Abstract

The City of Ann Arbor, Michigan suffered from recurring episodes of basement flooding from sanitary sewer backups during major rainfall events. An investigation was conducted to identify the circumstances controlling the flooding and to evaluate alternatives for mitigation of the flooding. Five major areas subjected to flooding were identified and a monitoring program was conducted in these areas. Due to the distributed nature of the flooding occurrences, a number of system deficiencies were identified. In addition, it was observed that system flows increased rapidly after the commencement of rainfall, leading to the conclusion that contributions from footing drains in older residences were a major contribution to the increased system inflows. Options investigated for mitigation of the basement flooding included system capacity increase by construction of relief sewers and pipe bursting, provision of underground storage facilities, and implementation of a footing drain disconnect program. Disconnection of footing drains was indicated to be the least cost alternative in most of the areas although uncertainties existed in the exact contribution of footing drains to system inflows due to the limited number of homes investigated during the field study. Additional considerations such as periodic overflows at the wastewater treatment plant during high rainfall events and pending sanitary sewer overflow regulations led to the decision to implement the footing drain disconnect program city-wide.

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