Technical Studies

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. To obtain the essential data, a new suspended sediment concentration (SSC) measurement method based on time domain reflectometry (TDR) technique was firstly proposed from 2006-2007 Water Resource Agency (WRA) supported projects. In later studies from WRA projects 2008-2009, TDR SSC measurement resolution was increased with proposed methodology, water temperature compensation and the probe design. Unlike optical and acoustic method, TDR SSC method is less affected by the soil particle size or type, and it is more economical, easy to be maintained, and applicable for high SSC monitoring. However, issues of TDR hardware temperature effect with ambient temperature fluctuation and probe fouling as field experiences need to be solved. Therefore, one of the objectives of the project is to improve the TDR SSC measurement resolution and accuracy in field measurements. The other is to develop the river SSC measurement platform based upon information technology for hydro-information integration.

To improve the TDR SSC practical performance affected by TDR hardware temperature effect, the TDR full waveform simulations is primarily implemented with influence factors (risetime effect) and signal processing methods, such as truncation adjustment, bandpass filter, and Time-variable filter (TVF). The results indicate that the TDR hardware temperature effect could be from the internal electronic component of time base or time interval. To minimize the TDR hardware temperature effect without major electronic components revision, the study reveals the idea by increasing probe length to achieve higher resolution within limited sampling interval. Then a spiral type probe is developed with experimental verification to increase the SSC measurement resolution and minimize the TDR hardware temperature effect. Also the new Teflon coating materials for probe fouling prevention are carried out. Further in-field tests including the spiral type probe and new Teflon coating materials evaluations are suggested in the next year project. All demonstration monitoring stations, including Neiwan, Shihgong, and ChiChi, were matained for further SSC monitoring.

The river SSC measurement platform contains (1) remote station construction and (2) main server establishment. The remote station construction is done based upon former studies. The main server consists “Data center” and “Control center”. The first component provides data communication, storage and consulting via Web interfaces. The “Control center” supports remote stations management and manipulation with authority. All afromentioned modules are planted well for next year execution.

Due to less torrential rain fall event for SSC collection from the Neiwan river station, the study suggests a new migrated station from exist one to provide more data of river sediment transportation, or the suggestion of river sediment profiling measurements in next year project.