A trunk drain is a large-capacity drainage channel or stormwater pipe which carries runoff from local street drainage systems to receiving waters. They are typically natural or artificial open channels located in a dedicated drainage easement or right-of-way. Pipes larger than a certain diameter may also be considered as trunk drains. They serve a number of sub-areas, are physically large, and any overflows are likely to cause direct damage and prolonged inconvenience.
Besides natural or artificial channels, trunk drainage systems can include:
- transitions and hydraulic structures;
- culverts and road crossings;
- naturally-occurring ponds and lakes; and
- artificial detention or retention storages.