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Irrigation water management


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Irrigation water management

  2. 2. IRRIGATION WATER MANAGEMENT November 14, 2012 CHAPTER 4 WATERLOGGING, DRAINAGE, CANAL MANAGEMENT & WUO 4.1 WATER LOGGING 4.1.1 Causes of water logging 1. Over irrigation The main cause of waterlogging is over-irrigation of the land The excess water applied to the land percolates deep into the ground and joins the water table. As the ground water storage is augmented, the water table rises. As soon as the water table comes close to the land surface, waterlogging occurs. 2. Inadequate surface drainage Waterlogging usually occurs when there is inadequate surface drainage of the irrigated land. Heavy precipitation combined with inadequate surface drainage causes flooding of the land. The prolonged flooding (or inundation) results in heavy percolation of water into the ground, which causes a rise of the water table and hence waterlogging. 3. Obstruction of natural surface drainage If a natural drainage (stream) near the irrigated land is obstructed by constructing an embankment for a road, a canal, a railway, etc., the flooding of the area may occur leading to waterlogging. 4. Obliteration of a natural drainage If an existing natural drainage is obliterated (or destroyed), it results in stoppage of natural flow and consequent flooding and waterlogging. Sometimes cultivators, while ploughing, obliterate the drainage. 5. Obstruction of natural subsurface drainage If there is an impermeable stratum below the land surface at a relatively low depth, it prevents the natural downwards movement of water into the subsoil. It may result in the formation of a high perched water table which may be the cause of waterlogging. Sometimes the foundations of structures, such as causeways, obstruct the movement of water into the subsoil and may cause waterlogging. 6. Impervious top layer If the top layer of the land is impervious such as black-cotton soil, it obstructs the flow of water in the downward direction. Such land is prone to waterlogging due to over irrigaion and flooding. 7. Seepage from canals Water seeps from the bed and sides of an unlined canal It adds to the ground water reservoir and there is a general rise in the water table, which may lead to waterlogging. For example, in the case of the Ganga canal, the water table rose from a depth of 12-2 in to about 4-6 m below ground level in 100 years of irrigaion. 8. Construction of a reservoir IRRIGATION WATER MANAGEMENT Page 2
  3. 3. IRRIGATION WATER MANAGEMENT November 14, 2012 If a large reservoir is constructed in the region, there is an increase in the water level on the upstream of the dam. Consequently, there is an increase in the inflow to the ground water storage and a decrease in the outflow from the ground water as base flow of the river. The adjoining area may get waterlogged. 9. Defective methods of cultivation If the defective methods of cultivation are used, there may be ponding up of water on the land surface which may cause waterlogging. The defective methods of cultivation include construction of high levees (bunds) which obstruct the natural drainage, inadequate preparation of land, failure to smoothen the field after tillage, improper disposal of spoil earth, improper selection of crops and growing crops which require excessive watering. 10. Defective irrigation practice Waterlogging may also occur due to defective irrigaion practice, such as adoping high intensity of irrigation, applying high depth of water and using defective method of application of water like wild flooding. 4.1.2 ILL EFFECTS OF WATERLOGGING Waterlogging of land causes a number of ill effects. Some of the main ill effects are given below 1. Reduction in growth of plants Because of waterlogging, there is absence of aeration in the roots of the plants due to which the plant growth is decreased. 2. Difficulty in cultivation As the land becomes waterlogged, the soil becomes slushy and puddled, and the cultivation becomes difficult. 3. Increase in salinity Waterlogging generally causes an increase in salinity of the soil. Salts of the soil move upward along with the water from the water table. As the water gets evaporated from the land surface, there is an accumulation of salts and the fertility of the soil is decreased. 4. Growth of weeds Due to the availability of excessive water at the land surface, there is grow the of water weeds. This results in a decreases of the crop yield. 5. Increase in natural plants and fora 6. Due to the availability of excess water at the land surface, there is an increase in natural plants and flora . The plants such as cat tail, reeds, bull rush, grass, etc grow in the marshy, waterlogged land and there is a reduction in the crop yield. 7. Increase in plant diseases Because of waterlogging, various diseases occur in the plants, which decrease their growth. 8. Fall in soil temperature There is a fall in soil temperature when the soil becomes waterlogged. Due to lower temperature, there may be a decrease in action of soil bacteria and the growth of plants may decrease. 9. Increase in incidence of malaria IRRIGATION WATER MANAGEMENT Page 3
  4. 4. IRRIGATION WATER MANAGEMENT November 14, 2012 The waterlogged land becomes a breeding place for mosquitoes which may cause malaria. Moreover, the climate becomes damp which may affect the health of community 4.1.3 MEASURES FOR PREVENTION OF WATERLOGGING The following measures are usually adopted for prevention of waterlogging or relieving the area, which are waterlogged. In general, all these measures aim at eliminating the causes of waterlogging discussed in the preceding section. 1. Controlling the intensity of irrigation In regions where there is a possibility of waterlogging, the annual intensity of irrigation should be kept low. In general, the average annual intensity of irrigation should not be more than 40 to 60%, i.e. the total irrigated area in a year should no be more than 40 to 60% of the culturable commanded area (CCA). 2. Providing a drainage system Waterlogging can be prevented by providing a properly designed drainage system, as discussed in the next section. 3. Lining of canals The seepage of water from the canals can be considerably reduced by lining of canals. Consequently, the water table does not rise and the waterlogging is prevented. 4. Lowering of the FSL of the canals The seepage of water from an unlined canal can be reduced to some extent by lowering the F.S.L. of the canal. The canal should be designed such that its F.S.L. is as low as possible, consistent with the requirements of flow irrigation for the commanded area. A low F.S.L. results in a small difference of water levels in the canal and in the field. Consequently, the percolation losses are decreased. Moreover, the head at the outlet is decreased which reduces the outlet discharge and prevents wasteful use of water. 5. Improving the natural drainage of the area The natural drainages such as streams and rivers should be improved. It involves removing obstructions to the flow such as weeds, bushes and other vegetations from the stream section. Straightening of the streams and canalising them into shallow wide reaches improves the natural drainage. Increasing the bed slopes of the streams also improves the drainage. The chances of waterlogging are considerably reduced if the natural drainage of the area is good. 6. Providing intercepting drains The water seeping from the unlined canal can be intercepted by providing intercepting drains parallel to the canal. This is especially useful when the canal has high embankments and the water table is already high. 7. Adopting well irrigation or conjunctive use of water If the well irrigation is adopted in the area, the water table goes down and the chances of waterlogging of the land are considerably reduced. In fact! a judicious IRRIGATION WATER MANAGEMENT Page 4
