1 Fast ERT to estimate pollutants and solid transport variation in water flow: a laboratory experiment L. SAMBUELLI 1 and C. COMINA 2 1 DITAG, Politecnico di Torino, Italy 2 DST, Università degli Studi di Torino, Italy (Received: April 17, 2009; accepted: December 15, 2009) ABSTRACT The understanding and evaluation of the phenomena related to pollutants diffusion, solid transport or lithic material deposition within a river have a prominent role in hydraulics and fluvial geomorphology. In this respect, the direct measurement of the amount of transported material is certainly one of the most difficult tasks in the field of river hydraulics due to the heterogeneity and representativeness of the samples. In this paper, we investigate the applicability of a very fast (about ten seconds or less), non-invasive electrical resistivity tomography to identify and estimate pollutant and solid transport variations in a fast water flow. To do this, three experimental tests, in a laboratory channel with a flow rate of 0.5 m/s, are presented using both a pollutant flow and different types of solid transport (fine and coarse sands). Data are interpreted by means of classical models that relate the variation in electric conductivity to variations in concentration or in volume fraction of suspended material. Whereas the identification and positioning of the pollutant or solid transport is successful, the estimation of governing parameters still remains mainly qualitative. 1. Introduction Process tomography using electrical capacitance and electrical resistivity tomography (ECT and ERT respectively), was developed in the last few decades of the 20 th century to monitor bi- phase or multi-phase mixture flowing, separating, decanting within pipes, cyclones and tanks in industrial plants (Xie et al., 1995; Tapp and Wilson, 1997; York, 2001). In particular, ERT has been used to carry out studies to monitor the extent of solids deposited during slurry conveying in a horizontal pipe (Fangary et al., 1998). Lucas et al. (1999) described a dual-plane ERT system, consisting of two electrode arrays placed circularly around two sections of a pipe, to measure the local solids volume fraction distribution and the local solids axial velocity distribution in solid–liquid flows. Wang and Cilliers (1999) showed that ERT can be a suitable method for the visualisation of regions of different density in flowing foam systems, assessing the ERT effectiveness also in liquid-gas mixtures. Yang and Liu (2000) studied the possibility of using ECT to reconstruct cross-sectional distributions of density in gas-solid mixtures. Warsito and Fan (2001) applied ECT to study gas-liquid and gas-liquid-solid mixture flows. All of the aforementioned applications deal with cylindrical bodies (pipes, cyclones, tanks) and the electrodes are placed on one or more circumferences orthogonal to the cylinder axis. These geometrical configurations, with electrodes covering the whole object boundary, assure an “optimum” conditioning of the inverse tomographic problem. In the past, moreover, soil Bollettino di Geofisica Teorica ed Applicata Vol. 51, n. 1, pp. 1-22; March 2010 © 2010 – OGS