The Intergovernmental Stormwater Committee’s proposed floodplain restoration project for the Beaverdam Branch of the Juniata River could cost as much as $5.9 million, according to the latest estimate by a consulting engineer.

That’s higher than the initial estimate of $3.1 million, largely because of the approximately $2 million cost of off-site disposal for 117 cubic yards of sediment deposited by the river in the floodplain over the years, according to Ben Uhler of Land Studies in Lititz, who spoke with the ISC board recently.

Engineers originally thought they could place the sediment on site, but discovered there isn’t room, Uhler said.

The new estimate should be around the absolute maximum cost of the project — and it may very well not be that expensive, Uhler said.

“We hope 5.9 really isn’t 5.9,” said ISC board Chairman Tim Brown, the Logan Township manager.

The ISC will seek grants to help pay for the work and will use money from reserves to pay the rest, Brown said.

There is currently $4.9 million in the reserve fund, into which the 10 municipal members of the council of governments pay annual assessments, based on a formula that takes into account stream mileage, impervious surface area and population.

The floodplain restoration project will involve about 0.8 mile of river, starting in the west near Hoss’s restaurant on Plank Road in Duncansville.

The original plan called for the work to extend about a mile to Allegheny Street in Hollidaysburg, but complaints from property owners on the eastern end has led the ISC to shorten the project by a quarter-mile.

The project is estimated to reduce the amount of sediment runoff into the river by about two million pounds per year, according to Uhler.

That is a little more than twice the original estimate for sediment reduction, even though the project length is 25% shorter, according to Uhler and Brian Smith of Keller Engineers, which is working with Land Studies.

The two million pounds of sediment reduction would take the ISC 1.5 million pounds per year past the organization’s current requirement to remove 1.4 million pounds per year by the end of 2025 — based on a seven-year permit that ends then.

That overage will give the organization a head start on meeting the requirements of the next permit issued by the state Department of Environmental Protection, according to ISC stormwater coordinator Chelsey Weyant.

What those requirements turn out to be for the next permit is uncertain — not only in terms of quantity, but also in terms of what contaminants will be involved, Weyant said.

Currently, it’s only sediment.

Under the new permit, there could be reductions required not only for sediment, but also nitrogen, phosphorus and even water volume, Weyant said.

Besides on-site disposal of silt, another expensive component of the Beaverdam project will be flow management, according to Uhler.

There is no way to pump the river flow around the project area, he said.

Nor is it feasible to dig a bypass channel, he said.

Workers will get done as much as they can when and where it’s dry, Uhler said.

When it’s necessary to work within the stream, they will use cofferdams to keep the flow to one side, then switch the flow to work on the other side, he said.

The project seeks to restore the floodplain as nearly as possible to its condition before the arrival of European settlers hundreds of years ago, according to Uhler.

Those settlers, their descendants and additional immigrants built an almost continuous succession of dams on virtually every waterway, with the headwaters of impoundments nearly touching the next dam upstream, Uhler said.

The water that backed up against those dams powered grist mills and lumber mills and created ponds for ice and to irrigate crops, he said.

Most of the dams are gone, but their legacy sediment they collected remains, filling in the natural floodplains several feet deep, according to Uhler.

Those sediment deposits are seen in the nearly vertical banks on the sides of streams and rivers.

During high water, streamflow trapped in the channels erodes those banks, taking sediment downstream.

When the sediment is removed in floodplain restoration projects, higher flows spread out and over the low banks easily, covering what are more natural-type wetlands, slowing the water and allowing more to percolate into the soils.

In a natural stream, it should be almost “imperceptible” where the banks begin, according to Uhler.

Mirror Staff Writer William Kibler is at 814-949-7038.