The extreme rainstorms that strike with increasing frequency—such as the Memorial Day weekend downpours in Texas -- are having devastating effects beyond the severe flooding they cause. Sudden and forceful rains overwhelm urban storm-drain systems, as water pours over roads, rooftops and other impervious surfaces, washing away dust, oil, trash and waste of all kinds. This dirty wash then runs into rivers, streams and lakes, and pollutes downstream drinking water.
Storm water has become a principal contributor to water pollution nationwide, according to the Environmental Protection Agency. More than 700 U.S. cities use combined storm-water and sewer systems, and many are now overwhelmed by the pollution problem. When their overflows foul nearby waterways, these cities face federal legal action under the Clean Water Act, and penalties that range from millions of dollars in fines to billions in mandated spending on traditional equipment such as pipes, tanks and treatment plants.
As more and more people move from rural areas to cities—by 2050, cities worldwide are expected to have 2.5 billion more people than they have now—the problem will only worsen.
The solution, fortunately, is rather simple: Constructed wetlands, green roofs, rain gardens and other forms of "green infrastructure" can capture and slow runoff, significantly reducing storm-water pollution. At the same time, they provide wildlife habitat, flood protection, green space, and cleaner air and water.