1905.] Hints on Water Supply. 



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It may be that in some districts which can yet depend upon 

 good supplies, the effects of the scanty rainfall during the 

 months which have passed may not be felt until later in the 

 year ; but it is important to remember that the degree of in- 

 filtration of all the rain which usually falls during the summer 

 months is so trifling as to be almost negligible as a means of 

 replenishment of springs and streams and well-sources. 



To appreciate the physical conditions which govern the pro- 

 vision of subterranean supplies, it is important to remember that 

 during the period of greatest rainfall, say from October to March, 

 the needs of vegetation and the evaporating power of the sun 

 are far less than during the remainder of the year, when these 

 two factors are usually sufficient to account for nearly all the 

 rain which falls during the drier period. It is, therefore, upon 

 the autumn and winter rains that we have to depend for the 

 maintenance of the supplies contained in the saturable " rocks/' 

 or in the fissures of " rocks," the substance of which is less 

 permeable. 



Broadly stated, a " land spring " is the overflow of an under- 

 ground water-bed, which may be compared to a dish filled up 

 with water-saturated earth. So long as the " level of satura- 

 tion " is maintained ever so slightly above the edge of the 

 dish, water will escape ; but unless that level be maintained 

 by additions from the surface, the overflow must cease and the 

 spring fail. This comparison is not, perhaps, scientifically 

 exact, but it may suffice to show that when a spring either 

 yields a diminished flow or fails altogether, the supply may 

 often either be increased or restored by lowering the level of 

 the overflow, or — to pursue the illustration, — by chipping a 

 piece out of the edge of the dish. This can be done, where the 

 nature of the soil permits, by digging a trench to the necessary 

 depth below the point where the spring bursts out. Perhaps 

 only a foot or two of digging may suffice to restore the flow ; but 

 if, after a depth of, say, 10 ft. or 12 ft. below that point has been 

 reached, the result is not satisfactory, advice should be taken as 

 to the practicability of a well at some distance above the spring- 

 point, that is to say, nearer to the centre of the dish. 



A trench of more than 30 in. in depth should be formed with its 

 sides sloping outwards, in order that they may be prevented from 



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