Development speeds shrinking changes to Western Pennsylvania riverscapes
By Aaron Aupperlee
Published: Saturday, July 20, 2013, 9:00 p.m.
Members of the Golden Triangle Water Ski Club depend on Nine Mile Island to break up the choppiness of the Allegheny River and create a smooth channel for runs down their slalom course.
But the island, acquired by the club in 2001, is shrinking.
“Our poor island is disappearing rapidly,” said Jack Hoffman, the club's president. “We're really unhappy that it's going down the tubes, but there's nothing we can do about it.”
In Western Pennsylvania, the Allegheny and Ohio rivers are home to dozens of islands. Rising and falling water levels, shifting currents and changing river bottoms naturally cause river islands to shrink, grow or move, said Helen Delano, a senior geologic scientist with the Pennsylvania Geological Survey.
Development along the shores of the rivers and changes to accommodate shipping speed up the snail-like pace of geological change.
In the Ohio, an Army Corps of Engineers project starting in September could stop erosion of Georgetown and Phillis islands, about 35 miles from Pittsburgh. They are part of the Ohio River Island National Wildlife Refuge.
Nearly all of the refuge's 22 islands are shrinking, said Deputy Manager Sara Siekierski. In the past 50 years, Georgetown Island shrank from 17 acres to 5. Phillis Island went from 26 acres to 20.
The project will build dikes around the islands and along the shipping channel, said Army Corps spokeswoman Sheila Tunney. The Corps will dump tons of sediment behind the dikes, using material dug up during annual dredging work. It typically pays $45 a ton to haul the sediment to a landfill. Over five years, the agency could save up to $600,000 by using it on the islands instead, Tunney said.
No such plans are in the works on the Allegheny, Tunney said.
Nine Mile Island, near Blawnox, was once about 20 acres, said Charles Bier, the Western Pennsylvania Conservancy's senior director for conservation science. The conservancy took ownership of the island in 1971. When the organization transferred it to the water ski club in 2001, about 5 acres remained above water, Bier said.
“As we've taken some of the sand and gravel out of the river, the speculation is that by changing the configuration of the bottom of the river, you change the pattern of the flows. Those flows can eat away at the islands,” Bier said.
The shrinking islands threaten the habitat of several species of endangered fresh-water mussels, Bier said. Some islands serve as nesting grounds for bald eagles and great blue herons. Siekierski hopes work in the Ohio will make its islands more attractive to fish, mussels and other species.
Historical photographs show that as Nine Mile Island shrank, neighboring Sycamore Island grew. Over the past 200 years, the island has grown from about 8 acres to 14, said Chris Beichner, executive director of the Allegheny Land Trust, which owns the island.
A slow current around the island has allowed sediment to build up, Beichner said.
Upstream, islands making up Allegheny River Islands State Park also have grown, said Matt Greene, the park's director.
Golden Triangle Water Ski Club members don't see a reversal of fortune in the future of their island.
Joe Deltondo, a club member for about 40 years, said he has watched shrinking conditions force the club to tear down a concrete building about to plunge into the river and move a picnic shelter.
“We've lost half of it since then,” Deltondo, 84, of Blawnox said of the island.
Aaron Aupperlee is a staff writer for Trib Total Media. He can be reached at 412-320-7986 or firstname.lastname@example.org.
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