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SUMMARY OF HYDROLOGICAL FEATURES

IN TAIWAN

1. Geography－Taiwan, an island province of the Republic of China, is 35,981 square kilometers( 13,892 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 and 2 ). 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 76％ of annual precipitation occurs from May through October and major portion is caused from storm rainfall. In 1975, there are 112 hydrometric stations and 1099 rainfall station in operation. Due to the 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 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 is about 67.1 billion cubic meters. However, only 22％ or 15 billion cubic meters are available for use during dry season ( Figure 4 and Table 3 ). The annual withdrawal of groundwater is estimated at 3.2 billion cubic meters ( Figure 5 ).

8. Summary of Hydrological Conditions in 1976

(1) Rainfall－Based on the island wide records the annual rainfall of Taiwan in 1976 is calculated at 2,280 millimeters, which is 6％ higher than that of the long term average, 2,430 millimeters ( Figure 6 ). Therefore, it can be considered 1976 was a wet year.

(2) Streamflow－Accordance to the streamflow records, the streamflow of the eastern rivers and the northern rivers is lower than the long term average. The recorded streamflow of the rivers in the central and south regions is greater than the long term average ( Figure 8 and Table 2 ).

(3) Floods－In Taiwan, most floods are caused by typhoon storms. In this year, only one typhoon, named Billie hit the island on August 9. Typhoon Billie caused severe flood damage in central and northern part of the island.

9. ERTS Photomap of Taiwan

The NASA Earth Resources Technology Satellite-1 ( ERTS-1 ) launched July 23, 1972 is the first satellite dedicated wholly to the sask of obtaining imagery of the earth’s surface for earth survey purposes. In order to introduce the applications of remote sensing technology to hydrology and water resources, four ERTS Photomaps of Taiwan are attached ( Figures 9).