LII. J. B. HENSON. 



general deterioration in the quality of the whole of the 

 water consequently follows. 



A few years ago the author designed a small syphon 

 suction dredge to be operated by the difference in head 

 between the water in tlie reservoir and that in the old 

 lagoon at about 20 feet lower level. The dredge was con- 

 structed and acted most efficiently; a large quantity of 

 sludge was removed without any appreciable disturbance 

 to the water in the reservoir; the results were beneficial. 

 The foregoing brief description of the waters which have 

 to be used, show the importance of subjecting them to 

 careful filtration and management. 



The present arrangements for filtering the water are as 

 follows : — A settling tank into which the water to be filtered 

 Is delivered from the pumps; four filter beds at a lower 

 level, each 100 feet square, on to which the water from 

 the settling tank is delivered by gravitation — the filter beds 

 have no roof over them ; a clear water tank at a lower level 

 into which the clear effluent from the filter beds flows. 



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 which receives the filtered 

 water 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- 



