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    "label": "Description of the Croton Aqueduct, John B. Jervis Chief Engineer, 1842",
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    "title": "Description of the Croton Aqueduct, John B. Jervis Chief Engineer, 1842",
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    "ocrText": "Google\nThis is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project\nto make the world's books discoverable online.\nIt has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject\nto copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books\nare our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.\nMarks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the\npublisher to a library and finally to you.\nUsage guidelines\nGoogle is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the\npublic and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to\nprevent abuse by commercial parties, including placing technical restrictions on automated querying.\nWe also ask that you:\n+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for\npersonal, non-commercial purposes.\n+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine\ntranslation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the\nuse of public domain materials for these purposes and may be able to help.\n+ Maintain attribution The Google \"watermark\" you see on each file is essential for informing people about this project and helping them find\nadditional materials through Google Book Search. Please do not remove it.\n+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just\nbecause we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other\ncountries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of\nany specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner\nanywhere in the world. Copyright infringement liability can be quite severe.\nAbout Google Book Search\nGoogle's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers\ndiscover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web\nathttp://books.google.com/\nGODFREY LOWELL CABOT SCIENCE LIBRARY\nof the Harvard College Library\nThis book is\nFRAGILE\nand circulates only with permission.\nPlease handle with care\nand consult a staff member\nbefore photocopying.\nThanks for your help in preserving\nHarvard's library collections.\nDigitized by\n34.163\nEnc\nG\nDigitized by Google\nDigitized by Google\nJerris\nDESCRIPTION\nOF THE\nCROTON AQUEDUCT;\nBY\nJOHN B. JERVIS,\nCHIEF ENGINEER.\nNEW-YORK:\nPUBLISHED BY SLAMM AND GUION,\nCORNER OF NASSAU AND SPRUCE STREETS.\n1842.\nDigitized by Google\nDESCRIPTION\nOF THE\nCROTON AQUEDUCT;\nBY\nJOHN B. JERVIS,\nCHIEF ENGINEER.\nI\nNEW-YORK:\nPUBLISHED BY SLAMM AND GUION,\nCORNER OF NASSAU AND SPRUCE STREETS.\n1842.\nDigitized by Google\nEng1078.42\n1051 beely\nProj Longfellors\nENTERED according to Act of Congress, in the year 1842, by\nSLAMM & GUION,\nin the Clerk's Office of the Southern District of New-York.\nDigitized by Google\nPREFACE.\nIT is seventy years ago since the subject of procuring a sup-\nply of pure and wholesome water for this city was first agitated\nin our Common Council. The population of the city was then\nonly twenty-two thousand, and notwithstanding it was at that\ntime considered a matter of the highest importance, yet it was\nreserved for this late day to plan and execute the Croton aque-\nduct.\nComparatively few of the inhabitants of this city are aware\nof the magnitude of the works erected, or the character of the\nobstacles overcome, in bringing a river forty miles, over moun-\ntains, streams and valleys, to pour its blessings in the midst of\na populous city. It has occurred to the publishers that they\ncould not perform a more gratifying or acceptable service to\nthe public than to present them a'full and complete description\nof the aqueduct from the pen of John B. Jervis, Esq. To the\neminent ability and devotion of this distinguished engineer are\nthe public mainly indebted for the successful accomplishment\nof this great enterprise. Although he has been connected with\nalmost all the great public works of this state, it will be the\nCroton Aqueduct that will transmit his name to all future gen-\nerations with enviable distinction.\nDigitized by Google\n4\nThis pamphlet contains a minute, full and accurate descrip-\ntion of the whole work, from the Craton river to the distribu-\nting reservoir, from Mr. Jervis's pen, and the publishers do not\nhesitate in making the assurance, that while it cannot fail to\nsatisfy the popular curiosity, it will be everywhere regarded as\nan acquisition in hydraulic science.\nTHE PUBLISHERS.\nOctober 14, 1842.\nDigitized by Google\nGENERAL DESCRIPTION OF THE LINE.\nTHE Croton Aqueduct was designed to supply the city of\nNew-York with an abundance of pure and wholesome water.\nIt commences about six miles above the mouth of the Croton\nriver, where a dam has been constructed to elevate the water\nof the river 40 feet, to the level of the head of the aqueduct,\nor 166 feet above mean tide. The course of the aqueduct passes\nalong the valley of the Croton to near its mouth, and thence\npasses into the valley of the Hudson. At 8 miles from the\nCroton dam it reaches the village of Sing Sing, and continues\nsouth through the villages of Tarrytown, Dobbs' Ferry, Has-\ntings, and Yonkers.\nAt the latter place it leaves the bank of the Hudson,\ncrosses the valleys of Saw-mill river and Tibbits' brook,\nthence along the side of the ridge that bounds the southerly\nside of Tibbits' brook valley, to within 3½ miles of the Harlem\nriver, where the high grounds of the Hudson fall away so\nmuch as to require the aqueduct to occupy the summit of the\ncountry lying between the Hudson and East rivers.\nThis formation of country continues to, and is terminated\nby the Harlem river, at the point where the aqueduct intersects\nit; which is one mile northwesterly from McCombs' dam.\nThe length of the aqueduct from the Croton dam to Har-\nIem river, is 32.88 miles, for which distance it is an uninter-\nrupted conduit of hydraulic stone and brick masonry. The\nhigh ground that bounds the northerly side of the Harlem river\nvalley, is very near the level of the aqueduct at that place; and\nthe width of the valley at the aqueduct level is about 1450 feet,\nDigitized by\nGoogle\n6\nor a little over one quarter of a mile ; over which a bridge is\ndesigned to be constructed (and is now in progress) at an ele-\nvation of 114 feet above the level of high tide in the Harlem\nriver, on which iron pipes are to be laid to convey the water\nacross the valley.\nThe shore on the southerly side of the river is a bold, pre-\ncipitous rock, rising at an angle of about 30 degrees, to a\nheight of 220 feet, or about 100 feet above the level of the bot-\ntom of the aqueduct.\nAfter crossing this valley, the aqueduct of masonry is re-\nsumed, and continued 2.015 miles, to the termination of the\nhigh ground on the north side of Manhattan valley.