Development of a new method for sediment transport measurement in SBT

For the effective operation of Sediment Bypass Tunnels (SBTs), in-situ sediment transport measurement is essential. However, the flow velocity within SBTs is significantly higher than in typical rivers, rendering existing measurement devices like Swiss plate geophones or Japanese pipe microphones susceptible to damage from gravel collisions. To address this, we are developing a method to measure sediment concentration by installing electrode plates on opposing banks of mountain rivers, applying a voltage across them, and measuring the electrical conductivity of the water. We anticipate that this approach, if applicable to SBTs, will provide a robust measurement technique capable of withstanding high-velocity gravel impacts. In developing this new method, we first conducted a water tank experiment to investigate the relationship between sediment concentration and the electrical conductivity measured by the electrodes. This revealed a clear linear correlation. Subsequently, we performed a flume experiment to verify the method's feasibility. We supplied water and sediment particles into the flume and measured the volumetric concentration passing between the electrodes. The total sediment transport calculated from this volumetric concentration and the flow rate closely matched the sediment input. Finally, we applied this method to three mountain rivers (the Hiki River, the Gamata River, and the Joganji River) to monitor sediment transport. The results indicated that while there was an issue of overestimating sediment concentrations, the method successfully captured sediment transport dynamics.