In August, 2001, an 8-inch storm event caused a 100 foot breach in the dam draining the pond and causing significant damage to the mill's intake structure and erosion of a major downstream highway. Responding to an emergency request by DNREC, our engineers were on site within hours of the breach to evaluate the failure.

Solution
A comprehensive engineering study performed by our structural, water resource and geotechnical engineers evaluated the existing condition, design, timber sluice gate, and concrete outlet box culvert control structure. Review indicated that the dam embankment consisted of sand with remnants of a timber cribbing structure filled with concrete, soil and stone. The deteriorated timber cribbing, erosion susceptible sand core, and overvegetated embankment did not meet design standards and were key in the dam's failure.

DNREC authorized our firm to prepare construction documents for the emergency repair of the breach. Limited funding combined with public pressures mandated that the design and construction be done quickly and efficiently while still meeting required engineering standards. Dam repairs also had to be sensitive to the historic character of the adjacent mill.

Construction drawings were completed and all necessary permits acquired by December 2001. A construction contract was awarded and total replacement was completed in less than 10 months. Fall rains quickly refilled the pond.
Key design elements included: removal of the remaining embankment; a unique steel sheet pile and clay cut off "core" in the new dam; a new earthen embankment over composite core. Stone riprap and innovative vegetated synthetic erosion control material for embankments stabilization; a new water intake pipe to power the mill; a unique system of reinforced concrete walls adjacent to the mill; replacement of unreliable "flash boards" with an operating steel gate system; and steel sheeting and concrete cutoff trench along the toe of the concrete outlet structure to control seepage and undermining.

Through a team effort by DNREC, the design team and the project contractor, this project was designed, constructed and returned to service in record time and within budget. The replacement dam's design preserves the areas' historic appearance and complements the adjacent historic mill.

Our participation in this project won an Honors Award from the Delaware Council of Engineering Companies.