Castle Rock water commission to weigh Walker Reservoir expansion agreement
The proposal would add storage for Inverness, Pinery and Cottonwood while Castle Rock retains its existing allocation, pays no expansion costs and could receive conditional compensation for storage lost during construction.
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Castle Rock’s Water Commission is scheduled to consider an agreement Oct. 28 to expand Walker Reservoir by about 350 acre-feet for three water districts. Castle Rock would retain its existing 150-acre-foot allocation and pay none of the expansion costs, but the reservoir would be unavailable for storage during construction.
The commission packet proposes that commissioners recommend Town Council approval. The agenda lists Nov. 17 as the Council consideration date; as of Oct. 23, neither meeting had taken place.
The proposal would increase the reservoir’s capacity from about 650 to 1,000 acre-feet. Inverness Water and Sanitation District would receive 100 acre-feet of the added capacity, Denver Southeast Suburban Water and Sanitation District (Pinery) 230, and Cottonwood Water and Sanitation District 20. The three districts would share design and construction costs in proportion to their added capacity; Castle Rock would receive none of the expansion capacity.
The draft agreement requires at least 60 days’ written notice before construction so members can remove stored water. While the reservoir is unavailable, Castle Rock could lease to Pinery some or all of the water volume it is calculated to have missed, initially at $564 per acre-foot. The agreement provides for monthly accounting. Participating districts would compensate Castle Rock at the same rate for missed volume not leased to Pinery, with the cost shared in proportion to their participation. The agreement treats Walker as a deemed delivery point for this accounting, not as a guarantee of physical water delivery or storage.
The packet’s full-year illustration estimates compensation could reach $190,350, based on up to 337.5 acre-feet of calculated missed volume at $564 per acre-foot. That volume includes up to 155 acre-feet of renewable supply and 182.5 acre-feet of return flows, using an assumption of 0.5 acre-foot per day for a year. Actual missed volume and compensation would depend on construction timing and duration, water-right priorities, exchange availability, hydrology and other legal or physical limits. The rate would adjust in a later calendar year to Castle Rock’s then-current raw-water lease rate.