著者

市川 正巳

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:00167444)

巻号頁・発行日

vol.33, no.3, pp.112-121, 1960-03-01 (Released:2008-12-24)

参考文献数

16

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狩野川台風に伴う豪雨によつて,狩野川上流地域に多くの山地崩壊が発生した.その分布密度の高い地域は,総雨量550~700mmの地域,とくに9月26日20-23時の降雨量分布にきわめてよく一致し,同種の岩石で占められる地域においても,雨量の多い地域にとくに崩壊が密集している.このことから,今次の狩野川上流域の山地崩壊は全く雨量型崩壊といえる.従来の研究では,崩壊した物質が, 1度の出水では100mの短距離運搬されるに過ぎないことが知られている.しかし,大見川上流筏場の軽石質砂礫層の大崩壊では,崩壊物質の98%が1度の洪水で数10km下流に流出したことが,原土と下流の洪水堆積物との比較によつて知ることができた. 洪水によつてどこに河岸の侵蝕と河床の堆積が発生するかは,そこの地形的特徴によつて決定することができる.すなわち,侵蝕堆積の地点における川幅と谷幅との比と,河床勾配との関係は第6図のようで,川幅/谷幅の比が大であつても,河床勾配が小であれば,その地点の河床に堆積が生じ,両者の比が小であつても河床勾配が大きい地点には侵蝕が発生する.このことから,ある地点の河床勾配に対応した川幅/谷幅の比を求めることができるので,洪水対策に重要な示さを与えることができるであろう.

著者

市川正巳 著

出版者

古今書院

巻号頁・発行日

1973

著者

市川 正巳

出版者

公益社団法人 日本地理学会

雑誌

地理学評論 Ser. A (ISSN:00167444)

巻号頁・発行日

vol.61, no.2, pp.89-103, 1988-02-01 (Released:2008-12-25)

参考文献数

79

被引用文献数

2 2

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Attention to the problems of desertification by many governments and the scientific communities in many countries has increasingly been paid in the last decade. The drought in the Sahel, which extended from 1968 to 1973, especially focused public attention on the problem of desertification. In response, United Nations Conference on Desertification (UNCOD) was held in Nairobi, Kenya, from August 29 to September 9, 1977. According to United Nations' definition(Biswas, M. R. and Biswas, A. K., 1980), “desertification is the diminution or destruction of the biological potential of land and can lead ultimately to desert-like conditions: grazing land ceases to produce pasture, dryland agriculture fails, irrigation fields are abandoned owing to salinization, waterlogging or some other form of soil deterioration”. The purpose of this paper is to make clear the present situation of desertification and its research in the world. The author explains the present situation and the problems of desertification in the world using distribution map showing the degree of desertification hazards prepared by Hopkins and Jones (1983). Aridlands divided into four types based on the degree of aridity such as hyper arid, arid, semiarid and subhumid regions, and three classes of desertification risk such as very high, high and moderate are shown on the map presented to UNCOD by UNESCO (1977). Then, the author has described the results obtained from the case study in South-East Spain, and conducted the comparative study on desertification taking place in South-East Spain and in semiarid region of northeastern Brazil. The author overviewed also the previous researches on desertification from the viewpoint of its definition, causes, reversibility or irreversibility, and degradation of tropical forests. Lastly, the author has emphasized that the desertification is the subject of interdisciplinary researches which should be faced in collaboration with various fields of science such as geography, politics, economics, cultural anthropology, hydrology, climatology, geomorphology, plant ecology, forestry, agriculture and so on. So, it is of importance to organize an interdisciplinary project team on desertification and to make clear scientifically the causes of desertification.