Preface This is a text book for agriculture and agricultural 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, mathematics, hydrologic and hydraulics to the state-of-the-art irrigation system design and management. Since major and medium irrigation projects are too costly and at the same time are not ecofriendly, the major thrust of research is now being imparted on low cost and easy to construct farm irrigation structures. The primary aim of the book is to design an optimum size small scale water harvesting structure which is the farm pond mostly used by the farmers in the farms. My goal 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 agriculture and agricultural engineering but also to all the practicing engineers, agriculturists, soil conservationists and agricultural extension workers who deal directly or indirectly with water management and other associated farm development works. However, the book cannot be used for design of complex hydraulic structures including dams and reservoirs. The book contains 23 solved problems, 238 short and long type questions, 42 tables, 55 figures and more than 138 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 12 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 Farm Pond Irrigation and Rainfed Agriculture. This chapter deals with the different advantages of irrigation including its effect on enhancing the agricultural production and productivity. It also gives an overview of different disadvantages of irrigation including large investments incurred on irrigation sectors (particularly on major and medium projects), and the mismatch between the irrigation potential created and actually used. The present scenario of crop production under the rainfed ecosystem with constraints is discussed in brief. The scope of augmenting the production through rainwater harvesting in farm ponds in rainfed ecosystems are also discussed in this chapter. Chapter 2 Types of Farm Ponds. The different classifications of farm ponds based on shape and size, method of construction and suitability to topographic situations are explained in this chapter. Lined and unlined ponds as well as shallow and deep farm ponds are also constructed in the farms and are presented in this chapter. The chapter also discusses the characteristic features of ponds suiting to local landscapes like sunken, barrage and diversion ponds. Finally the mode of selection of a particular type of pond in a farm is presented. Chapter 3 Location and Site Selection. It is very important to locate a suitable site for construction of farm pond. The criteria for selection of suitable site are discussed. The runoff generating capacity of the catchment in which the pond is located for construction and the factors affecting the runoff of the catchment are also discussed in this chapter. Chapter 4 Water Supply to Farm Pond. The two main sources of water supply to farm ponds are in-situ rainwater falling over the pond and runoff of the catchment entering the pond. The different climatic and physiographic factors influencing runoff of the catchment are discussed in this chapter. Runoff estimation by runoff coefficient, runoff percentage, Barlow's percentage, Stranges tables and curves, synthetic unit hydrograph method as well as rainfall-runoff modeling techniques are discussed. Methods to compute the runoff rate including rational and S.C.S. Curve Number method are also presented. Chapter 5 Water Demand from Farm Pond. Harvested water of the farm pond is mostly used to meet the irrigation demand of the crops grown in the command area of the pond. Irrigation demand of the crops is dependent on the water requirement or crop evapotranspiration. Estimation of crop evapotranspiration by lysimeter study, field experimental plots, soil moisture depletion studies and water balance method has been discussed in this chapter. Climatological approaches for the estimation of reference evapotranspiration including the practical based pan evaporation method are also presented. Methods to estimate the actual crop evapotranspiration by selection of appropriate crop coefficient is also included in this chapter. Chapter 6 Dimensions of Farm Pond: In this chapter, computations of various dimensions of farm pond like depth and side slope of the pond as well as various dimensions at the bottom, ground and top level have been presented. Design capacity/storage capacity of dugout and embankment farm pond has been set forth. Methods to find out the top water surface/water spread area and wetted surface area of farm pond has also been included. The chapter also includes a nomograph relating the depth, storage volume, top water surface area and wetted surface area for various sizes of farm ponds which will be helpful in computation of evaporation and seepage losses in farm pond. Chapter 7 Optimum Size of Farm Pond. Description of different models including the water balance model of rice and dry land crop, water balance model of farm pond and irrigation management practices to simulate the size of farm pond have been included in this chapter. User friendly software developed by using Visual Basic 6.0 program has been presented to simulate the size of the farm pond for various types of cropping systems, irrigation management practices, types of soil and climatic conditions. A flow chart for simulation of pond size for rice-mustard cropping system has also been presented. Chapter 8 Construction of Farm Pond. Methodology for the construction of farm pond, design of spillway with inlet and outlet structures, design of grassed waterways for safe disposal of excess water from the pond, design of earthen embankment including different cross sections are the main parts of this chapter. The seepage flow analysis through the earthen embankment has been included and procedures for the stability of embankment have been discussed. Chapter 9 Losses of Water in Farm Pond. The two major losses of water in farm pond i.e. evaporation and seepage are discussed in this chapter. Various methods to compute the evaporation of farm pond including water budget, energy budget, mass transfer, empirical and pan evaporation methods are included. Techniques to reduce evaporation and seepage losses in farm pond are presented. Discussions on various sealants and their cost effectiveness are set forth. The chapter also includes siltation of farm pond and methods to reduce it. Chapter 10 Efficient Use of Harvested Water of Farm Pond. This is the main chapter of the book. Several methods for quantifying irrigation requirements and schedules are presented. Techniques to decide the timing of irrigation to crops are discussed. Methods of irrigation and irrigation water measurement also form parts of the chapter. Different water lifting devices including indigenous methods and pumps are presented. Methods to increase the water productivity including land levelling and land grading are put forth. Results of water productivity of some field investigations are presented. Study of performance of farm irrigation system has also been included in this chapter. Chapter 11 Economics of Farm Pond Irrigation System. This chapter, contains methods to compute the initial investment and annual operating cost of farm pond irrigation system. Economic analysis by present worth technique is discussed and procedures to estimate the economic parameters are covered. Results of economic analysis of some field studies are also presented. Chapter 12 Farm Pond Maintenance. Maintenance of the farm pond against silting, control of aquatic weeds, maintenance of spillways and embankment of pond, reduction of pond bank erosion and cares to be taken while lining the farm ponds are discussed in this chapter. Chapter 13 Other Sources of Irrigation. Canal Irrigation, Well Irrigation, Lift Irrigation, Pitcher Irrigation are discussed in this chapter.

