1:45 PM - 3:15 PM
[HGG01-P03] Land-use change, landform transformation and their geomorphic impacts in mountain catchments in northern Vietnam
Keywords:Forest, Landform transformation, Landslide, Erosion, Sediment
It was internationally reported in July 2020 that seven typhoons caused several severe landslide disasters in the central region of Vietnam (Tien et al. 2021), but according to the statistics from 1991 to 2015, the highest number of deaths per 1000 population due to landslides occurred in the northern region (JICA 2018), the most mountainous area in the country. Satellite images show that shallow and deep-seated landslides have occurred in many areas in northern Vietnam (Furuichi et al. 2021, 2022), and increased discharge of suspended sediment due to accelerated soil erosion from disturbed land surfaces related to human intervention has affected downstream areas (Le et al. 2007, Vinh et al. 2014). However, only the limited number of research investigated those geomorphic processes in mountain areas in northern Vietnam by a field-based manner (Tien et al. 2016, Abe et al. 2021).
The area of Mu Cang Chai in Yen Bai Province in northern Vietnam is located at an altitude of 900-2000 m and has a mean annual rainfall of 1738 mm (2011-2020). Lithology of the area is dominated by rhyolite and rhyolitic tuff, often interbedded by shale. There often appear patterned landforms with distinct lineaments in large-scale local topography, which suggest the landform development has been considerably affected by the geologic structure that was likely build under the influence of tectonic activities. Many shallow landslides occurred on the steep slopes in the 2017 heavy rainfall event, and there is also at least a deep-seated, actively moving landslide. We installed river monitoring equipment in the rainy season of 2022 and the distinctively high turbidity exceeding 20,000 ppm (kaolin) was recorded in two separate events, which indicates severe surface erosion occurred in the heavy rainfall events likely in the specific areas of the catchment.
In Mu Cang Chai, the Hmong people have lived on slopes, while the Tay people have lived along the flat bottom of the valley. The Hmong grows rice along the narrow, terraced mountain creeks and cassava and corn on terraced slopes in the middle to lower parts of the mountain, while the Tay grows rice on the flat ground along wider streams. Forests in the upper part of the mountain are partially degraded at various levels due to trimming for securing daily energy and logging for making cropping lands, but according to the provisional data of suspended sediment concentration of river water and infiltration test on land surfaces under forest and degraded forest, surface erosion appeared not distinctively accelerated by the forest degradation. Nonetheless, the shallow landslides in 2017 occurred in the degraded forests, which may suggest the possible impact of forest degradation. Resent economic growth in Vietnam has brought development activities to Mu Cang Chai as well. Besides road development, houses, buildings and facilities are built on the levelled grounds frequently extended by cutting slopes behind the structures, and the soil and sediment derived by slope-cutting is relocated (i.e. dumped) downslope or to a close valley presumably with no consideration. Those types of landform transformation cause to generate new sources of sediment and new risks of landslides. At present in Mu Cang Chai, landform transformation appears to have strong impacts on the geomorphic processes, in addition to forest degradation.
Reference
Abe et al. (2021) 5th World Landslide Forum, Kyoto.
Furuichi et al. (2021) Abstract of presentation, HDS10-03, JpGU2021.
Furuichi et al. (2022) Abstract of presentation, HDS11-P05, JpGU2022.
JICA (2018) Baseline survey for developing strategy for disaster prevention in Vietnam (in Japanese)
Le et al. (2007) Journal of Hydrology, 334(1-2), 199-214.
Tien et al. (2016). Transaction, Japanese Geomorphological Union 37(1), 41-56.
Tien et al. (2021) Landslides, DOI 10.1007/s10346-021-01663-z
Vinh et al. (2014). Hydrology and Earth System Sciences, 18(10), 3987-4005.
The area of Mu Cang Chai in Yen Bai Province in northern Vietnam is located at an altitude of 900-2000 m and has a mean annual rainfall of 1738 mm (2011-2020). Lithology of the area is dominated by rhyolite and rhyolitic tuff, often interbedded by shale. There often appear patterned landforms with distinct lineaments in large-scale local topography, which suggest the landform development has been considerably affected by the geologic structure that was likely build under the influence of tectonic activities. Many shallow landslides occurred on the steep slopes in the 2017 heavy rainfall event, and there is also at least a deep-seated, actively moving landslide. We installed river monitoring equipment in the rainy season of 2022 and the distinctively high turbidity exceeding 20,000 ppm (kaolin) was recorded in two separate events, which indicates severe surface erosion occurred in the heavy rainfall events likely in the specific areas of the catchment.
In Mu Cang Chai, the Hmong people have lived on slopes, while the Tay people have lived along the flat bottom of the valley. The Hmong grows rice along the narrow, terraced mountain creeks and cassava and corn on terraced slopes in the middle to lower parts of the mountain, while the Tay grows rice on the flat ground along wider streams. Forests in the upper part of the mountain are partially degraded at various levels due to trimming for securing daily energy and logging for making cropping lands, but according to the provisional data of suspended sediment concentration of river water and infiltration test on land surfaces under forest and degraded forest, surface erosion appeared not distinctively accelerated by the forest degradation. Nonetheless, the shallow landslides in 2017 occurred in the degraded forests, which may suggest the possible impact of forest degradation. Resent economic growth in Vietnam has brought development activities to Mu Cang Chai as well. Besides road development, houses, buildings and facilities are built on the levelled grounds frequently extended by cutting slopes behind the structures, and the soil and sediment derived by slope-cutting is relocated (i.e. dumped) downslope or to a close valley presumably with no consideration. Those types of landform transformation cause to generate new sources of sediment and new risks of landslides. At present in Mu Cang Chai, landform transformation appears to have strong impacts on the geomorphic processes, in addition to forest degradation.
Reference
Abe et al. (2021) 5th World Landslide Forum, Kyoto.
Furuichi et al. (2021) Abstract of presentation, HDS10-03, JpGU2021.
Furuichi et al. (2022) Abstract of presentation, HDS11-P05, JpGU2022.
JICA (2018) Baseline survey for developing strategy for disaster prevention in Vietnam (in Japanese)
Le et al. (2007) Journal of Hydrology, 334(1-2), 199-214.
Tien et al. (2016). Transaction, Japanese Geomorphological Union 37(1), 41-56.
Tien et al. (2021) Landslides, DOI 10.1007/s10346-021-01663-z
Vinh et al. (2014). Hydrology and Earth System Sciences, 18(10), 3987-4005.