Loading on a submerged bar

Tails142

This is a problem that I've been trying to get my head around for a few years now :P

We all know, if you put a stick into a flowing river, you'll feel a force as the stick is pulled along with the flow of the water.

OK, so imagine you are designing a screen for filtering trash from a river. If you're trying to work out the maximum load on these bars where do you start...

Well this is as far as I have got, it's a trash screen so I imagine the worst case scenario to design for is that the screen is entirely blocked and is essentially acting as a retaining wall to the body of water, that's a simple enough equation, Pressure = density x gravity x depth and design and size your bars from there.

It's this next part I can't get my head around...

If the river is fast flowing, the water has energy stored in it, if the water is moving and passing through the screen does it ever exert more pressure than (density)*(gravity)*(depth) due to this kinetic energy?

I just can't decide if a flowing body of water exerts more pressure on a submerged surface than if the surface was retaining the water at an orifice.

I think the answer involves Froude's number, that's all I know ... I would welcome a steer from anyone in the right direction.

mickdw

Flowing water in an open channel for example will produce a pressure head greater than the water level in the channel so certainly the flow rate of the water has to be a design factor imo