The operations of the Flaming Gorge dam on the Green river, a tributary of the Colorado river in Utah, US, will become the focus of public debate as the US Bureau of Reclamation (USBR) seeks public comment on dam operations.

USBR is preparing an environmental impact statement (EIS) to detail the effects of operating the 152MW hydro dam so it will benefit the razorback sucker, the Colorado pikeminnow, the humpback chub and the bonytail chub — the four endangered fish of the Upper Colorado river basin.

The EIS project is to analyse only the environmental and social impacts of operating the dam to achieve flows recommended by the Recovery Implementation Programme for Endangered Fish in the Upper Colorado River Basin. The programme is an effort by Utah, Colorado and Wyoming to boost fish numbers and improve fish habitat, with the ultimate goal of removing the fishes from the federal endangered species list.

EIS recommendations call for the dam to modify its releases so the flows in the river below the dam would more closely mimic the natural hydrological conditions of the river, thus assisting the fish in their reproduction and growth. In addition to hydro power the dam provides a world-class trout fishery in the 4.6km stretch of river below the dam. Although the dam’s unnatural flows have altered the natural environment, its flood control capabilities have benefited farmers further downstream. Environmental groups, who claim that the fish are endangered because of the dams, are suggesting that the reservoir should be drained, allowing the Green river to flow freely again.

Construction of the arch dam was authorised on 11 April 1956, and began in 1958. The first unit went into operation on 27 September 1963, and the third and final unit in February 1964. The Flaming Gorge reservoir first filled in August 1974 to el 6040 with a head of 121m at the turbines.