Model Studies of Dropshafts for the Tunnel and Reservoir Plan

Abstract

This report describes the model studies carried out at the St. Anthony Falls Laboratory of the diversion structures and dropshafts to be incorporated into the Chicago Tunnel Reservoir Plan. The diversion structures will divert runoff from existing conduits at the surface to dropshafts used to transport the runoff down to deep tunnels which serve as temporary reservoirs. The model studies involved the construction and testing of two diversion structures, four vertical dry weather flow dropshafts, two sloping dry weather flow dropshafts, and three vertical storm water flow dropshafts. Also during the test program, various modifications were made on these basic models. The purpose of the model studies was to assist in the development of effective and practical diversion structures and dropshafts and to study their hydraulic operating characteristics for various flow conditions. Numerous modifications were made, with limited documentation of each, to develop an optimum design. When an optimum design had evolved, more detailed observations were made during which static and fluctuating pressures were recorded and black-and-white photos, colored slides, and colored movies were taken. Photographic documentation proved to be an excellent method of recording the overall hydraulic characteristics of the structures and the air entrainment and escape mechanisms.