Impact-Type Energy Dissipator for Storm Drainage Outfalls Stilling Well Design

An impact-type energy dissipator consisting of a vertical section of circular pipe affixed to the outlet end of a storm drainage outfall, termed a stilling well, was studied in the laboratory to determine the energy loss coefficient and the effects of the geometrical components of such a structure. The results were generalized and given in terms of dimensionless paramters. Investigations were conducted with a 0.99-ft-diameter model stilling well which had a 2-ft-diameter collar attached to the top to simulate a broad-crested circular weir, and incoming pipes with diameters of 0.33, 0.40, and 0.60 ft on slopes of 1 on 1, 1 on 2.2, and 1 on 4. The effects of the following geometrical components were studied: diameter of incoming pipe, slope of incoming pipe, diameter of stilling well, depth of stilling well below pipe invert, and height of well above pipe invert. The effects of these geometrical components on the dissipation of energy and on the distribution of flow from the well were determined for both partial and full pipe flows.