Numerical simulation of real debris-flows events

A one-dimensional model is presented to predict debris-flow runouts. The model is based on shallow water type assumptions. The fluid is assumed to be homogeneous and the original bed of the flow domain to be unerodible. The fluid is characterized by a rheology of Bingham type. A numerical tool able to cope with the nature of debris flows has been worked out. It represents an extension of a second order accurate and conservative method of Godunov type. Special care has been devoted to the influence of the source terms and of the geometrical representation of the natural cross sections, which play a fundamental role. The application concerns a monitored event in the Dolomites in Italy, where field analyses allowed a characterization of the behavior of solid-liquid mixture as a yield stress material. The comparison between numerical simulations and field observations highlights the impossibility of representing all phases of the flow with constant values of the rheological parameters. Nevertheless the results show that it is possible to separately represent the phase of the flow in the upstream reach and the phase of the deposition in the alluvial fan, with a good agreement with field observations

Numerical computation of a confined sediment-water mixture in uniform flow

The purpose of this paper is to simulate a laminar mud flow confined in a narrow rectangular open channel. The flow bed is an erodible layer made up of the same material involved in the flow; the equilibrium condition between the moving and non moving layer is assumed. The mud mixture under consideration is ruled by Herschel-Bulkley’s shear thickening rheological law. It is supposed that the local volumetric concentration is linearly increasing with the depth and it is constantly equal to its maximum value where the local velocity is smaller than a threshold value. Relations among rheological parameters and concentration are obtained through laboratory rheometric tests. Turbulence effects and Coulombian stresses are ignored. To get the flow velocity, the momentum equation has to be integrated along the flow cross section. Unfortunately, it is very difficult to integrate this equation using H-B rheological law, since there are different stress functions and it is not possible to know a priori the sub-domains of them (plug, non plug and bed regions). In the present work a modified rheological law, continuous over the whole domain of integration is employed and the momentum equation is integrated numerically. This modified law is obtained by adding a constant correcting the denominator in the H-B stress functions: strictly speaking, there are not dead zones or plug any more. However it is noteworthy that, using a small constant, the model produces a good simulation of plug and dead zone: that is velocity gradient is very small there. The mathematical model has two parameters: maximum concentration and threshold velocity. These parameters are adjusted by back-analysis with measurements from laboratory flume experiments in uniform flow conditions

river morphology monitoring using multitemporal sar data preliminary results

AbstractIn this paper, we test the capability of satellite synthetic aperture radar (SAR) images to enhance the monitoring of river geomorphological processes. The proposed approach exploits the recently introduced Level-α products. These products are bi-temporal RGB composites in which the association color-object, being physical-based, is stable whatever the scene is considered. This favors the detection of temporary rivers' characteristics for classification purposes in a change-detection environment. The case study was implemented on the Orco river (northwest Italy), where a set of 39 COSMO-SkyMed SAR stripmap images acquired from October 2008 to November 2014 was used to monitor channel planform changes. This preliminary study is devoted to assess the suitability of Level-α images for geomorphologist, with particular reference to the detection of phenomena of interest in river monitoring. This is prior for semi-automatic or automatic classification activities

RICOSTRUZIONE E MODELLAZIONE NUMERICA DI UN EVENTO DI FLASH FLOOD. Il caso di Atrani 2010

Dalle alluvioni del Salernitano del 1954 a quella di Atrani nel 2010 la ricorrenza degli eventi registra una tendenza crescente incrinando l’accezione stessa di eccezionalità del fenomeno calamitoso. In coda ormai ad un decennio di continua attivazione dei comparti tecnico-scientifici di settore, il supporto della ricerca scientifica agli strumenti di misura e mitigazione della pericolosità idraulica si concretizza particolarmente nella codifica di modelli matematici e numerici per la simulazione preventiva dei fenomeni generativi e di quelli propagativi dell’evento alluvionale. Lo studio ricostruisce l’evento di flash flood che il 9 Settembre 2010 ha investito l’abitato di Atrani (Costiera Amalfitana). Grazie ad una dettagliata attività di rilievo di campo, nei giorni immediatamente successivi all’evento, è stato possibile stimare alcune caratteristiche del fenomeno tra cui i valori di riferimento per i tiranti e le velocità della corrente. La formazione della piena è stata ricostruita attraverso il modello afflussi-deflussi geomorfologico del tipo WFIUH (Width Function Istantaneous Unit Hydrograph). L’idrogramma così ottenuto ha costituito la condizione al contorno di monte per la simulazione delle dinamiche propagative dell’onda di piena in area urbana. Per lo studio idraulico ci si è avvalso di un codice matematico-numerico originale (2D FLATModel) operante su griglie di calcolo non-strutturate. Gli strumenti utilizzati hanno fornito una simulazione dell’evento in buon accordo con le osservazioni di campo dimostrandosi quindi adeguati per la simulazione e la previsione degli eventi di flash flood in contesti analoghi a quello di studio

Continuous Monitoring of the Flooding Dynamics in the Albufera Wetland (Spain) by Landsat-8 and Sentinel-2 Datasets

