Effectiveness evaluation of flood defence structures in different geomorphological contexts

The flood risk in different geomorphological contexts of two less developed countries are investigated in order to evaluate the efficacy of the existing flood defence structures. In particular, a recent floodplain crossed by a wide meandering river and a narrow mountain valley flowed by creek with a torrential regime have been chosen for such analysis in North Albania and central Mexico, respectively. Both areas have been affected by disastrous floods in past years with considerable damages to properties and people. Some safety countermeasures have been performed over time, even if in a non-systematic way. For this reason, the current inclination to flood risk was assessed by means of a freeware software designed to perform one-dimensional (1D) hydraulic modelling for a full network of natural and anthropic channels (HEC-RAS software by Hydrologic Engineering Center River Analysis System). This new analyses take into account: i) the natural morphological variability along the river path, ii) the anthropic interventions on the fluvial dynamics, iii) the landscape appearance after the soil exploitation in the past years, and iv) all the changes induced by an exceeded informal urbanization. The reconstruction of the river and bordering areas geometric data was carried out according to the physical characteristics of the local environment: a bathymetric survey and near-river DGPS acquisitions for the open spaces of the Albanian floodplain, and traditional topographic methods for the highly vegetated Mexican valley. In both cases, the results show that the existing works are, on their own, poorly efficient in containing the predictable floods. Albanians levees seem underdimensioned, while the channelling works are too narrow to contain large amounts of water and solid transport as typical of the Mexican study area. Evidently, a new territorial planning is required in these areas, and some projects are now in place. However, it would be desirable that local authorities were profitably inspired by the criticalities here mentioned

The Geohazard Safety Classification: how resilience could play a role in the geo-hydrological hazards assessment of school buildings

The impacts of adverse events related to geological hazards are unevenly distributed among communities and groups of individuals concentrated in restricted workplaces. Their consequent safety level is the result of differential exposures to these events and of diversified levels of preparation to them. Nowadays, the exposure and coping ability as co-determinants of people's safety are of particular interest for institutions managing the schools systems. According to the disaster risk reduction experts, the geo-hydrological processes can be mitigated with knowledge and planning, physical and environmental protection measures, and response preparedness. UNISDR is promoting a global culture of safety and resilience through the integration of disaster risk reduction in school curricula. The Comprehensive School Safety (CSS) framework is intended to advance the goals of the Worldwide Initiative for Safe Schools and the Global Alliance for Disaster Risk Reduction and Resilience in the Education Sector, and to promote school safety as a priority area of post-2015 frameworks for sustainable development, risk reduction and resilience. In Italy, according the latest ministerial survey (June 2010), there are 41,902 school buildings. Their alarming condition in terms of safety for their daily occupants is reflected by 39 fatalities ascribable to structural failures in the last 21 years. In 95% of these cases victims are a sad tribute due to natural phenomena. A rigorous evaluation of the total risk of a school building, as defined by the well known risk equation (R=HxVxE), would require a complete probability density function describing the exposure to specific types of events of all the pupils and personnel in the school. In addition, the probability that the inhabitants are present in the school during an event should be estimated depending on the time of day, day of week, or month of the year, as well as on local holiday schedules. The inclusion of resilience as a component of risk allows us to refine the risk awareness, focusing attention on the cultural and social meaning of risk as a shared practice among communities that are potentially at risk. This project developed a method for assessing school hazard exposure (landslide, seismic, flood) and structural fragility/safe learning facilities (seismic response, dampness, plan configuration) which is non-invasive, fairly quick and objective. This tool, which is based on the GSC (Geohazard Safety Classification) definition, was tested in central Italy and optimized for a very wide variety of situations, so that it may be exported in schools (or in similar working places) of other geographical areas. The GSC was obtained as the complementary to one of the Index of Geohazard Impact (IGI), calculated modifying the equation of the specific risk, taking into account also the resilience as a damper, amplifier or invariant of the specific risk itself (IGI=max(HixVi)/rho). The variables of this new equation (hazard, vulnerability and resilience) can be quantified on the basis of ancillary data (thematic maps), results of the data processing of field surveys (seismic noise measure according to the H/V technique, thermographic images, GPS surveys) and the answers to an online questionnaire implemented on purpose

An electric and electromagnetic geophysical approach for subsurface investigation of anthropogenic mounds in an urban environment

Scientific interest in mounds as geomorphological features that currently represent topographic anomalies in flat urban landscapes mainly lies on the understanding of their origin, either purely natural or anthropogenic. In this second circumstance, another question is whether traces of lost buildings are preserved within the mound subsurface and can be mapped as remnants testifying past settlement. When these landforms have been modified in centuries for civilian use, structural stability is a further element of concern. To address these issues we applied a geophysical approach based on a very low frequency electromagnetic (VLF-EM) technique and two dimensional electrical resistivity tomography (2D-ERT) and integrated it with well-established surface survey methods within a diagnostic workflow of structural assessment. We demonstrate the practical benefits of this method in the English Cemetery of Florence, Italy, whose mixed nature and history of morphological changes are suggested by archival records. The combination of the two selected geophysical techniques allowed us to overcome the physical obstacles caused by tomb density and to prevent interference from the urban vehicular traffic on the geophysical signals. Eighty-two VLF-EM profiles and five 2D-ERTs were collected to maximise the spatial coverage of the subsurface prospection, while surface indicators of instability (e.g., tomb tilt, location, and direction of ground fractures and wall cracks) were mapped by standard metric survey. High resistive anomalies (> 300 and 400 Ωm) observed in VLF-EM tomographies are attributed to remnants of the ancient perimeter wall that are still buried along the southern side of the mound. While no apparent correlation is found between the causes of tomb and ground movements, the crack pattern map supplements the overall structural assessment. The main outcome is that the northern portion of the retaining wall is classed with the highest hazard rate. The impact of this cost-effective approach is to inform the design of maintenance and restoration measures based on improved geognostic knowledge. The geophysical and surface evidence informs decisions on where interventions are to be prioritised and whether costly invasive investigations are needed

GB-InSAR monitoring of slope deformations in a mountainous area affected by debris flow events

Abstract. Diffuse and severe slope instabilities affected the whole Veneto region (north-eastern Italy) between 31 October and 2 November 2010, following a period of heavy and persistent rainfall. In this context, on 4 November 2010 a large detrital mass detached from the cover of the Mt. Rotolon deep-seated gravitational slope deformation (DSGSD), located in the upper Agno River valley, channelizing within the Rotolon Creek riverbed and evolving into a highly mobile debris flow. The latter phenomena damaged many hydraulic works, also threatening bridges, local roads, and the residents of the Maltaure, Turcati, and Parlati villages located along the creek banks and the town of Recoaro Terme. From the beginning of the emergency phase, the civil protection system was activated, involving the National Civil Protection Department, Veneto Region, and local administrations' personnel and technicians, as well as scientific institutions. On 8 December 2010 a local-scale monitoring system, based on a ground-based interferometric synthetic aperture radar (GB-InSAR), was implemented in order to evaluate the slope deformation pattern evolution in correspondence of the debris flow detachment sector, with the final aim of assessing the landslide residual risk and managing the emergency phase. This paper describes the results of a 2-year GB-InSAR monitoring campaign (December 2010–December 2012) and its application for monitoring, mapping, and emergency management activities in order to provide a rapid and easy communication of the results to the involved technicians and civil protection personnel, for a better understanding of the landslide phenomena and the decision-making process in a critical landslide scenario