Introduction chapter `1


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irrigation water management B.E. VIII AS PER gtu syllebus

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Introduction chapter `1

  1. 1. CHAPTER NO 1 INTRODUCTION 1.1 Water resources management issues related to irrigated agriculture  Competition among agriculture, industry and cities for limited water supplies is already constraining development efforts in many countries. As populations expand and economies grow, the competition for limited supplies will intensify and so will conflicts among water users.  Despite water shortages, misuse of water is widespread. Small communities and large cities, farmers and industries, developing countries and industrialized economies are all mismanaging water resources. Surface water quality is deteriorating in key basins from urban and industrial wastes.  Groundwater is polluted from surface sources and irreversibly damaged by the intrusion of salt water. Overexploited aquifers are losing their capacity to hold water and lands are subsiding. Cities are unable to provide adequate drinking-water and sanitation facilities. Waterlogging and salinization are diminishing the productivity of irrigated lands. Decreasing water flows are reducing hydroelectric power generation, pollution assimilation and fish and wildlife habitats.  At first glance, most of these water problems do not appear to be directly related to the agricultural sector. Yet, by far the largest demand for the world's water comes from agriculture. More than two-thirds of the water withdrawn from the earth's rivers, lakes and aquifers is used for irrigation. As competition, conflicts, shortages, waste, overuse and degradation of water resources grow; policy-makers look increasingly to agriculture as the system's safety valve.  Once established, irrigation projects become some of the most heavily subsidized economic activities in the world. Case-studies indicate that irrigation fees are, on average, less than 8 percent of the value of benefits derived from irrigation.  Despite these huge investments and subsidies, irrigation performance indicators are falling short of expectations for yield increases, area irrigated and technical efficiency in water use. As much as 60 percent of the water diverted or pumped for irrigation is wasted. Although some losses are inevitable, in too many cases this excess water seeps back
  2. 2. into the ground, causing waterlogging and salinity. As much as one- quarter of all irrigated land in developing countries suffers from varying degrees of salinization.5 Moreover, stagnant water and poor irrigation drainage escalate the incidence of water-related diseases, resulting in human suffering and increased health costs.  Today, agriculture is often unable to compete economically for scarce water. Cities and industries can afford to pay more for water and earn a higher economic rate of return from a unit of water than does agriculture. (For economists, water flows uphill to money.) g obliged to give up water for higher-value uses in cities and industries. In some areas are now asked to pay for the water they receive, including the full cost of water delivery. In other areas, new regulations require farmers to pay for polluting streams, lakes and aquifers.  The irony is that irrigated agriculture is expected to produce much more in the future while using less water than it uses today.  Irrigation can help make yield-increasing innovations a more attractive investment proposition but it does not guarantee crop yield increases. The overall performance of many irrigation projects has been disappointing because of poor scheme conception, inadequate construction and implementation or ineffective management. The mediocre performance of the irrigation sector is also contributing to many socio-economic and environmental problems, but these problems are neither inherent in the technology nor inevitable, as is sometimes argued.  Irrigation projects can contribute greatly to increased incomes and agricultural production compared with rain-fed agriculture. In addition, irrigation is more reliable and allows for a wider and more diversified choice of cropping patterns as well as the production of higher-value crops.  Policy-makers need to establish a structure of incentives, regulations, permits, restrictions and penalties that will help guide, influence and coordinate how people use water while encouraging innovations in water-saving technologies.  In the past, supply-side approaches dominated water resource management practices. Water itself was physically managed through technical and engineering means that captured, stored, delivered and treated water. However, the era of meeting growing demand by developing new supplies is ending.
  3. 3.  In our present-day water economy, resource management is shifting away from the goal of capturing more water towards that of designing demand- and user-focused approaches that influence behaviour. 1.2 Role of remote sensing and GIS in study of irrigated areas – 1.2 Land grading Land grading is reshaping the surface of land to planned grades for irrigation and subsequent drainage. Land grading permits uniform and efficient application of irrigation water without excessive erosion and at the same time provides for adequate surface drainage. A plane surface (uniform row and cross slopes) is easiest to manage and maintain. It is necessary for following purpose- • To make a suitable field surface to control flow of water • To check soil erosion and • To provide for surface drainage. • In low rainfall areas, land grading • Produces a smooth uniform land surface, • Reduces runoff and induces infiltration of rain fall • Assures even moisture distribution. • On sloping ground, levelling eliminates small depressions, cuts and furrows which leads to concentration of runoff. • Proper land grading, coupled with surface drainage measures, reclaim unproductive poorly drained areas. 1.2.1 Phases of Land levelling operations 1. Rough grading-Consist of removal of irregularities such as mounds,dunes and ridges, and filling of pits and gullies. Prior to making the land grading survey, it is advantageous to remove heavy vegetative growth from the land. Land clearing consists of
  4. 4. removing some or all of the trees, bush, vegetation, trash and boulders and all roots. 2. Land levelling:-Land levelling reshapes land surface to planned grade.Land leveling requires moving large quantity of earth over considerable distance .Leveling operation leaves an irregular surface due to dumping of loads 3. Land smoothing:- irregularities from the land leveling are removed and a plane surface obtained by land smoothing which is final operation in land leveling. In addition land smoothing is often done prior to seeding as a regular land preparation practice. 1.2.2 Land levelling design methods 1. Plane method 2. Profile method 3. Plan inspection method 4. Contour adjustment method 1. Plane method Procedure: 1. Determine the centroid of the field 2. Determine the average elevation of the field 3. Compute the slope of the plane of best fit 4. Compute the formation levels, cuts and fills 5. Determine the cut-fill ratio Above steps are broadly explained as below 1. Determining the centroid of the field The centroid of a rectangular field is located at the point of intersection of its diagonals. The centroid of a triangular field is located at the intersection of the lines drawn from its corners to the midpoints of the opposite sides. To determine the centroid of irregular fields, the area is divided into rectangles and right-angled triangles. The centroid is located by computing moments about two reference lines at right angles o each other.
