Water table drains protect the road by directing water off it. This also strengthens the road by keeping the subgrade drier.
- The water table is deep so it helps drain the subgrade.
- The water table has been rock armoured to reduce erosion on a steep road section in a known problem area.
- The road has enough cross-fall to direct water into the drains.
- The water table can easily catch ground water flow from the cut bank.
- The water table has scoured out because it was forced to handle too much water flowing too fast.
- The culvert was too small and the spacing was too great.
- Too much water on a steep road can quickly cause road failure.