Use of air vent in siphon spillways to control outflow discharge from reservoir

Siphon spillways can release significant amount of water from the reservoir but this may cause flood at the downstream. To control the outflow discharge, we put an air vent at the siphon hood to allow regulated air inside the siphon. In this paper, we present techniques of controlling outflow discharge from a reservoir using air vent in siphon spillways. When siphon is working (Fig. 1a), the pressure is negative at the siphon crest and the discharge reaches the maximum. Depending on the air quantities through the air vent, the flow may stop suddenly (Fig. 1b) or still continue with the air inside the siphon (Fig. 1c). This means that, under the control of air vent, the outflow discharge can be reduced to the desired value between the maximum and the minimum. Particularly, an air slot with a designated shape is placed in the air vent for efficient control of air quantities. Both the numerical model of the Flow-3D and the physical model have been conducted to investigate the performance of the siphon spillways in order to find the relation between the air quantities in the air vent and the siphon outflow discharges.