Jan Blahut

Database of geo-hydrological disasters for civil protection purposes

This paper presents the results of a research concerning available historical information about natural hazards (landslides and floods) and consequent disasters in the Consortium of Mountain Municipalities of Valtellina di Tirano, in Northern Italy. A geo-referenced database, collecting information till 2008, was designed with the aim of using available data of historical events for hazard estimation and the definition of risk scenarios as a basis for Civil Protection planning and emergency management purposes. This database and related statistics about landslides and floods are shown, and a brief overview of historical disasters caused by natural hazards in the study area is presented. A case study showing how useful the database can be to define a simple but realistic scenario is described. Information availability and reliability is discussed and possible uncertainties are underlined. The study shows that collecting and making use of historical information for the definition of hypothetical scenarios and the evaluation of territorial threats is a fundamental source of knowledge to deal with future emergencies.

Physically based dynamic run-out modelling for quantitative debris flow risk assessment: a case study in Tresenda, northern Italy

Quantitative landslide risk assessment requires information about the temporal, spatial and intensity probability of hazardous processes both regarding their initiation as well as their run-out. This is followed by an estimation of the physical consequences inflicted by the hazard, preferentially quantified in monetary values. For that purpose, deterministic hazard modelling has to be coupled with information about the value of the elements at risk and their vulnerability. Dynamic run-out models for debris flows are able to determine physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk can suffer an impact. These results can then be applied for vulnerability and risk calculations. Debris flow risk has been assessed in the area of Tresenda in the Valtellina Valley (Lombardy Region, northern Italy). Three quantitative hazard scenarios for different return periods were prepared using available rainfall and geotechnical data. The numerical model FLO-2D was applied for the simulation of the debris flow propagation. The modelled hazard scenarios were consequently overlaid with the elements at risk, represented as building footprints. The expected physical damage to the buildings was estimated using vulnerability functions based on flow depth and impact pressure. A qualitative correlation between physical vulnerability and human losses was also proposed. To assess the uncertainties inherent in the analysis, six risk curves were obtained based on the maximum, average and minimum values and direct economic losses to the buildings were estimated, in the range of 0.25–7.7 million €, depending on the hazard scenario and vulnerability curve used.

Debris Flows Risk Analysis and Direct Loss Estimation: the Case Study of Valtellina di Tirano, Italy

Landslide risk analysis is one of the primary studies providing essential instructions to the subsequent risk management process. The quantification of tangible and intangible potential losses is a critical step because it provides essential data upon which judgments can be made and policy can be formulated. This study aims at quantifying direct economic losses from debris flows at a medium scale in the study area in Italian Central Alps. Available hazard maps were the main inputs of this study. These maps were overlaid with information concerning elements at risk and their economic value. Then, a combination of both market and construction values was used to obtain estimates of future economic losses. As a result, two direct economic risk maps were prepared together with risk curves, useful to summarize expected monetary damage against the respective hazard probability. Afterwards, a qualitative risk map derived using a risk matrix officially provided by the set of laws issued by the regional government, was prepared. The results delimit areas of high economic as well as strategic importance which might be affected by debris flows in the future. Aside from limitations and inaccuracies inherently included in risk analysis process, identification of high risk areas allows local authorities to focus their attention on the “hot-spots”, where important consequences may arise and local (large) scale analysis needs to be performed with more precise cost-effectiveness ratio. The risk maps can be also used by the local authorities to increase population’s adaptive capacity in the disaster prevention process.

Methods for the Characterization of the Vulnerability of Elements at Risk

Risk assessment is the process of determining the likelihood or threat of a damage, injury, liability, loss, or other negative occurrence that is caused by external or internal vulnerabilities and that may be neutralized through preventive action. More precisely, risk assessment is the systematic prospective analysis aimed at defining, as quantitatively as possible, the potential loss of life, personal injury, economic loss, and property damage resulting from natural and/or anthropogenic hazards, by assessing the exposure and vulnerability of people and property to those hazards. The risk assessment procedure, developed in the Mountain Risks project, is based on the following five steps: (1) Identification and analysis of the specific types of hazards that could affect a territory and its community; (2) Definition of the spatial and temporal likelihood of the damaging events considered in the analysis as well as their magnitude; (3) Inventory of the assets and study of the social and economic features of the study areas; (4) Assessment of vulnerability, evaluating all the hazard consequences for each dimension composing the systems at risk (physical/functional, economic, socio-cultural, ecological/environmental and; political/institutional); (5) Evaluation of the prospective cost of damage or costs avoided through mitigation strategies. Vulnerability assessment plays a crucial role both in ‘translating’ the assessed level of hazard into an estimated level of risk and in providing leading information in mitigation planning processes and emergency management strategies. Under this perspective, it is really difficult, or even impossible, to address risk assessment without assessing vulnerability first and it appears unquestionable that a multi-disciplinary approach is required in vulnerability assessment studies. In this section, the different components (dimensions) of vulnerability are analyzed, both theoretically and practically, and then different methodological approaches, applications and solutions are provided.

