Green Harbor Estuary Restoration and Tide Gates
The Town Engineer has recently accomplished necessary repairs and maintenance of the tide gates and water control structures on Dike Road. This dike was originally constructed in the late-1800’s to drain the approximately 1000-acre Green Harbor estuary and salt marsh for agricultural use. Although there are no longer active farms in this “polder”, golf courses, wildlife sanctuaries, cranberry bogs, an airport, and houses now exist in the area that had flooded with every high tide prior to dike construction.
The dike and tide gates operate to let water flow out of the upper Green Harbor River but prevent the flooding tide from passing upstream. Adjustable sluice boards control the minimum water-level upstream of the dike. This system and water management method results in poor water quality, especially during periods of little precipitation when the upper river is stagnant due to little or no flow.
We have considered re-establishing limited tidal flow upstream of the dike in order to improve water quality and restore estuarine habitat. While the potential environmental gains are very significant, care must be taken to ensure that no detrimental impacts to private or public property result. Careful attention to allowable flow rates and maximum allowable water level above the dike should permit a controlled amount of tidewater to flow upstream while safeguarding properties.
The US Army Corps of Engineers, Massachusetts Coastal Zone Management and Department of Environmental Protection have committed to help support Town of Marshfield-led efforts to allow more tidal flow into the upper Green Harbor River.
CZM funded a preliminary study of the upper Green Harbor River which was completed in draft format in early 2007. This study, headed by the Louis Berger Group, included experts from UMass-Dartmouth and Applied Coastal Research and Engineering who studied the ecology and hydrology of the upper river, as well as an assessment of the existing dike and tide gate structures. Findings were incorporated into a computer model of the system which was then tested to prove that it accurately modeled the river.
Initial conclusions from these efforts indicate that significant improvements to water quality and estuarine habitats (including fish and shellfish nursery areas) can be made with relatively low expense by modifying the tide gate structures and without threat to adjacent properties or businesses.
Please attend a meeting on Wednesday April 25, 2007 at 6 pm at Town Hall Hearing Room 2 where results of the study will be presented and improvements to the tide gates will be proposed.
If you have any questions please contact: Jay Wennemer, Conservation Agent at 781-834-5573.
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