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require a gradient of three feet to four feet per mile, whereas minor 

 ditches require at least eight feet per mile. In order to guard against 

 the erosion of the sides and the banks being undermined by the 

 water, the soil is cut open at an angle which varies according to its 

 nature. In sandy soil an angle of 45deg. is required ; in loamy 

 -soils, an angle of 60deg. or 70deg.; whilst clay may be cut almost 

 perpendicularly, as it has much tenacity. 



A velocity of three inches per second will remove fine clay ; of 

 six inches per second, fine sand ; eight feet, sand ; 12 inches, fine 

 gravel ; and 24 feet will carry off pebbles. Where the ground is 

 not too full of roots, an able-bodied man may dig from eight to 

 ten cubic yards per day. 



Surface Drainage is the more widely used-system adopted by 

 fruit-growers. Its chief objection is that it at times interferes with 

 horse-cultivation. It is chiefly used for draining boggy land, and 

 often prepares the way for deep drainage. 



For draining a slope or cutting of water rushing from a rising 

 catchment area on to a low flat below, these drains should be made 

 almost at right angle with the flow and empty into a main drain 

 below. The cost of making them is small, and if scoured before 

 the wet season sets in they often prove amply sufficient for draining 

 a piece of ground. 



Sinkhole Drainage. Amongst the limestone coastal ridges, 

 swamps are often met with which have a retentive marly bottom. 

 Underlying that hard pan, sand and limestone are again found. That 

 marl is rich, but as the surface soil above is shallow, and for the 

 greater part of the year partly under water, the ground is unfit for 

 fruit culture. In such hollow localities, where water cannot be 

 carried away by any of the other methods of drainage, holes sunk 

 through the retentive hard pan would carry the water away into 

 the porous soil below very economically. 



Deep Drainage is, if costly, for cultivated fields, the most 

 suitable system of improving wet land. Teams and implements 

 can run without obstruction ; weeds and rubbish are swept away, 

 and have no chance of taking a hold of the land, and the greatest 

 amount of benefit is derived from cultivated crops. It dispenses 

 with open ditches and prevents surface wash, and consequently 

 often great waste of fertility. The method consists in opening 

 deep furrows or ditches, filling them partly with brushwood, logs, 

 stones, or setting draining pipes in them and covering them up 

 with the soil thrown out when excavating the ditch. 



Blackboys and grass trees (Xanthoreas), which are plentiful in 

 the moister region of Western Australia, where drainage is chiefly 

 required, supply excellent material for drains. A trench is dug to 

 the required depth, sufficiently wide to allow two blackboy trunks 

 being laid side by side, the scales facing the way the water runs. 

 Over these a third blackboy stem is laid, the three forming a 

 triangular prism. The trench is then filled with earth, which is 

 trampled down to counteract subsidence, and a crown one or two 



