Geographia Polonica (2007) vol. 80, iss. 1

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The Significance of Trees and Coarse Woody Debris in Shaping the Debris Flow Accumulation Zone (North Slope of the Babia Gora Massif, Poland)

Marcin Matyja

Geographia Polonica (2007) vol. 80, iss. 1, pp. 83-102

Abstract

In August 2002 a debris flow with a total length of 760m occurred on the northern slopeof Poland’s Mount Babia Góra. The deposition zone stretched across a distance of 280m layingentirely within upper montane-zone spruce forest. The objective of this study was to determinethe influence of trees and coarse woody debris (CWD) on transport and deposition processeswithin the deposition zone, and to estimate the length of time during which CWD influencesslope processes. The greatest influence on deposition processes was found to be exerted by thepresence of CWD lying perpendicular to the debris flow axis. The 53% of CWD laying in thepath of debris flow formed steps intercepting deposits and slowing down surface runoff. Theimpact of standing trees on depositional processes is seen to be of secondary importance. Onthe other hand, piles of debris more than 1m in height on the up-slope side of trees are stableenough to change the direction of flow. Also the larger CWD is able to change or deflect thepath of debris flow. The relative decrease in velocity caused by trees and CWD ranges from 6%to 53%. This study shows that, in the case of low-energy debris flow, CWD and trees can significantlychange the flow morphology, decreasing its velocity and range, and increasing sinuosity(Si=1.3). The CWD enhances the roughness of the slope surface and restricts the delivery ofdeposits to the valley bottom. Dating of CWD shows that its decay time in aerial conditions is100–150 years.

Keywords: dendrogeomorphology, debris flow, CWD, slope evolution, timberline, Babia Góra, Poland

Marcin Matyja, Faculty of Earth Sciences, University of Silesia, ul. Będzinska 60, 41-200 Sosnowiec, Poland