A drainage ditch is a water channel, typically dug on the side of a road, field, or land surface, to capture and direct surface runoff water away from the area to prevent flooding and erosion. It is also known as a ditch, culvert, or canal. Another common term used for a drainage ditch is a gully, which is a narrow and steep-sided channel that carries drainage water from higher slopes to lower-lying areas. A swale is a type of drainage ditch, which is a shallow channel that uses vegetation to slow down and filter water runoff. A trench and a trough are also synonyms for a drainage ditch.