THE CITY DRAINAGE.

New Zealand Herald, Volume XLII, Issue 13032, 24 November 1905, Page 7

THE CITY DRAINAGE.

s MR. MESTAYER'S SCHEME CRITICISED. ;'.;'. REPORT FKOM AN ENGLISH ;'.v ;V'' ENGINEER. I MR. MESTAYER'S SCHEME CRITICISED. REPORT FROM AN ENGLISH ENGINEER. POINTS OF AGREEMENT AND DIFFERENCE. • 'AN ALTERNATIVE SCHEME SUBMITTED. CONSIDERATION DEFERRED TILL FEBRUARY. A XESGTHi* report >>;> the city drainage question, from Mr. U. Midgley Taylor, M.1.C.E., of London, was received by the City Council at its meeting last evening. ■ The Mayer, in introducing tho matter 6«dd the Council would be pleased to recoivt the report in connection with the system o: drainage. It was probably one of the most important matters that had yet engaged tin attention of the Council. ' It was not only a question for the present population, but alst one for those to come in future years, ant with regard to the financial aspect, it was without doubt, one of the most important matters that had been before the Council He-had had the report- fortthe last two, oi three days, and he had prepared a rougl statement of tho points in which Mr. Tay lor agreed with Mr. Mestayer, and of thost in which they did not agree. The Mayo: then read the following summary: — .". POINTS OF AGREEMENT. Mr. Taylor agrees with Mr. Mestayei that where direct discharge of sewage intc tho sea is possible this is 5 undoubtedly tht simplest and best course to adopt, provide* that it can be discharged in such a positior that no nuisance shall arise from subse : ' , quent deposition on the foreshore, but re carding Mr. Mestayer's proposed means oi disposal Mr. Taylor strongly emphasises hi: comment that any means of disposal othei than a crude sewage outflow must involve the treatment of the sewage, and conse quently the resewering of the.whole of th< city. Mr. Taylor agrees with Mr. Mestayo; that a sewage farm or intermittent filtratioi for Auckland would be unnecessary and ex pensive. -Ho also agrees in rejecting de composition and settling tanks. . POINTS OF DISAGREEMENT. Mr. Taylo; does not endorse Mr. Mes layer's proposal to, adopt a- biological me thod of septic tanks, with or without a sup plementary purification of the effluent b; bacteria beds at Cox's Creek. Mr. Taylo considers ' Cox's Creek unsuitable for dis charge of sewage, whether purified or not but it it proves the only available position then it is essential that a large ; degree o ', oxidation and purification be given to th sewage and the effluent conveyed in a pipto low-water mark outside the creek to dis charge intc the true tidal current of th harbour. . '.y-y' £;s&?:~?'y:*r\-:ir : '\:. i.f'i ' THE SEPTIC SYSTEM CRITICISED. Mr. Taylor in no wise agrees in the state ment that in the septic tank treatment pre posed the whole; of the solids ; are retain©' by the tan'- until broken up and liquefied . and that the sewage is modified in its na tare by the bacterial action in the tank s as to be"'deprived of ; its offensive properties On the contrary, he states that a septic tan effluent is one of the most foul-smellin liquids possible, to conceive; neither dot be agree with Mr. Mestayer's suggestio that the 'whole of the solid matters ar broken up and liquefied. Mr. Taylor i strongly of opinion that it is inadvisable t -. discharge ■a, septic tank effluent into 3 th harbour above, the. city until the effluer has been submitted to an oxidising process which would render it inoottous and swee! necessitating- the l ereetiba of adequate ox dising purification works m addition to th ' septic tank, should Mr. Mestayer's schem be adopted.: These works would require fc the present population nine acres and a-hali and when the population of 100,000 person has to be dealt with -nearly three time that area. An additional area would be r< quired for the disposal of sludge. The cos of the. purification works would not be i les than £76,000 for- the- present : pbpulatior and for the'ultimate population of IOG.OC about £200,000,- while a considerable annul expenditure would also be incurred. SUGGESTIONS AND ESTIMATES. 