592 Journal of AgricitUure, Victoria. [15 Oct., 1919. 



advantage. Such conditions will also govern tlie size of tiles for the 

 main drains, which should be 3-in, or 4-in. as the particular conditions 

 may warrant. 



The open ditch is preferable to main pipe drains for carrying off 

 the drainage from the laterals, and when being made, care should be 

 taken to see that the sides of the ditch are sloping. By so doing, the 

 erosion and falling in of the banks will be minimized. 



Open drains soon become clogged with dehris, and should be cleaned 

 out as occasion requires, in order to render them permanently effective. 



Depth of and Distance between Drains. 



In order to determine the depth and distance apart of the drains, 

 the nature of the soil must necessarily be considered. 



Where the soil is of a heavy and compact nature, with a retentive 

 subsoil, it is not, apart from the matter of expense, advisable to place 

 drains too deeply in the soil. If this were done, it is probable that 

 their efficiency would not be as great as if they were at a lesser depth of, 

 say, 2 ft. 6 in., or 3 feet. In soil lighter in character, it is advisable 

 to make the drains another 6 or 12 inches deeper. 



The depth at which drains are placed should govern the distance 

 between the drains, as a drain at a depth of 2 ft. 6 in. or 3 feet will 

 not be effective over so great a distance as one placed deeper in the soil. 

 Thus more drains will be needed where the depth is less. In the latter 

 case, the distance apart of the drains, in order to be effective, should be 

 from 20 to 40 feet, and placed midway between the rows of trees, whilst 

 if placed at a depth of 3 ft. 6 in. to 4 feet, in soil of a light character, 

 the drains would probably operate well if at a distance of 60 feet to 

 80 feet. 



Where the drains are placed at lesser distances apart, the water 

 table is deepened in comparison with the table created by drains placed 

 at greater distances. This is illustrated in plate 20. Between the 

 drains A and C, the water-table marked 1 is nearer the surface than 

 at 2, where the water-table has been formed by placing another drain 

 at B, midway between A and C. 



Thus it will be seen that underdrains do not create a water-table at 

 the same level over the whole area. At the part where the drain is laid, 

 the water-table is lowered to that level, but is considerably higher 

 mid-way between each drain. Where the rainfall is excessive, it is well 

 to supplement the work of under-drainage with surface drains which, in 

 their own way, do much to relieve the pressure placed upon the under- 

 ground drainage system; but surface drains alone are insufficient to 

 thoroughly drain the land. 



In plate 'No. 23 is shown an open drain made on a hillside to 

 prevent the surface water and seepage from the higher ground reaching 

 the orchard below. Before this drain was made in an orchard at 

 Diamond Creek, much trouble was experienced with wet conditions in 

 the orchard situated on the lower part of the hill slope, and caused many 

 of the young trees to remain stunted in growth. After the drain was 

 made, however, beneficial results followed at once, and the stunted trees 

 made good growth during the following season. 



By looking carefully at the illustration of this drain, it will be 

 .seen that stones were placed at the bottom of the ditch to prevent 