\nThis valley is 0.792 mile wide at the level of the aque-\nduct; below which it descends 102 feet. The conduit of ma-\nsonry here gives place to iron pipes, which descend into the\nbottom of the valley, and rise again to the proper level on the\nopposite side; from which point the masonry. conduit is again\nresumed, and crossing the Asylum ridge, and Clendinning val-\nley, is continued 2.173 miles, to the receiving reservoir at York\nhill.\nThis reservoir is bounded by 86th street on the north, 79th\nstreet on the south, 7th Avenue on the west, and 6th Avenue\non the east. It is 1826 feet long and 836 feet wide on the out-\nside angle of the embankment; containing an area of 35 acres,\ndivided into two divisions, and is (a little over) 5 miles from\nthe City Hall. From the receiving reservoir, a double line of\niron pipes three feet in diameter, are laid down in 80th street\nand 5th Avenue, to convey the water 2.176 miles to the dis-\ntributing reservoir at Murray hill. The location of this reser-\nvoir is on the 5th Avenue, between 40th and 42d streets, and is\nthree miles from the City Hall; it is 420 feet square on the\ncornice of the exterior wall, and contains an area of 4.05 acres,\ndivided into two equal divisions, and has an average elevation\nof 44.5 feet above the level of the streets around it.\nDigitized by\nGoogle\n7\nThe length of aqueduct from the Croton dam to the dis-\ntributing reservoir is 40.562 miles-to wit :\nMasonry conduit in Westchester county\n32.880\nDo.\ndo. on New-York Island\n4.187\nTotal length\n37.067\nReceiving reservoir from end of aqueduct to south-\neastern effluent gate house\n0.172\nDistributing reservoir.\n0.080\nIron pipes on bridge over Harlem valley\n0.275\nDo. do. across Manhattan valley\n0.792\nDo. do. between reservoirs\n2.176\n40.562\nIt is proper to add to the above, the length of the Croton\nreservoir, which has been formed by the erection of the Croton\ndam and other work necessary to obtain the water, at a suita-\nble level on the Croton river, as without this dam and reservoir,\nthe aqueduct would have required an extension of five miles to\nreach the proper level on the river; which is now attained by\nmeans of the dam. The entire length, therefore, from the point\non the Croton which has the requisite elevation, to the distribu-\nting reservoir, is 45.562 miles. The large mains running from\nthe distributing reservoir through the central part of the city,\nwould add about four miles, making. the total length of the\nmain conduit nearly fifty miles.\nDESCRIPTION OF THE COUNTRY THROUGH WHICH THE AQUEDUCT\nIS LOCATED.\nThe soil, earth and rock, of the country from the banks of\nthe Croton to the city of New-York, is of one general charac-\nter. The line cuts a small section of marble of inferior quality,\nDigitized by\nGoogle\n8\nabout two miles below the Croton dam. In running through\nthe State farm at Sing Sing, it passes a few hundred feet\n(mostly by a tunnel) in a marble of pretty fair quality for\nbuilding ; and again at Dobbs' Ferry and at Hastings it lightly\ncuts a similar rock ; at the latter place marble has been got\nout to some extent for market. No more marble was discov-\nered by constructing the aqueduct until it reached Harlem\nriver, where in excavating two of the coffer dams to obtain\nfoundation for the piers, marble rock was found in the bed of\nthe river. This is supposed to be a continuation of the stratum\nthat appears in Harlem valley at the Kingsbridge road, near\nthe Hudson river. With these limited exceptions, the prevail-\ning rock of this district is gneiss, of great variety in quality. In\nmany places it affords excellent building stone for ordinary\npurposes, and to some extent good blocks of hewn stone have\nbeen obtained. A very large proportion, however, of this rock\nis totally unfit for building purposes.\nThe surface soil is generally a sandy loam, containing a\nvery small proportion of argillaceous earth. Below the surface\nsoil, gravel, sand, boulders, or detached rock, have in most\ncases been found, and also hard pan to a considerable extent.\nA large proportion of the open cutting, and nearly the whole\ntunnel cutting, has been through rock. More than 400,000\ncubic yards of rock have been excavated.\nThe general formation of the country is extremely irregular,\nand unfavorable for the economical construction of such a work.\nCommencing at the Croton dam, on a level 40 feet above\nthe river, which descends from this point to tide-water, at the\naverage rate of 25 feet to the mile, the grade of the aqueduct\nwas compelled to encounter great irregularities of surface.\nVery little regular table-land could be found for its location.\nWhile the main ridge of high land, that lay on the left of the\nline in Westchester county, controlled the general location,\nnumerous spurs of ridges, of various forms and extent, bounded\nDigitized by\nGoogle\n9\nby deep ravines, rendered it impossible to avoid deep cutting\nand frequent tunnelling, through ridges, and heavy filling in\nthe valleys ; leaving a very limited proportion of the line in fa-\nvorable cutting. On the island of New-York, with the excep-\ntion of about one mile from Harlem river, there was no leading\nridge to control or guide the location; which rendered it more\ndifficult to decide on the conflicting claims of different routes.\nThere are on the line sixteen tunnels, varying in length from\n160 to 1263 feet, making an aggregate length of 6841 feet.\nThe height of the ridges above the grade level at the tunnels\nranges from 25 to 75 feet.\nThere are in Westchester county twenty-five streams cross-\ning the line of aqueduct, that are from 12 to 70 feet below the\ngrade line, and from 25 to 83 feet below the top covering of\nthe aqueduct. The most prominent of the valleys, are Louns-\nberry's, Indian brook, Sing Sing kill, Mill river, Jewell's\nbrook, and Saw-mill river; the foundations of which are in no\ncase less than 40 feet below the grade line, or 53 feet below\nthe top covering of the aqueduct. Besides those above-men-\ntioned, there are numerous brooks and valleys of less depth, re-\nquiring culverts, and artificial foundations to support the aque-\nduct. The level of mean tide at Harlem river is 120.66 feet\nbelow the grade line of the aqueduct, of which a more particu-\nlar description will be given hereafter.\nOn New-York island there are several deep and abrupt\nvalleys, along the precipitous rocky hill, that bounds the south-\nerly shore of Harlem river. But the most important valleys on\nthe island are Manhattan valley, Clendinning valley, and\nBowne's valley. A more particular notice of Manhattan and\nClendinning valleys will be given when describing the plan\nof work; the manner of construction for the others being\nsimilar to that for the valleys in Westchester county.\nDigitized by\nGoogle\n10\nDESCRIPTION OF THE PLAN OF WORK FOR THE AQUEDUCT AND\nITS APPURTENANCES.\nAqueduct.\nThe form and dimensions of the interior of the aqueduct are\nas follows : The bottom is an inverted arch ; the chord or\nspan line is 6 feet and 9 inches, and the versed sine 9 inches.