Experimental Study on the Limits of Flow Regimes for Different Configurations of Stepped Spillway

Abstract

Flow over a stepped spillway can be divided mainly into three flow regimes that are nappe, transition and skimming depending upon the discharge and the dimensions of the stepped spillway. The determination of the flow regime is a very important aspect in the design of stepped spillway due to the different properties for each flow regime. Experimental work on flow regime limits for stepped spillways has been conducted using twelve stepped spillway models. The models were manufactured with three downstream slope angles: 25, 35 and 45°, and four numbers of steps: 5, 10, 15 and 20. Five configurations of steps were tested, which are conventional Flat, pooled, porous end sills, pooled with gabions and porous end sills with gabions. The results revealed that the end sills highly affect flow regime type; this effect is primarily for the lower limits of skimming flow. Using end sills increases the range of transition flow regime (by increasing the lower limit of skimming flow) as well as increases the instabilities that occur in this flow regime. Gabions reduce the effects of end sills on the lower limit of skimming flow regime to near the limit of flat steps. New empirical equations were suggested based upon the experimental results.

Keywords: Flow Regimes, Gabions Steps, Nappe Flow Regime, Pooled Steps, Skimming Flow Regime, Stepped Spillway, Transition Flow Regime.