If you are designing a garden ‘water feature’, ie a stream which splashes into a pool, how can it be made to emit the most pleasing noise, for a given flowrate? Some current systems I’ve listened to provide a pretty consistent hiss, most unlike the natural stream or waterfall I suspect they are supposed to be impersonating (actually more like the effluent pipe from some highly efficient industrial process).
One possibility is to use an archimedes screw mechanism. This could most easily take the form of a hose wrapped around the outside of a pipe which would, when rotated axially by a small motor running at constant speed, deliver gouts of water from a reservoir).
Using a bank of such screws arranged concentrically (each with a different screw pitch), it would be possible to supply a large number of small dollops and a much smaller number of large dollops -somewhat more like the pink noise which might be expected to emanate from a natural waterfall.