Preface   This is a text book for Agriculture and Agricultural and Civil Engineers and will be very much helpful for the beginning students in irrigation. It is designed to guide students from a basic knowledge of soil, water and plant, hydrologic and hydraulics to the state-of-the-art of irrigation system design and management. The goal of the author is to present the principles and concepts of farm irrigation in a simple manner to maximize the students learning, understanding and motivation. The method and order of presentation have been carefully developed and classroom tested to make this book a useful and effective teaching tool. The book will not only be a helping tool to the students and teachers in Agricultural and Civil Engineering but also to all the practicing irrigation engineers, agriculturists, soil conservationists and agricultural extension workers who deal directly or indirectly with water management and other associated farm development works. The book is written covering syllabus of irrigation engineering which is taught in different State Agricultural Universities as well as in the department of Civil Engineering of different Engineering colleges. However, the design of complex hydraulic structures including dams and reservoirs are beyond the scope of this book. The book contains 95 solved problems, 638 short and long type questions, 95 tables, 188 figures and more than 180 references which will be immensely helpful to the students and design engineers. Several field experimental results have also been incorporated in the book at appropriate sections to make the book interesting for the readers. The book contains 16 chapters and each chapter contains several sections and sub-sections. The title of the various chapters and the contents of each chapter are as follows. Chapter 1: Irrigation and Water Resources Development in India: This chapter deals with necessities, advantages and disadvantages of irrigation on crop production and productivity and on environment. It also gives an overview of large scale investment incurred on irrigation sector and the mismatch between the irrigation potential created and that utilised in different places in the country in different plan periods. Irrigation development in pre-plan, plan and post-plan periods are briefly mentioned in this chapter. Scope and various techniques of augmentation of water resources are also discussed in this chapter. Chapter 2: Sources of Irrigation Water: Chapter two deals with hydrologic cycle and different components of hydrologic cycle including rainfall, its measurement and computation of average depth of rainfall by various methods. Runoff is a major part of hydrologic cycle which has been discussed here. Factors affecting runoff, estimation of runoff by different methods, estimation of peak runoff rate by rational and S.C.S. Curve Number method are also presented in this chapter. Chapter 3: Storage of Irrigation Water: Dams and reservoirs form major storage for irrigation water. Selections of dam site with different surveys are required for construction of the dam and reservoir. All these aspects have been covered in this chapter. Further, the chapter includes area-capacity determination of the reservoir, different storage zones of the reservoir, design capacity of the reservoir including mass curve method and procedures for estimation of seepage and evaporation loss of water in the reservoir including the means to reduce these losses. Finally sedimentation of reservoir including factors affecting sedimentation and various preventive and curative measures required for reducing reservoir sedimentation are all presented in this chapter.

1.1 Introduction Like animals, plants are living beings and so require water and air for their survival. In addition, they need water for preparation of 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. This results in reduction of yield of the crops. The reduction in yield depends on the amount of scarcity of water requirement of the crops. It also depends on the stage of crop growth and also depends on the types of the crops. Generally all the crops are sensitive to water stress during reproductive stage. 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 pulses, oilseeds, vegetables etc. which are also otherwise termed as dry land crops need less water compared to rice which is a water loving crops and perennial crops like sugarcane, banana 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.

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 under ground 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.

3.1 Introduction Water used for irrigation can be stored mainly in three sources i.e. soil reservoir, surface reservoir or groundwater reservoir. Accordingly the storage system can be defined as soil reservoir storage system, surface reservoir storage system or groundwater storage system. Each of these storage systems has its own merit and demerit. Some of the storage systems though economical but are not helpful to store the irrigation water for longer periods. On the other hand, some other storage systems are very costly, but the irrigation water can be stored there for a longer period. However, before adopting a particular storage system, economics of the system need to be calculated. The cost of installation of the system and the water stored in the storage system and its use as supplemental irrigation to the crops to increase the production in terms of monetary benefit need to be assessed and then the economics of the system should be computed. The storage system that gives maximum benefit-cost ratio and net present value should be adopted for storage of irrigation water. The different types of storage systems are discussed below.

