E. S. Bellasis

“ Where a road crosses a bridge or regulator, the bank should be at the same level as the road, the bank being gradually ramped back to its original level. The space in front of any quarters should have a slight slope for drainage, but otherwise be at one level and be connected with the road or bank by proper ramps. The berm or bank should be made at the exact level of the top of any pitching or side wall which adjoins it. Wing walls are frequently made too short, so that the earth at their ends forms a steep slope and is worn away, and the bank or roadway is cut into. ”

“ As a rule they over-water the land and frequently damage or spoil it by water-logging. They do not always keep in proper order the banks of the watercourses. The banks often breach and water escapes. Any area thus flooded is charged for if it is seen by an official. The engineers have power to close such a watercourse until it is put in order, but this would cause loss of revenue and is not often done. The real remedy for all this is, as already stated, rigid restriction of the supply. The people will then learn—they are already learning—to use water more economically. ”

“ When a branch receives, at any point, a temporary increase in its supply, owing [125] to the closure of a distributary for, say, three days, there will be a rise lasting for three days at a point further down. The rise will take some time to come to its height, and some time to die away. There will be about three days from the commencement of the rise to the commencement of the fall, or from the end of the rise to the end of the fall. If, either in the main canal or in a branch, there is any distributary into which full supply cannot be got, its turn can be increased accordingly. ”

“ 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. ”

“ 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. ”

“ A watercourse nearly always gives off branches and generally a system of turns is arranged by the farmers among themselves, each branch in turn taking the whole discharge of the watercourse for a day or part of a day, the other branches being closed by small dams of earth. To irrigate a field alongside the watercourse a gap is cut in its bank. For fields further away, smaller channels run off from the watercourses at numerous points. Several gaps and several field channels may be in flow at one time, and there is a dam in the watercourse below the lowest one. ”

“ Irrigation generally consists in giving the land a succession of waterings, one previous to ploughing and others after the crop is sown, each watering being of quite moderate depth. On inundation canals in India the waterings for the summer crop are thus effected but for the winter crop the land is deeply soaked during the flood season and is afterwards ploughed and sown. In Upper Egypt this system is emphasised, the water flowing into vast basins, formed by dykes, where it stands for some time and, after depositing its silt, is drained off. ”

“ When water flows or stands in an earthen channel or tank, or is spread over a field, losses occur from evaporation, percolation and absorption. Of these, absorption is by far the most important and, unless the contrary is stated or implied, it will be taken to include the others. The losses by evaporation are very small. The loss by evaporation from the surface of the water, even in the hot season in India when a hot wind often blows, does not exceed half an inch in 24 hours and on the average in India is only about a tenth of an inch in 24 hours. ”

“ So great, however, is the elasticity of a channel—by which is meant its capacity for adapting itself to varied discharges, a small change in the depth of water causing a great change in the discharge—and so considerable has been the uncertainty as to the real duty to be expected, that any mistakes made have not usually resulted in any serious trouble. ”

“ The distribution of the water of a canal as between the main channel and the branches, is effected by means of the regulators at the bifurcations. When the supply is ample and the demand great, the channels may all be running nearly full. When the demand exceeds the supply, the water may be reduced proportionately in each branch but this may result in the water of a branch being too low to give proper supplies to the distributaries or some of them, and in the water of a distributary not commanding the higher ground. ”

“ Remodelling should not be considered piecemeal, but regard should be had to the whole channel. When a distributary is remodelled the outlets should of course be dealt with as well as the channel. The chief thing to consider is not whether the channel as it exists is exactly as it was originally designed to be, but how it is doing its work and what kind of alteration it needs. Even when a simple silt clearance or berm cutting of a channel has to be undertaken, the work need not always consist in blindly restoring the channel to its original condition. ”

“ 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. ”

“ It is mentioned that there is no special reason for making the waterway of a regulator exactly the same as that of the stream, and that the waterway may be such as to give the maximum velocity considered desirable, and that the foundations of a bridge should be made so deep that it will be possible to add a floor, at a lower level than the bed of the stream—with the upstream and downstream pitching sloping up to the bed—so as to increase the waterway and so save pulling down the bridge in case the discharge of the channel is increased. ”

“ As far as possible the boundaries of divisions and subdivisions are co-terminous with those of the branches of the canal. A distributary is always wholly within a subdivision. At every regulator there is a gauge reader, who, supplied when necessary with permanent assistants, sees to the regulation of the supply. ”