\nThe masonry of the side walls rises four feet above the spring-\ning line of the inverted arch, with a bevel of one inch to a foot\nrise, or four inches on each side, which brings the width at the\ntop of the side walls 7 feet and 5 inches ; forming the abut-\nments of the roofing arch, which is a semicircle, having a radius\nof 3 feet 8½ inches, or a chord line of 7 feet 5 inches. It will\ntherefore be perceived, the greatest interior width is 7 feet 5\ninches, and greatest height 8 feet 51/2 inches. The area of the\ninterior is 53.34 square feet. In rock tunnels the roofing arch\nis generally dispensed with, but the bottom and sides are formed\nwith masonry similar to that above described. There is an\nexception to this form in the first 4.949 miles of the upper end\nof the aqueduct, where the side walls have an extra height, on\naccount of the bottom being depressed, to draw the water at a\nlower level from the Croton reservoir. The plan, dimensions,\nand character of masonry are as follows : In excavation, a bed\nof concrete masonry is laid down as a foundation. It is laid\nlevel across the bottom, three inches thick at the centre of the\ninverted arch, and curved on its upper surface, to form a bed\nfor the arch, which brings it 12 inches thick at the spring line,\nand is carried three inches thick under the side walls, or abut-\nments. The abutments are 2 feet 8 inches thick at the spring\nline of the inverted arch, and 2 feet at the top, or spring line of\nthe roofing arch. The inverted arch is of brick, 4 inches thick.\nThe roofing arch is also of brick 8 inches thick. The abut-\nDigitized by\nGoogle\n11\nments, or side walls, are of rubble stone, with a brick facing 4\ninches thick. Spandrels of stone are carried up solid from the\nexterior angle of side wall, on a line that is tangent to the arch.\nWhen. the bed of concrete is formed for the inverted arch, a\nbeavy course of plastering is laid over it, on which the arch is\nlaid. When the stone work of the side walls was up, the face\nthat received the brick lining had its irregularities filled with\nsuccessive courses of plastering, and finally a uniform course of\n1/4 of an inch in thickness over the whole, in front of which the\nbrick facing was laid up. A course of plastering was also put\nover the roofing arch. The concrete masonry was formed by\nmixing one part hydraulic cement, three parts clean sand, and\nthree parts fine broken stone ; in some cases fine pebbles were\nin part substituted for broken stone. The masonry was all\nlaid up in hydraulic cement, obtained mostly from the hydraulic\nlime of Ulster county. The mortar for the stone work was\ncomposed of one measure of cement to three of clean sharp\nsand, and for the brick masonry and plastering, one of cement\nto two of sand. It may be proper to remark, that every cargo\nof cement was tested by actual experiment, after it was brought\non the ground, before any was allowed to be used. This pre-\ncaution has had a very salutary influence on the character of\nthe work ; the cement in all cases where it is exposed to view,\nin its exterior, or broken up for examination, or otherwise, has\nappeared highly satisfactory. In the commencement of the\nwork, there was much difficulty in getting the workmen to lay\ntheir stone and brick in a thorough, full bed of mortar, which\nis obviously very important in hydraulic masonry. But a rigid\nsystem of inspection, requiring all imperfect work to be taken\ndown and relaid, was successful in obtaining work of great\ncompactness and solidity.\nDigitized by Google\n12\nThe area of a cross-section of masonry in the aqueduct is :\nConcrete masonry\n4.605\nStone in side walls\n21.572\nDo. in spandrels\n2.690\n28.867.\nBrick in arches and side facing\n13.658.\nTotal\n42,525 sqr. feet.\nA limited departure from the above area has been made where\npeculiar circumstances seemed to justify or require it ; the most\nimportant in extent is, where the aqueduct passes over low\ngrounds or valleys, and a dry wall of stone is raised to the\nproper level to support the conduit masonry ; and generally for\nthe depressed bottom on the 4.949 miles at the upper end of\nthe aqueduct, and in a few other cases in the first contracts,\nwhere the bottom arch and brick facing is 8 inches thick. On\nthe foundation walls, the concrete masonry is laid one foot\nextra thickness, and three feet extra width ; the base of the\nside walls is also increased, and the proportion of cement to\nsand in concrete and mortar for stone work is 1 to 21. In\nother respects the masonry in conduit, is similar on foundation\nwalls to that in excavation. The proportion of lime of aque-\nduct masonry on foundation walls over valleys, to that in\nexcavation is about as 1 to 8. The masonry of the aqueduct\nis covered with earth to a sufficient depth to protect it from\nfrost.\nCulverts.\nTo pass the streams that intersect the line, and the land\nfloods, there has been constructed under the aqueduct 114 cul-\nverts, whose aggregate length is 7959 feet. The span varies\nfrom 1½ foot to 25 feet. Those of 1½ foot span are of a square\nform, and are constructed by laying down a foundation of con-\ncrete masonry ; on which a course of well jointed stone, not\nless than 9 inches thick is laid, forming a stone platform on\nDigitized by\nGoogle\n13\nwhich well dressed stone is laid, one or two courses high, for\nthe abutments or side walls, and finished by a second course of\nwell dressed flagging, not less than 9 inches thick ; all the\nwork laid in hydraulic mortar. The culverts over 1½ foot span,\nwith the exception of three of 25 feet span, are constructed as\nfollows :\nA foundation of concrete masonry is formed, and in a few\ninstances some timber and plank is used with it ; on this an\ninverted arch of well dressed stone is laid in regular courses,\nto form the bottom channel of the culvert ; side walls or abut-\nments are thence raised to such height as required, the face\nbeing well dressed stone, laid up in courses, and backed with\nrough dressed work. An arch is then turned from the abut-\nments, with well dressed stone in regular courses. Wing walls\nat the ends are constructed in different forms as circumstances\nrequired.\nThe character of masonry in the large 25 feet culverts is\nsimilar to that above described, except they have no inverted\narch.\nThere are five road culverts of from 14 to 20 feet span,\nconstructed of masonry of the same character. All the culverts\nare of stone laid in hydraulic cement.\nVentilators.\nThere are 33 ventilators constructed to give free circulation\nof air through the aqueduct. Eleven of them are constructed\nwith doors that admit an easy entrance into the aqueduct.