Abstract

This chapter describes how long-term precipitation and infiltration records were developed for use in the performance evaluation of a proposed regional drainage tunnel shared by the cities of Detroit and Dearborn, Michigan. The precipitation record includes hourly precipitation data (rainfall plus snowfall) plus a calculation for snowmelt. Methodologies were applied to this record to develop 36 y of rainfall and snowfall plus snowmelt at 15-min intervals. Infiltration parameters are varied monthly based on long-term rainfall/runoff records, rather than assumed to be constant throughout the year. In addition, allowances have been made for incorporation of spatially non-uniform precipitation into the evaluation. The application of these precipitation and infiltration records has allowed an improved representation of the hydrologic factors contributing to combined sewer overflow (CSO) in Southeast Michigan over an extended simulation length. The implementation of these records has improved the capabilities of the continuous model for computing the long-term performance of proposed CSO facilities in Southeast Michigan, including the Proposed Regional Tunnel Project.

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