| Summary: | 碩士 === 國立屏東科技大學 === 土木工程系碩士班 === 92 === If a river is covered with many Eichhornia Crassipes, heavy rains will force the plant congeries to obstruct the flowing spaces between piers, which will result in drainage difficulty and hence jeopardize the safety of bridges and cause flooding problems. In this study, the Manning’s coefficients of channels covered with Eichhornia Crassipes were determined by open channels experiments. Furthermore, the water levels raised in upstream were simulated by applying the HEC-RAS model on the channels covered with Eichhornia Crassipes.
The Manning’s coefficients of the channels covered with Eichhornia Crassipes varied depending on the flowing velocities. The results showed that the scale of Manning’s coefficients was between 0.026 to 0.416, and the mean coefficient was 0.098. Therefore, Manning’s coefficient 0.098 was suggested at velocities between 0.76 to 11.65 cm/s. The difference of upstream water levels raised between the channels experiment and the model simulation was 29.78 % when the water discharge was 0.0166 cms and the root depth of Eichhornia Crassipes was 20 cm. The difference was 8.00 % when the water discharge was 0.0166 cms and the root depth was 15 cm; the difference was 6.46 % when the discharge was 0.0191 cms and the root depth of the plant was 13 cm. This study revealed that the closer the plant roots are the more approximate of both results by the channels experiment and the model simulation. This study also verified that upstream water levels would be raised when the channels were covered with Eichhornia Crassipes.
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