[EN] Satellite data are very useful for the continuous monitoring of ever-changing environments, such as wetlands. In this study, we investigated the use of multispectral imagery to monitor the winter evolution of land cover in the Albufera wetland (Spain), using Landsat-8 and Sentinel-2 datasets. With multispectral data, the frequency of observation is limited by the possible presence of clouds. To overcome this problem, the data acquired by the two missions, Landsat-8 and Sentinel-2, were jointly used, thus roughly halving the revisit time. The varied types of land cover were grouped into four classes: (1) open water, (2) mosaic of water, mud and vegetation, (3) bare soil and (4) vegetated soil. The automatic classification of the four classes was obtained through a rule-based method that combined the NDWI, MNDWI and NDVI indices. Point information, provided by geo-located ground pictures, was spatially extended with the help of a very high-resolution image (GeoEye-1). In this way, surfaces with known land cover were obtained and used for the validation of the classification method. The overall accuracy was found to be 0.96 and 0.98 for Landsat-8 and Sentinel-2, respectively. The consistency evaluation between Landsat-8 and Sentinel-2 was performed in six days, in which acquisitions by both missions were available. The observed dynamics of the land cover were highly variable in space. For example, the presence of the open water condition lasted for around 60-80 days in the areas closest to the Albufera lake and progressively decreased towards the boundaries of the park. The study demonstrates the feasibility of using moderate-resolution multispectral images to monitor land cover changes in wetland environments.This research was funded by the PhD course on Risk and Sustainability in Civil, Architectural and Environmental Engineering Systems of Salerno University (PON Research and Innovation 2014-2020 scholarship).Cavallo, C.; Papa, MN.; Gargiulo, M.; Palau-Salvador, G.; Vezza, P.; Ruello, G. (2021). Continuous Monitoring of the Flooding Dynamics in the Albufera Wetland (Spain) by Landsat-8 and Sentinel-2 Datasets. Remote Sensing. 13(17). https://doi.org/10.3390/rs13173525131

Percezione del rischio da frana: uno studio preliminare nel comune di Sarno (SA)

La nota presenta i risultati preliminari di un’indagine sulla percezione del rischio da frana da parte degli abitanti del comune di Sarno e sulla loro opinione e grado di conoscenza riguardo gli interventi di mitigazione del rischio, di tipo strutturale e non strutturale, realizzati a Sarno a seguito dei disastrosi eventi franosi del 5-6 maggio 1998. L’indagine è stata condotta, attraverso l’utilizzo di un questionario appositamente sviluppato allo scopo, nei mesi di marzo, aprile e maggio 2013. Il questionario è stato somministrato, attraverso interviste individuali, a 100 abitanti del Comune di Sarno residenti nella frazione di Episcopio, ovvero all’interno dell’area che ha registrato il maggior numero di vittime a seguito degli eventi del maggio 1998

Use of High Resolution Satellite Images for the Calibration of Hydro-geological Models in Semi-Arid Regions: A Case Study

In this paper we present the preliminary results of a project devoted to use hydrologic and remote sensing models and data for water resource management in semi-arid regions. The project is developed in the Sahel region of Burkina Faso, where a set of high resolution synthetic aperture radar (SAR) images was acquired. The rationale of the project along with the preliminary results obtained by the processing of high resolution Cosmo- SkyMed data are presented and discussed

Chute flows of dry granular media: Numerical simulations by a well-posed multilayer model and comparisons with experiments

Debris flows and avalanches are dangerous natural phenomena, characterized by the gravity-driven motion of granular media immersed in a fluid. For an appropriate hazard assessment or disaster mitigation by scenario investigation, it is crucial to capture the underlying dynamics of the granular solid phase. For this purpose, a multilayer depth-averaged approach represents a promising and computationally efficient tool over fully three-dimensional models. Here we use a mathematically well-posed multilayer model, which implements the µ(I)-rheology and a dilatancy law depending on the inertial number, I, and compare the numerical results of the model with laboratory experiments of steady uniform chute flows over an erodible bed. The well-posedness of the model for any value of I, which is essential to get convergent numerical solutions, is achieved by considering an approximation of the in-plane stress gradients, directly emerging from the µ(I)-rheology. The predicted velocity profiles show a very good agreement with the experimental ones, measured by particle image velocimetry (PIV). The volume fraction profiles by the multilayer model are also in good qualitative agreement with those measured by using the stochastic-optical method (SOM), while they tend to overestimate the volume fraction measurements in the more dilute upper region, closer to the free surface

Hydrological modeling in ungauged basins using SAR data

In this paper we propose a methodology devoted to exploit high resolution radars for monitoring water bodies in semi-arid countries. The proposed approach is based on appropriate registration, calibration and processing of SAR data, producing information ready to use by end-users. The obtained results were used to (i) estimate a relationship between surface and volume of water stored in reservoirs and (ii) validate a hydrological model that simulates the time evolution of water availability

Use of SAR data for hydro-morphological characterization in sub-Saharan Africa: a case study

In this paper we present the rationale and the preliminary results of a research project devoted to the appropriate and innovative use of remotely sensed data for water management in semi-arid regions. The study area is the district of Yatenga, northern Burkina Faso in the sub- Saharan belt of West Africa, where extreme climate conditions cause several problems: drought, floods, soil erosion. The data comes from the Italian Space Agency (ASI) Cosmo-Skymed program, which provides high resolution (1 meter) Synthetic Aperture Radar (SAR) images. Crucial peculiarity of the project is the use of open source software for data processing and hydrological modeling. Two different hydrological models have been selected. The Soil and Water Assessment Tool (SWAT) to be employed for the design of appropriate water management plans and soil erosion mitigation measures. The Width Function Instantaneous Unit Hydrograph (WFIUHD) model can to employed for the prevision of flood events and therefore for the planning of risk mitigation. The paper shows the preliminary results of the project obtained by the processing of the first available high resolution SAR data. In particular, the first step is the realization of a Digital Elevation Model (DEM). GIS tools have been set up for the DEMprocessing in order to derive the needed hydro-morphological basin attributes to support the geo-morphological rainfall- runoff (WFIUHD) modelin