250 



Journal op the Department of Agriculture. 



so prevent scouring of the canal. The bed of this basin must be 

 12 inches below the bed of the canal. 



(/) Earth Bank. — On the up-stream side of the dam the ground 

 must be ploughed over, and all soil containing any vegetation or 

 vegetable matter removed. Only soil free from these must be used 

 in the earth bank. The soil in the down-stream side of the dam 

 should not be disturbed. It will be well to commence operations 

 after some rain has fallen, or if this cannot be waited for to give the 

 seat of the earthen wall a wetting in order to ensure a proper bond 

 between the foundation of the earth bank and the soil being deposited 

 on it. It is wrong to bring absolutely dry soil on or into the earth 

 bank, as this will only be pulverized by the draught animals, and 

 no proper consolidated mass can be obtained. It is, therefore, well 

 not to plough over more ground than can be used in one shift of say 

 4 hours in order not to lose all humidity in the loosened ground. The 

 ground is conveyed to the wall by means of dam-scrapers pulled by 

 oxen or donkeys. 



C f'^s/- O^ IXo^ri 





A better consolidated wall will be made by using oxen instead 

 of donkeys as draught animals, for they are much heavier in weight 

 and have split hoofs. For bringing the earth into the wall endeavour 

 must be made to let the animals follow a course as much as possible 

 parallel to the centre line of the wall. The wall should be carried 

 out in layers of 6-incli thickness spread over the whole width of the 

 wall, having a slight dip towards the centre of the wall. These dams 

 are generally commenced after the rainy season and finished before 

 the wet season starts again. It may happen that the dam cannot 

 be completed before the rainy season starts, and in this case it will be 

 necessary to take precautions to allow floods to pass without doing 

 damage to the works already carried out. Any water gathered in the 

 storage basin can be tapped by means of the outlet pipe, and the 

 works can be resumed. No matter how thoroughly the work has 

 been carried out, settlement in the embankment must be anticipated 

 and provision made therefor. The embankment should, therefore, be 

 carried out 12 inches, higher than originally designed to allow for 

 this. 



{g) Pit clung. — The up-stream slope of the embankment is 

 provided with a 6 or a 9 inch dry-stone pitching resting on 4 or 6 

 inches of gravel. The stone mnst be hand-packed and must rest well 

 into the gravel. All openings in between the stone must be filled up 

 with smaller stone, and then rammed in with a 4-lb. hammer. The 

 idea of the pitching is to prevent the wave action drawing away thp 