  5. 5. IRRIGATION WATER MANAGEMENT November 14, 2012 combination of the canal irrigation and the well irrigation in the same region, known as conjunctive use of water, is an ideal solution of the waterlogging problems 8. Changing the crop pattern In regions susceptible to waterlogging, the crop pattern should be changed. The crop requiring heavy irrigation should be avoided and those requiring light irrigation should be encouraged. 9. Prevention of seepage from reservoir The seepage from small reservoirs can be reduced by lining the surface of the reservoirs. For large reservoirs suitably designed toe filters should be provided so that the seepage from the reservoirs is discharged into the natural streams. 10. Changing the assessment method If the water supplied to the cultivators is assessed on area basis, the cultivators have a tendency to use excessive water which causes waterlogging. By adopting the volumetric assessment of water, the excess use of water is controlled and the chances of waterlogging are reduced. 11. Adopting better methods of application of water By adopting efficient methods of application of water, such as sprinkler irrigation and drip irrigation, waterlogging can be prevented. 12. Educating the cultivators The cultivators should be apprised of ill effects of waterlogging. They should be trained to use water economically and avoid wasteful use of water. They should be told that waterlogging of the land is their personal loss, besides being a national loss. Because of waterlogging, the crop yield is reduced and there is a long-range damage to the land. 4.2 DRAINAGE SYSTEMS  A properly-designed drainage system is quite effective for prevention of waterlogging. It is also an effective method for reclamation of the waterlogged land. A well-designed drainage system is required in the regions where the water table is high and the irrigation facility is extended, such as delta regions.  It is desirable that drainage is considered as an integral part of an irrigation scheme, as is the practice in some advanced countries. In India, various drainage programmes have been undertaken to relieve the already waterlogged land. Moreover, in some of the new irrigation projects, a well-designed drainage system has also been included in the projects.  The design of a drainage system depends upon a number of factors. Before undertaking the design of a drainage programme, it is necessary to conduct topographical, geological and soil surveys. The properties of the soil, especially the permeability, should be determined. The depth of water table below the land surface should be ascertained. Moreover, the fluctuations of the water table during the year should also be studied. The quality of ground water should be determined. The salts in the soil and water should be ascertained. IRRIGATION WATER MANAGEMENT Page 5
  6. 6. IRRIGATION WATER MANAGEMENT November 14, 2012 4.2.1 Types of drainage systems The drainage systems can be broadly classified into two types. 1. Surface drainage systems(Open drains) 2. Subsurface drainage systems.(closed drain or tile drain) The subsurface drainage system consists of sub-surface drains to dispose of the subsurface water. The subsurface drainage is an effective method for the prevention of watering and for reclamation of already waterlogged land. Most of the discussions in this chapter is limited to the subsurface drainage. Open drains are constructed below the ground surface. These drains are open at the top. Open drains may be further classified into the following types: 1. Shallow open drain. 2. Deep open drains 1. Shallow open drains – The depth of shallow open drains below the land surface is relatively small. These drains are used to drain away excess irrigation water supplied to the agricultural field. These drains may also be designed to dispose of surface water due to rains. These drains are useful for reducing the percolation of water to the ground water reservoir below the water table. Because of quick drainage, the ponding up of surface water is reduced and thus waterlogging is prevented. Shallow open drains are, however, not much effective for the drainage of subsoil. Hence, these are not much useful for relieving the waterlogged land. 2. Deep open drains Deep open drains also have their tops open like shallow open drains, but they are relatively deeper. These drains are quite effective for draining out the subsoil and hence are useful for preventing waterlogging as well as for relieving the waterlogged land. These drains are commonly used as outlet drains for a closed drainage system discussed later. The type of drain most suitable for a particular site will depend upon the purpose for which the drainage system is required. A combination of various types of open drains and closed drains is often necessary for an efficient drainage system As a drainage system is quite expensive, the economic analysis should be done. A drainage system which gives the optimum degree of relief for a given investment should be selected. 4.2.1 DESIGN AND MAINTENANCE OF OPEN DRAINS Open drains should be properly designed so that they are quite effective. The following are the main design considerations. 1. Layout. As far as possible, open drains should be located so as to follow the path of the natural drainage of the area. All the open drains should discharge into an outfall drain which is either a large open drain or a natural stream. The location of the outfall drain can be adjusted to give the required bed slope to the open drains. 2. Discharge capacity Open drains should be designed to carry storm runoff, seepage water from subsoil and surface flow due to excess irrigation water applied to the land. As the storm runoff is very large, open drains are usually designed only for the storm runoff. The IRRIGATION WATER MANAGEMENT Page 6
