The Main Drainage and Sewage-Disposal of Edinburgh.” by WILLIAMFAIRLEY, Assoc

226 FAIRLEY ox THE MAIN DRAINAGE OF EDINBURGH. [Selected

(Paper No. 2841.) ‘‘ The Main Drainage and Sewage-Disposal of Edinburgh.” By WILLIAMFAIRLEY, Assoc. M. Inst. C.E. THECity of Edinburgh occupies an area of about 6,000 acres, and has a populationestimated at 261,000. Itssite varies in level between 26 feet and 330 feet above Ordnance datum, and may be said to consist roughly of four valleys, into which all the drainage gravitates.These valleys form part of the catchment-areas of three streams : (1) The Water of Leith, a river with an average flow of about 2,000 cubic feet per minute ; (2) The Craigentinny Burn, now a common sewer;and (3) The POWBurn, with an average flow of about 200 cubicfeet per minute. The rock substratum belongs tothe calciferoussandstones of the lower carboniferous period, and over a large area crops up to within a fewfeet of the surface. On the northernside of the city it is overlaid by thickbeds of sand, while patches of boulder clay occur over the whole area, most frequently in the western district. The average annual rainfall is 28.40 inches. A large number of the houses are completely fitted with modern sanitary appliances, and anabundant supply of waterfrom thePentland and Moorfoot Hills is distributed and laid on to all but a fewof the oldest class of buildings. The consumption of water is at present at the rate of about 40 gallons per head per day. Previously to the year 1870 all the mainsewers were constructed of rubble masonry of various cross sections; in many cases, where the cutting was through rock, a mere facing of masonry being required. That part of the city known as the “New Town,” laid out in the years 1767 to 1800 and 1802 to 1822, wasprovided with a system of main sewers, large enough in almost every case for a man to walk through them forinspection, the sizebeing frequently 6 feet by 3 feet, with flat bottom, battered sides and arched roofs. In the parts of the city more recently sewered, fire- claysalt-glazed pipes are employed,jointed with neat Portland cement and rope yarn ; or brick egg-shaped sewers. No general system of ventilation has as yet been introduced, but on all new

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] FAIRLEY ON THE MAW DRAINAGE OF EDINBURGH. 227 works ventilators havebeen placed at distances of 100 yards apart. During the year 1888 a beginning was made to carry out a system of ventilation for the main sewers in the central district; generally this has been accomplished by introducing ventilating-shafts with gratings in the centre of the roadways,and, in the vicinity of public parks, by forming outlets in the shrubberies, at some distance from the foot-walks. A difficulty will always present itself in districts which contain breweries andmanufactories, discharging hot liquids directly into thesewers, owing tothe emission of steam from the gratings on the roadways or streets, and consequent risk to horse traffic. For the pastfew years the averageexpenditure in drainage work andnew sewers has been about S11,OOO perannum. In designingnew sewers, the rule generally adoptedhas been to allowadischarging capacity equal to 42 gallonsper diem perhead of population inthe drainagearea, one-half of that quantity being assumed to pass off in eight hours, together with a rainfall of 2 inches in twenty-four hours. This rule has been adhered to in designing the greater portion of the recently constructed sewers,and gives a capacity sufficient for all ordinary requirements. Except in special cases no allowance is madefor subsoil water. The city is divided into three main drainage-districts (Plate 5). (1) The Water of Leith, or northern district; (2) The Craigen- tinny,or central district ; and (3) ThePowburn, or southern district, each areadischarging by a separate outfall to the sea. In allthese districts the sewagehas been utilizedby private enterprise for irrigating grass lands, the total area thus dealt with being about 360 acres. On the Water of Leith outfall there is an irrigation farm,at the head of the intercepting sewer, on the lands of Roseburn, with an area of 33 acres. This farm was formerly of much larger dimen- sions,being at onetime about 250 acres inextent, and almost entirely outside the city boundary; it has, however, beengradually curtailed,owing to the use of theland for building purposes. The Lochrin outfall-sewer passes in an open stream, through the portion at present under irrigation, the sewage being drawn off by a main carrier and distributed in leaders by gravitation, so as to flow evenly over the ground. Onlya small portion of the entire volume of the sewage is now required. The subsoil is mainly a stiff clay, and no proper system of subsoil- or under-drainage has been adopted ; the effluent water is caught by intercepting ditches and delivered direct into the Water of Leith. The whole area is Q2

