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Chatfield Reallocation Project Update

Chatfield Reallocation Project

Rick McLoud – AWRA Colorado Presentation August 25, 2009

Rick McLoud, the Water Resources Manager for Centennial Water and Sanitation District, gave a presentation to AWRA Colorado on August 25, 2009 about the ongoing Chatfield Reallocation Project. Chatfield Reservoir, an on-stream reservoir on the South Platte River southwest of Denver, was originally authorized in 1950 but not built until 1979 (14 years after a major flood on the South Platte River killed 8 people in Denver). The reservoir is owned and operated by the Army Corps of Engineers for flood control purposes, and is leased to Colorado State Parks for recreational purposes. Although the reservoir capacity is about 354,000 ac-ft, it is primarily kept empty in anticipation for the next major flood. Reservoir contents are typically less than 30,000 ac-ft (8 percent of capacity) for recreational purposes, leaving over 320,000 ac-ft of capacity for flood control. Previous studies have estimated the probably maximum flood at Chatfield to be 317,000 ac-ft. Denver Water currently has an agreement with the Corps that allows them to store water for recreation, and also permits them to access up to 16,600 ac-ft of emergency supply during drought periods.

The proposed reallocation project would increase storage in Chatfield by 20,600 ac-ft, increasing total storage in the reservoir to about 48,000 ac-ft. The increased storage would provide about 8,500 ac-ft of yield to meet water demands of 15 south metro Denver entities. The entities seeking reallocation storage space are primarily municipal, but also include agricultural and recreational entities.

Potential environmental effects of operation of the reallocation project are being studies in an ongoing Environmental Impact Statement (EIS) being conducted by the Corps of Engineers as the lead agency. The effects would be a result of an increase in water level fluctuations caused by seasonal filling and demands typical of municipal water demands. Water level fluctuations would increase from the existing swing of 9 feet to a fluctuation of 21 feet. Major environmental issues associated with the 12 feet increase in water level fluctuations include issues with wetlands, Preble’s jumping mouse (an endangered specie), and riparian bird habitat. Potentially beneficial effects are an improvement to the existing fishery at the reservoir. Several innovative approaches are being considered for mitigation options, including a debit/credit approach using “ecological function units” (EFUs) instead of acres of habitat. In addition to prioritizing mitigation of jumping mouse habitat, there are also mitigation options under consideration that would involve relocation of existing Colorado State Parks facilities around the reservoir to achieve “in kind” recreational experiences.

The Chatfield reallocation project participants have considered their alternative water supply options if the reallocation project is not approved. These options include purchase of agricultural water rights (agricultural dry-up), trans-mountain diversions to bring new supplies to the Front Range, local storage projects where available, and water reuse and conservation. The high cost and potential political hurdles of some of these alternatives cast doubt on the feasibility of the alternative supplies. Water reuse and conservation are possibly the most feasible water supply alternatives, but would not be enough supply by themselves. Compared to the total cost of Chatfield reallocation storage space of $5,000 to $6,000 per ac-ft of storage, local storage options may be much more costly.
The estimate date of completion for a draft EIS is currently December of 2009, which would be released to the public in January 2010 for public comment. An optimistic schedule for the final record of decision (ROD) is Fall of 2010. It would take about 2 years after the ROD to implement mitigation measures. Water could begin to be stored in the reallocation project as early as 2012.

A copy of Rick McLoud’s presentation can be accessed at the following link:
/uploaded-files/Newsletter/Chatfield Reallocation Presentation to AWRA 8 25 09a.pdf

Permanent link to this article: http://www.awracolorado.org/chatfield-reallocation-project-update/