◢Page Up

中　　文

Page Down◣

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 1985, 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

The climate of the first five months of 1985 in Taiwanwas normal. The monsoon season be9an on May 28. Its frontflooded southern Taiwan as the rainfall was more than300 mm. The monsoon ended in late June and was followedby typhoons season.

There were 19 typhoons occured in the Pacific Ocean in1985. Although they didn't directly landed in Taiwanarea/ three of them influenced Taiwan 9reatly. TyphoonHAL Passed through the Bass Strait on June 22. It didn'tbeing torrential rain/ but very strong wind blew throughthe North the Northeast and the Southwest coastal areas.

Typhoon NELSON Passed through the sea between Pen-Chia-Yuand Northern Taiwan on August 23. The wind blow in Pen-Chia-Yu was over grade 17, TaiPei and Keelung was overgrade 14. The rainfall ofuPstream Shihmen reservoir was548 mm. Typhoon BRENDA was coming westwards on October 3 and 4. As it was approaching the southeast coast of Taiwan Typhoon BRENDA suddenly went up north then changed its direction towards Northeast. As the result the North and the Northeast areas were completely understorm.

(2).Rainfall

The average annual rainfall in Taiwan in 1985 was 2,883

mm which was 15 % more than the Long-term ( 1949-1979 )

average annual rainfall of 2,510 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 | 3423 2570 2623 3118 | 2851 2075 2578 2679 | 120 124 102 116
Total | 2883 | 2510 | 115

(3)Streamflow

In 1985, 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 1985 was calculated at 74.2 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 338 observation wells in Taiwan area in 1985. 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 1985. 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 1985

The total amount of the annual consumptive water use in 1985 was calculated at 18.4 billion cubic meters, of which 14.1 billion cubic meters (81%) were used for irrigation; 1.8 billion cubic meters (10%) for domestic water supply; and 1.6 billion cubic meters (9%) for industrial use.

Unit：Billion (109)m3

Region | Agriculture | Domestic | Industrial | Total
North | 2.3 | 0.9 | 0.6 | 3.6
Central | 5.7 | 0.4 | 0.4 | 6.5
South | 5.3 | 0.4 | 0.6 | 6.3
East | 1.7 | 0.04 | 0.04 | 1.8
Total Taiwan Area | 15.0 | 1.8 | 1.6 | 18.4

(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.