Irrigation canal

“ Immense damage has been done by “water-logging” of the soil when irrigation water has been supplied to a tract of flat country and the clearance and improvement of the natural drainages has not been attended to. Any drainages crossed by the banks of the irrigation channels should be provided with syphons or aqueducts or else the drainage diverted into another channel. Very frequently the main line of a canal—whether great or small—in the upper reaches near the hills, has to cross heavy drainage channels or torrents and large and expensive works are required for this. ”

“ The Panama Canal might have been constructed at one level, but the cost of this, and the time occupied, would have been double that of making it a summit canal. The water of the river Chagres is to be impounded to form a lake of great extent that will not only supply water for lockage but will itself form part of the high-level reach of the canal, and ships will be able to traverse it at greater speed than in the rest of the canal.
Some Indian irrigation canals have been constructed so as to be navigable. The increase in cost has usually been enormously in excess of any resulting benefits. ”

“ For irrigation, there are times when the canal should be kept low so that large quantities of water may not have to be passed into the drainages when they are already filled by rain-water; for navigation the canal should always be kept up to its full level. For irrigation, even when the river or other source of supply is low, it is often necessary to go on letting as much water as possible out of the canal to supply crops, thereby reducing the level and the depth in the canal, especially at its end ”

“ One half of a miner's inch per acre was found to be necessary for the irrigation of the lands served by the various canals. It was further found that a surface flow of 7,500 miner's inches in the Gila river at the head of the irrigation system furnished more water than is needed to irrigate the entire acreage shown by the evidence to have been in cultivation in the year 1904 ”

“ It took four hundred mules and two hundred and fifty men two years to build it. The reservoir and canal tapping Merced river cost together two million dollars to build, and the work was constructed in such a substantial and scientifically correct manner, that it will be likely to last for ages. There is no other irrigation system in the State that is as well planned and carried out. ”

“ Sometimes, as in the low land adjoining a river, the ridges are ill defined or non-existent and the alignment is based entirely on the above rules. The rule as to following high ground need not be adhered to at the tail of any distributary if all the land to be irrigated at the tail is low and if there is a deep drainage line or other feature of the country such as to preclude the possibility of an extension of the distributary. Possible extensions should always be considered. In hilly districts an irrigation canal may have to run in sidelong ground along the side of a valley. ”

“ There are many similar and even better opportunities for irrigation development, such as the construction of a canal from the West Gallatin River near Bozeman. This canal would require no expensive diversion line, as its waters would become immediately available at the headworks, and by appropriating the 500 second feet of water flowing in the river, would reclaim at a minimum cost 50,000 acres, or twice the amount of land now cultivated there. Storage on the Upper Gallatin River would greatly increase the amount of reclaimed land. ”

“ In his reports on the subject he estimated that a region equal in size to New England, New York, Pennsylvania, and West Virginia could be recovered from the desert sands of Arizona and other regions in the West. In India, millions of pounds have been spent for irrigating canals and ditches. A single canal with its tributaries drawing water from the Ganges measures 3,910 miles in length, bringing into cultivation one million acres of land at an expense of fifteen millions of dollars. The idea of irrigation is not due to the advanced intellect of man ”

“ The diversion of a large stream from its channel into a system of canals demands a large outlay of labor and material. To repay this all the waters so taken out must be used, and large tracts of land thus become dependent upon a single canal. It is manifest that a farmer depending upon his own labor cannot undertake this task. To a great extent the small streams are already employed, and but a comparatively small portion of the irrigable lands can be thus redeemed; hence the chief future development of irrigation must come from the use of the larger streams. ”

“ There are also places on inundation canals where the land is high and is only irrigable during floods. At such places it is usual, on some canals, to allow the people to make cuts in the bank when the water attains a certain height. Owing to the high level of the country, nothing in the nature of a breach can occur. In one canal division where the above arrangement was in force, the people used to send applications to the Executive Engineer for leave to cut the banks. ”

“ On inundation canals the water at a regulator is sometimes headed up,—all branches being partially closed—in order to give more water to outlets in the upstream reach. There are even some regulators—or rather stop-dams—constructed solely for this purpose at places where there is no bifurcation of the canal or distributary. Any such heading up should be planned out beforehand and days for it fixed, and also the gauge reading. If the water, without any heading up, rises to the needful height on the gauge, nothing has to be done. ”

“ Elwood Mead, chief of irrigation and drainage investigations, U. S. Department of Agriculture, has given measurements showing the great loss by seepage and evaporation from irrigation canals, and has discussed methods by which the water-supply might be more economically utilized. ”

“ Regarding the percentage of area to be irrigated, it has already been stated that one canal or distributary irrigates a far higher percentage than another. Generally when there is a high percentage in any tract, it is undesirable to cut it down unless it has very recently sprung up to the detriment of other tracts. In some remodelling projects a uniform percentage is taken on the whole area including both new and old irrigation. ”

“ No reservoir or canal should ever be built to satisfy selfish personal or local interests; but only in accordance with the advice of trained experts, after long investigation has shown the locality where all the conditions combine to make the work most needed and fraught with the greatest usefulness to the community as a whole. There should be no extravagance, and the believers in the need of irrigation will most benefit their cause by seeing to it that it is free from the least taint of excessive or reckless expenditure of the public moneys. ”

