[madaxe_again]

I actually did a fairly lengthy research project on pretty much exactly this as a physics undergraduate - I wasn’t looking at swimming specifically, but rather boundary separation and Reynolds number in an open channel of varying depth.

The setup was simple - a constant head vessel to provide a constant but adjustable flow of water in from one end, and a little plastic boat sat in the middle of the channel, attached to a force gauge at one end of the channel. The outflow of the channel had a gate with an adjustable height in order to vary the depth. Also, a couple of dye injectors at different heights in the channel in order to see turbulent vs laminar flow.

The key finding was that at shallower depths, turbulent flow began much more rapidly and resulted in erratic but overall higher resistive forces on the boat. Deep water remained laminar for much longer, and could flow much faster before turning turbulent near the surface. This was the expected result, but it was nice to experimentally prove it.

So in short, the pool depth almost certainly impacts the point at which turbulence kicks in, and therefore athletic performance. It’s probably the dive/entry that is being most impeded, as that’s when the swimmer will largely be experiencing laminar flow.

[bonestamp2]

Is there a formula to calculate the ideal depth at which going any deeper results in diminishing returns? In other words, how deep should future competitive swimming pools be built to provide the most world record opportunities (and perhaps more excitement for spectators due to increased world records)?

[bjoli]

Does it manifest directly? The water has had some time to settle when they start.

[madaxe_again]

Yes. An object moving through water is more or less equivalent to water moving around an object, and the moment you cross a boundary condition, be it depth, velocity, viscosity, the phase transition is instantaneous to all intents and purposes.

I’d have entire days of experiments screwed up just by the water being slightly too warm or cold, or there being dust, or not enough dust, or sunshine, or… fluid dynamics are finicky.

[LorenzoGood]

Yes, but there will be no turbulence at the start of a swimming race.

[askvictor]

At some (shallow) point, does a 'ground effect' kick in? Or any sort of constructive interference?

[madaxe_again]

Yes, in a very shallow flow you retain laminar flow - but you wouldn’t be able to swim in it, as we’re talking 15mm or so.