The practice of widening levees to mitigate frequent river flooding is globally prevalent. This paper addresses the pressing issue of sand-filled widened levee failures under the combined effect of heavy rainfall and high riverine water levels, as commonly observed in practice. The primary objective is to illuminate the triggering mechanism and characteristics of such levee failures using the well-designed physical model experiment and Material Point Method (MPM), thus guiding practical implementations. Experimentally, the macro-instability of the levee, manifested as slope failure within the sand-filled widened section, is primarily triggered by changes in the stress regime near the levee toe and continuous creep deformation. Upon failure initiation, the levee slope experiences a progressive failure mode, starting with local sliding, followed by global sliding, and ultimately transitioning into a flow-like behaviour, which characterises the slide-to-flow failure pattern. The slope failure along the interface between the original and new levees is the result of shear deformation rather than the cause. Parametric studies conducted using the calibrated MPM model reveal a critical threshold for the widening width, beyond which the volume of sliding mass and travel angle exhibit no further variation. Increasing the cohesion of the river sand used for levee widening demonstrates the most pronounced improvement in levee stability in the face of the combined effect of intense rainfall and elevated river levels. The MPM-based evaluation of common slope protection measures demonstrates the superior protective benefits of grouting reinforcement and impervious armour layer protection, providing valuable insights for reinforcement strategies in levee engineering applications.

With the continued development of water resources in Southwest China, fluctuations in water levels and rainfall have triggered numerous landslides. The potential hazards posed by these events have garnered considerable attention from the academic community, making it imperative to elucidate the landslide mechanisms under the combined influence of multiple factors. This study integrates laboratory tests and numerical simulations to explore the instability mechanisms of landslides under the combined effects of rainfall and fluctuating water levels, as well as to compare the impacts of different factors. Results indicate that the sensitivity of landslide deformation decreases as the number of water level fluctuations increases, exhibiting a gradually stabilizing tendency. However, the occurrence of a heavy rainfall event can reactivate previously stabilized landslides by increasing pore water pressure and establishing a positive feedback loop with rainfall infiltration. This process reduces boundary constraints at the toe of the slope, promotes the development of an overhanging surface, and ultimately leads to overall instability and landslide disaster. Under the same rainfall intensities, the presence of water level fluctuations prior to rainfall significantly shortens the time for the landslide to reach a critical state. The key mechanisms contributing to landslide failure include terrain modification, fine particle erosion, and outward water pressure, all of which generates substantial destabilizing forces. This research offers valuable insights for the monitoring, early warning, and risk mitigation of landslides that have already experienced some degree of deformation in hydropower reservoir areas.

Study region: The Qinghai Lake basin, including China's largest saltwater lake, is located on the Qinghai-Tibetan Plateau (QTP). Study focus: This study focuses on the hydrological changes between the past (1971-2010) and future period (2021-2060) employing the distributed hydrological model in the Qinghai Lake basin. Lake evaporation, lake precipitation, and water level changes were estimated using the simulations driven by corrected GCM data. The impacts of various factors on the lake water levels were meticulously quantified. New hydrological insights: Relative to the historical period, air temperatures are projected to rise by 1.72 degrees C under SSP2-4.5 and by 2.21 degrees C under SSP5-8.5 scenarios, and the future annual precipitation will rise by 34.7 mm in SSP2-4.5 and 44.1 mm in SSP5-8.5 in the next four decades. The ground temperature is projected to show an evident rise in the future period, which thickens the active layer and reduces the frozen depth. The runoff into the lake is a pivotal determinant of future water level changes, especially the runoff from the permafrost degradation region and permafrost region dominates the future water level changes. There will be a continuous rapid increase of water level under SSP5-8.5, while the water level rising will slow down after 2045 in the SSP2-4.5 scenario. This study provides an enhanced comprehension of the climate change impact on QTP lakes.

