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SUMMARY OF HYDROLOGICAL FEATURES

IN TAIWAN

The island of Taiwan, which is located at lat. 21o54’－25 o18’ N. by long. 120 o01’－122 o00’ E., has a total area of 35,961 square kilometers. Its weather is subtropical with annual average relative humidity at about 80% and average temperature in plain area at about 16℃ in winter and 24－30℃ in other seasons. Snow falls in some of the mountains but has very little effect on island-wide water supply. Being located in the Southeast Asian Monsoon region, the island subject to northeast monsoon in winter and southwest monsoon in summer. Its mean annual rainfall is 2,340 mm but rather unevenly distributed; a greater part of the rainfall is caused by typhoon which occur generally in the period from April to November each year.

A central mountain range, which is at average elevation of 2,500m with thirty peaks over 3,000 m, runs longitudinally on the island. 70% of the island are mountains and hills and the other 30% are plains.

There are 61 major and minor rivers originated from the central mountain range. Most of the rivers are short and steep with very low flow in dry season but their specific flood discharges are very high. Scouring is serious in the upstream regions and the sediment is subsequently deposited in downstream channels, thus it makes water resources development difficult.

The river-stage measurements were begun in 1903 and the measurements of stream flow and sediment contents were started in 1915. However, the measurements were sporadical in nature. By the end of 1970, 132 stream flow gauging stations were operating; their distribution is shown in the Location Map of Hydrological Stations.

The average annual minimum runoff and average annual runoff of Taiwan are computed, is accordance with discharge data before 1970, at 20,148×106m3 and 52,323×106m3, respectively. The Map of Water Resources Regions, the Table of Minimum Runoff and Average Runoff, and Chart of Regional Minimum Runoff and Average Runoff in Taiwan are attached.

Because of rather high rainfall intensity and steep river slope, flood discharges are huge in Taiwan and the recorded maximum peak floods are shown in the Chart of Recorded Peak Floods in Taiwan as attached.