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 228 FAIRLEY ON THE MAIN DRAINAGE OF EDIKBUROH. [Selected under natural grass, and yields between four and five crops each season, the average rental beingbetween S20 and S30 per acre. On thecentral or Craigentinny drainage-area thereare two irrigation farms, both situatedon the north-eastern outskirtsof the city ; viz., the Lochend and the Craigentinny meadows. Lochend farm has an areaof 43 acres, of which 35 acres are commanded by main carriers led from the point at which the main outfall-sewer from thecity debouches intoan open stream. The sewage is pumped up on to the remaining 8 acres by an undershot water- wheel, 14 feet in diameter by 3 feet G inches broad, driven by the sewage flowing to the lower area, and it is then distributed by means of underground pipes and surface hydrants. The Craigen- tinny irrigation farm extends from the point where the stream leaves the Lochend farm, to the foreshore of the Firth of Forth, along which it spreads for a distance of about 14mile. This farm, [which has an area of about 236 acres, may be taken as typical of the others. The greater portion of these meadows was laidout upwards of two hundred years ago, and a part under Italian grass and other crops about fifty years ago. The surface of the ground is undulating, with a general slope seawards, and a large portion of it was formerly waste land, on which only sea-grass and whim could be grown. The subsoil varies between a stiff boulder clay and light sands and gravels. There is a complete system of under- drainage, consisting of 2-inch and 3-inch agricultural tile-drains, laid 10 yards apart and 3 feet deep. The sewage is led from the regulating-sluices and settling-tank along the higher grounds by main carriers 6 feet by 2 feet, delivering into secondary carriers 24 feetby 2 feet. From these carriers smallleaders andturf drains, 12 inches by 6 inches, are cut so as to distribute thesewage as evenly as possible over the surface of the meadow. The effluent water from the surface and the under-drains is caught by ditches, to be again used in irrigating lower levels, or delivered by the outletsinto the Firth of Forth.The secondary carriersdivide the ground into plots, each of about $-acre in area. Four crops areusually taken off theland annually, and occasionally, in dry and favourable years, five or six. The ground was originally sown with a mixture of natural and aquatic grasses, the latter in smallquantities, and it has not been broken up since, nor has it been cropped inany other way. The 50 acres under Italian grass are situated at a higher level than the main area of the farm, and are cropped in rotation with the arable land, the sewage being raised by a pumpdriven by asteam-engine at the farmbuildings. Two or three men, withthe occasional

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] FAIRLEY ON THE MAIN DRAIXAGE OF EDINBURGH. 229 use of a horse andcart, do all the labour required, regulating the sluices, repairing roads, andkeeping the carriers clear. From the month of May until the end of October, the whole of the sewage, amounting to about 800 cubicfeet per minute is utilized on the land, each group of plots being under water about twenty-four hours continuously once every three weeks. During the winter, irrigation work is only carried on during fresh open weather. The average rental received is about S36 per acre per annum. The dairymen, and otherswho take thecrops, cut the grass themselves as they require it, the proprietor attendingonly to the regular supply of water to the land, and the repairof the roads. Another sewage farm, theCraigmillar meadows, is situated outside the city boundary, on the Powburn or southern outfall. This farm has an area of about 48 acres, of which 32 acres were laidout about fifteen years ago, andthe remainder aboutthe year 1885. The subsoil is a stiff clay, and there is no system of under-drainage. The sewage is led on to the farm by an 18-inch pipe, and is distributed by two main leaders 3 feet wide by 2 feet 6 inches deep, the effluent mater flowing into an intercepting drain to again join the outfall sewer. The plots are laid out so as to secure as far as possible a uniform flow over the land, which is constantlyunder grass, and is divided into &-acre plots. The quantity of sewage usually delivered to the farmis about 140 cubic feet per minute. Each plot is flooded for about twenty-four hours once a fortnight. The usual yield of this farm is four crops per annum, but in dry years five crops may be secured. The average rental is 220 per acre per annum. One man, with the use, for the greater portion uf the time, of a horse and cart, attends to all the ordinary work, viz., regulating the sluices, clearing ditches, and repairing roads. All these sewage farms are in the hands of private individuals, and they no doubt form a good investment, for after the meadows have been laid out, the expenses entailed in the maintenance and management are verysmall. The grass, which is annually put up in lots andsold by public auction, is readily bought bycowkeepers and dairy-farmers. It cannot be said that these farmsplay an important part in thepurification of the sewage, the great bulk of the foul mater merely runs over the surface of the ground and deposits aportion of its suspended matter, but where under-drainage has beenprovided, the effluent isfairly clear and pure. The presence of the meadows has a tendency to lower the value of land for building purposes in the immediate vicinity. Although no distinct nuisance mayarise from them, theirnear neigh-

