Rains prompt dam gate openings

Published 12:02 am Wednesday, April 29, 2015

Shown is Gantt Hydro during a previous opening. | File photo

Shown is Gantt Hydro during a previous opening. | File photo

PowerSouth Energy Cooperative opened up gates at its Gantt and Point A Hydro plants to maintain proper pool levels after recent rains dropped in the area.

PowerSouth Corporate Communication Manager Mark Ingram said both plants run on a run-a-river mode.

“That means that to the extent practical, whatever water flows in the lakes, is released downriver at the same time,” Ingram said. “There is very little volume available in the lakes for water storage. This is especially true for Point A, which is smaller and shallower. PowerSouth strives to keep the lakes within six inches, high or low, of the normal water level.”

Gantt Lake covers a reservoir with a surface area of 2,747 acres, Ingram said.

The lake’s usable storage capacity is 14,645 acre-feet at a normal average pool elevation of 198 feet at sea level. An acre-foot is defined as the volume of one acre of surface area to a depth of one foot. An acre-foot is 43,560 cubic feet.

Point A reservoir covers a surface area of about 700 acres and has a usable storage capacity of 2,300 acre-feet at a normal average water surface elevation of 170 feet at sea level.

Combined, the Gantt and Point A facilities have an 8-megawatt capacity, which is enough to power approximately 8,000 homes, Ingram said.

Ingram said the recent rains propelled the company to run the overflow of water that’s coming down through the river.

“We have to keep both lakes at federal and state regulated pool levels,” he said.

Ingram said monitoring pool levels wouldn’t be possible without the aid of gauges.

“As water enters the upper end of the lakes from the rivers, it slows down,” he said. “As it slows down, much of the silt falls out. As the silt builds up, the upper parts of the lakes become shallow. This happens to all lakes on rivers with sandy or dirt bottoms. Once the upper end of the lake becomes shallow — when periods of high flow occur — the water levels upstream of this delta will be noticeably higher than the lower portion of the lake. This will happen no matter what level is maintained downstream at the dam.”

For example, Ingram said when it rained so much last week, they knew that water was going to come down stream and took action by opening the gates and running the hydro units as needed.

“As water was coming down, we’re already opening the gates to stay within the normal pool level,” he said. “Enough water was coming through by the run-a-river mode that we could generate electricity through that.”