Quantifying sediment deposition in sewers through hydraulic performance analysis

This study investigates the effects of fixed sediment deposition on the hydraulic characteristics of sewer flow to support the diagnosis of sewer blockage. Sediment beds extending over the entire pipe (i.e., continuous deposition) and localized deposits were examined under different flow rates and outlet control conditions. Continuous deposition changes the cross-sectional area of the sewer pipe, while localized deposits act similarly to short bottom obstructions. The energy losses induced by a localized deposit at various locations were found to be nearly identical, particularly in cases with backwater effects. To illustrate the relationships between the flow rate, water level, and deposit characteristics, hydraulic performance curves can be developed. The inverse problem, which involves estimating parameters characterizing sediment deposition using observed flow rates and upstream and downstream water levels, can be solved by matching hydraulic performance curves with numerous scatter points from actual monitoring data to obtain the best fit. As there is a wide range of sediment deposition patterns that result in the same overall energy loss, the concept of equivalent sediment bed height is introduced to be applied in real-world scenarios.