262 SOILS 



surface by underflow, or seepage from higher land. 

 Lands below large irrigation canals, and receiving 

 its seepage, are often sub-watered to such an extent 

 that they become marshy and unfit for cultivation 

 unless drained; in other cases they produce ex- 

 cellent crops without drainage or the need of any 

 surface irrigation. Of the same nature are certain 

 low lands that receive sub-watering from higher 

 land, either near-by or many miles away. The 

 springs and underground seepage from high lands 

 often follow certain strata of rocks and subsoil and 

 sooner or later come to the surface, watering the 

 land at that point uniformly and continuously 

 from below. 



METHODS OF MEASURING WATER 



The methods of measuring or apportioning 

 water are diverse. It is necessary that they be 

 accurate, especially when the water is purchased, 

 or when several farms are supplied from one ditch. 

 Usually, however, an irrigator receives water not 

 by measurement but by proportion; he is given a 

 certain proportion of the water in a ditch, as one- 

 fifth; and it is not measured by inches, but by 

 proportions of the whole. This is regulated verv 

 simply by placing an upright partition or " divisor r * 

 in the flume or ditch, one-fifth of the way across, 

 so that one-fifth of the water flows into the sluice- 

 way and the remainder passes on. But the ve- 

 locity of the water in the ditch is greater near the 

 centre than on the edges, so that those that use the 

 smallest amount of water always get less than they 

 are really entitled to. To correct this the ditch 

 is often broadened above the measuring box so 

 so that it flows through very slowly. If the 



