Comparison of Different Methodologies for Determining the Efficiency of Gully Inlets

This paper describes the different methodologies used to determine hydraulic efficiency of gully inlets based on an experimental investigation of a site located at the exit toll of Bandar Baharu Highway, Malaysia. The inlet efficiency was determined using selected methodologies proposed by other studies to determine the difference (% variance) between each method. Data was obtained from an experimental set-up with a 1:1 scale (with single carriageway) laboratory system consisting testing platform, gully system (grating, gully box) and inlet and outlet tanks. The set up was designed to mimic the real condition of the gully system on site. There are numerous methods proposed by other studies to determine the inlet efficiency, however only three methods were selected for this study. The selected methods are general equation-method 1, British Standard (BS EN 752) and DMRB (CD 526)-method 2 and UPC methodology-method 3. The experimental results showed that the percentage of difference found between these methodologies was between 2 and 7%. The aim of this paper is to outline some of the available methods to date, to establish inlet efficiency and hence advocate the use of the recently developed methods/equations in Malaysia.