著者

Hung Thai DINH Shigeko HARUYAMA

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.79, no.12, pp.725-737, 2006-10-01 (Released:2008-12-25)

参考文献数

15

被引用文献数

2 3 3

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This study aims to clarify the main ion concentrations in paddy field surface soil from 0 to 100cm in depth along the coast of the Red River Delta, Northern Vi etnam, represented by Nam Dinh Province. There is a relation between total dissolved solid (TDS) and Na+concentration. Na+and Cl- concentrations in paddy fields increase gradually and the abundance of Cl- concentration in soil proclaims the influence of seawater intrusion. Washing is reported to reduce the high salinity in the cultivation-layer soil of paddy fields. Furthermore, the impact of seawater intrusion on soil salinity of coastal paddy fields has been considered. The top soil layer of coastal salt-affected paddy fields has the highest sodium absorption ratio (SAR) values, and shows the strongest salinity influence in both the flood season and the dry season. Soil samples near the Day River mouth have high SAR values with considerable Na+ concentrations in the dry season. The exchange selectivity between Ca2+, Mg2+and Na+ has also been studied by considering changes in the SAR under different conditions of soil composition and land cover. In coastal agricultural land, the SAR in the surface soil layer can be used to evaluate the influence of salinity. The SAR in cultivated soil is used to assess the influence of salinity problems on the paddy field.

著者

Seiichiro OKETANI Shigeko HARUYAMA Sotham SIENG

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.80, no.12, pp.693-703, 2007-10-01 (Released:2010-03-12)

参考文献数

21

被引用文献数

4 4 3

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The purpose of this study was to examine the floodplain characteristics of the inner Mekong Delta, on the lower part of the Mekong River in Cambodia. Previous works have not investigated the floodplain characteristics of the fluvial dominated area of the Mekong Delta. To grasp the morphology of the study area, we first constructed topographical profiles from hydrologic maps and Space Shuttle Radar Topography Mission 3 data. Then, focusing on the morphology of the floodplain, we produced a land classification map based on aerial photo interpretation and field survey and identified the morphological structures of the study area. We classified the delta landforms as natural levee, back marsh, abandoned channel, alluvial terrace, swamp, point bar, and artificial landforms, including colmatages. We identified four floodplain zones. Zone A floodplains, along the upper part of the Mekong River, have cut-off point bar patterns. Those in zone B, along the lower part of the Mekong River, are linear, and develop back marsh widely. In zone C, along the Bassac River, the floodplains follow the river meanders, and are characterized by unevenly distributed artificial colmatages. Floodplains in zone D, along the Tonle Sap River, which has an extremely low gradient, display a unique geomorphology caused by seasonally reversed river flows.

著者

Kazuaki HORI Shigeko HARUYAMA Sotham SIENG

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.80, no.12, pp.681-692, 2007-10-01 (Released:2010-03-12)

参考文献数

18

被引用文献数

5 5 4

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This study analyzes three borehole cores to examine the sedimentary facies of the extensive floodplain of the Mekong River in Cambodia and discusses the relationship between sedimentary facies and surface topography. Sedimentary facies vary according to surface topographic features on the floodplain. Core PA, located near the end of an abandoned channel, records the history of the formation and subsequent filling of the channel during the Holocene. The channel was filled with interlaminated sand and mud overlain by grayish brown to dull reddish brown stiff mud during the last 4500 years. Core CK was located on the southwestern edge of an area of scroll bars and swales between the Mekong and Bassac rivers. In this core, muddy overbank deposits overlie sandy deposits that probably represent a point bar. The accumulation of the overbank deposits may have started around 2000 cal yr BP. Core TA was obtained from the floodplain along the west bank of the Tonle Sap River. Mottled stiff mud containing granules occurs about 1m below the surface and overlies subangular granules. Muddy overbank deposits corresponding to those of the other two boreholes are not present at the site despite frequent flooding of the Tonle Sap River.

著者

Le Thi Viet HOA Shigeko HARUYAMA Nguyen Huu NHAN Tran Thanh CONG Bui Duc LONG

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.80, no.12, pp.663-680, 2007-10-01 (Released:2010-03-12)

参考文献数

25

被引用文献数

6 13 1

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The Mekong River Delta is one of the world's largest deltas and plays an important role in Vietnam's economic development. Studies of flood propagation over the whole delta have been rare. In 2000, due to global climate change and La Niña phenomenon, the hydrological and meteorological situations were very complicated around the world in general, and in the Mekong River basin in particular. In Mekong Delta, flood occurred early and had two peaks in which the second peak was one of the highest in the past 80 years. This flood caused water levels in the upstream Mekong River basin to become about 1 to 3m higher than the third warning level, and caused extremely severe inundation downstream. In Vietnam, this flood caused damage totaling about 5, 000 billion VN dong (about 4 million US dollars at that time), and its level was used to consider the design elevation of flood control embankments. Thus, through study of this flood is necessary to mitigate flood damage and human suffering and to contribute to policy making and create the conditions for embankment elevation design.In this paper, analysis of the main characteristics of the flood of 2000 was carried out based on the observed data since 1926. Also, simulations were conducted using hydraulic models with topographical, hydrological and meteorological data. The flood simulations using hydraulic model for Vietnamese part of delta were carried out, especially for Dong Thap Muoi and Long Xuyen quadrant to analyze (1) how the flood was distributed spatially and temporally, (2) how long each inundation depth lasted, (3) the extent of the area of the flood, and (4) the effect of flood on paddy fields in 2000. The observed data and simulated results show that this flood was extremely large and complicated, causing severe inundation with the depth of 2.5m lasting more than one month from mid-September to mid-October. Flood in August affected strongly the summer-autumn crop paddy field. The area inundated to the depth of 2.5m was more than one thousand km2.

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.