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J7-8273: Recognition of potentially hazardous torrential fans using geomorphometric methods and simulating fan formation

Project Title Recognition of potentially hazardous torrential fans using geomorphometric methods and simulating fan formation
Project team:

UL FGG:
Matjaž Mikoš
Nejc BezakMarko KomacKlemen Kozmus TrajkovskiMatej MačekDušan PetrovičTomaž PodobnikarJošt Sodnik

Geological Survey of Slovenia:
Mateja Jemec Auflič
Bogomir CelarcPetra Jamšek RupnikJernej JežTina Peternel

Duration:

36 months

May 1, 2017 – April 30, 2020

Project Code: ARRS J7-8273
Lead partner: University of Ljubljana, Faculty of Civil and Geodetic Engineering
Project leader: Professor Matjaž Mikoš, PhD (UL FGG)
Project partner:

Geological Survey of Slovenia, Ljubljana

Source of finance:
Key words: geomorphology, digital terrain model, alluvial fans, debris flows, simulations, laboratory experiments, soil mechanics, rheological properties

Description

The project will focus on the determination of the shapes of alluvial (torrential) fans, especially detecting those that are shaped by debris flows. It will focus on the use of geomorphometric methods, and therefore the digital elevation model (DEM) and the digital surface model (DSM). We assume that on the basis of good knowledge of shapes, textures, and other characteristics of alluvial fan surfaces (presented with characteristic spatial variables) it is possible to identify significant differences between fans formed by the debris flows in their catchment areas, and other torrential fans that have a lower risk of a sedimentary event that could endanger the built environment and human life. The identified alluvial fans that will be evaluated as dangerous and with a potential for debris flows in their catchment area will be checked by using a mathematical model to simulate the triggering and movement of debris flows from their source areas to the deposition zone (i.e. fans), and compared to the existing forms of fans.

Rainfall, earthquakes, reckless excavation/construction use of material, and inappropriate land use have a decisive impact on the processes of slope mass movements. Among the various types, we will focus on alluvial fans and debris flows in their catchment areas. Debris flows are, beside rock falls, the most destructive type of slope processes, because they cannot be easily predicted in terms of the time of triggering, place of action, their severity (magnitude), high-flow velocities, and their capability to move over large distances.

Main goals

The main goal of the research project is the automatic determination and classification of fans, with an emphasis on their potential for the development of debris flows in their catchment areas. The basic hypothesis is that by using a high-resolution DEM or DSM, and the characteristic spatial variables, it is possible to distinguish between the fans caused by debris flows and the alluvial fans where debris flows are not expected and where only common torrential processes take place. Moreover, it is assumed that with such an approach the potentially dangerous fans can be distinguished from the more stable ones. In connection with the latter it is also assumed that we can identify potential areas of landslide occurrence.

The originality of the proposed project stems from the comparison of two completely different methodological approaches, i.e. the geomorphometrical analyses and the simulations of fan formation on the basis of mathematical modelling to simulate the triggering and movement of debris flows. The originality of the results is particularly manifested in the following:

  1. high quality in determining the type of fans, even individual parts of fans;
  2. accuracy – the resolution of the survey results of up to 1 m (completely different ‘dimensions’ in the modelling, as other applications reach a maximum resolution of 5–10 m);
  3. a geomorphometric approach by combining geographic information systems, remote sensing, and image processing methods;
  4. innovative indicators based on determining specific areas and eliminating atypical areas on the basis of a precise definition of the different types of fans in relation to debris and torrential flows;
  5. taking into consideration the characteristics of fan surroundings;
  6. taking into account various quality parameters of the input data, i.e. in this case DTMs and DSMs, in order to set the model parameters;
  7. the sensitivity analysis.

When producing the hazard map of debris flows we can integrate new elements, such as automatic determination of torrential fans, laboratory analysis of the rheological properties of soils, and testing different 2D models of debris flows triggering and movement, as typical types of mass movement on the slopes. The proposed project is a decisive step in this direction. The methodological approach, methods, and quality of the expected results will set an example for other parts of the world.

Project work packages

WP I Project management (II, 2017 to I, 2020):
Task (1) Interim reports and a final report;
Task (2) Addressing practical issues arising from the project
WP II (A) Spatial data acquisition and pre-processing (II, 2017 to III, 2017):
Task (1) DEM and DSM acquisition, quality control, gross and systematic error removal, improving quality;
Task (2) Obtaining other information about the fans (based on fieldwork, geological maps, etc.);
Task (3) Data homogenization.
WP III (B) Geomorphometric analysis for fan determination (IV, 2017 to IV, 2019):
Task (1) Classic geomorphological fan mapping in selected areas, and field sedimentological inventory to define the fan’s genesis; selection of key geomorphological characteristics of certain fan types;
Task (2) Processing variables (factors) for geomorphometric analysis;
Task (3) Analysis/modelling with spatial data, rheological information, and other relevant descriptive information;
Task (4) Comparison of the classical and developed methodology results.
WP IV (C) Applying the mathematical model to simulate triggering and movement of debris flows (I, 2018 to I, 2020):
Task (1) Application of 2D debris-flow models (Flo2D, LS-RAPID);
Task (2) Analysis using the new research method (greater Viscometer CONTEC) on soil samples;
Task (3) A comparison of both groups of analysis and sensitivity analysis;
Task (4) Comparison of geomorphometric analysis and simulations of the formation of fans.
WP V Dissemination:
(1) Methods of the research work;
(2) Results of the research work.