one eighth for shrinkage, the widths of one hundred and eighty and thirty-six feet bottom, require about three and one tenth and six and one tenth feet respectively in depth of excavation, and eight and nine tenths. and five and nine tenths in height of banks above the natural surface. 4. Culverts. The absence of rock for foundations, requires that the form of the culverts, and the material of which they are built, should be such as to prevent undermining at any time, and wear when heavily charged by the stream. By adopting the plan of circular pipes, built of well shaped hard stone or well burnt bricks, with secure cross and end walls, the culvert will be safe, with a pressure from within equal to that upon the exterior of the pipe; the latter will always be at least four feet of puddle, and (with the water in the canal, as it should always be in the season of rain,) at least five feet of water, in addition to the weight and strength of the masonry. 5. Aqueducts. The elevation of the beds and banks of four of the five large streams to be crossed by aqueducts, and the expense of high approaches to them, require that the abutments and piers be sunk deep into the valley of the stream. There is uncertainty of finding in the bottom ground suitable for masonry to rest upon, and the probabilities of scouring by the stream in times of great freshes, render the use of timber necessary, unless we incur the expense of making the abutments and piers of solid masonry, not less probably than twenty feet deep, and from fifteen to twenty feet thick. In the absence of reliable informatian as to the character of the bottom, piling, capped by a platform of solid timber, protected by fascines, piles, and rock, or its equivalent of paving, has been adopted as the plan upon which to base an approximate estimate. The thrust of the arches, having a rise of only one fifth of the span, requires abutments of great weight and thickness. It is met in part by the embankment and compact puddle, rising to the height of twentyeight feet and resting against the abutments on the rear, and in part by the form given to the wings. The same foundation is required for the wings, which may be exposed to undermining by the suction of the water after its escape from confinement under the arch. The tendency of the embankment and puddle resting against the inner face to press them outwards, is met in part by their circular form, the convex side being next to the pressure, and one end being in line with the parapet and resting against it and the rear of the abutment. The thickness of the parapet is more than is requisite to resist the pressure of the water. But in an aqueduct with water way only six feet deep and twenty feet wide, and with less than six feet for the play of the boat, I have seen parapets of cut stone six feet thick disturbed by blows from passing boats. 6. Locks. All lift locks which may be placed upon the main stem of the canal used as one of irrigation as well as navigation, with its depth of water varying from five to ten feet, will be open to two objections which it is desirable to avoid : First-There must be an expensive appendage (flume) for passing around the lock, the water required for irrigation and loss below the lock; and, Second-The lock must be adapted to the passage of a boat, with any height of water within the limits named, on either or both of the reaches above and below it, making each lock practically a guard lock. A lock of seven feet lift between two reaches of five feet depth of water each, requires the side walls to rise to twelve feet above bottom of canal in the reach below the rock. If the water be raised to ten feet in the upper reach, the height of the walls must be increased to seventeen feet. The height of the walls of a lock of eight feet lift will be, in the two cases, thirteen or eighteen feet above canal bottom. A suitable coping will add one foot in height in each of the supposed cases. The difference in the cost of the two classes of rocks, viz: with and without a variable height of water, is considerable. The more costly class will be required for the six locks of seven feet lift each on the seventy-first and seventy-second miles, and for the nine locks of eight feet lift each on the line between the one hundred and sixty-sixth mile and Cache Creek Slough, as in both cases the canal will be one of irrigation as well as navigation. But if the route to Cache Creek Slough should be abandoned, and the main trunk of the canal be extended to and terminate at a point near Suisun City, or some other point to which tide water approaches more near to ground high enough for the grade of the canal of irrigation, its extension to tide water may be a canal of navigation only; it may be without grade and without variation in the height of water surface in the reaches between the locks. Supposing the extension made, and the locks and reaches adapted to a uniform depth of six feet of water, with eight locks of eight feet lift each, the height of the walls of one only of the eight locks would be eighteen feet above bottom of canal (nineteen with coping,) the other seven rising to fourteen (and with coping fifteen) feet above the same level. The flumes will be small and may be of simplest and cheapest construction, and easily repaired or rebuilt. The modifications in the route which I have suggested an examination into, if they should lead to the removal of the six locks from the seventy-first and seventy-second miles to the lower end, and particularly if they should be placed in a branch simply of navigation, would much improve the project and largely reduce the cost of locks and flumes. The tide lock, whether upon the line to Cache Creek Slough or to Suisun, will be upon ground that may require additional precaution in the foundation, especially at the tail of the lock. Deep soundings in the mud, for which I had not the time and means, must be made before the best place can be determined. 