  5. 5. 2. Determine the average elevation of the field Adding the elevations of all grid points in the field and dividing the sum by the number of point give the average elevation.
  6. 6. 3. Compute the slope of the plane of best fit. The slope of any line in the x or y direction on the plane which fits the natural ground surface, can be determined by the least squares method. in which S=slope of line in a p1ane, dimensionless* D= distance from the reference line, m H= elevation of the grid point, m n = number of grid points 4. Compute the formation levels, cuts and fills: nDD nHDDH S /}){()( /)})({()( 22
  7. 7. With the elevation of the centroid determined, the formation level of any point (the elevation which the point should attain after land grading operation) may be determined, using the computed or assumed values of Sx and Sy.
  8. 8. Mark the existing and computed elevation on grid points and compute cut/ fill 5. Computation of earthwork volumes of field : Vc = L² ∑ C² ---------------------- 4(∑ C + ∑ F) L² ∑ F² Vf = -------------------------- 4 (∑ C + ∑ F) In which, Vc = Volume of cut, m³ Vf = Volume of fill, m³
  9. 9. L = Grid spacing, m ∑ C = Sum of cuts on four corners of a grid square,m ∑ F = Sum of fills on four corners of a grid square, m 2. PROFILE METHOD, The profile method of land leveling design consists of plotting profile of the grid lines and then lying the desired grades on the profile Some designers are prefer to plot profile at approximate right angles to direction of irrigation or drainage other plot them downfield. The method is specially adopted for leveling design of very flat lands or land with undulating topography on which it is desired to develop a fairly uniform surface relief. Essentially it consists of a trial and error method of adjusting grades on plotted profiles until the irrigation criteria are met with and the earthwork balance is attained.
  10. 10. 3. PLAN INSPECTION METHOD This method is adapted for moderate to flat land slope. The grid point elevations are noted on the plan, and the design grade elevations are determined by inspection after the careful study of the topography. It is largely a trial and error procedure. In selecting the elevations formation level the designer must simultaneously consider the down field slope, cross slope, earth work balance and haul distance. The desired cut fill ratio and volumes of earthwork are estimated from the summation of cuts and fills. The grades are frequently adjusted to obtain favourable earthwork balance and to maintain the down field and cross slopes within safe limits.
  11. 11. 4. CONTOUR ADJUSTMENT METHOD The contour adjustment method of land levelling designs consists of trial and error adjustments of the contour lines on a plan map. The method is specially adapted to the smoothening of steep lands that have to be irrigated. A contour map is drawn and the proposed ground surface is shown on the same map by drawing new contour lines. The uniformity of downfield slope is controlled by the uniformity of the horizontal spacing between contours, and the cross slopes can be examined by scaling the distance between contours at right angles to the direction of irrigation. A balance between cut and fill can be approximated by maintaining the proposed contour in an average position with refrence to original contour at same elevation.
  12. 12. The design elevation of grid points can be determined by interpolation between the design contour 1.2.3 Criteria for land leveling - Criteria for land grading are influenced by the The characteristics of soil profile, prevailing land slope, rainfall characteristics, cropping pattern, methods of irrigation and other special features of the site, including preferences of the farmer. 1. Soil profile conditions – A soil survey of the area to be levelled is necessary before undertaking the leveling work. The soil survey map will show  The nature of the top soil, subsoil and the materials under the subsoil.
