FLOOD10319

• County: Arapahoe
• County: Jefferson
• Stream Name: South Platte River
• Basin: South Platte
• Title: Chatfield Reallocation Study Storage Use Patterns
• Date: 2/1/2003
• Prepared For: CWCB
• Prepared By: Brown and Caldwell
• Floodplain - Doc Type: Project

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SECTION 6

MODEL AND RESULTS

6.1 MODEL DESCRIPTION

An Excel Spreadsheet model was developed to simulate the various inflows, demands and pools
sizes. The model was a direct solution, daily model. A starting storage value of zero acre-feet
was assumed for each simulation. The storage value for the next day was computed as:

6S = I - 0

Where

6S = change in storage,
I = inflow, and
o = outflow (demand plus evaporation)

Evaporation was computed based on the reservoir area vs. capacity curve for Chatfield Reservoir
(D. S. Army Corps of Engineers, Omaha District, August 7, 2000, see Appendix B herein) and
monthly evaporation rates. Evaporation was prorated between the conservation storage pool and
the reallocated storage pool. If the resulting total storage after netting out the evaporation was
less than zero, reservoir outflow was adjusted to set storage to zero. If the result was greater than
the maximum storage allowed, a spill was added to the outflow. This process was repeated for
every time step in the model. Charts were linked to the model to show the results in graphical
form.

The normal maximum level ofthe Denver Water operations pool in Chatfield Reservoir is
5432 feet MSL; however, this pool level fluctuates. The three reallocated Chatfield Reservoir
storage pools were assumed to be on top of the fluctuating Denver Water operations pool.
Consequently, the water surface levels for the reallocated Chatfield Reservoir storage pools will
also fluctuate. For example, the water surface elevation for the full 20,600 acre-feet reallocated
storage pool will not always be 5,434 feet MSL; actual elevation will depend on the volume of
storage in the Denver Water operations pool.

6.2 MODEL RESULTS

6.2.1 General

Modeling results for the combinations of three proposed reallocated Chatfield Reservoir storage
pools and five potential target releases are presented graphically in a series of five figures for
each reallocated storage pool/user:

.

Figures I-A through 15-A present inflows to storage, spills and storage for each
scenano.
Figures I-B through 15-B present demand (target releases), the actual releases
from reallocated storage (met demand) and evaporation.

.

P: \Data \GEN\CWCB\Chatfie ld\Report 12 ,02\RevisedChatReport 1 03\Report2-03 ,doc

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