The Influence of In‐Channel Obstacles on River Sound

Abstract

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. Here, 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 (REs), we were able to customize the course's obstacles, creating towers of different heights and placements. We then ran a varied flow discharge of up to 10 m3 s−1. We used data collected from microphones, a hydrophone and cameras to monitor the flow and to understand the processes occurring. In addition 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 the relationship between white water value and sound relationship having an R2 between 0.35 and 0.82. 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 RE height.