Rivers transport branches, logs, and man-made debris—especially during floods. When this material jams at bridges, culverts, or intakes, it restricts flow, raises upstream water levels, and accelerates scour and structural damage. Debris barriers intercept large floating objects while allowing water and most sediment to pass. By controlling where debris collects, they protect critical infrastructure, reduce flood risk and maintenance, and create safe access points for removal. Because performance depends on spacing, orientation, and hydraulic conditions, simulation could improve the design process of these structers: it lets engineers quantify forces, backwater rise, deposition, and failure modes across flood scenarios, and optimize the barrier to capture what we want and pass what we must.
Case Description
The simulated scenario is roughly based on a debris barrier similar to the one shown in the photo below, taken by one of our engineers near Oberstdorf, Germany. The model represents a 30 m long river channel with a trapezoidal cross-section: 11 m wide at the bottom and 15 m wide at the top. The debris barrier consists of vertical piles, each 4 m high with a cross-section of 0.8 m. The spacing between individual piles varies between 1.7 m and 2.0 m, allowing water and sediment to pass while intercepting larger debris.
For the simulation, the channel was loaded with a flow rate of approximately 49 m³/s, corresponding to a water depth of around 2 m and an average flow velocity of about 2 m/s. The debris used for the evaluation included logs with lengths of 2.1 m, 3 m, and 6 m, each with a density of 700 kg/m³. This configuration was used to assess hydraulic performance, debris capture efficiency, and potential backwater effects under realistic flow and debris-loading conditions.
Results
The results are presented through a series of videos, each highlighting different perspectives of the simulation. The sequence begins with the top view in the engineering visualization, where the movement of debris along the stream can be observed particularly well. This is followed by its rendered counterpart, offering a direct comparison between the raw simulation output and a more realistic depiction of the flow and debris.
Next, the side view is shown in both engineering and rendered modes, providing insight into flow depth, vertical debris movement, and barrier interaction from a cross-sectional perspective.
As mentioned and shown above, the simulation used nine logs: three measuring 6 m, three measuring 3 m, and three measuring 2 m, with the largest logs placed downstream of the shorter ones. The debris moved perpendicular to the barriers, and this arrangement—combining perpendicular approach with a size order from large to short—was intended to maximize the likelihood of the barriers capturing all logs.
During the first impact, all three 6 m logs were caught and initially held back the smaller ones. The side view reveals how the diagonal section of the barriers pushed all logs toward the water surface. However, after the initial collision, the smaller logs were gradually forced downward by the flow. One by one, they submerged beneath the larger logs and slipped under the barrier. This result demonstrates that even in a configuration designed to optimize debris retention, smaller logs can escape and continue traveling downstream.
The following diagram shows the surface water level over time, recorded along a sample line located 6 m upstream of the barriers. The sharp spikes at the beginning (the first marked with a vertical blue line) correspond to the moments when individual logs pass the sample line. After the logs collide with the barriers, a noticeable rise in water level occurs, indicating that even 6 m upstream a backwater effect develops within a short time. The maximum water level is reached at around 8 seconds (marked with a red line), which coincides with the moment when more debris begins to escape, reducing the temporary damming effect.
The final video provides an overview of the entire simulation, combining isometric and top-view perspectives in a seamlessly edited sequence. It offers a dynamic yet informative presentation of the flow, debris movement, and barrier interaction, giving both a clear technical impression and an engaging visual summary of the results:
