A study of the road sediment build-up process over a long dry period in a megacity of China

Highlights: • The longest build-up study over 41 days in dry period was conducted. • The classical power model fits well in short dry period. • Sin function model is more suitable for longer dry period. • An "unexpected" phenomenon during build-up process was discovered. • Size, density and mineral composition of particles are critical to build-up. -- Abstract: The build-up of urban road deposited sediments is the key to study the quality of stormwater and the associated receiving waterbody in urban catchments. In the past, many sediment build-up field studies were conducted between 7 and 20 days. It is generally assumed that the cumulative amount of pollutants reaches equilibrium and be represented as a mono-growth curve such as the power function. However, the dry period between two rain events in many areas in Northern China may be much longer than 20 days, especially for spring and fall seasons. This research was conducted for 41 days during a long dry period in 2017 in Tianjin, a megacity of China. The variability of the road sediment build-up process and the intrinsic and extrinsic factors which influence the process variability were investigated. It has been found that the normally used mono-growth curve (such as the power function) may be suitable for the short-term build-up process in area with less interference (sparse human activity area, R² > 0.6). The double-bell shaped curve (sin function) fits better for the 41-day study, a longer period build-up study (R² > 0.9). An "unexpected" phenomenon at which the particulate load was rapidly decreased in the first three sampling days was observed. This remarkable phenomenon can undoubtedly be well represented by the sin function instead of the power function. Compared to the power function, the goodness of fit of the sin function is increased by 30%–130%. Particle size, as an important characteristic affecting the behavior of particles, was considered in the build-up model. This research may bring people's attention to study the long-term road sediment build-up process and their impacts on the receiving water quality.