Avista Utilities will begin work shortly on a $4 million project that will replace the spill gates in its diversion dam on the main channel of the Spokane River directly west of the Division Street bridge.


The dam, which is in Riverfront Park, diverts water into the south channel of the river past the Opera House and into an underground intake pipe that serves the utilitys Upper Falls Powerhouse, at the west end of the park a half-mile downstream.


The Spokane-based utility has awarded a contract to Robert B. Goebel General Contractor Inc., of Spokane, for the project, which Avista spokesman Hugh Imhof says will take roughly a year to complete.


Goebel will use a barge on the water and a spot near an amphitheater in Riverfront Park to store materials for the project, Imhof says.


The job involves removal and replacement of aging wooden control gates with modern components, Avista says. It adds, All construction is being done above the high water mark on existing concrete, and no ground disturbance is needed in the riverbed. No impacts on aquatic life are expected. Imhof says the project did require a special permit from the state, and we have that.


While the project is expected to take a year, it will be shut down periodically when runoff in the river is high or the publics use of popular Riverfront Park is heavy, the utility says.


The diversion dam was built in 1922 and is used to divert water for aesthetic purposes as well as power production, Avista says.


It says that electricity from the Upper Falls Powerhouse was instrumental in meeting demand for power during Spokanes early industrial development and once helped power the Spokane areas electric streetcar system.


The diversion dam is 300 feet long and 35.5 feet high at its tallest point, and can store 800 acre-feet of water. An acre-foot of water is sufficient to cover an acre of land under one foot of water.


The Upper Falls Powerhouse has a generating capacity of 10 megawatts, or enough power to serve 6,500 homes.