Development of Sediment Monitoring During Heavy Rainfalls: Fid-Bau Portal

Development of Sediment Monitoring During Heavy Rainfalls

Lin, Chih-Ping / Chung, Chih-Chung / Chang, Yu-Chia / Chang, Tzong-Shen

Abstract Due to geological weathering and climate change, soil erosion in watershed is becoming a serious problem in Taiwan. Sediments affect water quality during heavy rainfalls and their deposition reduces reservoir capacity. Monitoring of sediment movement is crucial to estimate sediment yield and analyze watershed dynamics related to slope stability. It also plays an important role in reservoir management during heavy rainfalls. While suspended-sediment concentration (SSC) can be observed by manual sampling and lab testing, it is difficult to predict the right sampling timing and mobilize field crew during storms. Currently, there are no effective measuring techniques for automatic SSC measurement, particularly in fluvial environment. Existing methods provide an accuracy much influenced by particle sizes of suspended sediments, function only in a limited range of measurement and are not cost effective for field maintenance and wide spatial coverage. This paper introduces an innovative method based on time domain reflectometry (TDR) that may lead to an effective solution for monitoring of sediment movement. TDR is a monitoring technique based on transmission lines, in which a time domain reflectometer transmits an EM wave and receives a reflected EM wave, and wherein various TDR sensing waveguides can be designed to monitor different physical quantities, such as soil moisture content (based on dielectric permittivity), electrical conductivity, water level, and displacement. A TDR SSC probe is designed and a new travel time analysis method with temperature correction procedure is proposed for accurate determination of SSC. Unlike optical and acoustic method, TDR measurement is shown to be insensitive to sediment particle size. Other advantages of the TDR method include low-cost transducers, durability, and multiplexing capability. Results of laboratory evaluation and field monitoring are introduced.