POTENTIAL LARGE WOODY DEBRIS RECRUITMENT DUE TO LANDSLIDES,BANK EROSION AND FLOODS IN MOUNTAIN BASINS: A QUANTITATIVE ESTIMATION APPROACH

In‐depth knowledge of the fluvial corridor and surrounding slopes and forest vegetation is needed for a better understanding of wood recruitment or inputs to rivers. The information available in Central Spain on hydrogeomorphic processes and forest distribution enabled the evaluation of potential wood recruitment from three sources: landslides, bank erosion and fluvial transport during floods on a regional scale. The method presented here is based on a geographical information system (GIS) and on multi‐criteria and multi‐objective assessment using fuzzy logic principles. First, the areas potentially affected by landslides, bank erosion and floods were delineated, and a vegetation analysis was carried out to obtain the vegetation resistance and forest density. Several scenarios were proposed based on the process frequency and severity. Using this method, the volume of potentially available wood can be estimated for each scenario. Fourteen river basins in populated areas were selected for further analyses and field survey. Observations of in‐stream storage of woody debris and tree disturbances were used to interpret the woody debris dynamics throughout the watershed and validate the obtained results. This method offers a suitable approach to define a watershed's capacity to recruit wood material to streams by delineating the source areas and estimating the order of magnitude of the wood volume in each case. The results may be useful to characterize the dynamics of woody debris from the perspective of the potential hazard of its transport during floods, and they can also be used for forest and river management and restoration. Copyright © 2012 John Wiley & Sons, Ltd.