The Eurasian beaver population is rapidly expanding across Central Europe, where these ecosystem engineers substantially modify landscapes through the construction of dams and wetlands. Although their activities can lead to land-use conflicts, they also provide significant benefits, including enhanced surface and subsurface water retention, reduced flow velocities, and increased habitat diversity. Current research suggests that cascades of beaver dams can attenuate and delay peak flows, positioning them as potential nature-based solutions for flood protection. However, a significant knowledge gap remains regarding their effectiveness during extreme flood events under the specific climatic and geographical conditions of Central Europe.
The project “Beaver Dams and Wetlands as Nature-Based Solutions for Flood Protection in Central Europe” sought to address this gap through hydrological modelling. A beaver dam capacity model was developed for Saxony to identify streams with suitable conditions for beaver dam establishment. Based on this assessment, the Lockwitzbach catchment was selected as the study area for detailed hydrological modelling. A HEC-HMS model was subsequently set up, calibrated, and validated using observed rainfall–discharge datasets. Three beaver dam scenarios were defined: (i) no dams, (ii) small to medium-sized beaver ponds, and (iii) medium to large-sized beaver ponds. The locations and characteristics of beaver ponds and dams were derived from the beaver dam capacity model using ArcGIS tools.
Design rainfall events with return periods of 2, 5, 10, and 20 years were applied, using both historical data and future climate projections, to generate flood hydrographs. In total, 24 simulations were conducted, combining the different dam scenarios and rainfall events. The results indicate that, under the examined conditions, beaver dams only slightly alter the flow regime and provide very limited peak flow mitigation—less than 1% peak reduction for the small dam scenario and less than 2% for the larger dam scenario. The primary reason for this limited effect is that beaver ponds are typically full by default, as beavers construct dams to maintain water levels as high as possible. Consequently, during flood wave passage, the ponds offer minimal additional storage capacity for flow attenuation—approximately 1% of the total flood wave volume in the small dam scenario and about 2% in the large dam scenario.
Furthermore, as discharge increases, beaver dams are subjected to progressively higher hydraulic forces. The results show that during Q20 flood events, the majority of dams are overtopped by water jets exceeding 25 cm, and a substantial proportion may fail under such conditions. The overall conclusion of the project is that, under all examined scenarios and circumstances, beaver dams do not function as an effective nature-based solution for flood protection. While beaver dams deliver numerous benefits to the landscape—particularly in terms of biodiversity enhancement and water retention—significant high-flow mitigation cannot be considered among them, at least for flood events capable of posing a serious threat in Central Europe.