Valley Topography Research Articles

Two-layer multi-state SPH modelling of momentum growth and its feedback in viscous debris flow on wet bed sediment

Flow-momentum growth and resultant feedback from bed-sediment entrainment significantly influence the mobility of debris flows and valley topography. Existing models inadequately capture the mass and momentum growth regulated by scale-sensitive, time-dependent pore water pressure in erodible beds, which exhibit pronounced anisotropy and nonlinearity. In this study, we propose a three-dimensional, two-layer, multi-state smooth particle hydrodynamics (TLMS-SPH) model to assess the flow-momentum growth of debris flows on wet beds. Herein, an enhanced Drucker-Prager (DP) yield criterion is integrated into the Herschel-Bulkley-Papanastasiou (HBP) rheology to mitigate particle collapse induced by gravitational perturbations in steep terrains. Particularly, an efficient hydro-poro-mechanics-based pore water pressure algorithm is presented and embedded in the SPH scheme to simulate the pore pressure response. To address the size effect, we rigorously tested the method through a series of full-scale, well-documented entrainment experiments. The results demonstrate that the model effectively captures and reproduces the complex dynamics of flow-momentum growth, manifesting in erosion-induced excessive volume and mobility changes. Our method establishes a clear link between volumetric water content and pore pressure response, further underscoring its capability to delineate levee-channel and deposition morphology. This study represents the first attempt to model debris flow on beds of varying wetness from a particulate perspective.

Effects of valley topography on ozone pollution in the Lanzhou valley: A numerical case study

Valley topography is recognized for its role in constraining pollutant dispersion, which frequently results in elevated pollutant concentrations within valley regions. However, the specific mechanisms by which valley topography influences daytime ozone (O3) production, nighttime O3 depletion, and diurnal variations in O3 concentrations remain inadequately understood. This study employs the online WRF-Chem air quality model to conduct sensitivity analyses, examining the effects of valley topography on summer O3 concentrations in Lanzhou, a valley city in western China. The results indicate that valley topography generally reduces surface temperature and wind speed while also lowering the planetary boundary layer height (PBLH), which ultimately leads to increased concentrations of primary pollutants. Nevertheless, the impact of valley terrain on O3 is time-dependent, with concentrations decreasing during the day and increasing at night. In Lanzhou, valley topography contributes to a 4.4% reduction in daytime O3 concentrations. This reduction is largely due to the blocking of solar radiation by surrounding mountains, which results in a 7% decrease in shortwave radiation (SR) and a 17% decline in PBLH, subsequently limiting O3 chemical production. Although valley topography restricts pollutant dispersion, the overall effect during the day is a net decrease in O3 levels. In contrast, nighttime valley topography leads to a notable 19.8% increase in O3 concentrations. This increase is driven by mountain breezes transporting O3-rich air from the slopes into urban areas, along with a 67.4% reduction in nitrogen oxide (NO) levels. Despite intensified NO titration within the valley, the combined effect of these local wind patterns contributes to elevated O3 concentrations at night. These findings offer valuable insights into the unique factors contributing to urban O3 pollution in areas with complex valley topography.

Effect of valley topography on dynamic response of arch dams

Arch dams are typically built in the mountain and gorge regions with complex terrain. In the current engineering practice, foundation models are commonly simplified as the half-space with the canyon of regular geometry. The complex topography conditions above the dam crest are neglected. This study investigates the effect of realistic valley topography on the dynamic response of arch dams. The direct finite element method is generalized and applied to the dam-reservoir-foundation system with realistic valley topography. The input ground motions are transformed into the effective earthquake loads at the truncated boundaries by performing several dynamic reaction calculations using one-dimensional (1D) and two-dimensional (2D) auxiliary finite element models. The effect of valley topography on the seismic response of the Baihetan arch dam is evaluated as a case study. Results indicate that the valley topographic irregularities significantly influence the dynamic responses of the arch dam, including relative displacement and stress distribution. Notably, the valley topography effect on the seismic response of arch dams depends on the incident ground motions and is hardly predicted in advance, demonstrating the necessity to account for the realistic topography conditions.