\nThey rise 14 feet above the surface of the ground over the\naqueduct, and are constructed with well dressed stone, circular\nin their form, slightly beveling or tapering towards the top,\nwhere the opening is 15 inches in diameter. They are placed\nat a uniform distance of one mile, except where they are ren-\ndered unnecessary by a waste weir, which serves all the pur-\nposes of a ventilator. At this distance apart, they are found to\nafford a free and sufficient ventilation.\nDigitized by\nGoogle\n14\nWaste Weirs.\nThere are six waste weirs constructed on the line of aque-\nduct, SO arranged as to allow the water to pass off when it rises\nto the proper height ; with gates to draw the water from the\naqueduct when necessary. They are constructed with well\ndressed stone ; the gates and gate frames are of cast iron, fitted\nto stone jambs and lintels ; the frames are faced with brass for\nthe gates to work against, and the gates are operated by a\nwrought iron screw rod and brass nut, working in a cast iron\nsocket. The water from the weir or gates, falls into a well,\nand is then carried off through a culvert to the outside channel.\nA stone building with a brick arched roof is erected, so as to\ninclose the waste weir and its appurtenances.\nCroton Dam.\nThe southern shore of the Croton river at the point where\nthe dam is located, is a gneiss rock ; moderately sloping up\nthe hill from the water's edge, but not appearing to extend far\ninto the river. The dam required to be raised 40 feet above\nlow water in the river ; and it was an important object to\narrange the plan so as to obtain a rock foundation for the\nmasonry.\nTo effect this, the northern abutment was located as far in\nthe river as the rock was supposed to extend, and from this to\nbuild up the dam to the level where the top line intersected\nthe natural slope of the hill, and then to cut the hill away ;\nmaking an opening sufficient for the waste weir of the dam.\nIn prosecuting the work, it was found the rock descended\nmore rapidly into the river than was supposed, which induced\nthe moving of the abutment further towards the hill than at\nfirst located ; and finally, an artificial foundation had to be\nmade for a small portion of it. It was intended to make the\nwaste of the dam 100 feet, with abutments of eight feet high ;\nDigitized by\nGoogle\n15\nbut in consequence of the disappointment in regard to the ex-\ntent of the rock in the river, it was found difficult to obtain the\ndesired length of water way, and it was concluded to raise the\nabutment to 12 feet at the lower end, and 15 feet at the upper\nend, and allow the water way to remain an average length of\n90 feet for this height. The natural rock formed the southern\nabutment, and the aqueduct being on this side, the water was\nconducted to the gateway at its head, by a tunnel, cut 180 feet\nthrough the rock ; this allowed the gateway to be located on\nsolid rock, in a situation not exposed to the floods of the river.\nThe water enters the gate chamber by an archway through\nthe second bulk-head. The gate chamber is provided with a\ndouble set of gates ; one set of guard gates, of cast iron set in\ncast iron frames, and one set of regulating gates, made of gun\nmetal, set in frames of the same material ; the gates are all 18\nby 40 inches, and there are nine gates in each set. They are\nall operated by means of wrought iron screw rods.\nThe gate chamber and bulk-heads are constructed of well\ndressed masonry, laid up in hydraulic cement.\nIn the north abutment a waste culvert has been constructed,\nwith suitable gates of cast iron, to draw the water down in the\nreservoir at such times as it may be necessary, to facilitate the\nmaking of any repairs that may be required, and to discharge\nthe river at ordinary times during the construction of the work.\nFrom this abutment the old channel of the river was filled by\nan embankment, with a heavy protection wall on the lower\nside, which was raised 15 feet above the waste weir of the\ndam, and designed to be 50 feet wide on the top, but was not\ncompleted the full width, when the unprecedented flood of\nJanuary, 1841, carried it away. The embankment stood well,\nand gave no indications of failure, until the water rose to near\nthe surface, and passed through between the frozen and un-\nfrozen earth about 20 inches below the top. After the breach\nwas made in the embankment, large masses of heavy ice came\nDigitized by\nGoogle\n16\ndown from the reservoir, which soon broke down the unfinished\nprotection wall, and carried off nearly the whole embankment.\nThe masonry of the dam and abutment sustained but little\ninjury. Such a flood had not been anticipated, and the water\nway proved insufficient to pass it off. Had the embankment\nbeen completed the full width, and the protection wall carried\nup to the full height it was intended to carry them, the work\nmight have proved adequate to the emergency. It was deter-\nmined to fill the gap made by this breach, (about 200 feet\nlong,) by a structure of hydraulic stone masonry, adapting 180\nfeet as waste weir. This work presented all the difficulties it\nwas originally intended to avoid, by carrying the work par-\ntially into the hill. It was necessary to form an artificial\nfoundation, and carry up a heavy body of masonry, in the\nchannel of the river, which in some parts had 15 feet in depth\nbelow its ordinary level; subject in ordinary seasons to frequent\nand sudden floods, and affording no means to form another\nchannel for it to pass, until the work could be accomplished.\nHad it been admissible to construct the dam with timber,\nthe difficulties would have been far less. But the importance\nof the object it was designed to secure, and its great height, de-\nmanded the most permanent and durable structure that could\nbe made.\nThe greatest height of the weir of the dam is 40 feet above\nthe low-water level, and 55 feet above the bed of the river.\nThe width of masonry, at low-water line of river, is 61 feet.\nThe form on the lower face commences on a curve, described\nby a radius of 55 feet, and continues to within about 10 feet of\nthe top, when a reversed curve, on a radius of 10 feet, carries\nthe face over and meets the back line of the wall. The back\nline is carried up vertically, with occasional offsets. The main\nbody of the work is laid up of rough stone ; the curved face of\nlarge and closely cut stone, with four heavy courses at the\nDigitized\nby\nGoogle\n17\nbottom dovetailed together, the joints cut to the line of radius\nof curve.\nAbove the masonry an embankment of earth is filled in, and\nextends to 275 feet in width on the bottom, with a slope of one\nto five on the up-stream face. The north end of the new weir\nis terminated by an abutment that rises 12 feet above it. From\nthe toe of the masonry an apron is extended 35 feet, composed\nof hewn timber secured by ties, bolts, and treenails, in a very\nsubstantial manner, and filled for 16 feet from the stone work,\nwith concrete masonry, and the remainder with loose stone, and\ncovered with a course of 6 inch white elm plank. A second\napron is partly made which is to extend 30 feet further.