  13. 13.  It will show the depth to sand, gravel, hard pans, rock or other material that might limit the depth of cut, as well extent of such areas.  Alkali spots will be outlined and depth to water table shown.  This information will help in the best possible layout for land leveling.  Where deep cuts are unavoidable and the soil is shallow, the harmful effects of top soil removal may be mitigated by scraping and storing the top soil, which is then replaced by the new grade after the movement of the subsoil material. The process involves moving the same soil twice. Hence, it is an expensive procedure which should be justified.  Bench levelling, in which the field is levelled in small strips, minimises the harmful effects of severe top soil removal.  Soil surveys furnish information relative to infiltration characteristics and hydraulic conductivity of the soil.  If the subsoil and substratum are sand or sandy loam, and the infiltration rates are high, the irrigation intervals must be shorter. 2. Land slope –  If the land is very steep and undulating, and the soils are shallow, it may not be possible to shape the surface to uniform slopes on good irrigation grades.  Such areas should be left without any major land grading operations being done and should be kept in pasture for as much of time as possible, in order to prevent severe soil erosion.  The development of a uniform non-erosive grade in the direction of irrigation and the removal of excess slopes should be the aim of a high quality levelling job. This is particularly true for surface irrigation methods like border strip  A good land grade, designed in accordance with the infiltration characteristics of the soil, the size of the irrigation stream available, the crops to be grown and the erosion hazard from rainfall, permits uniform water distribution and high irrigation efficiencies.  Usually, excessive cuts are necessary to eliminate cross slopes. To reduce the extent of cuts, the field is divided into parts and the levelling is done in strips at different elevations, separated by low ridges.  The practice is commonly called bench levelling, especially if there is considerable difference in elevation between adjacent strips. The width of benches will be influenced by the farming equipment to be used and the earthwork involved.
  14. 14. 3. rainfall characteristics –  The rainfall characteristics of an area are important in determining the maximum and minimum grades allowable for a field.  Minimum grades must meet the drainage requirement of amount of rainfall. 4. Cropping pattern –  The kind of crop to be grown should be considered in selecting the irrigation or drainage method and resulting land grading criteria.  A high value crop with high labour requirement may justify high degree of levelling to reduce labour and production cost.  Cultivated crops such as vegetables may justify a high levelling cost whereas fodder crop justify low cost. 5. Irrigation methods –  Each method of irrigation has its own limitations. The criteria for land grading must specify slopes within these limits.  When several methods of irrigation are to be used on same field of requirements of the most restrictive method must be adapted. 6. other consideration –  Field subdivision based on natural boundries should be considered for entire plan itself even though only a part of farm may be levelled in first year.  It May be possible to sub divide the farm area into narrow stripson approximate contours.  Each strip is considered as separate field for land levelling design. plans for levelling should include use of waste soil.  Irrigation and drainage design must be designed at the same time 1.2.4 Layout of Fields, and Irrigation and Drainage Systems  Prior to levelling design, the land develop programme must be planned so that the location of field boundaries, irrigation water supply system, and farm roads are known.  The levelling plan of individual field must provide for furnishing material or absorbing the excavated earth from areas. It must also provide for the proper ratio between excavations and fill.  A topographical map of the farm area is necessary for planning the field layout, water conveyance system and field drains.
  15. 15.  The topography is a major factor selecting the method of irrigation, estimation of number and kind of water control structures and determining the need for land levelling.  The elevations of the source of water supply, the land between the water source and the area to be irrigated and the different parts of the farm are be irrigate and the drainage outlets must be known to properly farm irrigation system.  Field channels and underground pipelines to irrigation water to the field are located along the upper reach of the irrigation runs. They are perpendicular to the direction of irrigation for irrigation methods.  The water surface in field should be 20 to 30 cm higher than the ground to be irrigated. If possible these channels should be level (less than 0.1 per cent slope) so that water checked up for a maximum distance.  Where topography permits, the water supply lines may be located as to serve the fields on either side of irrigation the location of the supply lines is determined by standard route-type survey.  A profile of each proposed centre line is needed to compute the amount of excavation is required. Field arrangement: -  Laying out fields of workable size and shape is important to successful irrigation.  The fields are laid out as nearly rectangular as possible. Sharp turns in field boundaries should be avoided as possible in order to facilitate the use of modern equipment.  The field length is based on the allowable length of run for the irrigation method.  Field length may be limited by ownership boundaries. The width of the field depends on cropping system, operating schedule and type of farm equipment used,  Border and check basin methods of irrigation, the width of a field is a multiple of the width of the irrigation strip.  The width of border or basin is based on the size of the irrigation stream and the type of equipment used in land preparation.  Subdivision of fields is based on ownership boundaries, obstructions, soil boundaries, land slopes and cropping systems. It is important to retain the existing facilities of irrigation, drainage and farm roads as much as possible.
  16. 16.  In most cases, the contour map of the area indicates the most advantageous way to subdivide the land for grading.  The following contour patterns may warrant subdivision of land for successful irrigation farming: 1. Separation of fields may be desirable along the line of slope change for sharp change in slope. 2. Separation of fields at the bend is desirable for surface irrigation methods for straight contour topography. 3. Contour lines either close together or far apart means slope is steep or flat. In such cases, the lengths of the fields are kept to the minimum required for efficient irrigation so as to reduce the amount of cuts and fills required. 4. Non uniform slope may be set apart to be graded invidually as unit. 5. Excessively irregular areas may be planned for rrigation with sprinkler or drip methods. Field road system:-  It is essential to provide a field road system for ready access to all areas of the farm for farm equipment, transportation of farm produce, and easy operation of the irrigation system. Field roads are provided above irrigation channels and below field drains. Drainage:-  Good drainage, both surface and subsurface, is essential for successful irrigation.  Provision should be made to drain the excess rainfall promptly and safely. Surface drainage may be needed to prevent or modify saline- alkali conditions in a soil by leaching.  If the land is not naturally well drained, artificial drainage must be established at the same time the irrigation system is installed.  Seepage from overirrigated areas at higher elevations and irrigation canals can damage lands in the low-lying area.  Interceptor drains may be necessary at the upper boundaries of the low-lying area to divert the seepage and prevent water logging.  Integrated irrigation and drainage planning is often necessary for laying out a farm area for efficient water use.