ASCHFLOW : a dynamic landslide run-out model for medium scale hazard analysis

BackgroundLandslides hazard analyses entail a scale-dependent approach in order to mitigate accordingly the damages and other negative consequences at the respective scales of occurrence. Medium or large scale landslide run-out modelling for many possible landslide initiation areas has been a very difficult task in the past. This arises from the inability of the run-out models to compute the displacement with a large amount of individual initiation areas as it turns out to be computationally strenuous. Most of the existing physically based run-out models have difficulties in handling such situations. For this reason, empirical methods have been used as a practical mean to predict landslides mobility at a medium scale (1: 10,000 to 1: 50,000). They are the most widely used techniques to estimate the maximum run-out distance and affected zones not only locally but also regionally. In this context, a medium scale numerical model for flow-like mass movements in urban and mountainous areas was developed.Results“AschFlow” is 2-D one-phase continuum model that simulates, the entrainment, spreading and deposition process of a landslide or debris flow at a medium scale. The flow is thus treated as a single phase material, whose behavior is controlled by rheology (e.g., Voellmy or Bingham). The model has been developed and implemented in a dynamic GIS environment. The deterministic nature of the approach makes it possible to calculate the velocity, height and increase in mass by erosion, resulting in the estimation of various forms of impacts exerted by debris flows at the medium scale.ConclusionsThe developed regional model “AschFlow” was applied and evaluated in well documented areas with known past debris flow events. The “AschFlow” model outputs can be considered as an indication of areas possibly affected with a defined intensity for one or more landslide events. From a user perspective the “AschFlow” model can be seen as a standalone model which can be utilized for a first assessment of potentially impact areas.

Methods for Debris Flow Hazard and Risk Assessment

Debris flow events yield a threat to different components of mountainous environments not only as the result of the process evolution but of the interaction with human systems and their coupled vulnerabilities. A variety of models exists for characterising the hazard that the different mass-flow phenomena present. In the case of dynamic run-out models, they are able to forecast the propagation of material after the initial failure and to delineate the zone where the elements at risk will suffer an impact with a certain level of intensity. The results of these models are an appropriate input for vulnerability and risk assessments. An important feature of using run-out models is the possibility to perform forward analyses and forecast changes in hazards. However, still most of the work using these models is based on the calibration of parameters doing a back calculation of past events. Given the number of unknown parameters and the fact that most of the rheological parameters cannot be measured in the laboratory or in the field, it is very difficult to parameterize the run-out models. For this reason the application of run-out models is mostly used for back analysis of past events and very few studies attempts to achieve a forward modelling with the available run-out models. A reason for this is the substantial degree of uncertainty that still characterizes the definition of the run-out model parameters. Since a variety of models exists for simulating mass-flows and for identifying the intensity of the hazardous phenomena, it is important to assess these models, perform a parameterization and reduce their uncertainties. This will enable to improve the understanding to assess the hazard and will provide the link with vulnerability curves that will lead eventually to generate risk curves and quantify the risk.

The Importance of the Lessons Learnt from Past Disasters for Risk Assessment

Within the Mountain Risk Project, the study area of the Consortium of Municipalities of Valtellina di Tirano (Italian Alps), has been selected in order to collect both kinds of knowledge, scientific and local, and to correlate it to the levels of preparedness and perceived risk of the population. A quantitative survey was performed using a comprehensive questionnaire to evaluate several aspects related to the response capacity. In the meantime available historical information about natural hazards (landslides and floods) and consequent disasters have been collected and organized in a comprehensive database designed with the aim of using such data for hazard estimation and definition of risk scenarios as a basis for Civil Protection planning and emergency management purposes.