BOARD00177 ‎(2)‎

• Board Meeting Date: 5/23/2007
• Description: Flood Section- CWCB Resolution - Support for Chatfield Reservoir Reallocation Project
• Board Meetings - Doc Type: Memo

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STATE OF COLORADO

. Colorado Water Conservation Board

Department of Natural Resources
1313 Sherman Street, Room 721
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
www.cwcb.state.co.us

MEMORANDUM

Bill Ritter, Jr.
Governor

To:
From:
Date:
Re:

Colorado Water Conservation Board Members
Tom Browning, Chief, Flood Protection Section ~
May 10, 2007
Agenda Item 20 - May 22-23, 2007 CWCB Meeting
CWCB Resolution - Support for Chatfield Reservoir Reallocation Project

Harris D, Sherman
Executive Director

Rod Kuharich
CWCB Director

Dan McAuliffe
Deputy Director

.

Backg:round
Population growth along the Front Range continues to create demand for water supply in the South Platte River
Basin for beneficial use to meet municipal, industrial, agricultural, and incidental instream needs for enhancement
of environmental and recreational opportunities. The CWCB has contracted with the Omaha District of the U.S.
Army Corps of Engineers (Corps) to investigate the feasibility of reallocating existing storage space within
Chatfield Reservoir (situated at the confluence of Plum Creek and the South Platte River in the southern portion of
the Denver Metro area). The contract, known as a Feasibility Cost Share Agreement (FCSA), outlines the roles and
responsibilities of the Corps and the CWCB pertaining to a Feasibility ReportlEnvironmental Impact Statement
(FRlEIS) for the Chatfield Reservoir Reallocation Project (Project).

The fundamental scope of the Project is to look at the feasibility of converting flood control storage space in
Chatfield Reservoir, owned by the Corps, into water supply storage space. The maximum volume for the
reallocation analysis has been set at 20,600 acre-feet based on an Antecedent Flood Study model that was approved
by the Corps. The FRlEIS effort is analyzing a 7,700 acre-foot alternative as well as a "no action" alternative for
the purposes of the National Environmental Policy Act (NEPA). From a flood control perspective, the Corps has
determined that through updated watershed modeling, antecedent flood criteria, and administrative operations of the
reservoir during conditions of flooding, water supply storage space can be made available without adversely
impacting the existing flood protection function of the facility.

An original consortium of 16 water users (now 15) signed Letters of Commitment with the CWCB pledging cost-
share funding assistance and legitimate interest in potentially receiving "shares" of the reallocated storage space
within the reservoir. Each water user would be responsible for ultimately purchasing their allocated storage space
amount pursuant to a future contract between the CWCB and the Corps authorizing use of the space for water
supply purposes.

.:

The total cost of the project is estimated to be on the order of $100 million which includes the cost of the storage
space (payment to the Corps for use of the facility), cost of environmental mitigation, and cost of recreation
mitigation. In addition, annual O&M costs would be required as part of the Project's operation. Chatfield Reservoir
is home to one of the most highly utilized recreational areas in Colorado operated by State Parks, and facilities at
the site would need to be relocated or retrofitted to account for increased water surface elevations (up to 12 feet
during normal operations). Significant environmental mitigation will also be necessary to ensure equitable
ecological function prescribed by NEP A. Despite the mitigatable impacts, the Project has enormous benefits
including a partial solution to the water supply shortages identified in SWSI for the South Platte basin.
Colorado Water Conservation Board
Flood Protection. Water Supply Planning and Finance. Stream and Lake Protection
Water Supply Protection. Conservation and Drought Planning