ABSTRACT

Affected by the increasing environmental awareness and laws, many wetland authorities have carried out habitat creation projects, hoping to restore or strengthen the ecological functions of wetlands. One of the methods is the Controlled Reduced Tide system (CRT). However, the effectiveness of the related projects remains to be verified. Considering that the relationship between the characteristics of created wetland culverts and habitat quality is rarely established in related literature. This study established a one-dimensional hydraulic model to quantitatively analyze the impact of different culvert opening sizes and elevations on the magnitude of water level changes in wetlands. And then use Habitat Suitability Index (HSI) to evaluate habitat quality. This study takes as an example the created wetland in Xucuogang Important Wetland, Taoyuan City, which was completed in 2020. The current opening area of the culvert connecting the inner and outer of the wetland is 4.05 square meters and the bottom elevation is about 0.54 meters. This study used the common teals (Anas crecca) as the target species to establish the HSI for the exceedance probability of submergence. The research results pointed out that the current water level variations in the wetland are insufficient, unlike the large tidal range outside the wetland, and the average HSI is only 0.12. When the culvert opening area is increased to 25.13 square meters and the bottom elevation is fixed, the variations of water level inside and outside of the wetland have the smallest difference. The culvert opening area is called the "critical area". At this time, the average HSI of the wetland is increased to 0.15. The bottom elevation of the culvert is increased when it drops to -0.5 meters and the opening area is fixed, there is the smallest difference between the highest and lowest water levels inside and outside the wetland. In this study, it is called “critical bottom elevation”. At this time, the average HSI of the wetland can be increased to 0.31. The results were shown that the larger the opening area of the culvert and the lower the bottom elevation, the water level changes inside and outside the wetland will tend to be consistent, which is also helpful to increase variations for the water level changes in the wetland. Therefore, future related habitat restoration and construction projects should consider the tidal characteristics, and determine the water level regulation system, and discuss the critical situation, so as to benefit more habitat diversity in the wetland.

Keywords: Tidal wetland, Water level regulation, Critical area, Critical elevation, Water level change, Habitat suitability index.