4.1 Introduction Discharge 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. If a stage-discharge (also called as gauge-discharge) relationship for a particular gauging site is developed, then daily measurement of discharge in the gauging site is not required. Discharge can be estimated from the developed relationship of discharge versus stage if the measurement of stage is known.

5.1 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. Small farm reservoirs are normally used for irrigation to crops as well as to meet the live stock water demand. Normally the large live stocks like horse, cattle require 20 thousand litres of water per head per year whereas the small live stocks like sheep, goat, pigs require 2 thousand litres of water per head per year. Adding the irrigation demand to the livestock demand, total water requirement of the reservoir is calculated. In addition to this, water used for industrial, domestic and other sectoral purposes are to be added to irrigation and livestock demand to estimate the total water demand of the reservoir.

6.1 Soil 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. 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.

7.1 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. These three things are: (i) When to irrigate? (ii) How much to irrigate? and (iii) How to irrigate? In fact these three things form the core concept of irrigation scheduling.

8.1 Introduction After knowing when to irrigate and how much to irrigate, next important thing is how to irrigate the crop field. Methods of irrigation play 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 subirrigation, 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:

9.1 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.

10.1 Introduction Irrigation is an age old practice. It has been practiced for thousands of years. It is chiefly used to irrigate rice in wetter areas; especially in Asian countries and dry land crops including vegetables and fruits in dry land areas having low rainfall in all most all countries. Devices for irrigation water lifting range from age old indigenous water lifts to highly efficient pump. Unlike canal irrigation where water is fed to the fields through gravity system, water from the surface and sub-surface sources is lifted either mechanically by pump or manually by any indigenous lifting devices. Irrigation by lifting water from a lower level to a higher level is called as lift irrigation. Several types of indigenous water lifting devices are in vogue in India since ancient times. These are animal or/and manually operated ones, the animal operated ones being more efficient than the manually operated ones. The earliest water lifts were simple man-powered devices, many of which are still being used with modifications in different forms. With gradual improvement, principles of simple machines, like the liver, pulley, screw etc. were employed in smooth lifting of water from surface and sub-surface sources. The selection of a suitable water lifting device for a particular situation depends on the following factors: (i) Characteristics of source of water and the lifting device (ii) Amount of water to be lifted (iii) Depth of water table (iv) Type and amount of power available and (v) Economic status of the farmers.

11.1 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.

12.1 Introduction Rainfall is the major source of water that contributes lion’s share for irrigation to crops. Before it reaches the earth, it is to a great extent pure in nature. By the time it falls on the ground surface, it comes in contact with various types of gases and suspended materials of the atmosphere and also after it flows as runoff on the surface it gets dissolved with many types of salts, impurities etc. that render the water to be impure. Many a time the industrial waste, agricultural wastes, pesticides, fungicides, chemical fertilizers etc. get mixed with water and make it unsuitable for irrigation use. Water being a universal solvent, it dissolves all most all organic impurities, salts etc. which makes it objectionable for both domestic and agricultural uses. Irrigated agriculture is dependent on an adequate water supply of usable quality. In the past, water quality concerns were neglected because good quality water supplies were plentiful and readily available. This situation is now changing in many areas. Especially, in the arid and semi-arid zones, water quality is fast deteriorating which is posing threat to irrigated agriculture. Conceptually, water quality refers to the characteristics of a water supply that will influence its suitability for a specific use. On the other hand, it refers to the situation of how well the quality meets the needs of the user. There are three quality indicators. They are physical, chemical and biological indicators. Even a personal preference such as taste is a simple evaluation of acceptability. For example, if two drinking waters of equally good quality are available, people may express a preference for one supply rather than the other; the better tasting water becomes the preferred supply. In irrigated agriculture, emphasis is placed on the chemical and physical indicators of the water and rarely the biological indicator is considered important.

