SEWAGE FARM.

Auckland Star, Volume LXVI, Issue 203, 28 August 1935, Page 5

SEWAGE FARM.

QUOTED AS MODEL. t CHRISTCHURCH SCHEME. AUCKLAND'S DIFFICULTY. Quoted as a model where similar difficulties are encountered the sewage farm at Bromley, Christchurch, deals efficiently with the sewage needs of that city, of over 120,000 population. It has been in existence for close on 65 years and has converted an area of sand into one of the finest grazing areas in Canterbury. Sedimentation tanks and treatment works deal adequately with 13| million tons of sewage annually, and discharge a purified effluent that is odourless and practically colourless. An irrigation system using this effluent has brought 220 acres of waste land into production. Melbourne has used the same idea with success, but it is necessary to state that that city has a similar condition of small rainfall, and flat country and sea coast conditions that would make any outfall scheme difficult and expensive to achieve. Auckland, it is stated definitely, could not adopt a similar scheme with any hope of continued success. The heavy rainfall here and topographical conditions would create storm-water difficulties that could only be overcome with great expense. Paris and Adelaide. Paris, which has one of the largest broad irrigation systems, with a sewage farm totalling 12,000 acres, is now suffering to a great extent from this "sewage sickness," and it has been reported that there is a most offensive odour in the vicinity of the farm. Adelaide, South Australia, also has a similar scheme to that existing in Canterbury, but' plans are now being considered for the adoption of a better method of sewage disposal in the existing conditions, and the ultimate

abandonment of the irrigation process. However, while it is a system that it seems could not bo applicable in the solution of Auckland's problem, it is interesting to see how another New Zealand city is dealing with the matter. In Christchurch an ocean outfall has proved impossible without huge expenditure and observations taken over a number of years. Even then its success could not be guaranteed for certain combinations of wind and current would lead to deposits on the beaches. It was this knowledge that led the early city engineers to cast around for some other method and the farm scheme was adopted. It means that none of the sewage goes out to sea, and while in a confined area it is responsible for some nuisance, this is inseparable from such a scheme. Begun In 1880. The first sewers were connected in the city about the years 1880 to 1883, and the irrigation scheme was begun at the same time with two small paddocks. To-day the actual area irrigated is 220 acres, but the Drainage Board has acquired a total area/ of 760 acres, sufficient to allow of the trebling of the scheme to meet the needs of the city and suburbs for many years. Only recently the board bought the old Bromley rifle range from the Government, the area adjoining tfce board's property near New Brighton. Thirteen and threequarter million tons of sewage are disposed of annually. Last year the cost of operating the farm was £3407, but against that a return of £1138 was shown in grazing fees from the irrigated property. The expenses could therefore be calculated at £2329, a small sum when compared with the huge expense entailed in other parts for the provision of what may or may not be a satisfactory ocean outfall. Clearing The Water. The system serves the whole of the metropolitan area of Christchurch, including several of the boroughs which for all practical purposes may be accepted as part of the city. The sewage is brought in one big intake to the sedimentation tanks. Each of the three tanks covers' three-quarters of an acre, with a depth of 12 feet. It takes six hours for the sewage ,to pass through, in the process being freed of offensive content. When the effluent emerges from the outlet it is free from any deposits and practically colourless. The tanks are cleared at regular internals.

From the outlet the effluent is conducted by an intricate series of channels round the' 220-acre block and used for irrigation purposes. The land, which now provides some of the best grazing ground in the vicinity of Christchurch, was formerly sandhills, covered with rough scrub and tussock. There are in all 78 paddocks and each in turn is irrigrated on the flooding principle. A series of outlets from the main channel regulate the flow of the effluent over the areas, so that the effluent is distributed evenly. The paddocks range in size from two and a half to four aires. All Water Utilised. Twelve men are employed on the farm under the supervision of Mr. A. Nankivell, who has been in charge since 1904. He joined the staff himself in 1901 whei. only 40 acres were irrigated and has since seen the area grow year by year. The men work in three shifts under a careful system which ensures adequate Ireatment for all the paddocks in turn. All the water from the tanks U utilised. The paddocks are amply drainea, the drainage being conducted to the estuary a few hundred yards away. At the present time the area of 220 acres carries 105 head of cattle, but there have been as many as 500 head on the farm at one time. Lesson for Auckland. The few residents in the near vicinity have had occasion to complain of a nuisance at certain times of the year, but as an engineer explained, with such a system it could not be avoided. Only with the provision of a port for Christchurch on the estuary could an ocean outfall be secured, and it might be that even under those circumstances the nuisance would not be entirely overcome. Christchurch is fortunate to this extent, that its scheme has grown with the city and thus there has been a huge saving in expenditure. In any large city an area of up to 1000 acres would be required and the initial expense would be considerable, particularly as it would probably require the redrafting of the whole plan of reticulation. Even then, as other large cities have found out, it might not be as successful as it is in Christchurch. Auckland can, however, learn one lesson from the Southern city. It can replace its multitude of local authorities with a central authority, which can handle whatever scheme is adopted eflvfiently.