1 If Cox's Creek is adopted for the outfal Mr. Taylor > suggests the "' sewage -: from' tfc southern side of the' city should be; grav fated through a tunnel in preference to b ing lifted over the hill by ejectors. M Taylor agrees with Mr. Mestayer's proposj regarding drainage >at low-lying • areas, bi suggests one- central pumping station i preference to- several ejectors. He does m , agree with Mr. Mestayer's estimate of tl ' cost, but increases it from ■ £232,000 i £365,075, not including cost of land. AN ALTERNATIVE SCHEME. Mr. Taylor puts forward an alternate scheme, viz., that the sewage be discharge ' in'its crude state into the tidal waters i Okahu Point, on the east side of Hobson Bay, such discharge to be ; limited to th top of the flood and the whole of the eh ' ,t»'de. Mr. Taylor forwards a plan showin the main intercepting sewer, commencin at Cox's Creek and following approximate! the lines chosen by Mr.-Mestayer, but fallin in ar opposite direction to Stanley-stree thence up a tunnel under Parnell to Hoi rein's Bay, thence to. the point of the ou fall. This alternative scheme avoids tl necessity of interfering with or relaying tl existing sewers through the city, the pr sent outfalls being used as storm water ove flows. At the outfall - at Okahu Point would be necessary to construct storaj tanks for the five hours during v which tl discharge would.be stopped. The.estima of the cost of the alternative scheme given us £310,000, exclusive of way-leav< through private property. The report coi tains many detailed suggestions,,, but tl foregoing gives a general outline of tl points of agreement or difference with M Mestayer's report on the principles of tl scheme. " Mr. Taylor concludes by stating that g • though he has not had the advantage < studying the true formation of the groun he is in possession of sufficient informatk to satisfy himself that the. only satisfactoi way of dealing with the sewage of Auo land would be on the lines of a scheme 1 has described^ EXTRACTS FROM'. MR. ] TAYLOR'S REPORT. _ Mr. Taylor's report, which it's voluniino \ document, opens by referring to the rate of i >:> urease of the,population of the city, which, ; ; says, indicates an average increase of tiearlv; per cent, in five years. On the assumption'th the same rate will be maintained for the'ne CO year*, the population of the city (which dc not include any of the suburban areas), won than be 100,000, and the report is framed on tl ; •,,•... fcanx.v.Xbe supply of- water at present is <; ciliated at a little over SO gallons daily per he« - and *k>? is the rate of sewage flow adopted the calculations. k ; , : . ; ; THB.PKEBENT SYSIKM. . Scaling with the sting drainage -is the cii the.report says The city is at present drain ' en the •' combined" system": 'Chv. is to say; t sewers a;* as carriers not only for the fe*aj but also for nearly alt the rainfall which hi j-s-»vsporatefl 'V absorbed. As far as we- c RatherCfrom the infocmaticu available, the < J- ■ feting sewers are in itair order,' and genera l sufficient for the purirese they have to serv nod our opinion is Mat supposing a scheme c be devised by which the combined sewage a rainfall waejiing-the existing sowers could intercepted mid 'J?.«is '.•.!(.';. then such .i «ch?i would ,be quite . as satisfactory and decided cheaper, than a project involving . the re-sew. ing of the whole of the city in order to ;id<.' watt is known as the '" separate" system. '' PRINCIPLES OF SEA-BOARD DRAIN'AfiE. The.report states that the best and cheapi / system of ! drainage, in rpgi«rd to both init cost and annual upkeep, is a . "combined" sj . tern, by which the crude Hewege and rainfall a :■• ■ discharged into - the . sea water ; direct, alwa fi«;V, provided .1 suitable outfall can bo; obtained..;.: , such case, if the discharge is confined to pi perly ascertained periods of the tide, and I . . towage released at a considerable distance boh low water mark, it was incontrovertible that, t ■■:■ '. ; *«'» '.-. water --.readily •' oxidised and rendered im ■ ««f)u» the' organic matter of the sewage. . Wf tho "combined" system, .'however, the amount liquid flowing into &- sowers during times; t\cc«ivc. rainfall must be: of great volume, although the existing sewers at Auckland we .-'■ "eli capable of carrying off an■ excessive.rainf* . . . » a new intercepting sewer were designed. ..;•■.-■ convey the whole discharge of the existing . er», it, would have to be of.enormous dimensioi ,'■•. it. was qsjica unnecessary to niako the intercai . :.."■■«• syrteqj earn-. the whole rainfall in the lira fio; « heavy storm, "and s» a-.jgenoral-rule, the, i ■ -v •: iJweepling sewer should be limited to canyii ist wr a fetal smotttit of liquid equal to-sue limes I -...' si? wtither flow of thCj«c%vag*.v The balance, *. :i,My.ef:U(jUid brought down to the intercept!)

