1,720,977 research outputs found
Combining numerical simulations and normalized scalar product strategy: A new tool for predicting beach inundation
No full textThe skills of the Normalized Scalar Product (NSP) strategy, commonly used to estimate the wave field, as well as bathymetry and sea-surface current, from X-band radar images, are investigated with the aim to better understand coastal inundation during extreme events. Numerical simulations performed using a Nonlinear Shallow-Water Equations (NSWE) solver are run over a real-world barred beach (baseline tests). Both bathymetry and wave fields, induced by reproducing specific storm conditions, are estimated in the offshore portion of the domain exploiting the capabilities of the NSP approach. Such estimates are then used as input conditions for additional NSWE simulations aimed at propagating waves up to the coast (flood simulations). Two different wave spectra, which mimic the actual storm conditions occurring along the coast of Senigallia (Adriatic Sea, central Italy), have been simulated. The beach inundations obtained from baseline and flood tests related to both storm conditions are compared. The results confirm that good predictions can be obtained using the combined NSP-NSWE approach. Such findings demonstrate that for practical purposes, the combined use of an X-band radar and NSWE simulations provides suitable beach-inundation predictions and may represent a useful tool for public authorities dealing with the coastal environment, e.g., for hazard mapping or warning purposes
Coastal sensitivity/vulnerability characterization and adaptation strategies: A review
Full text linkCoastal area constitutes a vulnerable environment and requires special attention to preserve ecosystems and human activities therein. To this aim, many studies have been devoted both in past and recent years to analyzing the main factors affecting coastal vulnerability and susceptibility. Among the most used approaches, the Coastal Vulnerability Index (CVI) accounts for all relevant variables that characterize the coastal environment dealing with: (i) forcing actions (waves, tidal range, sea-level rise, etc.), (ii) morphological characteristics (geomorphology, foreshore slope, dune features, etc.), (iii) socio-economic, ecological and cultural aspects (tourism activities, natural habitats, etc.). Each variable is evaluated at each portion of the investigated coast, and associated with a vulnerability level which usually ranges from 1 (very low vulnerability), to 5 (very high vulnerability). Following a susceptibility/vulnerability analysis of a coastal stretch, specific strategies must be chosen and implemented to favor coastal resilience and adaptation, spanning from hard solutions (e.g., groins, breakwaters, etc.) to soft solutions (e.g., beach and dune nourishment projects), to the relocation option and the establishment of accommodation strategies (e.g., emergency preparedness)
Seawater intrusion assessment along the Volturno River (Italy) via numerical modeling and spectral analysis
Full text linkSurface and groundwater salinization are becoming a significant challenge to inland water quality, negatively affecting people and ecosystems in coastal areas. Even if rivers provide critical pathways for seawater intrusion, this salinization phenomenon has received relatively little attention compared to other salinization mechanisms. To assess the distribution of salinity along the final reach of the Volturno River (Italy), an entire hydrologic year was modeled using the HEC-RAS software. The model was fed with high resolution time-series measurements (time interval of 10 min) of water surface elevations at both river mouth and Cancello Arnone (a hydrometric station located 13 km inland). Field observations and remote sensed data were used to perform the hydrody-namic analysis. The model showed good performance indicators (R2 = 0.878, NSE = 0.870, and MAE = 0.037 m) and well caught hydrometric variation over the simulation period. The tidal component was affected by dissi-pation moving upstream and showed the capability to shape the salinity profile during dry periods. Whereas during wet periods, even if a strong tidal component is present, the profile is totally regulated by the river discharge. The analysis of the salinity distribution, modelled via the Water Quality module, revealed the massive contribution of the river discharge in limiting seawater intrusion. A correlation between intrusion events and hydrometric stages was established over twenty years (2002-2022), showing a consistent trend between intrusion occurrence and the surface water storage anomaly in the lower Volturno River calculated by Global Land Data Assimilation System (GLDAS) model. Although the 1D approach here used may lead to uncertainties in the reproduction of the involved hydrodynamic and salinization processes, the results are useful for the under-standing of seawater intrusion in rivers, and may be utilized to study seawater intrusion in aquifers
Steady streaming under a surface wave propagating over a rough bottom: A model of the bottom boundary layer
No full textThe steady streaming generated by nonlinear effects at the bottom of a propagating surface wave is determined when the bottom is characterized by a roughness, the size of which scales with the boundary layer thickness. Therefore, the cornerstone contribution by Longuet-Higgins, who considered a smooth bottom, is extended to sea waves and sandy bottoms characterized by a grain size that ranges from fine silt to fine gravel. For values of the grain size d* up to 0.05 delta* , delta* being the thickness of the viscous bottom boundary layer, the velocity profile is practically coincident with that predicted by Longuet-Higgins. If the grain size is further increased, the steady velocity component becomes larger and reaches a maximum value that is approximately 70% larger than that predicted by Longuet-Higgins. The maximum of the steady velocity component is attained for d* = 0.6 delta*. A further increase in d* leads to a decrease in the steady velocity component that, however, keeps always larger than that predicted for a smooth bottom. As the roughness size increases up to the values typical of medium sand, the steady velocity component increases. Then, a further increase in the roughness size leads to a decrease in the steady streaming even though, in the range of the roughness size presently investigated, the steady velocity component is always larger than that predicted for a smooth bottom
Assessing the flood risk to evacuees in outdoor built environments and relative risk reduction strategies
