Cohasset CC Receives Regulatory Comments on Cat Dam NOI

It doesn’t look good for the Self-styled Environmental 20, namely Little Inner Harbor abutters at Cat Dam who want to ‘pool’ the tides to the detriment of human and marine wild life.

It appears the  Cohasset Conservation Commission hearing scheduled for  Thursday, March 10 at 7PM will be rescheduled at the request of The Environmental 20. At the upcoming hearing the Cohasset Conservation Commission will consider technical reports from regulatory boards and commissions before making its final recommendation on the Notice of Intent NOI) submitted to them by the majority of the Cohasset Board of Selectmen who have endorsed the NOI presented to them by the Environmental 20, assisted by Harbor Engineering, LLC and Lucas Environmental, LLC.

Division of Ecological Restoration

Hunt Durery, Acting Deputy Director

Division of Ecological Restoration


Durery said   “….during neap tides, the leakage through the gates only allows Inner Little Harbor (ILH) water levels to drop 2-4 inches below the top of the gate. Further, during the majority of tide cycles, the ILH low water level remains equal to, or above, the top of the gates.

In summary, tidal elevations measured at the Nichols Road (Cat) Dam site for several studies provide consistent empirical documentation of the ILH tidal dynamics. The function of the tides gates and the tidal restriction/impoundment they create when closed have been evaluated and determined to be significant factors in the impairment of ILH.

Eric Hutchins, Fishery Biologist

National Oceanic and Atmospheric Administration
Hutchins said…”These comments are based on a review of the current NOI, prior NOI submitted by CLE Engineering on behalf of the town (and subsequently withdrawn), information from numerous prior studies and reports on the hydrology, ecology, and impairments of Inner Little Harbor (ILH), and our extensive experience assessing and restoring degraded tidal wetland systems throughout the Commonwealth. Since 1994, DER and its and partners have helped municipalities and other landowners assess and restore over 1,000 acres of degraded wetlands through completion of over 70 wetland restoration projects, several of which are located in Cohasset. The vast majority of these projects reduced or eliminated restrictions to tidal flow caused by man-made obstructions – including dams, dikes, culverts, and tide gates – to enhance the ecological health of upstream estuarine habitats. The NOI under review by the Commission proposes alteration of resource areas under the MA Wetlands Protection Act from two types of activities: 1) changes to the Cat Dam tide gate operation protocol, and 2) maintenance / repair of the Cat Dam tide gate infrastructure. I address both activity types below.

The current NOI proposes to increase tidal influence during the cooler winter months by keeping all three gates open from December through March. Compared to the historic gate operation schedule, this would increase winter season tidal exchange by 44 consecutive days. This change would benefit the ecology of the ILH system because it would increase tidal influence in a manner consistent with natural tidal dynamics that are the primary drivers of estuarine ecosystem processes and condition. However, due to the winter-season-only timeframe of this proposed increase, the benefits it would generate are unlikely to significantly reduce the impairments to the ILH system. As prior ILH studies clearly document, the majority of impairments occur during the warmer growing-season months when biological activity is highest. This warmer season time frame is when the artificial restriction of tides and impoundment of water cause the greatest negative impacts to the chemical, physical, and biological condition of ILH. The currently-proposed gate operation protocol for April through November would keep all three gates closed except for twice per month when the gates would be opened for two days and then closed again. The very limited and intermittent nature of warmer season tidal exchange proposed under this operation protocol is unlikely to improve – and, in fact, is likely to further degrade – the ecological condition of ILH. As stated above, the most important driver of ecological processes and conditions within ILH and all other estuarine systems is tidal influence. The ILH system evolved over several thousand years in adaptation to natural tidal dynamics with the ebb and flow of ocean water in and out of ILH twice per day. Both the existing and proposed tide gate operation protocols for the warmer months result in very unnatural tidal dynamics within ILH that force extreme fluctuations, or “swings”, in the system’s chemical, physical, and biological conditions. These swings impede the system’s ability to maintain naturally-balanced ecological dynamics (e.g,. like Little Harbor) and are a major reason why ILH does not support healthy estuarine conditions and fish and wildlife habitats. Because the current NOI proposes to double these “swing” events from once to twice per month, and because these events would likely cause net negative alterations to the wetland resource areas present, DER believes the proposed warmer season gate operation protocol does not meet the performance standards of the Wetlands Protection Act and should not be permitted as a salt marsh restoration project. To significantly improve the ecology of ILH, a more natural tidal regime should be restored to the system, especially during the warmer growing season. The current proposal for intermittent tidal flushing twice per month, separated by long periods of impounded water with greatly reduced tidal exchange, is not a viable solution to achieve meaningful ecological restoration for the ILH system. To achieve significant restoration and reduction of impairments, DER recommends that the three gates be opened permanently year-round to allow full natural tidal exchange to the extent the Cat Dam structure will allow.

