| Summary: | 碩士 === 逢甲大學 === 水利工程與資源保育研究所 === 98 === Transport of sediment in rivers is one of the complicated physical phenomena in hydrologic process. The situation is more complex in Taiwan because of its unique geographic features such as: steep bed slopes in high mountains, narrow and small watersheds, and short river reaches. The enormous amount of sediment that is delivered to waterways following terrestrial rainstorms induces severe sedimentation in downstream channels and reservoirs; subsequently causing dangerous water logging in low-lying areas and reducing reservoirs capacity. These results not only degrade the living quality of the area but also threatened the properties and life for residents of Taiwan.
Techniques for sampling suspended sediment concentration (SSC) presently rely on manual methods in Taiwan. Manual methods are costly, time-consuming, unable to reflect instantaneous SSC hydrograph in time of need, and limited by accessibility and inclement weather conditions. An SSC sampling technique using the capacitance sensor that is automatic, real-time, and continuous has been proposed in this research. The SSC measurement is based on the principle of electric capacitance and the research consists of experimenting with the parallel capacitor plates that are subject to flow velocity, material and surface area of the capacitors, the distance between the two capacitor plates, and water temperature. Experimental results demonstrate the following results.
1. The output of capacitance sensors and hence the SSC vary slightly with flow velocities. The ratios of sensor outputs between the water with velocity and stagnant water are within 0.4%.
2. Capacitors made of copper resulted in better electricity output of SSC relations than those made of stainless steel, with R2 reaching 0.98.
3. Differences from varying the surface area of the plates are not significant. This conclusion may be subject to the different plate area used in the experiment.
4. The R2 of the linear SSC and electricity output relation resulting from plate distance of 0.5 cm is better than that of 1.0 cm, which are 0.98 and 0.97 respectively.
5. Temperature fluctuation will affect the results of capacitor sensors as the results indicated that when the temperature increased, the output of capacitance sensors also increased.
This research also demonstrated that better results can be obtained when the plates are designed with the following conditions: area of 5x5 cm2, made of copper, and plate distance 0.5 cm. When the reference SSC is below 50 g/L, the errors are within 30%; when the reference SSC is above 50 g/L, the error tends to reduce to within 10%, with an uncertainty within 0.25 g/L. With these results, it can be seen that capacitance sensor technique has great potential in future SSC monitoring applications.
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