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SUMMARY OF HYDROLOGICAL FEATURES

IN TAIWAN

1. Geography－Taiwan, an island province of the Republic of China, is about 35,961 square kilometers in area. The Tropic of Cancer traverses the island throught its southern half.

2. Topography－Steep mountain terrain above 1,000 metera in elevation covers about 32％ of the island; hills and terrace land between 100 and 1,000 meters make up 31％; and alluvial plains below 100 meters, where communities and farming activities and industries are concentrated, comprise the remaining 37％ ( Fig.1 )

3. Climate－The climate is subtropical. Northeast monsoon prevails from October through March. During the summer and autumn, typhoons and thunderstorms bring in abundant rainfall. The growing season in the plains extends throughout the year.

4. Geology－The mountains in Taiwan are dominated by sedimentary rocks, weak, fractured, and deeply weathered. Heavy erosion occurs because of intense rainfall and high velocity of water flow and is further aggravated by earthquakes which damage the stability of the hill slopes. Where soils exist, plant cover is usally desnse.

5. The Rivers－The rivers are short and steep, and torrential during storms. ( Fig.2 and Table 1 ) The flow rises and recedes rapidly with rainfall. Floods carry tremendous amount of sediments. The flow in the spring season is low, and is almost all diverted for irrigation use. The combination of steep and narrow valleys, weak geology, and high floods, and sediments makes the rivers very difficult to control.

6. Hydrology－About 79％ of annual precipitation occurs from May through October. Typhoon rainfall is very intense. A storm recorded in 1963 in a northern watershed 763 square kilometers in area averaged 1,375 millimeters in 64 hours, or 914 millimeters in 24 hours.