Shaking table test for near-valley underground station: Influence of diaphragm walls

Diaphragm walls are commonly employed as a permanent support for the building of metro stations near urban valley, and in conjunction with the interior sidewalls of the station structure to withstand the pressure from surrounding soils. Despite their prevalent use, the effect of underground diaphragm walls on the seismic response of stations is not yet fully understood. In this paper, a series of 1-g shaking table tests is designed to investigate the seismic response of a near-valley station with underground diaphragm walls within the elastic range. Modeling the stratum-structure-diaphragm walls system is accomplished by employing granular concrete reinforced with galvanized steel wires and synthetic model soils, and a station without diaphragm walls is included, serving as a benchmark for comparative analysis to understand the influence of diaphragm walls on the seismic behavior of the station. The experiment was designed for three depth-to-width ratios (DWRs), i.e. 1/3, 1/4, and 1/8, of arc-shaped valley topography, as well as the seismic excitations for the test include actual seismic records with the amplitude of 0.2 g, 0.4 g, and 0.8 g, respectively. Results show that the underground diaphragm walls enhance the lateral stiffness of the near-valley station compared to structures without diaphragm walls, and thus significantly reducing the racking deformation of structure during earthquakes. The presence of diaphragm wall would decrease the amplification of dynamic earth pressure caused by valley effect at the structural sidewalls, and significantly reduce the lateral vibration and shear effect of the station near a valley with a larger DWR. Notably, bending moment response at the connection between the diaphragm walls and structural sidewalls are dramatically amplified under strong seismic loading, and such adverse effects gradually increase with the DWR of the valley.

Effect of Valley Topography on the Behavior of Asphalt Concrete Core Walls in Earthen Dams

Effect of Valley Topography on the Behavior of Asphalt Concrete Core Walls in Earthen Dams

Assessment of factors and mechanism contributing to groundwater depressurisation due to longwall mining

Assessment of mining impact on groundwater is one of critical considerations for longwall extension and sustainability, however usually constrained by limited data availability, hydrogeological variation, and the complex coupled hydro-mechanical behaviour. This paper aims to determine the factors and mechanism of groundwater depressurisation and identify knowledge gaps and methodological limitations for improving groundwater impact assessment. Analysis of dewatering cases in Australian, Chinese, and US coalfields demonstrates that piezometric drawdown can further lead to surface hydrology degradation, while the hydraulic responses vary with longwall parameters and geological conditions. Statistical interpretation of 422 height of fracturing datasets indicates that the groundwater impact positively correlates to panel geometry and depth of cover, and more pronounced in panel interaction and top coal caving cases. In situ stress, rock competency, clay mineral infillings, fault, valley topography, and surface–subsurface water interaction are geological and hydrogeological factors influencing groundwater hydraulics and long-term recovery. The dewatering mechanism involves permeability enhancement and extensive flow through fracture networks, where interconnected fractures provide steep hydraulic gradients and smooth flow pathways draining the overlying water to goaf of lower heads. Future research should improve fracture network identification and interconnectivity quantification, accompanied by description of fluid flow dynamics in the high fracture frequency and large fracture aperture context. The paper recommends a research framework to address the knowledge gaps with continuous data collection and field-scale numerical modelling as key technical support. The paper consolidates the understanding of longwall mining impacting mine hydrology and provides viewpoints that facilitate an improved assessment of groundwater depressurisation.

