With a big share of their city served by combined sewers that carry both wastewater and stormwater runoff, Portland, Ore., officials have worked for more than 20 years to greatly reduce the occurrences of overflows triggered by heavy rains.The city launched a 20-year program of construction, redesign and education to reduce overflows into the Willamette River and the Columbia Slough as required by the Oregon Department of Environmental Quality. When the project began in 1991, the city averaged more than 50 overflow incidents per year resulting in the release of combined stormwater and raw sewage into the rivers running through
