Expressway Main Drain and Storm Water Pump Station Study

Ray S.T. Cheng, Partner, Alvord, Burdick & Howson, L.L.C.
Shih-Min Tung, Hydraulics Engineer, Illinois Department of Transportation
Chinliang Wang, Hydraulics Section Chief, Illinois Department of Transportation

A hydraulic report has been prepared for the Illinois Department of Transportation's (IDOT) Pump Station No. 27. The pump station, located at Interstate Highway 94 (I-94) and 110^th Street, Chicago, Illinois, receives storm water from a 400-acre tributary area through three sewer main drains, totaling 6.5 miles in length in I-94, I-57 and Stony Island Avenue, and discharges water to Lake Calumet through a 1-mile long outlet channel. Pump Station No. 27 has eight (8) 30,000 gpm pumps and is the largest IDOT storm water pump station in the Chicago area. There are 58 sub-basins which contribute surface runoff to the main drains and the pump station.

Hydrological analyses and hydraulic calculations were performed to estimate the peak flow rates and volume of the storm water to the main drains and the outlet channel, determine the adequacies of the main drains and outlet channel and propose improvement alternatives. In determining the flow rates in the main drains and the inflow hydrograph from main drains to the pump station, the conventional highway approach suggests accumulation of all inflow hydrographs from the sub-basins to the main drains without considering the time lag effect of each inflow hydrograph through the main drains. Because the main drains studied are 6.5 miles long, this approach would result in unrealistic peak flow rates through the main drains and to the pump station and affect the results of the evaluation.

This paper summarizes and compares hydrological estimations of storm water to the main drains, pump station and outlet channel with and without consideration of the time lag effect in the main drains and the time lag effect between the peak pumpage rate and surface runoff to the outlet channel. Hydraulic evaluations of main drains using different procedures and methods are also compared and discussed in the paper.