ix.] WARPING 295 



Warping. 



The operation of "warping," or "colmetage," is 

 only possible in the vicinity of tidal estuaries, where 

 lands exist below the level of high water, and is in 

 this country practically confined to the estuaries of 

 the Humber and Ouse. Warping is carried out by 

 the construction of a wide drain protected by sluices 

 from the tidal river to the low land, which is first 

 divided by embankments into compartments of various 

 sizes up to 150 acres. When the embankments have 

 become consolidated, the flood tide, heavily charged 

 with suspended matter which is really fine earth 

 brought down by the river, is admitted into the 

 compartment, where it deposits most of its silt and 

 is allowed to run off when the level of the water in 

 the river has fallen during the ebb. The operation 

 is repeated until a layer of silt has formed 1 to 3 

 feet thick over the land, which is then dried and 

 brought under crop. As the chief deposit is always 

 near the mouth of the drain, where the velocity of 

 the silt-bearing current is first checked, the position 

 of the inlet must be shifted about to secure a 

 uniform deposit all over the land and to distribute 

 the valuable fine silt which settles furthest from 

 the inlet. In some cases the sluice gates are auto- 

 matic, and water is admitted and drawn off at 

 every tide, but in others only every other tide is 

 admitted, thus giving time for the deposit of the finer 

 particles, and greatly improving the character of the 

 resulting land. As a rule, only the spring tides are 

 utilised, because the suspended matter is then at its 

 maximum, and the process is confined to the summer 

 months, to avoid danger from flooding when there is 

 much land water about. In exceptional cases land 



