Abstract
Numerical simulations were executed to clarify the occurrence condition of water surface fluctuation, that occurs at the drop in the irrigation canal and makes division of irrigation water difficult, for the case the downstream side of the drop was regarded as uniform flow state. As a result, the three type of flow regime, supercritical flow, plunging flow and streaming flow, occurred by the difference of shape of stilling pool in drop, at the condition of the same drop length and discharge. Furthermore, big fluctuation of water surface was observed in spite of the condition of plunging flow that is said to be most stable. The occurrence condition of water surface fluctuation was clarified by using two indices, one was the ratio of the specific energy of upstreamside of the drop to the drop length, the other was the aspect ratio of the drop part including the stilling pool.
