AFFORESTATION OF WATER CATCHMENT AREAS. 19I 



23. Afforestation of Water Catchment Areas. ^ 



Ey George Baxter, M.Inst.C.E. 



Afforestation is without doubt of great value in relation to 

 the collection, conservation and purity of water. 



It is now universally recognised that certain diseases are 

 water-borne, particularly typhoid fever. It is therefore the 

 plain duty of the Local Authority to place every barrier they 

 can between sources of pollution and the public. Local 

 Authorities are not only expected to discourage, but, where 

 at all possible, to abolish absolutely human habitations and 

 farming operations on their Catchment Areas. This may 

 almost be treated as an axiom of public health. 



Apart from the question of ensuring purity of water-supply, 

 there is no doubt that an afforested watershed is beneficial for 

 other reasons. It prevents sudden and heavy flooding, and 

 consequently less debris is carried down by the streams to silt 

 up the reservoir. All masses of woodland increase the humidity 

 of the air, and this tends to increase rainfall. The influence 

 of forests on evaporation is also very marked. It has been 

 proved by experiment that the evaporation in woodlands is 

 less than half of that which obtains in free and open areas in 

 the same district, and there is thus saved to the water-supply 

 a considerable portion of the precipitated rain which would 

 otherwise be lost by the action of sun and wind. 



It has been objected that wooded drainage areas may pollute 

 the water-supply on account of the enormous quantity of 

 dead leaves decaying on the watershed, or blown about and 

 carried down by the feeders to rot in the reservoirs. Eminent 

 physicists have proved, however, that the sour humus of a 

 forest is antagonistic to pathogenic bacteria, and the last 

 objection is guarded against in all skilfully designed works 

 by planting the first hundred yards next the water-course with 

 irregular clumps and bands of gorse and shrubby small-leaved 

 plants to form leaf-traps. 



I am strongly in favour of laying the watershed derelict, and 



1 This report was furnished by Mr George Baxter, engineer and manager 

 to the Dundee Water Commissioners, at the close of last year, in response 

 to a request of the Water Committee of that town that he should report 

 on the advisability of afforesting the catchment area from which the 

 Dundee water supply is obtained, and the employment which could be given 

 in connection therewith. 



