Warping was costly as specially made sluice gates had to be built, and embankments with sloping sides had to be constructed around the fields in order to contain the water.
As the tide ebbed, the water was allowed to escape slowly back into the river, having deposited most of its mud on the surface on the enclosure in which it had been penned.
The result was a perfectly flat field, and if warping was carried out, during the several spring tides, for two or three years, a layer of fertile silt of perhaps a metre or more, would have been laid down.
[1] As the process was expensive it was generally the prerogative of wealthy landowners and could only practically be carried out where the land to be improved was in a few hands, and agreement could be reached to share the costs.
The first reliable report of warping seems to come in the 1730s from Rawcliffe, which is near the confluences of the Ouse with the Aire and the Don, where a small farmer called Barker used the technique.