, iii»iii««i>l«ilill»lM—»—«t»»^»—.an——»—»— ; sewer over that which it is -designed to carry would be so diluted that it ,-ould with .safety be '; discharged' directly into the sea through 'atom :; overflow's. It must also be borne in mind that £ : sewer carrying six times the dry: weather flow < will convey nil the average rainfalls from the district, and, were such a system adopted .at Auckland, ha'; present -: outletsj" \vhioh would ; net as tho storm ; ovejerflows, would only come intc ; operation in times of excessive rainfall, If f suitable point of ; outfall could not bo obtained ' then the discharge of crude sewage into the • see ; ', was :i inadmissible, as under * improper.i condition! a sea; outfall ; caused va-nuisance over a very -con siderable area. In some cases the. sewage should be > properly > treated ; and ,; purified : before ; beiti? ; discharged into the sea; and : then a "separate," ; or :." partially separate" system: became a. neces sity. That is to say, the bulk of the raitifal of '- the district should \be dealt with by i the ex isting sewers, and the limited portion of rainfal derived from back roofs and yards, together Witt ; the/sewage; should bo : collected : and i dischargee :by means ? of ; a new* separate system of sewers Tho ' report was '■■ founded upon "the 5 assumptior that the Harbour Board would have no object to ; discharges of .; highly diluted sewage througl 'storm overflows, or to -•■ the discharge iof • crude sewage under proper conditions in a suitable position distant .from the city. SEPTIC TANK THE.iTMKNT. The septic tank principle, which has beer largely adopted ?of late in the Old Country, is referred to as follows:—"An analysis of crude sewage entering .;a, septic tajik, compared with - that: of the ; effluent leaving the tank, 'Shows t largo percentage «. : purification; that is to say. the complex nitrogenous bodies, which are re presented on analysis by -' albumcnoid ammonia,' are broken - down into the '■ less ; complex salts o ,ammonia,", which -on: analysis are shown as " free ammonia.* It must be borne in mind, however .that, this - chemical': purification is far from being evident; to the : eye and nose, as the liquid leav ing a ■■' septic tank sis dark, turbid,: and ;higblj charged with putrefying suspended matter, am it possesses a mos; penetrating, pungent, and ob jectiouabie smell. Judging from our .'own espe rience with septic tanks, wo can in no wise agree with? Mr. Mestayer's: statement that ■-' the whole of the' solids are retained by the tank until bra ken up and liquefied, and the scwa*gc is so modi fled in its nature; by the bacterial action in the tank as to be deprived of its offensive properties, as, in fact, we, knew that a septic tank effluent is one of the roost foul-smelling liquids possible te conceive. Neither do we agree with Mr. Mcs layer's suggestion that, the whole of the solid matters are broken up and liquefied. "It is per fectly : true that the : amount '. of sludge producee by a septic tank process is not pearly as largo as thai produced by a chemical process, but in the case of a chemical amount of solids be ing : carried off with i- the, liquid is > probably not more than five to six grains per gallon, and there fore a larger amount of. solid , matter must be retained by the tank, together with the wholt of the . chemicals which have been added, *;: The sludge difficulty has, however, not been over come by v the septic: tank i. process, though the quantity ;of \ sludge, produced is less than that from, a chemical process." ' COST" OF MB, MESTATER'S SCHEME. In referring to Iho probable cost of Mr. MeS' layer's.-scheme,'■ the . report ssys:—lt appear.! to us, judging from the schedule Sof- 1 . current prices for labour and ;■ materials, that the sunn placed by ; Sir. • MesUaycr against the several itemi are not sufficient to cover the cost .of the work , raid we have made independent, estimates on, twe bases, .the flrsii for ~. the,:: present i population-i-ol 33,000, and the other for an assumed future population ■: of i 100,000, '. in each case following : upor the lines adopted by Mr.- Mestayer, as shown or his drawings, but making provision : for., such further works which ;we deem essential to the sue cess ;of .; the scheme. , We : now give; these -: esti mates, as , follows;— 1, ■ Intercepting • sewer, includ ing all manholes, -tunnels, • storm ;. water over flows,* etc.; For" present population, £53,000; foi 100,000 persons, £313,000. 