Lorne Street Naturalized Stormwater Management Pond

In 2019, following four major flooding events in five years, the Town of Sackville constructed a naturalized stormwater pond near Lorne Street (Phase I and II) to store approximately 40,000 m3 of stormwater during major storm events. The flooding adversely affected businesses and residents in this area, posing a limit for economic growth and causing accessibility concerns for emergency services. Prior to the construction of the stormwater pond, the Town upgraded stormwater and sanitary municipal services in the area. The Lorne Street projects encompass stormwater management upgrades to transport the stormwater flows that normally flood the Lorne Street area and redirect them to the Tantramar River. This system is ideal for flood risk reduction and is designed to protect and enhance other ecosystem services—including recreation and habitat space. These actions were identified as priorities in the 2016 Sackville Corporate Climate Change Action Plan (CCCAP), which details climate change impacts affecting the municipality, including changing precipitation patterns, sea level rise, intensifying storms and storm surges, and rising temperatures. Phase III of the project, currently awaiting funding, would include a second retention pond and add an additional 60,000 m3 of storage.

Identifying Actions

A series of flood scenarios were developed for the CCCAP and the plan recommends a series of actions to address each identified priority area, including Lorne Street. Mount Allison University conducted a community vulnerability assessment for Sackville and hosted several workshops with the public to identify areas of risk and vulnerability to flooding. The CCCAP identified the following actions to be undertaken by 2021 to mitigate flooding and increase resilience in the Lorne Street area: 1) Undertake a hyrdo-technical study of the watershed to assess adaptation options; 2) Undertake Lorne Street infrastructure upgrades; 3) Create an integrated, community-wide approach to stormwater management; 4) Construct stormwater retention ponds of adequate size to accept increased precipitation. Additional engineering studies were undertaken, and the sizing of the stormwater retention ponds was based on a PCSWMM stormwater model, in which various inputs were used to appropriately size the ponds. The new ponds were sized based on a 1 in 100 year return period, 24 hour design storm, and consideration was given to tidal impacts which further limit the ability of water to drain from the site. During a rainfall event, the new ponds were designed to retain the water during the high tide and allow the water to discharge during the ±six (6)-hour window when the tides are low enough to allow drainage from the site. The complete stormwater management strategy for the Lorne Street (Phase III) area includes requirements for additional storage volume, to reduce peak flows and provide runoff storage when tide levels are high. This will be accomplished through the provision of two stormwater management control areas.

Implementation

Actions to mitigate flooding in the Lorne Street area took place in two phases with an anticipated third phase currently awaiting funding. The initial phase of the project included the complete road reconstruction of Lorne and Saint James Streets, focusing on upgrading the aged and deteriorated infrastructure. Phase II encompassed the retention pond and stormwater management upgrades to transport the stormwater flows that normally flood the Lorne Street area and redirect them to the Tantramar River. Phase III of the project will include:

  • Construction of a new stormwater retention pond;
  • Repurposing the abandoned Pickard Quarry and construction of a new outlet, dyke and control structure to create a stormwater retention pond which will connect to the Town’s existing stormwater infrastructure that leads to Lorne Street.
  • Ditching upgrades and re-alignment, connecting the Lorne Street area to the ponds and subsequently to the Tantramar River;
  • Construction of a new sediment basin in the new ditch upstream of the aboiteau;
  • New culvert installation underneath Canadian National Railway (via jack and bore method);
  • Installation of new culverts at various roadway crossings (via conventional open trenching methods).

Outcomes and Monitoring Progress

The project was put to the test in August of 2021 when more rain fell during a single storm in Sackville than in the entire month of August combined. The rain filled the town’s new retention pond, had sewage pumping stations working at capacity, and caused isolated flooding at spots throughout town. The new infrastructure fared well and held the water that came down to Lorne Street but the Town noted that the worst of the storm had not come at high tide. And, despite the storm not hitting a one-in-100-year levels, the system and stormwater pond were at capacity. The August 2021 storm also placed a strain on the town’s sanitary sewer system due to the infiltration of stormwater. This emphasizes the need for Phase III and the additional 60,000 m3 of storage capacity.

Next Steps

This phase of the flood control project is a short-term solution and the town is working towards obtaining funding for Phase III to construct a second large retention pond to conduct all of the water from the Lorne Street area to a new, double-gated aboiteau for discharge into the Tantramar River. The Town also continues to urge people to install back flow prevention on their sanitary and storm sewers in their homes.

Resources

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