TEMPLE — Plans are in the works for a new $37 million reservoir that would cover more than 400 acres in Coryell County.

The Coryell County Off-Channel Reservoir is a future project of the Brazos River Authority that was identified in the 2012 State Water Plan of the Texas Water Development Board.

The reservoir would be next to Cowhouse Creek, northwest of South Purmela, and would include a 4,767-foot earth-fill embankment dam on Cowhouse Creek. The conservation pool would have a storage capacity of 15,380 acre-feet and would cover 445 acres of countryside, said Lauren Mulverhill, Water Development Board spokeswoman.

The 445 acres consist mostly of cropland, pasture and mixed rangeland.

Potentially 3,365 acre-feet per year would be available for impoundment, Mulverhill said.

The off-channel project will be able to provide raw water before treatment and transmission of treated water to entities in Coryell County at a unit cost of $1,007 per acre-foot or $3.09 per 1,000 gallons, according to the Brazos G Regional Water Planning Group.

The Brazos River Authority did not provide a timeline for the start of construction, but the cost is estimated at $37.4 million, according to the planning group. That amount includes dam construction, land acquisition and other costs.

More common

Off-channel reservoir construction is becoming more common. Water is diverted from a primary stream during high flows to store in a reservoir built on a smaller tributary stream. That stored water is saved for when the primary stream’s ability to provide water is impeded during droughts.

Some other advantages of the off-channel reservoir system include: less impact on the environment than an on-channel reservoir; lower cost for storage because of the reduced size of the dam and spillway area; and opportunities to do the construction in phases as water demands increase.

Lake Alcoa is an example of an off-channel reservoir in the Brazos G area.

Primary impacts from the project include probable adverse effects on stream flow below the diversion point, which would contribute to declines in dissolved oxygen and higher temperatures during the summer, and displacement of terrestrial wildlife when the reservoir is filled, according to the Brazos G study.

The area was first identified in 2000 among a list of other locations as uniquely suited for a reservoir, according to the Texas Water Development Board.

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