  17. 17. 1.3IRRIGATION METHODS – 1.3.1. Choice of irrigation methods  Soil characteristics,  Topography,  Availability of water,  Type of crop,  Size of stream,  Rate of infiltration,  Depth of water,  Amount of water,  Possible erosion of soil. 1.3.2 Methods of irrigation 1. Surface irrigation 2. Subsurface or subirrigation 3. Overhead or sprinkler irrigation 4. Drip irrigation Methods of irrigation coming under different groups are as follows: 1. Surface irrigation methods A. Methods involving complete flooding of the soil surface 1. Wild flooding 2. Border or border strip irrigation a. Straight border b. Contour border 3. Check or check basin irrigation a. Rectangular check b. Contour Check 4. Contour ditch irrigation B. Methods involving partial flooding of the soil surface 1. Furrow irrigation a. Straight graded furrow b. Straight level furrow c. Contour furrow d. Alternate furrow e. Raised bed and furrow 2. Corrugation 3. Basin and ring irrigation C. Surge irrigation 2. Subsurface irrigation methods
  18. 18. A. Irrigation through lateral supply trenches B. Irrigation through underground pipes or tiles 3. Overhead or sprinkler irrigation methods A. Nozzle line system B. Rotary head sprinkler system C. Fixed head sprinkler system D. Propeller type sprinkler system E. Perforated pipe method 4. Drip or trickle irrigation method 1.3.3 SURFACE IRRIGATION METHODS Surface irrigation refers to irrigating lands by allowing water to flow over the soil surface from a supply channel at upper reach of the field. Principals involved in surface irrigation are: (i) Field is divided into plots or strips to uniformly irrigate the soil to a desired depth throughout the field, (ii) Water is discharged at the highest level of the field allowing water to flow down the gentle slope by gravity flow, (iii) Water loss by run-off or deep percolation is avoided, (iv) Efficiency of irrigation is kept at a high and (v) Size of stream should be such as to have an adequate control of water. Crops in India are irrigated mostly by surface irrigation. Surface irrigation includes methods such as border, check, contour border, contour check, contour ditch, furrow, corrugation, basin and ring methods. The land surface is either completely or partially wetted while irrigating the crops. Advantages of surface irrigation are weightier over disadvantages, particularly under conditions where lands are subdivided into small plots and farmers are relatively poor. 1.3.4 Advantages and limitations Advantages of surface irrigation are:  Variable sizes of streams can be used,  large flow of water can be easily controlled,  water is conveyed to fields by channels,  cost of water application is quite low,  skilled personnel are not required. Limitations are:  considerable land is wasted in construction of channels and bunds,  initial cost of construction of reservoirs, water courses, field channels and bunds is quite high,  lining of channels and water courses involves considerable cost,
  19. 19.  unlined water courses and channels require frequent repairs,  erosion of unlined channel bed and sides often occurs,  rodents and animals often cause damages to channel bunds,  weeds g r o w easily on unlined channels that require frequent cleaning and  channels and bunds interfere with movements o f farm tools, machinery, carts and animals. 1.3.5 Wild Flooding It is refers to irrigating fields that are relatively flat and level by allowing water from supply channels to flow over the land surface along the natural slope without much guidance by channels and bunds. Wild flooding is further divided by controlled flooding and free flooding Adaptability -  Fields are relatively smooth or slope gradually and uniformly towards the natural drainage course,  labour is expensive,  soil is deep and is not likely to crust badly,  proper land levelling could not be done and  proper method of irrigation could not be initiated.  Grasses, fodder and close growing grain crops and pastures on large ranches are irrigated by this method.  an abundant supply of cheap irrigation water.  The size of stream, flow depth, land slope and water intake rate influence greatly the efficiency and uniformity o f water application. Advantages and disadvantages Advantages  the land does not require precise land levelling and grading,  water application is quite easy and cheap and  skilled labour is not required. Disadvantages  flooding is uncontrolled,  uniform wetting of land cannot be achieved,  greater amount of water accumulates in lower spots  higher points may remain unwetted,  excessive loss of water by percolation and run-off may occur,  water application efficiency is low,  sensitive crops may get damaged by excess water accumulation in lower parts o f the field, and  Crop growth and yield are poorer in higher parts of the field as well as in lower spots owing to improper irrigation. 1.3.6 Border or Border Strip Irrigation
  20. 20. Border method involves irrigating a field by dividing the same into long narrow strips separated by low parallel borders (bunds). Each strip is irrigated individually by supplying water at upper end. The method is also termed border strip method. Border strips are laid along the general slope of the field or across the general slope when the field slope is more. There are two methods of border irrigation, straight border irrigation and contour border irrigation. Fig. 1.1 Layout of border strip irrigation method Adaptability –  Where depth and topography permit the required land levelling at a reasonable cost and without permanent reduction in soil productivity.  Soil having moderately low to moderately high infiltration rate.  Not used for high infiltration rate.  As well as not suited for low infiltration rate  Suitable for all close growing crops like wheat, barely and fodder crops.  Suitable for crops which requires standing water.  Best suited for land having slope less than 0.5 %. 1.3.7 Advantages -  no land is wasted for making channels excepting the supply channels  borders can be used for growing crops,  efficiency of water application is high,  variable stream size can be efficiently used,  construction of borders is easy and does not involve much cost  labour requirement is quite low, and
