EXPERIMENTAL STUDY ON THE SIDE CHANNEL SPILLWAY AND ITS IMPACT ON THE JUMP, CROSS FLOW AND ENERGY DISSIPATION

Abstract

The utilization of the side channel spillway as the primary component of dam is generally due to the limitation of the available space to construct conventional spillway with design discharge capacity. Some impacts may only be identified through the hydraulic physical model study; these include the presence of the chaotic jumps at the downstream of the spillway crest, the cross flow on the steep channel, as well as the performance of the energy dissipation in the stilling basin. This paper presents the result of the experimental study of three-dimensional behaviour of flow over the entire components of the side channel spillway of Bener Dam, Indonesia. The main dam and its appurtenant components, i.e., the reservoir, the spillway crest, the spillway channel, and the energy dissipaters were built, and various discharges were introduced to study the hydraulic performance of the spillway crest, the stilling basin, the chute, and the energy dissipater. The observed data were collected and then analysed. The results show that firstly, some chaotic hydraulic jumps were found at the stilling basin at downstream spillway crest. These chaotic hydraulic jumps would produce significant vibration that may endanger the nearby structures. Secondly, the presence of the cross flow along the steep channel downstream of the stilling basin may also need to be eliminated in such that its impact on the rise of water surface level does not create any objection. This may be carried out through the installation of baffles along the spillway channel bed. Thirdly, the presence of the hydraulic jumps at the energy dissipater basin under the design discharge has proven that the energy dissipater has performed well where local scour around the downstream structure was found to be not significant. However, to anticipate the raising of the water surface elevation at the energy dissipater basin, increasing the elevation of energy dissipater wall from +212.50 m to +215.00 m is highly recommended.