Using Smart Sensors for Measuring Impact Forces of Large Wood (LW)

River systems in forested catchments are affected by flow-wood interaction processes. There are benefits of having large wood (LW) in stream channels, yet large quantities of available wood in stream channels can also cause destruction, particularly at high rates of transfer and accumulation. Due to the destructive impacts on property, infrastructure and environment, a better understanding of the interactions between LW and flow hydraulics is required. Towards this aim, we have developed a fully scaled hydraulic flume experiment in the Water Engineering Laboratory at the University of Auckland, where LW movement behaviour and impacts on channel boundaries and hydraulic structures can be studied. To record the detailed movements of woody elements, we have employed six custom-designed smart sensors, implanted into wooden dowels and then released into the channel. The innovative smart sensors record detailed information on acceleration, rotation, and orientation in all three dimensions (nine-degrees of freedom). Real-time measurements of acceleration, angular velocity and magnetic field strength provide some novel insights into LW transport and deposition processes. Here we focus on the measurement of impact forces that arise due to interaction of a miniature log with channel boundaries and river crossing infrastructure. Impacts are captured at acquisition rates of up to 100 Hz. Our methodology may be useful for obtaining high quality data of LW movement processes without the inherent limitations of field conditions, e.g. high turbidity, night time conditions and inclement weather. The results gained could be applied in future design measures for river crossing infrastructure and will inform freshwater and forestry management.