Sentence:  Large fields are surrounded by embankments, dykes are cut, and sluice hates placed; when <WSD>warping</WSD> is in progress the gates all along the dykes to the tidal river, miles away, are opened. 
Meaning of the word marked with <WSD> tags:  To fertilize (low-lying land) by letting the tide, a river, or other water in upon it to deposit silt and alluvial matter.