Model Studies of Storm-Sewer Drop Shafts

A long-range program of storm-sewer construction prompted the Department of Public Works of the City of St. Paul, Minnesota, to develop an improved design for high-head drop shafts. Past designs required frequent inspection and maintenance at the base of the shaft to prevent failure of the structure. Preliminary model tests indicated that destructive forces of the falling water were primarily responsible for the damage to the base of the shaft. An experimental study led to the development of an impact-type of energy dissipator which removed excess energy from the flow and created stable outflow conditions, with a minimum air entrainment.