Power turbines and migrating fish usually mix with poor results, but that may soon change on the Susquehanna River.
PPL Corp. is proposing to add two generating units at its Holtwood Hydroelectric Plant as part of a plan to boost the passage of American shad over the dam.
It and other utilities have invested tens of millions of dollars to build fish passages at four hydroelectric dams that have blocked the first 55 miles of the river to fish migration for nearly a century.
Elevators known as fishlifts were built over Conowingo Dam—the first one encountered by migrating fish—in 1991. That was followed by lifts at the next two dams, Holtwood and Safe Harbor, in 1997, and a fish ladder York Haven in 2000.
Despite the investments, the passage at Holtwood has been a problem whenever flows down the river are high.
Shad find their way upstream by swimming against the current. Fish passages are usually designed to use flow from power generation units to help attract the fish to the passage.
At Holtwood, though, whenever the river flow exceeds about 40,000 cubic feet per second—a common occurrence in many years—the river “spills” over the 55-foot-high dam. That attracts the fish to the base of the dam where they remain, rather than to the $21 million fish lift at the powerhouse on the east side of the dam
In spring 2004, only 3 percent of the 109,360 shad that were lifted over the downstream Conowingo Dam were lifted over Holtwood—it’s worst performance ever. In 2002, only 16 percent of the Conowingo fish passed Holtwood, and in 1998 and 2000, only about a fifth of the fish made it past.
But in low flow years, as many as 56 percent of the Conowingo fish have also made it past Holtwood.
For fish that can’t get past Holtwood, the trip over the Conowingo Dam is a road to nowhere: there is no suitable spawning habitat for American shad between the two dams.
Scientists have tried different methods to steer fish to the lift: a study completed last year attempted to use high frequency sounds to guide fish, but with little success.
Under the new plan, PPL would increase power production from 108 megawatts to 233 megawatts at the dam by adding two new generators. That would steer more water through the powerhouse containing the turbines and thereby reduce the likelihood of water spilling over the top of the dam except during extreme events.
In addition, the utility is proposing several other improvements, including the construction of a small inflatable dam downstream that would help guide migrating fish to the passage.
“We think the proposal has benefits for all of the parties involved,” said George Lewis, a PPL spokesman. “It addresses some of the problems we have identified with getting fish to the fishlift. And it enables us to generate additional hydroelectric power,”
The project has the added benefit of helping PPL comply with the requirements of a 2004 Pennsylvania law that requires electric utilities to produce increasing amounts of their electricity from renewable sources, such as wind, solar, biomass and hydroelectric, in coming years. If the improvements allow electricity from the dam it to be certified as low-impact hydroelectric, it would go even further toward meeting the state regulations.
Fishery officials, who have been concerned for years about the frequent fish passage bottleneck created at the dam, are hopeful about the proposal.
“We’re excited about the prospect of great improvements to fish passage at Holtwood if this goes through,” said Mike Hendricks, a fisheries biologist with the Pennsylvania Fish and Boat Commission.
The expansion, he said, would mean water would not spill over the dam unless it exceeded 60,000 cfs—a rate that would be restricted to extreme events.
“It pretty much doubles the hydraulic capacity of the dam,” Hendricks said. “That means that in most situations in the spring, all the flow is going to be going through the powerhouse. And thus, all the shad are going to migrate toward that area.”
Once the fish are over Holtwood, they would be free to swim to the Safe Harbor lift which, on average, successfully passes 75 percent of the shad that make it past Holtwood. Shad spawning habitat on the Susquehanna starts after fish make it over Safe Harbor, biologists say.
Lewis said PPL does not have a firm cost estimate for the project. The utility is planning a series of hearings on the proposal during the coming months to get public input before deciding whether to submit an application to the Federal Energy Regulatory Commission to proceed with the project.
The project would likely take 24 –30 months to construct, Lewis said. If it proceeds, he said the hope was to complete the project by the end of 2010—which marks the 100th anniversary of the dam’s construction.
“It would be a fitting way to kick off the second century for the plant,” Lewis said.
Information about the project, including a schedule of public hearings, can be found at http://www.holtwood2010.com
Fish passage on the Susquehanna
The American shad is a migratory fish that spends much of its life in the ocean but returns to its native rivers to spawn. Its restoration has long been a goal of the Bay Program because the fish links upstream areas with the Chesapeake.
The Susquehanna River once contained the largest spawning area for American shad on the East Coast, with reports from colonial times indicating that the fish swam as far upstream as New York to spawn.
But for most of the past century, the river has been closed to migratory fish by four major hydroelectric dams that were constructed in the early 1900s. Between 1991 and 2000, the utilities that own the four dams located on the lower 55 miles of the river invested tens of millions of dollars on fish passages to allow shad and other migratory fish to return to their historic habitat.
It’s a major endeavor: Nowhere on the East Coast do fish face more dams en route to their spawning grounds. The goal is to eventually get 2 million shad a year past the dams. The most that has made it over Conowingo Dam, the first encountered by the fish, was 193,574 in 2001.