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 230 FAIRLEY ON THE MAIN DRAINAGE OF EDINBURGH. [Selected bourhood is notfree fromdisagreeable odours, especially in damp warm weather. As at present conducted, these farms make no pretensions towards purifying the sewage, but as a profitable means of utilizing the sewage of a large city, by increasing the yield of poor land and thereby enhancing its agricultural market value, they are entitled to favourablethe considerationof municipal auth0rities.l The northern drainage-district comprises the whole catchment-area of the Water of Leith and its tributarystreams, so far as they are within the municipal boundary, together with a portion of theadjacent burgh of Leith.Within the city of Edinburgh there are 2,760 acres, with an estimated population of about 130,000, and an averagesewage-discharge of 1,113 cubic feet per minute. Until the year 1863 the whole area drained into the river, which consequently became so polluted that frequent complaints weremade of itsunsanitary condition. A step towards improvement was effected bycarrying the sewers across tothe central part of the stream, where a considerable volume of water was continually flowing. The sewage was thus carried quickly out of the city, and was not left inpools and on the banks as formerly. As thecity increased, further measures hadto be takento remedy the nuisance. In 1862 the requisite parliamentary powers were obtained to construct a main intercepting-sewer along the course of the river to the sea. This work was begun in 1864 and finished in 1867, the engineers being Messrs. D. & T. Stevenson. The intake is near the western boundary of the city, at a point where the Lochrin Burn, now almost wholly covered, joins the river.The sewer follows closely thewindings of theWater of Leith, at a sufficient depth to intercept the main sewers discharging intoit on each side, and terminates on the foreshore at a point called the “Black Rocks,’’ in the Firthof Forth; the total length, comprising about 2,560 yards of egg-shaped brick sewer, is 5 miles 1 furlong 8.89 chains. The remainder of the outfall consists of cast-ironpiping between 2 feet and 3feet in diameter. For a considerable part of its course the sewer was in very wet and soft ground; and in the neighbourhood of blocks of high buildings the trench required to be carefully timbered. Along the shore at Leith the track was 20 feet from the quay-walls of the harbour, the sewer here being a 3-fOOt 6-inch iron pipe, which was con- tinued to theoutfall at the Black Rocks, 17 feet below high water of spring tides. As the point of discharge is near to deep