\nAt 300 feet below the main dam, a second dam is in pro-\ngress, which is to be 9 feet high, constructed of timber, stone\nand gravel, which will set the water back over the apron of\nthe main dam, and form a pool to check the water as it falls\non it.\nA coffer-dam was constructed in the river to inclose about\n120 feet of the work, from which the water was pumped by a\nsteam-engine, and a concrete foundation laid down on a very\nfirm hard pan. The remainder of the foundation was made by\nsinking timber piers at suitable distances, running parallel with\nthe dam, and filling the spaces between them with concrete\nmasonry. In preparing the specifications for this work, the\nmethod and order of prosecuting it, was particularly designed,\nand from which no material departure has been found neces-\nsary ; the structure is now nearly completed.\nThe contractors, Messrs. McCullough, Black, McManus,\nand Hepburn, have evinced a highly commendable energy and\nability in its prosecution.\nThis dam sets the water of the river back five miles, and\nforms a reservoir of about four hundred acres, and has rendered\nit necessary to construct several new roads and bridges as a\nsubstitute for those covered by the flow ; the principal of which\n2\nDigitized by\nGoogle\n18\nis the Somerstown turnpike. The grounds lightly flowed on\nthe margin, have been excavated so as to give dd feet for the\nleast depth of water. From this reservoir the water flows into\nthe bulk-head, at the upper end of the tunnel, from a level ave-\nraging 10 feet below the surface.\nAQUEDUCT BRIDGE AT SING SING.\nThe Sing Sing kill, where it crosses the line of aqueduct,\nruns in a deep and narrow gulf, the bottom of which is 63 feet\nbelow the grade line, or 76 feet below the top covering of the\nmasonry. Over this gulf an aqueduct bridge has been con-\nstructed. Near the north end of the valley that spreads out\nfrom this gulf, a road culvert, or arched viaduct has been con-\nstructed under the conduit. The principal work here is the\nlarge arch directly over the gulf. It is 88 feet span, and 33\nfeet rise ; the form is an oval drawn from five centres; the\nabutments are commenced on the solid rock, near the bottom of\nthe gulf. The work is constructed of well-dressed stone ma-\nsonry, laid in hydraulic cement. Open hance walls are carried\nup over the interior and above the solid spandrels, and united\nat the top by brick arches. The spaces between the hance\nwalls are carried entirely across the crown of the arch, to afford\nas much facility as possible for any water that might leak from\nthe conduit to pass off. The depth of arch stone at the spring\nline is four feet, and at the crown three feet. The parapets\nand walls of the conduit are carried up with an opening of six\ninches between them, more effectually to guard against the ef-\nfects of frost, and to carry off any water that might leak from\nthe conduit, and prevent its being absorbed by the outer or\nparapet wall. The conduit over this bridge is constructed of\nstone and brick masonry, so arranged as to receive a lining of\ncast-iron ; the iron being set back so as to receive a facing of\nbrick over the bottom and sides, which is further secured by\nthree courses of hydraulic cement plastering.\nDigitized by\nGoogle\n19\nIt is not probable that any considerable quantity of water\nwould have escaped, if there had been no other security than\nthe stone and brick masonry but it is hardly possible to make\nmasonry SO perfectly impervious, that it will not show wet, or a\nsweating appearance on the exterior wall, and the action of\nfrost in this climate, will produce in such cases a deterioration,\nthat may be slow, but will eventually destroy the work : hence\nthe importance of using every precaution to guard against the\nsmallest leakage. This bridge was erected under the contract\nof Young and Scott of Philadelphia, and the work conducted by\nAndrew Young (of the firm), who was the first contractor to\ncommence work on the aqueduct. It is due to Mr. Young to\nsay, this work was thoroughly executed ; the arch proved this,\nwhen on striking the centres, it did not settle over + of an inch,\nand has not changed since. This I consider a very small set-\ntlement for so large an arch.\nHARLEM RIVER BRIDGE.\nThe width of the river at the place where the aqueduet\nline crosses it, is 620 feet at ordinary high water mark ; as has\nbeen before stated, the shore on the southern side is a bold rock\nrising from the water's edge, at an angle of about 30 degrees,\nto a height of 220 feet : on the northern side, a strip of table-\nland forms the shore, and extends back from the river 400 feet\nto the foot of a rocky hill, which rises at an angle of about 20\ndegrees to a few feet above the level of the aqueduct: the ta-\nble-land is elevated about 30 feet above the river: the channel\nof the river to which the water is reduced at very low ebb\ntides, is 300 feet wide, and the greatest depth 16 feet : each\nside of the channel the bed is a deep mud, covered from three\nto four feet at ordinary flood tide : next below the mud there is\na thin stratum of sand, and this is followed by a stratum of sand\nand large boulders intermixed ; below the stratum of boulders,\nDigitized by\nGoogle\n20\nor detached rock, there has been found in the coffer dams for\ntwo piers, Nos. 8 and 9, a compact marble rock, and in the\ncoffers for Nos. 7 and 10, a stratum of clay and sand, that is\nquite impervious to water, and affords a good medium for piling.\nThe general plan of the bridge now in progress of construc-\ntion, is as follows : Across the river there are 8 arches, each of\n80 feet span, resting on piers that are at each extremity and in\nthe centre 20 feet wide at the spring line of the arches; with\nintermediate piers that are 14 feet wide at the spring line ; on\nthe south of this range of large arches there is one arch, and on\nthe north 6 arches, each of 50 feet span, resting on piers 7 feet\nwide at the spring line, and two abutments that terminate the\narch work of the bridge. From the abutments a continuous\nfoundation wall of dry stone work is extended to the gate\nchambers on each side.\nThe whole length of the bridge is 1450 feet ; the height of\nthe river piers above high water line is 60 feet to the spring of\nthe arches, and 95 feet above the lowest foundation that has\nbeen put down; the arches are semicircular, and the height\n100 feet to the soffit, or under side, at crown ;-to the top of\nthe parapets 114 feet above the ordinary high water line of the\nriver, and 149 feet above the lowest foundation of the piers\nthat have been commenced. The width across, on the top of\nthe parapets, is 21 feet ; the exterior of piers, spandrels and\nparapets has a bevel of 1 in 48, and have openings in the inte-\nrior walls.\nThe space between the parapets is arranged to receive and\nprotect from frost two cast iron pipes, each four feet in diame-\nter, which are to lie 12 feet below the grade line of the aque-\nduct, to which they will descend from the gate chambers at the\nends of the bridge. The object of using pipes in this case, is,\nmore effectually to secure the conduit from leakage, that might\neventually injure the masonry of the bridge, and it incidentally\nallows the bridge to be constructed of less height.