SPATIO-TEMPORAL SPECIFICS OF HYDRO-GEOMORPHIC PROCESSES IN HEADWATER PARTS OF MID-MOUNTAINS RECONSTRUCTED BASED ON TREE-RING DATA: A CASE STUDY FROM THE HRUBY JESENIK MOUNTAINS (CZECH REPUBLIC)

摘要

Debris flows and debris floods cause frequent geomorphic hazards, even in the mid-mountains of Central Europe. In the Hruby Jesenik Mountains (Eastern Sudetes, Czech Republic), strong anthropogenic interventions have created specific conditions for erosion, transport and accumulation of material released by debris flow/flood events. We present a detailed spatio-temporal reconstruction of the hydro-geomorphic process activity in two adjacent sub-catchments using dendrogeomorphic methods applied to the steep, narrow channels. An analysis of 172 sampled trees [Picea Abies (L.) Karst.] revealed 14 torrential events since 1943 in the Klepa. csky stream sub-catchment and 11 events since 1897 in the Keprnicky stream sub-catchment. Identical events were identified in 1965, 1991, 1997, 2002 and 2010. The event return periods were comparable with return periods from the foothills of the European Alps. A higher frequency of events in the first sub-catchment may be caused by the presence of a deep-seated landslide, steeper slopes and a higher susceptibility to shallow slope deformations. Different spatial patterns of events were presented using the Kernel Density analysis in ArcMap 10.1. Clusters of affected trees in the valley floor during the last decades may be due to increased erosion below the check dams and increased accumulation above. The presence of check dams and slope stabilization works since the 1960s has mitigated the processes in several gullies, but due to the current non-interventional management, the risk of their damage is increasing, particularly when increased activity is observed in the adjacent unprotected gullies.