  21. 21.  easy disposal of possible excess surface water that may accumulate at the tail end can be made through a drainage channel at the end o f strip. Limitations  precise land levelling is essential,  initial cost of land preparation and land grading is high,  there are chances of excess water intake in the upper reach of the strip,  excess water accumulation may occur at the tail end of the strip if the supply of water is not closed on time or proper drainage is not made,  the method is unsuitable for uneven and undulating land with shallow soils and  enough skill is required in applying water. 1.3.7 Types of border strip irrigation - 1. Straight border irrigation Border strips are constructed along the general slope of the field. When fields can be levelled to desirable land slopes economically and without affecting its productivity straight border are easier to construct and operate. 2. Contour border irrigation Border strips are constructed along the contour(across general slope) when the land slope exceeds the safe limit of soil erosion, land is undulating and the land levelling is not economically feasible. They are designated as contour borders or contour border strips. They are also termed bench border strips when they are constructed in bench terraces. To construct strips, ridges are laid out along the contour strong enough to sustain pressure of water and high enough to contain water along the contour (Fig. 7.2). The design criteria and irrigation method are essentially the same as with border strip method. The size of strips may however be shorter than usual. They are made level crosswise and slightly sloping longitudinally as graded border strips. The width of a strip is decided by the amount of earth work and the cost involved. The vertical interval between adjacent benches should be 30 cm, but it should not exceed 60 cm. Water supply channels are laid out along the slope with provision for drops and other measures to prevent channel bed erosion. Drainage channels with adequate provision for erosion control should be ensured at the down end o f the strip to drain out the excess rain water.
  22. 22. Fig 1.2 Layout sketch of contour border irrigation 1.3.9 Design considerations or design criteria for border strip method –  The width of border usually varies from 3 to 15 m depending upon size of irrigation stream available and degree of land levelling practicable. As per irrigation stream size width of border can be reduced but not less than 3 m.  The length of border strip depends upon how quickly it can be wetted uniformly over its entire length. It also depends on infiltration rate, slope of land and size of irrigation stream available. For moderate slope to moderate stream following lengths are adopted
  23. 23.  Types of soil Length of strip Sandy loam soils and sandy soil 60 to 120 m Medium loam soils 100 to 120 m Clay loam and clay soil 150 to 300 m  The longitudinal slope of strip mainly depends on type of soil and it should neither excessive nor too flat. Excessive slope leads to erosion of strip and too flat slope slowly moves water. Type of soil slope Sandy loam to sandy soils 0.25 to 0.60 % Medium loam soils 0.20 to 0.40% Clay to clay loam soil 0.05 to 0.20 %  Size of irrigation stream – The size of irrigation stream depends on infiltration rate of soil and width of border strip. As per fine and coarse textured soil stream size varies low to high. The size of irrigation stream also varies with depth of water supply. A smaller stream is used to apply greater depth as well as larger stream is used to apply shallower depth. 1.3.10 Design STEPS of border strip irrigation method –  The length, width and slope of border strip are determined.  The depth of water required is estimated from the measurement of actual soil moisture content before irrigation.  The infiltration – time relationship of soil under existing soil conditions and vegetation is determined. The relationship can be established from actual measurement or from previously established relationship. Time required to irrigate crop can be determined by- t = 2.303 y I log10 q q-IA Where t = time required for irrigation y=average depth of water I = rate of infiltration A = irrigation area q = discharge  The desired infiltration opportunity time is determined. Opportunity time means the time necessary for soil to absorb the estimated depth of irrigation water.  The hydraulic resistance is estimated on the basis of soil surface roughness and hydraulic characteristics of crop.  The water front advance is predicted.
  24. 24.  The irrigation system is designed to obtain the optimum water application efficiency and border length. The procedure is proposed by hall.
  25. 25. 1.3.11 Check or Check Basin Irrigation Check method consists of dividing the field into several relatively level plots called checks surrounded by low bunds. They are irrigated with comparatively large flow of water. Small checks are level while bigger ones are slightly sloping along the length. A check is also termed as check basin. There are two methods of check irrigation, rectangular check method and contour method. Adaptability  Suited for smooth gentle and uniform land slopes.  Soils having moderate to low infiltration rates.  Steep slopes require complex layout and heavy land levelling.  Both row crops and close growing crops can be grown.  Method is especially adapted for grain and fodder crops in heavy soil where water is slowly absorbed and stand for long time.  Also suitable for permeable soil.  Different kind of crops can be grown in same field without making major changes.  Usuful where leaching requires to remove salt.
