RESTORATION OF THE ELEUTHERIAN MILLS DAM &
ADJACENT MILLRACE
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Duffield Associates was retained by Hagley Museum and Library (Hagley) in 2005 to perform a review of the existing Eleutherian Mills Dam on the Brandywine River at the location of the original DuPont Powder Works. The dam and adjacent millrace were built in 1803 by the DuPont family to harness the power of the Brandywine River for their use in gunpowder production. Hagley was interested in restoring the dam to its historical configuration. The dam was operational; however, it was in a deteriorated condition and the timber faced spillway was completely missing in some areas.

Duffield Associates' project team assessed the condition of the dam and the spillway including researching and reviewing historic documentation from the 1800's and 1900's. A detailed field review of the dam was completed under challenging conditions given the location of the structure in the Brandywine River. Traditional investigative methods such as test borings or other physical testing were impractical given the necessary permitting and associated costs. Several alternatives for repairing/ reconstructing and refacing the dam spillway were developed by Duffield's team. Alternative repair materials were evaluated but FSC wood facing was ultimately selected as the most suitable to replicate the historic wood facing.

Once a preferred alternative was selected, Duffield Associates then worked closely with state and federal regulatory agencies to obtain permits for the dam restoration project. The permitting was completed within an expedited timeframe so restoration construction of the dam could take place during the late summer months, when river flows are historically at their lowest.

Modifying the adjacent millrace to enable future passage of migratory fish (such as American Shad) around the dam was also considered as part of this project. Development of a fish passage mechanism was done collaboratively with local and federal regulatory agencies including the U.S. Army Corps of Engineers, U.S. Fish & Wildlife, National Marine Fisheries, Delaware Department of Natural Resources and Environmental Control, Delaware State Historic Preservation Office, and the Brandywine River Conservancy.

Hagley contracted CGC Geoservices, an affiliate company of Duffield Associates, to perform the restoration of the dam and adjacent millrace. Construction of the spillway restoration began in July 2009. Duffield Associates provided field engineering support during the construction to make adjustments to the design as necessary based on the actual conditions uncovered during construction as well as to deal with the challenges of construction in the middle of the Brandywine River.

This project was awarded the 2010 New Castle County Historic Preservation Award for Industrial Technology Restoration.

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Hagley Magazine - Rebuilding the Eleutherian Mills Dam