Toronto’s Rivers Come Alive in 2005! ~ Edwards Gardens ~ M. Beukeboom

Edwards Gardens and Wilket Creek Park are popular places to walk and enjoy the Don Valley.

The Event On August 19, 2005, Toronto experienced torrential rainfall that flooded its valleys halting traffic and damaging low-lying parks On August 19, 2005, Toronto experienced torrential rainfall that flooded its valleys halting traffic and damaging low-lying parks Bridges and trails were washed away Bridges and trails were washed away

Paved paths were picked up with the flood waters and moved! The flood water left fresh sediment in its wake Though not good for the pathway, fresh sediment supplies new nutrients to yield healthy vegetation and also replaces eroded sediment to maintain or build the banks.

Protection Measures What was done to protect the valley prior to the flood? What was done to protect the valley prior to the flood?  Geotexiles and Gambian baskets

Geotextiles are fabrics that are used on slopes to hold soil in place and help prevent erosion.

Gambian baskets are wire baskets filled with small boulders. They act as a barrier for the riverbanks and aid drainage. These baskets didn’t survive the erosive power of the flood and were washed downstream – deposited when the river no longer had the energy to carry them.

How a river works…

Deposition When the water slows down (reduces velocity), its carrying capacity reduces (it has less energy to carry a load). When the water slows down (reduces velocity), its carrying capacity reduces (it has less energy to carry a load). With less energy, the river begins to drop what it is carrying. Coarse (heaviest) sediment is deposited first such as gravel and sand. With less energy, the river begins to drop what it is carrying. Coarse (heaviest) sediment is deposited first such as gravel and sand.

River flow is slowest on the inside of a bend. River flow is slowest on the inside of a bend. Below is a gravel bar. It is much larger than it used to be because of the flood. The flood carried more sediment than normal and therefore deposited more than normal. Below is a gravel bar. It is much larger than it used to be because of the flood. The flood carried more sediment than normal and therefore deposited more than normal.

The drink bottle is for scale and indicates the size of the coarse material carried and then deposited by the river The drink bottle is for scale and indicates the size of the coarse material carried and then deposited by the river Some of the gravel is very angular suggesting that it did not travel far Some of the gravel is very angular suggesting that it did not travel far The more rounded sediments have rolled and collided with other sediments in the past to give them their current shape The more rounded sediments have rolled and collided with other sediments in the past to give them their current shape

The river flooded over its banks and travelled a new path The river flooded over its banks and travelled a new path As the water levels receded and energy reduced, sediment was deposited revealing the path the river took during the flood. As the water levels receded and energy reduced, sediment was deposited revealing the path the river took during the flood. Present river Path of flooding river

Also notice in this picture that the coarser material (gravel) is deposited on the fringe of the path where the flow rate would have been slowest. Also notice in this picture that the coarser material (gravel) is deposited on the fringe of the path where the flow rate would have been slowest. The finer material (fine sand and silt in this case) is in the centre of the path. The finer material (fine sand and silt in this case) is in the centre of the path. Coarser sediment Finer sediment

Along with deposition, there’s erosion Along with deposition, there’s erosion The sediment has to come from somewhere! The sediment has to come from somewhere! Newly exposed banks

Erosion occurs on the outside of the bend Sediment and vegetation removed from the bank will eventually get deposited.Erosion

The river flows fastest on the outside of a bend because the water molecules are playing “catch up” with their cousins travelling the shorter path on the inside of the bend The river flows fastest on the outside of a bend because the water molecules are playing “catch up” with their cousins travelling the shorter path on the inside of the bend The river has lots of energy at this point and picks up sediments The river has lots of energy at this point and picks up sediments Note: Deposition on the inside of the bend Trees on the bank fall as the soil beneath them washes away Trees on the bank fall as the soil beneath them washes away

More evidence of erosion and deposition

Vegetation is caught on the bridge showing how high the river got Vegetation is caught on the bridge showing how high the river got Large branches are trapped on these high banks suggesting the strength of this flood! Large branches are trapped on these high banks suggesting the strength of this flood!

This shows the path of the “new” flooding river, spilling over the banks, crashing through the trees, and flattening the grass This shows the path of the “new” flooding river, spilling over the banks, crashing through the trees, and flattening the grass Direction and path of the flood waters

Mass wasting also occurred Mass wasting also occurred Beside are block falls and below are translational slides Beside are block falls and below are translational slides

News Release Described as a "once in a thousand year" event - the worst flood in Toronto in 51 years. Described as a "once in a thousand year" event - the worst flood in Toronto in 51 years. Up to 183 mm (over 7 in) of rain fell in a few hours. Up to 183 mm (over 7 in) of rain fell in a few hours. Roadways and bridges were washed out Roadways and bridges were washed out Insurance claims exceeded $500 million Insurance claims exceeded $500 million Finch Avenue West was completely washed out by Black Creek creating a huge 7 m (23')deep hole (see link at the end of this slideshow) Finch Avenue West was completely washed out by Black Creek creating a huge 7 m (23')deep hole (see link at the end of this slideshow)

The End! Click on the slideshow linked below showing the incredible strength of the flood waters on the roads! /