Irrigation works

by E. S. Bellasis

P₁ - PₐW = V² - v²2g.

This quantity (since v is small) is not much less than h₀ or V²2g. In other words, the water levels of two cisterns with an air-space between them differ only a little, or h₁ is small.

The above case (two cisterns and air-space) is mentioned in Hydraulics, Chap. V. The principle is simply that the velocity head at the air-space is reconverted into pressure head by passing the stream through a gradually diverging tube. In the absence of such a tube the velocity head would be wasted by causing eddies in the downstream cistern.

If the downstream cistern is a watercourse whose water-level is considerably lower than that of the upstream cistern or distributary, V is obviously unaffected. Also P₁ is obviously reduced. Therefore, by Bernouilli, v is increased, or the stream does not fill the expanded tube and there are eddies in the tube. The water-level in the watercourse may even be lower than the end of the tube. The discharge is unaffected.

In practice there are, of course, resistances, but this fact does not affect the general conclusions stated above. The minimum working head (difference between the two water-levels) which gives a constant discharge is greater than would be the case in the absence of resistances. This “minimum working head for modularity” has been found to be ·21 foot, ·42 foot, and ·61 foot, the corresponding values of the “depression,” h₀, being respectively 1 foot, 2 feet, and 3 feet. When the working head is less than the above, the discharge is less and it depends on the working head. The depression should, according to Kennedy, be about 1·75 feet, but it may be more.

The chief difficulty in using the gauge outlet as a module is that the air vent can be stopped up. This converts the apparatus into a compound diverging tube (Hydraulics, Chap. III., Art. 17). 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.

---

INDEX.

