Original paper
Evaluating sediment dynamics in tributary trenches in an alpine catchment (Johnsbachtal, Austria) using multi-temporal terrestrial laser scanning
Rascher, Eric; Sass, Oliver
Zeitschrift für Geomorphologie, Supplementary Issues Volume 61 Supplementary Issue 1 (2017), p. 27 - 52
published: Apr 1, 2017
DOI: 10.1127/zfg_suppl/2016/0358
ArtNo. ESP023106101002, Price: 29.00 €
Abstract
The linkage of landscape units by sediment transport and its degree is among the most im- portant factors during smaller time scales (several years to decades) determining the sediment yield of a catchment. In our study area (Johnsbach Valley, Styria, Austria), huge amounts of sediments are available due to surrounding brittle dolomite bedrock which is a challenge for river management. In the context of a renaturation project, it is important to understand where the sediments derive from and how they move through the system. In our study, we investigated several tributary trenches of the Johnsbach River to clarify the sediment dynamics and the degree of coupling to the main creek. Terrestrial Laser Scans from several points were carried out half-yearly for approximately two years between summer 2013 and autumn 2015. The results show that if only the first and last survey in each sub-area are considered, the amounts of erosion and accumulation are underestimated at least by a factor of two compared to the full dataset of 4 – 5 scans, because erosion and deposition in different periods may be cancelled out. This applies for both erosion and deposition. Accordingly, the calculated surface changes are minimum amounts because more surveys would have yielded higher rates. According to the 2-yr period, ~7400 m3 yr–1 were eroded in the surveyed areas and ~9900 m3 yr–1 were deposited. Only a minor portion of ~650 m3 yr–1 was delivered to the Johnsbach River. At two sub-sites (Unnamed V and Langgries), coupling to the river was evident while at one site (Gseng) there was no coupling to the main creek at all. At Langgries, erosion occurred in the upper area of a long gravel field and transport and deposition prevailed lower down; the transport into the Johnsbach River obviously occurred discontinuously in batches. In the areas Langgries and Gseng there is strong evidence that the rates of erosion and deposition are still governed by gravel mining 1– 2 decades ago.
Keywords
digital elevation model • connectivity • seasonal patterns • sediment dynamics • alpine catchment