Jelliff Mill Dam Renovation Project

After the Department of Environmental Protection (DEP) classified Jelliff Mill Pond Dam as a threat to downstream properties in January of 2010, New Canaan along with declared in April of 2012 that Jelliff Mill Pond Dam existed within the regulated 100-year floodplain and would require substantial modification in order to meet all applicable FEMA and Town of New Canaan Flood and Erosion Control Board requirements.

The process of erecting a code compliant structure commenced on July 9 with the destruction of Jelliff Mill Pond Dam and, a month later, Trinkaus Engineering has accomplished the following:

-Removal of trees and brush from the river channel downstream of the plan

-Removal of the old masonry stone wall found in the middle of the downstream channel about the culverts under Jelliff Mill Road

-Installation of stone filter berm and riprap protection downstream of the dam face

-Removal of one of two top stones from the eastern end of the dam (closest to the building) to create an opening of three to four feet in length and approximately ten to twelve feet in depth (varies per thickness of stone) to allow lowering of water surface upstream of dam

- Removal of additional surface stone to widen the top opening and facilitate the removal of the second layer of stones to lower the water surface to 12 feet or so

Note: The sequence of stone removal will continue until the bottom of the existing dam has been reached, by the opening of the dam along the eastern edge only. This will minimize the transport of accumulated sediments from above the dam. As the water surface is lowered, the accumulated sediments will be slowly dewatered in place, which will facilitate their removal.

Ultimately, a new dam made of concrete (rather than stone) that is capable of withstanding the flow of 1,230 cfs (cubic-feet-per-second) will be constructed while the pond is drained. The new design will eliminate overtopping at the west end where the spillway abutment shows major erosion due to the forces of the storm flows.

The underlying structure of the building on site and the bridge will, for the sake of space, be addressed at a separate time. 

Find the full, 53-page report here. 

About this article: The Jelliff Mill Pond Dam renovation project is ongoing and extensive. This article will act as a source for major updates and advancements in construction. Stay Patched in here to get the latest on this project from Inland Wetlands.