Flood Protection by Forests in Alpine Watersheds: Lessons Learned from Austrian Case Studies

Abstract

This chapter highlights the influence of mountain forests on runoff patterns in Alpine catchments. We discuss the forest impact at different spatial scales and bridge to the requirements for an integrated natural hazard risk management, which considers forest as an efficient protection measure against floods and other water-related natural hazards. We present results from a wide range of research studies from Austria, which all reveal the runoff-reducing effect of forest vegetation in small and medium-size catchments (< 100 km2). Forests also contribute to runoff reduction in heavy rainfall events in macro-scale catchments (> 100 km2), e.g., by reducing surface runoff and delaying interflow, but above all by stabilising slopes and therefore reducing bedload transport during major runoff events. To avoid that forests become a hazard due to enhanced driftwood release, managing of steep riparian slopes for a permanent forest cover (“Dauerbestockung”) is a basic prerequisite. Often protective effects of forests are impaired by man-made impacts like dense forest road networks, insensitive use (e.g., false design of skid roads, compacting machinery, forest operations during adverse weather on wet and saturated soils), and delayed or omitted reforestation and regeneration. Flood risk management in mountain regions should include Ecosystem-based Disaster Risk Reduction (Eco-DRR) measures, with particular emphasis on sustainable and climate change-adapted management of protective forests. This will require integrated and catchment-based approaches such as comprehensive management concepts coordinated with spatial planning, and verifiable, practicable and correspondingly adapted legal guidelines as well as appropriate funding of protective forest research to close the existing knowledge gaps.