| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 104 === Water is the necessary resource for living creatures. Human beings usually build hydraulic structures to satisfy human’s water needs. Excessive water usage impacts the natural environment of rivers. The key factor to protect the river ecology is the reserved discharge in the river. Traditionally, this reserved discharge is determined for single objective or is determined as a minimal discharge rate which did not consider the complexity of the river ecology. In addition to ecology, the reserved discharge also affects the water usage for human beings. Therefore, the influence analysis for different scenarios is necessary for balancing both side of water needs. The main purpose of this study is developing a systematic way to propose alternative scenarios for trade off analysis among river ecology, human activities, and natural environment. For these alternative scenarios, this study not only considers water quantity, water quality, and duration time, but also evaluates the corresponding impact related to human water usage and ecological environment.
This study applies the proposed method to Dahan River. Current Dahan River is under the situation of excessive use. The ecological environment at the downstream river is seriously damaged. This study collects the ecology, hydrology, and geology data to assist the determination of the environmental discharge management targets. Each management target is quantified using different evaluation methods. Eight alternative scenarios are proposed based on the combination of these quantified indices. These alternative scenarios are then compared with the current system, as defined the based case or Case 0. The Shortage Index (SI) and the integrated hydrology changes are used to evaluate the impact of human water usage and ecological environment.
The study found that the lowest impact scenarios for human water usage and ecological environment are Case 3 and Case 4 respectively. In Case 3, with comparison of Case 0 for Taoyuan area, the SI value increases 0.136 which indicates a slightly negative influence for human water usage. For river sections 1, 2, and 4, the integrated hydrology is reduced by 1.7%, 1%, and 0.1% respectively. This reduction refers slightly improvement for these river sections. In Case 4, with comparison of Case 0 for Taoyuan area, the SI value increases 13.3 which indicates a severely negative influence for human water usage due to high reserved discharge rate. On the other hand, the river ecology is improved according to the integrated hydrology is reduced by 10.3%, 13.8%, 10.5% and 10.4% for river sections 1 through 4 respectively.
In this study, the environmental discharge is represented by river status. In addition, multiple quantitative management objectives are considered to evaluate the impacts for human beings and ecology using alternative scenarios. The results can be a decision reference for government and interested parties.
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