The response of the bridge to the assessment of flood damage is constrained by a restricted examination of soilspecific vulnerabilities and the hydrodynamic forces linked to local scour. The research study will, consequently, aim to address these knowledge gaps in assessing the structural susceptibility of bridges to flooding in very stiff clay (type B) and medium dense sand (type C) soil. This research aims to analyse the behaviour and response of the bridge model when subjected to varying depths of local scour across different soil types. To accomplish this objective, a three-dimensional numerical model is employed for a standard three-span reinforced concrete bridge. In the conducted experiment, a total of 192 scenarios were simulated, considering four distinct levels of local scour depth across two different soil types. The analytical results indicated a notable increase in pier displacement because of the augmented scour depth. The recorded displacement in medium dense sand exhibited a 42 percent increase because of the rise in scour depth. Consequently, it was determined that the impact of erosion caused by flooding on bridges spanning rivers must be accounted for when designing the bridges' foundation.

Landslides are mass movements of rock, soil, or debris under the influence of gravity. These phenomena occur due to the loss of slope stability or imbalance of external loads. The intensity and consequences of landslides depend on various factors such as topography, geological structure, and precipitation regime. This study investigates the characteristics of rainfall-induced landslides in red basaltic soils on the basis of field investigations, geotechnical surveys, and slope stability modeling under anthropogenic triggers. The results indicate a close relationship between soil moisture and shear strength parameters, which significantly influence slope stability. A real-time observation system recorded groundwater level fluctuation in relation to surface runoff and precipitation rates. It is revealed that intense rainfall and low temperatures regulate soil moisture, resulting in a reduction of cohesion and shear strength parameters. These findings enhance the understanding of landslide mechanism in basaltic soil regions, which are highly sensitive to precipitation. The results also highlight that human activities play a significant role in triggering landslides. Therefore, a real-time monitoring system for rainfall, soil moisture, and groundwater is essential for early warning and supports the integration of smart technologies and Internet of Things (IoT) solutions in natural disaster management.

Direct shear creep tests have scarcely been used for long-term creep behavior studies of landslides in the Three Gorges reservoir area. In this study, based on field investigations and monitoring of the Huangtupo Landslide, direct shear creep tests were performed on the sliding zone soil of Riverside Slump #1, and the creep characteristics of sliding zone soil after varying cycles of reservoir water level fluctuation were studied. Using the creep results, the Mohr-Coulomb parameters were obtained by numerical simulation, and the deformation pattern of the reservoir landslide was analyzed. The results show that the direct shear creep of sliding zone soil can mainly be divided into stages of attenuation creep and steady-state creep. Under the same shear stress, with the increase of loading-unloading cycles N, the soil's strain and shear strain rate in the sliding zone decreased accordingly, and the long-term strength gradually improved. As the shear stress increases, the shear strain rate increases and the creep of the soil in the sliding zone has an obvious time effect. Our numerical simulation results showed good agreement with both the landslide deformation monitoring data and direct shear testing data. The Burgers model is suitable for describing creep deformation of landslides under fluctuating reservoir water levels. Under high shear stress, the fitted curve showcased both attenuation and constant velocity characteristics. Numerical simulation and burger model can reflect the direct shear creep test characteristics well. These research findings can provide an important reference on the creep characteristics of landslides, potentially aiding geotechnical engineering applications.

The weak mechanical properties of weak interlayers are crucial for controlling landslide deformation and failure under water level fluctuation. The instability and failure of landslides in reservoirs can lead to unpredictable consequences. In this study, the reservoir bank landslide with a weak interlayer was selected as the research subject. The material composition, structural characteristics, mechanical properties, and permeability of the landslide were determined through field investigations and tests. Additionally, a physical model test was conducted to explore the groundwater variation rules and deformation failure modes of landslides with weak interlayers under different water level fluctuation rates. The results indicate that due to the low permeability of the interlayer, there was a significant lag in monitoring data such as pore water pressure within the interlayer under the same water level fluctuation rate. At the same point, the faster the water level fluctuation rate, the greater the degree of lag. The deformation and failure mode of landslide with weak interlayer under reservoir water level fluctuation can be summarized as the following five stages: slope toe erosion stage, cracks on slope surface and interlayer stage, micro-collapse of slope toes and crack expansion of slope surface and interlayer stage, local micro-collapse of slope toe and crack penetration of slope body stage, crack development leads to landslide of slope body stage. This study provides theoretical support for prevention and control of landslides with weak interlayers in the gravel soils of reservoirs.

