Experimental Study of Hydraulics of Drill-Drop Manholes.

The results of an experimental study of a drill-drop manhole used in the City of Edmonton, Alberta, Canada, are presented. A drill-drop manhole is a vertical drop manhole connected to a deep trunk sewer with an upper manhole and a lower manhole. The upper manhole diameter is only two or three times that of the lower manhole. Further, the flow in the upper manhole is dominated by the momentum of the incoming flow and as a result, the weir and orifice outflow types occurring in a relatively larger upper reservoir do not occur in drill-drop manholes. Instead, four regimes were discovered: deflected jet, stable pool, filling and emptying, and full pipe flow regimes. Dimensionless head-discharge curves were developed for the upper manhole for all flow regimes, and an expression for the sum of the losses in the upper manhole, including the entrance loss to the outlet pipe was found from the experimental results. Effects of outlet diameter and its length, inlet diameters, and their elevations were studied. [ABSTRACT FROM AUTHOR]