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.

河流的声响可从潺潺溪流的低语变为轰鸣奔腾的洪流。此前我们已证实，通过采集河流水面以上的声响，有望实现河流水位的预测。本研究借助急流水槽模拟实际尺度的河道，探究了河道构型变化如何改变水位与声压级之间的关联。本研究以块体作为糙率单元（roughness elements, RE），可灵活设置水槽内的障碍物，构建不同高度与布设位置的塔状结构。实验中通入的变流量最大可达10立方米每秒。我们通过麦克风、水听器与摄像机采集的数据对水流进行监测，以此解析其中发生的物理过程。除声响处理外，我们还通过图像分析计算水面白浪的面积，以明确声响产生的物理机制。分析结果表明，水面以上声响的最主要来源为水流与糙率单元相互作用产生的白浪；水面白浪面积与声响之间的决定系数（R²）范围为0.35至0.82。在对声响的影响因素方面，我们发现糙率单元的高度相较于其空间分布更为关键，且糙率单元越高，声响与水位之间的对数关联效果越好。我们认为，在天然河道场景中开展监测时，障碍物较高的区域监测效果最佳，且声响-水位关联的质量取决于障碍物的高度。