7. Flumes for passing water around the locks. Between Stations Nos. 562 and 575, on the seventy-first and seventysecond miles, the canal descends forty-two feet by six locks of seven feet each. To pass the large body of water required for irrigation below these locks requires costly works, which must also be carefully built. The quantity of water entering the canal with a full head of ten feet will be six thousand seven hundred and forty cubic feet per second. It will be gradually reduced, between the spring and autumn, from ten to five feet in depth, and the quantity then entering will be two thousand two hundred and ninety-seven cubic feet per second. About sixty-five hundredths of the whole will be required below the lock, viz: four thousand three hundred and eighty-one cubic feet per second in spring, and fourteen hundred and ninety-three cubic feet in autumn. Any passage way for this large body of water should be self-regulating and independent of the attention of the employés of the canal. It should pass the water with safety and certainty, day and night, and at all seasons, and be interrupted only in case of a breach in the canal or other cause requiring a drawing off of the water. It would seem at first sight that the variation in the height of water surface in the canal generally, viz: from ten to five feet, should apply to the whole of the canal above and to each of the reaches between these six locks, and that the passage way for the water from one to the other must be made to suit the varying height in the canal. There is not, however, any necessity for it. There is no objection to the maintaining of a greater depth of water in the canal for a few miles above the upper one of the six locks and in the reaches between the locks, than there will be in the canal generally, with any flow less than ten feet of depth. It will be an advantage to reduce the current and maintain a greater depth. We have, then, only to find the most simple and safe passage way for the larger quantity, viz: four thousand three hundred and eighty-one cubic feet of water per second, with a depth of ten feet in the canal, and it will pass any less quantity without reducing the water too much for navigation if the bottom of the passage way be not placed too low. Long sluice ways and simple weirs or dams are the most usual forms of structures for passing large feed around locks. Both require firm foundations to resist the shock of the water at its entry upon the lower level. The foundation is a large item in the cost. A long sluice will contain large quantities of material, and if built dry it will be unsafe. A weir will be more compact, and is the plan I propose for the six locks. Between Station No. 1,329 (on the one hundred and sixty-seventh mile) and the tide lock at Cache Creek Slough, there will be nine lift locks, each of eight feet lift. The quantity of water to be passed around the first one of the nine locks is four hundred and fifty cubic feet per second, about one fifteenth of the whole quantity entering the canal. It will diminish with each mile, and the quantity will be less at each successive lock. As the foundation and side walls of a weir are so large a part of the cost in construction, and are nearly as great for a short as for a long weir, I propose, for the small flumes required at these nine locks, to substitute a pipe or culvert to pass under the cross bank. It has been explained under the head of "Locks," that if the main trunk of the canal should be extended to the vicinity of Suisun, or some other point where high ground suitable to the grade of the canal approaches nearer to tide water than it does upon the route to Cache Creek Slough, the size of all these flumes will be reduced. Their cost will be but a small part of that in the estimate on the line to Cache Creek Slough. Sluice-ways, or waste-gates, must be provided for the purpose of distributing water for irrigation, and to relieve the canal of water. The size of each one will be finally regulated by the quantity of water to be discharged through it, and its position by the form and drainage of the country contiguous. For the present, I propose one of average size, to be estimated for each mile. The length of the canal from the head gates to Station No. 1,329 (on the 167th mile) is.. Making the length of the survey.. The main trunk of the canal would probably be extended from Station No. 1,329.... To the vicinity of Suisun, distant by the grade it would follow (rejecting 24 miles additional for connection with tide) probably... Making the length of the canal of irrigation........... Miles. 