Preface This text book is designed to guide students from a basic knowledge of soil, water, plant, hydrologic and hydraulics to the state-of-the-art of irrigation system design, planning and management. The book will be helpful to the students of Agriculture, Agricultural and Civil Engineering and other related fields. The goal of the authors is to present the principles and theories of irrigation engineering in simple manner to maximise the students’ learning, understanding and motivation. The book is written in simple and lucid languages which will make the students interesting in reading the book and understanding the concept of farm irrigation very effectively. The book is written covering the entire syllabus of Irrigation Engineering which is taught in various State Agricultural Universities and is written as per the recommended syllabus of fifth Deans’ Committee meeting of Indian Council of Agricultural Research (ICAR), New Delhi. The book will not only be helpful to the students at under-graduate and post-graduate level, but also will be a helping tool for all practising irrigation engineers, agriculturists, design engineers, researchers, extension personnel and all others who are directly or indirectly associated with irrigation science and engineering. The book contains 78 solved problems, 542 short and long questions, 65 tables, 135 figures and 136 references which will be of immense help to the students and design engineers. Several field experimental result are also presented at appropriate sections in various chapters in this book which will attract the attention of the students in the subject matter. In addition, the book contains a number of multiple type questions with answers. These multiple type questions are prepared covering all the chapters of irrigation engineering. These questions will help the students who prepare for various competitive examinations including GATE, NET, ARS, JRF and SRF examinations of ICAR. The book contains 11 chapters and each chapter contains several sections and sub-sections. The title of each of the 11 chapters and various sections and subsections are as follows: Chapter 1: Introduction: This chapter deals with importance of water for agriculture, purpose of irrigation, merits and demerits of irrigation. It also contains the classification of different irrigation projects, major and medium irrigation projects in India and water resources potential available in different river basins. It also gives an overview of large scale investment incurred on irrigation sectors and status of irrigation potential developed and utilisation in various plan periods. Scope and various techniques of augmentation of water resources development are briefly discussed at the end of this chapter. Chapter 2: Sources of Irrigation Water: Chapter 2 deals with hydrologic cycle and different components of hydrologic cycle including rainfall, its measurement, computation of average depth of rainfall and study of variability of rainfall. Runoff, which is a major component of hydrologic cycle has been discussed in details. Estimation of runoff by various techniques, computations of peak rate of runoff by different techniques including Rational method and SCS-Curve number method are discussed. Factors affecting runoff including climatic and physiographic factors are discussed in this chapter. Chapter 3: Discharge: Measurement of Irrigation Water: Chapter 3 deals with various techniques for measurement of discharge or irrigation water including volumetric method, weirs including rectangular, trapezoidal and triangular weir, proportionate weir/sutro weir, flumes including parshall and cutthroat flume, water metres, meter gate, spillway and syphon spillway. Finally discharge measurement through orifices and mouth pieces are presented in this chapter. Chapter 4: Water Requirement of Crops: Various methods of computation/ measurement of crop water requirement like lysimeter, field plot experiment, soil moisture depletion studies and water balance model are discussed in this chapter. Estimation methods including aerodynamic method, combination method, and empirical methods covering Thornwaite method, modified Blanney-Criddle method and Pan evaporation method are also presented in Chapter 4. Finally estimation of actual crop evapotranspiration from potential crop evapotranspiration, crop coefficient and its variation with different crops at different crop growth stages are discussed in chapter 4. Chapter 5: Soil Water Plant Relationship: Different terms related to soil water like density, unit weight, bulk unit weight, void ratio, porosity, saturation moisture content etc. are discussed in this chapter. Determination of soil moisture content by methods like oven dry method, sand bath method, pychnometer method, tensiometer method, neutron probe method, electrical resistance method, calcium carbide, radiation and torsion balance method etc. are discussed in chapter 5. Other important topics like soil moisture suction, soil moisture potential curves, measurement of soil water potential, field capacity, wilting point, readily available soil moisture, flow through soil columns in horizontal and vertical direction and effect of soil moisture stress on crop yield are presented finally in chapter 5. Chapter 6: Conveyance of Irrigation Water: Chapter 6 discusses various types of canal systems and canal alignments, distribution system for canal irrigation, inundation and perennial irrigation etc. Computations of discharge capacity by various methods along with Manning’s, Chezy’s and Kutter’s formulae are well discussed in chapter 6. Derivation of economic channel section and discharge computation based on economic channel section is a part of this chapter. Designed conditions of unlined and lined channels, design of channels in alluvial soil based on Kennedy’s and Lacey’s theory are important sections in chapter 6. Garret’s and Lacey’s diagram are presented for design of channels which have been presented in this chapter. Underground water conveyance system, its advantages and disadvantages are presented in chapter 6. Underground water pipe distribution system, materials of pipe, testing of pipes, structures of underground water conveyance system, design of underground pipe line water distribution system, structures used for conveyance of irrigation water including drop structure and chute spillway are discussed at the end of this chapter. Chapter 7: Losses of Water in Canal and Control: The two major losses of water in canal command and reservoirs are seepage losses and evaporation losses. Measurement of seepage losses by ponding, inf low-outf low and seepage meter are discuss in this chapter. Different methods to reduce seepage in canals are presented in chapter 7. Discussions on reduction of seepage including sealants like clay, cement concrete, brick lining, polythene lining, bentonite, asphalt, pre cast, cement mortar, lime concrete, soil cement, shortcrete, boulder lining etc. enumerated in chapter 7. Economics of lining and its justification is also discussed and placed in this chapter. Chapter 8: Irrigation Scheduling: Irrigation scheduling is the most important part of irrigation engineering and so this is discussed well in this book. In this chapter the timing of irrigation and amount of irrigation are discussed. Various methods based on plant indicators, physiological growth stages, soil moisture regime concept, water balance technique and climatological approach based on IW:CPE approach are presented in this chapter. Water management of rice including water saving irrigation technique presented in this chapter will help the rice farmers to economise the irrigation water and enhance water productivity. Chapter 9: Methods of Irrigation: Methods of irrigation plays a crucial role in irrigation scheduling. In chapter 9, we have discussed it vividly. Different methods of irrigation including uncontrolled and controlled method, free flooding, contour laterals, border strip method, check basin, ring basin and ridge and furrow method are discussed and presented in this chapter. Hydraulics of border, check basin and furrow method including their design criteria are also discussed in this chapter. Adaptability of these irrigation methods are finally discussed in chapter 9. Chapter 10: Land Levelling and Grading: A properly levelled and graded land ensures equi-distribution of irrigation water and at the same time enables to economise the irrigation amount in crop field. It saves timing of irrigation in field and augments water application and distribution efficiency. In chapter 10, application efficiency and irrigation uniformity is discussed. Land levelling operation for efficient use of water is discussed in this chapter. Land leveling, land grading, rough grading, objectives of land grading and factors affecting land grading are also discussed in chapter 10. Chapter 11: Efficiency of Irrigation System: Performance of irrigation system is assessed through study of different efficiencies of irrigation like conveyance, water storage efficiency, distribution efficiency, water application efficiency, water use efficiency etc. All these efficiencies and criteria to evaluate them are discussed in chapter 11. Some sample calculations to evaluate these efficiencies are presented in this chapter that will help the students to easily grasp the subject matter.

