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SUMMARY OF HYDROLOGICAL FEATURES

IN TAIWAN

1. Geography－Taiwan, an island province of the Republic of China, is 35,961 square kilometers( 13,885 square miles ) in area. It is located in the subtropical region with the Tropic of Cancer traverses the island through its southern half.

2. Topography－Steep mountain terrain above 1,000 meters 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, It is 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 are short and steep, and torrential during storms. ( Fig.2 and Table 1 and2 ). Hydrographs usually characterized by high peak and short duration, with heavy silt content. Flow in winter and spring seasons is much lower than in summer period, Shortage of water usually occurred during February to May.

6. Hydrology－About 80％ of annual precipitation occurs from May through October and major portion is caused from storm rainfall. In 1974, there are unfavorable natural conditions many difficulties have been encountered for the measurement of streamflow and sediment.

7. Evaluation of Water Resources－Based on long term island wide rainfall records, the average annual rainfall of the total area is calculated at 2,430 millimeters ( Figure 3 ) which equivalent to a total volume of 87.4 billion cubic meters. Average annual runoff of the water source region above elevation 100 meters is about 54.3 billion cubic meters. However, only 23％or 12.5 billion cubic meters are available for use during dry season ( Figure 4 and Table 3 ). The safe yield of ground water is estimated at 3.5 billion cubic meters ( Figure 5 ).

8. Summary of Hydrological Conditions in 1974

(1) Rainfall－Based on the island wide records the annual rainfall of Taiwan in 1974 is calculated at 3,103 millimeters, which is 28％ higher than that of the long term average, 2,430 millimeters ( Figure 6 ). Therefore, it can be considered 1974 was a wet year.

(2) Streamflow－In accordance with the annual rainfall in 1974 most of the stream gaging stations observed abundant flow which is greater than the long from average ( Table 2 and Figure 8 )

Floods－In the typhoon season two major storms caused extensive flooding along the east Cost and in the Longing River Basin. The first major flood, caused by typhoon Wendy occurred at the end of September; the second flood, caused by typhoon Bess occurred in the mid-October. The Lanyang Area was severely effected during typhoon Bess; As a result, 14 persons were killed, railroads. Highways, flood protecting facilities as well as irrigation cauals were damaged. The total value is estimated at NT$91,000,000.