  26. 26.  Conserves rainfall in basin and infiltrate water without soil erosion or runoff.  Method results in high water application and distribution efficiencies. Advantages and limitations  Variable size of streams can be effectively used,  It can be adopted for a wide range of soils,  Water application efficiency is high,  There is no loss of water by run-off,  Rain and irrigation  Water can be effectively used for wetting the root zone soil,  Water-logging condition can be easily created for rice crop,  Leaching down of salts can be easily done and  Provision for drainage of water is not usually necessary except in high rainfall areas. Limitations are:  Precise land levelling is necessary,  Considerable land is wasted by bunds and channels,  Crop yields are low on bunds whenever crops are grown on them,  Labour requirement is high for preparing the land for irrigation,  High capital investment required initially, and  Movements of farm animals, implements and machinery are often restricted by bunds and channels. 1.3.12 Types of check basin 1. Rectangular check irrigation In a relatively uniform land with a gentle slope, checks may be rectangular and sometimes square. They may be a few square meters in size for vegetable crops to as large as one hectare or more for wet land rice crop. The size of a check is a function of the water intake rate of soil, land slope and the available stream size. In lighter soils the size of a check may necessarily be small to achieve uniform wetting and in heavier soils the size may be large. A sketch layout plan o f check method is given in Fig. 1.3. Fig 1.3 LAY OUT OF CHECK BASIN METHOD
  27. 27. Contour check irrigation  In sloping and rolling lands contour checks are constructed by raising bunds or ridges along contours having vertical intervals of 15 to 30 cm. Checks at the end of the adjoining contours may sometimes be joined at suitable places to make them continuous. They are almost uniformly level or gently sloping and are often small. A contour check is also termed contour check basin.  Supply channels discharge water into contour checks and run along the slope provided with check gates, turn outs and drops with measures to prevent Channel bed erosion. They are sometimes interconnected at suitable places.  The design criteria and the method of water application is essentially the same as with the rectangular check method. Contour checks are suitable for growing vegetables, forage and grain crops including the rice crop. 1.3.13 Design considerations of check basin - 1. Size and Shape of basins :-  The size of the check basins depends on the infiltration rate of soil. In general the size of the basins may vary from one metre square, used for growing vegetables and to as large as one or two hectares or more, used for growing rice under wet land conditions.  However, for medium soils plots of area 0.04 to 0.05 hectare may be suitable. Further circular or rectangular plots are preferable to square plots. As such for land which is level or is very gently sloping, the basins are rectangular in shape.  However, for sloping land the basins or plots are prepared by constructing the levees along contours having vertical intervals of 60 to 120 mm and connecting them with cross levees at convenient places. These are called contour levees or checks. In this case the plots or basins have some odd shapes depending on the configuration of the contours of the land. 2. Size of irrigation stream:-  The size of the irrigation stream should be such that required amount of water can be delivered in small portion of time.  The size of irrigation stream, however, depends on the infiltration rate of the soil. As the infiltration rate of the soil increases, the stream size must be increased or the size of the basin reduced in order to cover the area of the entire basin in a short period of time.  A useful thumb rule in this regard is that the water spread in the entire basin should be covered in one fourth the time required to infiltrate the net depth of irrigation water. Thus by careful selection of the size of the check basin and stream size to suit the infiltration characteristics of the soil, it is possible to arrive at the design of check basin which will give high value of water distribution efficiency. 3. Bunds  Bunds around a check may be temporary for a cropping season or semi permanent as for paddy fields. They may be 25 to 30 cm high in case of small
  28. 28. checks and 50 to 100 cm high for large checks depending on the size of checks and the depth of water to be ponded.  Temporary bunds of a check are narrow and of low height for small check basins. Semi-permanent bunds may be wide for movements of farm machinery. They may suitably be used for growing crops. 4. Channels and laterals  Water is conveyed to checks by a system o f supply channel, laterals and field channels.  Laterals or field channels are laid out in such a way that a channel passes through a set of two rows of checks. Such a channel is used to irrigate checks on both the sides.  A supply channel is constructed on the upper reach of the field and laterals usually follow the slope, if there is any. 1.3.15 Furrow Irrigation Methods Furrow irrigation refers to irrigating land by constructing furrows between two rows of crops or alternately after every two rows of crops. It wets the land surface only partly and water in the furrow moves laterally by capillarity to the unwetted areas below the ridge and also downward to wet the root zone soil. Furrow irrigation is adopted to irrigate all row crops such as maize, cotton, groundnut, sugarcane, tobacco, potato and vegetable crops on ridges. Plantation and fruit crops are also irrigated by furrow method Furrow irrigation saves a considerable amount of water by reducing the evaporation loss. Evaporation is low here as only a part of the land surface is wetted. The saving may be as much as 30 per cent over other method of surface flooding like border strip or check basin method. Usually furrows are constructed after every row of crops. Adaptability –  irrigate crops like bean, tomato and potato that are sensitive to wet soils at the base of plants and to crops such as sugar beet and safflower that are susceptible to fungal diseases like root rot.  Land must be graded and properly levelled  Both pervious and impervious type of soil land can be irrigated by it  Not suitable for sand having high infiltration rate  Groundnut and vegetable crops such as onions, cabbage and chillies are irrigated by laying out furrows after every two rows of crops. This practice saves more water than when furrows are made after each row of crops.  Besides, it prevents an accumulation of salts near the plant bases in areas where salts are a problem. Advantages and limitations Advantages of the method are: a. great saving of water over other flooding methods, b. variable sizes of streams can be used, c. a large size stream can be controlled by discharging water in several furrows, d. the water application efficiency is very high,
