Hydraulics characteristics of tipping sediment flushing gate C. H. J. Bong, T. L. Lau and A. Ab. Ghani ABSTRACT This paper highlights the preliminary study on the potential of a tipping flush gate to be used in open storm drain to remove sediment. The investigation was carried out by using a plasboard model of the tipping flush gate installed in a rectangular flume. Steady flow experiment was carried out to determine the discharge coefficients and also the outflow relationship of the tipping flush gate. The velocity produced by the gate at various distances downstream of the gate during flushing operation was measured using a flowmeter and the velocity at all the points was higher than the recommended self-cleansing design available in the literature. Preliminary experiment on the efficiency of flushing was conducted using uniform sediment with d 50 sizes of 0.81, 1.53 and 4.78 mm. Results generally showed that the number of flushes required to totally remove the sediment from the initial position by a distance of 1 m increased by an average of 1.50 times as the sediment deposit bed thickness doubled. An equation relating the number of flushes required to totally remove the sediment bed for 1 m with the sediment bed deposit thickness was also developed for the current study. C. H. J. Bong (corresponding author) T. L. Lau A. Ab. Ghani River Engineering and Urban Drainage Research Centre (REDAC), Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia E-mail: bhjcharles@feng.unimas.my Key words | flushing, open storm drain, sediment, self-cleansing design, tipping gate INTRODUCTION Sedimentation in sewer systems and open storm drains had caused problems such as a reduction of hydraulic capacity (Bong et al. in press), odours due to anaerobic processes and source of pollutants during storm events (Bertrand- Krajewski et al. ). Various techniques have been devel- oped to clean sewers of sediments which are based on both mechanical and hydraulic principles. However, for most developing countries, removal of sediments from open storm drains often involves manual handling which is costly. Among the various techniques, the one based on hydraulic effects mainly consists of creating a flushing effect by discharging a volume of water during a short period of time. The flushing effect could be created by stor- ing water in upstream chambers and discharged through a gate or tipping bucket located above water level or mobile tipping plates like the Hydrass gate (Chebbo et al. ; Lorenzen et al. ). These devices allow the production of successive flushing waves at high velocities sufficient (Bong et al. ) to scour and transport sediments and rep- resent an automated cost-effective solution for sewer cleansing. Various experimental studies are also available in the literature on the effect of flushes from flushing devices such as sluice gates/lifting gates (Campisano et al. , ), vacuum flushing (Guo et al. ) and the Hydrass gate (Bertrand-Krajewski et al. ). Figure 1 shows examples of flushing devices used in sewers for sediment flushing. This paper describes a preliminary study on the potential of using a tipping flush gate in an open storm drain to flush out sediments. A preliminary model of a self automated tipping gate with a scale reduction 1:2 from the original one to be installed in an onsite open drain for the next part of the study has been designed and tested in an experimental flume for the hydraulics characteristics. Preliminary experiments on the efficiency of flushing have also been conducted in the same exper- imental flume using uniform non cohesive sediment with d 50 sizes of 0.81, 1.53 and 4.78 mm. Results from this preliminary study could provide better understand- ing of the tipping flush gate characteristics for further study. 1 © IWA Publishing 2013 Water Science & Technology | in press | 2013 doi: 10.2166/wst.2013.498 Uncorrected Proof