Riparian Forests and large woody Debris Supply in Mountain Torrents
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log jam in a torrent
reach
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Introduction
Dead wood
generally is recognized as an important ecological and structural component of
torrents. However, during flood events, for example in August 2005 in
Switzerland, driftwood often cause serious problems such as log jams at bridges
or culverts which frequently have the effect of overbank flooding and
sedimentation with a high damage potential.
Several
mitigation measures exist to reduce driftwood problems: 1) engineering
measures, e.g. retention of driftwood, 2) removal of large woody debris (LWD)
or cutting LWD to smaller pieces which are less dangerous in connection with
log jams, and 3) management of riparian forests with the objective to reduce
LWD input in the torrent reaches.
For
economical reasons, management and utilization of riparian forests are more and
more extensified or completely given up. A research project was set up at the
WSL with the aim to investigate certain aspects of the effects of riparian
forest management on LWD supply in torrents.
Methods
A total of
10 torrents with different types of riparian forests are investigated in
different regions of Switzerland. In each torrent a 1000 m long
study reach is selected and a complete LWD inventory is conducted. LWD is
defined as pieces of wood ≥ 0.1 m in diameter and ≥ 1.0 m in length located
within the channel. In addition, topographical parameters, hillsolpe processes
and comprehensive characteristics of the forest stands adjacent to the torrents
are collected. The relations between certain stand characteristics of the
riparian forests and the amount of LWD in the specific torrent reaches are
expected be the basis for discussions concerning the optimal conditions of the
forests stands and the management strategies to achieve the designated stand
characteristics.
Results
The results of the investigation are described in
the project-report Rickli and Bucher (2006).
Publikationen
und Links
Rickli,
C. und Bucher, H.U., 2006: Einfluss ufernaher Bestockungen auf das
Schwemmholzvorkommen in Wildbächen. Projektbericht zuhanden des Bundesamtes für
Umwelt BAFU. Eidg. Forschungsanstalt WSL. 94 S. (PDF-File)
Rickli, C., 2009: Schwemmholz in Wildbächen. In: Forstliche Arbeitsgruppe Naturgefahren FAN
(ed) Wildbacheinzugsgebiete - Prozesse, Gefahren und Schutzmassnahmen.
FAN-Tagung September 2009. 16 S. (PDF-File)
Rickli,
C. und Bucher, H.U., 2006: Schutzwald und Schwemmholz in
Wildbacheinzugsgebieten. FAN-Agenda 1/06: 17-20. (PDF-File)
Waldner
P., Rickli C., Köchli D., Usbeck T., Schmocker L., Sutter F., 2007.
Schwemmholz. In: Bezzola G., Hegg C. (eds.), Ereignisanalyse Hochwasser 2005,
Teil 1 - Prozesse, Schäden und erste Einordnung. Bundesamt für Umwelt BAFU,
Bern und Eidg. Forschungsanstalt für Wald, Schnee und Landschaft WSL,
Birmensdorf, p. 181-193. pdf: http://www.bafu.admin.ch/publikationen/index.html?action=show_publ&lang=de&id_thema=1&series=UW&nr_publ=0707
Zusammensetzung
ausgewählter Schwemmholzablagerungen der Unwetter vom 19.-23. August 2005: http://www.wsl.ch/forschung/forschungsprojekte/schwemmholzablagerungen/index_DE
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