For example, a millrace is a sluice that channels water toward a water mill.
From the en.wikipedia.org
All the rooms have views over the idyllic gardens, which are bisected by a tranquil millrace.
From the telegraph.co.uk
Near the sawmill shore, near what might have been safety, the ice simply ended in a deep flow of river water from the millrace.
From the theatlantic.com
The tangential water inflow of the millrace made the horizontal wheel in the shaft turn like a true turbine, the earliest known.
From the en.wikipedia.org
Follow the millrace to another stile by the weir before bearing left across the next field to a gate on the left of a high wall surrounding the National Trust's Nunnington Hall.
From the gazetteherald.co.uk
These grooves formed the millrace, increasing the speed of the water as it approached the sawmill so that it would have adequate force to turn the mill's huge waterwheel.
From the en.wikipedia.org
More examples
A channel for the water current that turns a millwheel
A sluice is a water channel that is controlled at its head by a gate (from Dutch word 'sluis'). For example, a millrace is a sluice that channels water toward a water mill. The terms "sluice gate", "knife gate", and "slide gate" are used interchangeably in the water/wastewater control industry.