Influence of urban surface roughness on build-up and wash-off dynamics of road-deposited sediment.

An in-depth understanding of the impacts of surface roughness on road-deposited sediment (RDS) build-up and wash-off is essential for the estimation of surface runoff loads and design of RDS control measures. In this study, RDS build-up and wash-off dynamic processes were investigated on paired asphalt and concrete road surfaces with 35 days of continuous sampling during different natural rainfall events. Our results showed that RDS build-up loads and grain size composition were affected by surface roughness, while the impact of surface roughness on the length of the dynamic equilibrium period was not notable. Selective wash-off of RDS with different effects according to grain size are more likely to occur on asphalt road surfaces during rainfall-runoff, but the RDS wash-off percentage is not affected by surface roughness during snowmelt-runoff. Both total apparent depression depth and micro-depression structures influence RDS build-up and wash-off dynamics. These results imply that surface roughness has combined effects on RDS build-up and wash-off dynamics during the generation and control of urban diffuse pollution.