2. Reticulation sewers 53 miles s.w. pipes, allowing for double lines o: sewers ;.-; in :; stretits ~ where v- tramways ' occur: -* Foi present population, £101,500; for 100,000 persons - £101,500. 3. Alterations to existing sewers, gas and water * (Mr. Mestayer's ;estimate):: For pre sent population, ;; £2000; ;for 100,000; persons £2G00..i; 4. Shone system complete, including en gines, ; -coitipressiora;; ejectors, stations, and c.i mains (Mr. Mestayer's estimate): For .present population, £2000; for 100,000 persons, £2000 5. . Septic tanks for , a population 'of 100,000, will balancing tanks, automatic tide valves, and iron work, complete, i £30,000. 6. Bacterial and storn - beds, and, outfall to low water, for popuiatiot of. 100,000, £163,000. ; Septic tanks for present population, with balancing tanks,;automatic tide valves, S and; ironwork, v complete, £12,000. 8 Bacterial and storm ; beds, and outfall ,to low water, for present population, £76,000. Engineer ing. and contingencies, 15 per cent.: For presen population, i £37,575; for 100.000 persons, £53,325 9. Compensation (Mr. Mestayer's estimate): - Fo: present; population, £1000; for 100,000 persons £1000. .10.. Alterations to existing house drains 14,000 houses at £4 . each (Mr. : Mestayer's , esti mate): For present population, £56,000; : foi 100,000 .persons, £56,000. ! 11. Laying nous, drains :in streets (Mr. .' Mestayer's estimate): :Fo present population, 1 ' £20,000; for 100,000 persons £20,000. * 12. Ten acres of land at Cox's Creek 13.r Way-leaves through private : property.;. .To ; tals: For present population, -£365,075:, for 100,0& persons, j £485,825. ;•To ' both the above amouut must ;be > added the; cost of land at Cos's Creel and the price to be paid for? way-leaves througl prrivate property. These totals would appea to compare with * figures; derived front " Mr. Mes .layer's, estimate of £220,000 and £232,000 respee , tively. We have no doubt, however;: that ou: figures 'would "■; be "--found J in practice Vtolbe ■; ap proximately correct, : but we should > like to' em , phaiise ; this point-—lf ;we are ■ too . high in these estimates, : then J the. further: estimate ..which' w< give at the end'of this report ./or' an : ; alternative : scheme** will 'also' 1 ; be > correspondingly in excess as lit; is based upon precisely • the same rates ant .charges. - THE ALTERNATIVE SCHEME. In outlining the alternative scheme for a crude sewage outfall to Okahu Point,-Mr. Taylor says ,*'. We are. convinced ; i that a - discharge of crude sewage, under proper conditions, which wil hereinafter '?. be described, could with gafety be allowed to take < place at that- point, and that n< nuisance of any description whatever would arisi either to; the foreshore or to the harbour, pro .vided the discharge were; carried to a consider able distance below, low-water mark." EFFECT OF SEA WATER ON SEWAGE. .* In regard to the effect of sea water on sewage ;Mr. Taylor says:—Tlieveffect;: of the mixing o crude sewage in a ? fresh ; conditionf with large volumes of. sea water is that the organic matte of : the sewage ■■■ rapidly becomes - disintegrated broken) up, and: oxidised ■ into harmless matters We could ■ quote . many : outfalls in this count of : seaside '• towns ;where sewage : ; discharges . take place at all. states of. the ■ tide, and where the foreshore in : not affected in the slightest by tin sewage; discharges, neither is the sea' contatnina , ted, asv bathing i takes: place upon the shore it clcse proximity to the point of outlet. FLOAT EXPERIMENTS AND STORAGE " TANKS. « In order to ascertain the correct hours of dis charge, Mr. Taylor suggests that a aeries o float ;; experiments, - extending over at least *1' days, be conducted. The floats, he savs, shoule be put into the sea off Okahu Point at time ranging, from four, hours before high water.up t< •lx; hours after high water, and the course tha the floats 'take should be carefully plotted on : chart, the 'direction and strength of the wine being at the same time noted. ■; A tidal diagram indicating the rise and fall of the: tide in Auckland : Harbour should ; also be prepared dtirinj the period of, the float experiments. :: He ' antici pates that these float; experiments will show tha it would be, perfectly safe to discharge the crud< sewage: from;, about "li:hours,; before high wate ,until _ about half-an-hour before lowi.wtfter."