September 11, 2014
John S. Howard
Director FERC Compliance, Chief Dam Safety Engineer
FirstLight Power Resources/GDF Suez
Northfield Mountain Station
99 Millers Falls Road
Northfield, MA 01360
Re: Study 3.1.2 Addendum: Additional investigations to look at ice as a cause of erosion
I have reviewed the addendum to Relicensing Study 3.1.2 “Northfield Mountain/Turners Falls Operations Impact on Existing Erosion and Potential Bank Instability” dated August 12, 2014. The purpose of the study addendum is to more closely consider ice as a potential cause of erosion, since ice is likely to be more present in the Turners Falls pool during winters after the Vermont Yankee nuclear power plant closes down at the end of 2014. As part of my review of the addendum, I spoke with a scientist at the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL) who is knowledgeable about river ice. I received and reviewed several related publications from her. Below are comments submitted on behalf of the Connecticut River Watershed Council (CRC).
1. Reviewing the CRREL database on historic ice jams along the Connecticut River, contacting USGS for similar information, and contacting TransCanada to obtain information about ice sheet development and ice break-up at their upstream hydropower facilities makes sense.
2. Based on my conversation with the CRREL staff person, useful field data for modeling the force of ice along a riverbank bank includes ice thickness, stage records, and pre-winter vs. post-winter surveys of bank morphology. CRC recommends that 1) FirstLight collect field information and historical information on ice thickness, 2) that the study report include stage records or river level recordings for the winter, and 3) that FirstLight conduct pre-winter and post-winter surveys at established representative transects already monitored as part of this study.
3. As for photographs, these would also be helpful. Photos should verify ice thickness. They should be taken at the representative transect locations that are accessible in the winter. The sites listed in the proposal include many locations that are not interesting in terms of erosion (French King bridge, the Turners Falls dam), and in fact have little connection to the rest of the study. The addendum does not explain how FirstLight will know when the right time is for taking ice sheet formation and ice break-up photos. More detail is needed about how FirstLight staff and/or consultants plan to monitor the river and decide on the best day for a photograph. The site list should be modified to include sites that are already part of the study.
4. As for correlating air temperature to ice formation and break-up, we recommend reviewing CRREL research in addition to using the Simons & Associates studies (for example, see http://faculty.babson.edu/goldstein/goldsteingroup/TN04-3.pdf). If local temperature and ice data will be used, please identify the source.
5. Lastly, we recommend the field work for this component of Study 3.1.2 take place both this winter and next. Each winter is very different, and though Vermont Yankee may be operating this December, there may be information the rest of the winter will offer that won’t be available the next winter. Moreover, if taking photographs at the right time proves to be difficult, the first winter could help iron out the kinks. Also, if FirstLight’s temporary license amendment is approved by FERC, FirstLight will likely be asked to do a pre-winter and post-winter survey of bank transects that could fit nicely into this study as well. One of the papers I obtained also speaks to the longer term effects of icing that would not be observable in a single year:
“River-ice influences on channel morphology potentially are multiple and complex, besides the aforementioned influences on local depth and sediment transport. They are describable in terms of impacts on the channel cross section, thalweg sinuosity, anabranching and avulsion, local scour beneath the toe of an ice jam, and local bed aggradation occurring beneath and immediately upstream of an ice cover. Observations of alluvial channels indicate that morphology changes can occur over a wide range of time and length scales. Some morphology changes, such as the local scour described earlier, or a meander loop cutoff, can occur rapidly, within the duration of an ice jam. Other morphology changes, such as thalweg realignment in response to an altered rate of flow energy dissipation, can occur slowly, not being realized during a single winter.”
“Review of Alluvial-channel Responses to River Ice” by Robert Ettema, M.ASCE1. Journal of Cold Regions Engineering, Vol. 16, No. 4, December 1, 2002
I am happy to forward you or anyone else the research studies I received from CRREL. Thank you for the opportunity to provide input on the addendum to study 3.1.2.
Andrea F. Donlon
Cc: Bob Kubit, MassDEP
David Foulis, MassDEP
Kimberly Noake MacPhee, FRCOG and other Streambank Erosion Committee members
Ken Hogan, FERC