Evaluation of a Permittivity Sensor for Continuous Monitoring of Suspended Sediment Concentration

Due to the large spatial and temporal variations inherent in sediment transport, suspended sediment measurement is challenging. The overall goal of this research was to develop an inexpensive sensor for continuous suspended sediment monitoring in streams. Specifically, this study determined if the gain and phase components of permittivity could be used to predict suspended sediment concentrations (SSC). A permittivity sensor, comprised of an electrode, power source, and a control box or frequency generator, was constructed and tested using kaolinite suspension at concentrations of 0, 500, 1000, 2000, 3000, 4000, and 5000 mg L-1. The impact of temperature (10°C, 20°C, and 30°C) and specific conductivity (0, 250, and 500 µS cm-1) on sensor gain and/or phase output at multiple frequencies was also evaluated. Partial least squares (PLS) regression techniques were applied to gain and phase data for 127 frequencies ranging from 50 Hz to 120 MHz. The three models with the lowest error between predicted and actual SSC values for validation were further tested with nine levels of independent validation data. The largest model error (error > 50%) occurred at 0 and 500 mg L-1. As SSC concentrations approached 1000 mg L-1, the prediction accuracy increased for the top three models; error varied from 1% to 45% at concentrations of 1000 to 5000 mg L-1. Model 3A, a phase-based model, preformed the best. Model 3A was able to predict six of the nine independent validation treatment levels to within 300 mg L-1. Future research will provide additional laboratory and field testing of the prototype sensor.