240 lEETGATION. 



exists than the Rurki Manual, to which therefore the student is 

 referred. 



The following paragraph adapted from Ribbentrop's " Hints on 

 Arboriculture in the Punjab," describing the system followed in 

 Changa Manga, will be found interesting as well as instructive : — 



" There are three descriptions of irrigation cuts, (i) the rajbahas 

 or main feeders, (ii) the secoKdary feeders, and (iii^ the trenches 

 or distributing channels. The rajbahas receive the water direct 

 from the canal by means of a water head or Mogha, the secondary 

 feeders convey the water from the rajabhas to the different points 

 of the area to be irrigated and the trenches bring the water up to 

 the plants. The width and depth of the first two classes of 

 channels of course depends on the area which they are required to 

 serve. The width of the section of a rajabaha may be from 12 to 

 14 feet at the top. The exact dimensions to give to the secondary 

 feeders, of which there is one for each compartment, are more 

 difficult to calculate and depend not only on the area of the com- 

 partment in question, but on the fall attainable. The trenches are 

 only r X 1'. In loam the large channels are given sloping sides 

 of about 45°. In sandy loam or sand the cant is stronger, increas- 

 ing in fact with the looseness of the soil. It is of the utmost 

 importance to give an uniform fall to the feed channels, otherwise 

 silting up of the beds and the destruction of embankments must 

 ensue. The fall we adopt depends chiefly on the fall in the canal 

 and the height of the weirs from which we receive the water. We 

 have everywhere tried to obtain the highest fall possible up to a 

 maximum of from 1 to 1^ feet per 1000. Care is to be taken that 

 the excavated earth fi'om the feed channels is thrown up equally 

 on both banks. The silt and vegetation that collects in the chan- 

 nels is cleared each time they are to be used," 



