Experimental analysis of road surface flow characteristics

•Analyzed road surface flow through hydraulic experiment.•Assessed the impact of slope conditions and rainfall.•LSPIV was used for in-depth flow field study.•New formulas for interception efficiency were developed.•Study aids in effective urban rainwater management. The rapid increase of impervious surfaces in urban areas has significantly altered the rainwater runoff landscape, necessitating an evaluation of the capacity of urban drainage systems as a part of global rainwater management plans (encompassing both gray and green infrastructures). However, no clear standard has been established for the appropriate analysis of surface flow characteristics that take into account the topographical and rainwater runoff conditions of urban roads. In this study, a hydraulic model experiment was performed, parameterized by road slope conditions (longitudinal slope: 2 to 10 %, transverse slope: 2 %), grate inlet geometric conditions (50 to 150 cm), and rainfall intensity conditions (design frequency: 5 to 30 years), to develop a method for estimating road surface flow. The results indicated that the grate inlet interception efficiency varied from 62.43 to 85.46 % for a 50 cm inlet length, 65.43 to 89.73 % for 100 cm, and 68.14 to 91.44 % for 150 cm. Similarly, the flow width in the gutter ranged from 82 to 129 cm, which is contingent on road slope and rainwater runoff conditions. Using the experimental results, a regression analysis was conducted to develop formulas for calculating the grate inlet interception efficiency considering flow width. The developed empirical formulae exhibit significant probabilities of ≤0.05 and high coefficients of determination, such as 0.99 for the grate inlet interception efficiency and 0.96 for flow width. Compared to the empirical formulas proposed in previous research, the developed formulas in this study demonstrate superior precision and broader applicability, thereby providing a reliable tool for the design and construction of urban drainage facilities.