著者

Masahiko OYA

出版者

The Association of Japanese Geographers

雑誌

Geographical review of Japan, Series B (ISSN:02896001)

巻号頁・発行日

vol.68, no.2, pp.218-242, 1995-12-31 (Released:2008-12-25)

参考文献数

26

被引用文献数

2 3

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After World War II Japan faced the simultaneous problems of food shortages and flood hazards. To resolve these problems, agricultural and civil engineers were requested to obtain information on alluvial plains which provide land for major food production in the Japanese Islands. Fortunately, Japanese geographers had already begun to study the alluvial plains as depositional geomorphology, greatly aided by the availability of aerial photographs. These circumstances gave birth to the Geomorphological Survey Map Showing Classification of Flood Stricken Areas. The maps enable us to estimate the features of flooding not only of the past but also of the future. The reason why such a survey map serves the purpose of defining the type of flood is that the irregular surface of the plain, however slight, as well as the sandy and gravelly deposits, were formed by repeated floods. Consequently, the micro-topography of the plain, i.e., fans, natural levees, deltas, etc. tell the history of past floods. From this point of view, the author compiled the first “Topographical Survey Map of the Kiso River Basin (Nobi Plain) Showing Classification of Flood Stricken Areas” in 1956. The accuracy of the map was actually confirmed by the high tide caused by the Typhoon Ise-Bay in 1959, i.e., three years after the preparation of the map. The results of the flood were almost the same as those predicted by the map. It is especially noteworthy that the area of invasion of flooding, caused by the high tide, coincides exactly with the delta area. This close relationship between high tide and geomorphology is manifested in many other cases, for example, in the routes of high tides and features of flooding in each geomorphological unit. Utilizing the combination of geomorphological units, the flood type is classified into the following three types: overflow type, concentration type, and a combination type. An example of the overflow type is seen in the lower reaches of the Kiso River and Han River, the concentration type in the Chikugo River, and the combination type in the Vientiane Plain along the Mekong River. The map is useful for estimating not only flooding but also soil liquefaction sites caused by earthquakes, and for the selection of bridge sites.

著者

Shigeko HARUYAMA Masahiko OYA Yoshio MIZUHARA

出版者

Tokyo Geographical Society

雑誌

Journal of Geography (Chigaku Zasshi) (ISSN:0022135X)

巻号頁・発行日

vol.101, no.2, pp.89-106, 1992-04-25 (Released:2010-10-13)

参考文献数

7

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We have conducted our research on the influence of the eruption of the Kelud Volcano on the Kali Brantas, conservation of the river basin, mitigation of the resulting volcanic and flooding hazards, and development process of the basin.For this purposes, we have made geomorphic land classification maps in the Kali Brantas Basin, utilizing the aerial photographs (scale is around 1/40, 000) and LANDSAT Images which were taken in 1972.The Kali Brantas is located in the eastern part of Java, i. e. easternmost part of the Himalaya-Alps Orogenic Zone. The Kali Brantas originates in Mt. Arjuno and round the foot of the Butac and Kelud Volcanos which are active volcanos, and then pours into the Madura Strait.The southern part of the Kelud Volcano consists of the following geomorphic elements: piedmont gentle slope of the volcano, a slightly hilly area on the gently sloping terrace, valley floor plain, marsh, abandoned river course, steep slope, etc.The Kali Brantas plain consists of the following geomorphic elements: natural levees, back-swamps, a delta, lagoon, sand-spits, etc. Natural levees are developed well around the city of Kediri and the river bed is higher than that of the adjacent plain.The Kelud Volcano has erupted approximately once every 15 years. We have a record of its eruption since 1, 000 years A. D. The eruption in 1919 was especially severe, and about 3, 800×104m3 of “Lahar” flowed down to have killed 5, 100 persons. Due to the eruption in the year 1586, about 10, 000 persons were killed.In order to mitigate the damage by “Lahar” a tunnel for decreasing water in the crater was constructed during the Dutch Colonial period. This drainage tunnel reduced the volume of the water from 4, 000×104m3 to 2, 000×104m3 in 1966. After the construction of the tunnel, the lahar damages decreased. However, aggradation as a result of this eruption reduced the depth of the crater about 50m to destroy the tunnel. Then the tunnel was repaired again.After 1970, thre lowering of the river bed has occured partly because of the construction of dams, particularly the construction of “Sabo” dam for “Lahar” and partly the because of the volcanic eruption. Although the lowering of the river bed decreased the possibility of the flooding, it becomes difficult to take the water for irrigation.In February 1990, the Kelud Volcano erupted again. And a lot of volcanic ash was deposited on the southern slopes of the volcano. The tunnel disappered again. So we must look again for the tunnel. Directly after the eruption, torrential rainfall occurred at the upper reaches of the Brantas River. The erosion in the upper reaches was remarkable and a lot of sand and gravel flowed down to the middle reaches and several reservoirs were burned immediately.In conclusion, we would like to indicate that it is very important to predict the geomorphological changes of the river basin in the case of making development plain of the river basin.