Methodologies for Estimating the Hydraulic Efficiency of Non-surcharged Clean Grate Inlets, Clogged Grate Inlets and Continuous Transversal Grate Inlets

The urban drainage system of cities is composed of two major and minor subsystems linked by drain inlets to form the dual-drainage system. Therefore, the sewer inlet capacity has a significant influence on the dual-drainage system workability. However, most of the design models and studies focus on the subsurface discharge capacity and neglect the inlet capacity. A reliable drainage system design has to take into consideration the hydraulic efficiency of the lining elements (grate inlets) and the effect of clogging on their efficiency. In this study, the main methodologies for determining the hydraulic efficiency of grate inlets are presented. In a comparative study on the hydraulic efficiency of clean grate inlets, the general hydraulic efficiency formula of Eq. (1) and the formula of Eq. (2) adopted by British Standard and Design Manual for Roads and Bridges and the UPC methodology in Eq. (3) showed similar results with low variance of 2–7%. However, Eq. (3) of the UPC methodology is the most accurate as it considers the majority of the parameters involved in the hydraulic interaction at the grate inlet. Moreover, the UPC methodology of Eq. (3) is proved to be applicable for grate inlets under clogging conditions with high reliability. The approaches presented in this paper can be used in numerical models to provide a reliable accurate simulation of the hydraulic behaviour at the single and continuous grate inlets.