After decades of drainage issues, public input meetings, engineer reports and various Drainage Act appeals, excavators have rolled through most of the South Innisfil Creek Drain (SICD) and famers finally have the drainage they need. But, to an average passerby, the drain may look more like a beautiful creek that had always been that way. In this case, the drain is being restored and upgraded using innovative natural techniques that were designed to improve drainage, while also addressing water quality and enhancing aquatic habitat.
The Innisfil area is home to both intensive farming and development. The main drain is over six miles long, was first constructed in 1903 and drains more than 20,000 acres before emptying into the Innisfil Creek, the Nottawasaga River and finally Georgian Bay and the Great Lakes.
Jeff Dickson (P.Eng. drainage), Chris Pfohl (CET, EP, sr. aquatic ecologist) and the team at R.J. Burnside & Associates Limited worked on the SICD with Jeremy Nyenhuis, Drainage Superintendent for the Town of Innisfil, in cooperation with the Department of Fisheries and Oceans Canada (DFO) and the Nottawasaga Valley Conservation Authority (NVCA). The contract went to R&D Excavating LTD, and construction began in 2021. Much of the project is expected to be completed by the end of 2024.
Because the SICD is classified as fish habitat, improvements were especially tricky. It is often said that necessity is the mother of invention and, in this case, the drainage requirements as well as the environmental restrictions challenged the design team to take drainage to a whole new level.
The most noticeable design innovation is the nearly three miles of two-stage drain. Drainage tiles outlet onto the upper vegetated bench where sediments and nutrients are deposited. This improves water quality, meaning drain cleanouts will be needed less frequently.
The bench of the main drain was vegetated with sod mats that were sourced on-site. The drain was widened by approximately 25 feet, and the native grasses with their root systems intact were carefully removed in mats that were six to 12 inches thick and three to five feet long. The mats were placed onto the bench of the drain once it was constructed to elevation and width; after placement, the sod mats were watered, instantly revegetating the drain. Within weeks, the job site looked completely naturalized.
Many of the materials used to stabilize the sections of degraded drain bank were also found on site. Trees or woody material (primarily cedar) and root wads, which were cut, salvaged, and removed prior to or during excavation, were anchored or pinned into and along the drain banks and combined with live stakes such as dogwood or willow, effectively stabilizing quite a few eroding outside bends. A French drain was also made of logs at the bottom end of an oxbow which was re-purposed as a wetland to provide additional water holding capacity during larger flows as well as habitat for green frogs, turtles and birds.
Another noticeable feature is a Barefoot Box Culvert that replaced two corrugated steel pipes running under the 4th Line in the upper reach of the watershed. It is an eight-foot high by 20-foot wide precast concrete structure with perforations in the bottom designed to promote and allow groundwater upwelling to support fish habitat. Designed by Burnside’s Pfohl, the capacity of this culvert allows for high flows to pass safely under the roadway, and contributes cooler, fresher water into the drain.
Just downstream of this culvert, various sizes of stone substrate were added to the bottom of the drain to enhance existing fish spawning areas, and a number of riffle-pool sequences were created to boost water quality and provide habitat. A riffle is a shallow gravel area that produces a steeper gradient change in the drain bottom followed by a pool where fish species can rest and find refuge when flows are low.
Dan and Julia Rice of R&D Excavating worked closely with the Burnside Team to bring the engineering drawings to life. They had worked on similar projects, but never one of this size and complexity.
Many of the drain’s features will be described in an upcoming video and are detailed in two bulletins in Burnside’s series Drains Done Differently, available on their website. The team has hosted tours for stakeholders to demonstrate how drainage and habitat can co-exist.
As we look to the future and weirder weather in the forecast for farmers, along with a growing concern for water quality and our natural environment, the South Innisfil Creek Drain demonstrates that drains can be done differently and that both needs can be met. DC
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