Discussion of 'Bottom Aeration of Stepped Spillways' by Michael Pfister,Willi H. Hager, and Hans-Erwin Minor

摘要

The authors are to be congratulated for a systematic investigation of the development of bottom air concentration downstream of an aerator. The concept of an aerator located at the first vertical step face to add air to the chute bottom is interesting. The discussers have the following suggestions to offer on the aspects related to stepped spillways. Stepped spillways are generally designed for lower values of unit discharge. Geringer and Officer (1995) reported that the studies on stepped spillways have been limited to dams with maximum unit discharge up to 15 m~3/s/m. The energy dissipation over the surface of stepped spillway decreases with the increase in unit discharge. This trend was noticed in experimental observations and reported by Christodolou (1993), Sorenson (1985), Bayat (1991), and Tozzi (1994). Stephenson (1991) stated, "Energy dissipation can be increased until the stage when the water depth is approximately one-third of the critical depth, beyond which it is very difficult to increase the energy dissipation further." Therefore for higher unit discharges, the stepped spillways may not be efficient from the consideration of energy dissipation.