How do you calculate it for say an 18’ high levee in New Orleans?
This question probably has a factual answer.
Moved from IMHO to GQ.
Resultant force=1/2pgD^2W where p=density of water (1.94 lbm/ft^3), g=gravity (32.2 ft/s^2), D=depth of wather and W=width of submerged surface.
This question definitely has a factual answer.
Thank you.
You’re welcome, I neglected to mention that W is the projected width onto the vertical plane.
Do you have a link to how the equation was derived?
Thanks again.
Isn’t it affected by the number of blues singers on the levee at the time of the breach?
Can’t find a link but:
dP/dD=pg or in words the change in pressure over the change in depth is density tiems gravity.
Multiplying by dy and integrating yields P=pgD+Constant. In this case the constant is zero becuase air pressure acts on all surfaces so P=pgD. In order to calculate the total pressure on the surface we write an equation for an infintesimally small piece of area and integrate. If you are facing the surface lets call X the horizontal axis and D is the verticle. Now, force is Pressure times area with our area being dXdD. So our equation is F=PdA=pgDdX*dD. We need to integrate that equation twice, for X from 0 to W where W is the width and for D from 0 to Y where Y is the depth.
Now, since the pressure doesn’t vary in the X direction the integration results in W. That leaves us with F=WpgDdD. Since w, p and g are constants in the D direction we can pull them out of the integral. F=(Wpg)int(D,dD,0,Y). The integral of D is 1/2D^2. We plug in our limits and find int(D,dD,0,Y)=1/2Y^2. Putting that back in our equation we get F=WpgY^2/2. I don’t know if that explanation helps, I suspect it won’t, but I couldn’t find a good webpage.
this was the best I could find after a brief look.
Well, I knew 1/2D^2 was in integral to find force over depth. 
Thanks again.
It’s just the volume of a right triangular prism 1 unit wide multiplied by the weight of the water in the prism and the length of the levee in the same units as those of the prism.