\nDigitized by\nGoogle\n21\nTo make the capacity of the pipes for conveying water,\nequal to that of the aqueduct, an extra fall of two feet has been\ngiven across the bridge, and the aqueduct on the southern side\nof the river is constructed two feet lower than the regular\ngrade, to accommodate this arrangement. It is intended in the\nfirst place to put down pipes 3 feet in diameter, and to increase\nthe size as the wants of the city may require.\nThe foundations of all the land piers but two have been\nput down, with bearing piles to support them ; they are placed\nbelow high water line ; and 5 to 6 of the base courses of ma-\nsonry have been laid on each ; the remaining land pier and\nboth abutments will have a rock foundation. There are seven\npiers in the river, the foundations of four of which have been\nlaid ; for two of them solid rock has been obtained at a depth\nbelow high water line of 17 feet for one, and 35 feet for the\nother. The pier next the northern shore has a piled founda-\ntion ; to prepare it, an excavation of 16 feet was made, passing\nthrough the strata of mud, sand and detached rock, whence the\npiles could be properly driven.\nThe piles were of oak, from 16 to 35 feet long, and driven\nat 21, feet apart from centre to centre. The other pier (called\nNo. 10 in the general series) for which a piled foundation has\nbeen prepared, is near the centre of the river channel. The\nstratum of boulders lies much lower at this place, and required\nan excavation to be carried 30 feet below common high water\nline, before a suitable stratum for driving piles could be reached.\nWhen the excavation was carried to this depth, boring was\nmade to ascertain if rock could be found for the foundation ;\nbut after going down without success to a depth of 70 feet be-\nlow high water, the effort was abandoned, and the driving of\npiles commenced, as the only means of securing the foundation.\nThe piles were driven at three feet apart from centre to centre,\nto the depth of 30 to 35 feet.\nIt may be remarked, that all the piling for the bridge has\nDigitized by\nGoogle\n22\n\" come home\" with great regularity and firmness, and gives\ngreat confidence that it will afford an unyielding support to the\nstructure. The foundations for the water piers are yet to be put\ndown ; two of them will probably require bearing piles to sup-\nport them, and rock is expected to be found for the other. The\ncoffer dams are all put down and embanked, and the work of\nemptying them is soon to commence.\nA temporary pipe 3 feet in diameter is laid down, (partly on\nthe embankment of the coffer dams) which now conveys the\nwater across this valley.\nGate chambers are arranged at each end of the bridge,\nwith gates to regulate the water, and the one on the north end\nhas a waste weir to discharge the surplus water that at any\ntime the pipes might not be able to carry.\nThe bridge is to be constructed of well-dressed granite.\nIt may very properly be inquired, if the water can be car-\nried temporarily across this valley by iron pipes, why construct\nthis expensive bridge? The reply is, that a plan was prepared,\nand the work put under contract, to construct a low bridge\nwith one arch for water way ; but a supposed value which was\nattached to the future navigation of the river, was so pressed\nupon the legislature, as to induce them to pass a law, requiring\nthat the under side of the arches should be 100 feet above or-\ndinary high tide in the river. The law, therefore, and not the\notherwise necessity of the case, has controlled the plan for\ncrossing this valley.\nMANHATTAN VALLEY.\nThe water is conveyed across this valley by means of iron\npipes. A gate chamber is placed on each side, by which a\nconnection is formed between the conduit of masonry and the\niron pipes ; and gates prepared for regulating the flow of water\nin the same manner as before described for Harlem river. The\nDigitized by\nGoogle\n23\nwidth of the valley is 0.7917 miles from gate chamber to gate\nchamber, and the depth at which the pipes are laid in the cen-\ntre, is 102 feet. Two cast iron pipes, each three feet in diam-\neter are laid down, and provision made for two more, to be laid\nwhen they shall be required for the wahts of the city. In order\nto give the pipes sufficient capacity to discharge the quantity\nof water required, an extra head of three feet is given in cross-\ning the valley.\nCLENDINNING BRIDGE.\nThis bridge is constructed over a valley of the same name,\nthat is situated about equally distant between Manhattan valley\nand the receiving reservoir. The greatest depression is 50 feet,\nbelow top of aqueduct, and the valley is 1900 feet across.\nThe line of aqueduct runs 100 feet westerly of, and parallel\nto, the 9th Avenue.\nIn the plan of the city, streets are laid out, but not yet\nopened, that cross the aqueduct at right angles. For three of\nthe streets archways are constructed under the aqueduct for\ntheir accommodation when they may be opened for use. The\narchways for each street are, one for carriage-way of 30 feet\nspan, and an arch on each side for side walks of 10ₜ feet\nspan. The style of masonry is similar to that before described\nfor the Sing Sing bridge, and the same method of open walls\nand cast iron lining is also adopted. That part of the bridge\nwhich has no provision for street arches, is composed of a con-\ntinuous wall of masonry, carried up on a bevel of 1/2 its rise.\nto the grade line of the aqueduct, where it is 30 feet wide the\noutside or face of this wall for one foot in breadth, is laid in\nhydraulic mortar, and the remainder is laid dry. The method\nof laying up this dry masonry was to lay a course of large stone\nin such a manner as to give them the greatest solidity, and with-\nin a few inches of each other ; after the course was laid over\nDigitized by\nGoogle\n24\nthe work, the interstices were thoroughly filled with small\nbroken stone, well pounded in, and levelled up to receive the\nsucceeding course. (The'same plan was adopted in all the dry\nfoundations which were laid up to support the conduit over low\ngrounds.) After the foundation was carried up to the proper\nheight for the conduit masonry, parapets of hydraulic masonry\nwere carried up to the level of the roofing arch of conduit, be-\ntween which the conduit masonry of the usual form (excepting\nthe side walls, which were 12 inches extra thickness) has been\nconstructed, and covered with earth to protect the sides and top\nfrom frost ; the earth covering being secured by turfing carried\nover from parapet to parapet. The work presents a very sub-\nstantial and finished appearance.\nRECEIVING RESERVOIR.