■'■',■ II anticipates that , if crude sewage ; were discharge! at other; states ,of ■ the tide it ■: would be carriee up too near to the proposed harbour extensioi works and to the city, and in view of this i would become necessary : to • erect ' storage tank on the foreshore at ; the; point of outfall, so a to limit the : discharge ot * sewage to the exac period which would be determined from a con side ration of the float experiments. MAIN LINE OF OUTFALL. ; Mr..Taylor states that he has prepared a plai and section showing, as well as possible from tin information at his disposal, what -he considers t< be ,the;most. satisfactory line, gradients, and si» of sewer : for '. the proposed outfall. -,-". The sewc commences snear: Cox's Creek, with a 21m pipe with a gradient, of J. in 240, and 'continues an proximately, on the ;i lines chosen by Mr. Mes layer for his , outfall. so far as it extends, bu falling in an opposite direction, i and terminatini with a f oft , Sin: by 4ft 6in egg-shaped sewer, at i gradient of lin 3001). Sir. Taylor has dividee the city up into certain drainage areas, ane increased the size of the sewer from time te time as the,several drainage areas join"-.the inter cepting sewer,, so -as "'to take . tho ■> whole of ? the sewage; and about five additional volumes of rain fall. ;• He ' says that it must be distinctly under stood; that, in selecting the line 'and ,making tin section the whole of the ; knowledge of the locality is derived from the plans and sections which "hav'i been submitted,, and these plans do not carry thi information i. as far ; as;: Okahu ; Point, and neithe do they, give; us entirely accurate information o the line in fiucstion. ft must, therefore, be un deiwtood that the route suggested ;is only np proximate,, and,must:; be occurstelv;surveyed': be fore the precise line could be determined'. I EXISTING SYSTEM OF DRAINAGE. I ' With 3 new gravitation outfall sewer laid on line j suggested, there would be no necessity whatever ii Mr. Taylor's opinion, to interfere with, or relav the existing sewers through the city. H says:—As we have already stated, we can find in statement that the totjsting ■sewer» are it! bin order; or, generally speaking, not sufficient fo their purpose. Where : any portion of the exist ing system is found to be in an unsound con ditiott, It, can be dealt with, and renewed ' Iron time to time as occasion arises, 4 but as far as tin general details of thei scheme are concerned «■ can perceive no necessity to interfere in any wa l with the main sewers/ of the city; : . .WORKS TO BE OF. FULL SIZE. I ■...!■ Mr. Taylor deals with the low-lying areas, tin required capacity of the--works si the outfal site, and other details, and goes on to say:—"Al though the.scheme we have descril<edi 3 designee to. lake the sewage of a population of -100,000 while the present population is only 38,000, i is,, nevertheless, necessary in carrying. out j scheme of this nature to construed at tiic oittse the whole of Mr. works of capacity sufficient fo the ultimate population; The reason for this is ,a» regards the outfall works, that 4 where in tcreepling sewer carries not only sewage, bit rainfall, it will, during periods of heavy; rainfall .; run- full; whatever the 'population drained ■ ma] be- Of. course, with 'the present population the dilution <.-• sewage would be- very much large: 'than the six-times rate that •■ we have ? itien'.ioij'c tor (he ultimate population. Wis also con venicnt and economical to construct the.'outfaj sewer full size In the 'first' instance, as thin clan ! of : work cannot be enlarged from; time to lime.' ;, j} " -1; -' -(f ESTIMATE OF COST. \ n 'The following-estimate is given ot the coat o the alternative scheme: :—(1) Mam . intercept in; sewer, .including oil manholes,- tunnels, ~ storm water oversows, etc., ; £200,000; ii) ei-j outtal pipe, £5000; (3) storage Utiles. £30,000; (4) north cm gravitation sewer,, including nil manholes tunnels;- storm-water'.;overflows,'- etc.', £li0<): (;"i •low-level intercepting Bewei-, including all man holes, -. tuaiicls, < etc.. ' £10,!>G0; (6) 1 ; retlculatioj

