Abstract
Debris floods are mass movement events which are usually triggered by intense short duration rainfall events. They often occur on alluvial fans in an alpine environment. Due to their sever geohazard potential they pose a serious threat to infrastructure and human life. To minimize their threat understanding of their past magnitude occurrence is crucial. Dendrogeomorphology has proven to be a highly useful method in studies of past slope mass movements. However, establishing magnitudes of past events has so far been based on indirect indicators, such as: spatial distribution of affected trees, characteristics of tree injures and sedimentological records. In this study we present a method that directly estimates the magnitudes of past debris flood events on an alluvial fan using dendrogeomorphological and meteorological data sets. The studied dendrogeomorphological data set is based on tree-ring series from 105 sampled trees (Picea abies, Abies alba and Larix decidua) growing on an active alluvial fan in a typical alpine environment of the Julian Alps in NW Slovenia. Based on sudden growth suppression thirteen debris flood events since 1903 were dated. Meteorological data from a nearby meteorological station was used to determine the exact triggering meteorological event for ten events. Comparing the It index of affected trees and calculated return period of an individual triggering meteorological event established the magnitude of debris flooding. We showed that more trees are affected at high return period/intensity of the triggering meteorological event and therefore higher magnitudes of debris floods. This research presents the first combined use of dendrogeomorphological and meteorological data sets for magnitude estimation of historic debris flood events which could be successfully applied in similar environments.
Highlights
In the Alpine environments the majority of sediment supply on alluvial fans is mobilised during major rainfall events (Harvey, 2012)
The number of sampled trees available for the analysis at a given year and the number of trees affected by growth suppressions for the RgL group are present in the Fig. 3
Based on the amount of growth suppressions at the site of the Rančev graben alluvial fan only a low magnitude debris flood event occurred. As these potentially triggering meteorological events took place outside the growing season, predominantly in the year 2000, growth suppressions recorded in the tree-ring record of 2001 can be attributed to the causes of the low magnitude debris flooding in autumn 2000
Summary
In the Alpine environments the majority of sediment supply on alluvial fans is mobilised during major rainfall events (Harvey, 2012). In order to minimize the debris flood hazard risk data on their past magnitude, timing and location is needed Such information can be used in hazard mapping and spatial planning, as it can provide potential flow directions of future debris floods, areas of possible channel avulsions, and areas vulnerable to debris flood events (Jakob and Bovis, 1996; Skermer and VanDine, 2005; Bowman, 2019). This is quite problematic, because historic data
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