1 The area underirrigation was, in the case of Lochend and Roseburn, reduced during the year 1594.

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] FAIRLEY ON THE MAIN DRAINAGE OF EDINBURGH. 231 water, the natural sweep of the currents tends to carry away the sewage seawards. The connections between the main drains from the city were made as shown in Fig. l. The iron-pipe sewer has a carrying-capacityequal to the calculatedvolume of sewage discharged from its drainage- area,together with a pro- portionateamount offlood- water,and all above that quantity passes over the weir into the river. At five points sluices were inserted to facili- taterepairs whenrequired. Whenthis scheme was car- riedout, the estimated dis- chargewas only GO0 cubic feet per minute ; but, since the completion of the work, the population on portions of thedrainage-area has increased-in some cases fivefold-so that at the present time the quantity at the intake is 450 cubic feet per minute, and at the outfall 1,340 cubic feetper minute, ordinary dry-weather flow. The cost of the works was about $70,000, entail- ing speciala drainage-rate of Fig. 2. 2s. 6d. per pound on therental within the area. In 1888 a scheme was proposed to construct a large intercepting- sewerto relieve the Water of Leith pipe along the side of the river. An Act of Parliament was obtained, and the work has now been completed. The line of the new sewer follows the course of the 1864 pipe for a portion of its course, but divergesat Stockbridge (about midway) horn theriver bank, and follows a more direct lineto the sea. The section of the culvert is circular throughout, with the exception of a short length at Leith Docks. The size varies between 4 feet diameter and 9 feet 3 inches by 7 feet 2 inches. The portion near the do& is in badground, and as the sewerwould there be subject to internal pressure due to tidal action, it was constructed of a special section, FI). 2, designed by the Author, formed of cast-iron seg-

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 232 FAIRLEY ON THE NAIN DRAINAGE OF EDINBURGH. [Selected ments lined and covered with cement concrete. This design was. found to afford greatfacilities for rapidconstruction in bad ground. The central or Craigentinny drainage-districtcomprises an area of 1,455 acres, with an estimated population of 107,000, the dry- weather sewage-discharge being about 800 cubic feet per minute- Thisdistrict contains the densely populated part of thecity knownas the ‘LOld Town,’’ which covers theridge between Holyrood Palace and the Castle, with the sloping ground on each side, and it is chiefly inhabited by the poorer classes. It contains also upwards of thirty breweries and numerous other manufac- tories. The main sewers on each side of this ridge consist for the most part of brick egg-shaped culverts, of sizes varying between 3 feet 6 inches by 5 feet 3 inches and 4 feet by 6 feet; these two lines of sewers form a junction within a few hundred yards of the municipalboundary, and subsequently flow inan open stream throughthe sewagefarms of Lochend andCraigentinny to the Firth of Forth. Part of the main sewer, from the south side of this district, passes through the Queen’s Park along the base of Arthur’s Seat-a hill 822 feet in height. As the greater portion of the drainage-area consists of paved streetsand yards, with closely-built tenement houses, and as,. owing to the steep inclination of the ground the storm-water is discharged during heavy rains with great rapidity, the authorities. experienced considerable trouble from the flooding of the public park. Borings along the valley showed that it had formerly been the site of an ancient lake, and was made up of beds of clay, marl, peat and decaying vegetable matter, the ground subsiding as the decay proceeded. A new sewer was constructed in a line parallel to the old one, and consisted of an egg-shaped brick culvert 3 feet 4 inches by 5 feet, set in Portland-cement mortar. Piles of creo- soted memel, 9 inches square and 5 feet to 30 feet long, shod with. malleable-iron shoes weighing 25 lbs. each, were driven in pairs. 8 feet apart. The pileswere driven in a cutting of an average depth of 14feet, asteam derrickwith a %-foot jib,set on a triangular framework, thepivoted centre and foot of each leg travelling on rails along the side of the track on a four-wheeled bogie, being used. After the piles had been driven to the required depth, the tops were cut square, and flat-bottomed rails weighing 70 lbs. per lineal yard were laid in %-foot lengths, resting on the piles. The concretefoundation for the sewer was then laid, encasing therails. This arrangement in10-foot cuttingcost $4 per lineal yard complete; the sewer itself, constructed in brickwork

