Large wood recruitment and mobility in steep mountain streams of contrast European landscapes

Abstract

We present a comparative study of large wood (LW) mobility in two steep channels (0.06<S<0.20) of contrast European landscapes during major hydro-geomorphic events of similar magnitude. We investigated a headwater perennial stream draining Central European medium-high mountain relief (the Klepáčský, Hrubý Jeseník Mts, Czech Republic; A≤2.5 km2) and an ephemeral Mediterranean steep stream (the Sfakiano Gorge, Crete, Greece; A≤52 km2). Both studied hydro-geomorphic events were partially accompanied by debris-flood or debris-flow character of sediment transport including significant content of LW. The minimal estimations of transported LW volume were 71.3 m3 along 1.7 km long reach in the Klepáčský and 49.4 m3 along 4 km long reach in the Sfakiano Gorge. Despite completely different characters of hydrologic regimes, riparian zones and valley confinement settings, living trees in the valley floor played crucial role in wood deposition and development of large jams in both environments. The trees living in the valley floor were the main source of LW in the studied Mediterranean channel, whereas long-term LW recruitment from very steep hillslopes or rock cliffs was quite negligible. On the other hand, previous windstorms in the Klepáčsky caused notable delivery of LW from adjacent hillslopes and LW recruitment by bank erosion occurred only at spatially-limited semi-confined parts of the valley.