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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 1984, there were 125 hydrometric stations and 1158 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).

7. Assessment of water resources—Based on island wide records from 1949 to 1979, the average annual rainfall for the entire Taiwan area is 2510 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).

8. Summary of Hydrological Events in 1982

(1) Climate

There were many typhoons In Pacific Ocean in 1983, but none attacked Taiwan Re9ion. The climate of the first five mouths was normal. However between May 31 and June 3 a continuous downpour unleashed a flood on the mountains. All of a sudden Nantou Yunlin Chiayi and Tainan re9ions were buried in water. After June little rain fell and an Island wide drought began especially in the north. On the last ten days of August the stron9 southwest air current brought Pourin9 rain to Put an end to the drought.

(2) Rainfall

The average annual rainfall In Taiwan in 1983 was 2314 mm, which was 8% less than the long-term (1949-1979) avera9e annual rainfall of 2510 mm.

Re 田 on | Average annual rainfall in mm For the years indicated | Average annual rainfall for 1984 as % of that for
1984 | 1949-1979
North Central South East | 3335 1958 1911 2699 | 2851 2075 2578 2679 | 117 94 74 101
Total | 2400 | 2510 | 96

(3)Streamflow

In 1984 the annual streamflow of most river basins was lower than that of long-term (1949-1979) average, except Tachia and Wu basins in the central region as well as Erhjen and Kaoping Basins in the south region. The total streamflow of river systems in 1983 was calculated at 61.2 billion cubic meters which was 8% percents less than that of the long-term (1949-1979) average of 67.5 billion cubic meters. The stream-flow of major river basins are shown in Table 2.

(4) Groundwater

There were 332 observation wells in Taiwan area in 1984. The investigation of groundwater level was implemented by Taiwan Provincial Water Conservancy Bureau (Total 312 Wells) and Bureau of Public works of Taipei Municipal Government (Total 11 Wells). The average annual recharge of groundwater in Taiwan was estimated at 4 billion cubic meters. However, 3.8 billion cubic meters were withdrawn in 1984. Excessive groundwater withdrawn from Chiayun Coastal Area and Pingtung Coastal Area were recorded. It induced the land subsidence in both areas.

(5) Water consumpotion in 1984

The total amount of the annual consumptive water use in 1982 was calculated at 17.1 billion cubic meters, of which 14.1 billion cubic meters (82%) were used for irrigation; 1.7 billion cubic meters (9%) for domestic water supply; and 1.5 billion cubic meters (9%) for industrial use. The following table shows the water use in various regions in 1983.

Unit：Billion (109)m3

Region | Agriculture | Domestic | Industrial | Total
North | 2.1 | 0.9 | 0.6 | 3.6
Central | 5.7 | 0.4 | 0.4 | 6.5
South | 5.6 | 0.4 | 0.5 | 6.5
East | 1.7 | 0.04 | 0.04 | 1.7
Total Taiwan Area | 15.1 | 1.7 | 1.5 | 18.3

(6) The Operation of major reservoirs

There were 31 reservoirs in 1984. The total storage and effective capacity of existing reservoirs are 1.97 and 1.48 billion cubic meters respectively. The effective capacity of 9 major reservoirs is 1.39 billion cubic meters, which is 94% of that of all reservoirs.

The analysis of water utilization and sedimentation for major reservoirs in 1984 is shown in Table 6.