Geospatial modelling of large-wood supply to rivers: a state-of-the-art model comparison in Swiss mountain river catchments

Different models have been used in science and practice to identify instream large-wood (LW) sources and to estimate LW supply to rivers. This contribution reviews the existing models proposed in the last 35 years and compares two of the most recent geographic information system (GIS)-based models by applying them to 40 catchments in Switzerland. Both models, which we call here the empirical GIS approach (EGA) and fuzzy-logic GIS approach (FGA), consider landslides, debris flows, bank erosion, and mobilization of instream wood as recruitment processes and compute volumetric estimates of LW supply based on three different scenarios of process frequency and magnitude. Despite being developed following similar concepts and fed with similar input data, the results from the two models differ markedly. In general, estimated supply wood volumes were larger in each of the scenarios when computed with the FGA and lower with the EGA models. Landslides were the dominant process identified by the EGA, whereas bank erosion was the predominant process according to the FGA model. These differences are discussed, and results are compared to available observations coming from a unique database. Regardless of the limitations of these models, they are useful tools for hazard assessment, the design of infrastructure, and other management strategies.