INTRODUCTION 21 



float experiments, however, may be misleading is shown by an 

 instance at Sydney, New South Wales, where it was found that 

 the iloats at the proposed Bondi outfall site drifted northward, 

 whereas when the sewage came to be discharged it flowed to 

 the south-east in a black stream, " widening until it gets about 

 half a mile from the outlet, when it disappears." It is 

 suggested that the influence of the air currents on the floats 

 was greater than that of the water currents.^ This would show 

 the utility of the deep-weighted tube float we recommend in the 

 next chapter. 



In many towns the sewage is stored in a culvert or intercept- 

 ing sewer, or in a covered storage tank, and let out on the 

 ebbing tide, with the object of being carried well out to sea 

 before the return. But the disposal of crude sewage in this 

 way is never satisfactory, especially where shellfish are gathered 

 from the coast. Previous treatment by an approved method 

 should always be adopted, and probably in the future will be 

 made compulsory. In some places the sludge is intercepted in 

 large catchpits before entering the tank, and either disposed of 

 on land or carried out to sea. 



It is rarely possible to extend a pipe line across the foreshore, 

 and to discharge the sewage into deep water, even at the lowest 

 ebb of spring tides, at a point where the tidal current has a 

 seaward set, as has been lately accomplished with great expense 

 and difficulty by the Llandudno Urban District Council. Here 

 it was necessary to cover the pipes with a great quantity of 

 stone for their protection, and the original estimate of cost was 

 greatly exceeded. Where the geographical conditions are not 

 so favourable, as in estuaries, and also on the almost unbroken 

 shore-line of many coasts, there is almost a certainty that the 

 sewage will be retained in the neighbourhood, or will be brought 

 back by eddies and currents even if carried out some distance, 

 as has happened at Brighton. In America, where the infection 

 of oyster-beds by sewage has been a question of importance for 

 the last eleven years, the great majority of cities discharge 

 untreated sewage.^ Thus, out of an urban population of 

 28,000,000, 6,500,000 discharged raw sewage into the sea, 

 harbours, or estuaries, 20,500,000 into inland streams or lakes, 

 and only about j, 000,000 had sewage purification works. 



^ Davis on " Sewerage Systems of Sydney, ^.^.W.^'' Proceedings of the Institute 

 of Civil Engineers, 1902. 



- Fuller, Transactions of the American Society of Civil Engineers, vol. liv., 

 part E, 1905, pp. 148, 149. 