Changes in human settlement environments and their drivers in valley cities located in arid and semi-arid regions: A case study of Lanzhou in Western China

Development of urban human settlement environments (HSEs) is an integral part of promoting high-quality and sustainable regional development and constructing a beautiful China. The city of Lanzhou, located at the geometric center of China, is the only provincial capital traversed by the Yellow River. Given the constraints posed by the valley topography and the need for economic development, the development of this HSE, which is located within an arid region, poses considerable challenges. Evidently, an understanding of the evolution of HSEs and drivers of changes in them contributes to high-quality, sustainable urban development in arid and semi-arid regions. An analytical model was developed using the parameters of relief degree of land surface, human comfort days, the land cover index, nighttime light index, and precipitation. This model was used in combination with population density and the gross domestic product to analyze the spatial distribution of Lanzhou's HSE and its drivers. The results showed that landscapes in Lanzhou underwent significant changes between 2000 and 2022, with an increase in building-up land (+0.946%), cultivated land (+0.134%), and forest land (+0.018%) and a decrease in grassland (−1.10%). There was significant outward expansion of the main urban zone of Lanzhou and of various county towns, with the increase in building-up land being most prominent. During this period, there were significant changes in the periphery of the core urban area and county towns in Lanzhou, with decreases moving from the urban center (the highest value) to the surrounding areas (Yongdeng County had the lowest value). The correlation between the HSE and population density grew stronger in Anning and Chengguan Districts but became weaker in Xigu and Qilihe Districts. Spatiotemporal variations in the HSE were primarily caused by climate change, followed by human activities, and were also influenced by the valley topography. Overall, the spatial distribution of population density and the HSE in Lanzhou demonstrated good consistency under the influence of economic development and urbanization.

Study of Wind Field and Surface Wind Pressure of Solar Greenhouse Group under Valley Topography Conditions

There is a wind interference effect between greenhouses in a group arrangement of solar greenhouse groups. To ensure the structural integrity of greenhouse groups situated in valleys, it becomes imperative to analyze both the wind pressure distribution patterns and the wind interference effects. This arises from the recognition that the wind load coefficients applicable to solar greenhouse groups nestled within valleys deviate from those observed in flat plains. The application of the contour modeling method facilitated a realistic reconstruction of the authentic topography within the study area. Subsequently, a wind field simulation was executed specifically for the constructed valley. The resultant wind field data for the studied valley area were then obtained. In the valley, nine solar greenhouses were systematically arranged in a three by three configuration. Special attention was directed towards assessing the surface wind pressures derived meticulously from the simulated wind field and wind direction angle of 0°. The findings elucidate the following: (a) The wind speed ratio exhibits a diminution on the leeward side of the mountain as compared to the windward side, with a notably reduced wind speed ratio observed in proximity to the mountain. (b) An amplification effect is discernible in the peripheral zone adjacent to the leading row of greenhouses, proximate to the incoming airflow. Particular emphasis is warranted regarding the reversal of wind direction observed in the secondary row of greenhouses positioned along the north wall and front roof, specifically at a wind angle of 0°, owing to the pronounced influence of interference effects. Hence, when undertaking the design and construction of a cluster of solar greenhouses within the valley terrain of Tibet, meticulous consideration must be directed towards both the meticulous calculation of wind loads within the periphery of the greenhouses and the judicious selection of the grouping’s location.

Pre-disposed tectonic subsidence controls flood hazards and unplanned urbanisation dominates the flood disasters in the Pliocene to Holocene Kashmir basin, NW Himalayas

The Pliocene to Holocene Kashmir basin of NW Himalaya, India, is prone to various geological and climatic hazards routinely connected to the climatic and structural setting of the Himalayan intermontane basins. The topographic expression of the basin is a direct consequence of the active plate tectonic convergence between the lithosphere plates of India and Eurasia. However, the role of the tectonic framework and its contribution to flood hazards has remained an unresolved research question. Our previous work has contributed towards this problem, and here, we extend our previous work by producing robust evidence in support of the role of active faults and tectonic topography in shaping the flood hazards in the Kashmir basin and its implication for the other similar basins in the world. The Landsat 8 Operational Land Imager-Thermal Infrared Sensor (OLI-TIRS) and Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images were used to extract pre-2014 floodwater bodies and 2014 flooded areas in the Jhelum River valley of the Kashmir region, respectively. Water pixels were extracted using the modified normalized difference water index (MNDWI) methods, and similarly, the flood depth and duration (in days) were computed. The flood depth was correlated with the Jhelum River valley's topography, morphology, and geology. The slope and topography were also associated with the 2014 flood disaster to map the influence of the pre-disposed structural setting of the basin on flood vulnerability. The results suggest that flood disasters were mainly related to the unplanned built area, which remains the dominant factor in how flood hazards have turned into disasters. The results reveal the tectonically derived structural configuration of the basin mainly contributed towards the flood hazards, which is the primary predisposed structural framework to dictate flood hazards since the formation of the basin ∼4.0 million years ago. Therefore, the primary outcome of our work is the strong evidence that flood hazards are related to the structural setting of the basin, which includes topography and geology, while the transition of flood hazards into disasters is mainly because of unplanned urbanization.

