looking for scour velocity threshold for concrete

[stormboy]

YAR! designing a debris deflector structure for a very steep stream. bed grades along the base of the deflector in the order of 15%. It is a constant flow stream and I am concerned about scour of a concrete slab proposed for the creek bed. I'm fishing for advice on permissible velocities vs concrete properties for continous flow conditions. There are a lot of papers around but they all seem to deal with short term scour potential under peak velocities during flood events. I'm worried about the day to day trickle flow over 50 yrs or so.

 

[gbam]

Are you more concerned with the abrasion from sediment within the flow or the chemical composition of the water? Either way try contacting a conc pipe supplier. They may be able to provide information on the long term impact in your scenario.

 

[cvg]

you should be worried, it could scour much faster than 50 years. Your velocities will be nearly 20 feet per second, well in excess of the threshold for erosion. But the amount of scour is very dependant on the amount and qualities of the sediment. See attached paper on concrete erosion.

You may want to consider one or more of the following methods to reduce the erosion:

- reduce the amount of sediment by trapping it

- reduce the velocity to perhaps 5 feet per second or less

- increase the durability of the concrete

- increase the thickness of the concrete, especially the cover over the steel

 

[Ryb01]

gbam has a good recommendation. You could also try the American Concrete Pipe Association or American Concrete Association for additional details, research and direction.