Rivers and lakes are polluted as a result of conventional approaches to urban landscaping and stormwater management. Urban areas are covered with hard surfaces - buildings, streets, driveways, walkways, parking lots. Stormwater systems are engineered to facilitate or speed-up runoff, leaving a legacy of poor water quality. Health problems related to water pollution in general are estimated to cost Canadians $300 million per year.
Large concentrations of toxic chemicals, such as oil, polycyclic aromatic hydrocarbons (PAHs) and heavy metals, wash from the urban environment into the storm sewer system when it rains or during spring snow melts. Hardened surfaces disrupt the natural water cycle and prevent rain from soaking into the ground, bypassing the natural filtration of soil and vegetation.
It is estimated that combined sewer overflows from cities around the Great Lakes amount to hundreds of billions of litres of raw sewage and stormwater each year. Further, the under-funding of updating and replacement of storm sewers is expected to continue for at least two decades and will continue to contribute to degradation of receiving waters.
Credit: My Eco Project.org
In summary, stormwater runoff impacts water quality and quantity by:
- transporting pollution directly into lakes and rivers;
- eroding shorelines, loss of topsoil that hastens further runoff;
- warming up surface water, making it more susceptible to waterborne bacteria and hazardous to fragile marine life;
- overflowing sewage treatment facilities, allowing untreated human waste to flow directly into surface water; and
- robbing groundwater aquifers of adequate recharge capacity