Geoenvironmental Disasters

In this research, the concentrations of nitrates were investigated in well water sampled from the irrigated perimeter of Beni Moussa (Tadla plain, Morocco), and human health risks via ingestion and dermal pathways for individuals in different age brackets were assessed using the chronic daily intake, the dermal absorbed dose and hazard index (HI). The results showed that the groundwater NO3 contents were between 4.20 to 80.46 mg L− 1, with an average of 32.11 mg L− 1, indicating anthropogenic inputs caused by the infiltration of nitrates not consumed by plants or surface industrial and domestic wastewater into the shallow aquifer. Compared to the Moroccan standard, 17.78%, 40.00%, 37.78% and 4.44% of sampled wells showed poor, fair, good or excellent quality, respectively. For non-carcinogenic risk, the oral ingestion of nitrate appeared to be the main exposure pathway for local human receptors causing the high non-carcinogenic risk, and the dermal exposure met within the accepted precautionary criterion. Infants in the study area are more likely to experience adverse effects to higher nitrate level in groundwater (3.04E-01 < HI < 1.80E+ 00), followed by female (2.39E-01 < HI < 1.41E+ 00), then male (2.22E-01 < HI < 1.31E+ 00) and finally children (2.08E-01 < HI < 1.23E+ 00). The resulting spatial variation in HI values was greatly influenced by human activities and population density. The results of this study could help to shape effective environmental management measures for enhancing the groundwater quality and ensuring safe drinking water.

With mature hydrocarbon industry, Northern South China Sea (NSCS) is a hot spot for future economic development. However, the local government and researchers lack of estimations about damages brought by a submarine landslide-generated tsunami. According to oceanographic surveys, eleven landslides in different scale have been discovered in Baiyun Depression of NSCS. Hence, the need to study potential tsunamis generated by submarine landslides in NSCS is urgent and necessary. This research, focused on potential threat linked to local tsunami sources, is in its early stage in China but it is of capital importance for the local people, local government and offshore economics. Taking landslide S4 for example, the formation, spreading and run-up are predicted. As calculated, the greatest height of tsunami generated by Landslide S4 is 17.5 m, occurring near Dongsha Islands, and the greatest run-up formed on the coastal line is 5.3 m, occurring near Shanwei City; the general height of waves attacking the coastal line is no more than 1.5m, but abnormally high waves might occur in 32 regions. Prediction of tsunami generated by Landslide S4 suggests that local landslides in NSCS may trigger tsunami hazards. Therefore, more efforts shall be made to investigate potential damages caused by a submarine landslide, particularly the submarine landslides at Baiyun Depression in NSCS.

In principle, the mechanical properties of soil particles are irreversibly changed after particles are subjected to heating. Accordingly, this study performed ring-shear tests on calcareous sand samples subjected to high temperatures to qualitatively investigate the influence exerted by the degradation of the calcareous sand, caused by the thermal effect, on the large displacement shear characteristics of the samples. The effects of the shear velocity and normal stress on the quasi-static shear behavior of the calcareous sand samples were analyzed. The influence of the thermal effect on the quasi-static shear flow behavior of the samples is primarily reflected in the change in the particle mineral composition, particle hardness, and sample density. These variations result in changes in the shear strength, residual shear stress, macroscopic friction coefficient, and other shear characteristics of the calcareous sand samples. Both the shear velocity and the high temperature affect the fluctuation amplitude of the residual shear stress. The results have great theoretical and practical significance in terms of explaining the instability mechanism of a slope. Moreover, a feasible and effective technique is proposed to investigate the large-displacement shear behavior of soil subjected to the thermal effect exerted by a long-runout landslide.

Landslide risk analysis is a common geotechnical evaluation and it aims to protect life and infrastructure. In the case of sensitive clay zones, landslides can affect large areas and are difficult to predict. Here we propose a methodology to determine the landslide hazard across a large territory, and we apply our approach to the Saint-Jean-Vianney area, Quebec, Canada. The initial step consists of creating a 3D model of the surficial deposits of the target area. After creating a chart of the material electrical resistivity adapted for eastern Canada, we applied electric induction to interpret the regional soil. We transposed parameter values obtained from the laboratory to a larger scale, that is to a regional slope using the results of a back analysis undertaken earlier, on a smaller slide within the same area. The regional 3D model of deposits is then used to develop a zonation map of slopes that are at risk and their respective constraint areas with the study region. This approach allowed us to target specific areas where a more precise stability analysis would be required. Our methodology offers an effective tool for stability analysis in territories characterized by the presence of sensitive clays.

The Southern Suez Canal Province (SSCP) has recently encountered hydro-environmental hazards such as water logging and soil salinization, both of which impede the efficient land use planning. This study aims to assess the hydro-environmental threats to SSCP and identify the key factors that contribute to their occurrence. Previous research has demonstrated that the Gulf of Suez Rifting-related tectonic movements have a significant impact on the entire SSCP region. The influence of tectonic setting on the development of hydro-environmental dangers was not examined in almost any studies. Remote sensing, GIS, hydrogeological, and geophysical techniques are used to identify and assess topographic, hydrogeological, and tectonic variables that affect hydro-environmental hazards in the SSCP. This study found that the distributions of water logging, saturated soil salinization, urban areas, and vegetation cover changed more dramatically between 1984 and 2015. The expansion of water logging area (+10.68 km2 rating +0.35 km2/y), saturated saline soil (+24.40 km2 rating +0.79 km2/y), and urbanized area (+58.43 km2 rating +1.89 km2/y) is strongly associated to the expansion of vegetation cover (+188.13 km2 at a rate of 6.07 km2/y). This could imply that growing agricultural expansion and urbanization are influencing the dominance of hydro-environmental hazards in SSCP. The distribution of water logging features identified on the land cover map corresponds closely to a buried horst structure dominating the middle part of the surveyed area. The lowland water logging features of the SSCP provide support for the hypothesis that the buried horst structure that dominates the Miocene and pre-Miocene strata has an impact on the thickness and groundwater flow regime of the quaternary aquifer that lies above. The present study came to the conclusion that the shallow depth of groundwater, the vast expanse of newly cultivated lands, the impervious clay layer beneath the thin topsoil layer, and the low topography are the key factors influencing the development of water logging and soil salinization features in SSCP.

