208 Journal of Agriculture, Victoria. [10 April, 1918. 



greater body of excavated subsoil, on being returned to its original 

 position, often becomes puddled, and forms a catcbment for surface 

 water. 



In planning the sub-drainage system of an orchard composed of level 

 land, it is often preferable to provide an open head ditch, into which the 

 lateral parallel pipe drains are made to deliver the water, rather than 

 connect them with a 4-inch main pipe drain. The bottom of the ditch 

 should be from 4 to 6 inches below the point of water delivery from the 

 pipes so that the latter may not become blocked up with silt, &c. The 

 ends of the pipes entering the open drain should be covered with gal- 

 vanized Avire netting, -^-inch mesh, to exclude rats and other vermin. 



When minor surface inequalities occur in the plane of a slope to be 

 drained, these may be OA'.ercome by altering the depth of the lateral drains 

 at the various points where required to insure gravitation to the maiii 

 drain. Where several planes, with possibly various degrees of decline, 

 are involved in the drainage system, however, main drains, whether open 



Surface' J/evel' 



Plate 159. — Cross Section of a Tile Drain. 



or piped, must be carried systematically along the lowest parts. The 

 small parallel drains of each plane should, Avlien practicable, run directly 

 down the greatest fall, and junction at the necessary angles with the 

 larger drain. 



Steep inclines, owing to cross impervious under-strata or spewy sub- 

 soil, need under-draining more than much less abrupt slopes which offer 

 better natural drainage. 



Plate 159 depicts in cross sections a tile drain in course of construc- 

 tion. When the soil lends itself to free Avorking, the drain excavation 

 is usually commenced by opening up as deep a furroAv as possible with 

 the plough. This is made deeper still by the use of an ordinary spade, a 

 special draining spade completes the work, as shown at (a). A draining 

 scoop cuts out the portion of clay marked (h), thus rectifying inequali- 

 ties in the grade of the bottom decline, and offering a solid and suitable 

 bed for the tiles. The drain pipe (c) is shoAvn in position on the tile 