• Absorption, [16], [159].
• Alignment, principles of, [4].
• Alignment, centrality in, [5].
• Alteration in line, [59].
• Assiut Barrage, [11].
• Assouan Dam, [11].
• Banks, construction of, [138].
• — protection of, [139], [175], [178].
• — width and height of, [56].
• Banks and Roads, [53].
• Basin Irrigation, [11].
• Berms, [53].
• Bifurcations, [47].
• Bifurcation, head needed at, [45].
• Borrow pits, [55].
• Branches of Canals, [3].
• Breaches in Banks, [176].
• Bricks used for canal work in India, [88].
• Bridges, [8], [80], [87], [130].
• — Skew, [29], [42].
• Bushing of banks, [178].
• Canal and branches, [20], [47].
• Canal, bed width of, [51].
• — supplied from reservoirs, [3], [13].
• — inundation, [1], [45], [79], [127], [156].
• — perennial, [1].
• Capillarity, [16].
• Cattle Gháts, [81], [173].
• Cement for lining channels, [160].
• Chainage, [93], [118].
• Channels, alterations in, [97].
• — enlargement of, [97], [139].
• — gradients of, [50].
• — side slopes of, [52].
• Colonization Schemes, [64].
• Command, [2].
• Commanded area, [4].
• Contour lines, [37].
• — plan, [26], [36], [63].
• — survey, [37].
• Crops, failure of, [103], [142].
• — kinds of, [101].
• Culturable commanded area, [26], [113].
• Curves and bends in channels, [8], [139].
• “Delta,” 22, [110].
• Deputy Collector, [96].
• Designs and Estimates, [60].
• Design of canals, [2], [26], [30], [47], [147], [156].
• Discharge of canal during rabi, [52], [118].
• Discharge observations, [107].
• Discharges of Punjab rivers, [145], [157].
• Discharge tables, [106].
• — through an outlet, [61].
• Distance marks, [93].
• Distribution of water, [14], [118], [125].
• Distributaries, [3], [20], [44], [46].
• — best system of, [71].
• Distributary, bed width of, [68].
• — design of, [60].
• — height and width of banks, [68].
• — kharif, [156].
• — longitudinal section of, [69].
• — major and minor, [41].
• — off-take of, [51].
• — remodelling of, [128].
• — side slopes of, [69].
• — strip of land for, [69].
• — with three fourths full supply, [45], [68], [166].
• Divide Walls, [33], [169].
• Divisions, canal, [96].
• Drainage, [10].
• Drainage Crossings, [8], [156].
• Duty of water, [21], [25], [39], [148], [153], [154].
• Duty, improvement of, [24], [102], [158].
• Eastern Jumna Canal, [31].
• Efflorescence called “Reh,” [15].
• Egypt, irrigation in, [11].
• Embankments, [9], [33], [156].
• Escapes, [9], [100], [180].
• Estimates for work, [59].
• Evaporation, [16].
• Executive Engineer, [96].
• Extensions of canals, [127].
• Extra land, [58].
• Falling Shutters, [32].
• Falls, [8], [81], [87].
• — incomplete, [87], [130].
• — notch, [86].
• Field book, [101].
• — map, [101].
• — register, [101].
• Final line, [59].
• Flow and lift, [11].
• Full supply duty, [64].
• Full supply factor, [64].
• Ganges Canal, [31].
• Gauges, [10], [103], [104], [183].
• Gauge reader, [96], [98], [105], [184].
• Gauge reading, [105], [121].
• — register, [105], [106], [108], [111].
• Gibb’s module, [164], [186].
• Guide banks, [35].
• Head for distributary, [82], [83].
• Headworks, [2], [30], [98], [99], [137].
• Indents for water, [98], [108], [110].
• Inundation canals, [1], [45], [79], [127], [156].
• Irrigation boundaries, [33], [129].
• — in various countries, [1].
• — registers, [113].
• — unauthorised, [101].
• Kennedy’s gauge outlet, [168], [193].
• — Rules for channel design, [48].
• Kharif or Summer Crop, [23].
• Kutter’s co-efficients, [51].
• Lift irrigation, [11], [142].
• Lime for making channels watertight, [162].
• Longitudinal section, [69], [130].
• Losses of water in channels, [16], [38], [159].
• Low supplies, [118], [123].
• Lower Chenab Canal, [25], [144].
• Lower Egypt, [11].
• Lower Jhelum Canal, [144].
• Maintenance work, [138], [171], [174].
• Marginal Embankments, [9].
• Masonry works, [29], [80], [89].
• — — large scale site plan, [89].
• — — type designs, [89].
• Mills, [8].
• Minors, question of desirability of, [75].
• Modules, [162], [186].
• Navigation, [12].
• Needles and horizontal planks, [85].
• Oil for lining channels, [160].
• Older Indian canals, [10], [68], [98].
• Outlet, discharge of, [61].
• — registers, [113].
• Outlets, [15], [61], [66], [67].
• — applications regarding, [140].
• — design of, [76].
• — on inundation canals, [79].
• — on older canals, [68].
• — positions of, [65].
• — remodelling of, [131].
• — register of, [113].
• — size of, [114], [134].
• — temporary, [78].
• — variability of duty on, [66].
• Parapets, width between, [77].
• Patwari, [96], [101].
• Percolation, [16].
• Perennial Canals, [1].
• Pitching, [90].
• Plan, large scale, [59].
• Postal system, [97].
• Profile walls, [91], [94].
• Project, sketch of, [26].
• Proportion of land to be irrigated, [27], [156].
• Puddle for lining channels, [160].
• Punjab, projects for canals in, [144].
• Punjab rivers, [145], [147].
• Quarters for regulating staff, [88].
• Rabi or winter crop, [23].
• Railings, [88].
• Rain, [9], [22], [100].
• Ramps, [88].
• Ratio of bed width to depth, [50].
• Reduction in size of channel, [128].
• Registers, irrigation, [113].
• Regulation of supply, [103], [121], [127].
• Regulators, [7], [80], [84], [184].
• — permissible heading up, [85].
• Remodellings of channels, [127].
• — of outlets and watercourses, [131], [134].
• Rest Houses, [95].
• Reservoirs, [13].
• Rules for designing canals, Kennedy’s, [48].
• Scheme, cost of, [28], [59].
• Sides, falling in of, [139].
• Sidhnai canal minors, [41].
• Silt, clearance of, [97], [138], [139].
• — deposit, [15], [97].
• — trapping at Headworks, [47].
• Silting and scouring, [15], [48], [98], [139].
• Sirhind Canal, [19], [144].
• — — silting in the head reach of, [98].
• Soil, water-logging of, [10], [24], [102].
• Spoil Banks, [52], [57].
• Subdivisions, canal, [95].
• Subdivisional officer, [96].
• Suboverseer, [96].
• Superintending Engineer, [96].
• Supply carried, [100].
• — distribution of, [14], [118].
• — mean and full, [27], [46], [122].
• — regulation of, [103], [104], [106], [127].
• Syphons, [7], [71], [87], [181].
• Tailing of one channel into another, [40].
• Telegraph, line of, [97].
• Training of rivers, [33].
• Trial lines, [58].
• Trial pits, [58].
• Triple canal project, [144].
• Tunnels, [13].
• Turns, or rotational periods of flow, [14], [118].
• Type cross sections, [56].
• Under-sluices, [32].
• Upper Bari Doab Canal, [19], [144].
• — Chenab Canal, [33], [144].
• — Egypt, [11].
• Upper Jhelum Canal, [50], [144].
• Velocity, [12], [50].
• Village lands, [62].
• Watching banks, [175].
• Water, payment for, [12], [100], [102], [142], [143].
• Water level, fluctuation in, [100], [124].
• Watercourse, limit of size of, [74].
• Watercourses, [4], [20], [65].
• — applications regarding, [140].
• — for trees, [58].
• — remodelling of, [131].
• — with poor command, [67], [133], [166].
• Waterings, [11], [24].
• Water-logging of the soil, [10], [24], [102].
• Wave, travel of, down a channel, [124].
• Western America, canals in, [12].
• — Jumna Canal, [31], [39].
• Wing Walls, [89].
• Works, arrangement of, [89].
• — two or more close together, [89].
• — urgent repairs of, [137].
• Zilladar, [96].

Harvey & Healing, Printers, Manchester Street, Cheltenham.