166 1-8 12 3-8 178 4-8 166 1-8 22 188 1-8 The quantity of water to be distributed for irrigation is six thousand five hundred and seventy-one cubic feet per second. Dividing it by the distance, we get thirty-four and eighty-six one-hundredths cubic feet per second as the quantity to be delivered for irrigation by the sluices on each mile. But the openings which would serve to deliver this quantity of water, with the full head of ten feet, would require nearly four and half days to relieve the canal of the whole quantity contained in it. Occasions may require that the canal be promptly relieved, and the sluices should be of dimensions to suit the emergency. An opening thirty inches square is large enough when the sluice gate has to be of cheap construction and be managed by one man. If set near the bottom of canal, its discharge, with the full head of ten feet in the canal, would be about ninety cubic feet per second. The canal is widest at the head, viz: one hundred and eighty feet on bottom, and diminishes in width to thirty-six feet at the lower end, with ten feet depth; the average section of water is one thousand two hundred and eighty square feet. The quantity in one mile is six million. seven hundred and fifty-eight thousand four hundred and six cubic feet, which running under a full head would pass through an opening thirty inches square in a little less than twenty-one hours; but in draining the canal, nearly forty-two hours would be required. One sluice-way upon each mile, with four such openings, will drain the canal in less than ten and a half hours. This size and number I adopt. There being no rock foundations for the sluices, timber must be employed. Unless we incur very great expense in sinking them deep in the ground, they will in time decay and must be renewed. It is not advisible therefore to build masonry superstructures, but to build the whole of wood, with the addition of a paving at the outlet. 9. Outlets Overfalls. From various causes the canal will be subject at times to an influx of water exceeding its capacity. An accident at the head, or at any one of the many points along the canal, may throw an excess of water upon a reach, which should find an escape unaided by the employés of the canal. A portion of the drainage of the country is necessarily admitted, and although it is in small returns, the aggregate may be considerable in times of very hard rains. Weirs or overfalls should therefore be established, so as to pass this water over the banks of the canal as soon as it rises above the height of ten feet. It is plain that the more numerous these wastes may be, the more safe will be the canal against accidents to its banks from the causes I have named. But their cost limits their number and extent, which for this estimate I will confine to one for each six miles of the canal; the length of the waste to be equal to the width of the water surface in the canal opposite to it. Generally, ridges or elevations of ground through which the canal passes may with advantage be selected as the sites of the wastes. For safety in the estimates they will be calculated at the cost of placing them on banks twelve feet high. These overfalls will not be required until the demand for water causes the full depth of two feet to be run in the canal. Time will therefore be allowed to collect the materials for their construction and for its transportation upon the canal at the lowest rates. 10. Crossings-Bridges. Ways of passing over the canal must be provided. They are not a part of the canal, but are rendered necessary by it. The more numerous they may be, the greater will be the convenience to the public. But the cost of their maintenance, as well as the interest upon the cost of construction, must be paid in the rates of tolls and water rents by the people who employ the canal. The convenience of numerous bridges will, therefore, be weighed with the cost to themselves, until the wealth and population of the country will distribute the expense amongst a great number. At present, I estimate one for each six miles in length of the canal. To establish and maintain a ferry where the travel is great or the canal narrow, will cost more than the interest upon the cost of construction and the wear and tear of a bridge. Where the canal is very wide, the population scanty, and the passing unfrequent, a ferry may serve for a time. I have, however, thought it best to estimate bridges of cheap construction, and admitting of repair and renewal without interruption to the use of the canal. To allow free passage to boats plying upon the canal there should be a space of twelve feet between the surface of the highest water in the canal and the bottom of the bridge. They must, therefore, be twentytwo feet high, and the earth approaches to them must rise to the same elevation. The team towing the boat must pass under the same span of the bridge with the boat. This requires that the towing path, and a width of the canal sufficient for the passage of a loaded boat, with the minimum depth of five feet of water in the canal, be embraced in a space larger than is necessary for other spans of the bridge. By means of a wall, a track for the team is made to occupy a part of the slope of the bank under the bridge, and the top of the bank of the canal is occupied by the slope of the earth approaches, and by a bent, upon which one end of the long span rests. On account of the great size of agricultural implements used in the valley, and the great weight moved by wagons, the bridge must be of greater width and strength than is usual upon ordinary roads. 11. Branch Canal from Station No. 341, on the forty-fourth mile to Sacramento River, and along the river to the head of Sycamore Slough. At the time of making the survey in the field, this auxiliary was not thought of, and was not surveyed. It was afterwards adopted in the office, as a means of reducing the width of the main trunk of the canal, |
