Monitoring Sewer Sediment Deposits with Passive Temperature Sensors.

Paper presented at XXIX IAHR World Congress

Abstract:

Sustainable urban Drainage Systems (SuDS) are becoming a common solution to address the increase in flow discharges, runoff volumes and pollutants concentrations caused by urban expansion. Among them, the use of permeable pavements is nowadays widespread due to their demonstrated effectiveness in managing and treating stormwater. However, there is great uncertainty in how the clogging of permeable pavements affects their long-term performance in terms of permeability reduction and pollution removal efficiency. Therefore, this study focused first in assessing the influence of clogging on the rainfall drained through porous asphalt slabs of 0.4 m x 0.4 m x 0.15 m. The hydrology behaviour and removal efficiency of the asphalt were analysed for different scenarios and grades of clogging by adding surface sediment loads between simulated rain events. For this purpose, the slabs were disposed in a tailored 1 m² experimental bench, which consists of a drippers-based rainfall simulator that can generate uniform and realistic rainfalls of 30, 50 and 80 mm/h of intensity. Then, for different sediment mixtures, consecutive build-up and wash-off experiments were carried out to analyse the long-term hydraulic and pollution removal efficiency of the asphalt. The water flow drained from the test slabs was collected and the flow discharge and the sediment concentration were measured to determine the permeability and sediment trapping efficiency temporal evolution. The overall objective is to quantify how the permeability and removal efficiency changes as the pavement becomes clogged, and to investigate the influence of the sediment grain size in the process. In addition, a porous layer of the asphalt analysed was used for the retrofitting of an impermeable concrete surface of a 36 m² full-scale street section physical model that uses the same system to simulate rain. The objective is to analyse the impact of the porous asphalt layer on the hydrology and the mobilization of pollutants under full-scale and laboratory-controlled conditions, and to compare with previous tests developed using a conventional impervious concrete pavement. The initial results showed that the permeable pavement layer disposed over the street concrete surface reduces by 50% the peak of the drained flow in the worst case studied (rain intensity of 80 mm/h during 300 s), presenting also a lag of more than 3 minutes. This confirms and quantifies the benefits of this type of permeable pavement in urban stormwater management and, together with the analysis of its long-term performance, contributes towards more efficient implementations and maintenance strategies.