  7. 7. IRRIGATION WATER MANAGEMENT November 14, 2012 drains so designed will automatically take care of the discharge due to other causes. It is not necessary that the open drains should be designed for the maximum discharge due to exceptionally intense storm because it will be highly uneconomical. These drains are designed for a somewhat smaller surface runoff. A judicious estimate of the surface runoff should be made to obtain the discharge capacity of the drains. The design discharge is usually determined from the Boston Society formula, where Q is the discharge (cumecs), A is the catchment area (km2), and C is the discharge coefficient which depends upon the type of terrain and the average yearly rainfall. Its value varies from 0-80 for an average yearly rainfall of less than 25 cm to about 80 0 for an average rainfall of more than 76 cm in the hilly regions. An average value of about 8-0 is usually taken. The drainage systems are usually designed for a discharge of 0.11 cumecs/km2 to 0.44 cumecs/km2 3. Velocity of flow. The velocity of flow in an unlined channel should be such that neither scouring nor silting. However allowable soil velocity depend upon type of soil. Alternatively, the Manning formula can be used to determine the velocity, after assuming a suitable value of the rugosity coefficient (N). Thus The value of N depends upon the type of soil and the hydraulic radius of the channel. A value of 0.025 to 0.045 is usually assumed-, smaller values are for greater hydraulic radius and vice versa. The velocity of flow can also be obtained from Elliot's formula, where A is the cross-sectional area (m2), P is the wetted perimeter(m)and h is the bed fall in cm per km 4. Section of drains Open drains are usually of the trapezoidal section. These are designed using the principles of unlined irrigation channels. The bed width and depth for the design discharge are usually determined by Lacey's formula. The drain bed should be taken below the subsoil water table so that the drain carries the seepage discharge during and after the rains. As an approximation, the bed width may be taken equal to 0-8 times the Lacey wetted perimeter. The depth is fixed after considering the economy of digging below the subsoil water table. Moreover, it should be adequate to carry the normal flood discharge below the natural surface level. The following relation between the bed width (5) and the depth (D) is commonly used. where 0 is the side slope angle with the horizontal The side slopes are usually 1:1, 1 5:1, 2:1 and 3:1 for clay, silty loam, sandy loam and sandy soils, respectively. IRRIGATION WATER MANAGEMENT Page 7
  8. 8. IRRIGATION WATER MANAGEMENT November 14, 2012 Depending upon the type of soil, the bed width usually varies from 0-3 to 1-2 m and the depth from 0-6 to 1-5 m. 5. Provision of a cunnette As a deep open drain is usually designed for the storm runoff, the discharge is quite small when it is carrying only the seepage discharge, A cunnette (i.e. a small subdrain in the bed of the main drain) is provided to carry the seepage discharge when there is no storm runoff (Fig. 311). If the cunnette is not provided, the seepage discharge flows with a small depth over the entire width of the open drain with a small velocity. It leads to silting and the weed growth. With the provision of the cunnette, the seepage water flows only through the cunnette at a relatively high velocity. The weed growth is considerably reduced. Moreover, for maintenance the aquatic weeds are to be removed only from the cunnette section and not the entire section. The cunnette is provided in the centre of the main open drain. With this arrangement, the full section of the main drain carries the discharge only during and after the storm. For the rest of the period, the water flows only in the cunnette. 6. Free board A liberal free board should be provided above the maximum water level (or F.S.L.) of the drain. 7. Banks Suitable banks are provided if necessary on either side of the open drain. The borrow pits, if required, are kept inside the drain section. Roads, 3 to 6 m wide, are usually provided on both sides of the drains with a discharge greater than 5-7 cumecs and on one side for smaller discharge. No continuous bank is generally provided in the outfall reach of the open drains where the spilling over the drain is small and not expected to submerge a large area or where the spilled water comes back to the outfall drain. In other cases, a continuous bank is constructed on the side of the drain on which heavy spilling is likely to occur. In cases where the heavy spilling is likely to occur on both sides of the drain, continuous banks are provided on both sides. Where continuous banks are provided, the waterway provided between the banks should be sufficient to carry the peak flood discharge. Maintenance of open drains Because for most of the time, open drains carry a low discharge due to silt-free seepage, there is a profuse weed growth in the section. If a cunnette is provided, the weed growth IRRIGATION WATER MANAGEMENT Page 8
  9. 9. IRRIGATION WATER MANAGEMENT November 14, 2012 usually occurs only in the cunnette section. The main maintenance problem is to keep the drains free from weeds. In India, the weed is usually manually cleared. However, some implements are also available which can be used to remove weeds from the drains. The maintenance of open drains usually consists of the following operations. 1. Removal of weeds, manually or by machinery. 2. Flattening of side slopes of the drains to prevent sloughing of sides. 3. General silt removal from the bed and sides. 4. Removal of bushes and grass from the inside slopes. 5. Maintenance of roads provided on the banks. 6. Filling the depressions and cuts formed by rain water. 7. Protecting the banks by rip rap and by flattening the side slopes to prevent caving-in of slopes. 8. Repair of culverts, if any, and painting of the distance marks. Disadvantages of open drains Open drains have the following disadvantages. 1. Some of the valuable agricultural land is wasted for the construction of open drains. 2. Open drains obstruct the normal farming operations. 3. For communication across wide drains, culverts are required, which increase the cost. IRRIGATION WATER MANAGEMENT Page 9
  11. 11. IRRIGATION WATER MANAGEMENT November 14, 2012 4.3 CLOSED DRAINS Closed (or subsurface) drains are provided below the ground surface at a depth of 1 to 1.50 m. Closed drains are usually in the form of tile drains (porous earthen ware) or pipe drains. The spacing and slope of the drains depend upon the type of soil, climate and the topography of the area. The tiles butt against each other with open joints. These drains are covered up with earth. They do not obstruct the normal farming operations. Moreover, they do not put any area out of cultivation. Discharge Closed drains are designed to carry only the seepage discharge, which depends upon the rate of infiltration. Although the rate of infiltration can be theoretically evaluated if the soil permeability profile is known, the process is tedius. In practice, closed drains are designed for the discharge determined by empirical formulae. Alternatively, these can be designed on the basis of experience gained from the existing drains under similar conditions. Diameter and spacing The diameter of the tile drains usually varies from 10 to 30 cm. The spacing of the tile drains depends upon the permeability of soil and the depth and diameter of the drains. The spacing varies between 15 and 45 m. The closer spacing is for soils of low permeability. The more is the depth of drains, the more is the drainage area and the smaller is the spacing of drains. Similarly, the greater the diameter of the drains, the closer is the spacing. Depth The depth of drains depends upon outfall conditions, cost of the drainage scheme, crop requirements, salt content of the soil and various other factors. However, the depth should not be less than 1 m below the ground surface so that the drains are not damaged due to vehicular traffic and the farming equipment plying over the ground. [Note. The depth is measured from the ground surface to the bottom of drain ] Slope The drains are usually laid at a slope not steeper than 1 in 500. Filter cover To ensure effective drainage, the drains should be placed in a pervious material [Fig. 31-2 (a)]. If the drain has to be placed in an impervious soil, it should be surrounded by a properly designed filter [Fig. 31-2 (b)]. It usually consist of coarse sand and bajri (river sand). However, other materials such as gravel, corn cobes, safflower, straw, etc. have also been used as the filter. IRRIGATION WATER MANAGEMENT Page 11
