Angelo Cavallin

Databases and GIS for landslide research in Europe

Abstract Within the project “The Temporal occurrence and forecasting of landslides in the European Community” a review of the use of databases and GIS for landslide research has been accomplished. It shows a high potential of these techniques in storing spatial and temporal landslide data (landslide inventories) and in applying different modelling approaches to landslide hazard assessments at various scales. There are three major strategies in European landslide research using GIS and database technologies. At medium and broad scales different combinations of landslide data with factor maps (e.g. slope angle, lithology and geomorphological units) lead to static susceptibility and hazard assessments, which allow probability evaluations for future landslide occurrences. At local scales process models to simulate trajectories of paths for slope processes and deterministic slope stability models are in use. In landslide frequency analysis, temporal database information are correlated with recent and historical triggering factors (e.g. precipitation and precipitation indices) to calculate temporal probabilities for landslide forecasting. However, despite encouraging progress in applying computer technologies in European landslide research, the potential of these tools is still largely untested. Furthermore, it is clear that sophisticated technology cannot replace field work, interdisciplinary research strategies, and critical testing of the reliability of the model results.

Three dimensional hydrogeological modelling application to the Alverà mudslide (Cortina d’Ampezzo, Italy)

Within the framework of Geographic Information System (GIS), the distributed three-dimensional groundwater model MODFLOW has been applied to evaluate the groundwater processes of the hydrogeological system in the Alvera mudslide (Cortina dAmpezzo, Italy; test site in the TESLEC Project of the European Union). The application of this model has permitted an analysis of the spatial distribution of the structure (DTM and landslide bottom) and the mass transfer elements of the hydrogeological system. The field survey suggested zoning the area on the basis of the recharge, groundwater fluctuation and drainage system. For each zone, a hydraulic conductivity value to simulate the different recharge and the drainage responses has been assigned. The effect of rainfall infiltration into the ground and its effect on the groundwater table, with different intensity related to different time periods, have been simulated to reproduce the real condition of the area. The applied model can simulate the positive fluctuations of the water table on the whole landslide, with a different response of the hydrogeological system in each zone. The spatial simulated water level distribution is in accordance with the real one, with very small difference between them. The application of distributed three-dimensional models, within the framework of GIS, is an approach which permits data to be continually updated, standardised and integrated.

3D reconstruction of the multi-layer aquifer in a Po Plain area

Lo studio espone e descrive un metodo per la creazione di un modello fisico pienamente tridimensionale relativo agli acquiferi presenti all’interno di un’area compresa tra i fiumi Adda ed Oglio, partendo dall’inserimento e dalla creazione sia di superfici geologiche tratte da letteratura che create ex-novo a partire da dati stratigrafici e da studi geologici. Una volta definite e ricostruite le principali geometrie dei corpi geologici e sedimentari, a partire dalle quali e ricostruita la griglia stratigrafica di calcolo, lo studio propone una metodologia di ricostruzione della distribuzione tessiturale dei sedimenti (suddividendoli in termini fini, medi e grossolani), precedentemente utilizzata dal gruppo di ricerca di idrogeologia del DISAT (Dipartimento di Scienze dellAmbiente e del Territorio e Scienze della Terra - Universita degli Studi di Milano Bicocca) che integra una grande quantita di dati disponibili, un buon dettaglio e un aggiornamento continuo delle informazioni. Le ricostruzioni create tramite questa procedura automatizzata (che risulta pero molto flessibile ed applicabile per ogni acquifero, purche si disponga di sufficienti dati e di una sufficiente conoscenza geologica) si trovano in accordo con quanto riportato in letteratura, sia per quanto riguarda l’eterogeneita spaziale orizzontale dei depositi (da Nord a Sud e da Ovest ad Est) sia per quanto riguarda l’eterogeneita spaziale verticale (depositi continentali superficiali contro i depositi profondi di origine marina). Lo studio evidenzia come una ricostruzione della distribuzione tessiturale sia importante per un duplice motivo: da un lato permette di comprendere meglio le dinamiche deposizionali caratteristiche di una certa area studio, dall’altro permette, in un secondo momento, di stimare le proprieta idrogeologiche ed idrauliche dei depositi a fini di implementazione in modelli di flusso.

