lxxxii. ABSTRACT OF PROCEEDINGS. 



The end of the pump delivery pipe in the settling tank is 

 provided with an apparatus for spraying the water whereby 

 its complete aeration is secured. Aeration is hardly required 

 for the river water, but is necessary for the storage water 

 which, being of a stagnant character, is deficient in air. 

 Three systems of piping are provided for the filter beds — 

 one to supply them with water, one to convey away the 

 effluent to the clear water tank, and one to collect and 

 convey away waste, scour, and overflow water. Each 

 system of piping is provided with the necessary stop valves, 

 but there are none of the automatic control arrangements 

 which are usually found attached to modern types of filter 

 plant. The main effluent pipe winch receives the filtered 

 w T ater from each of the four beds has a stop valve on it at 

 its outlet at the clear water tank. This valve did not exist 

 in the original design, and was subsequently added to pro- 

 vide better control over filtering operations. 



The sludge — largely composed of decayed vegetation — 

 which lay in the bottom of the old lagoon, was not wholly 

 removed when the reservoir was formed, and is added to 

 by the death and decay of water weeds which grow luxuri- 

 antly in the reservoir. Endeavours have been made from 

 time to time to get rid of the weeds, and large quantities 

 have been removed, but fresh growths rapidly replace them. 

 The sludge has a deleterious action on the quality of the 

 water. During summer the water rises in temperature ; 

 when the cold of winter comes the surface layers are 

 chilled and sink and displace the bottom water. A vertical 

 circulation ensues which brings up the stagnant water 

 which has been lying in contact with the sludge, and a 

 general deterioration in the quality of the whole of the 

 water consequently follows. 



The filtering medium is clean river sand 2 feet 6 inches 

 in depth, resting on 6 inches of fine gravel, under which 



