In recent years, a series of typhoons brought a large amount of rain to Taiwan. Landslides occurred in many mountain areas including the upper catchments of Kaoping River basin. The drinking water shortage caused by the high turbidity of source water raised the questions of reservoir sedimentation and watershed management. Due to the geological and meteorological conditions, the natural hazards occurring in the mountain area are difficult to avoid, but the human and property damages can be minimized. To reduce the human and property damages in the mountain area, a sound watershed management strategy is required. The Kaoping River basin is the largest and the most intensively used river basin in Taiwan. It is 171-km long, drains a catchment of more than 3,625 km2, and has a mean flow of 239 m3/s. It serves as a water supply to the Kaohsiung City (the second largest city in Taiwan), several towns, two counties, and a number of large industries (electronic, steel, petrochemical, etc.). Although the mean annual rainfall in this river basin is close to 3,000 mm, over 90% of which appears in the wet season. The period of high flow rate in the stream usually occurs in the late spring and summer due to the impacts of monsoon and typhoon. Taiwan Environmental Protection Administration (TEPA) has developed a three-part classification system (Classes A, B, and C) for Kaoping River based on the purpose of water usage and degree of protection for each stream section. Basically, the upstream is classified as Class A, mid-stream is Class B, and the downstream near the outfall is Class C. Thus, the highest degree of protection is given to Class A. Recent water quality analysis by EPA indicates that the Kaoping River is polluted and the water quality can not meet the TEPA standards. Investigation results show that the major concern is the high turbidity caused by the stormwater, which results in the high concentrations of suspended solids (SS). Results from the review of recent information on the water usage and investigation of the water quality demonstrate that non-point source (NPS) pollutants are now the major causes of turbidity, SS, and nutrients in the river. In the Kaoping River basin, most of the upper catchment is used for agricultural activities. In the upper catchment, NPS pollutants mainly associated with stormwater runoff from agricultural land uses can be quite diffuse and difficult to treat. Agricultural NPS pollution is considered to be the largest single category resulting in these environmental problems. An integrated watershed management model (IWMM) was applied for simulating the water quality in the Kaoping River watershed. The model includes a global atmosphere module, a land module, a human impact module, a canopy module, and a global ocean module. Those modules can be linked and managed by a graphic user-interface. The model was calibrated and verified with field data, and was used to investigate potential NPS pollution management plans. Simulated results indicate that NPS ammonia loading contributes 35% of the total nutrient loadings during the dry seasons from 2002 to 2005. However, the contributions of NPS nutrient loading increased to 80% of the total nutrient loadings during the rainy seasons. Results indicate that rainfalls and storms caused a significant increase in the NPS nutrient loadings into the water bodies. The NPS pollution also had serious impact on the Kaoping River water quality. A comprehensive turbidity and NPS remedial strategy for Kaoping River basin management has been proposed. The NPS pollution management strategy consists of the following measures: 1. construction of the watershed geographical information system (GIS) and real time water quality monitoring systems, 2. source (fertilizer) reduction, and 3. construction of grassy buffer zone or other natural treatment systems for NPS control. The turbidity control strategy consists of the following measures: 1. application of TMDL for turbidity and SS control, 2. application of technical strategies for sediment erosion control, which includes (1) surface runoff control using structural and nonstructural solutions, (2) soil stabilization by bioengineering solutions (e.g., plant growing), (3) BMP application for farming (e.g., contour farming), (4) soil stabilization by hard structural solutions (e.g., stream bank stabilization), and 3. Roads in the watershed should be well-planned, constructed, and maintained.

Nonpoint Source pollution,Turbidity,Kaoping River