Hydraulic Model Study of the Market Avenue Retention Basin (MARB)

Abstract

This report presents the results of a physical model study of the Market Avenue Retention Basin (MARB) located in Orand Rapids, Michigan. The model study was conducted for Dell Engineering, Inc. and the City of Orand Rapids, MI. The MARB described herein is a combined sewer overflow retention basin located in Orand Rapids, MI. The facility consists of a pumping station with ten pumps and three retention basins. The sump is designed to function through a ten foot operating range, with an additional pump coming on-line with each one foot rise in the sump level. The water enters the first basin through any of the ten pumps and discharges into Basin Two through an outfall channel when the elevation reaches 622 ft. Basin Two is a large triangular shaped area with eight elevated channels that water is allowed to overtop and enter Basin Three. Because this is a combined sewer plant the number of pumps in operation, and hence the pumping rate, varies with the magnitude of the storm event. Each 'PU1Tt1' is'rated at 105 million gallons per day (MOD), giving the maximum basin capacity of 1050 MOD when all ten pumps are in operation. The initial scope of this study focused on the hydraulic efficiency of Basin Two as a secondary sedimentation basin. The objective was to determine if short-circuiting occurred, and if so, to test various baffle arrangements to mitigate the short-circuiting. During the assessment process, it became clear that in addition to its capacity as a settling compartment, Basin Two was also being used as a disinfection chamber. With this in mind, and since it is impOliant for disinfection to occur properly, sufficient chlorine contact time with all effluent is necessary. Since the model study of the existing facility confirmed that the necessary contact time was not being achieved, alternative baffle designs were developed to increase the residence time to that needed for satisfactory disinfection. The results of this model study illustrate the efficiency of Basin Two as a sedimentation basin as well as a retention basin for chlorine disinfection. The information obtained from the experiments is given in the results section of the report and except where noted, all data has been scaled to existing facility values. A forty-minute video presentation supplements this report. The video shows the experimental runs for the three most favorable baffle designs at both 30% and 100% of the design flow.