Selective Withdrawal Devices

In order to control the water temperature below Flaming Gorge, four adjustable 20 by 30 feet gates are moved similar to shutters - lowered onto one another one by one to reach lower water depths. (Refer to diagram on main page.)

In a nutshell, calculations are made and the gates are raised or lowered to achieve the desired temperature. These gates (Selective Withdraw Devies) are used from May until October to maintain a temperature of 50 to 55F.

Reference - Selective Withdrawal at the Flaming Gorge Dam by Alexa La Plante


Water Temperature on the Green River Controlled by Flaming Gorge Dam

With the completion of Flaming Gorge Dam, downstream water temperatures became generally colder and more constant (see the graph below "Post-dam, 1963-1978).

Water temperatures below Flaming Gorge Dam on the Green River in Utah

Mean monthly temperatures from 1963 to 1978 ranged from 4C in March to 9C in November. Maximum water temperatures occurred three months later and minimum temperatures one month later than in the pre-dam days.

Tuning Water Temps via Selective Withdrawal

In 1978, a multilevel water intake structure (diagramed below) was installed on the dam to release warmer waters from Flaming Gorge during the summer in an effort to enhance trout growth (i.e., create an optimal feeding temperature).

Diagram of shutter gate used to control water temperature on the Green River in Utah

The results with a selective withdrawal - mean summer water temperatures increased from 6C to 12C. The maximum annual water temperatures increased from 9C to 15C and occurred in July as opposed to November. Again, the graph at the top of the page shows the temperature ranges after 1978 moving closer to the curve of the pre-dam temperatures.

Reference - Long-Term Dynamics of an Invertebrate Assemblage Downstream from a Large Dam by Mark R. Vinson