Why do river sounds make it easier to fall asleep

http://riversoundswebsite999.jigsy.com/entries/general/how-come-natures-noise-assist-you-to-rest

The crash of ocean waves, the babbling of brooks, the pitter-patter of rain on shingles — A lot of people swear by these watery sounds that will help them drop asleep and remain in la-la land. Why does flowing