« sewers; in low level area, £5000; (7). pumping machinery, house, storage tank, screens, rising ■ main, etc., £3500; (8) connections with existing sowers, extension of existing outlets, alterations r to gas water mains, say,. £4000; engineer- ■ ing and contingencies, 5 per cent.. £40,425: * total, £309,925 (say, £310,000). To this estimate must be added the cost of way-leaves-through ' private property. POSSIBLE SUBURBAN CONNECTIONS. On file question of the possibility of draining Parnell and v other .? suburbs into the new system, ■. "Mr. u Taylor says:—"ln accordance with -our instructions we/ have':.'confined our : scheme" to the city of Auckland, but we may point out that , the borough %of i Parnell, and 1 certain "other outlying [ districts, are so situated that .they .can be drained , by gravitation into the ■ niniu intercepting sewer, ; which we have 'recommended. The only alter- : ation, which , would have to i be. made *in the .scheme.: if these oiltlyiiifr districts' were included is the enlargement of the main intercepting • sower and works below the point of junction " : \ CONCLUDING RECOMMENDATIONS. 11l conclusion Mr. Taylor says:—"ln presenting this alternative scheme to the serious consideration of your Council: we would point out that, although we have not : had the advantage of i studying the problem on the ground, we are in / possession 'of sufficient information to satisfy oil ' selves that the only satisfactory wav of dealing with - the sewage problem at Auckland will be on ■. the lines of the scheme ■we have - described. It is obvious, however, that the lino for the main intercepting sewer wants carefully surveying,- to select the most, suitable course for the outfall -to ; take. When this survey has been made, and the float, experiments referred to in paragraph 23 have, been conducted, we shall be glad to further consider the whole matter, and report as to any amendments or departures: in Die scheme which may be .necessitated by this fuller information: .meanwhile, : should :.;. there be any other , matters upon which information is desired, wo shall bo pleased, to give the matter our further consideration. ■.. ■ The Mayor, after reading- his summary, wont on to say that the matter was so important that ho thought' the Council would be pleased, to learn of the points of difference and agreement- that 'evening. The Council had, in the. report, material for serious reflection, and" it was not a matter that sborkl be hastily decided upon. : The Council was a business council < that: recognised its responsibility in such an important mini:ter, and ho moved that the report be printed- and circulated amongst members of the Council,: and sent ito the : newspapers, and that the Council consider , it iat the; first meeting in January. The holidays were close- at hand, aid : the question required most careful consideration. j Other information would be necessary, of course, before the Council could possibly hope to justify a decision in ■■ the., matter,: and therefore he thought it wise to have the report circulated, : : Mr. R. Fan-ell said the new engineer would scarcely hanre been, appointed by January. The Mayor : We are all pleased to see this report from one of the highest experts in England. ;■;•; Mr.' G. Knight suggested that the matter might be deferred till the first meeting in February, when the city engineer would probably have been appointed. The Mayor agreed to alter the date till the first week in February. Mr. L. J. Bagnall said lie would second the Mayor's motion. He considered the summary read by the Mayor showed that the Council did : the right: thing in submitting Mr. Mei-tayer's'reportto so competent a man as Mr. Taylor. In a. matter of this kind it was right the Council should have the best opinion and the most expert knowledgo ilia it could get before it incurred the large expense that would be ; necessary, to cany out a scheme of this kind. Mr. Farrell agreed that the report should bo most carefully considered. ; The Mayor's motion was then carried, and consideration deferred, thereby, till: February. The Council also passed a vote of thanks to the High Commissioner -for his 'services in connection with communications ■ and negotiations between the Council and Mr. Midgley Taylor.