  12. 12. IRRIGATION WATER MANAGEMENT November 14, 2012 The U.S.B.R. recommends the following criteria for the design of filter. (a) Uniform material, (b) Graded material, IRRIGATION WATER MANAGEMENT Page 12
  14. 14. IRRIGATION WATER MANAGEMENT November 14, 2012 4.4 LAYOUT PLANS OF A TILE DRAINAGE SYSTEM A tile drainage system (closed-drain system) usually consists of a number of lateral drains (also called laterals or branch drains) which collect water from the area being drained. These lateral drains discharge the collected water into the main drains (also called the mains). Sometimes, the laterals discharge into a sub-main drain, which is usually a closed drain. The submain drain then discharges into the main drain, which is usually an open drain. The main drain discharges into an outfall drain, which takes the water to a natural stream or a river. The layout of a tile-drainage system depends upon the topography of the area being drained. The layout is so planned that it effectively drains all the area. The following factors should be considered while selecting the layout of a closed-drain system. 1. Mains should be aligned along natural drainage lines as far as possible. 2. Mains, being quite expensive, should be as short as possible. On the other hand, the laterals should be as long as possible. 3. Mains and laterals should be straight as far as possible. 4. The laterals should be parallel and equally spaced to ensure uniform drainage and lowering of the water table, and the maximum coverage of the drainage area. 5. The selected system and layout should ensure satisfactory and equitable drainage of the affected area. 6. The outlets of the drains should be as few in number as possible. 7. The laterals should be laid across the natural slope as far as possible 4.4.1 Various Layout plans The following layout plans are commonly used for a closed drain system. 1. Natural system 2. Grid iron layout 3. Herringbone system 4. Double main system 5. Intercepting drain system 6. Grouping system 7. Random system 1. Natural system In the natural system, the mains and laterals are provided along the natural drainage lines [Fig. 31-7 (a)]. This system is preferred in rolling topography. 2. Grid iron layout In the grid iron system, laterals are provided only on one side of the main [Fig. 31-7 (b)]. This system is used when the land is practically level or when the land slopes away from the main 3. Herringbone system In the Herringbone system, the laterals join the main from each side alternatively [Fig. 317 (c)] This system is used when the main is located in a depression. In this system, the land along the main is double-drained This is, however, necessary because the system is located in a depression and it receives more drainage than that from the land on the adjacent slopes 4. Double main system In this system, there are two separate mains. Both these mains have their separate laterals [Fig. 31-7 (d)]. This system is provided where the depression is very wide. This system helps reduce the length of laterals It also eliminates the break in the slope of laterals at the edge of the depression 5. Intercepting drain system In an intercepting drain system, there are no laterals. Only a main is provided at the toe of a slope to intercept the entire drainage [Fig. 31-7 (e)]. This arrangement is used for hilly land IRRIGATION WATER MANAGEMENT Page 14
  15. 15. IRRIGATION WATER MANAGEMENT November 14, 2012 6. Grouping system In a grouping system, there are a number of small drainage systems which are grouped. Water is collected from the small drainage system and discharged into a natural drain or stream [Fig. 31-7 (f)]. This system is used where the topography and wetness vary considerably over the field. 7. Random system (Zig zag system) In the random system, the laterals are laid at random to drain the wet area. The main is located at the natural drainage line. The individual wet areas are connected to mains through laterals (and submains, if necessary ). 4.5 canal irrigation management Water resource projects cover a wide range of activities. Water is a scarce resource, especially in arid and semi-arid countries and is essential for all forms of life. It is essential that the efficiency in the use of water must be maximized. Maximization of water use efficiency requires careful planning and good project management. The paramount objective in the efficient management of an irrigation system is to ensure that water is distributed in adequate quantities and at proper time throughout the command area to IRRIGATION WATER MANAGEMENT Page 15
  16. 16. IRRIGATION WATER MANAGEMENT November 14, 2012 meet the requirements Of the crops grown. Proper regulation of the canals and the distribution of the required quantity of water are essential to obtain efficient use of irrigation water. The water from the reservoir/barrage/weir is released to the main canal through the head regulator. The main canal feeds two or more branches, which operate by rotation and may or may not run full, depending on the discharge available. Main canals run continuously throughout the irrigation season. Branch canals supply water to a large number of distributories which must run at full supply level by rotation. Distributories supply water to .water courses from which it is let into thecrop fields. 4.5.1 regulation of canals. The process of distribution of irrigation water in a canal system is called 'regulation’ or 'rostering'. 'Regulation' is specially required in canal systems where: (i) the demand is only on a part of the system and water is to be conveyed to that part only, or (ii) the demand is on the entire system but the available supply is not enough to meet the full demand. For instance, irrigation canals in the Bhakhara Canal Circle run in rotation for a period of nine months in a year, while in the remaining three monsoonic months they run to their full discharge capacity. In the Bhakra Canal System, the channels in one group run for eight days and remain closed for 18 days when the water supply is directed to other groups of channels. The supply of the main canal is distributed to different 'branches' or 'distributories’ in accordance with the demand on different channels. The main aim of rotation of water distribution is to regulate and evenly distribute the water over the command area of the canal system. 4.5.1 operation and management of canal system operation 1. Discharge vs. volume control. Operation of irrigation systems is aimed to control discharge and volume. Discharge control is most common. Discharge control may be direct or, more commonly, indirect through control of water level. Some of the irrigation systems are designed and operated to control the volume of water in canal reaches. This technique requires the availability of storage. either on line storage capacity in the canal itself or in intermediate reservoirs or tanks to which the excess flow is released. Dynamic regulation is an example of volume control methodology applicable to irrigation canals without intermediate storage reservoirs. For systems with intermediate storage within the canal, the control may be composite, i.e., discharge control for the canal reaches and volume control for intermediate reservoirs with closed loop feedback linked to the supply. 1. Types of controls of water releases. Most gravity irrigation system are based on upstream control of water. All control are set according to the discharge to be released from the main intake structures. IRRIGATION WATER MANAGEMENT Page 16
