How muck from the mouth of the Don River becomes new land for the Leslie Street Spit
Every spring and fall, PortsToronto scoops thousands of tons of mud and silt out of the Keating Channel, the manmade waterway at the mouth of the Don River. The dredging reduces the risk of dangerous flooding, but it also serves another purpose: once the muck is extracted, workers haul it across the inner harbour and carefully deposit it in specially reserved “cells” on the north side of the Leslie Street Spit, where it will eventually make new land, enlarging the existing wildlife preserve.
Here’s a look at how PortsToronto keeps the Don River flowing.
The dredging is done with a 60-year-old, crane-like piece of equipment called the Derrick 50 (pictured above), which is equipped with a claw that can hold up to 2.6 cubic metres of material. During fall, the Derrick works five days a week. It’s towed into place using a barge and then anchored with metal supports.
The goal of the dredging is to remove mud and other debris that washes down the Don River. Without the periodic purge, the Keating Channel would eventually become blocked, which would pose a flood hazard.
The material scooped up from the bottom of the Keating Channel, most of it mud, is deposited into a barge with four compartments. In total, the barge can hold about 300 tons of muck, which is roughly equivalent to 200 scoops from the Derrick 50. Five full barges a day are ferried to a lagoon on the north side of the Leslie Street Spit.
PortsToronto dredges the Keating Channel to an approximate depth of 5.8 metres, which is more than two metres shallower than the rest of the harbour. “Here, there’s no commercial boat traffic, so we can go to whatever is needed for the health of the river,” says Angus Armstrong, PortsToronto’s harbour master.
Operating the Derrick 50 is a technical challenge. Everything from the raising and lowering of the bucket to the swing of the crane is controlled by clutches, levers, and cables. The noise from the Caterpillar engine inside the control box is deafening as dredge operator Don Murphy lifts the bucket from the water and drops another load in the barge. “It’s just mud, sediment. Some trees sometimes,” he says. “I wasn’t operating at the time, but a couple of years ago we got a Porsche. It was in two pieces.”
Once the barge is full, a crew from Toronto Dry Dock, a marine company contracted by PortsToronto, takes over the operation. The M. R. Kane, a tugboat, pushes the 300-ton barge under the Cherry Street lift bridge and out into the open harbour. All the while, operator Douglas Hopp tracks the vessel’s location and speed while keeping detailed navigational notes in a logbook.
The crossing of the Toronto Harbour is smooth on this particular day, but, when the weather is bad, piloting the barge can be a challenge. “There are times we can’t go across,” says Hopp. “Even if the barge is empty it gets thrown around very badly.” Recreational vessels pose another hazard. “For the most part people stay out of our way, but occasionally you have to blow the horn at them.”
Hopp guides the barge to a precise location marked on his GPS and paper maps before dropping his muddy cargo into the lake. All drops are carefully logged and planned in advance. In 60 years, the lagoon will be filled to a depth of 10 feet, and eventually it will capped with a layer of clay and shale, creating new land that will be turned into a wildlife habitat by the Toronto and Region Conservation Authority. Another lagoon to the east was completely filled with dredged material in 1997 and is currently under TRCA management.
The Leslie Street Spit is still a work in progress. During the week, dump trucks from construction sites across the Toronto region continue to deposit clean fill on the city side of the man-made landform, adding to its bulk. Combined with PortsToronto’s filling of the lagoons, the manmade landscape of the spit is continually in flux.