13.1 Introduction In agricultural lands, when the pores of the soil within the root zone of the crop get saturated with the subsoil water due to infiltration of high rainfall, excess irrigation or heavy seepage loss in the unlined canal systems, the air circulation within the soil pores get totally stopped. This phenomenon is called as waterlogging. In canal commands where there is continuous flow of water in the canals and canals are mostly unlined, there is heavy loss of seepage which raises the ground water table. This raising water table sometimes comes up to the ground surface which impedes surface drainage. By capillary action, under ground water rises to the crop root zone and submerges the roots of the crops for most of the time. This situation is called as waterlogging which creates salinisation and alkalinisation problems affecting the plant growth. The height to which soil water rises above the water table by capillary action is called as capillary fringe. Generally, the height of the capillary fringe varies from 1 to 1.5 m. When the water table comes to 1.5 m below the surface of the soil, the land is said to be waterlogged. At times, due to poor drainage conditions, surface water cannot be freely drained out. The stagnate water in these low lying areas also causes waterlogging which enhances the weed growth consequently affecting the crop yield.

14.1 Introduction Groundwater is an important source of water for irrigation. It is the most abundant fresh water resource of the earth. Underground water reservoirs contain large stock of fresh water resources. Total quantity of groundwater within 800 m distance below the ground surface is more than 30 times the total water in all fresh water lakes, more than 60 times the total water in soil and other unsaturated rock materials, more than 300 times the water vapour in the atmosphere and 3000 times the average volume of all rivers and rivulets in the world (Lenka, 2001). But the distribution of groundwater is not uniform. At some places, it lies below a few metres whereas at other places, it is a thousand metres or more below the ground surface. In some places, there is abundant groundwater potential whereas at other places there is meager potential. Groundwater is the water reaching the groundwater reservoir from the infiltrated water of precipitation which constitutes an important component of the hydrologic cycle. It is only the part of the subterranean water that occurs in the saturated pores of the containing rock materials underlain by water held in a zone of aeration. It should not be confused that all the water present in soil below the ground surface is groundwater.

15.1 Introduction The laws governing the flow of water in wells are referred to as the hydraulics of wells. Just like surface water flows from a higher elevation to a lower elevation by gravity, groundwater also flows from a region of higher water table to a region of lower water table. This difference of water table measured by any two piezometers divided by the longitudinal distance between them is called as hydraulic gradient. Hydraulic gradient plays a dominant role in deciding the flow of groundwater. This hydraulic gradient together with the hydraulic conductivity of the aquifer material forms the main law of well hydraulics called as Darcy’s law. An understanding of Darcy’s law together with some other laws as discussed subsequently in this chapter is essential in order to know the discharge of a well in a particular formation. Darcy’s law is valid for studying groundwater flow in alluvial formations. However, it is not valid for aquifers having hard rock areas.

16.1 Introduction Producing more crops, livestock, fish and forest products per unit of water use is an essence of water productivity and is highly essential for both food and environmental security. A variety of options exist for improving the productivity of water in agriculture through breeding, better management practices and supporting policies and institutions. It is imperative to identify a range of means to enhance water productivity in agriculture, assess their potential and the consequences of their adoption. The production systems to be considered can vary from purely rainfed to irrigated, and from dry zones to semi-humid monsoonal areas. The productivity of water used in agriculture has almost doubled during 1961 to 2001, It is mainly due to increases in crop yields. Irrigated rice yields doubled and rain-fed wheat yields rose by 160% in that period, with little variation in water consumption per kilo of output. Globally, FAO estimates that water needs for food per capita halved from about 6 m3/day to less than 3 m3/day during 1961 to 2001 which is a significant saving and an equally significant gain for other water users. According to an estimate, a 1% increase in water productivity in food production enables to save about 24 lit/day of water per head of population, while a 10% increase would equal current domestic water consumption. Importance of saving water in agriculture can be realised from the above observation.

Index A Absorption 379 Accumulated 60 Accumulated infiltration 200, 224 Acetylene gas 151 Acidic water 526 Acidifiers 417 Acidity 475 Actual crop evapotranspiration 127, 132 Actual evapotranspiration 126, 181, 578 Additive model 166 Advancing front 194 Advection 127 Aeration 443, 449 Aerobic rice 575, 576 Aerodynamic method 112 Air compressor 524 Air diffuser 360 Air lift pump 360, 523 Air pipe 360 Air release valve 249 Air release vents 310 Air vents 90, 312 Air vessel 343 Albedo 117 Alcohol method 148 Alkaline 108, 404, 407, 417, 422 Alkalinity 165, 383, 406, 409, 466, 475 Alternate furrow 219 Amendment 415, 417, 429 Animal power 330 Animal powered water lifts 338 Annual benefit 387