\nThis reservoir is 1826 feet long and 836 feet wide, and in-\ncluding its embankments contains 35.05 acres, and its area at\ntop water line, 31 acres, divided into two divisions : the north-\nern division is designed to contain 20 feet depth of water, and\nthe southern 30 feet in depth. But they are not fully excavated\nin some parts, where rock occurs, it not being deemed suffi-\nciently important to incur the expense of excavation in rock for\nthe increased capacity that would be obtained. The reservoir\nhas a capacity for 150,000,000 imperial gallons, as it now\nstands. The reservoir is formed with earth banks, the interior\nhaving regular puddled walls to render them impervious to wa-\nter ; the outside protected by a stone wall, laid up on a slope\nof one horizontal to three vertical, the face laid in cement mor-\ntar and the inside dry : the inside is protected by a dry slope\nwall, laid on the face of the embankment which slopes 1½\nhorizontal to one vertical. The embankments are raised four\nfeet above the top of water line, and are 18 feet wide on the\ntop, excepting the high banks on the southern division and the\nwestern bank on the northern division, which are 21 feet wide.\nDigitized by\nGoogle\n25\nThe greater part of the embankments for the northern division\nare of moderate height ; but a portion of the eastern and west-\ntern banks of the southern division are 38 feet high above their\nbase. Vaults or brick archways are constructed, in which iron\npipes are laid, so arranged that the pipes from the northern di-\nvision connect with those from the southern division, and thence\npass off to the distributing reservoir, and to supply the adjacent\ndistricts. The main vault is on the eastern side ; it is 540 feet\nlong and is 16 feet span ; that on the western side is 400 feet\nin length, and 8 feet span designed for supplying at a future\nday the district on the North river side above 42d street. The\npipes are all provided with stop cocks, and SO arranged that\nthey can receive the water from either division ; except one\npipe from each division, that leads to the distributing reservoir.\nIt is intended to carry three lines of pipes, each three feet diam-\neter to the distributing reservoir, (at present only two lines are\nput down,) and the arrangement will allow two pipes to be\ndrawn from either division, so that in the event of emptying one\ndivision for repairs, the other would supply two pipes for the\ndistributing reservoir, and all other pipes having a connection\nwith each division would be in full supply, notwithstanding the\nsuspension of one division, A pipe is put through the division\nbank, with a stop cock, to allow the water or not, as may be\ndesired, to pass from one division to the other.\nThe aqueduct intersects the reservoir at right angles with\nits westerly line, and 252 feet south of the north-westerly\ncorner.\nAt this point a gate chamber is constructed, with one set of\ngates to pass the water into the northern division, and another\nset to pass it into a continued conduit of masonry constructed\nwithin the embankment of the reservoir to the angle of the\nsouthern division, where it enters by a brick sluice into this di-\nvision. This arrangement gives the power of directing the\nDigitized\nby\nGoogle\n26\nwater into either division, or both, at the same time, as may be\ndesired.\nIn the division bank, a waste weir is constructed to carry\noff the surplus water from either division, when it rises to the\nproper height.\nDISTRIBUTING RESERVOIR.\nThis reservoir occupies the highest ground in the vicinity,\nand higher than any part of the city south of it ; the site is\ngenerally known as Murray Hill.\nIn order to maintain the elevation of the water, it was ne-\ncessary to raise the walls of the reservoir to an average height\nof 451 feet above the grade of the streets that bounded it on\nthree sides ; the greatest height being, 49 feet, and the least\n39 feet ; the foundations were sunk five feet below the grade\nof the streets. The walls are of hydraulic stone masonry, con-\nstructed with openings, to reduce the quantity of masonry and\ngive a more enlarged base.\nThe openings are made by an exterior and interior wall,\nconnected at every ten feet by cross walls ; which are carried\nup to within 17 feet of the top, and there connected by a brick\narch thrown from one to the other, and the spandrels between\nthem levelled up solid, and a course of concrete put over the\nwhole, 6 inches thick, which reaches a level 10 feet below the\ntop ; whence the exterior wall is carried up single to the top\nThe exterior wall has a bevel of one to six, and is uniformly\nfour feet thick from the bottom to the top of the connecting\narches; the inner wall is carried up plumb, with offsets, the\nlower section six feet thick, the middle section five feet,\nand the upper section four feet thick. The space between the\nexterior and interior walls, at 41 feet below the top, is 14 feet,\nor 24 feet from the outside of exterior to inside of interior\nwalls ; and the space between them at the spring of connect-\nDigitized by\nGoogle\n27\ning arches, in consequence of the bevel of the exterior wall, is\nreduced to 9 feet and 9 inches, and from outside of exterior to\ninside of interior walls, 17.75 feet.\nThe cross walls are four feet thick at bottom, and have one\noffset of six inches on each side, at 8 feet below the spring line\nof connecting arches ; they have an opening 6 feet high, and 11,\nfeet wide, at a suitable level near the bottom, to allow a drain\nto be formed, to collect any water that may leak through the\nwork, and carry it off in sewers provided for that purpose, and\nalso to allow persons to go in and examine the work.\nSome modifications in the cross walls are made to accom-\nmodate the gate chambers, and connect the corners of the work.\nOn each corner of the reservoir pilasters 40 feet in width are\nraised, projecting four feet from the main wall, and in the cen-\ntre, on the streets and 5th Avenue, there are pilasters 60 feet\nwide and projecting 6 feet from the wall. The pilaster in the\ncentre, on the 5th Avenue, rises 7 feet above the main wall,\nand all the others 4 feet above. Doors are placed in the cen-\ntral pilasters on 40th and 42d streets, which give access to the\npipe chambers, to work the influent and effluent stop-cocks,\nfrom which chambers, an entrance is made to the openings in\nthe walls.\nIn the central pilaster on the 5th Avenue, an entrance is\nmade by a door to a stairway that leads up to the top of the\nwalls. On the outside walls an Egyptian cornice is laid, which\naccords with the general style of the work. The pilasters are\nlaid in courses, and well dressed ashlar face, and the main wall\nwith coursed rubble work, rough hammer-dressed. Inside of\nthe walls of masonry, a thorough puddled embankment of suit-\nable earth is formed, 58 1₃ feet wide at the line of reservoir bot-\ntom, and sloping on the inside face one and a half to one for 24\nfeet high, and one to one for the remaining 16 feet high, and\nmaking with the walls on top a width of 17 feet; the faces of\nthe banks are lined with a course of rubble hydraulic masonry\nDigitized by\nGoogle\n28\n15 inches thick, and coped with dressed stone. The bottom is a\nvery impervious hard-pan, on which two feet of puddled earth\nis laid, and this covered by 12 inches of hydraulic concrete.