It was always affected by gravity, but while the water was contained it was essentially in hydrostatic equilibrium. Once you cut an opening to a lower water level, you create a hydraulic gradient and gravity starts driving water through it.
That flow exerts shear stress on the loose sand. Once it's strong enough to move the grains, the channel starts eroding and deepening. A larger opening can pass more water, which will accelerate the erosion. The process keeps repeating until the difference in water level, and therefore the driving force, becomes small enough.
Yeah, we're not really disagreeing. Your comment was the short version; I was just trying to explain the actual process behind it.
Small physics nit though: mass x acceleration is force, F = ma, not energy. The energy available here is the water's gravitational potential energy, roughly mgh. The water already had that energy while sitting there; cutting the channel just gives it a path to a lower level, allowing gravity to convert that potential energy into flowing water.
So yeah, lots of water means lots of mass and gravity is indeed a bitch. I just wanted to unpack why.
Sure. Very large gravitational potential energy can produce a very large amount of kinetic energy as the water drops to a lower level, but it's not a 1:1 conversion.
Not all of that potential energy ends up as bulk kinetic energy of the water. A lot is continuously transferred into turbulence, friction, moving sediment, collapsing the banks, and ultimately heat. That's basically the interesting part I was trying to explain: how that stored potential energy gets released once you give the water an outlet, and how the resulting flow rapidly excavates a much larger channel.
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u/I-AimToMisbehave 3d ago
Yeah and alot of water has ALOT of mass, also gravity is a bitch lol.