The District of North Cowichan will begin emergency repairs this week after two major water lines were found exposed in the Cowichan River.
The main trunk lines, which supply drinking water to about 22,000 residents in the south end of North Cowichan and Crofton, were discovered in a “significant scour hole” about 875 metres downstream from the Trans-Canada Highway bridges south of Duncan.
The district said the erosion had lowered the riverbed by about one metre, and also compromised the stability of the south-side dike, which protects Boys Road, Cowichan Tribes lands, the Boys Road water treatment facility and the municipal well field from flooding.
The two exposed trunk mains cross the Cowichan River from the Boys Road Water Treatment Facility. A third main, the Cowichan Valley Regional District sanitary force main, is located just downstream of the two pipes.
According to North Cowichan’s engineering department, the mains are normally buried one to two metres below the riverbed.
The exposed pipes were discovered by municipal crews in early June.
Tom Rutherford, strategic priorities director for the Cowichan Watershed Board, said the scouring was likely caused by heavy winter rains that bring debris such as logs into the river. High flows during the winter months can also move gravel and alter the river’s course, he said.
North Cowichan Mayor Rob Douglas said council has approved emergency construction to protect the pipes and dike.
“If left unaddressed, this situation could result in catastrophic water main breaks and dike failure,” Douglas said in a statement on Wednesday.
The $4.5-million project will be completed during a designated fisheries window starting Friday and continuing through to Sept. 15.
Emergency clearance granted by Fisheries and Oceans Canada and the Ministry of Environment says this is when the risk to trout and salmon in the Cowichan River will be lowest.
The work will include construction of isolation berms and the excavation and removal of gravel from the riverbed.
Crews will then lay a new gravel cushion over the exposed pipe, install layers of stones to form upstream and downstream sills, and reinforce the south-side dike.
The river and dike project is the first step in the Boys Road Trunk Main replacement project, which will upgrade aging water infrastructure with larger pipes to improve long-term capacity and reliability for the South End and Crofton areas.
North Cowichan said addressing the exposed trunk mains in the Cowichan River immediately is a “critical early action” to protect the existing system and lay the groundwork for future improvements.
