Debris flow hazard assessment on torrential fans

V disertaciji je obravnavana problematika ocenjevanja nevarnosti zaradi delovanja drobirskih tokov na hudourniških vršajih. Glavni poudarek raziskave je problematika, ki se je v preteklih raziskavah izkazala za težavno in sicer gre za klasifikacijo hudourniških območij, iz katere bi bilo razvidno ali je izbrano hudourniško območje nagnjeno k delovanju drobirskih tokov. Na izbranem nevarnem območju pa ocenjevanje magnitude potencialnega drobirskega toka in določeni deli postopka matematičnega modeliranja gibanja drobirskih tokov, predvsem povezani z reološkimi karakteristikami mešanice in vplivom topografskih podatkov o terenu, ki so osnova za izdelavo modela. Disertacija se v prvem delu osredotoča na določanje parametrov hudourniških območij in analizo različnih metod za njihovo klasificiranje. Na podlagi analize večih metod je predlagana klasifikacija na nevarna, prehodna in nenevarna hudourniška območja, ki je predstavljena na izbranem testnem območju. V analizo smo vključili v tujini in Sloveniji razvite metode in orodja s tega področja. V drugem delu disertacije je poudarek na ocenjevanju magnitude potencialnega drobirskega toka z modelom LS-Rapid, ki je uporabljen na hudourniškem območju Bele, kjer je prikazana uporaba modela za določanje nestabilnih območij na nivoju celotnega hudourniškega območja. Uporaba modela za ocenjevanje količine sproženega materiala pa je prikazana na primeru plazu Stože, kjer je izvedena analiza plazu, ki se je sprožil novembra 2000. Za določanje parametrov modela LS-Rapid, ki jih za potencialne zemeljske plazove ni možno natančno določiti, smo podali napotke o določanju mejnih vrednosti, ki so uporabne za modeliranje potencialnih zemeljskih plazov. Zaradi modeliranja gibanja drobirskih tokov na hudourniških vršajih so bile za potrebe določanja reoloških karakteristik drobirskega materiala izvedene raziskave v geomehanskem laboratoriju na vzorcih materiala, ki smo ga odvzeli na izvornem mestu plazu Stože. Na podlagi testiranja smo podali navodila, kako za model Flo-2D določati reološke karakteristike potencialnih drobirskih tokov. Prikazana je tudi analiza vpliva različnih topografskih podatkov na rezultate modeliranja gibanja drobirskih tokov. Uporabljeni so bili tako komercialni kot tudi javni topografski podatkipredvsem uporabni so se izkazali najnovejši LiDAR-ski podatki. Na podlagi lastnih rezultatov in predlogov je na koncu disertacije podan predlog metodologije za ocenjevanje nevarnosti zaradi delovanja drobirskih tokov na hudourniških vršajih in usmeritve za nadaljnje delo.PhD thesis deals with debris flow hazard assessment on torrential fans. Its main focus is on the known problems pointed out with the already performed research, such as is the way of preliminary classification of torrential catchments to determine those, which are prone to trigger debris flows, furthermore, how to estimate magnitudes of potential debris flows triggered in these torrential catchments, and finally, open questions with regard to debris-flow mathematical modeling on torrential fans, especially their rheological characteristics to be used in mathematical models and how topography influences modelling results. In the first part, we focus on geomorphological parameters of torrential catchments and various methods for classification of torrential catchments prone to debris-flow triggering. Based on analysis of the selected methods, a new classification method was proposed for classification of debris-flow prone catchments, transitional catchments and catchments with no debris- flow hazard. This new method was then tested in selected torrential catchments in Slovenia. For debris-flow magnitude assessment, we applied the LS-Rapid triggering model. With its application in the Bela torrential catchment (NW Slovenia), we could identify several active landslides and potentially unstable areas, which could under unfavorable conditions turn into active landslides and trigger debris flows. A detailed study and debris-flow modeling was then carried out on the Stože landslide (NW Slovenia), which was triggered in November 2000. For debris-flow model parameters, which cannot be determined with sufficient reliability without analyzing soil samples in detail in a geomechanical laboratory, we proposed an estimation of their limit values, which can be used for potential landslide modeling. Soil samples were taken from the Stože landslide source area for testing in a geomechanical laboratory. In this way, rheological properties of a potential debris flow could be determined, and then used in debris-flow mathematical routing model on a torrential fan. Based on our own laboratory study, and additionally testing of the Flo-2D model, we proposed instructions how to assess potential debris-flow rheological characteristics. Furthermore, with the Flo-2D model we tested the influence of different topographical datasets on debris-flow modeling results. We applied different publicly available topographical data and commercial LiDAR data to develop DEM with different resolutions. The debris-flow modeling results, obtained by using new public available LiDAR based data and the Flo-2D model, turned out to be very /plausible. Finally, we comprise single steps described in previous sections into a new methodology for debris-flow hazard assessment on torrential fans, culminating in the debris-flow hazard mapping. The PhD thesis ends up with some recommendations for further research in this field