This project performed ongoing maintenance on long-term monitoring platforms of Shihmen Reservoir to monitor the sediment transport based on former related projects ‘Study of Shihmen Reservoir Water and Sediment Transport Monitoring, and the Development and Application of Density Current Simulation Model’ (2007-2011) and ‘Shihmen Reservoir Long-term Monitoring Project and Desilting Operation Simulation Analysis’(2012-2013). This project attained the automated monitoring of sediment transportation in reservoir and real-time data transmission system, in order to instantaneously master the crucial information of sediment transport and density current in reservoir during floods, providing guidelines to the reservoir management operation on water supply, flood control and desiltation. In addition to automated monitoring, this project conducted manual observation on sediment transport during flood events to identify historical hourly reservoir sediment load and reservoir outlet sediment discharge, and also the transport characteristics of density flow in the reservoir region. Current state and silting prevention of the reservoir are hence quantifiable according to these manual measurements, which are used to evaluate the performance of the planning and design on reservoir desiltation operation enhancement.
As the extension of previous sediment transport observation operation, this project continued to maintain and improve existing manual and automated monitoring stations, including the hardware maintenance of automated monitoring platform and probe replacement, function enhancement of upstream monitoring station and outlet discharge pipelines at downstream stations.
This project performed sediment transport monitoring during flood events with both manual observation and automated TDR measurement operation in typhoon events of Typhoon Matmo, Fung-wong, Chan-hom, Soudelor, and Dujuan.
After the commissioning of desilting tunnel since 2013, the sediment discharge ratio increased to 35% in Typhoon Soulik (2013), 37.2% in Typhoon Trami (2013), 36% in Typhoon Soudelor (2015) and 32.6% in Typhoon Dujuan (2015).
Based on observational data from 2008 to 2015, there are three main conditons for density current formation in Shihmen Reservoir:
1.Peak inflow is greater than 1,800 cms.
2.Peak sediment concentration load (ppm) is greater than 17,500 ppm.
3.Inflow load of Q > 300 cms sustained for more than 35 hours.