\nThe reservoir is divided into two divisions by a wall of hy-\ndraulic masonry, at the toe of which a sloping bank of puddled\nearth is raised 18 feet high and covered with rubble ma-onry ;\nthis wall is 19 feet thick at the bottom, 6², feet thick at top\nwater line, and four feet at top. In this wall a waste weir is\nplaced, with a well of-two falls, together 52 feet, from which\nthe 'waste water enters a sewer in 42d street, and passes off\nabout one mile to the Hudson river. In each division there is\na waste cock to draw the water from the bottom.\nThe reservoir is designed for 36 feet of water, and when full\nwill stand 115 feet above mean tide. The walls rise 4 feet\nabove the water line. An iron railing is to be p'aced around\nthe walls on top of the cornice. The capacity of this reservoir\nis 20,000,000 imperial gallons.\nGRADE LINE OF AQUEDUCT.\nThe general declivity of the aqueduct in Westchester\ncounty is 0.021 foot per hundred, or a fraction over 13 inches\nper mile.\nThe top of the conduit pursuing this grade, corresponds with\nthe top of the dam on the Croton ; but in order to adapt the\naqueduct to draw at a lower level from the Croton reservoir,\nthe bottom grade was depressed at the head 2.93 feet, and a\ndeclivity of 0.0113 foot per 100 feet, or 0.59664 foot per mile\nfor 4.949 miles, where it intersects the regular grade. The top\nof the aqueduct was depressed only 0.583 foot, and carried level\n2276 feet, where it intersected the regular grade line of the top.\nThis gave an extra height of side walls, enlarging the capacity\nof the aqueduct, more than equivalent to the diminution of de-\nclivity, and provides for drawing from the reservoir to a depth\nDigitized\nby\nGoogle\n29\nof 6 feet, and still leave the capacity of the conduit 35,000,000\nof imperial gallons.\nThe grade of the aqueduct from Harlem river to Manhattan\nvalley, is the same as the general declivity in Westchester\ncounty; but that from Manhattan valley to the receiving reser-\nvoir 2.1727 miles, is 9 inches per mile. It has been stated, the\nextra fall given for the pipes at Harlem river, is 2 feet, and\nat Manhattan valley 3 feet ; between the reservoirs there\nis a fall of 4 feet, when both are full but it is expected\nsomething more than this will be required at times, to furnish\nthe full quantity that will be wanted. The pipes are provided\nwith waste cocks at the depressions, and air cocks at the summit\nbends.\nThe first contracts for work on the aqueduct were made in\nApril, 1837 ; at which time about ten miles of the upper end\nwas advertised but in consequence of the proposals being\nconsidered too high, only about half of it was contracted for.\nAbout the middle of May, the contractors generally entered on\nthe work contracted for. In September following, about 16\nmiles more was put under contract ; in May, 1838, the balance\nof the line to Harlem river was put under contract ; and the\nwork on the Island, except the grading of the 5th Avenue for\npipes, in October following. In consequence of legislative\ninterposition, the Harlem river work was re-let in August,\n1839.\nThe work was so far completed, as to permit the water to\nbe let in from the Croton dam on the 22d day of June, 1842 ;\nand it was admitted into the distributing reservoir on the 4th\nof July following. There is yet considerable work to be done\nat the Croton dam, the receiving and distributing reservoirs,\nwhich will probably all be completed in September or early in\nOctober. The Harlem river bridge will require at least two\nyears to complete it. At the latter place, a temporary pipe\nconveys the water across the valley.\nDigitized by\nGoogle\n30\nThe following extract is taken from my report of the 12th\ninst. to the Board of Water Commissioners :-\n\" Since the water was introduced into the aqueduct, the\nvelocity has several times been ascertained ; though not in so\nperfect a manner as I intend to have it done, as soon as other\nduties will allow the time necessary. Sufficient data, however,\nhave been obtained to show, that the capacity of the aqueduct\nfor delivering water will be at least 15 per cent. greater than\nthe calculated flow. I have not been much disappointed in\nfinding the flow of water in the aqueduct to exceed the calcu-\nlation, as all my observations on the currents in canal feeders,\nhave led me to believe, the formulas laid down give rather less\nthan the actual result. The flow of water through the pipes\nacross Manhattan valley, and also the temporary pipe across\nHarlem river, being attended with circumstances somewhat\ndifferent, has led some very intelligent persons to predict, that\nour expectations would not be realized in these cases ; it there-\nfore may be proper to observe, the trial has proved such pre-\ndictions to have been not well founded ; as the flow through\nthe pipes has in a very exact manner corroborated the antici-\npated capacity, as compared with that in the aqueduct.\nThe Croton reservoir, (which has received the name of\nCroton lake,) covers about 400 acres of land, and is available\nas a reservoir for 500,000,000 imperial gallons of water, above\nthe level that would allow the aqueduct to discharge 35,000,000\ngallons per day. The flow of the Croton is about 27,000,000\ngallons in twenty-four hours at the lowest stages, which con-\ntinues, with moderate rises by occasional rains, from two to\nthree months in the year. This may be considered the minimum\ncapacity of the river. When the wants of the city shall require\na daily supply of 35,000,000 gallons, it will be necessary,\nduring the season of lowest water, to draw daily from this\nreservoir 8,000,000 gallons, to make up the deficiency in the\nnatural flow of the river. This amount the reservoir would\nDigitized by\nGoogle\n31\nsupply for 62 days, without any aid from occasional rains ;\nwhich may safely be relied upon, to keep up the required supply\nfrom the reservoir, beyond any drought we have ground to\napprehend. The supply of the Croton, from its daily flow,\naided by this reservoir, may therefore be taken with great con-\nfidence at 35,000,000 gallons; which will be very ample for\nthe wants of the city for a long time to come; and when the\nday arrives that it will require a larger quantity, it may be ob-\ntained by constructing other reservoirs further up the stream,\nwhere there are abundant facilities for such purposes.\"\nThe total cost of the aqueduct, from the Croton dam to the\ndistributing reservoir inclusive, will be nearly 9,000,000 of\ndollars.\nNew-York, 27th July, 1842.\nDigitized by Google\n7\nDigitized by Googl\nCABOT SCIENCE LIBRARY\nCABOT\nMAY 11 1997\nBOOK DUE\n3 2044 044 828 309\n3 2044 044 828 3"
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