What is urban runoff ?
As residential & commercial developments continue to cover natural environments , rainwater needs to be channeled somewhere , but where does it all go ?
As we build and develop our cities and communities with various hardscape surfaces such as roads , parking lots and buildings , we increase the amount of rainfall runoff and the many pollutants it takes along its urban path and the eventual discharge into our estuaries , streams , lakes and oceans . Our natural landscapes — forests , wetlands and grasslands — used to trap rainwater and snowmelt and allow it to slowly percolate into the ground . When we develop these urban and suburban areas , rainfall has no place to go and typically has to be managed through a complicated network of conventional storm drains and flood control systems , such as dams , dikes , detention facilities and stream bank stabilization techniques .
The cost of engineering and implementing these complex systems is staggering . Rather than providing retention or infiltration , these conventional stormwater management systems transfer greater water volumes downstream , taking along with them solid waste , sediments and a host of pollutants that dramatically impact natural habitats , human health , and the vitality of many businesses . Here are some of the many effects urban runoff has to our health , our quality of life , and our economy :
• Streambank and streambed erosion
• Flooding and property damage
• Over siltation and sedimentation in lakes , streams , rivers , estuaries and oceans
• Increased water temperatures
• Harm to plant and aquatic life
• Harm to coastal shellfisheries
• Harm to sport fishing and tourist industries
• Human illness
• Impacts to drinking water supply
• Overall aesthetic losses
The most dramatic consequence of increases in the volume and rate of stormwater runoff is flooding and property damage . One study estimated that because of the increase in impervious cover in a watershed , a flood event that should be expected once in 100 years could occur once every 5 years when the impervious cover reaches 25 percent in an area , and could become an annual event when impervious cover reaches 65 percent .