I visit this forum too often.
Ok. Abreviated version.
Ground effect is a phenonemon experienced by birds and planes. The effect starts at a height roughly equal to the span of the wings above the ground.
The airfoil ( wing ) creates lift by virtue of the upper surface being longer ( curved )than the lower surface. The upper airflow speeds up to meet its mates that take the slow route under the wing.
( flat )
In speeding up, the air molecules spread out and the pressure drops relative to the under wing pressure. ( same amount of molecules occupy a greater space - vaccum effect )
The wing is literaly sucked up from the top ( LP ) and to a lesser degree pushed up from the bottom. ( HP )
The 'push up' accounts for 30% of the lift and is primarily created by angle of the wing ( angle of attack ) giving a compression effect under the wing and the relative pressure to the upper wing area.
Ground effect is a cushioning effect created by trapping air between the wings and the ground. Push up effect can increase by up to 75%.
Drag increases with speed. Usually the air taking the slow route under the wing tries to take an even shorter cut up over the end of the wing tip. It corkscrews up and is sucked in by the upper surface ( LP ) and strikes the wing on its top surface destroying lift and where there is no lift there is drag. This is the spiralling wingtip vortex or 'tornado'
referred to earlier.
In ground effect however a plane can fly slower and still stay up thanks to the cushioning effect of ground effect. Ground effect decreases lift induced drag. The drag is reduced because the speed is lower and the exaggerated cushion of air under the wing plays a part in blowing away the wing tip vortex preventing it from curling around and striking the uppersurface of the wing. Thus better lift etc.
Water is incompressible and man does not look like a wing. Ground effect has no bearing on a diver at the bottom except for the negative effect of the dynamic cushion. lifting him upwards and backwards.
The diver drags a layer of water around with him and this layer may retard on the floor ( sucking him back and down ) and a wave may form on his chest striking the floor in a forward motion ( dynamic cushion )buffering and retarding his forward movement. The kayaker in the previous post has hit the nail in the teeth with his example.
A diver swimming close to the floor will likely suffer from Bernouli's principle ( lift, but in reverse ) where he is sucked down onto the floor behind the dynamic cushion formed in-front of his chest. He consistently drags his fins and bumps his knees due to the suction downwards. ( Like a boat travelling at speed in a canal close to the wall is sucked to the wall.)
The diver then adjusts his hands (angle of attack) upwards to gain altitude, rides up on the ground wave which moves backwards towards his waist but the lower body does not respond ( bernoulli ) so he swims at a positive angle of attack for many meters trying to escape the floor exposing a poor profile to the water, increasing drag and surfacing prematurely.
ha!
Skin.
