STORAGE AND REGULATION OF WATER. LXI. 



Water being stored and raised, it becomes necessary so 

 to lay out and construct the distributing channels that the 

 largest possible proportion of it shall be delivered on the 

 land it is proposed to irrigate. The loss to the Victorian 

 Irrigation Trusts from this cause is very great, amounting 

 in many cases to between 40 and 50°/° of the total quantity 

 raised. The experience of many of the Victorian irriga- 

 tionists is that if their properties had been properly pre- 

 pared and levelled, two or three times the area they now 

 work could have been irrigated with the same amount of 

 water. In fact the testimony of all the persons who irrigate 

 land goes to prove that money is well expended upon the 

 preliminary work in connection with designs and levels. 



The gradients of the drains mast be such that on the one 

 hand no scouring out will take place, and on the other that 

 no silting up of the channels will be caused. As to the cross 

 sections, that of a semi-hexagon will give the maximum 

 discharge, but the banks will have too steep a slope. A 

 better form is to make the bottom and sides tangents to a 

 semi-circle, when the top width will in all cases be equal 

 to the sum of the slopes. The great loss due to evaporation 

 may often be reduced by altering the sections of the drains, 

 but in porous ground some protective measures must be 

 taken. 



At Mildura, lime concrete has been laid along the main 

 channels and laterals, to the thickness of 3 inches in the 

 former and 2 inches in the latter. The proportions used 

 were 4 of broken stone, and 1 of slaked lime, and the cost 

 was for the 3 inch 1/8 per square yard, and for the 2 inch 

 1/1| per square yard. It has stood fairly well, but cracks 

 do occur in it which permit of a certain amount of leakage. 

 An improvement on this, though of course it would be 

 more expensive, would be to have marsupial netting 

 embedded in concrete 3 inches thick, such as I have used 



