Gateway Mall Berm

In 2019, the Town of Sussex constructed the Gateway Mall berm to protect residents and businesses from flooding caused by heavy rain, exacerbated by ice jamming and the spring freshet in the Kennebecasis River. Over 12,000m3 of berm was constructed, stormwater infrastructure was replaced, a duckbill backflow valve was installed to prevent backflow of stormwater and the river, and a pumping station was constructed to handle storm runoff during flood conditions. The berm was put to the test in December of 2020 and successfully held back the river during another extreme rainfall event. The construction of the berm has been part of a larger effort to mitigate ongoing flood risk. In 2019, the Town also released a community-wide flood risk mitigation plan that provided conceptual designs, refined project costs, and identified benefits/risks for six flood risk mitigation projects. The plan also identified properties and stakeholders affected by each of the identified flood risk mitigation projects and identified potential downstream risks associated with flow transfers from the recommended diversion projects.

Identifying Actions

The Town engaged an engineering firm to study and develop a hydraulic model for the Gateway Mall area where historical, recurring flooding has taken place. The study identified an existing partial berm behind the Gateway Mall that, if it extended further along that stretch of the Kennebecasis River, could help in stop river flood waters from rising so high that they spill onto the mall parking lot. Given the extent of the damage from previous floods and the opportunity to obtain cost-sharing funding for the construction of the berm through Public Safety Canada’s National Disaster Mitigation Program, a technical review committee identified this berm as a priority flood mitigation project.

Simultaneously, a community-wide Flood Mitigation Master Plan was being undertaken with the Town of Sussex and Village of Sussex Corner. Five other projects were identified as high priority, including two diversion channels that would return the flow of water to its prehistoric path to battle against the rising waters residents and businesses are increasingly faced with. In all, the six projects proposed could cost over $24 million. That success of the master plan will also rely on the execution of a handful of smaller projects spanning the two municipalities and is expected to take more than five years to complete.

Implementation

The Gateway Mall flood mitigation berm is located between Gateway Street and the Kennebecasis River, which is adjacent to NBDTI Route 1 eastbound within the Town of Sussex. The flood mitigation berm was constructed using imported fill with a lower permeability core to minimize water seeping through the embankment. The berm was designed to mitigate future flood damages from high water levels and backwater effects from the Kennebecasis River. Over 12,000m3 of berm was constructed, and culverts were removed and replaced with storm sewers. The main storm sewer outfall was replaced, and a duckbill backflow valve was installed to prevent the stormwater and river from backflowing. A pumping station was constructed to handle storm runoff during flood conditions and a mobile pumping station was also purchased.

Outcomes and Monitoring Progress

The Gateway Mall Berm was completed in the spring of 2020 just in time to prevent a much larger flood in the area in December when the Town was hit with extreme rainfall again. Ground monitoring and drone footage showed the berm functioning as expected.

Next Steps

The broader flood mitigation plan identifies five more priority berms and/or channel diversion projects as well as significant stormwater infrastructure upgrades to mitigate community-wide flooding issues. Prior to further project implementation, an extensive community engagement process will be undertaken with residents and business. Next steps also include understanding any changes to flood risk, confirming return on investment for these priority projects, and applying for federal and provincial funding to support the costs.

Resources

Link to Full Case Study

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