with stone sills, cost 35s. per lineal yard. The sewage fromltthe central area is, from the nature of the works &c. situated in it, extremely foul. The Powburn, or southern, drainage-district comprises an area of 1,690 acres, with an estimated population of 17,000, the dry- weather sewage discharge being about 120 cubic feet per minute. About two-thirds of its area is covered by villas and suburban residences, the remaining portion not yet being built over, but buildingis proceeding rapidly.The whole district occupies a regular slope, ranging between 300 feetand 136 feet above Ordnancedatum, and it fornlerlydrained into an open stream running along its southern boundary. When the population and the rolume of sewage was small, these drains passing down the slope discharged directly into this stream, which is called the POW Burn, and joins the Braid Burn, a comparatively pure stream, at the eastern boundary of the city. Subsequently to 1880, this sewage was intercepted by theformation of a pipe-drain,and lateron a brick culvertwas constructed to pointa beyond the cityboundary. The Braid Burn, 3 miles from its junction with the POWBurn, fallsinto the Firth of Forthnear the town of Portobello, a watering-place much frequented by the residents of Edinburgh. Frequent complaints were made by the Portobello Corporation, of the pollution of the stream caused by the sewage from Edinburgh, and after litigation the referee recommended that an outfall sewer should be carried direct to thesea, with a discharge within a short distance of the Water of Leith outfall. In 1884, a Bill was promoted in Parliament for powers to carry out the above scheme, and the work was begun in April, 1886, Mr. John Cooper beingthe engineer. Thedistance from the outfall at thesea to the junction with the existing city system is 4 miles 19 yards, and, in order to allow the work to be carried out expeditiously, thecontract was let in two sections. Thisnew outfall is distant 1,640 yards from that of the Water of Leith sewer, the sewage from the central or Crajgentinny district being intercepted and discharged along withthat of thePowburn district at a point 108 yards beyond the low-water mark. On the foreshore the sewer consists of cast-iron socket-pipes, 3 feet 6 inches in diameter, supported on piles of greenheart timber, 12 inches square,with two cross-bearers andone top-piece 12 inchesby 6 inches. Thesubstratum was a bed of clay of greatdepth, thickly interspersed with boulders, -and great difficulty wasex- perienced in the pile-driving. At the outlet an apron 8 feet by 5 feet was formed, consisting of greenheart sheet-piling 12 inches

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 234 FAIRLEY ON THE MAIN DRAINAGE OF EDINBURGH. [Selected by G inches with 3-inch planking. The Board of Trade required that a beacon should be erected at the seaward end of the outfall to mark the line of the pipes. At high-water mark, a concrete retaining-wall was built for a distance of 30 feet on each side of the sewer. At the public road, where the brick sewer begins, an overflow chamberwith a man-hole was formed of 18-inch brickwork in cement, with scabbled ashlar-sills, the wall on the seaward side being of freestone ashlar in 16-inch courses. A wrought-iron penstock with l&-inch gun-metal facings 1%-aserected against the mouth of the outlet pipe, the framework being 4 inches deep of I-inchmetal bolted to theashlar work. Fromthis chamber an overflow pipe, 24 inches diameter,was brought through the concrete wall to discharge on to the beach. By an agreement with theproprietor of the Craigentinny Estate, provision had to be made to intercept the sewage discharged on the foreshore from thecentral outlet of thecity, and for this purpose a cast-iron pipe, 2 feet 10 inches in diameter,was laid across the beach, joining the %foot 6-inch pipe at an angle of 45". The intake, whichis under the railway, hasa catchpit or tumbling bay, consisting of a heavy concrete sill 2 feet thick, and side walls of 18-inch brickwork in cement, coped with ashlar work, and fitted with a malleable-iron grating.The seaward side is 18inches higher than theother, so that in case of the pipe becoming choked the sewage would overflow on to the beach as formerly. At the main outlet the sewage is discharged into a strong current, the genera,l set of which is north-east; any floating matter istherefore carried out to sea, clear of Portobello and the bathing beaches along the coast. The lowersection of the contract included the work on the foreshore, together with l mile 1,000 yards of brick- sewer, terminating at a point on the public road at Duddingston, within 100 yards of the Braid Burn. The culvert consists of an egg-shaped sewer 5 feet 3 inches by 3 feet 6 inches and 5 feet by 3feet 4 inches, built of 9-inch radiated composition-brick and cement,, with stone sills. In the irrigated land the leaders for the sewage had to be kept running in troughs across the trench during operation, cast-iron pipes, supported clear of the made-up ground beingput in after the trench was filled. In thearable land, the field under-drains were in many cases intersected, and intercepting-drains of 4-inch tiles were laidalong the side of the trench, at an average depth of 4 feet, connection being made where necessary to the sewer manholes for discharge. Bythe Act of Parliament an agreement hadbeen come to that the London

