The Bureau of Reclamation has scheduled a series of water releases Monday from Lake Nighthorse to test the outlet channel to the Animas River.
Releases ranging from 15 to 150 cubic feet per second will show how well improvements to the natural stream Basin Creek and small check dams work.
The total amount of water to be released wont exceed 500 acre-feet. An acre-foot covers a football field to the depth of 1 foot.
Nets strung across the channel will ensure that no fish or eggs in Lake Nighthorse reach the Animas River to potentially affect endangered fish in the San Juan River to which the Animas is tributary.
Basin Creek was the natural outlet for runoff from Ridges Basin. With the construction of the dam, runoff ceased for the time being.
Now, Basin Creek is five miles of engineered channel on the upper reaches and a natural channel with 11 check dams made of concrete and rip-rap on the lower stretch.
The check dams dissipate the force of water between the dam and the Animas River. In effect, they negate 200 of the 500 feet of difference in elevation between the two points.
The dam is part of the Animas-La Plata Project that provides potable water for three Native American tribes and nontribal partners in Colorado and New Mexico.
Officially, the A-LP remains in its construction phase but will be turned over soon to an operations, maintenance and replacement association on which all partners have a seat.
Some partners will take water from Lake Nighthorse. But partners in New Mexico two water districts and the Navajo Nation will take Lake Nighthorse water released to the Animas River.
The water releases Monday will indicate the performance of Basin Creek, including how long it takes water to reach the river.
The information will help A-LP partners in New Mexico determine how far in advance to call for water.
Lake Nighthorse has a capacity of 123,541 acre-feet.