1.1 Importance of Water for Agriculture All animals and plants require water for their survival. Animals cannot prepare their own food. They depend on plants for their food. Plants need water for preparation food by the process of photosynthesis. Majority of this water requirement of the crops is met from different forms of precipitation. However, when the water requirement is not fully met from precipitation, then growth of the crops is affected. Water requirement of crops depend on many factors. It depends on the type of crops, irrigation schedules practiced, soil texture, position of groundwater table below effective root zone of the crop and management practice followed in crop cultivation. The dry land crops need less water compared to rice which is a water loving crop. The perennial crops like sugarcane, banana etc. need more water than other crops like cereals, pulses, oilseeds etc. Water requirement of crops is partly met by the upward flux of groundwater. The capillary rise of shallow water table in the form of upward flux helps in meeting the water requirement of crops to some extent. The upward flux depends on the type of the soil, effective root zone depth of the crop, depth of water table below effective root zone depth of the crop and potential gradient of soil moisture suction. If the soil is heavy like clay, effective root zone depth of the crop is more (deep rooted crop) and position of ground water table is near to ground level (shallow water table), then the upward flux is more. Due to rainfall or application of irrigation water, some amount of water is recharged to soil reservoir. This recharged water is stored in the soil as soil moisture content. The stored moisture or called as water in the soil reservoir helps in supporting water requirement of crops also. The heavy soil like clay has more moisture retention capacity than the light soils like sandy soil. The residual soil moisture held in clay soil is released slowly and supports more soil moisture to the crops for a longer period than the sandy soil which has less soil moisture retention capacity. After meeting the water requirement of crops from all sources including different forms of precipitation, ground water contribution by capillary rise and residual soil moisture, if there is any shortage of water, then this shortage should be met from other sources which are called as irrigation. It is to be noted that irrigation is not the natural phenomenon of supply of water; rather it is the artificial means of supply of water to the crops. Irrigation may, therefore, be defined as the science of artificial application of water to the crop in accordance with the crop requirement for better nourishment of the crops.