  17. 17. IRRIGATION WATER MANAGEMENT November 14, 2012 The objective is to maintain the water level upstream of each cross regulator to control the back water profile in the upstream reach. The backwater profile determines the head at off takes in reach. 2. water control structures. Canal structures like gates/ outlets combine the adjustability of the structures and the level of automation in operations. Some systems are fully adjustable, i.e., every structure has movable parts that can be set according to demands. Other systems have no provision for any manipulation, such as the fixed proportional distribution devices, 3. manually operated gated structures. Manually operated systems have control regulators which are adjustable. Each structure has to be manipulated by irrigation staff when a change in the flow regime is scheduled or occurs. The difficulty in operating the systems is due to the numerous structures to be adjusted simultaneously when the flow regime is changing. 4. fixed systems. These systems, known as 'structured systems' have been largely developed in India, pakistan, and Nepal. Water delivery is organized around pulses of constant discharge with a varied frequency. Distribution is proportional and the structures are fixed permanently at the construction stage. The non-adjustable structures are limited to minor canals. 5. automatic / semi-automatic systems. Hydraulically automated system are equipped with control of the structures that control water levels in canals over a wide range of discharges. Usually, the control of water level is achieved by mechanical movements of regulator gates, driven by hydraulic forces without an external source of energy or human intervention, variations of water level may still occur at locations remote from the control regulator, 6. water distribution pattern at field level in canal irrigation systems. Different methods of water distribution are followed in canal irrigation. The following are the essential requirements of a proper water distribution system:  Ensuring the supply of designed flows in the minor distribution channel at each outlet;  Developing proper distribution network of field channels up to each land holding in the command area of the outlet;  Working out irrigation schedules, allocating a time and day for the flow of water to each individual farmer. Different water distribution practices are being practised in India and other countries to ensure equity and to meet the crop demands. a. The warabandi or osrabandi is a system of delivery of water in rotation amongst the cultivators sharing water from a canal outlet.  Wara means turn and bandi means fixation. Warabandi means fixation of turns. In warabandi method, the available water is allocated to cultivators in proportion to their landholdings. Warabandi system has successfully held its IRRIGATION WATER MANAGEMENT Page 17
  18. 18. IRRIGATION WATER MANAGEMENT November 14, 2012 sway over the canal systems of the Indo-Gangetic plains and in Pakistan during the past several decades.  It has its main thrust on equitability of distribution of water (The basic principle underlying the warabandi system of managing irrigation water is that the available water, whatever be its quantum, is allocated to cultivators in equal proportion to their landholdings and not only to some of them to meet their total demand.  This principle imposes water scarcity conditions, which necessarily lead to the adoption of more efficient water management practices by the farmer. Socially, it stands for equitable distribution of water to the largest number of farmers in the command area of an outlet/distubutory.  In warabandi system the distribution of water is carried out by keeping the stream of water as constant and regulating the time of its flow. The entire time in a week is allocated to farmers. Time once lost cannot be regained. So, if for any reason, a farmer is unable to receive his share of water there is no way of compensating him.  Similarly, if the flow of water is less than the authorized quantity due to some technical defects, the loss suffered on this account cannot be compensated. It, therefore, becomes necessary that distributories and water courses must flow as programmed. Warabandi is considered to be a powerful tool for promoting better water utilisation. 5. Roster of turns.  In the rotation water supply (warabandi) system, a predetermined quantity of water is provided to each irrigator once a week. The duration of time the water supply is allowed per unit area of the irrigated land under the command of the outlet is determined by dividing the number of minutes in a week (10,080) by the area of land to be irrigated in hectares. Thus, in an outlet command area of 40 ha, the time allowed per ha to a farmer is 10,080 is 252 minutes or 4 hrs and 12 minutes in a week. A 2 ha farmer will get 8 hrs. and 24 minutes. The cycle of turns on a water course or its branch starts from its head, proceeds downwards and ends at its tail. The supply has to be cut-off from head when the last farmer is having his turn. The length of upper portion of water course which has been filled with common pool time (bharai) can be discharged only into the tail end fields and normally the total time spent on its filling is to be recovered from the tail end farmer. But the tail end farmer does not receive all this water at a constant rate. When the supply is cut-off from the head end, it starts depleting at tail and gradually approaches zero. Such a supply, beyond a limit is not efficient from the point of view of field application. The tail end former is to be compensated for it and this is done by allowing him a certain discount on the recovery of the filling time (bharai) time.  Thus, the lower reaches of a water course gains from the recession. However, in actual practice there is usually a discrimination in water supply in a water course. It is usually the tail end farmer who is usually deprived of water. The seapage loss in a watercourse is not reflected in the warabandi system. The utilisation of irrigation supplies is left entirely to the cultivator, who is under no obligation to grow any particular crop in the area. In Andhra Pradesh, a 7-day rotation is worked out by IRRIGATION WATER MANAGEMENT Page 18
