CHRISTCHURCH DRAINAGE.

Globe, Volume XXIV, Issue 2633, 14 September 1882, Page 3

CHRISTCHURCH DRAINAGE.

Tbis morring a party consisting of present and former membsrs of the Ohristohuroh Drainage Board and several other gentlemen —the party numbering about twenty five—were driven from the Board's office to the Sandhi'ls for the purpose of inspecting the result of the first matalment of the sewage of Ohristohurch being turned on to the reserve belonging to the Board. A call on the road was made at the pumping station, where everything was found to be in the neatest order. One of the engines and one set of pumps were in motion. The work of pumping had been stsrted on the previous evening. The machinery worked with very little noise, and, notwithstanding the massive size of the several pieces, there was no peroeptible vibration of the building. The maohinery in motion is capable of discharging into the outflow pipes 550 cubic feet, or 3300 gallons, of water per nv'nute; the four pumps r-e calculated to be able to dispose of the sewage of a town having 90,0 C ) inhabitnfs. This morning the driving wheel of tbe engine was making about seventeen revolutions per minute on a pressure of 261bs of steam.

The collecting tank, which is an immenße ■amp that receives by gra-pi'ition the discharge from the sewers reticulating Christohuroh, is within a few yards of the engine house. It has a history of its own, having been constructed by the exercise of extra* ordinary ingenuity and patience in the face of difficulties sufficient to discourage the efforts of any ordinary person. The engineer to the Board, himself no mean authority, after experiments, did not aornple to say that the estimate he gave of its cost might prove altogether wide of the mark. The treacherous nature of the ground—a quicksand—indeed, for a time, rendered it doubtful whether or not the tank could be made at all. However a contractor was found to undertake the task, and did his work in an eminently satisfactory manner. On the surface of the ground there is not much to be seen now of the trouble Mr Parsons found, but it is certain that the fixing of this tank was the most difficult part of the whole soheme. At the time of the visit the ooveu were lifted, and the sewage was seen discharging i' elf at a depth of about 25ft from the pipe through a sieve grating, which au'ests the largest of the solid matters that find their way so far. There i* a pit at the back of the grating into which these solids fall. It was not explained what quantity *f! thus arrested, or what arrangements existed for their removal, but doubtless these details have been oarafully provided for. Although the trap shaft through which the grating was to be seen noted as an upcast, there wn only a very faint effluvium to be deteoted. The liquid flowed into the tank with a not rapid ourrent.

After leaving the pumping station the party drove due er*t about two miles from town to the boundary of the reset vo. Alighting, a short walk brought them to a point where iron pipes starting from the pumping station end. A concrete lift of about 6ft n height conveys the sewage into open box fluming which in its turn gives plaoe to an open race, carried along sidelings, or embankments, as rendered necessary to suit the contour of tha land. The pumps, as said before, had been going from the previous night, and the sewage was rushing with considerable velooity through the fluming, but had not advanoed mora than ICDO feet in the open raoe. This is easily accounted for, as the race Is constructed of sand only. The batter of its banks is secured by manuka scrub securely pegged down; a plan by the way whiob, while answering perfeotly its design, would, in oase of a grass fire, be found to be the cause of trouble. The ground of the reserve is more than rough, it is hillooky, the little valleys or holes being considerable depressions. The general formation, however, will allow of a series of ponds being formed, making a chain from the e-_d of the fluming to the sea beach, which, of course, is the ultimata sewage-shed of the soheme. The engineer is sanguine that a great quantity of the liquid will disappsar by percolation, that, in short, very little _ will have to put over the bexch. It is to be supposed that due allowanoe has been made for the possibility of tho sediment making the ponds named watertight, and thus converting them into stagnant reoeptaoles of filth. There seems, too, the contingency, if the ponds are discharged of water by evaporation and filterige, of the residuum producing stinks of the most pungent deßoription. This experience alone can determine, and at present the speculation is useless. It is quite certain, however, tint although tho open raoe is carried through a section bristling with the stuff which the City Oounoil has for years past been shooting there, and at the time of inspection a hot north-wester was blowing, there wss soaroely the suspioion of a bad smell, and the liquid brought by the sewers was soaroely disoolored. Until, however, several of the " settling ponds " have been filled and have I bee a standing for some time, the matter is scarcely ripe for investigation. The system comprises two engines and two sets of pumps j their oapacity has been noted above—94Ooft of cast iron piping 2£t in diameter, in sections of 12ft; fluming, 3ft by 2ft, 650 ft in length, open race 1850 ft to the first settling pond, and 300 ft asyetdiscon' neoted. The amount of sewage pumped in the last four weeks was 20,50O J O00gals, the running time 119 hours, the cost of working machinery, including wages, about £7l,