| 摘要: | The recorded history of floods occurring in the Taipei Basin may be traced back to the 1900's. Although the Government of the Republic of China has spared no effort to reduce the flood hazard during the past few decades, it appears to be more serious than ever before.
In view of the fact that floods are a natural phenomenon and that flood hazards result from the geographic factors (both natural and cultural) of the drainage basin subject to flooding, this paper intends to discuss, from the geographic viewpoint, the regional characteristics of the floods in the Taipei Basin and to suggest the most satisfactory method for flood control.
This paper includes four major sections: The first is devoted to the analysis of the flooding characteristics in the area, while section 2 deals with the factors causing flood hazards. In section 3, an account of the patterns of floods is given. Section 4 suggests some proper methods of flood control. Finally, a summary of the results obtained in the study is made.
Ⅰ. Flooding characteristics
The analyses of flooding characteristics includes: the magnitude and frequency of the flood, the duration of the flood, the area subject to flooding, how it changes because of the differences of typhoon routes and the constructions of levees, the amount and characteristics of flood damages, and how it changes due to the intensive cultivation on the flood plain.
Ⅱ. Factors causing flood hazards
Factors causing flood hazards include both physical and cultural factors:
1) Concerning the physical aspects, this paper discusses how the flood problems are intimately tied up with geographic location, meteorological condition of typhoon, topography, hydrology, the management of the Tam-Shni River Catchrnent area, and the sinking of the Taipei Basin.
2) Regarding the cultural aspects, special attention has been paid to the changes of land-use in the areas subject to flooding in the Taipei Basin. Owing to the dramatic changes from agricultural land into residential and industrial areas, the former farm lands have already been encroached upon by the steadily increasing population. As a result, the flooding characteristics have changed significantly. Inadequate drainage capacities are responsible for the flooding of accumulated rain water in residential districts. However, some structures and high stem plants impeding flood flows have also been pointed out.
Ⅲ. Patterns of flooding
Based on the flooding characteristics, the flooding areas in the Taipei Basin are divided into three different types:
1) Tide-torrent combined flooding areas: Areas around the mouth of the Taipei Basin and to the left of the lower reach of the Tam-Shni River have always been flooded, caused not only by torrents but also by tide. These are always the most heavily damaged areas in the Taipei Basin.
2) Torrent flooding areas: Areas along the foothills surrounding the Taipei Basin are subject to torrent flooding only. Owing to rapid erosions and thick deposits, serious damage has been reported now and then.
3) Accumulated-rain-water flooding areas: This type of flooding only occurs in highly populated districts, such as the cities of Taipei and Young-ho. This is because these districts are surrounded by levees and lack of perfect drainage capacity. They experience slight damage several times a year.
Ⅳ. Suggestion of some proper methods for flood control
As flooding characteristics very with regions and times, there are no common methods applicable to different areas. The existing structures for flood control have been carefully examined. The most satisfactory methods for flood control must be proposed with reference to the flooding characteristics concerned. In this paper, some essential points that should be taken into consideration in drafting proper methods for flood control have been suggested. The study reveals that the government-planned flood-preventing river through Erh-Chung is imperfect in solving flood problems in the Taipei Basin. Alternatively, ten proper methods for flood control have been recommended in this study. In a ward, for the water problems in the Taipei Basin including floods, water shortage in summer, and lowering of ground-water table, the propounded methods lay emphaes on the following:
1) constructions of reserviors and dams at middle or upper reachs of the rivers as well as more levees along the river banks in the Taipei Basin.
2) developments of reserviors and dams at middle or upper reachs of the bottom of the Taipei Basin.
3) The exorbitant land uses on floodplain and pumping for ground water must be strictly controlled. |
