Author(s): L. Toombes

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Keywords: Dropshaft; Cascade; Energy dissipation; Air entrainment

Abstract: The energy dissipation characteristics of stepped cascade spillways have been recognised for over three thousand years. In the last century the trend in spillway design has been strongly in favour of smooth spillways with a separate hydraulic jump dissipation basin, which are considered simpler, easier to standardise, and cheaper. Only in recent years have new construction techniques such as roller compacted concrete revitalised interest in a traditional design. Like the hydraulic jump basin, the vortex dropshaft is the regular choice for large dropshafts. However they can require large, expensive de-aeration chambers, particularly when discharging into pressurised tunnels. Although not common, cascade dropshafts, where the shaft is subdivided by a series of steps, have been used for over a century. Recent model studies of a cascade dropshaft design have demonstrated excellent energy dissipation and air release over a wide range of discharge and tailwater combinations, virtually eliminating the need for a separate de-aeration chamber.

DOI:

Year: 2011