  29. 29. e. wide ranges of soils can be irrigated, f. losses of water by evaporation, run-off and deep percolation are reduced, g. there is no erosion hazard, h. furrows act as drainage channels in high rainfall areas i. furrows are helpful in lands with high salt concentration as salts accumulate on the upper part of the ridges and crop planted at the lower end of the ridges is safer. Principal limitations of the method are: a. land requires precise grading to a uniform slope, b. labour requirement is high for grading land and making furrows, c. skilled labour is necessary to control water in furrows, d. erosion of furrow bed is anticipated if furrows are not properly graded, and e. the method is unsuitable for light irrigation. 1.3.16 Types of furrow irrigation Classification of furrow irrigation methods The methods are: Straight graded furrow irrigation, straight level furrow irrigation, contour furrow Irrigation, alternate furrow irrigation and raised bed and furrow irrigation. Straight graded furrow irrigation Straight furrows constructed along the prevailing land slope or made sloping to a non- erosive grade are called straight graded furrows. For long and deep furrows, grading is made to achieve quick water coverage of furrows. Methods of construction and irrigation of furrows have earlier been stated. For irrigating row crops in large farms, straight graded furrows are laid to allow the use of the largest practical stream to increase the water application efficiency. Water is allowed first to cover the furrow in the quickest possible time with a larger stream and then the stream is cut back to a smaller size to allow just the amount required to meet infiltrated water. Water supply is completely cut when the desired depth of water has infiltrated in the upper reach of the furrow to avoid losses through deep percolation and run-off. Water logging at the tail end of the furrow should be avoided. A drainage channel is made at the end of furrows to drain out excess water during high rainfall and when water logging occurs owing to careless irrigation. Straight level furrow irrigation Furrows are made level and straight throughout its length. They are suited to soils having low infiltration rate and moderate to high water holding capacity. They are constructed in uniformly level lands and in small fields with short furrows. Water is allowed to fill the furrows very quickly and then allowed to stand for sufficiently long time to permit adequate infiltration to wet the crop root zone. Water supply to furrows is cut-off when the required depth of water is discharged into them. The same size of stream is maintained from the beginning till the end of irrigation. Comparative advantages and limitations of level furrows irrigation are as follows: Level furrows have certain advantages over the graded furrows:  Considerable amount of water is saved as there is no loss of water by runoff, and deep percolation takes place,  no grading of land is necessary in a level land and in small plots,
  30. 30.  there is no erosion hazard,  uniform wetting of root zone soil with high water application efficiency is achieved. The limitations  the furrow capacity must be large to hold sufficient water for infiltration and to control large flows and  a uniform levelling of land is required. Under Indian conditions, farmers resort to short level furrows in their small plots due to fragmentation of lands. In many areas the available small streams lead to the use of short level furrows for irrigation. Contour furrow irrigation Contour furrow method of irrigation is adopted in an uneven and rolling topography. When the longitudinal slope exceeds the safe limits for graded furrows, furrows are constructed along the contour. Furrows are either graded or made level depending on the types of soils and length of furrows. Contour furrows are usually short to avoid soil erosion. Graded contour furrows are given a gentle longitudinal slope. The supply channel or pipe line runs down the slope discharging water into furrows. Bunds along contours are raised at certain intervals to prevent breaches damaging fields at lower levels. The supply channel is cither grassed or structures are constructed to prevent erosion of the channel bed and sides. Advantages:  steeper lands where straight graded or level furrows are likely to get eroded can be irrigated  comparatively a larger stream can be used without much risk of soil erosion in furrows along contours,  relatively a high application efficiency can be achieved. Limitations are:  coarse textured soils and soils that develop cracks are unsuitable,  breaches in furrows may increase the erosion hazards, length of furrows is usually short,  grassed supply channels and structures water pipe lines are required for carrying water down the slope, and  instant watch is needed to look for possible breaches and repair the same immediately, if there is any. Alternate furrow irrigation When the supply of water is limited, irrigation is applied through alternate furrows. Besides, this alternate furrow method is adopted where salt is a problem. Water is discharged in alternate furrows keeping the in-between furrow dry. In the subsequent irrigation, water is allowed to flow through the alternate furrows that had been kept dry on the previous occasion. This method saves quite a good amount of water and is very useful and crucial in areas of water scarcity and salt problems. Raised bed and furrow irrigation Raised beds of 1 to 1.5 m width or wide ridges alternating with furrows are often constructed for growing vegetable crops, particularly those vegetable crops that creep on soil surface. Fruits of those vegetables get damaged on coming in contact with the moist soil. Two rows of plants are usually raised on two sides of a bed or ridge. A furrow runs between two rows of the adjacent ridges or beds and supplies water to the plant rows The method assures saving of a large amount of water. The surface soil of beds or ridges remains dry and the creeping plants-and their fruits are not damaged.
