Coupling acoustic devices for monitoring combined sewer network sediment deposits

Combined sewer networks display some unique features that are not easily reproducible in the laboratory and have yet to be well understood. The transport of organic and mobile sediments, present in large quantities despite the use of optimal design practices, dramatically changes sewer flow patterns and the interaction between flow and sediment. To understand both the flow patterns and transport features of these complex environments, it is therefore necessary to install instrumentation in situ. For this paper, two distinct acoustic techniques were coupled in order to measure both the sediment interface and velocity. For this purpose, a 2 MHz rotating head acoustic profiler and a 10 MHz acoustic Doppler velocimeter (ADV) were jointly installed to survey the position of sediment deposits and measure velocity patterns. Results were compared with measurements recorded in different environments, where both coarser and finer soft deposits were present. These results typically showed good agreement between the interfaces detected using velocity measurements on coarse deposits, while the presence of soft deposits demonstrated the need for coupling measurements techniques that can correctly assess the sediment interface.