UAV Imagery for Measuring Large Wood Volume and Distribution: Ground Truthing Results and Sources of Error

abstract: UAV imagery offers great potential in determining precise environmental measurements. This study identifies and quantifies errors and their causes/sources between UAV imagery- and field-derived measurements of large wood (LW) and cross-sectional valley topography in several forested headwater stream valleys in the Ozark Highlands, Missouri. UAV imagery was collected at six sites following best practices for producing high resolution orthophotos and elevation models through Structure-from-Motion photogrammetry. Field-based measurements of LW were completed along 5 m wide valley cross-sections in which all LW > 1 m in length and 0.1 m in diameter were recorded. Topographic surveys were performed along the centerlines of the LW transects. The same assessments were performed using UAV imagery and ArcGIS. Our sites showed high (>= 0.85) R2 values between field and UAV-GIS topographic surveys. Differences between measurements of LW dimensions tended to be larger with R2 ranging from 0.42 to 0.88. Overall 78 percent of standing trees and 60 percent of LW pieces were identified in the UAV imagery. The main source of detection and measurement error was due to vegetation/canopy cover. This study furthers our understanding of the applications and limitations of UAV derived data for environmental assessments.

Evaluating density-weighted connectivity of black bears (Ursus americanus) in Glacier National Park with spatial capture–recapture models

BackgroundImproved understanding of wildlife population connectivity among protected area networks can support effective planning for the persistence of wildlife populations in the face of land use and climate change. Common approaches to estimating connectivity often rely on small samples of individuals without considering the spatial structure of populations, leading to limited understanding of how individual movement links to demography and population connectivity. Recently developed spatial capture-recapture (SCR) models provide a framework to formally connect inference about individual movement, connectivity, and population density, but few studies have applied this approach to empirical data to support connectivity planning.MethodsWe used mark-recapture data collected from 924 genetic detections of 598 American black bears (Ursus americanus) in 2004 with SCR ecological distance models to simultaneously estimate density, landscape resistance to movement, and population connectivity in Glacier National Park northwest Montana, USA. We estimated density and movement parameters separately for males and females and used model estimates to calculate predicted density-weighted connectivity surfaces.ResultsModel results indicated that landscape structure influences black bear density and space use in Glacier. The mean density estimate was 16.08 bears/100 km2 (95% CI 12.52–20.6) for females and 9.27 bears/100 km2 (95% CI 7.70–11.14) for males. Density increased with forest cover for both sexes. For male black bears, density decreased at higher grizzly bear (Ursus arctos) densities. Drainages, valley bottoms, and riparian vegetation decreased estimates of landscape resistance to movement for male and female bears. For males, forest cover also decreased estimated resistance to movement, but a transportation corridor bisecting the study area strongly increased resistance to movement presenting a barrier to connectivity.ConclusionsDensity-weighed connectivity surfaces highlighted areas important for population connectivity that were distinct from areas with high potential connectivity. For black bears in Glacier and surrounding landscapes, consideration of both vegetation and valley topography could inform the placement of underpasses along the transportation corridor in areas characterized by both high population density and potential connectivity. Our study demonstrates that the SCR ecological distance model can provide biologically realistic, spatially explicit predictions to support movement connectivity planning across large landscapes.

