Proceedings of the General Meeting of the Association of Japanese Geographers

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1.Introduction
Tam Giang lagoon, one of the biggest in Asia, is located in Thua Thien Hue Province, Central Viet Nam. Its area is about 22,000 ha with a length of 70 km along the coast, connected to 5 of 8 districts in Thua Thien Hue Province, comprising 32 communes. Approximately 300,000 inhabitants (18% of provincial population - 2006) live around the lagoon in 326 villages. Around 195,000 people are directly involved in lagoon activities, and 7,500 labourers specialising in lagoon exploitation. About 10,000 people take the lagoon surface to be their residence. Since aquaculture has been regarded as a suitable alternative, fishers wanted to convert natural lagoon areas into the cultured fisheries areas with high valuable species. Opening scale of aquaculture area, types of culture and participation of social classes has set the complicatedness of resource management, environmental and socio-economic issues. It effects directly or indirectly on the change of lives of local people, widening the gap between the poor and the rich around the lagoon. The purpose of this paper is to examine the change of resource management of local communities and environmental issues under aquaculture development. Simultaneously, we discuss how to manage and develop suitable lagoon by community-based resources management in the Tam Giang lagoon. This research used questionnaires, field observation, and interview with fishers, farmers, leaders of communes and experts from relevant agencies in Thua Thien Hue Province to analysis and evaluate. The data and related documents were gathered on March and September, 2006.

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This study examines records of annual maximum floods on six major rivers in the Kanto and Hokkaido regions of Japan between 1960 and 2002. Analysis of the Kanto river records indicates that the study period can be divided into two sub-periods. Period 1 (1960 to the early 1980's) was a period of smaller average floods and fewer large floods and Period 2 (the early 1980's to 2002) was a period of larger average floods and more frequent large floods. Analysis of the Hokkaido river records indicates that the differences in flood magnitudes are more limited.
Annual maximum floods in Kanto can be attributed to typhoons and heavy rain during the summer rainy season while those on Hokkaido are mainly due to spring snowmelt. Of these three causes, typhoons are usually responsible for the largest magnitude floods. The limited effects of typhoons and heavy rains during the summer rainy season on rivers in Hokkaido accounts for smaller differences in flood magnitudes between the two periods.
For Kanto, analysis of the record of typhoon tracks and daily precipitation (1-day and 3-day totals associated with the typhoons responsible for annual maximum floods and the 30-day totals prior to the events) suggest that there have substantial increases in rainfall associated with typhoons responsible for annual maximum floods in Period 2.
We also provide data suggesting that the increase in rainfall amounts brought by typhoons can be linked to major shifts in global atmospheric circulation patterns such as ENSO and the PDO.

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Synthetic Aperture Radar Interferometry (InSAR) has now become a tried and tested method for detecting spatial distribution of surface displacement. The Advanced Land Observing Satellite (ALOS or "Daichi") was launched in January 2006, with three remote-sensing equipments including the Phased Array type L-band Synthetic Aperture Radar (PALSAR). Its high coherency enables us to detect high resolution surface displacement data. The Geographical Survey Institute analyzed the crustal movement of the Noto Hanto Earthquake in 2007 and estimated a detailed fault model using ALOS's PALSAR interferometric images. In addition to such wide-area elastic deformation caused by the faulting, we found a number of small patterns which seem to reflect local surface displacement. In combination with interpretation of landforms and field survey, we concluded that such patterns are indicating the existence of small scale - within few centimeters or few tens centimeters - movement of landslides triggered by the earthquake. We analyzed up-down and east-west components of displacement from two sets of SAR images and clarified the detailed features of surface movement that are consistent with the expected movement of landslides. We consider that the SAR interferometric images provide us exhaustive distribution of small scale surface displacement of landslides which is difficult to detect by the field reconnaissance or photo interpretation, and must be effective information for disaster prevention measures.

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