24 DEACON ON THE LIVERPOOL WATERWORKS. [Minutes Of (Paper No. 2975.) “The Vyrnwy Works for the Water-Supply of Liverpool.”’ By GEOROEFREDERICK DEACON, M. Inst. C.E. ITis obviously impossible, within the limits of a Paper suitable for publication in the Proceedings of the Institution, to describe each part of the Vyrnwy Works. The Author proposes, therefore, to restsatisfied with presenting a general andcomparative account, and to refer to details only where theyinvolve distinct novelty or points which appear to him useful for future guidance. HISTORICAL. Having,at the instance of the Corporation of Liverpool in 1876-7, made an investigation concerning thewater-supply available from various valleys and lakes to the northof Liverpool, and from severalvalleys in North Wales, theAuthor in 1877 reported upon two sources, namely Haweswater in Cumberland and the River Vyrnwy in Montgomeryshire. In these reports he claimed for Haweswater nearly every advantage that Liverpool could desire; but concerning the Welsh project he wrote, “the Vyrnwy possesses all the more important advantages of Hawes- water, with some advantages which Haweswaterdoes not possess.” The Vyrnwy is a tributary of the Severn, formed from the junction of many streams in an alluvial tractsome 780 feet above the sea, suppliedfrom an averageannual rainfall exceeding 70 inches, andsurrounded by mountainsrising to a height of 2,000 feet. So considerable a volume of pure water at so great au elevation had not escaped the notice of the late Mr. J. F. Latrobe Bateman,2 whohad included the areain his North Wales projectfor the supply of London laid before the Royal Commission on Water- supply of 1867-9. It is interesting to notice also that the lateMr. Hamilton Fulton3 laidbefore the same Commission a very excellent The discussion upon this communication was taken in conjunction with the preceding one by Mr. Hill descriptive of the Thirlmere supply for Manchester. * Report of the Royal Commission on Water-Supply, 1869, vol. i. pars. 4-40. Ibid, par. 54. Downloaded by [ University of Sussex] on [19/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] DEACONON THE LIVERPOOLWATERWORKS. 25 project for the supply of the Metropolis from South Wales, which included the areanow being utilized for the supplyof Birmingham. Between two such good things as Haweswater and the River Vyrnwy it was not in human nature-certainly not in municipal nature-to avoid differences of opinion, andtwo strong parties championed the two schemes respectively. However, the Author, havingfurther investigated and surveyed the Vyrnwy project, reported ingreater detail on the 1st August, 1878, andagain recommended its adoption. Butthe advocatesfor thenorthern scheme werestill dissatisfied, andin February, 1879, thelate Mr. Thomas Hawksley and the late Mr. Bateman, Past-Presidents of the Institution of Civil Engineers, were respectively asked to reply to a series of questions touching the relative advantages of the two projects invarious particulars, physical,chemical and financial. Happily there was no want of agreement in essential particulars,and the balance of their opinions wasstrongly in favour of the Vymwy. This view havingbeen adopted by a majority in theCorporation of Liverpool, the Author was instructed, during the summer of 1879, to complete the surveys and prepare the parliamentaryplans, and from September, 1879, the lateMr. Hawksley acted jointly with him in promoting the passage of the Bill through Parliament. On the 6th August, 1880, the Act received the Royal Assent, and on the 14th July, 1881, the memorial stone recording the commence- ment of the works was laid. In 1885, Mr. Hawksley retired from the work, and the undivided responsibility fell upon the Author. In July, 1892, the undertaking havingbeen practically completed was opened by the Dukeof Connaught. The beginningof the works, and thecompletion of Lake Vyrnwy and of the aqueduct respectively, have been recorded in the terse and stately languagewhich will still be read when, in the nature of things, the principal uses of the works-though not the works themselves-shall have ceased to be. The first inscription is on the frieze of the southern tower of the masonry dam, Fig. 5, Plate 4, and records, as follows, the yea%before the permanent works were begun, and in which the Act of Parliament authorizing them was passed, OPVS . INCHOATVM M DCCCLXXX while the frieze of the tower, 660 feet to the north, chronicles the passage of a decade thus :- OPVS . ABSOLVTVM M DCCCXC. Downloaded by [ University of Sussex] on [19/09/16]. Copyright © ICE Publishing, all rights reserved. 