1.1 Introduction Water is the basis of all forms of life. It supports life system not only to the plants but also to all other animals. The embryo from the conception till birth floats in the liquid medium. Cell, the basic unit of life, contains as high as 95- 98% water. Cellular metabolism is controlled by content of water. 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. 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 the effective root zone of the crop and management practice followed in crop cultivation. The pulses, oilseeds, vegetables 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 and banana. 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. The residual soil moisture 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 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 is called as irrigation.

2.1 Introduction Farm ponds are the most commonly used source of ex-situ water harvesting structures. It has wide adaptability in farmers’ fields and used as handy source for water supply to crop fields. It has been used since time immemorial not only as an assured source of water supply to crops but also to meet demands in other sectors. However, these ponds have wide variations in shape and size as per the method of construction and their suitability for different topographic conditions. Most of the ponds, initially constructed in fields have regular shape. However, as time progresses and because of the poor or no repair and maintenance, these ponds loose their regular shape and become irregular.

3.1 Introduction Different types of farm ponds with their characteristics features are discussed in this Chapter. It is observed that farm ponds can be constructed at different sites starting from the plain areas with relatively flat slopes to valley terrain having steep slopes. The choice of a particular type of pond largely depends on the kind of water supply available and on the existing topography of the site selected. In general for valleys with bottom width less than 100 m, barrage ponds may work well whereas valleys with bottom width more than 100 m, diversion ponds find suitable. 3.2 Collection of Basic Information Basic information on different data relating to the soil, climate, plant, topography, groundwater table, catchment characteristics, and livestock populations are to be collected for the area where pond has to be constructed. Estimation of water supply from different sources and water demand form the pond for various purposes are to be done and a pond water balance study needs to be done before designing a pond in a particular place.

4.1 Introduction A farm pond is basically small scale water harvesting and water recycling structure. It harvests water mainly in the rainy season when there is abundant rainfall producing sufficient runoff and the harvested water may be used for single or multiple cropping. When there is deficient supply of water to the crops it may supplement as supplemental irrigation. The leftover water in the pond can be used for growing another crop in winter when there is no or less rainfall. Ij addition, the stored water in the pond can be used for domestic and other uses and rearing fish. Thus it serves as viable medium for integrated farming system in rainfed farming ecosystem. Before designing a pond in a given location, it is very important to estimate the total quantity of water supply to the pond. The two main sources of water supply to pond are (i) in situ rainfall and (ii) runoff (some times called as discharge) generated from the catchment and conveyed to the pond. Some times there is groundwater contribution to the pond when the pond is unlined and the underlying groundwater table with reference to the ground level is at lower elevation than the depth of water in the pond such that there is a hydraulic gradient in the direction of underlying groundwater level to the water level in the pond.

5.1 Introduction A farm pond 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. It is no doubt a viable source for integrated farming system. In addition, the water of the pond can be used for domestic and to some extent for the industrial uses. It is also a good source for recreational use. Total water demand of the pond 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 pond, 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 pond, gives total irrigation demand of the pond. Farm ponds 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 pond is calculated. In addition to this, if the pond water is used for industrial, domestic and other sectoral purposes, then water used in all such sectors are to be added to irrigation and livestock demand to estimate the total water demand of the pond.

