238 



CASSELL'S POPULAR GARDENING. 



venting the mains from being silted up, as too often 

 happens when the collecting di-ains enter the dis- 

 charging mains at right angles. In cases where the 

 main may be carried along almost in the middle of 

 the area to be drained, no two tributaries should 

 meet opposite to each other, as shown at Fig. 14, as 

 then the two currents might about neutralise each 

 other, and a deposit of silt be left in the main, the 

 natural legacy of two currents, of almost equal 

 strength, meeting at right angles. 



The Depth, of Drains.— Much, as has already 

 been hinted, depends on the local soil and subsoil; 

 and where the system of cutting off the subterra- 

 nean excess of water is adopted, very deep drains 



Fig. 13.— Angle of Secondary Drain. 



may sometimes prove the most efficient. All garden 

 drainage should also be deeper than that of fields. 

 The tilth, the cultivation, the roots of the plants, 

 are all far deeper in the garden, and hence the 

 absolute necessity of deeper drains. In addition to 

 this, fruit gardens should be more deeply drained 

 than vegetable, though the roots of the latter will 

 occasionally find theii- way into and block up drains 



Proper Arrangement. Improper Arrangement. 



Fig.l4 .—Meeting op Tributaries. 



a yard or more deep. In aU gardens in which 

 fruit or ornamental trees and shrubs are grown, the 

 drains should be at least four feet deep. Allow- 

 ing a foot or so for the drainage material of stone 

 or rubble drains, this would allow a clear three 

 feet from the surface of the soil to the top of the 

 drainage material. In the case of tile drains, three 

 feet six or three feet nine inches clear would be left 

 between the crown of the tile and the surface of the 

 mould. But for the expense another foot might 

 very well be added to the four here recommended 



for garden drains, as garden tilths, especially those 

 devoted to tbe cultivation of the best vegetables, 

 can hardly be too deep, nor rich ; and by the ojjera- 

 tions of natural laws and the application of manures, 

 the tilths have a tendency to grow as deep as the 

 drains. 



Frequently, too, the depth has to be curtailed, owing 

 to the fact that the natural outlets — that is, ditches, 

 streams, or rivers — are so exceedingly shallow. It 

 is generally an expensive operation to deepen these, 

 not seldom impossible ; and hence the natural outfall 

 must too often be made the measure of the depth of 

 the main drains. 



Unless this is found sufficient it should never be 

 accepted as the only possible outfall without testing 

 and trying for a lower one ; and, indeed, the depth 

 and direction of the main drain should always be 

 determined first. This found, and the general 

 average elevation of the land to be drained also 

 ascertained, the possible depth of the drains becomes 

 a mere matter of calculation. 



If sufficient depth and to spare is found to exist, 

 it is easy to choose out of this excess ; but if a useful 

 depth cannot be commanded, some other lines at a 

 lower level must be found for the main di-ains. 



Fall of Drains — The exact ratio of falls is 

 really of little moment so long as the water runs, 

 and the choice of any special fall, as a quarter or half 

 an inch to ten feet or twenty feet, is seldom com- 

 pletely in the power of the drainer. Where the 

 drains are made parallel with the fall, they simply 

 follow the same level, or nearly so, as, of course, it 

 would be undesirable or mischievous to follow the 

 ups and downs of any trifling surface irregularities. 

 In these cases the workmen are mostly provided 

 with a stake furnished with a cross-bar across the top 

 to keep it on the exact level of the surface. (See 

 Fig. 21.) By placing a second cross-bar across to 

 indicate the Avidth of the drain, a handy test of the 

 correct size and depth of the drain is always on the 

 spot. 



A very simple way of securing an even fall in the 

 bottom of drains where the surface is uneven, is to 

 use long borning-stakes with cross-bars, as already 

 described. Place one permanently at the farther 

 end of the drain, or at any handy distance where the 

 level has been ah-eady ascertained; place another on 

 the tiles already laid ; and the third against the work 

 proceeding. If the three can be sighted at once the 

 drain has the proper fall. Another way is to find 

 the entire fall from one end to the other ; calculate 

 how much that amounts to for every ten to twenty 

 feet ; nail or screw a piece of wood on to one end of 

 the straight-edged spirit or foot-level, and place this 

 end on to the lowest part of the drain. When the 



