The Drainage Mill is used to reduce the level of the water table in nearby fields. The area was badly flooded in 1938 by the sea and the mill was working continuously 4 months to drain the land although it was a further 5 years before the salt levels reduced for farming to resume.
Re TG4522 : Horsey Drainage Mill (National Trust), is this the one that features on the current RAC advert for in-car activities for kids to play? The advert shows something like this location, but the road appears to run to the left of shot in a very straight line with the mill on the right. The cut wuth the boats moored on it looks from the advert to run exactly parallel to the road.