HYDRAULIC AND ECONOMIC-BENEFITS OF DOWNSPOUT DIVERSION

A downspout diversion program in an urban area is evaluated to assess the impacts on sanitary sewer flow volumes and cost effectiveness. San itary sewer flows and wastewater treatment cost data are compared for the five years before and 1.25 years after the downspout diversion was completed. In order to establish a cause and effect relationship betw een flow volumes and downspout diversion, measurements of precipitatio n, consumption patterns, and system loss (maintenance, fire flows, mai n ruptures) for the before and after time periods were obtained. The r esults indicate the downspout diversion contributed to a reduction of over 25 percent in the mean flow volumes within the sanitary sewer col lection network during all rainfall events, with flow reductions rangi ng from 25 percent to 62 percent for rainfall depths between 6 mm (0.2 5 inches) and 25.4 mm (1.0 inches). Costs incurred for wastewater trea tment were also reduced significantly, as overtime for overflow mainte nance was eliminated. Downspout diversion is a viable nonstructural al ternative for stormwater flow reduction in highly urbanized communitie s which may lack available space for large scale detention facilities.