  19. 19. IRRIGATION WATER MANAGEMENT November 14, 2012 which the farmer gets a weekly amount of water based on a maximum consumptive use calculation for an 'average' cropping pattern, a 65% overall irrigation efficiency, the irrigable area of his farm and the size of the rate of flow at the outlet (head end of the water course). 7. Shejpali and other systems of water distribution.  The Shejpali and block system of water distribution in the outlet command area of canal systems is practiced in Maharashtra, parts of Gujarat and Karnataka. Under this system, estimates of expected water availability are made. Applications are invited from the farmers seeking information on the crop to be grown and the area to be irrigated under each crop. Water is then sanctioned taking into account the total demand and the water availability. A schedule called shejpali, giving turns to different irrigators for the sanctioned crop area on outlets is prepared for each rotation of the canal system. In the block system, a long-term agreement for the supply of water for 6 to 12 years is done, especially in case of perennial crops. A system called rigid shejpali, in which definite dates and durations for the supply of water to a particular field area are recorded on the passes issued to the farmers for the sanctioned area has been introduced during the second half of the twentieth century. In the shejpali system, the farmers are supplied water, in turn, from tail to head, as per the schedule prepared and communicated in advance. The shejpali system gives consideration to the crops to be grown, contrary to the warabandi system. The canal outlets are equipped with gates to facilitate the operations.  In many of the irrigation projects of southern and north-eastern states, as well as many south and south-east Asian countries where paddy is the main crop, the irrigation flow below the canal outlet is allowed from one field to another through surface flooding. This system of water distribution is referred to as the 'localised system' of irrigation for paddy areas. However, the practice usually result in insufficient water distribution and fertilizer use efficiency.  It may be seen from the preceding discussion that the water delivery schedules presently followed require substantial improvements. They are not adequate to meet the specific requirements of the crops. Except for the warabandi system, they do not take into account the filling time and the gain resulting from recession flow in water courses. None of the methods give consideration to conveyance losses in the water distribution system. 4.6 night irrigation in canal system Most of the canal irrigation systems in South and southeast Asia and many other countries continue to flow throughout the day, and much of the night flows are inefficiently used or are wasted, unless effective procedures are adopted for their effective utilization, the importance of efficient utilization of night supplies of canal system has not received the right attention in many of the systems. Night irrigation usually requires extra labour and costs. It requires smaller stream flows and well graded fields. Paddy, tree crops and other widely spaced crops are more adaptable to night irrigation, as compared to other crops. IRRIGATION WATER MANAGEMENT Page 19
  20. 20. IRRIGATION WATER MANAGEMENT November 14, 2012 Inefficient water application, breaches in channels, and wasted water flowing into drains are common during the night, reuse of night drainage water lower down is sometimes possible. Substantial loss of water in the night has been reported by many workers. Loss of water during the night under the warabandi system of water distribution is negligible. Warabandi system does not distinguish between day and night. Farmers have accepted the system without complaints. Water is taken at night according to schedule and conflict is low. However, the major features favouring the adoption of the warabandi system are nearly level land, consolidated rectangular land holdings and water scarcity. But elsewhere, especially under undulating topography warabandi is rare and utilization of night, water supply is usually inefficient, Possible measures of combating the problems of managing canal flows during the night are (i) reducing irrigation at night—by regulating sluice releases or diversion of flows, providing intermediate storage in canal command areas, diversion of flows for travelling time, redistributing daytime water, and passing water to drains and escapes, and (ii) improving irrigation at night—by manageable stream flows, convenient field shaping and water application methods, choice of crops and distribution of flows in distinct zones. It is observed that: "It is difficult to estimate how much water is currently saved at night through intermediate storage in tanks or canals, diversion to 'travelling', or closure of head works, but it is probably quite a small proportion. A reasonable estimate may be that 40% of the canal irrigation water on medium and major systems is either applied in night irrigation or sent into drains at night ... Night irrigation is often inefficient. Supervision is difficult and minimal ... Night flows are often diverted to crops which tolerate flooding, mainly paddy, or are allowed to flow into drains." Factors affecting night irrigation Cl)Topography and size of holaing._ The smaller and more sloping the field is, the more difficult night irrigation becomes. Some large flat fields can be left to flood all night. An extreme case is the Gezire Scheme in Sudan, where impervious soils and flat land permit water to be left to spread unattended. Likewise, some large-scale irrigation schemes in western countries with very large fields could be left unattended at night, and changes made during the day. At the other extreme are the sloping fields with small basins which are difficult to irrigate during the night. (ii) soil type. The ease, difficulty and efficiency of irrigation at night also depend on the type of soil. Night irrigation is easier on soils which are not sticky, and which make stable bunds. Night irrigation is often difficult in black cotton soils. Hence, the warabandi, as followed in northwest India cannot be adopted as such in black soils. (iii)Size of irrigation stream. Handling stream flows is harder at night. The optimal night flow should normally be lower than the day supply, especially on difficult terrain. This requirement is often overlooked in irrigation planning and design. (iv) crop. The ease and efficiency of water application at night depend on the crop and its stage of growth, as well as the topography and the size of fields. The easiest crops are paddy and trees: paddy can be flooded. Over flows may not raise serious problems. Similarly, trees are IRRIGATION WATER MANAGEMENT Page 20
  21. 21. IRRIGATION WATER MANAGEMENT November 14, 2012 tolerant to standing water for some hours. Crops which are widely spaced or in early stages of growth are easier to irrigate at night than those which are tall, dense, or in their later stages of growth. 4.6 Jurisdiction of Surface and Groundwater  Jurisdiction on the use of water varies from country to country. In many countries both surface water and groundwater are by law the properties of the state, to be used for the welfare and development of the nation. Under the Indian statutory law, as interpreted and applied by the courts, all surface water is public property, whether it is natural flow of a stream or river or storage behind a dam or natural lake.  The responsibilities apportioned to the states and the centre (Union) by the Constitution fall in three categories, as listed in Schedule VII: The Union list (List I), the State List (List II) and Concurrent List (List III). Regulation and development of inter state rivers and river valleys fall under the Union Government to the extent that it is declared by the Parliament by Law in the public interest.  Water supplies, irrigation and canals, drainage and embankments, water storage and water power are essentially within the power of state. The states have the preeminent position in relation to water resources development and utilization in India. Thus, not withstanding the power granted to the Union Government in Entry 56, water is perceived as a 'State Subject' as per Entry 17 of the Constitution of India.  