Banca dati idrogeologica TANGRAM©: strumento per elaborazioni quantitative di dati per la valutazione delle acque sotterranee - The hydrogeological well database TANGRAM©: a tool for data processing to support groundwater assessment

At the Department of Earth and Environmental Sciences of the University of Milano-Bicocca (DISAT-UNIMIB), a hydrogeological well database, called TANGRAM©, has been developed and published on line at www.TANGRAM.samit.unimib.it, developing an earlier 1989 DOS version. This package can be used to store, display, and process all data related to water wells, including administrative information, well characteristics, stratigraphic logs, water levels, pumping rates, and other hydrogeological information. Currently, the database contains more than 39.200 wells located in the Italian region of Lombardy (90%), Piedmont (9%) and Valle d’Aosta (1%). TANGRAM© has been created both as a tool for researches and for public administration’s administrators who have projects in common with DISAT-UNIMIB. Indeed, transferring wells data from paper into TANGRAM© offers both an easier and more robust way to correlate hydrogeological data and a more organized management of the administrative information. Some Administrations use TANGRAM© regularly as a tool for wells data management (Brescia Province, ARPA Valle Aosta). An innovative aspect of the database is the quantitative extraction of stratigraphic data. In the part of the software intended for research purposes, all well logs are translated into 8-digit alphanumeric codes and the user composes the code interpreting the description at each stratigraphic level. So the stratigraphic well data can be coded, then quantified and processed. This is made possible by attributing a weight to the digits of the code for textures. The program calculates the weighted percentage of the chosen lithology, as related to each individual layer. These extractions are the starting point for subsequent hydrogeological studies: well head protection area, reconstruction of the dynamics of flow, realization of the quarry plans and flux and transport hydrogeological models. The results of a two-dimensional distribution of coarse, medium and fine sized material in the first 80 meters of depth are presented here for a study area located within the Province of Brescia (Italy).

GIS Potential for Regional and Local Scale Groundwater Hazard Assessment

We present two applications of GIS technology to groundwater studies aimed at the assessment of pollution risk. The first study were carried out over the entire Po Plain, an highly developed area that depends entirely on groundwater for water supply; the second regarded a small portion of it. The research aimed at producing maps of the factors controlling groundwater-pollution risk to support decision-making for an effective land planning and management. The proposed risk-assessment procedure considers factors related to natural vulnerability, hazard due to human activities, and costs resulting from pollution. To evaluate existing hazard, a census was carried out over a test area. Industrial, agricultural and quarrying sites were mapped, and industrial activities were divided into four groups according to national waste type regulations. A land information system was used to store and manage the vast amount of spatial data and to prepare thematic output maps.

Estimation of Information Loss When Masking Conditional Dependence and Categorizing Continuous Data: Further Experiments on a Database for Spatial Prediction Modelling in Northern Italy

Prediction patterns are generated using different data sets from a database for landslides hazard in northern Italy. A direct supporting pattern of the distribution of 28 complex landslides was previously used to obtain their spatial relationships with five categorical indirect supporting patterns representing the spatial context of the landslides: geology, land use, and permeability in addition to internal relief and slope, the latter two categorized into five classes. The five indirect supporting patterns were selected to minimize the effects of conditional dependence on prediction patterns by a Weight-of-Evidence model. The same set of patterns is reanalysed applying the Empirical Likelihood Ratio model using also uncategorized continuous supporting patterns: aspect, curvature, and digital elevation, in addition to internal relief and slope. The resulting prediction patterns are compared in terms of prediction rates and target-uncertainty patterns.