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SUMMARY OF HYDROLOGICAL FEATURES

IN TAIWAN

1. Geography—The area of Taiwan, an island and also a province 'of the Republic of China, is 36,002 square kilometers (13,900 square miles). It is located in the subtropical region with the Tropic of Cancer traversing its southern part.

2. Topography—The area of steep mountain terrain above 1,000 meters high covers about 32% of that of the island; hills and terraces between 100 and 1,000 meters high make up 31%; while alluvial plains below 100 meters high, where most communities, farming activities and industries are concentrated, cover the remaining 37% (Fig. 1).

3. Climate—The Climate is subtropical. The Northeast monsoon prevails from October through March of the next year. Typhoons and thunderstorms bring in abundant rainfall from May through September. The crop-growing season in the plains extends throughout the year.

4. Geology—The mountains in Taiwan are dominated by sedimentary rocks. They are 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.

5. Rivers—Rivers in Taiwan are short and steep and torrential during storm periods. Hydrographs are characterized by high peaks and short duration, with heavy silt content. Streamflom in winter and spring seasons is much lower than that in summer period. Shortage of water usually occurs in Feburary through May.

6. Hydrology—About 78% of annual precipitation falls from May through October, with major portion provided by storms or typhoons. In 1989, there were 131 hydrometric stations and 982 rainfall stations in operation. Due .to the unfavorable natural conditions, many difficulties were encountered for the measurements of streamflow and sediment, (Fig. 2, Table 1 and Table 2).

Assessment of water resources—Based on island wide records from 1949 to 1986, the average annual rainfall for the entire Taiwan area is 2,504 millimeters in depth or 90 billion cubic meters in volume. The average annual runoff is about 67.5 billion cubic meters However, only 22% of it, about 14.9 billion cubic meters, is available for use during the dry season. The annual pumped groundwater is estimated at 3.8 billion cubic meters, (Fig. 3, Fig. 4, Fig. 6 and Table 3).