1) English water trench 2) Riffle 
A leat (also lete or leet, or millstream) is the name, common in the south and west of England and in Wales, for an artificial watercourse or aqueduct dug into the ground, especially one supplying water to a watermill or its mill pond. Other common uses for leats include delivery of water for mineral washing and concentration, for irrigation, to s...
• (n.) An artificial water trench, esp. one to or from a mill.
A manmade water channel usually built to supply water to a mill.
Leat noun [ Confer Lead to conduct.] An artificial water trench, esp. one to or from a mill. C. Kingsley.