How to tetrofit detention basins

[uncivilized]

I work in a very flat area. We often use interconnected lagoons (ponds) as detention storage. We also undercut the lagoons 2-3 feet deep for sediment storage. Recently the reviewing agencies are requiring retrofits in front of the connecting pipes between the ponds in order to store more sediment. A retrofit is basically a filtering mechanism designed to slow the water down in order to get more settling. However the pipes are often under water which makes construction difficult. Also I worry about flooding due to putting an obstruction in the pond. Has anyone else addressed this issue? Thanks in advance.

 

[LCruiser]

Yes. Browse around here:

http://www.nrcs.usda.gov/

 

[TerryScan]

We are required to have forebays at pipe entry points into ponds. Typically, these were formed by a sump/berm configuration after the end of the pipe containing a volume of 2% of the 2 year storage volume. In wet ponds, inspectors found this type of construction "melted" when constructed of earth. Stone seemed to migrate as well. The latest configuration they are asking for is gabions or a "modified gabion" berm consisting of parrallel chain link fence with 6" rip rap filling between the fences. The height of the fence is 1' below the normal pool. The width between the fences is equal to the height. The posts are to go below the bottom the same length as the height on 4' centers. Filter fabric is placed below the rip rap. The parrallel fences are tied together with 1/8" galvanized steel rope, 2 per post pair.