22 AGRICULTURE IN THE TROPICS [PT. I 



Irrigation is a matter of great importance in the tropics, 

 because near the equator, where the rainfall is plentiful enough, 

 the standard crop is rice, which requires definite irrigation, and 

 because further away from the equator the rains only fall for 

 part of the year, and are often uncertain, so that without a 

 guaranteed water supply the raising of crops would be a very 

 precarious matter. 



In some places, where there are no streams, the rain water 

 is simply held in the fields by damming them up, but as a rule 

 the water is obtained from the streams, little or big, in the 

 neighbourhood, by damming them up by what are often called 

 anicuts (weirs), and thus diverting the water into the fields. 

 These anicuts may be of all sizes, from the tiny dams in use in 

 southern Ceylon, of a few yards in length across a little brook, 

 to the stupendous anicuts across some of the large rivers in 

 India, and which irrigate hundreds of square miles, often at a 

 great distance. 



By means of the anicut, the water of the stream, which 

 would otherwise simply run to waste, is prevented from doing 

 so before it has done all the irrigation required of it. It is 

 diverted into a channel which only falls at the minimum slope, 

 and is consequently made to water as much land as possible, to 

 which it is conveyed by a system of canals and sluices. The 

 canals continually subdivide, and form a system not unlike the 

 branches of a tree. In the simple irrigation of a small valley, 

 as in the low country of south Ceylon, no irrigation sluices or 

 gates are definitely made, but the water is simply dammed up 

 or diverted as required by hand labour with piles of mud. In 

 the great irrigation works of India, on the other hand, most 

 elaborate systems of gates, sluices, and canals are made, and 

 the water is distributed through these under skilled super- 

 intendence. 



At first the Indian Government only made the main 

 channels, and left the cultivators to construct the minor 

 channels for the actual distribution, but this led to great 

 abuses and serious waste, and now the whole system of canals 

 is made by the Government in the first instance. 



Where the water has thus been provided by the Government 



