Tuesday, January 27, 2009

HEA details early plans for hydro sites

By Jenny Neyman
Redoubt Reporter

Kenai Hydro is in the preliminary stages of investigating the feasibility of four hydro projects near Moose Pass.

Todd Bethard, an engineer with HDR Alaska, explained the project concepts as they stand so far to a group of Cooper Landing residents Jan. 21. He said the projects are designed to limit visual impacts and harm to recreational and mining uses, fish and the environment.
Grant — Dam would make reservoir
Kenai Hydro is considering building a 9-foot-high concrete dam across the natural outlet of Grant Lake to use the lake for water storage, which would increase the project’s potential power output. The lake could hold 38,200 acre-feet of water, with the lake level rising 9 feet above and 25 feet below its natural elevation as water is stored and released. An aboveground steel pipe, called a penstock, would follow the topography of Grant Creek down to a powerhouse built at 530 feet elevation. An existing dirt mining road north of Falls Creek would be extended to allow access to the dam and powerhouse, and would avoid existing trails. Overhead transmission lines would connect the powerhouse to existing lines along the Seward Highway.

Estimated power capacity would be 4.7 megawatts. With the dam and water diverted through the penstock, the section of creek just below the lake outlet would be “dewatered,” Bethard said, and water would be returned to the creek after it ran through the turbines. Bethard said the lake supports some fish — stickleback and sculpin — but previous studies don’t show fish migration in the upper reaches of the creek. HDR plans to return water to the creek above where migratory salmon use it for spawning.

“So we’re looking at taking water from areas of the creek that don’t have fish in them,” Bethard said.

The project would be similar in concept to Chugach’s dam at Cooper Lake, which is blamed for destroying fish runs in Cooper Creek. Paul McLarnon, a biologist with HDR, said the difference is that water in Cooper Creek today actually comes from Stetson Creek, which is colder than Cooper Lake.

“The water out of Grant Lake is put it back into Grant Creek,” he said. “It’s the same water. There wouldn’t be a temperature difference there.”

Community members were concerned about the possible effects of removing and returning water to the creek, whether running the water through turbines would increase water temperature, and what effect that may have on fish.

“That’s something we definitely want to study. I don’t know that right now,” McLarnon said.

Falls — Water may go to Grant Lake
To the south of Grant Lake is Falls Creek, so named for a 100-foot waterfall and smaller falls. Previous studies in the 1980s concluded the large waterfall impedes fish passage in the upper reaches of the creek, although salmon use the lower reaches of Falls Creek.

The creek isn’t suitable for a dam and water storage, Bethard said, so HDR is considering two other options. A run-of-river intake structure would be built, probably at 800 feet of elevation, to divert water into a 40-inch diameter steel penstock. Run of river means water is diverted out of the creek with a structure built to the creek’s water level, rather than a dam higher than the water level storing up larger volumes of water behind it. The intake would include a sluiceway to release incremental water flows.

The penstock could divert water to a powerhouse built at 500 feet elevation with a rated capacity of 3.9 million kWh. Water would be returned to the creek below the powerhouse, with the section of the creek between the intake and water release being dewatered. Existing mining roads with additional short stubs could be upgraded to provide access. If this method is used, the powerhouse would be shut down November to April, Bethard said.

But the preferred idea is to take the water from Falls Creek over to Grant Lake and add to the water capacity there to increase the potential power output of that dam.

“If we can take water to Grant we do see a little more of a benefit. Diverting is the preferred alternative,” Bethard said.

That would could mean Falls Creek goes without water year-round, unless biological studies show some level of instream flow must occur to maintain fish habitat.

Ptarmigan – Tunnel would carry water
South of Falls Creek, the proposed Ptarmigan Lake project would include an intake structure at the outlet of the lake, a gatehouse and an outlet control structure that would control the amount of water released into the creek.

“Ptarmigan is a very productive system,” McLarnon said of the waterway’s fish usage.

Bethard said the project would maintain a certain amount of water release for fish.

It would also involve a 9-foot-diameter, tunnel just shy of 1.5 miles long to bring water to the powerhouse, which would be built at 550 feet elevation. A new, half-mile road near Kenai Lake would provide access to the powerhouse, which would be built across from Ptarmigan Campground. Another new, single-lane access road, this one two miles long, would be built from the powerhouse to the gatehouse. Bethard said tailings from the tunnel could be used for road construction, as aggregate for concrete, for the foundation of the powerhouse or possibly sold to the Alaska Department of Transportation.

The Ptarmigan project has a capacity of 3 MW, but power output would depend on how much water is left in the creek and how much is diverted through the powerhouse. HDR estimates 3.2 million annual kWh production if 34 percent of the water is used for power, 6.4 million kWh if 67 percent is used for power, and 9.7 million kWh if all the water goes to power, although that number is for modeling purposes and wouldn’t likely happen, Bethard said.

Crescent — Trench would follow trail
On Crescent Lake, the original plan was to bring a penstock down Crescent Creek Valley, but that was abandoned when a suitable intake site wasn’t found. The upper reaches of the creek are productive grayling habitat, and farther down is a steep canyon that presented engineering hurdles, Bethard said.

Now the plan is to replace the bridge over Crescent Creek at the lake outlet with a concrete bridge that would control water release into the creek and allow for fish passage, Bethard said. On the other end of the lake, a 7,750-foot tunnel or deep trench would be dug to install a 13,000-foot steel penstock that would take water from the east end of the lake past Carter Lake and down the mountainside to a powerhouse at 550 feet elevation. The trench would traverse the valley between Carter and Crescent Lakes along roughly the same route as a popular hiking trail.

Bethard said the tunnel or trench would be dug and penstock installed in the winter to minimize harm to the vegetation. Vegetation that’s dug up would be replaced and is expected to regrow, he said. The pipe would re-emerge near the outlet of Carter Lake and travel above ground down the mountainside to the powerhouse.

The existing Crescent Lake trail could be used to access the outlet flow structure on the west side of the lake. On the Carter Lake side, HDR would put in a new, single-lane, 2.5-mile road up past Carter Lake to access the intake structure on Crescent. Bethard said HDR considered just widening and using the existing trail, but the first part is probably too steep for that.

The Crescent Lake project has a rated capacity of 5.8 MW, but energy output would again depend on how much water is used. In its modeling, HDR figures 23.4 million kWh if no water is released through the creek, 16.1 million kWh if 33 percent of the water goes down the creek, and 8.8 million kWh if 66 percent of the water is released.

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