Technical Studies


Improvement Study On Sediment Measurement TechniquesIn Natural Rivers

The rivers and creeks in Taiwan have characteristics of small basin, high flow velocity, and rapid change between base flow and storm flow, most transportation of suspended sediment occurs in a few torrential rain incidents. 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. The SSC has high spatial and temporal variability. Efficient and automated techniques for high SSC monitoring are yet to be discovered.

This study performed an exhaustive literature review on SSC monitoring techniques. Besides, a new method based on time domain reflectometry (TDR) was proposed. SSC monitoring techniques differ in measurement sensitivity, measurement range, and effect of sediment particle size. Appropriate instrumentation depends on the site conditions and requirements. TDR method possesses several advantages over other methods including low-cost sensors, durability, maintainable, multiplexing capability, and multi-functions (e.g. water level, rain gauge, and soil moisture, etc). But the sensitivity to low SSC needs further improvements.

A pilot automatic monitoring station incorporating optical turbidity meter, acoustic attenuation meter, TDR instrument, and automatic pump sampler was established at Nei-Wan hydrology station. Data collected by this pilot station will be used to demonstrate continuous monitoring during a storm event and compare the performance of different monitoring techniques.