2.1 Introduction Rain and snow are the two chief sources of water of the earth. In-situ conservation of rainwater helps the plants to meet some of their consumptive uses directly. Not all the amount of rainwater that falls at a point is conserved by the soil reservoir to support the plant growth. Some part of it flows over the soil surface as surface runoff and some seeps down as infiltration and finally adds to the underground reservoir. Therefore, rain or snow, which is not used directly by the plants, becomes a potential source of either surface or ground water for irrigation. In areas with extreme low temperature, snow contributes major source of water supply wherever, in humid and sub humid regions, rain is the principal source. Precipitation, rain or snow, is the first stage of the continual cycle of water in its round from atmosphere to the earth and return by evaporation from water bodies, snow surfaces and land surfaces. The continual cycle of distribution of water is governed by the process called as hydrologic cycle. Thus, precipitation or atmospheric water is the first form of water above the earth’s surface, the second form being the surface water on earth and the third form is the subsurface water or underground water. The study of occurrence, distribution and circulation of precipitation through the unending hydrologic cycle forms the basic part of study of hydrology. As mentioned above, the part of precipitation that is not used by the plants in-situ flows over the soil surface as runoff and contributes to either surface or ground water supply. Engineering hydrology is the science that deals with the estimation of runoff and its transmission from one place to the other, besides dealing with the properties of water in nature. For, an engineer, surface and groundwater are the two most important components to deal with. But due to lack of data of stream flow, it is usually necessary to study precipitation, evaporation and percolation to indirectly determine the availability of surface and groundwater. For planning and management of water resources systems, an engineer has to estimate (i) water resources potential of a basin, (ii) dependable yield for irrigation and hydel power generation and industrial water demand (iii) probability of occurrence of floods with their magnitude, (iv) sediment yield and transportation (v) hydrometeorology (vi) new sources of water for irrigation (vii) stream flow forecasting by use of precipitation data (viii) water control, navigation, control of soil erosion and control of pollution of water bodies and (ix) operation and maintenance of river valley projects. For estimation of the above mentioned parameters, it is important to understand the hydrologic cycle properly.

3.1 Introduction Irrigation water that is supplied to crop fields is defined by a term commonly called as discharge which is also called as rate of flow. Discharge is defined as the volume of water flowing through a cross section in a unit time. It can be expressed as cubic metre per second (cumec), cubic feet per second (cusec), litre per sec (lps) etc. one cumec is equivalent to 35.5 cusecs or 1000 lps. The measurement of discharge is very important in everyday life starting from deciding the amount of irrigation to be supplied to a crop at a particular growth stage, or amount of water supply for domestic and industrial uses, for flood control and power generation etc. It plays a vital role in water resources planning. 3.2 Methods of Discharge Measurement The various methods of discharge measurement can be broadly classified into the following types: (i) volume method of discharge measurement (ii) flow measuring structures such as orifices, mouthpieces, flumes and weirs.

4.1 Introduction A reservoir that collects and harvests in-situ rainfall as well as runoff from the catchment area can be used for many purposes: the most important of which is the supply of water to crops as supplemental irrigation. The water of the reservoir can be used for domestic and industrial uses. It is also a good source for recreational use. Total water demand of the reservoir including irrigation to different crops in different seasons, domestic and other non-agricultural uses are to be assessed. While estimating the crop water requirement and irrigation requirement, various crops to be grown in the service area of the reservoir, their water requirements, crop duration, extent of coverage and water management practices followed are to be taken into consideration. Multiplying the irrigation requirement with crop coverage area, volumetric irrigation water requirement of crop can be found out. Summation of irrigation requirement of all crops grown in service area of the reservoir gives total irrigation demand of the reservoir. 4.2 Water and Irrigation Demand of Crops Of the various demand of water from the reservoir, irrigation demand of crops grown in the command area of the reservoir is very important. Most of the crop water demand is met from rainfall. However, when the rainfall is deficient to meet the crop water demand, then the deficit is met from the stored water of the reservoir in the form of irrigation, more commonly called as supplemental irrigation. The irrigation to the crops is required mostly to meet the evapotranspiration requirement of the crop. Before discussing the water and irrigation demand/requirement of crops, it is essential to know some commonly used terms frequently used.

5.1 Soil Soil and water are the two most important natural resources required for crop production. Without soil, no crop can be produced even if there is availability of plenty of water. It is vital not only for agriculture but also very vital for sustenance of life. No building can stand on any place without soil. Soil gives foundation support for any building. The term ‘soil ’is defined in various ways depending on the general professional field in which it is used. However to an agriculturist, soil is the substance existing on the earth surface, which grows and develops plant life. It contains all vital elements including its inherent fertility contents that support the growth of plants. For an engineer, soil is the unaggregated deposits of mineral and organic particles covering major part on the earth crust. It includes widely different materials like boulders, sand, gravel, clays and silts. Soil is produced by the weathering of solid rocks. The formation of soil is due to geologic cycle continuously taking place on surface of the earth. The geologic cycle comprises weathering or denudation, transportation, deposition and upheaval, again followed by the above mentioned processes. Weathering may be natural or artificial. In natural weathering, physical processes like temperature changes, flow of water, ice, wind and rain play the role. In artificial weathering animals especially human beings interference causes soil erosion and formation. It is obvious that it takes hundreds of years to form one inch of soil.

