The utilization of water resources in the Ta-Chia River Basin(TCRB) is very intensive and the Basin is the main source for water supply, power generation and irrigation in greater Taichung area. The mountain slopes of the TCRB were severely destabilized by the 921 Earthquake in 1999. In addition, during July to October in 2001, Toraji, Nari, and Lekima typhoons hit Taiwan Island successively. Affected by heavy rainfalls brought by these typhoons, landslides, floods, and debris flows occurred frequently in the TCRB. As a result, highways blocked, houses buried by debris flows, and people died or missing. Therefore integrated conservation and management of TCRB is essential.
The study analyzed topographic, geologic, hydrometeorologic, and social-economic that affect soil and water related problems of the TCRB. The past and ongoing conservation and regulation works have been evaluated and appropriate actions and suggestions were proposed based on past experiences. The study intends to provide information useful for basin resource conservation and environmental policy decision-making for sustainable management in TCRB.
This study shows that sedimentation yield of the Ta-Chia River Basin accumulated mainly in 28 sub-basins from She-Gang Dam to De-Ji Dam. To reduce slope erosion and reservoir sedimentation, landslide area (about 31.62 km2) and potential debris flows (65 sites) have to be put in top priority. As for the severe landslides along Ta-Chia River banks, the protective buffer zones should be established to prevent or alleviate the downward movements of soil and help controlling water quality. Besides, the government has to bring an ecological concept into engineering structure design to pursue watershed protection and ecological conservation purposes to restore the land. Success or failure of management and conservation works in the Basin depend on adequate cooperation from the public and land users, especially for proper reasonable land utilization. Public participation can help the Government to evaluate the consequences and causes of the problems as well as feasible solutions.
In recent years, social and economic situations in Taiwan had changed significantly. The exploitation and development of public lands resulted in excessive, inappropriate and illegal land uses. Although areas covered by forests in the TCRB remained the same, areas planted for fruits and vegetables increased significantly. Temperate-zone fruit trees and high elevation vegetables appeared in headwaters areas above De-Ji Dam and excessive land cutivatiation also happened in middle to lower elevation stream slopes of Ta-Chia River. The effective regulation of excessive land uses is difficult due to limited manpower of the Government as well as the incompleteness of GIS for proper land exploitation identification. The residential and agricultural use of lands along in the river channel occurred at headwaters area of Ta-Chia River mainstream due to the official river regulation lines reached only up to Ten-Lun Dam.On the other hand in order to make reasonable land utilization in the TCRB, Forestry Bureau has to identify forest land boundaries as soon as possible in order to ensure people's property rights and to help avoid unnecessary disputes on land. For agricultural slopes, the Soil and Water Conservation Bureau has to properly minimize illegal exploitation according to the Soil and Water Conservation Act. As for river area, Water Resources Agency has to effectively suppress illegal uses of lands along creek banks.
Since the Ta-Chia River is the major water resource for greater Taichung area, the water quality is an essential evaluation component. The water quality in the Ta-Chia river is good for now. The government has to establish an improved water quality monitoring system in order to monitor water quality changes in the Basin.
In the future, for ecological conservation it is important to establish an ecology database with long-term records and observations for variety species and to analyze correlations between species and the environment. It is also necessary to promote through properly planned and implemented public information and education program the meaning of ecology conservation and avoid detrimentally affect environment so as to protect important habitats for plants and wield animals can be preserved.
Comprehensive basin management is not a new concept. It has been recognized for a long time. However, it was not emphasized in the past because of limitations of government regulations and not enough collaboration between government agencies. In order to comply with changes of social environment and development needs of Taiwan, comprehensive basin management will be the way to go in the future.