If drainage systems are not maintained, moisture will be retained in the structure and pavement deterioration will increase. If a road agency is unable to maintain its drainage systems, experts say, then it likely will be better served by designing a road structure without a drainage system.

A road drainage system can be degraded with aggregate, sand, clay or dirt from the pavement structure itself, from material and refuse dumped on the pavement, and by mud and gravel washed down in the roadside ditch.

Lastly, plastic and corrugated metal pipes can separate or be crushed, often during construction. That’s why systems should be inspected via video “snake” right after construction is completed, and then periodically thereafter. Maintenance forces should mow around the system outlet pipes at least two times each year, and should mow and clean roadside ditches as well.

A telescoping-boom, wheeled excavator is ideal for digging out clogged, silted drainage ditches, or for cutting weeds with an attachment. Headwalls protect outlet pipes, help limit erosion where there drainage system empties, and help workers identify the location of outlets, which otherwise might become overgrown or silted-in.

“The accumulation of sediment in culverts happens ‘out-of-sight and out-of-mind’ and that the very process of sedimentation, slow or sudden, is pervasive and nearly inevitable,” says Gerry Sackett, Gerryrigs, Charlottesville, Va.

“The hydraulic capacity of a culvert pipe is specified and is considered as a constant. The gradual accumulation of sediment within the culvert, and resulting reduction of design capacity are not factored in. It seems to be generally expected that the velocity of drainage flow will scour the barrel of a culvert and keep it clean, but in reality, this is not the case.”

Water may freely flow through an unencumbered culvert, and carry with it, particulate material in suspension, Sackett says. However, when the flow meets natural grade at the outlet of the pipe, the friction and irregularity of the natural grade (including stones, grass or debris) slows the current and makes it roll. Heavier particles (detritus and debris) settle out and the process of sediment accumulation is begun.

To reduce sedimentation of culverts, Sackett has developed the Culvert Inlet Protection Device, or CIPD, which was approved for testing by Virginia DOT in 2010 and by Georgia DOT in 2012.