22G FEEtlMINABT TEEATMESTT OF WATEE-tOaaED tAlM). 



In the interior of the Himalayas, where unsaleable refuse-wood 

 from timber-sawings is available in large quantities, wood may 

 be used instead of stone in constructing box and couple drains, in 

 which case it will always be advisable not to omit the packing of 

 small stones. 



When stones or straight small wood are not obtainable cheap 

 enough or in sufficient abundance, drains similar to rubble, box, or 

 couple drains may be made with tiles or bricks, whole or broken 

 as the case may require. In ordinary tile drains, semicylindrical 

 tiles are placed on a flat sole, as represented in Fig. 71. A simpler, 

 and, for this country, more economical plan would, however, be to 

 burn entire the cylinders moulded for ordinary roofing tiles and to 

 arrange them so that the narrow end of one cylinder iits into the 

 broader opening of that next above it in the drain. Pipe-tile 

 drains will seldom be used on account of the expense. 



The best trenching tools for cutting drains are spades, shovels 

 and hoes in soil free from stones, and picks and mattocks in stony 

 soil. The spades should be of sufficient width, according to the 

 diminishing width of the excavation. A shovel much bent at the 

 neck and pointed (Fig. 72), or a spade with the handle consider- 

 ably bent, are very convenient to finish the bottoms of drains with. 

 Gauges (Fig. 73), showing the depth and width of the drains, are 

 indispensable, as are also instruments for giving the exact fall re- 

 quired. A large level, like a mason's ordinary level, spanning 

 about 10 feet and with the tie-bar graduated to read degrees or 

 gradients by means of the plumb-line, is an excellent instrument 

 for the latter purpose. 



A system of drains may comprise three inter-subordimated 

 classes of cuts or channels : — 



(1) The collecting or ■primary drains or cuts, which are intended 

 to collect the excess water from the layer of soil to be drained and 

 pass it on to the next larger drain ; 



(2) The receiving or secondary drains or cuts, the object of 

 which is to connect together the primary channels and carry away 

 their accumulated waters ; and 



(3) The main or outflow drains, which, when the area to b« 

 drained consists of more than one little drainage basin, unite several 

 receiving channels into a single system and conduct the total 

 Volume of excess water to the nearest large stream. The main 

 drains are often the natural drainage channels widened and 

 straightened and given the necessary fall. 



