Understanding sediment wash-off in road drainage systems under intense rainfall and high sediment masses: Insights from a large-scale modeling facility

The main objective of this paper is to analyze, through a unique large-scale modeling facility, the RDS wash-off under various scenarios of intense rainfall and high RDS masses. A 1:1 scale physical modeling facility was used to allow precise measurement of the RDS wash-off phenomenon under two different rainfall intensities (30/50 mm/h) and three initial RDS masses (100/150/200 g/m²). The accumulated and discharged masses of RDS in the different components of the modeling facility (roadway/RW, gully pot/GP and manhole/MH) were collected at the end of the wash-off simulations. The results suggested the following sequence of intervention in the components of the drainage system to control pollution associated with fine RDS (< 63 μm): MH (59.2 %) > GP (31.2 %) > RW (9.6 %). The wash-off simulations suggested the following maximum (30/68 g/m²), minimum (16/38 g/m²) and minimum (2.15/2.61 g/m²) limits on the mass of RDS remaining on the RW, removed by the GP and discharged into the MH, respectively. These mass limits were relevant to understand the RDS behavior and to suggest improvement strategies for the RW cleaning systems (coarse/fine fractions washed-off: 80.3/81.7 %), GPs (coarse/fine fractions removed: 75.3/49.6 %) and MHs (coarse/fine fractions discharged: 5/32.1 %). Finally, the results suggested that the size fractions <63 μm and between 500 and 1000 μm were representative of the wash-off for the finest and coarsest fractions of the RDS, respectively.