CHAPTER V. 



-^*>tS^tft>^h~a^ 



The Effects of Forest Covering upon the Catchment Areas 

 of Reservoirs- 



As tte storing of water, and the proper arrangement of tlie surface areas 

 supplying our reservoirs, is a matter of vital importance to the welfare 

 of individuals and well-populated districts in this country, I devote this 

 short chapter to a consideration of how far the planting of trees on the 

 ground from which the water-supply is obtained, aSects its supply. 



In a country like this, where the annual rainfall is so very uncertain 

 and not evenly distributed over the twelve months of the year, and where, 

 in certain districts of it, the supply of water — it may be for the season— is 

 secured from a few heavy thunderstorms only, it is of the utmost impor- 

 tance that every means should be adopted in order that the catchment 

 areas should be managed in such a way that the loss of this may be 

 reduced to a minimum. As a means to this end I advocate the covering 

 or protecting of the catchment areas with a crop of ligneous growths. 

 Let us, however, lool^ at the subject for a moment, and give the reasons 

 for making this recommendation. 



As a rule, the surface areas from which the reservoirs in this country 

 derive their supply of water, consists of hard-baked soil into which any 

 moisture seldom or never penetrates, consequently the reservoirs are 

 dependent entirely upon the surface flow alone for the supply of water 

 to fill them. Hence, two disadvantages arise to the proper management 

 of the reservoirs — first, if a very heavy fall of rain occurs, a large 

 quantity of valuable water is lost by overflowing ; and, secondly, the 

 catchment area is washed clean by the heavy fall of rain, and all debris 

 and loose soil lying upon it is hurled down with the rush of water : the 

 ^es^dt being injury to the quality of the water and the gradual silting up 

 of the reservoir. Now, in such a case as this, the covering of the catch- 

 ment areas with forest growth would diminish the quantity of sUt brought 

 down by the heavy falls of rain, and the roots of the trees having 

 rendered the soil open and porous, the surface flow would be retarded at 

 the time, wMle the reservoirs would be fiUed more gradually, and the 

 flow into them would continue long after the rains had ceased ; hence 

 no loss of water by overflowing would occur. 



• There is no doubt that large quantities of water are annually lost from 

 the reservoirs of this country by evaporation. This occurs in two ways — 

 first, upon the catchment area, the surface of which, being hot and dry, 