Dating the late Miocene marine sediments around the southern middle Durance valley (Provence, SE France): new evidences for a Tortonian age

The present study aims dating the topmost 50 m of a 115 m-long core retrieved from a valley located in the Cadarache Area (Upper Provence, South East France). Based on burial dating by in situ produced cosmogenic nuclides (10Be, 26Al and 21Ne), and paleomagnetic analyses, a Tortonian age was determined for the sedimentary succession exhibited in the core. In addition, thin sections, grain size analyses and quartz morphoscopy were used to characterize a shallow marine environment and to correlate the sediment core to the surrounding exposed sections. When comparing the studied sedimentary record to global sea level estimates, we establish that the local Tortonian transgression was not synchronous with the global scale sea level high-stand, but happened more likely later, during a global regressive trend. The timing of the Tortonian flooding in Upper Provence was therefore most probably driven by regional tectonic forcing. Finally, the Tortonian shallow marine sediments are topped by lacustrine tight carbonates. These carbonates protect the marine sediments from the following major erosional events resulting from the Messinian sea level drop and from interglacial-glacial fluctuations that both yielded to the present-day valley topography.

Vegetation destruction during an extreme flood: Multilevel modelling of an entire river in southern Korea

AbstractHuman‐induced climate change causes extreme weather events, and flooding induced by heavy rainfall in the riparian system is no exception. The southern Korean Peninsula witnessed record‐breaking rainfall during the summer of 2020, resulting in an extreme flood event that caused extensive damage to the riparian ecosystem along the Seomjin River. This study was aimed at identifying the composite factors of riparian vegetation destruction along the entire river. Based on a spatially explicit multilevel approach, it was found that large‐scale geomorphic characteristics (i.e., alternation of plain and valley topographies) appeared to be essential determinants of hydraulic characteristics of the channel (e.g., shear stress and specific energy), which were the leading causes of vegetation destruction. Moreover, at small spatial scales, several trees situated upstream of a vegetation patch protected other plants on the patch from the direct hydraulic impact of the flood, thereby serving as ‘shield’ trees. These findings indicate that scale‐dependent fluvial biogeomorphic processes take place during extreme flood events; hence, identifying the optimal scales of these processes and associated factors could help in further understanding riparian hydrology from a biogeomorphic point of view. This study suggests that hydrologists consider both geomorphological and ecological factors when studying hydrological processes.

Altitude Correction of GCM-Simulated Precipitation Isotopes in a Valley Topography of the Chinese Loess Plateau

Altitude is one of the important factors influencing the spatial distribution of precipitation, especially in a complex topography, and simulations of isotope-enabled climate models can be improved by altitude correlation. Here we compiled isotope observations at 12 sites in Lanzhou, and examined the relationship between isotope error and altitude in this valley in the Chinese Loess Plateau using isoGSM2 isotope simulations. Before altitude correction, the performance using the nearest four grid boxes to the target site is better than that using the nearest box; the root mean square error in δ18O using the nearest four grid boxes averagely decreases by 0.37‰ compared to that using the nearest grid boxes, and correlation coefficient increases by 0.05. The influences of altitude on precipitation isotope errors were examined, and the linear relationship between altitude error and isotope simulations was calculated. The strongest altitude isotopic gradient between δ18O mean bias error and altitude error is in summer, and the weakest is in winter. The regression relationships were used to correct the simulated isotope composition. After altitude correction, the root mean square error decreases by 1.21‰ or 0.86‰ using the nearest one or four grid boxes, respectively, and the correlation coefficient increases by 0.13 or 0.08, respectively. The differences between methods using the nearest one or four grids are also weakened, and the differences are 0.02‰ for root mean square error and −0.01 for the correlation coefficient. The altitude correction of precipitation isotopes should be considered to downscale the simulations of climate models, especially in complex topography.

