October 30, 2025
No Comments
WMHO has taken action at its own expense over the past months to complete critical studies that are needed for this project and the design of the road and dam. These studies are all essential steps before a design for the restoration of the dam and the road can be engineered, and WMHO remains committed to continuing this work while awaiting FEMA’s determination.
The following studies are either completed or in progress:
Stony Brook Grist Mill Summary – Completed
The results of the Stony Brook Grist Mill study is that the structure is incorporated into the western end of a small earth embankment beneath the western part of Harbor Road.
The upstream (south) side of the road embankment across from the mill is retained by a bulkhead made of timber piles braced by steel tie rods. The timber bulkhead is in fair and good condition with visible deterioration of the timber sheathing planks on the upstream face. The bulkhead ends at the mill wheel sluiceway.
The downstream (north) side of the road embankment next to the Grist Mill is retained by historic stone masonry structures, which form retaining walls and a spillway. The main stone retaining wall extends from the spillway to the Stony Brook Grist Mill, where the wall is roughly 8’ to 10’ feet high and also serves as the south foundation wall of the Grist Mill.
In the engineers report the re-established dam and roadway can be accomplished without demolition or major reconstruction of the existing grist mill structures.
The existing stone masonry walls within and adjacent to the Grist Mill are sensitive to deformation and vibrations. To mitigate risk of damage to the existing walls, heavy vibrating compactors should not be operated on roadway subgrade adjacent to the walls and trenching or excavation for utilities should be limited in depth.
Ground Penetrating Radar – Completed
By using ground penetrating radar (GPR) it is determined there is an underground concrete structure that is 4 feet below the road surface and 3 ½ to 4 feet wide.
The structure appears to extend from the front of the Mill to the spillway.
Borings – Completed
The subsurface investigation consisted of three (3) geotechnical borings. The borings were taken from the surface of Harbor Road to depths ranging from 50 feet to 62 feet. Special tools were employed as the borings were advanced to collect samples of the soil for classification.
The geotechnical investigation findings enable interpretation of the subsurface soil strata beneath the roadway. These include a shallow layer of sandy backfill placed during construction of the embankment, underlain by natural glacial soil. The natural soil layers include sandy glacial outwash soil deposited as glaciers melted and retreated, as well as some deeper layers of clay deposited prior to glacial retreat. The clay layers may be beneficial to reducing water seepage through or beneath the west end of the embankment when the Mill Pond is restored.
The results of the boring tests will help with design and repair of the road.
Preliminary Hydraulics – Conceptual Alternatives Completed
The engineering company completed a preliminary Hydrologic Modeling to assess runoff from the August 2024 storm event, which was a contributing factor in the dam failure. The company also modeled four standard design storms to develop preliminary flow estimates. These results will guide the conceptual sizing of the new spillway.
Phase II will continue the hydrologic / hydraulic study in a more detailed matter that includes the existing and proposed drainage from surrounding areas.
