Challenges

In June 2015, after many years without incident, foundation seepage (a boil) and evidence of turbid discharge were observed in the channel immediately downstream of the spillway. This posed immediate risks to the Town of Milton, a short distance downstream.

Hatch recommended immediate, controlled reservoir drawdown to manage this risk.

Solutions

• Hatch conducted initial inspections, assessments, instrumentation reviews, surveillance instructions, risk studies, and advised the client on the dam condition and the risks it posed.
• Assisted the client in the design and construction of a reinforced concrete stilling basin to dissipate the significant energy within spillway flow releases and thereby avoided significant erosion at the toe of the dam that could lead to dam failure.
• Remedial grouting within the body of the dam to enhance the seal between the concrete box culvert and the adjacent sheet pile cut-off wall.
• Constructed erosion protection at the emergency overflow spillway.

Highlights

• Hatch designed the preliminary diversion channel scheme and construction sequencing which was adopted in the construction phase.
• Quantitative risk assessments tools were applied to inform the client of the risk profile and potential loss-of-life consequences regarding a potential dam breach in this highly populated, urban area.
• Hatch’s engineering intervention restored the dam to its full recreational potential and significantly improved reliability and safety, reducing risks to the natural environment and downstream communities.