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] FAIRLEY ON THE MAIN DRAINAGE OF EDINBURGH. 235 Road, which has a double line of tramways and also considerable vehicular traffic, should be tunnelled, and that no opening should be made inthe roadway. Thedepth at this point was about 23 feet. Shafts 6 feet square were accordingly sunk on each side of the road, in private ground, and a mine was driven 7 feet by 8 feet, lined with sleepers 10 inches by 4 inches and 8 feet long. The sewer, after being built, was packed round with Portland- cement concrete in the ratio of 'i to 1. The cost complete for this work was 55 10s. per lineal yard. A storm-overflow was constructed at Duddingston, the sewer at this point being 29 feet above the level of the Braid Burn. The upper section of the work was commenced at this point, drainage for the water from the cutting being obtained by means of the overflow. This section terminated in a junctionwith the POW- burn intercepting-sewer, already mentioned, at a point 259 yards distant.From the point where the sewerleaves thepublic road at Duddingston,until it crosses the roadway at Craig- millar, a distance of 1,667 yards, the course is through the park of Duddingston House, theproperty of theDuke of Abercorn, in which it was stipulated that no manholes or ventilators should be employed. The cutting here was through extremely wet and soft ground,slips were frequent,and at one pointwhere the ex- cavation was 24 feet deep, 700 cubic yards slipped into the trench. The whole of the trench had to be close-timbered with 64-inch by 24-inch battens, and in some parts with 2-inch flooring-boards and straw-packing, the waling being 11 inches by 3 inches, with 6-inchsquare cross-pieces. Wherethere was any danger of the sills not being firmly bedded, a layer of cement concrete, in the ratio of 5 to 1, 4 feet wide and 15 inches thick, was laid as a foundation. The Braid Burn had to be crossed three times ; this was readily accomplished by leading the stream througha trough, with framing formed of 11-inch by %inch planking, and 14-inch lining, the ends being puddled with clay. As already mentioned, the water of the Powburn sewer is used by the proprietor of the Craigmillar estate for irrigating meadow- land; an outlet had therefore to be formed in the new sewer to give off therequired volume of sewage. Thearrangement for drawing off the sewageconsists of an outlet chamber andan 18-inchiron-pipe conduit, having a gradient of 1 in 500. The main sewer, at this point, drops 9 feet by means of reverse curves each having a radius of 14 feet. Thesiphon across thestream comprises two chambers, of 9-inchbrickwork in cement with concrete-sills 12 inches thick, connected by an 18-inch iron pipe

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 236 FAIRLEY ON THE MAIN DRAINAGE OF EDINBURGH. [Selected laid 18 inches below the level of the conduit. The entire length of this outlet sewer is 4 miles 19 yards, with a difference of levels from the intake to the outfall of 163 feet. As the greater portion of the work wasthrough private grounds, thecontractor was. allowed by the Corporation a width of 25 feet on each side of the sewer, the surface damages being paid by the city ; but the contractor, Mr. John Best, of Leith, had to provide proper fences and to pay for any ground required outside the limit. In private groundsshafts 2 feet square, formed of 9-inchbrickwork with stone covers 9 inches thick, were brought up to within 18 inches of the surface about every 150 yards. Thetotal cost of the workwas about S40,000, exclusive of superintendence.

The Paper is accompanied by the map which is reproduced in Plate 5, and by tracings from which the Figs. in the text have been prepared.

Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. J. S.SIWCLAIR. Minutas of Froceedmgs of The InstCmtion of CivllEngineers Vol.CEl Session1894-95.Part IIL Downloaded by [ UNIVERSITY OF OXFORD] on [13/09/16]. Copyright © ICE Publishing, all rights reserved.