Using Space-Time Image Velocimetry to assess characteristics of flow through full-scale leaky dams for flood hazard reduction
Date:
Anthony Jones, Julia Knapp, and Sim Reaney
Leaky dams are an in-channel nature-based solution and a natural flood management intervention constructed in headwater streams to reduce runoff rates and attenuate flood peaks. Despite their widespread implementation, their hydraulic performance under high-flow conditions remains poorly constrained due to a lack of high-resolution observations when dams are actively storing floodwater. This lack of detailed performance characterisation is a barrier to uptake, particularly among the engineering community that designs flood mitigation schemes. This study presents the first application of Space-Time Image Velocimetry (STIV) to quantify surface flow velocities upstream and downstream of channel-spanning (≥4 m wide) leaky dams under controlled, repeatable high-flow conditions. Experiments were conducted along a 170 m white water rafting course, providing an intermediary setting between laboratory flumes and natural catchments that enables controlled flows. Three channel-spanning leaky dams were installed in sequence and tested using both natural (pine log) and engineered (pre-cut commercial timber) designs with systematically varied degrees of leakiness. Drone-based imagery was analysed using STIV to derive spatially distributed surface velocities, which were coupled with a maximum entropy method to estimate discharge.
Results demonstrate that dam leakiness is the dominant control on both upstream and downstream flow velocities. Velocities upstream of the dams decreased linearly with reduced leakiness (R² up to 0.97), while velocities downstream of the dams increased due to flow acceleration through dam gaps, revealing a clear trade-off between upstream flow attenuation and downstream jet strength. When arranged in sequence, leaky dams produced a cumulative reach-scale effect, with mean upstream velocities decreasing by approximately 0.15 m s⁻¹ per dam along the experimental reach. A full-scale partial dam failure was also captured, showing a rapid increase in downstream velocity and highlighting the transient residual flood risk associated with structural compromise.
These findings provide new empirical insights into the hydraulic functioning, cumulative effects, and failure behaviour of leaky dams, while demonstrating the value of STIV as a non-invasive tool for monitoring these interventions under high-flow conditions.
How to cite: Jones, A., Knapp, J., and Reaney, S.: Using Space-Time Image Velocimetry to assess characteristics of flow through full-scale leaky dams for flood hazard reduction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10434, https://doi.org/10.5194/egusphere-egu26-10434, 2026.