Development of methodology for correlation between precipitation and variation of concentration of suspended sediments in urban runoff

ABSTRACT

The hydrological and hydrosedimentological cycles are directly related, being possible to observe the influence of the first on the second in the alteration that the dynamics of the sediments in the water courses undergo due to the flow (Q) and precipitation (P). Several studies seek to study the relationship between the two cycles and evaluate the influence of hydrological characteristics on water quality parameters, such as suspended sediments, as a way to identify new methods and knowledge that assist in the treatment of waters and management of watersheds. The present work aimed to propose a methodology that allows relating precipitation data with the concentration of suspended solids (C_ss), to study the seasonal behavior of the C_ss and to investigate the occurrence of Mass First Flush (MFF) in the surface flow of the evaluated events. A programmed automatic sampler collected runoff samples from 28 precipitation events, which were sent to the laboratory to determine the C_ss. At the same time, rainfall monitoring in the region of collection was carried out and the height of the flow water flow was measured to determine the flow. The method proposed in the study, which considers the precipitation in the seven days prior to the event, obtained coefficients of linear relationship with values of R² = 0.7394 and R² = 0.8154 for the peak ($C_{ss}^{peak}$) and average ($C_{ss}^{avg}$) suspended solids concentration data, respectively. It was observed that the MFF phenomenon occurred in most of the events studied, showing the transport of most solids at the beginning of the flow. In the seasonality analysis, it was found that the characteristics of the seasons have a direct influence on Css transport.

Keywords:
water cycle; hydrosedimentological cycle; mass first flush