Seepage deformation in sand results from complex water-soil interactions, which are the primary reasons of sand surface collapse, as well as instability and deformation in dam foundations, building foundations, and slopes. Frequent fluctuations in groundwater levels cause changes in the direction, velocity, and pore water pressure of groundwater within the sand. Further research is essential to fully understand the characteristics and mechanisms of sand seepage deformation under varying groundwater conditions. In this study, natural undisturbed sand samples were collected. Laboratory seepage deformation tests were conducted to simulate continuous rises and falls in groundwater levels, exploring the response characteristics of internal erosion and hydraulic behavior of the sand under varying groundwater flow rates and directions. The results show that: As groundwater flow rate increases, the sand undergoes multiple episodes of seepage deformation, which includes the processes of structural stability, seepage deformation, and seepage failure. Initially, the hydraulic gradient for seepage deformation is small, and the particles carried by seepage are small. With a further increase in groundwater flow velocity, the hydraulic gradient rises, larger sand particles are migrated by seepage, and seepage failure may eventually occur. When the karst groundwater level is lower than the elevation of the sand bottom (H-2 < z(2)) and the sand bottom is in a negative pressure state, the hydraulic gradient of seepage deformation is usually smaller than that observed in the other two states of positive pressure. In these cases, pore water pressure exerts an upward buoyant force, while in the negative pressure state, the pore water pressure transforms into downward suction. This downward suction aligns with the direction of gravitational forces and downward seepage force acting on the sand, making seepage deformation of the sand more likely. Sands with greater unevenness, finer particle, and lower density are more prone to seepage deformation but failure at different hydraulic gradients.

Beyond flood protection to prevent severe damage, the restored floodplain grassland in Austria provides ecosystem services in terms of carbon balance. Net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco) were quantified by the eddy covariance (EC) method before, during and after a severe flooding event. Our results show that the carbon balance is heavily influenced by water level in the study site. The diurnal variations influenced by various degree from the flood are analysed, showing the average daily GPP of the floodplain grassland in Marchegg dropping from 1.048 g C m-2 day-1 before the flood, down to 0.470 g C m-2 day-1 during the flood. The study demonstrates that the restored floodplain grassland in Marchegg functions as a robust CO2 sink with a cumulative NEE of 38.8 g carbon per m2 over the three-month study period, despite temporary disruptions caused by flooding events. The findings emphasise the considerable potential of floodplain grassland restoration for carbon storage and climate change mitigation, with the new data from the EC station offering valuable insights for future restoration projects. Finally, this supports the adoption of the new EU Nature Restoration Law and the need for restoring wetlands, floodplains and rivers to secure water availability and biodiversity in these unique ecosystems. NBS and more specifically as Soil and Water Bioengineering (SWBE) are methods with ecological advantages and a huge potential for sustainable recreation of nearnatural ecosystems. It is of crucial importance to prove these beneficial effects, and to quantify them transparently in terms of quality assurance and use of resources in a sustainable and eco-friendly way.

AimsEnvironmental stresses can influence root mechanical strength, the impact of submersion of the water level fluctuation zone on the root mechanical strength of Cynodon dactylon was evaluated in this study.MethodsVariations in the physicochemical properties (root weight density and root activity), mechanical strengths (tensile and pullout strength) and failure types of C. dactylon roots were investigated using a submersion experiment with 8 durations (0, 15, 30, 60, 90, 120, 150, 180 d), with a treatment without submersion serving as the control (CK). Additionally, corresponding variation in the microstructure of the roots was observed.ResultsThe root weight density, root activity, root tensile strength and pullout strength of C. dactylon rapidly decreased, followed by a gradual decrease with increasing duration, and the reductions during the first 15 d of submersion accounted for 65.15%, 75.86%, 61.14% and 68.26% of the maximum reduction during the submersion process, respectively. Negative power function relationships were found between root mechanical strength and root diameter. Submersion increased the proportion of fracture failures during the pullout process. Moreover, the influence of submersion on root mechanical strength and failure type was regulated by a reduction in root activity.ConclusionsSubmersion deteriorates the mechanical properties of C. dactylon roots and alters their failure type.