Towards urban drainage sediment accumulation monitoring using temperature sensors

Abstract

Sewer sediments are among the main concerns related to urban drainage system management as they represent the largest contribution of suspended solid loads during rainfall events due to their resuspension. This study presents a novel methodology to detect and assess bed deposits in urban drainage systems based on temperature monitoring by using well-known thermodynamics and sediment properties. To illustrate the heat transfer processes in a liquid–sediment system and their relation to accumulation, a lab-scale experimental campaign was performed using sewer sediments and simulating water temperature gradients in sewers. Wastewater temperatures showed a marked daily pattern, while the presence of sediment dampened dynamics. Sediment thickness could therefore be estimated from the time evolution of the temperature differences measured between the bottom of the sediment bed and the water phase. Likewise, experimental data were used to calibrate a 1D heat transfer model, from which several sediment accumulation scenarios were simulated by using real wastewater temperature series. Thus, the influence of sediment properties on accumulation processes was assessed, and the range of potentially measurable sediments within an optimal range of [5–20] cm was identified. As a conclusion, temperature measurements and heat transfer model analysis can be used to approximate and monitor the sediments deposited in urban drainage systems. Future studies will extend the method to spatially-resolved sediment monitoring and active temperature sensing to improve sediment accumulation monitoring capabilities.