Why does the Pretty River Dyke need to be maintained?
The dyke is a flood control structure, and requires maintenance to ensure it functions as designed.
A recent study found that vegetation such as trees and large shrubs has continued to grow on the dyke, slowing down the flow of flood waters and reducing the capacity of the corridor which in turn could lead to flood waters spilling over the dyke during a Provincial Regulatory Storm Event. The 1961 Timmins Storm Event is one example.
According to the Government of Canada, on the day that the Timmins Storm Event occurred, temperatures during the afternoon were over 25°C, skies were cloudy and an occasional roll of thunder could be heard. By 6:00 in the evening, heavy rain began which lasted for a couple of hours. Light rain commenced again about 9:00 p.m. and continued until 11:00 p.m., when it became a torrential downpour for over an hour. During the heavy rains thunder was continuous and accompanied by an occasional burst of hail.
Although the downpour only lasted a few hours, it ripped roads apart, smashed houses, undercut foundations, and damaged personal property. A mother and her four children were drowned in a house on the bank of the creek.
Will River Trail still be available for recreational use?
Yes. The River Trail will still be available for recreational use.
The maintenance work will be separated into short sections along the dyke. Each section will start and end at an access point, so trail users will have opportunity to exit the trail to avoid work crews.
Phase One of the project will be completed in the Fall of 2021.
Phase Two is divided into two parts: assessing and making an inventory of the trees and remove the hazardous trees. This phase is anticipated to be completed by the end of 2022.
How is the project funded?
The project has been funded through the Province of Ontario, the Town of Collingwood and NVCA.
This project is reliant on municipal funding, as the flood control structure greatly benefits the residents of Collingwood.
How will this affect the wildlife that currently live in the area?
The Pretty River Dyke will continue to contribute as an urban fish and wildlife corridor. Trout and salmon will continue to move upstream to their spawning grounds with the young moving downstream to Georgian Bay. Low shoreline shrubs will continue to support fish habitat and nesting/foraging birds. Opening of the canopy will likely increase wildflower cover which will improve habitat for pollinator species (including Monarch butterflies - a Species at Risk) and increase foraging habitat for several bird species. Life will continue to move upstream and downstream through the corridor.
Tree and large shrub removal will take place outside of the breeding bird season to minimize impacts on nesting birds. Low vegetation that may be disrupted during tree and large shrub removal will quickly "bounce back" from this disturbance.
Why is Collingwood at risk of flooding?
Portions of the Town of Collingwood is at risk of flooding as the town was built on a shallow floodplain. Some of the most notable floods are the 1912 Victoria Day Flood and the 1942 St. Patricks’ Day Flood. In the 1970s, the Pretty River Dyke was built to reduce the risk of flooding in the urban areas of Collingwood.
What will the dyke look like after the vegetation is removed?
Currently, dense tree, shrub and ground cover are covering the small stone which protects the banks from the erosive forces of flowing water. After the trees and large shrubs are removed, the stone will be more visible. Looking from the recreation trail, the river will also be more visible.
What will happen to fish and wildlife habitat?
It is important to strike a balance for community safety, water quality and habitat protection. Although trees and large shrubs must be removed to ensure flood waters can flow through the dyke, groundcover such as grasses and wildflowers along the dyke will not be removed. These plants are important habitats for pollinators, including Monarch butterflies, a species of concern. Groundcover is also a great foraging source for many birds.
Low shrubs such as dogwood and willows along the edge of the water will not be removed to continue to support fish and wildlife habitat. Ground cover and low shrubs retained along the dyke system will quickly recover from any disturbance associated with removal work. The urban natural corridor associated with the Pretty River will continue to function.
How will the vegetation be removed?
The vegetation will be removed in two phases for every section (see map of Pretty River Floodplain for location of sections)
Phase One – Remove the Understory (small material)
This phase includes removing small woody material such as smaller trees and large shrubs along the slope of the dyke. Lower shrubs such as dogwoods and willows along the edge of the water will not be removed. To prevent the spread of invasive species, the vegetation will be disposed at an approved site such as a municipal landfill or a composting facility.
Phase Two – Assessing and Removing Select Trees.
Once Phase One is completed, NVCA will inventory and assess the larger trees and shrubs and develop a plan to remove those that are compromising the flood capacity of the Pretty River Dyke. More information about Phase Two will be available after Phase One is completed.
Maintenance work will begin on Sections 4 and 5 of the Pretty River Dyke. Phase One will start in the Fall of 2021, and Phase Two is expected to start in 2022. To protect nesting migratory birds, vegetation removal will not take place between April through July.
Maintenance work will be ongoing, and residents should expect regular vegetation removal along the dyke, as well as regular trail closures for visitor safety