The amplification effect of river valley topography on the seismic response of a tunnel near a valley: simulated using the boundary element method

Many tunnels are inevitably built in or near valley terrains, which greatly amplifies the seismic response of the tunnel. This paper considers the interaction between the valley terrain and tunnels, proposes a high-precision indirect boundary element method (IBEM) for simulation, and verifies the correctness of the method. The impact of factors such as incident-wave type, incident-wave frequency, and distance between the tunnel and the valley on the seismic response of the tunnel is then analysed in detail. The numerical analysis demonstrates that the stress of the tunnel can be approximately doubled when the distance between the river valley and the tunnel is 10 m due to the scattering and coherence effects of seismic waves. However, when this distance is greater than 50 m, the presence of river valleys has little effect on the stress of the tunnel. The stress at the right shoulder of the tunnel and the displacement amplification effect on the valley slope is significant compared to other areas. The findings of this study provide theoretical guidance for the seismic fortification and disaster avoidance of tunnel structures near river valleys.

Mapping Variations in Bedrock Weathering With Slope Aspect Under a Sedimentary Ridge‐Valley System Using Near‐Surface Geophysics and Drilling

AbstractUnderstanding how soil thickness and bedrock weathering vary across ridge and valley topography is needed to constrain the flowpaths of water and sediment production within a landscape. Here, we investigate saprolite and weathered bedrock properties across a ridge‐valley system in the Northern California Coast Ranges, USA, where topography varies with slope aspect such that north‐facing slopes have thicker soils and are more densely vegetated than south‐facing slopes. We use active source seismic refraction surveys to extend observations made in boreholes to the hillslope scale. Seismic velocity models across several ridges capture a high velocity gradient zone (from 1,000 to 2,500 m/s) located ∼4–13 m below ridgetops that coincides with transitions in material strength and chemical depletion observed in boreholes. Comparing this transition depth across multiple north‐ and south‐facing slopes, we find that the thickness of saprolite does not vary with slope aspects. Additionally, seismic survey lines perpendicular and parallel to bedding planes reveal weathering profiles that thicken upslope and taper downslope to channels. Using a rock physics model incorporating seismic velocity, we estimate the total porosity of the saprolite and find that inherited fractures contribute a substantial amount of pore space in the upper 6 m, and the lateral porosity structure varies strongly with hillslope position. The aspect‐independent weathering structure suggests that the contemporary critical zone structure at Rancho Venada is a legacy of past climate and vegetation conditions.

Shaking table test for near-valley subway station - Part I: Seismic site effects

As a typical local irregular topography, valley would have a significant influence on the seismic distribution around the local site as well as on seismic responses of near-valley underground structures, which has been evidenced by ground motion observation and field seismic records. However, current knowledge on the seismic site effects of the valley is limited to analytical solutions or numerical methods, and lack of experimental data from physical models. In this paper, a physical model test method based on 1g shaking table for arc-shaped valley topography is proposed, and a series of shaking table tests are carried out to investigate the seismic site effects induced by the valley topography. Details of experimental setup include not only the dynamic similitude design, the laminar model container and the model soil, but also the design and fabrication of arc-shaped valley topography with three kinds of depth-to-width ratios, i.e. 1/3, 1/4, and 1/8, as well as procedure for simulation of seismic excitations considering harmonic waves and actual seismic records. The free-field test case without valley site is also involved and taken as a benchmark comparison to better understand the seismic site effects of valley terrain. Acceleration sensors are placed and embedded in the model soil with different buried depths and distances to the local valley site in order to record the overall free-field seismic responses as well as the local topography effects. Results show that the dynamic response on the surface of model soil exhibits strong spatial variability due to the impact of the local valley topography. Results also indicate the ground acceleration increases within the local site, and the amplification effect is most pronounced at the valley top. The influence of the valley on the acceleration response of the ground is more significant when the predominant frequency of the seismic motions is higher and closer to the natural frequency of the site under different seismic motions. Furthermore, when the depth-to-width ratio of the valley increases, the acceleration amplitude at the valley top gradually increases, and the predominant frequency of Fourier spectrum at the valley top is also amplified. Notably, the Arias intensity amplification factor of the surrounding strata increases significantly due to the local valley topography, and the Arias intensity is also increased with the depth-to-width ratio of the valley.

