The influence of in-channel obstacles on river sound

The sound of a river can change from a babbling brook to a thunderous torrent, and we have previously shown that there is the potential to predict river stage from the river's sub-aerial sound. We examined how alterations in channel configuration can change the relationship between stage and sound pressure level using a white water course to simulate a real world scale channel. By using blocks as roughness elements (RE) we were able to customise the courses obstacles, creating towers of different heights and placements. With running a varied flow discharge of up to 10 cumecs through. We used data collected from microphones, a hydrophone and cameras to monitor the flow and to understand the processes occurring. Further to sound processing, we used image analysis to calculate the area of white water on the surface of the water to determine the mechanism for sound production. Our analysis showed the likeliest source of sub-aerial sound is from white water being produced from the flow's interaction with the REs, with an R2 range of 0.35 to 0.82 from our white water value and sound relationship. In terms of influence on sound, we found that the height of the REs is more important than their spatial distribution, with the taller the RE, the better the logarithmic relationship between sound and stage. We suggest that monitoring in a natural setting will work best in the places with the tallest obstacles and that the quality of the sound-stage relationship is dependent on height.