Falling asleep next to rivers has always seemed to provide me with sound sleep and vivid dreams. I assume that some of this has to do with being outside, moving, breathing, and sleeping with the elements, but I also have always harbored the suspicion that the sound of a river is well suited to striking a balance between a resting and active mind.
I spend a fair amount of time in the field this quarter listening to sounds of water, rapids, and trickles, and thinking about the mechanics of the sound for this reason; trying to piece apart the root of the noise and the relationships between the flow patterns and sound patterns.
River noise is often classified as white noise, which means that the cumulative audible effect of all the water hitting itself is random pulses of soundwaves around a central frequency. If sound is coming from a waterfall, this central frequency must be controlled by the amount of water moving over the falls and the geometry of its impact- like the hydraulic descriptions which use ratios of head above the drop to depth below as an index. Submerged holes therefore would tend to emit less noise than a plunging nappe, or falls, but the frequency depends primarily on the amount of water.
Ellen Wohl somewhere pointed out that if you can hear a river it is a good indication of supercritical flow. I find this to be credible from my observations in the field. Since it would either take a hydraulic jump or a falls of some sort to produce a sustained impact of water against itself, supercritical flow would be involved either way.
The mechanics of the flow and patterns of pulses within rivulets are for the most part far too fast and complex for me to tease apart, but through river noise there do tend to be strains of distinct gurgling, bubbling, and splashing. I think that it might be this combination between chaos and patterns that makes it a healthy noise for the brain and for sleeping next to. Its not dull monotonous white noise like an unplugged television, but neither are the patterns consistent like a drumbeat. The aberrant splashes tickle the subconscious and blow cobwebs from the interstices of our minds.
While I now know this isn’t entirely true, I also enjoy musing on the fact that rivers and white noise are a chaotic assemblage of all different frequencies. To me this has meant that any song I could imagine is in there somewhere; the beat, the horn section, the fiddle and the tap shoes. Next time you are falling asleep next to a river try me and let me know if you can’t find whatever it is you are looking for.