Shaking table test for near-valley subway station - Part Ⅱ: Seismic response of the station

With the expansion of metro lines in cities especially in megacities, the number of tunnels and subway stations built near urban valley are rapidly growing. However, the influence mechanism of valley on the nearby subway station, which is due to the strong spatial variability of local valley topography during earthquakes, has not been well-understood. In this paper, a series of 1g shaking table tests is performed to investigate the seismic performance of a typical two-story, three-span subway station nearby the valley topography. The stratum is simulated by synthetic model soil (a mixture of sand and sawdust) and the model structure is made by granular concrete with galvanized steel wires. Note that this is done according to the similitude ratio design to ensure the consistency of the structure-soil flexibility ratio between the prototype and the model. The arc-shaped valley topography with three kinds of depth-to-width ratios, i.e. 1/3, 1/4, and 1/8, are designed and fabricated, and a subway station test without valley site was also considered and taken as a comparative benchmark to better understand the seismic response of the subway station affected by the valley topography under harmonic motions and actual seismic records. Result shows that the acceleration response of the top slab of the near-valley structure is significantly larger than that of the case without valley site, and what's more interesting, the subway station exhibits strong lateral racking under the horizontal transverse motion. The active dynamic earth pressure on the sidewall of the near-valley structure is dramatically increasing due to the valley topographic effect. The bending moments of the sidewall close to the local valley is also significantly amplified compared to the benchmark test without valley site, except for the moments of central columns. Results also indicate that, the acceleration amplitude at the top slab gradually increases with the depth-to-width ratio of the valley, and the lateral racking of the near-valley structure is more pronounced when near the valley with a larger depth-to-width ratio under earthquakes.

The scattering of seismic waves from saturated river valley with water layer: Modelled by indirect boundary element method

River valley topography will cause local amplification effect and significant spatial variation effect of ground motion. In this paper, an indirect boundary element method (IBEM) is proposed to solve seismic wave scattering in sedimentary valleys. A ``water layer - soft sedimentary layer - poroelastic halfspace'' model is established, and the effects of water layer, soil parameters of sedimentary layer and terrain on incident P and SV waves are discussed in detail. The numerical results demonstrate that the scattering characteristics are closely related to the depth of water layer, porosity, the location of observation points, et al. The surface displacement amplitude decreases with increasing water layer thickness, with a maximum reduction of 16.2%. Moreover, the peak ground acceleration (PGA) is significantly larger and the seismic response is stronger when the observation point is located outside the valley compared to the observation point inside the valley. The influence of porosity on Fourier spectrum and response spectrum curve is mainly reflected in the peak value and predominant frequency. The research results can provide a theoretical basis for the seismic fortification of the structures around the saturated sedimentary valley.

Living on the Edge—Mismatches and Expectations in a Changing Landscape

This paper deals with the confrontation between the forms of urbanisation of Lisbon, Portugal, that extends its fringes over the Alcântara Valley. This same Valley—topography and hydrography—plays as determinants of the occupation that will assume distinct narratives. This gradual process is explained through three narratives about (1) the urbanisation of the margin driven by industrialisation and the construction of a stigmatised periphery, (2) the imposition of large capacity infrastructures far beyond what is local, (3) the system of open spaces and landscape projects and the urban brink that the valley claims. The debate focuses on the answers that the urban and landscape project, necessarily going through urban planning and its practical and theoretical scopes, i.e., Urbanism and urban planning thinking, especially in a broad present seeking to discuss both sides of the coin: on the one hand, an urban rehabilitation with public space for all, on the other hand, a qualified and central space that attracts real estate investment that may bring effects contrary to those expected. The article seeks to contribute (1) to a broader perception of the superimposition of processes that transformed the Alcântara Valley, (2) to a fuller dissemination of the urbanistic experiences in the city of Lisbon since this city is still vastly underrepresented in the international (primarily Anglo-Saxon) literature, (3) to deepen the debate between urban rehabilitation, urban regeneration, consequences and opportunities practiced is still trying to cope with.