| Summary: | 碩士 === 中華大學 === 土木工程學系碩士班 === 99 === In the past, Taiwan ignored the importance of river ecology and instead focused on flood control and the utilization and development of rivers in order to protect the safety of its citizens, their property, and public facilities. As a result, the natural habitat of river organisms has gradually deteriorated, and bio-diversity of rivers has been severely impacted. In recent years, however, ecological conservation has emerged as an issue of increasing significance. How to maintain the volume of river water required by organisms for survival and create a suitable habitat are vital concerns in the environmental management of rivers.
The river segment researched in this study was the Daqi Bridge segment in the upstream area of Wu River. The research methods were as follows: River 2D was used as the main computational software. This model was combined with on-site surveys, WinGrid, and HEC-RAS to construct a digital elevation model (DEM) of the Daqi Bridge segment. Data on catchment area, constant flow, and annual peak-flow frequency were used as a basis for simulation. The simulations were used to investigate how Habitat diversity (H’) under artificial structures affects the weighted usable area (WUA) of Rhinogobius candidianus and Acrossocheilus paradoxus, and examines the relationships among these elements.
Research findings were as follows:
1.Under constant flow, the Habitat diversity (H’) of the original river stretch was 0.47; following the construction of three spur dikes, Habitat diversity (H’) was reduced to 0.41. The value of Habitat diversity (H’) was 0.39 after the construction of a 1m river weir and 0.26 after the construction of a 2m river weir. The main reason for these phenomena is that the addition of these structures led to an increase in deep pools of water and reduced shallow streams. This made the river environment less diverse, which was not beneficial to the organisms that were the subjects of this study.
2.The simulation results of the River 2D showed that construction of spur dikes not only deflected the current away from the river banks but also reduced flow velocity surrounding the dikes. This provides a protective area during periods of flooding. Under a constant flow, the construction of a 2m river weir produced optimal WUA; within a 5 cms flow, construction of a 1m river weir also produced optimal WUA. Under a flow of 100 cm or more, the significant increase in flow meant that the WUA of the original river conditions was improved. Within a 10-year return period, constructing three spur dikes can produce optimal WUA.
3.Results showed that the increased water level caused by high river flow had submerged the sandbars and thickets originally on the river shore. However, the flow velocity in this new region of water was still lower than that of the main riverbed, which created the possibility of its development as a new habitat.
4.Simulation results showed that higher Habitat diversity (H’) implied higher WUA. However, the flow rate affects the distribution of flow conditions. Under different flow conditions, Habitat diversity (H’) may still be similar. For example, when Habitat diversity (H’) was 0.5 under original river conditions, the WUA of Rhinogobius candidianus showed a maximum-minimum difference of approximately 300 m2.
5.In the four simulation cases, the linear relationship between WUA and Habitat diversity (H’) was the most significant under a 1m river weir. After the construction of a 2m weir, the habitat diversity was reduced and Habitat diversity (H’) decreased, which resulted in a non-linear relationship between WUA and Habitat diversity (H’).
|
|---|