Full text linkClimate-change induced disasters, like floods, are expected to increase in the future. In outdoor built environments, flood risk to evacuees depends on interactions between floodwater spreading, built environment features, flood-induced modifications, and individuals’ reaction in emergency phases. Disaster risk reduction strategies should mitigate the immediate flood impacts and improve the community resilience, while being easy-to-implement and effectively supporting evacuees during the initial phases of the emergency. Simulation-based methodologies could support safety planners in evaluating the effectiveness of such strategies, especially if basing on a micro-scale-oriented approach that represents emergency interactions between each individual and the surrounding outdoor built environment. This study adopts an existing micro-scale simulator (FlooPEDS) reproducing experimental-based flood evacuation behaviours. According to a behavioural design-based approach, simulation results focus on individual responses in the outdoor built environment through Key Performance Indicators (KPIs) aimed at providing evidence of critical interactions between evacuees, floodwaters and the outdoor built environment. A case study is selected by considering different flood scenarios to test such KPIs. Risk reduction solutions are then provided, and their effectiveness is checked by simulations. Results show the micro-scale and behavioural design-based approach capabilities in proposing multi-scenarios solutions (e.g.: architectural elements to support evacuees; emergency planning)
Esperimenti in larga scala sull'effetto del raggruppamento delle onde sulla morfodinamica della zona di battigia
No full textModel based quantification of salinization dynamics under changing hydrological conditions in the Volturno River (Italy) coastal aquifer
Full text linkThis work presents a semi-coupled modelling approach to study salinization dynamics in the Volturno River coastal aquifer (Italy), distinguishing among different salinization mechanisms. The area is of particular interest, given its location in the Mediterranean region, a climate change hot-spot. A 1D HEC-RAS numerical model was built up and run for a decade (2010-2020) to quantify the areal extent and timing of salinization events due to seawater encroachment within the Volturno River mouth. The results were used as input in a 3D SEAWAT model that incorporated salinity variations on a monthly basis for the same period. The SEAWAT model was down-scaled from a large calibrated MODFLOW model of the whole Campania region. Both national and worldwide databases were used to constrain the models. The model was then compared with 9 high resolution vertical profiles of porewater salinity obtained using a continuous coring sediment sampler, providing good model performance indicators (R2 = 0.867, NSE = 0.808, and RMSE = 3.926 g/L). Results highlight an increasing groundwater salinization pattern due to intrusion from the Volturno riverbed. The classical mechanism of seawater wedge intrusion from the coastline was minimal, while large inland portions of the model domain were characterized by high salinity (up to 75 g/l) due to remnant paleo seawater trapped into peaty and silty-clay aquitards. This physically-based modelling approach could be replicated in any coastal porous aquifer (if hydrological and hydrogeological datasets are available) to identify and quantify the salinization mechanisms and to help water managers to implement tailored solutions in the most affected areas
Human stability during floods: Experimental tests on a physical model simulating human body
Full text linkUrban floods are becoming more and more intense and frequent allover the world. Extreme events are the main triggering factors of such floods, and merit attention for what concerns the urban planning and emergency strategies. Numerical models aimed at investigating the optimal paths for evacuees escaping a flooded urban environment may be used by local authorities to properly understand how to improve people safety and mitigate the flood risk. Implementation of empirical laws in such models to describe the people stability in flooded areas is thus crucial to understand the behavior of evacuees and rescuers during emergency conditions. Laboratory experiments have been undertaken using a physical model representing a human body at quasi-natural scale, towed by an electrical engine in the water at rest. This represents a novel laboratory approach which exploits a non-inertial reference frame in motion with the model. The experimental results, obtained using different combinations of water depth and flow speed, have led to empirical laws which outline the stability conditions occurring when either the model front or the model back faces the flow, these respectively corresponding to Backward Toppling Instability (BTI) and Forward Toppling Instability (FTI). Such laws have been found through comparison with reference literature works, using various statistical methods. The FTI condition has been seen to largely improve the human stability compared to BTI, in contrast to the results of previous literature works, which stated an overall similarity between the results of the two toppling conditions. To better understand the role of the water flow during the different tests, hydraulic forces and moments have been measured. It has been seen that dynamic and static effects are comparable during high-speed conditions, especially due to a relevant fluid-model interaction and an increase of the water-surface level, while dynamic effects are negligible during low-speed conditions. The results of the present contribution can represent an important step forward for the numerical models applied to the framework of urban and emergency planning
Quantifying the impact of evapotranspiration at the aquifer scale via groundwater modelling and MODIS Data
Full text linkIn shallow alluvial aquifers characterized by coarse sediments, the evapotranspiration rates from groundwater are often not accounted for due to their low capillarity. Nevertheless, this assumption can lead to errors in the hydrogeological balance estimation. To quantify such impacts, a numerical flow model using MODFLOW was set up for the Tronto river alluvial aquifer (Italy). Different estimates of evapotranspiration rates were retrieved from the online Moderate Resolution Imaging Spectroradiometer (MODIS) database and used as input values. The numerical model was calibrated against piezometric heads collected in two snapshots (mid-January 2007 and mid-June 2007) in monitoring wells distributed along the whole alluvial aquifer. The model performance was excellent, with all the statistical parameters indicating very good agreement between calculated and observed heads. The model validation was performed using baseflow data of the Tronto river compared with the calculated aquifer-river exchanges in both of the simulated periods. Then, a series of numerical scenarios indicated that, although the model performance did not vary appreciably regardless of whether it included evapotranspiration from groundwater, the aquifer-river exchanges were influenced significantly. This study showed that evapotranspiration from shallow groundwater accounts for up to 21% of the hydrogeological balance at the aquifer scale and that baseflow observations are pivotal in quantifying the evapotranspiration impact
- …
