Wood storage in three mountain streams of the Southern Andes and its hydro‐morphological effects

This study analyses large wood (LW) storage and the associated effects on channel morphology and flow hydraulics in three third-order mountain basins (drainage area 9–12 km2) covered in old-growth Nothofagus forests, ranging from the temperate warm Chilean Andean Cordillera to the sub-Antarctic Tierra del Fuego (Argentina). Amount, characteristics and dimensions of large wood (>10 cm diameter, >1 m long) were recorded, as well as their effects on stream morphology, hydraulics and sediment storage. Results show that major differences in LW abundance exist even between adjacent basins, as a result of different disturbance histories and basin dissection. Massive LW volumes (i.e. >1000 m3 ha−1) can be reached in basins disturbed by fires followed by mass movements and debris flows. Potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams, with a gross sediment volume stored behind wood dams of around 1000 m3 km−1, which appears to be of the same order as the annual sediment yield. Finally, the presence of wood dams may increase flow resistance by up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd.

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