflow requirements with a 20,600 acre-foot allocation pool. The desired demand
was met 90.8 percent of the time during the simulation and resulted in an average increase in
lake elevation of 6.22 feet. During the summer months the average lake increase was 6.90 feet.
Figures 3-A, 3-B, 3-C and 3-D show the detailed results ofthe simulation.

P:\Data\GEN\CWCB\Chatfield\Report 12.02\RevisedChatReport 1 03\Report2-03 .doc

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