A11 developments can impact on lands abutting them but a residential subdivision in Hull, Quebec gives an interesting overview of problems faced and overcome.
Stormwater runoff patterns were substantially altered by the development after construction of the subdivision started in 1992. Much of the runoff is now directed into the existing Ruisseau Leamy channel, increasing normal storm flow volumes to 6.98 cubic metres per second. Peak storm flows have increased to 10.45 cubic metres per second, with a velocity of 3.48 metres per second.
The increased flows resulted in significant stream bank erosion taking place in an area downstream from the new subdivision where the Ruisseau Leamy channel runs through the back lots of homes built in 1980. The result was a loss of valuable soil and a negative impact on water quality.
Responsibility for corrective action fell upon the City of Hull, who retained the consulting engineering firm of Jean- Luc Allary and Associates to find an erosion mitigating solution. Under the terms of reference, property owners in the affected area would have input into the decision-making process. A solution that blended easily into the surrounding native woodlands and vegetation was mandatory. Compounding the situation was the fact that the existing soils in the channel were predominantly soft, weak clays. These clays are extremely prone to frost heave and differential settlement.