6.1 Introduction In order to increase the production and productivity of crops, provision of irrigation system is highly essential. A project that makes use of weir or a barrage for providing irrigation to fields is called as direct irrigation system. On the other hand, a storage irrigation system makes use of storage reservoir by construction of dams. In order to provide irrigation by both the schemes, it is necessary to have a network of canal systems. A canal is an artificial channel, generally trapezoidal in shape constructed on the ground to carry water to the fields. The canal systems that provide water to the fields include main canals, branch canals, distributaries, minors and watercourses. It is imperative to design the canal systems properly for a certain realistic value of peak discharge that must pass through them so as to provide sufficient irrigation to the command areas. The flow irrigation that provides irrigation water to the fields may be of two types i.e. Inundation irrigation and Perennial irrigation.

7.1 Introduction The entire amount of water that is diverted at the canal head regulator does not reach at the field for use of irrigation. Major amount of it is lost on way during its movement in the canal systems. During the passage of water from main canal to outlet at the head of the water course, water may be lost either by evaporation from the surface or by seepage through the peripheries of the channel. These losses are sometimes very high, and may go up to 50 % of the total water diverted into the main canal. Evaporation losses are low and may go to a maximum of about 7 percent of total losses. The major loss of water in the conveyance system is the seepage loss. Seepage loss depends on the channel geometry and evaporation loss is proportional to the area of free surface. In determining the designed channel capacity, a provision of these water losses must be made. The provision for the water lost in the watercourses and in the field however, already made in the outlet discharge factor, and hence no extra provision is made on that account. However, excluding the above two losses, there is operational loss which when added to the evaporation and seepage losses, the total losses goes up the maximum 50 percent level. The operational loss includes spillage, over-toping, leakage through rodent holes, dead storage, initial infiltration and evapotranspiration from the vegetation along the watercourse. Evaporation and seepage losses of the canals are discussed below.

8.1 Introduction For maximization of yield of crops, it is essential to provide irrigation to crops. When either the natural sources like rainfall, dew, snowfall and other forms of precipitation or when the capillary rise of groundwater is not sufficient to meet the crop water demand, then there is need to supply irrigation. This irrigation water is a precious resource and need to be used cautiously. There are three important things need to be understood for optimum utilization of irrigation water with basic purpose to maximize the yield and returns. 

9.1 Introduction After knowing when to irrigate and how much to irrigate, next important thing is how to irrigate the crop field. Methods of irrigation plays a very crucial role in deciding how to irrigate the crop fields since all the crops do not require same methods of irrigation. Depending on the sources of water available for irrigation, type of crop to be irrigated, quantity and quality of water to be applied and other economic considerations, methods of irrigation will vary. Irrigation water may be applied to the crops by flooding it on the field surfaces as surface irrigation, by applying it beneath the soil surface as sub irrigation, by spraying it under pressure as sprinkler or overhead irrigation or by applying it in drops around the root zone of the crop as trickle irrigation. The commonly used methods of irrigation are described in schematic diagram as follows

10.1 Application Efficiency and Irrigation Uniformity All irrigation systems have some non-uniformity. This non-uniformity influences yields and irrigation efficiency especially application efficiency. If the net amount of water applied during irrigation is the same as that required to fill the soil water deficit, then because the distribution of water is never perfect, half of the field will receive too much water while the other half will receive too less water. In such a context, a farmer will try to apply more irrigation water to his field so that a larger fraction of the field has an adequate amount. This will tend to have higher percolation and runoff and thereby declining the application efficiency. An alternative to adding extra water is to improve the uniformity of water application. A major advantage when the uniformity is improved is that the amount of deficit in the area under irrigation is reduced and the potential for water logging and salinization is also reduced.

11.1 Performance of Farm Irrigation Systems The performance of farm irrigation systems is determined by the efficiency with which water is delivered to the field and utilized to the fullest amount possible with minimum losses due to seepage and percolation, runoff, evaporation and other operational losses. The efficiency of the irrigation system will increase if the conveyance losses, application losses and other losses are reduced to a great extent. 11.1.1 Overall Efficiency The overall efficiency of a farm irrigation system is defined as the percent of water applied to the farm that is used for irrigation on the farm. Irrigation efficiency otherwise called as overall system efficiency is defined.

Q. 1. Which of the following countries has the highest per capita water availability. India USA China Pakistan Q. 2. Total cultivated area in India is 328 M ha 188 Mha 142 M ha 305 M ha