Q&A: Auxiliary SPillway and Trencher

Learn more about Auxiliary Spillways and why they are being included in the dam projects. Find out how a trencher works and how the contractors are using it. 

Q: What is an Auxiliary Spillway? 
A: Pictured below is the Secord Dam auxiliary spillway. The auxiliary spillway is a secondary spillway that will pass water from an extremely large storm event if the primary spillway exceeds its capacity. This provides a controlled way to manage high water flows. The water would get diverted into this large concrete basin then passed through a chute and returned to the river further downstream of the dam. None of the dams previously had auxiliary spillways – this is a new and very important safety feature.

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Q: What is the Trencher at Edenville Dam and what does it do? 
A: To better control seepage through the embankments, a seepage cutoff wall is being constructed along the upstream edge of the crest of the embankments down to the glacial till. To build the wall, a trencher excavates the soil to depth and continually mixes it with bentonite (an absorbent swelling clay) and cement. This creates a strong and impermeable wall. There will be short sections of steel sheet piling to connect the wall to the existing spillways.

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