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

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

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

Modeling Watershed Response in Semiarid Regions With High-Resolution Synthetic Aperture Radars

In this paper, we propose a methodology devoted to exploit the outstanding characteristics of COSMO-SkyMed for monitoring water bodies in semiarid countries at a scale never experienced before. The proposed approach, based on appropriate registration, calibration, and processing of synthetic aperture radar (SAR) data, allows outperforming the previously available methods for monitoring small reservoirs, mainly carried out with optical data, and severely limited by the presence of cloud coverage, which is a frequent condition in wet season. A tool has been developed for computing the water volumes retained in small reservoirs based on SAR-derived digital elevation model. These data have been used to derive a relationship between storage volumes and surface areas that can be used when bathymetric information is unavailable. Due to the lack of direct measures of river's discharge, the time evolution of water volumes retained at reservoirs has been used to validate a simple rainfall-runoff hydrological model that can provide useful recommendation for the management of small reservoirs. Operational scenarios concerning the improvement in the efficiency of reservoirs management and the estimation of their impact on downstream area point out the applicative outcomes of the proposed method

Modeling hydrological response of structured soils

2013 - 2014The hydraulic processes that control the water movements through the soil strictly depend on the configuration and distribution of the soil pores... [edited by author]XII n.s

Temporal evolution of flow-like landslide hazard for a road infrastructure in the municipality of Nocera Inferiore (southern Italy) under the effect of climate change

In recent years, flow-like landslides have extensively affected pyroclastic covers in the Campania region in southern Italy, causing human suffering and conspicuous economic damages. Due to the high criticality of the area, a proper assessment of future variations in event occurrences due to expected climate changes is crucial. The study assesses the temporal variation in flow-like landslide hazard for a section of the A3 “Salerno–Napoli” motorway, which runs across the toe of the Monte Albino relief in the Nocera Inferiore municipality. Hazard is estimated spatially depending on (1) the likelihood of rainfall-induced event occurrence within the study area and (2) the probability that the any specific location in the study area will be affected during the runout. The probability of occurrence of an event is calculated through the application of Bayesian theory. Temporal variations due to climate change are estimated up to the year 2100 through an ensemble of high-resolution climate projections, accounting for current uncertainties in the characterization of variations in rainfall patterns. Reach probability, or defining the probability that a given spatial location is affected by flow-like landslides, is calculated spatially based on a distributed empirical model. The outputs of the study predict substantial increases in occurrence probability over time for two different scenarios of future socioeconomic growth and atmospheric concentration of greenhouse gasesTemporal evolution of flow-like landslide hazard for a road infrastructure in the municipality of Nocera Inferiore (southern Italy) under the effect of climate changepublishedVersio

Estimation of debris flow critical rainfall thresholds by a physically-based model

Abstract. Real time assessment of debris flow hazard is fundamental for setting up warning systems that can mitigate its risk. A convenient method to assess the possible occurrence of a debris flow is the comparison of measured and forecasted rainfall with rainfall threshold curves (RTC). Empirical derivation of the RTC from the analysis of rainfall characteristics of past events is not possible when the database of observed debris flows is poor or when the environment changes with time. For landslides triggered debris flows, the above limitations may be overcome through the methodology here presented, based on the derivation of RTC from a physically based model. The critical RTC are derived from mathematical and numerical simulations based on the infinite-slope stability model in which land instability is governed by the increase in groundwater pressure due to rainfall. The effect of rainfall infiltration on landside occurrence is modelled trough a reduced form of the Richards equation. The simulations are performed in a virtual basin, representative of the studied basin, taking into account the uncertainties linked with the definition of the characteristics of the soil. A large number of calculations are performed combining different values of the rainfall characteristics (intensity and duration of event rainfall and intensity of antecedent rainfall). For each combination of rainfall characteristics, the percentage of the basin that is unstable is computed. The obtained database is opportunely elaborated to derive RTC curves. The methodology is implemented and tested on a small basin of the Amalfi Coast (South Italy). </jats:p

Effects of climate change on shallow landslides in a small coastal catchment in southern Italy

In different areas of the world, shallow landslides represent a remarkable hazard inducing fatalities and economic damages. Then, the evaluation about potential variation in frequency of such hazard under the effect of climate changes should be a priority for defining reliable adaptation measurements. Unfortunately, current performances of climate models on sub-daily scales, relevant for heavy rainfall events triggering shallow landslides, are not reliable enough to be used directly for performing slope stability analysis. In an attempt to overcome the constrains by gap in time resolution between climate and hazard models, the paper presents an integrated suitable approach for estimating future variations in shallow landslide hazard and managing the uncertainties associated with climate and sub-daily downscaling models. The approach is tested on a small basin on Amalfi coast (southern Italy). Basing on available basin scale critical rainfall thresholds, the paper outlines how the projected changes in precipitation patterns could affect local slope stability magnitude scenarios with different relevances as effect of investigated time horizon and concentration scenario. The paper concludes with qualitative evaluations on the future effectiveness of the local operative warning system in a climate change framework