Disrupted Connectivity: The Impact of Check Dams on Bedload Transport and Sediment Storage in the Gürbe Catchment

Check dams are widely implemented in Alpine torrents to mitigate natural hazards and regulate sediment fluxes, yet their influence on sediment transfer and connectivity remains poorly constrained. In particular, it is still unclear how a series of check dams can modify sediment connectivity, specifically the erosion, and deposition patterns along the sediment cascade. We address this gap in the 12 km² Gürbe catchment at the northern margin of the Swiss Alps, where a steep, geomorphologically active channel reach has been engineered by approximately 100 check dams. The Gürbe torrent originates in low-erodibility Mesozoic limestones and transitions downstream into highly erodible Flysch, Molasse, and glacial till. A glacially conditioned knickzone at ~1200 m a.s.l. marks the onset of strong channel incision and enhanced hillslope–channel coupling (Schmidt et al. 2026). Downstream of this knickzone, the channel steepens by about 3°, traverses a landslide-prone corridor, and finally reaches the alluvial fan, forming a reach that is almost entirely controlled by check-dam structures.

We investigated the impact of check dams on bedload transport using repeated uncrewed aerial vehicle (UAV) - based photogrammetric surveys, which allowed us to quantify volumetric changes of the channel bed and to track erosion and deposition patterns through time (seasonal to annual and decadal). Our results show that bedload transport within the engineered reach is highly discontinuous, particularly during frequent low- to moderate-magnitude flow events. Check dams interrupt sediment continuity and create a succession of closely spaced erosion and deposition zones, leading to pronounced spatial variability in sediment dynamics over short distances. Even during moderate floods, gravel-bar re-working differs markedly between adjacent dam sections. Sediment inputs strongly control these dynamics. Material delivered from upstream is repeatedly reworked as it passes through successive check-dam compartments, alternating between reaches dominated by deposition and by erosion. In contrast, lateral sediment inputs, especially from landslides, promote net deposition and progressive accumulation of stored bedload material that is only mobilized during larger, less frequent flood events. Further downstream segments with lateral input of sediment derived from tributaries as well as non-regulated channel reaches are characterized by enhanced sedimentary dynamics, leading to abundant channel reorganization.

Overall, the check-dam system exhibits a tendency toward net deposition and sediment storage on decadal timescales, with dams acting as temporary buffers that trap bedload. These accumulated sediments form a latent sediment stock that is episodically released during major events, when channel erosion intensifies and stored material is excavated and transferred downstream. Our findings demonstrate that check dams fundamentally shift bedload transport from a relatively continuous process toward a pulsed, event-driven regime characterized by persistent reworking, long-term accumulation, and episodic phases of intensified erosion and transport.

Schmidt, C., Mair, D., Akçar, N., Christl, M., Haghipour, N., Vockenhuber, C., Gautschi, P., McArdell, B., and Schlunegger, F.: Quantifying erosion in a pre-Alpine catchment at high resolution with concentrations of cosmogenic ¹⁰Be, ²⁶Al, and ¹⁴C, Earth Surf. Dynam., 14, 33–53, https://doi.org/10.5194/esurf-14-33-2026, 2026.