Changes

==Post-development hydrologic changes==

==Post-development hydrologic changes==

===Water quantity changes===

===Water quantity changes===

While rainfall intensity, soil and vegetation characteristics, slope length and steepness all play a role in the timing and rate of runoff generation, the creation of impervious surfaces – including rooftops, driveways, roads and parking lots – disrupts rainfall’s ability to penetrate the soil surface and infiltrate.  In heavily urbanized, well-drained areas, the time of concentration is significantly reduced due to the relative smoothness of impervious surfaces, and the dense network of stormwater [[conveyance]] infrastructure including gutters, catch basins and subsurface pipes.  

While rainfall intensity, soil and vegetation characteristics, slope length and steepness all play a role in the timing and rate of runoff generation, the creation of impervious surfaces – including rooftops, driveways, roads and parking lots – disrupts rainfall’s ability to penetrate the soil surface and infiltrate.  In heavily urbanized, well-drained areas, the time of concentration is significantly reduced due to the relative smoothness of impervious surfaces, and the dense network of stormwater conveyance infrastructure including gutters, catch basins and subsurface pipes.  

In urban areas which use stormwater ponds to control the peak flow of runoff entering receiving environs the net volume of runoff remains the same, but the rate of release is controlled (left). In older urban areas where stormwater ponds are not commonly in use, the timing and rate of release of stormwater to the receiving environment is uncontrolled, and this is representative of approximately 85% of the pre-existing urban areas throughout Ontario.

In urban areas which use stormwater ponds to control the peak flow of runoff entering receiving environs the net volume of runoff remains the same, but the rate of release is controlled (left). In older urban areas where stormwater ponds are not commonly in use, the timing and rate of release of stormwater to the receiving environment is uncontrolled, and this is representative of approximately 85% of the pre-existing urban areas throughout Ontario.

 

The large volumes of stormwater runoff produced under such circumstances over stress conventional stormwater systems leading to flooding, erosion, habitat destruction, degraded water quality, damage to infrastructure systems and post-flooding health-related concerns including mould growth and contaminated water.

The large volumes of stormwater runoff produced under such circumstances overstress conventional stormwater systems leading to flooding, erosion, habitat destruction, degraded water quality, damage to infrastructure systems and post-flooding health-related concerns including mould growth and contaminated water.

===Water quality impacts===

===Water quality impacts===