Streamflow

Colorado’s rivers and streams support fish, wildlife, and other habitats; irrigate agricultural land; enable water recreation; and provide drinking water for millions of Coloradans. Planning considerations for the proposed Wild Horse Reservoir Project help Aurora Water to minimize changes to rivers and streams.

Off-Channel

An important consideration was developing an off-channel project where water would be conveyed in and out of the proposed Wild Horse Reservoir via pipelines. This means that the proposed project would not block or dam existing rivers or streams.

Existing Water Rights

The proposed project was designed to efficiently integrate into our existing system to provide additional storage capacity for emergency water reserves. The water that would be supplied to the proposed project would be from existing Colorado and Arkansas river water rights that are currently being conveyed to Spinney Mountain Reservoir. This means no new water rights, just smarter storage, reuse and system reliability.

Potential Streamflow Changes

Water projects that collect and store water from Colorado’s rivers and streams can potentially affect streamflows. To determine potential streamflow changes from the proposed Wild Horse Reservoir Project, Aurora Water conducted a streamflow impact analysis in coordination with a federal agency and their third-party hydrology expert. The analysis compared changes in streamflow for the Colorado, Arkansas, and South Platte rivers based on Aurora’s future water supply baseline with and without the proposed project. Based on the analysis, all streamflow changes from the proposed project in average years would be comparable to natural streamflow variations. Learn more about how the proposed project would work.

Colorado River

Streamflow modeling shows that monthly average flows in the Colorado River basin—specifically Homestake Creek and Eagle River—would not change in average and dry years due to the proposed project. In very wet years—like 1983 and 1984 when there was severe flooding in Eagle County—monthly average flows downstream of Homestake Creek would slightly decrease for two months in the summer.

Why there are essentially no streamflow changes due to the project:

Water supplied to the proposed project from the Colorado River would be from existing water rights.
Because these existing water rights allow the water to be reused, Aurora Water prioritizes Colorado River water rights and has already been using all the water legally and physically available from these existing water rights.
The proposed project will not change Aurora Water’s operation of the Homestake system.

Arkansas River

Streamflow modeling shows changes to monthly average streamflows in the Arkansas River basin during average or wet years would be comparable to natural streamflow variations. In dry years, monthly average streamflows would see larger increases at two gages in a single month during the year, but all other streamflow changes would be comparable to natural variations.

Why there are minimal streamflow changes due to the project:

Aurora Water is a signatory to the Arkansas Voluntary Flow Management Program (VFMP)—which manages streamflow in the Arkansas River for recreational and environmental benefits—and will continue to work with Arkansas VFMP partners to meet streamflow goals.
Water supplied to the proposed project from the Arkansas River would be from existing water rights.
Because these existing water rights allow the water to be reused, Aurora Water already prioritizes Arkansas River water rights.
Water would flow downstream and Aurora Water would exchange water—that is, trade water downstream for water upstream—to be conveyed to the proposed project for storage.

South Platte River

Streamflow modeling shows changes to monthly average flows in the South Platte River during average years would be comparable to natural streamflow variation.

In dry years, some larger decreases in streamflow above and below Eleven Mile Reservoir earlier in the year would result from Aurora Water storing more water in Spinney Mountain Reservoir to maintain agreed-upon releases and minimum streamflow throughout the drier summer months. Streamflow changes throughout the rest of the year would be comparable to natural variations.
In wet years, some larger increases in streamflow above and below Eleven Mile Reservoir in two months during runoff would result from Spinney Mountain Reservoir being fuller and more water going downstream. Streamflow changes throughout the rest of the year would be comparable to natural variations.