“ Since no irrigation is usually done directly from the canal and branches, they are designed without any particular connection between the level of the water and that of the country traversed. Dangerously high embankments are of course avoided as far as possible. The bed is designed at such a level that the excavation and embankment at any place will be, as nearly as possible, equal. Land in India is cheap. When the excavation exceeds the embankment the balance is made into a spoil bank. When the excavation is less than the embankment the balance is got from borrow-pits. ”

“ We all know that when we stir tea in a cup so as to make it spin, the liquid rises at the rim of the cup and curves down into a depression in the middle, and the greater the spin the more marked this effect is. It is, we know, the centrifugal force produced by the spin that makes the tea remain high at the rim of the cup. If, while the tea is thus spinning, a teaspoon is held so that it dips slightly below the surface of the liquid near the rim, it will obstruct the flow of the outer portion of the liquid, which will fall in towards the depression in the middle. ”

“ The people will disturb matters to some extent by enlarging watercourses, but there is a limit to this and it can be met by an occasional reduction of an outlet. A distributary, when once its outlets have been carefully adjusted, attains to something approaching perfection in its working. Any excess in the supply is taken partly by the upper outlets but part of it gets to the tail. ”

“ A Subdivisional Officer generally receives a steady stream of applications from members of the irrigating community regarding—among other matters—outlets or watercourses. Generally these applications are made over to the zilladar to be reported on. In a large number of cases the applicant states that the irrigation of his land or “holding” is not satisfactory, or has fallen off, and sometimes he asks that it may be transferred, wholly or in part, to another watercourse which he thinks will give a better supply. ”

“ Again, the people may, if the outlet gives a plentiful supply, often keep it closed, but there is no record of such closures nor would the people admit that they occur. These causes may all operate in one direction—on a whole distributary this cannot happen to the same extent—and thus enormous differences in duty may occur. There is no way of arriving at the proper size for an outlet except trial. Observations of the discharges of the outlets are of very limited use. The discharge may vary according to the particular fields being irrigated. ”

“ The drainage of the whole tract irrigated by a canal must be carefully seen to. The subsoil water level of a tract of country is nearly always raised by an irrigation canal. The rise near to a canal or distributary is due to percolation from the channel and is inevitable. [3] The rise at places further away, if it occurs, is due to over-watering or to neglect of drainage. ”

“ Of course much depends on whether the canal is to irrigate when the river is low or only when it is high, and whether or not there is to be a weir in the river. In Upper Egypt, it is common for a high level canal taking off far upstream, to divide into two branches, one for the land near the river and one for the land towards the watershed, and for both branches to be crossed—by means of syphons—by a low-level canal which irrigates the low ground. ”

“ If the tract is small or narrow, and particularly if it is not very flat, it may be obvious that there is only one line on which the irrigation channel can conveniently be constructed but in any considerable scheme a contour plan of the whole tract is absolutely necessary. The surveys for such a plan are expensive and take time and it is desirable, as far as possible, to settle beforehand the area over which they are to extend. ”

“ On the inundation canals of the Punjab a watercourse often discharges 10 c. ft. per second, and is several miles long and requires heavy clearances, but the people have no particular difficulty in managing it. Kennedy, a great authority on questions of irrigation, states that the length of a watercourse may be three miles. This, if the angle made by a watercourse with the distributary is 45°, gives rather more than two miles as the width of the strip to be irrigated. ”

“ A common case is that in which the channel is not remodelled—or at least its water level remains very much as before—but merely the outlets are altered in number, position or size, or in any or all of these. If the land irrigated by an outlet is high, the irrigation may be far short of what was expected, and the size of the outlet may have to be increased or its site shifted, generally upstream. This is often done at the request of the people, and at their expense. ”

“ 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. ”

“ 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. ”

“ The lift from a canal watercourse is a few feet, that from a well may be 50 feet or more.
Most persons consider that a system of charging for water by volume would be a very great advance on present methods. It has been said that if the water were wasted it would be difficult for the cultivators to bring home the responsibility to any individual. This objection does not seem to have great force. Every individual would have a direct interest in economising the water, and any cultivator who was habitually careless would soon be detected by the others. ”

“ The discharge is, of course, increased, and it becomes dependent at all times on the working head. Another difficulty is that any rise or fall in the water-level of the distributary (and such rises and falls may occur owing to silting or scour, however carefully the discharge may be regulated) alters the discharge somewhat, though not to the same degree as in an ordinary outlet with a working head of, say, ·5 foot. In short, Kennedy’s gauge outlet, or “semi-module” as it is sometimes called, can modify but not do away with the variations of the discharges of outlets. ”