Hydro dams don't cause serious erosion, owner says

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BELLOWS FALLS — After further review, the owner of three Connecticut River hydroelectric dams says those facilities are likely not causing any significant riverbank erosion.

In connection with the proposed relicensing of the Wilder, Bellows Falls and Vernon dams, the Federal Energy Regulatory Commission earlier this year ordered Great River Hydro to take a closer look at erosion issues in the river corridor. Great River's response, filed after additional studies at 21 monitoring sites, indicates that the company's conclusions haven't changed: Only "flood discharges" that exceed flows caused by dam operations are capable of eating away at the Connecticut's banks.

"Project operations should not ... be considered capable of causing significant bank erosion," Great River's new report says.

Great River Hydro, a subsidiary of Boston-based ArcLight Capital Partners, earlier this year completed the nearly $1.07 billion purchase of 13 hydroelectric stations on the Connecticut and Deerfield rivers. The dams' previous owner, TransCanada, already had begun relicensing proceedings for the Wilder, Bellows Falls and Vernon facilities prior to the sale. The dams' federal licenses will expire at the end of April 2019.

Great River Hydro administrators have said they are moving full speed ahead with relicensing, and the company met a federal deadline to file a formal license application by May 1. But after groups including the Connecticut River Conservancy questioned the company's erosion conclusions, FERC officials in July decided that Great River's analysis was "incomplete and inconsistent with what was required in the approved study plan."

Great River was ordered to submit revised erosion reports by Nov. 15.

There has long been concern among river activists, residents and some governmental officials that hydro dams operations — and the resulting changes in water flows and elevations — cause more erosion than natural flows do.

But Great River Hydro's latest report claims that's not the case. After FERC's order for further erosion considerations, the company says it undertook "robust" studies in connection with 21 monitoring sites along the Connecticut River in Vermont and New Hampshire. The additional work included "two-dimensional hydraulic monitoring" as well as samples of sediment taken at each monitoring site. The hydraulic modeling was supposed to simulate dam operations during "low, medium and maximum operational flows."

The results, according to Great River's report, show that "entrainment" of riverbank sediment — meaning sediment being picked up by flowing water — is "highly unlikely" at 16 of the 21 sites. At the other five sites, sediment entrainment is "possible during maximum operational flows" but is still "considered unlikely," Great River says.

The company cites several reasons behind that conclusion, including the fact that riverbanks at two of those five monitoring sites are stable.

Great River also says the numerical values used in its studies are conservative and likely underestimate the water-flow forces needed to cause erosion. Additionally, the company says the presence of vegetation and wood along the base of riverbanks can slow actual erosion rates. Of the five monitoring sites where it might be possible for dam operations to cause erosion, "four have some vegetation or tree roots, sometimes dense growth," Great River's report says.

The bottom line, the company says, is that "flows occurring under (dam) operations, while perhaps capable of sediment entrainment in isolated incidents, cannot be responsible for widespread bank sediment entrainment or bank erosion."

The company's new erosion report has not yet spurred any formal responses filed with FERC.

Andrea Donlon, a river steward at the Connecticut River Conservancy, said the conservancy and its consultant will be examining Great River's report and its methodology. She noted that there will be further opportunities for public comment during dam relicensing proceedings.

Mike Faher writes for VTDigger and the Brattleboro Reformer. He can be contacted at mfahrer@vtdigger.org.


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