Summary: The Detroit Water and Sewerage Department conducted a voluntary, pilot downspout disconnection program to verify its effectiveness in reducing stormwater inflow and resulting Combined Sewer Overflows (CSO) and to assess public acceptance. The pilot program was conducted in four areas in the City of Detroit. Side by side test pilot sites, ranging from 18 to 40 acres, were monitored for approximately two years to obtain baseline data. Downspout disconnection was then performed in one test site while the other test site served as a hydrological control. Both test sites were maintained for an additional 6 months to a year to determine the effectiveness of the downspout disconnection. 577 downspouts were disconnected by the pilot program at a cost of between $243 and $278 per downspout. The program was well received by the public. The pilot project results demonstrate that residential downspout disconnection will reduce the percentage of Directly Connected Impervious Area (DCIA) between 40 and 44% when applied city-wide. Continuous wet weather simulations were then conducted for the entire city using 36 years of historical precipitation data. The simulations indicate that downspout disconnection may reduce the annual volume of CSO by approximately 2 billion gallons.

This website provides basic information about the Boston Water and Sewer Commission's Downspout Disconnection Program. It has been referenced here because it includes a short instructional video aimed at property owners. The link to the video is at the bottom of their page.

This document from the City of Toronto helps to illustrate the mechanics of a downspout disconnection program in a major city.