Detection and quantification of suspended sediment concentration and stratification in open channel flows: Development and first results using electrical resistance tomography

Understanding the transport and deposition of sediment (such as sand and clay) is essential to allowthe modelling and prediction of sediment dispersal, and the development of depositional morphology, within modern environments and ancient sedimentary basins.

Electrical Resistance Tomography (ERT) has previously been used to provide a measure of particleconcentration within moving suspensions. These measurements are normally performed in a mixingvessel or a pipeline, which usually has a circular cross section. In such cases, the ERT measurementemploys electrodes around the boundary of the container that allows measurement of multipleprojections from all around the container. However, measuring the concentration of a flow in arectangular channel without disturbing the flow cannot use these well-established sensor rings. Thispaper investigates the use of a linear sensor array in the channel bed, and a U-shaped sensor array inthe channel bed and walls, to measure spatial and temporal gradients in sedimentconcentration/conductivity of a channellised flow. Additionally, since deposition from suspension ontothe channel bed will produce sediment deposits, the morphological character of these sediment layersis a valuable parameter in analysis of the flow dynamics. ERT is also used to measure the evolvingheight of such layers. However, the sediment itself may lie directly on top of the measuring electrodes,if the electrodes are arranged at the bottom of the channel. This will hence reduce the sensitivity of thetomography system and presents a further challenge for the measurements.

To overcome the problems with the effect of sediment-covered electrodes and the limited number ofprojection angles of a linear sensor configuration, the properties of a U-shaped sensor will beexplored. Due to the additional projection angles and electrodes in a U-shaped sensor that are notburied in the sediment, it is expected these will allow better estimation of the changing thickness andsurface morphology of the sediment layers. This paper presents the first results of measurements ofsuspended sediment concentration and sediment deposition using linear and U-shaped tomographicsensors.