The legislation is substantially framed within the content of the state boundaries. As river basins often extend over many states, disputes arising in inter-state river basin utilization are decided through interstate agreements or tribunal awards. Under the Constituion of India, Article 262, deals with the adjudication of disputes relating to waters of inter-state rivers or river valleys and Entry 17 of List II and Entry 56 of List I of Seventh Schedule deals with items that fall within the purview of the state legislation and the parliament, respectively.  Article 262 states as follows: "Parliament may by law provide for the adjudication of any dispute or complaint with respect to the use, distribution or control of the water of, or in, any interstate river or river valley."  In case of groundwater, the legal and absolute rights rest with the owner of the overlying land. In many cases, this system has led to de facto rights to the land owner when he can construct a deep tubewell which will drain water from a much larger area of influence of groundwater than the land area belonging to the owner. This may deprive his neighbours from their fair share of water. Over-exploitation of groundwater leads to adverse effects.  The above situation on the rights of surface and groundwater brings to focus, in addition to development and environmental issues, the need for appropriate legislation to control water and provide for people's participation for efficient irrigation system management. IRRIGATION WATER MANAGEMENT Page 21
  22. 22. IRRIGATION WATER MANAGEMENT November 14, 2012 4.7 National Water Policy  India adopted a National Water Policy in 1987 for the planning and development of water resources to be governed by national perspectives. It emphasizes the need for river basin planning. Amongst the priorities in the allocation of water for various needs, drinking water is given the highest priority, followed by irrigation, hydropower, navigation, and industrial and other uses.  As water resources development is a State responsibility, all the states are required to develop their state water policies within the framework of the National Water Policy. Since the adoption of the policy in 1987, a number of new issues and challenges emerged in the development and management of water resources.  Therefore, in 2002 the National Water Policy (1987) was reviewed and updated. The revised National Water Policy (2002) has the following priorities in water allocation: (1) Drinking water, (2) Irrigation, (3) Hydro-power, (4) Ecology, (5) Industries, (6) Navigation and other uses.  However, it has been stipulated that the priorities could be modified or added if required by the area/region specific considerations (Ministry of Water Resources, 2002). The revised policy has stressed that in the planning, implementation and operation of a water resource project, the preservation of the quality of environment and ecological balance should be primary considerations.  An integrated and multi-disciplinary approach to the planning, formulation, clearance and implementation of projects, including catchment area treatment, command area development and the rehabilitation of the people adversely affected by the project are envisaged.  The drainage system should form the integral part of an irrigation project right from the planning stage. The involvement and participation of beneficiaries and other stakeholders should be encouraged from the project planning stage. Integrated coordinated development of surface and groundwater resources and their conjunctive use should be envisaged right from the project planning stage.  There should be periodical assessment of the groundwater potential and its quality. Exploitation of groundwater should be regulated to prevent its use to exceed the recharging capabilities of aquifers and ensure social equity. There should be a close integration of water use and land use policies.  Municipal and industrial effluents should be treated to acceptable levels and standards before discharging them into natural streams. Minimum flow should be ensured in the perennial streams for maintaining ecology and social considerations. Drought-prone areas should be made less vulnerable to drought-affected problems through soil moisture conservation measures and water harvesting procedures.  The water sharing and distribution amongst states should be guided by a national perspective with due regard to water resources availability and needs within the river basin/sub-basin. Water resources development will have to be planned for a hydrological unit. IRRIGATION WATER MANAGEMENT Page 22
  23. 23. IRRIGATION WATER MANAGEMENT November 14, 2012 4.8 PARTICIPATORY IRRIGATION MANAGEMENT FARMERS PARTICIPATION IN MANAGEMENT.  The traditional systems of irrigation the world over have had a built-in system of distribution of water among the beneficiaries, thereby linking utilization with the creation of irrigation potential.  In india the management of tanks and small scale river diversion schemes have involved the irrigators in the maintenance, distribution as well as in modalilities of conflict resolution. There was an unwritten convention among the farmers under a tank to use water on a weekly rotation.  One among the beneficiaries acted as the coordinator and leader for water distribution within the unit. Similarly, supply of water among fields on a particular day was decided by mutual agreement. The system on the whole, worked with minimal government intervention.  Against this background, major canal irrigation project planners of the 20th century did not concern themselves with developing a proper system of water sharing and infrastructure maintenance at the farm level.  The responsibility of the irrigation department is deemed to end at the point where water leaves the outlet. The planners and executors of irrigation projects have tended to focus largely on engineering aspects with little attention to socioeconomic dimensions and modern methods of water management.  There has been a general lack of constructive and functional relationship between irrigation officials and the farmers. Thus, the farmer who had the most important stake in the proper management of irrigation water as the ultimate beneficiary, had little role to play in the management of irrigation water under the prevailing system.  This realization lead the government to emphasis the need for the participation of farmers in the management of irrigation water during the Sixth.. Plan and its reiteration during the Seventh Plan. In 1987, the ministry of Water Resources, Govt, of India, issued guidelines to state governments to involve farmers' organizations to take over maintenance, management of water, allocation and collection of water charges and collection of water charges and to develop participatory mode of management on distinct segments of the irrigation system.  Participatory irrigation management refers to the involvement of irrigation users in part or all the aspects of irrigation management and at part or all levels. This implies initial planning and design, construction, supervision, financing, decisions, rules, operation, maintenance, monitoring and evaluation of the system.  'All Levels' refers to the full physical limits of the irrigation project, comprising of harnessing water at the headworks, conveyance, distribution, and application systems.  Even though the intent to create farmers' organizations has been expressed during the Sixth and Seventh Plans, the visible efforts to involve farmers in the form of Water Users' Associations(WUAs) in different states have been made in late 1980s and early 1990s to manage irrigation water from outlets, minors, and distributories of the canal systems. IRRIGATION WATER MANAGEMENT Page 23