On 14–18 March 2019, the UNESCO Chair 2019 Field School on Geoenvironmental Disaster Reduction has been held in Shimane University, Japan. The field school comprised two-day field work and three-day academic lectures. Thirty three graduate students from China, Italy, Nepal, Indonesia, France, and Japan participated, and 14 visiting professors from China, Italy, Czech Republic, Belgium, France, Russia, Indonesia and Japan were invited to give academic lectures on the topic of geoenvironmental disasters reduction.

In the early morning of 20 August 2014, a high-intensity/low-duration rainstorm occurred in Hiroshima City, in southwest Japan. Within 3 h, the rainfall exceeded 200 mm, which is more than twice the monthly-average for this area. This heavy rainfall triggered 107 debris flows and 59 shallow slides, which caused 44 injuries, and 74 deaths. 133 houses were destroyed and an additional 296 houses were severely damaged. Most of the debris flows occurred in heavily weathered granite slopes, while others occurred in weathered hornfels slopes. A field investigation on two of the gullies in which the debris flows occurred was conducted in order to better understand the characteristics of the debris flows. The main purpose of this investigation was to understand the geomorphological and geological conditions, the soil properties, and the initiation/traveling mechanisms of the debris flows. The longitudinal and cross-sectional profiles along the two gullies were measured, beginning at the source areas and ending at the downstream limits of the deposition areas. For soil property determination, disturbed and undisturbed soil samples were collected for laboratory tests which included in-situ density measurement, grain size distribution analysis and triaxial compression tests. In the triaxial compression tests, consolidated-undrained compression tests under different confining stresses were conducted to measure the strength parameters of the strongly-weathered granite. Pore-water pressure controlled triaxial test was conducted to simulate the failure process of the slope given an increase of the pore-water pressure. Chemical analyses of the granite samples were also conducted in order to understand the degree of weathering of the granite in the debris flow gully. A high intensity, short duration, localized rainfall event initiated debris flows in very steep slopes. These were initiated as a thin sliding mass in weathered coarse-grained granite and hornfels, and became two different types of debris flow after traveling down the slopes. The slope angle and the cross section of the gully, and the grain size of the debris significantly controlled the motion behavior of the debris flows.

Ground failures in a slope due to gravity, are commonly known as landslides. Depend on the compositional, geological, and structural characteristics of the unstable initiation zone and the erosional composition of the propagation zone decide the complete particle size distribution of the moving mass and its gradation. This information is most important for the study of downslope movement. Only laboratory sieve analysis cannot fulfil this target because the natural debris contains a wide range of particle sizes, especially boulders. The combined method of scaled image analysis and laboratory sieve analysis or the combined method of line-grid analysis and laboratory sieve analysis was proposed to fulfil the requirement. To study the proposed combined methods, five different locations within the downslope propagation zone from the Aranayake landslide in Sri Lanka were surveyed and analyzed. In image analysis, the high-resolution scaled image of deposited debris was analyzed by computer-based image analysis for particle sizes. Small particles were addressed by the laboratory sieve analysis using the representative debris sample taken from the same location. If the boulder sizes within the debris are too big to address this method, then the Line-grid method was performed. The particles in every 0.5 m along a measured line of debris deposition were measured in this method. If the selected location contains small particles that cannot measured manually, the representative sample was used for the laboratory sieve analysis to fulfil this range. The results of three locations indicated a 40% distribution of < 10 mm and a 60% distribution of > 10 mm representing the general distribution of the debris. Two distributions deviated from the general distribution that was surveyed and analyzed from special locations of the “near boundary of flow path” and “slope change zone” of the landslide. The combined methodology yielded successful results of complete particle size distribution for the wide range of particle sizes in debris. The variation of the particle size distribution curves of debris along the downslope depositions is planned to be used for the study of downslope propagation, damage zone assessment studies, and predicting the representative composition of future failures.

Koshi flood of August 2008 in eastern lowlands of Nepal affected around 2.64 million people in India and Nepal, including 65,000 people and 700 ha fertile land in Nepal. It was calculated that 25% of the affected cultivated land of Shreepur, Haripur and western Kushaha villages in Sunsari district are still barren and remain filled with flood sediment of sizes from clay to sand even after 8 years. The issues of land change from fertile to barren because of flooding and characteristics of the sediments in terms of cultivation are the foci of this research. Field measurement and information from questionnaire survey showed that the depth of the flood sediment are highly variable in impacted zones. They are divided into central red, red, yellow and green zones as per the thickness of the sediments. The sediments from sieve analysis has also shown that the degree of fineness is greater towards the green zones and texture has shown function of distance : T = f (d). The average thickness varies from 0.10 m in green zone to 4.5 m in central red zone in new channel area of the flood. The crop yield is also 50–75% greater in green zones than in the other zones. Changing in cultivation practice from traditional crops to cash crops have increased income up to 200–300% in the aggraded land. Changing in cultivation practices and removing layer of flood sediment in shallow sedimentation area are the major overcomes against the flood sediments. The study concluded that the agricultural practices in aggraded land depends on sediment textures, composition, and thickness of the sediments.