Hydraulic Model Studies of Sewer Transition

Abstract

A contract was awarded to the St. Anthony Falls Hydraulic Laboratory to perform a hydraulic model study of energy losses in a combined sewer for the Minnesota Highway Department. The sewer is located in the vicinity of 38th street South and Hiawatha Avenue in Minneapolis, Minnesota. The sewer passes under redesigned State Highway 55. The new highway design requires a modification of the existing sewer. The proposed new sewer design includes a change in geometry from the original circular 9.25 ft pipe section to a 4.25 ft high by 16 ft wide box, a length of box section, and then a transition back to the original 9.25 ft pipe section. The crown of the pipe is depressed 5 ft to the top of the box section with the invert remaining at the present grade. The depression of the sewer crown allows the highway gradeline to be lower than it was for the old Highway 55. The transition had to be designed so that a minimum of headloss would result from the change in geometry.