Maintenance / Repair of the Cat Dam Tide Gate Infrastructure – The NOI proposes to repair the tide gates and associated infrastructure. This work would involve modifications to infrastructure and significant construction activities (such as site de-watering) that are located within, and can have a major impact on, wetland resource areas. The NOI does not provide any engineering drawings or other information detailing this construction work. As required for similar construction projects, design plans stamped by a P.E. and additional detailed information about construction methods, materials, sequencing, etc. should be provided in the NOI application so that the Commission can effectively evaluate the proposed work in relation to the Wetlands Protection Act regulations and town bylaw. This information will also be needed for several other state and federal permits that are required prior to commencing this type of work

Edward Reiner, Senior Wetland Scientist

United States Environmental Protection Agency, Boston

Reinder said…..For over the past decade I have been acting in the position as the Gulf of Maine Habitat Restoration Coordinator for the NOAA Restoration Center.   In this capacity I have been actively involved with the identification, evaluation, design, permitting, construction and ecological monitoring of dozens of tidally restricted coastal wetlands in Massachusetts, New Hampshire, Maine as well as assisted with a few projects in maritime Canada.    In addition to following the situation at the Cat Dam site, I have actively participated in the two recently completed tide restriction projects that were sponsored by the Town of Cohasset at Border Street and at Jacobs Meadow.  Based on my combined academic and field experience focused on tidally restricted coastal wetlands I cannot concur nor support the proposal in the attached NOI to significantly manipulate and minimize natural tide flow to the coastal wetlands upstream of the Cat Dam.  I am not aware of any other tide restriction project in the Gulf of Maine where  substantiating a case where the level of daily, weekly and seasonal manipulation such as proposed for the Cat Cam site would be environmentaly beneficial.  I view the proposed management of the tide gate as a clear negative impact to the functions and values of this wetland.  My recommendation would be for the town to manage the Cat Dam tide gate to its fullest open capacity on an on-going daily basis.

Based on the information within the NOI, the Town of Cohasset is in good position to restore full tidal flow to the upstream wetland complex.   By pursuing full tidal restoration you have the opportunity to support the near coastal resources that are so important to the commercial and recreational fisheries interests in Cohasset and neighboring communities.  In addition to ecological benefits of  keeping the Cat Dam tide gates in full and open position you will reduce the time and cost associated with operation and maintenance that is proposed in the current NOI.   The level of operations proposed in the NOI will also result in reduced safety liability with town staff and or volunteer labor having the responsibility or ability to adjust the tide gate.  Tide gates are inherently dangerous structures and minimizing the need to make ongoing setting changes should be avoided to the extent practicable.   Based on my assessment of the Cat Dam site you should consider an alternative to altogether remove the tide gate in order to maximize ecological benefits while reducing long term financial burdens associated with on-going operations and maintenance.

1.  EPA does not support the current proposed NOI tide gate operation plan.

2. The existing tide gates when closed and operational in their normal condition, retain open water in the upstream Inner Little Harbor area.

3. Water quality as well as shellfish and wildlife habitat would continue to be impaired under this proposed operational plan..

4. The impairment is caused by the impoundment of water behind the tide gates during the intended closed tide gate operations. Any prolonged impoundment of tidal and brackish water behind the Cat Dam Nichols Road tide gates is detrimental to water quality and habitat for fish and wildlife.

5. Further, the periodic opening of the tide gates stresses the ecology of the Inner Little Harbor area because of the fluctuating physical, biological and chemical characteristics.  In contrast, consistently greater flushing and fuller drainage would improve water quality and habitat for fish and wildlife.

6. EPA believes that implementation of the CLE Engineering Inc Tide Gate Operations and Maintenance plan dated May 12, 2010 would comply with the Wetland Protection Act as well as the federal Clean Water Act goal “to restore the physical, chemical and biological integrity of our nations waters.”

Sara Grady

Ecologist/South Shore Regional Coordinator for Mass. Bays Program

North and South Rivers Watershed Association


Grady said…This system requires regular tidal flushing on a daily basis.  Short
duration flushing events such as those proposed will only temporarily improve water quality as water from Little Harbor and Massachusetts Bay enter the system. Once the gates are closed again, the “new” water quickly warms up because ILH is so shallow. It also has  oxygen fluctuations typical of a eutrophic system –  hypersaturation during the day when algal mats and phytoplankton are producing great quantities of oxygen, and hypoxia and anoxia at night when metabolic
activity of ILH’s organisms pulls the oxygen out of the water.

This (the above) is the phenomenon that was misinterpreted by the E20 group in their presentation from December 6th, which is not included with the NOI filing but should be, as it serves as the foundation for some of the management detailed in the NOI. In this presentation, they noted that oxygen quantities were lower in Inner Little Harbor when water levels were higher (due to an influx of Massachusetts Bay water.)  This is due to the high biological oxygen demand of the system, which is typically supported by high photosynthetic rates. When the comparatively oxygen-poor water from Massachusetts Bay enters Inner Little Harbor, oxygen is quickly consumed. Another reason that the system should be exposed to daily flushing in lieu of short-term periodic flushing is that such events are a shock to the system. The organisms in Inner Little Harbor are estuarine species and as such are adapted to the daily fluctuations in salinity and water  level that accompany a daily tidal regime.

John Logan

Fisheries Habitat Specialist

New Bedford, MA office

Logan said….Given the high ecological value of salt marshes and estuarine ecosystems (Boesch and Turner 1984; Costanza et al. 1997) as nursery, foraging, and spawning habitat for a range of commercially and recreationally important finfish and shellfish species, MarineFisheries recommends the restoration of natural tidal flow to allow the ILH-LH complex to attain a more natural state. The operation schedule proposed in the most recent NOI will promote further eutrophication of ILH while limiting natural movements of shellfish larvae and fish between these embayments. Maintaining an open tide gate year-round would alleviate these concerns and increase the overall function of this important fisheries habitat.

In summary, MarineFisheries has the following comments:

Opening the tidal gates throughout the year would restore a more natural tidal flow to the ILH-LH complex.

A more natural tidal flow would benefit the salt marshes in the system, as well as a wide variety of species, including winter flounder, prey fish of bluefish and striped bass, and shellfish.

The proposed operation schedule, with restricted tidal exchange from April through November, occurs during the peak period of biological activity in the region.

© Copyright 2011 Tanna K, All rights Reserved. Written For: Tinytown Unleashed

  1 comment for “Cohasset CC Receives Regulatory Comments on Cat Dam NOI

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