Monitoring of Sediment Transport in a Reservoir using Time Domain Reflectometry

Due to geological weathering and climate change, soil erosion in watershed is becoming a serious problem in Taiwan. Large amount of sediment transports to reservoirs during typhoon events and affects the water quality. Density currents in reservoirs have high sediment concentration. The accumulated sediments have significantly reduced the reservoir capacity. Monitoring of sediment transport in a reservoir plays an important role in reservoir management. The existing techniques for suspended sediment concentration (SSC) monitoring, such as optical and acoustic methods, are sensitive to particle size or limited in measurement range. Furthermore, these techniques may not be cost effective for field monitoring due to the required maintenance and spatial coverage. A new technique based on time domain reflectometry (TDR) was recently introduced. It possesses several advantages including particle-size independence, low-cost transducers, durability, and cost-effective multiplexing. This study modified the TDR technique for better field applicability and demonstrated how it can be deployed as a full monitoring program for reservoir management through a case study in the Shihmen reservoir, Taiwan. Monitoring stations at upstream riverbank and outflow channels were installed with fixed protective structures to provide inflow and outflow sediment-discharge records. To capture the characteristics of density currents, multi-depth monitoring stations were designed and deployed on floats in the reservoir. Some of the data collected during Typhoon Fung-Wong are presented as an example to demonstrate the effectiveness and benefits of the monitoring station.