17:15 〜 18:45
[HGG02-P04] ベトナム北部山地流域における河川土砂運搬の空間パターンを用いた土砂起源地の特定
キーワード：Turbidity、Suspended sediment concentration、Discharge、Sediment transport、Land-use、Chisan
The northern region of Vietnam, the most mountainous area in the country, has faced active sediment movement which is driven by various hillslope processes that are likely affected by various land-uses. Our study aims at uncovering important sources of sediment and quantifying fluvial sediment transport at a catchment-scale, in order to assess and reduce disaster and environmental risks in mainland Southeast Asia, where such risks have not yet been well documented.
Our study catchment, c.a. 200 km2 in area and located in Yen Bai Province, northern Vietnam, is largely underlain by rhyolitic tuff and volcanic rocks, often intervened by shales. The catchment has altitudes between about 900 m and 2000 m a.s.l. Deforested and terraced agricultural fields are extensively distributed on footslopes and middle slopes, while they are not observed on the slopes where soil layers are thin. Forest types vary, but include degraded forest composed of regenerated shrubs and bush.
We reported provisional data in a previous paper (Furuichi et al., 2023), indicating that (1) the distinctively high turbidity exceeding 20,000 ppm (kaolin) was recorded in two storm events during the rainy season in 2022, (2) surface erosion appeared not distinctively accelerated by the forest degradation, and (3) landform transformation appeared to have strong impacts on the erosion processes.
In the rainy season in 2023, we conducted intensive field campaigns for sampling and measurement of fluvial sediment transport in the study catchment, followed by laboratory analysis of the samples. This paper reports results of the field and laboratory works, which quantitatively uncovered catchment-scale fluvial sediment transport and important sediment sources. We also discuss possible countermeasures on mountain slopes, called Extended Chisan Techniques, for reducing fluvial sediment transport.
We intend to contribute this paper to making a dialogue with a socio-economic study conducted by Sekine and Isoda (2024) who focused on land-use change and its socio-economic and environmental sustainability in the same mountain area in northern Vietnam.
Reference
Furuichi T, et al. (2023) Sediment sources and discharge as disaster and environmental risks in an upstream mountainous catchment in northwestern Vietnam. Abstract of presentation, Session 181, INQUA 2023, Rome, Italy.
Sekine R, Isoda Y, (2024) Expansion and sustainability of terraced rice fields in Sapa, northern Vietnam. Abstract of presentation, JpGU 2024, HGG-02.
Our study catchment, c.a. 200 km2 in area and located in Yen Bai Province, northern Vietnam, is largely underlain by rhyolitic tuff and volcanic rocks, often intervened by shales. The catchment has altitudes between about 900 m and 2000 m a.s.l. Deforested and terraced agricultural fields are extensively distributed on footslopes and middle slopes, while they are not observed on the slopes where soil layers are thin. Forest types vary, but include degraded forest composed of regenerated shrubs and bush.
We reported provisional data in a previous paper (Furuichi et al., 2023), indicating that (1) the distinctively high turbidity exceeding 20,000 ppm (kaolin) was recorded in two storm events during the rainy season in 2022, (2) surface erosion appeared not distinctively accelerated by the forest degradation, and (3) landform transformation appeared to have strong impacts on the erosion processes.
In the rainy season in 2023, we conducted intensive field campaigns for sampling and measurement of fluvial sediment transport in the study catchment, followed by laboratory analysis of the samples. This paper reports results of the field and laboratory works, which quantitatively uncovered catchment-scale fluvial sediment transport and important sediment sources. We also discuss possible countermeasures on mountain slopes, called Extended Chisan Techniques, for reducing fluvial sediment transport.
We intend to contribute this paper to making a dialogue with a socio-economic study conducted by Sekine and Isoda (2024) who focused on land-use change and its socio-economic and environmental sustainability in the same mountain area in northern Vietnam.
Reference
Furuichi T, et al. (2023) Sediment sources and discharge as disaster and environmental risks in an upstream mountainous catchment in northwestern Vietnam. Abstract of presentation, Session 181, INQUA 2023, Rome, Italy.
Sekine R, Isoda Y, (2024) Expansion and sustainability of terraced rice fields in Sapa, northern Vietnam. Abstract of presentation, JpGU 2024, HGG-02.