164 president's adbress — section h. 



vegetable growth compared with porous bricks moistened 

 with sewage." 



It must be conceded that rain-water in excess is incon- 

 venient, and in some cases may do considerable damage, but 

 it may certainly be allowed to flow off the surface by means 

 of the ordinary surface drains, and it is far better to construct 

 special storm-water channels to relieve low-lying districts 

 than to admit storm-water into sewers. These storm-water 

 channels will only be necessary for probably one-fifth of the 

 length of the sewers, and they need not be constructed at so 

 low a level. Where sewage has to be raised by artificial 

 means is is obviously an advantage to keep the volume 

 constant and reduce it to a minimum, which means the 

 exclusion of rain-water. Again, in the chemical treatment of 

 sewage, or its disposal on a sewage farm, it is most desirable 

 to avoid the uncertain volume of fluid due to rainfall, which 

 in the case of a farm comes at a time when the ground is 

 saturated and least requu-es irrigation. It follows, therefore, 

 that in many inland town in Australia the separate system 

 would be the most convenient and economical, as it has 

 proved to be in America, provided that the upper end of each 

 branch sewer is provided with an automatic flushing tank of 

 sufficient capacity to secure the thorough daily cleansing of 

 so much of the conduit as from its limited flow is liable to 

 deposit solid matters by the way. In Sydney, Dunedin, 

 Wellington, Auckland, Hobart, and other similarly situated 

 towns, there exists a considerable area round the harbours 

 which cannot be included in a purely gravitation scheme, 

 and which could be most conveniently and economically 

 dealt with on Shone's system, and I believe that this system 

 will be largely used in AustraHa and New Zealand in future 

 sewerage works. 



The position of the main outlet or outlets has an impor- 

 tant influence on any scheme of sewerage. If the town is 

 situated near the estuary of a rapid tidal river, or near the 

 sea, so that the sewage may be discharged without creating 

 a nuisance, it generally becomes the most economical method 

 of disposal. As to whether sewage may be safely disposed 

 of by disciiarging into a tidal river, the question can only be 

 decided with reterence to the volume and velocity of the 

 river and the quantity of sewage it is proposed to discharge 

 into it. We must clearly distinguish between the contami- 

 nation of a well where the water is stagnant and the air not 

 frequently changed and the conditions existing in a rapid 



