preventing erosion of backfilled material in marine trenches

[lbarker]

I am looking at options for the installation of a marine outfall. One of the options is to lay the outfall pipe in a trench, and backfill the trench with the excavated material (chalk).

I want to ensure that the backfilled material won't be eroded from the trench through wave and current action. Is it possible to dimension the trench to ensure that the material won't be removed, or will it need scour protection?

Thanks

 

[cloa]

Where is the site? The answer to probably varies enormously. I believe in the NorthWest of Western Australia a simple trench would be impossible due to strong currents.