A long, narrow open hole that is dug into the ground, usually at the side of a road or field, used especially for supplying or removing water or for dividing land. (Cambridge Dictionary)
A long narrow excavation dug in the earth. (Merriam – Webster)
A narrow channel dug at the side of a road or field, to hold or carry away water. (Oxford Dictionaries)
A ditch is a long narrow channel cut into the ground at the side of a road or field. (Collins Dictionary)
Cove irrigation ditch.