When forested land is logged and changed to pasture or is developed for other uses, less rainfall is caught and retained by the trees and soil. More runs off the land, increasing the flow in downstream ditches, creeks and streams. With “intense” development, more land is covered with impervious surfaces such as asphalt or roofs, dramatically increasing runoff. The increase will, if not managed, result in the erosion of creek banks and downstream lands will be flooded.
The City of Abbotsford requires development of urban lands to be accompanied by stormwater management measures. Runoff from large roofed areas is encouraged to be infiltrated into the ground. Runoff from other areas is directed to large holding ponds or tanks, where it is released at a rate which attempts to mimic the pre-development runoff patterns. In some developments, management techniques such as rain gardens, biofiltration swales, and absorbent soils are or will be used to filter runoff (to remove pollutants) and to further reduce the peak flows.