  31. 31. Fig 1.4 layout of furrow irrigation
  32. 32. 1.3.17 Design considerations of furrow method - 1. Spacing of furrows - The spacing of furrows is determined by the spacing desired for the rows of most of the cases one furrow is provided for each row of the plants. The crops like potatoes, maize and cotton are planted 600 to 900 mm apart and have one row of plants between two furrows. However, vegetable crops such as carrots, onions, etc., are spaced 300 to 400 mm apart and other have two rows of plants between two furrows. Thus in each of these cases the furrow spacing may be 600 to 900 mm. In orchards furrows may be spaced 1 to 2 m apart and in some cases the spacing of furrow may be as much as 3 to 4 metres. Moreover, certain wide spaced crops such as water melons, fruit trees and berries generally require more than one furrow between two rows of plants. In general furrows should be spaced close enough to ensure that water spreads to the sides into the land between the furrows and the root zone of the crop to replenish the soil moisture uniformly 2. Shape and Size of furrows. The shape and size of furrows mainly depend on the soil conditions and type of crop. In general the furrows used are either V shaped, U shaped, parabolic shaped or trapezoidal shaped as per the requirements of soil stability. Further for widely spaced crops large furrows and for closely spaced crops small furrows are used. For soils of low permeability a wide furrow is preferred since it gives more area for the water to infiltrate. On the other hand when the soil is quite permeable, narrow and deep furrows may be used to avoid excessive percolation at the upper reach. However, in general in furrow irrigation a wide and shallow furrow is preferable. Further furrows of 75 to 125 mm depth are suitable for vegetables and other row crops such as sugar beet, potatoes, cotton, etc., while for some other row crops and orchards furrows of 200 to 300 mm depth are required especially when the soils are of low permeability. 3. Furrow length – The furrows should neither be too long nor too short. This is so because if a ; too long water may infiltrate to a greater depth at the upper end of the furrow by the time it reaches the lower end. This results in excessive deep percolation losses and over irrigation at the upper end of furrow. On the other hand short furrows require supply channels to be spaced too close with consequent loss of land and increase in labour requirement. The furrow length is considerably affected by hydraulic conductivity of the soil. Thus furrows must be shorter for porous sandy soils than for light clayey soils or heavy soils. For clayey soil length of furrow is 300 to 400 m while for sand it may be 60 to 300m.
  33. 33. The furrow length is also influenced by the slope, rate of advance and depth of application on besides the type of soil. The stream size, slope and furrow length should be so adjusted that the percolation are a minimum. 4. Furrow slope – The slope of the furrow controls the velocity of flow of water in the furrow. Thus steeper slopes lead to higher velocities of flow of water in the furrows which may result in more erosion of soil in the furrow. Moreover, as the furrow slope increases, the rate of infiltration slows down and the side spread of water into the land decreases, with the result that wastage of water may occur at the end of the furrow. If the furrow slopes are too less then proper surface drainage may not take place with the result that excessive deep percolation losses may occur. Further a minimum furrow slope of 0.05% is needed to ensure surface drainage. However, in soils having very low infiltration rates, the furrows are usually level without any slope being provided along their lengths. These furrow are known as level furrows in which the water is ponded until it is absorbed by the soil. 5. Furrow stream size : - Water is supplied to the furrows from a supply channel or a concrete pipe placed underground at the upper end of the field. From the supply channel water is supplied to the furrows either through small opening made by cutting the bank of the channel, or through small portable siphons. For siphons about 1.2 m long curved pipes of small diameter are used which are made of light weight plastic, aluminium, galvanized iron, or rubber. From the concrete pipe water is supplied to the furrows through vertical riser pipes. Sometimes aluminium pipe provided with gated openings and placed on the ground surface is used for supplying water to the furrows. Small, easily adjustable gates in the pipe facilitate control of quantity of water supplied to the furrows. A tail channel at the end of the furrows to collect water for reuse at lower levels. The stream size of the furrow should be such that it will not cause erosion and most uniform irrigation would be obtained. The size of the furrow stream usually varies from 0.5 to 2.5 litres per second. Qm= 0.60/ s Maximum non erosion stream size in litres per second= Qm SLOPE of furrow in % = S D = qt 3600/WL W = furrow spacing in m L = furrow length in m D = depth of water applied q = stream size in litre per second t = duration of irrigation