26 DEACON ON THELIVERPOOL 'WATERWORKS. [hfinutes of Lastly on the frieze of the Korton Tower, Fig. 25, Plate 5, and Fig. 27-the most northerly balancing reservoir of the aqueduct-- from which on a clear day Liverpool may be seen, the story of the work is briefly told as follows :- HAEC * AQVA DE.SABRINAE-FONTIBVS.DERlVATA LXXX m : PASS : PER * ARDVA . AC - PLANA CAMBRENSlS.ET*lNTERlACENTlS*AGRl AD * VRBEM . LIVERPOL : IMPENSIS * MVNIC : PERDVCTA . EST A:S: MDCCCXCll GENERALFEATURES. The Reservoir,now knownas Lake Vyrnwy, differs only iu magnitudeand details of constructionfrom other numerous reservoirs employed for impounding flood waters and conserving them for use in periods of comparative drought. Of aqueducts on the other hand, there arebroadly two kinds and their combinations. (1) The open or closed culvertcontouring the hillsides and passing across the valleys by bridges, with the water flowing at the hydraulic gradient,of which the ancientRoman aqueducts are the best knowntypes. (2) The entirelyclosed conduit, subject to the unbrokenpressure from end to end due to the initial head of water, as in most short aqueducts of the cast-iron ageand in some longaqueducts of wrought-iron or st,eel in America. (3) The combination of types (1) and (2), in which the hydraulic gradient is followed wherever tunnelling or contouringis practic- able, and in which the valleys arecrossed by invertedsiphon-pipes under pressure, asin the case of the Loch EatrineAqueduct for the supply of Glasgow, and the Thirlmere Aqueduct for the supply of Manchester. (4) The combination of types (1) and (2), in which the hydraulic gradient is only followed where it is necessary to tunnel, and is elsewhere only reached where the pressureis purposely broken by balancing-reservoirs between the source and the service-reservoir. The Longdendale Aqueduct for the supply of Manchester, and the Rivington and Vyrnwy Aqueducts, both for the supply of L'mer- pool, are exa.mples of this treatment. The Vrynwy Aqueduct is shown in plan at Fig. 1, and in longi- Downloaded by [ University of Sussex] on [19/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] DEACON ON THELIVERPOOL WATERWORKF. 27 tudinal section at Fig. 2, Plate 4, with the Vyrnwy reservoir at the southernend, the Prescotservice-reservoirs at the northerneud, and intermediately, besides other special works, the four tunnels, five balancing-reservoirs, sixriver crossings, thirteenrailway crossings, and six canal crossings including the Weaver Kaviga- tion and the Manchester Ship Canal. THEVPRNWT RESEEJ-OIR. LakeVyrnwy is chieflyremarkable asthe largest artificial reservoir in Europe, and as the first in Great Britain in which a high masonry dam was employed. The valley is the site of a post- glacial lake basin,thelower, or south-eastern,extremityinthe Lower Silurian, and the upper, or north-western, extremity in the Upper Silurian rocks. In 1876-7, when the Author first visited it, the River Vyrnwy wound through an alluvial tract of gravel, sand and peat, extending towards the source for about 5 miles from the narrower part of the valley, where thealmost sluggish river gave place to a rapid stream. The maximum depth of this rock basin below the alluvium is unknown, but there are indications that, as inthe case of otherglacial basins, it is considerable. To determine the highest part of the then hidden rock bar near the lower end of this alluvial strath, 177 borings and probings, and thirteen shafts were sunk, and, by means of these, actual contours were drawn, anda model made of the surface-rock. These contours showed that the maximum depth of rock, sound or unsound, along the shallowest bar was 40 feet to 45 feet below the surface, from which it increased higher up the valley to unknown depths, a fact entirely consistent with the glacial origin of the basin. When, in the course of excavation, the dislocated rock wassubsequently removed from this bar, there was exposed to view the watertight portion of the natural dam by which the post-glacial lake had been impounded. This watertightrock was on the average6 feet to 7 feet lower than the surface rock which the contours hadshown, and the deepest point was about 60 feet below the riverbed. The alluvium had not only silted up the basin formerly occupied by water, but had been carried by the floods of the river which subsequently traversed it, to a further height of 40 feet or 45 feet at the siteof the dam, so that while the depthof the modern lake at the dam is only 84 feet, the dam at one point of its base is subject to the full head of 144 feet. Below the sillof thedam and abore the outlet to the aqueduct,Lake Vyrnwy contains 12,131 milliongallons. Its area is 1,121 acres. Downloaded by [ University of Sussex] on [19/09/16]. Copyright © ICE Publishing, all rights reserved. 28 DEACON ON THE LIVERPOOL WATERWORRS. Winutes of In a single foot of depthimmediately below the overflow, the lake contains about 304 million gallons ; 5 feet lower a foot of depth contains 292 million gallons ; at 10 feet it contains 281 million gallons, and at 15 feet a foot contains 270 million gallons, figures which clearly show the exceptionally favourable character of the basin as a reservoir. The average cross-section of this remarkable sheet of water does not differ widely from a horizontal base 2,000 feet wide, with a depth of water over it of 70 feet, and end slopes of 21 to 1.