Debris fence in channel
Debris fence in channel
(OP)
I am designing a debris fence to be constructed across a channel at the downstream end of a rock energy dissipator. The fence is to be constructed with chain link fabric on heavy steel pipe posts. The fence will be 3 feet high to catch the first flush debris during a 5-yr to 10-yr storms and would be overtopped for storms greater than that. Assuming the fence becomes totally blocked with debris, what should be the basis for determining the hydrodynamic force on the fence for sizing the posts and their spacing. I have considered the totally blocked fence as a sharp crested weir but have not found any information on calculating the pressure on the surface (fence) below the weir crest. I am thinking of using the hydrostatic pressure due to the total depth of water flowing over the fence less the hydrostatic pressure at the top of the fence.





RE: Debris fence in channel
good luck
RE: Debris fence in channel
The dynamic forces for most channel flow situations are negligible. For instance, if the flow was five ft./sec. (which is really cooking), the dynamic force is about 6 additional inches of water.
RE: Debris fence in channel
v^2/2g = 0.388 feet of water = 4.66 inches of water
additional pressure of 4.66 in. of water =0.17 psi = 24 lb/sf
If v= 10 ft/sec,
additional pressure = 96.7 lb/sf
Whether or not this is negligible you mat determine for yourself.
good luck
RE: Debris fence in channel
RE: Debris fence in channel
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: Debris fence in channel
http://www.kristar.com/media/brochures/ntspecs.pdf
RE: Debris fence in channel
RE: Debris fence in channel
Swearingen and JedClampett: I think you're both agreeing that the hydrostatic force will be the trapezoidal pressure diagram equal to the height of the fence but based on the total depth of water. See the attached calculation.
Sam74: my dissipator is at the end of a concrete trapezoidal channel.