Assessment of the Impact of Beaver Dams on Flow Conditions, Retention Capacity, and Water Resources in the Junikowski Stream in Poznań

Beaver dams can substantially modify flow conditions and increase local water retention, particularly in small urban and peri-urban streams exposed to hydrological alterations and increasing water deficits. This study evaluates the influence of beaver dams on hydraulic conditions, retention capacity, and water resources in the Junikowski Stream in Poznań, Poland. Field surveys, geodetic measurements, and spatial data were used to develop a one-dimensional hydraulic model in HEC-RAS. Three management scenarios were analysed: a channel without impoundment structures, the 2022 configuration including beaver dams and two artificial weirs, and the 2025 configuration representing a more developed beaver-dam cascade together with the functioning weirs. Simulations were conducted for a range of characteristic and probability flows to assess changes in water levels, inundation extent, and retained water volume. The results show that beaver dams exert the strongest effect under low-flow conditions, when they significantly increase water levels and improve local retention. Their hydraulic influence decreases with increasing discharge, although they continue to affect the spatial distribution of water in the valley. The proposed artificial structure may partly maintain retention benefits in the event of beaver dam degradation or removal. The findings demonstrate that beaver dams may function as effective nature-based solutions supporting water retention and potentially contributing to drought resilience and sustainable management of urban stream valleys.