“ In flat valleys, owing to the land nearest the river having received successive deposits of silt in floods, the ground generally slopes away from the river and a canal can irrigate the low land even if taken off at right angles to the river. But to irrigate the high land near the river and the land where it rises again towards the hills or watershed, a canal taking off higher up the river is necessary. ”

“ The number of acres irrigated annually by a constant discharge of 1 c. ft. of water per second is called the “duty” of water. In India on perennial canals the duty may be as much as 250 or even 300 acres. On inundation canals which flow for only five months in the year and are situated in tracts of scanty rainfall and light or sandy soil, the duty may be only 70 acres. The duties of most existing canals whether in India or elsewhere, are known only approximately. The duty is calculated on the average discharge entering the canal at its head less the water which is passed out at escapes. ”

“ There is no easy way of closing these outlets or at least of keeping them closed if the cultivators choose to open them, but it is easy to close a whole distributary and so regulate the supply. This is the chief reason why watercourses in India do not usually take off direct from the canals.
The presence of silt in the water of a river from which a canal is drawn is often spoken of as being a great evil. If it is an evil at all it is a very mixed evil. The deposits of silt in the channels have been enormously reduced by the application of scientific principles of design. ”

“ In the case of a distributary, this is necessary in order that the water-courses may run downhill, and since the water in the canal and branches has to flow into the distributaries, the canal and branches must also be in high ground. Another reason for adopting high ground is that all the channels should, as far as possible, keep away from the natural drainage lines of the country and not obstruct them. Also a channel in high ground is cheapest and safest. When a channel is in low ground it must have high banks which are expensive to make and liable to breach. ”

“ The case of the Sirhind Canal, already referred to (Chap. IV., Arts. 5 and 6) , is a notable example. The canal (fig. 6) is more than 200 feet wide, the full depth of water 10 feet, and the full discharge about 7000 cubic feet per second. In 1893 when the irrigation had developed, and it became necessary to run high supplies in the summer—July, August, and part of September—the increase in the silt deposit threatened to stop the working of the canal. ”

“ It is desirable to be able to give a distributary its full supply even when the canal is low. Generally the slope of the country along any line is greater than would be suitable for the bed, and “falls” are introduced. The off-take of a distributary is generally just above a fall and there is generally an ample margin between its [52] F.S. level and that of the canal. The discharge of the canal during the greater part of the rabi may be only about half the full supply. This discharge should be estimated and the water level corresponding to it calculated and shown on the longitudinal section. ”

“ Sometimes the lake is so deep that the water cannot be lifted directly to the main canal, and thus be carried off, and when this is the case a series of dykes and canals at different levels has to be made, and the water transferred successively from one to another. The land thus reclaimed is wonderfully fertile, since in wet seasons superfluous water can always be quickly removed, and in dry seasons thorough irrigation can be effected still more easily and quickly. ”

“ A pitched bend can be made anywhere.
When a river floods the country along its banks as in parts of Egypt and of the Punjab, it is generally necessary to construct marginal embankments before irrigation can be introduced. The canal may take off at a point where flooding does not occur or it may pass through the embankment. [2] If it passes through at a point where flooding occurs, a masonry regulator is constructed to prevent the floods from enlarging the gap and breaking into the country. ”

“ The Northern Pacific and Yakima Irrigation Company is surveying for another canal, to cost six hundred thousand dollars, and to have a length of one hundred and ten miles. A still greater scheme is on foot to expend about two million dollars in extended irrigation and in constructing dams in the mountains for the storage of water, which will be wanted when the eight hundred thousand acres, now reserved for the pleasure of the Indians, shall be thrown open to settlement. ”

“ In order to develop irrigation, numerous syndicates have been formed, as some of the land was held in small parcels by proprietors and farmers who had neither the funds nor the power, in opposition to intervening landowners, to obtain branches to conduct the water from the main irrigating canal to their properties. The price charged for the water is regulated by the price charged for corn on the basis of 1·66 bushel per acre irrigated. ”

“ Unlicensed boats pay 6d. per ton for a single trip. The charge for third-class passengers on boats is one-eighth of a penny per mile.
Between the river Tumbaddra and the river Pennar there is a large canal, which was originally constructed by the Madras Irrigation Company, and, although intended primarily for an irrigation line, was fitted with locks, in order to enable it to be used for navigation. This canal is, however, only available for about eight months of the year, as the water supply in the river has to be passed on for use in the Kistna Delta. ”

“ A large force of men was employed, and the attempt was prosecuted with vigor. Two hundred men, twenty teams, two pile-drivers and two stern-wheel river steamers were employed, and the work was carried on night and day. The intention was to construct a 600-foot dam across the west branch of the river, and thereby control the canal service by diverting the water into the east branch—except at such times and in such quantities as were necessary for irrigation. ”

“ The vastness of the arid areas which without irrigation yield no crops at all or only cheap millets and pulses makes his works of inestimable benefit to the people and a source of revenue to the State.
Canals before annexation.—In the west of the province we found in existence small inundation canals dug by the people with some help from their rulers. These only ran during the monsoon season, when the rivers were swollen. In 1626 Sháhjahán's Persian engineer, Ali Mardán Khán, brought to Delhi the water of the canal dug by Firoz Sháh as a monsoon channel and made perennial by Akbar. ”

“ There are at this moment at least 100,000 horse water power available and made no use of in the great irrigation canals. The canals will convey the goods to and from manufactories, and the irrigation will set free millions from agricultural labour for such work. ”