6.1 Introduction Farm ponds used in farmers’ fields are generally square shaped or rectangular shaped pyramidal structures. It has a regular side slope, depth, and top and bottom dimensions. It may be excavated/dugout pond or embankment pond. In excavated pond, the pond is constructed below the ground level. Water is collected in the pond by gravity from the adjacent catchment. In embankment type, the pond is partly above the ground and partly below. This type of pond has higher storage capacity than the dugout type pond. This type of pond has a berm and dyke/embankment around the pond. The embankment has some side slope. The pond has bottom dimensions, dimensions at the ground level as well as some dimensions at the top above the embankment. In this chapter, various dimensions of pond like depth, side slope of the pond, as well as the various dimensions at bottom, ground and top level will be discussed.

7.1 Introduction The practice of rainwater storage in the pond is quite common but still there is a need to improve its design. Most of the ponds used for rainwater storage are designed on thumb rule: either they are under or over designed. An over designed farm pond can meet the supplemental irrigation needs of the crop but it may not be economical. On the other hand, an under designed pond though economical, may not be able to meet the irrigation needs of the crops at all times. It is reported that in some case up to 20% of the farm area is used for construction of farm pond. These farm ponds are found not to be optimal. Although these ponds are able to meet the crop water demand at most of the stress periods, but considering the economics, they are observed not to be optimal. The big size farm ponds need large areas to be wasted for the digging of the structures. They need huge investment for their construction and lining. Hence, proper scientific studies are needed so that its storage becomes adequate to save the crops from the adverse effects of the drought in monsoon and to assure the possibility of growing a second crop in the winter and at the same time, it is economical also. Simulation studies by daily water balance models of both the crop field and the pond help to understand the availability of water in the pond to meet the supplemental irrigation demand of the crops.

8.1 Introduction After deciding the optimum size of farm pond and its dimensions, the next step begins the construction of farm pond. Further the site selection and location of the pond in the selected site to be finished before the construction of pond starts. The selection of site and location of farm pond areas have been discussed in Chapter 3. In this chapter, discussion on methodologies for construction of farm pond including spillways, inlet and outlet structures, design of grassed waterways and embankment have been presented. As a guiding principle, the construction of farm pond involves the following steps: 8.2 Site Clearing The area where the pond is to be constructed has to be inspected first. The site where pond has to be dug out should be cleared to an extent of about 10 m from all sides of top dimensions of the pond. All bushes, shrubs, stumps and other unwanted materials should be dug out and removed. If there are roots of plants, they should be uprooted. The land may be ploughed and harrowed, if necessary, to get a more or less even topography.

9.1 Introduction The water harvested in the farm pond is a very valuable commodity. Every care should be taken so that not a single drop is wasted. The two major forms of losses in farm pond are (i) evaporation losses and (ii) seepage losses. Evaporative water loss (Eloss) and losses due to seepage are the two vital natural outflow components of unlined farm ponds. Studies conducted byGuerra et al. (1990) and Pal et al. (1994) indicated that the seepage loss from unlined ponds amounts to 45-67 per cent whereas the Eloss constitutes 30 per cent of the total out flow from the system. Water losses by evaporation and seepage were 5.3 and 9 mm day-1, respectively amounting to 70% of total storage in the ponds (Syamsiah et al.1994). Estimate of evaporation across the country indicates that it is as high as 2000 mm in the semi-arid tropics. Annual average value of the evaporation loss varies from 1400 to 1800 mm across major parts of the country: the value being highest in west Rajasthan, parts of Saurasthtra and Tamilnadu and lowest in coastal Mysore, Bihar plateau and east M.P. Reliable statistics reveal that about 70 M ha m of water evaporates from the water bodies and land surfaces out of the total annual precipitation of about 400 M ha m received by the country. The total evaporation losses from the water surfaces are about 5 M ha m from the total storage of 15 M ha m in the reservoirs including ponds, lakes spread all over the country (Belgaumi et al.,1997). In this section, the methods to estimate the losses like seepage and evaporation and various techniques to control them are discussed.

10.1 Introduction Rainwater is the main source of water for agriculture but its current use efficiency for the crop production is low ranging between 30-45%. The rising demand for water for non-agricultural uses is proportionately decreasing its share for agricultural uses. Efficient methods of water harvesting in the farm reservoirs including farm ponds and its management for subsequent uses in agriculture with improved water use technologies are vital for increasing the productivity and reducing poverty in rainfed ecosystems. It is not to be forgotten that the harvested water in the pond is a very valuable commodity. It may be used for industrial use or for irrigation in agriculture. The harvested water is also a good source to meet the water demand of domestic animals and for human beings (Fig. 10.1). The stored water of the pond can be used for fish farming, tree plantation, intensive irrigation to small area and extensive supplemental irrigation to rainfed crops. Stored water in a pond is developed resource and is, therefore, more expensive than the natural resource. Hence, there is a need to utilize it judiciously and efficiently.