  24. 24. IRRIGATION WATER MANAGEMENT November 14, 2012  Farmers have also been involved in the management of irrigation water from tanks, and deep tubewells. These organizations in different states are registered under State Cooperative Acts or Irrigation utilization and Command Area Development Acts and their variants. 4.9 water user organizations The water users' associations under the participatory irrigation management system are ;ed with the responsibilities  to improve the water delivery service through better operation and maintenance;  to achieve optimum utilisation of available water form canals, tanks, and tube wells;  to achieve equity in the distribution of water amongst water users;  to promote economy in water use and to increase water and land productivity;  to optimise the conjunctive use of precipitation and groundwater with the water delivered from the canal system;  to assist farmers in crop planning, and frequency and duration of water supply;  to inculcate a sense of ownership and responsibility amongst the farmers and to ensure collection of water changes;  to develop professional relationship between the water users and state irrigation agencies;  to generate local resources in cash, kind or labour for operation and maintenance; and  to assist farmers' association and its members in other spheres of activities (e.g., agro-industries and marketing) for their upliftment. Thus, the water users associations are charged with the responsibilities of integrated management of water, including conveyance, distribution and application to optimally utilise the water resources for enhancing crop production. 4.10 People's Participation in Managing Irrigation Systems in India/WUO. The first Water Users' Associations (WUAs) were established in the 1980s. About 4,400 WUAs had been formed by March 1997, managing an irrigated area of about 3,97,100 ha under major and medium irrigation tubewells), about 10,400 WUAs had been formed managing an irrigated area of about 50,000 ha.* The WUAs are formed and work on the basis of executive instructions/guidelines laid down by each state government. As of 1998, the only state which has passed legislation exclusively for farmer participation in the management of irrigation systems is Andhra Pradesh. In 1994, the Government of Andhra Pradesh promulgated Andhra Pradesh Irrigation and Command Area Development Act, 1984, which authorised the creation of Command Area Development Authorities and 'Pipe Committees'. The pipe committees, charged with the responsibilities of internal distribution of water below the outlet and maintenance of the water courses and field channels, were the first step in the direction of participatory irrigation management. However, there were problems due to the lack of coordination between the irrigation and IRRIGATION WATER MANAGEMENT Page 24
  25. 25. IRRIGATION WATER MANAGEMENT November 14, 2012 command area development authorities, and poor reliability of water supply at the outlet. In 1995, the(Govt. of Andhra Pradesh issued an order to promote Water Users' Associations (WUAs) for the management of irrigation systems at the minor level covering areas of 400 to 750 ha. The WUAs are to function as autonomous bodies on democratic lines and are responsible for the maintenance and operation of irrigation network within the area of their operation. To begin with, the WUAs were required to cover about 2,68,000 ha command area of Sriramsagar, and 65,000 ha command area of Srisailam Right Bank Canals. In Gujarat, in 1997, 33 WUAs at the minor level of canal projects were formed. The Mohini Coperative Distributory Society which was formed in 1979 in the command area of Bhestan minor of the Ukai Kakrapar Irrigation Project made spectacular success due to government backing, effective local leadership, and an income generating cropping system. The Government of Gujarat has taken a policy decision to distribute water on volumetric basis to water users farmers' associations at the level of the minors of Sardar Sarovar Irrigation Project. In Rajasthan, 3,483 'outlet committees' were formed in the command area of Indira Gandhi Nahar Pariyojana, each outlet commanding an area of 200-300 ha. The State of Madhya Pradesh has a provision for water panchayats in its Irrigation Act. Several WUAs have been formed in Karnataka by the Cooperative Department with the support of the Command Area Development Authority. The Government of Maharashtra, with the help of NGOs, organised farmers in the command area of two minors of major irrigation projects to evolve methodology and approach for involving in managing irrigation systems. The state of Tamil Nadu has a tradition of contributing voluntary labourers for digging and maintenance of water courses and field channels below the minor. In 1982, the Centre for water Resources, Anna University, Chennai initiated pilot projects on farmers' participation in rehabilitation and management of irrigation tanks. The farmers in the command area of each tank formed WUAs which were registered under the Tamil Nadu Society Registration Act, 1975. The Agricultural Engineering Department, responsible for the Command area Development Programme in Tamil Nadu, has initiated 2,770 Water Users' Farmers' Associations at the outlet level in Lower Bhavani, Kaveri, Vaigai, Parambikulam Aliyar and Sathanpur irrigation projects for distributing water, resolving conflicts and organising agricultural extensions activities for the benefit of farmers. In Uttar Pradesh, outlet committees have been constituted for the distribution of water in Sharada Canal Command. Till 1992, the Government of Uttar Pradesh had constructed 28,626 deep tubewells for irrigation. In 1992, the government started pilot projects by transferring the operation and management of about 100 tubewells for a period of five years to Tubewell Cooperative Societies comprising farmers of the tubewell commands. Government of West Bengal has implemented participatory irrigation management in the commands of low capacity and high capacity irrigation tubewe Involvement of farmers on different aspects and levels of water management varies in different st states of India. All the states envisage the retention of ownership of the main systems from headwork to the branch canal of the major and medium projects. In different states of India, Water Users' Associations are envisaged at outlet, minor and distributory levels. These associations have different responsibilities in respect to maintenance, operation and collection of water charges. The rules for water allocation and IRRIGATION WATER MANAGEMENT Page 25
  26. 26. IRRIGATION WATER MANAGEMENT November 14, 2012 distribution also differ form one state to the other. The performance of the programme of participatory irrigation management in India is yet to be evaluated. IRRIGATION WATER MANAGEMENT Page 26