77/7: SOU.. r>3 



outlet. Drainage from the river, canals and higher lands 

 infiltration is a great source of subsoil water. In 

 Kii'vpt infiltration often raises the water table to very near 



o*. i / 



the soil surface, and evaporation without drainage causes 

 saltness of the soil. In low-lying lands the only possible 

 way of lowering the water table and preventing saltness 

 is by drainage, either by draining the soil or tapping the 



Drains in Sandy Soi/ 



Drains in Clay Soil 



n 





FIG. 1. LOWERING OF THE WATF.K TABT.K BT DRAINS. 



infiltration water from the higher neighbouring lands 

 by means of an infiltration drain. The degree to which 

 the water table is lowered by a drain depends chiefly on 

 the permeability of the soil. Close to the drain the water 

 table will be lowered to nearly the level of the water in 

 the drain ; further away the water table will be higher 

 owing to the resistance offered by the soil to the horizontal 

 motion of the water. Half-way between the drains the 

 water table will be nearest to the surface. 