11.1 Introduction Economic analysis is the most important parameter for determining the optimum size of farm pond. It is, no doubt that a big size farm pond can meet the irrigation demand of the crops grown in the command areas in addition to meeting the other demand in the command areas. But a big size farm pond is an oversize structure which necessitates large investment to be incurred which may not be economically viable. On the other hand, a small size structure may not be able to meet the crop water demand and also other demands in the command areas and so is called as under-designed structure. It has been observed that as the size of the farm pond gradually increases from a certain minimum size, the total investment cost increases. At the same time, the benefits from the increasing storage capacity of the farm pond also get increased. In such cases, from a purely business point of view, the most economical capacity is that which provides the highest rate of return on investment. As the size of the farm pond increases, the proportion of the benefit/profit to the cost also increases from certain minimum size, attains maximum value at a particular size and then declines as the size further increases. This particular size of the farm pond at which the net profit is maximum, is called as the optimum size. It is to be noted that at the optimum size, the other economic indicators like the benefit-cost ratio and internal rate of return are also high. The variation of net profit with size of the farm pond is a concave curve. The size of the farm pond corresponding to the peak of the curve which represents the highest net profit is the optimum size of the pond. The principle of obtaining the optimum size of farm pond is to first assume a certain minimum size say five percent of the farm area and conduct the economic analysis by studying the costs and net profits of the assumed size. Then the size is gradually increased and the economic analysis is conducted for each increased size. Then a curve relating the size of the farm pond and net profit is drawn. Such a curve is generally concave shaped. The size of the structure corresponding to the maximum net profit gives the optimum size. It is to be noted that any size chosen more or less than the optimum size would give less net profit and benefit-cost ratio than that of the optimum size.

12.1 Introduction Farm ponds are used for multipurpose including as a viable source for supplemental irrigation to rainfed crops, a good place of entertainment, a vital place for wild life habitats, livestock and fish and aquatic plants. Like any other structure, the farm pond needs regular repair and maintenance for effective operation. The purpose of construction of the pond will be fruitful and the life span of the pond will be enhanced if proper care and maintenance are taken. In this chapter some salient discussions on care and maintenance of the pond are mentioned. 12.2 Maintenance Against Silting The farm ponds constructed in medium to deep black soils are subjected to getting silted up. Hence, periodic desilting to restore the original storage capacity is required. If the pond is used for supplemental irrigation to crops, then desilting may be done once in every 5 to 10 years depending on the amount of silt getting deposited in the pond. The breaches and rill formed in the spoil bank and shoulder bunds should be immediately repaired. The inlet and outlet structures should be maintained periodically. The silt deposited in the silt trap should be removed periodically. In areas where silt carried by the runoff is more, a vegetative filter near the inlet structure may be used. The pond may be desilted manually if it is small in size otherwise mechanical measures may be used to desilt. It is easy to desilt the pond when it is dry. A Simple and inexpensive method to desilt the pond is to stir the water of the pond and then allow the desilted water move away from the pond through the outlet (Belgaumi, et. al., 1997). Fig. 12.1shows a badly maintained pond with excess silting and weed infestation causing severe reduction of its storage capacity.

In addition to farm ponds, irrigation to crops can be met from other sources. The main sources can be broadly classified as: (i) Canal irrigation, (ii) Well Irrigation and (iii) Lift irrigation. In arid and semi arid areas, where availability of water is scarce, pitcher irrigation is practiced. These sources of irrigation are briefly mentioned as follows. 13.1 Canal Irrigation To feed the world population of 8 billion in 2025 AD, it is necessary to bring more area under irrigation because irrigated farms typically get higher yield under provision of irrigation. The food production will have to increase by about 50 percent to feed some two billion more people by 2025 AD, and a large part of that increase needs to come from irrigated agriculture. It is reported that the yield of different crops are generally 2-3 times higher than the crops grown under rainfed conditions. Furthermore, it is possible to raise 2-3 crops round the year under irrigated agriculture whereas hardly a single crop is successfully grown in a year under rainfed condition. It is reported that about 40% of the world’s food production comes from only 17% of the irrigated land of the world (Sivanappan, 2000). Everybody is aware of the fact how the irrigation played a crucial role to make the Green Revolution in India successful. A major part of irrigation is achieved by canal irrigation through different irrigation schemes. A project that makes use of weir or a barrage for providing irrigation to fields is called as direct irrigation scheme. On the other hand, a storage irrigation scheme 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 including 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. These canals have to be aligned and excavated either in alluvial soils or non-alluvial soils; depending upon which they are called alluvial canal or non-alluvial canal.

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