Preface This book Irrigation & Agricultural Drainage Engineering is intended as a text book in the area of irrigation and drainage for the students of agricultural engineering in particular and agricultural science in general. However, this book also may be useful for agricultural extension workers and the professional working in this area. Irrigation and drainage is a vast area. It is not possible to include everything of it in a book. Drip and sprinkler are the most important and advanced methods of irrigation. It deserves more detail discussion. These are being tried in separate book. The contents of the book may enable one to acquire some basic requirements which an irrigation and drainage manager must have. The contents include basics along with some information toward research achievements, importance and usefulness so that the students get interested to the subject and at the same time help them to attend the institutional and competitive examinations. The book contains good numbers of numerical as example and task to get the students familiar to the requirements, complicacies, and possible remedies in actual working condition. Excepting the traditional broad and short questions, multiple choice questions are also set in every chapter to assist the students in successful preparation for the entrance examinations in PG programs and the competitive examinations like State and Union PSC, etc. The author is thankful to Indian Council of Agricultural Research (ICAR), Ministry of Agriculture, Govt. of India and Indian National Committee for Irrigation and Drainage (INCID), Ministry of Water Resources, Govt. of India for financial support in conducting research works, the outcome which are found relevant have been included in this book. The author gratefully acknowledges the support of Bidhan Chandra Krishi Viswavidyalaya and my esteemed colleagues in this university who are the basis of everything in preparation of this book. I would acknowledge the great contribution of Dr. A. K. Bhattacharya, erstwhile eminent Scientist and Teacher, IARI, New Delhi. The touch of his personality and knowledge and recognition I enjoyed during the research work conducted under his guidance funded by ICAR and the complimentary offer of his book ‘LAND DRAINAGE-Principles, Methods and Applications’ inspired me a lot to put the best effort to academics and research. In this opportunity I would like to mention my students over the years that I have come across; their respect and thankfulness, their curiosity and originality in ideas has encouraged me to go ahead. I will feel rewarded if this endeavor can help them in anyway. Every effort is made to acknowledge the sources of information in the text. If any omission remains, it is inadvertent, and will be corrected if noted or pointed out. I would like to thank New India Publishing Agency, New Delhi for the support of publication of this book.

1. 1 Introduction Irrigation is the artificial application of water needed to the crop field. It is the process of uniformly wetting the root zone depth. The wetting may be done over the land surface or below of it. The application of water in excess to the requirement or accumulation of water in crop field due to rain or unplanned seepage is not considered as irrigation. However, irrigation is supplemental to rainfall. Irrigation water is considered as single most important inputs for crop production.

Measurement of water used in irrigation ensures the application of required amount of water in crops. Knowing the rate of flow the adjustment to period of control at gates, etc. can be done to regulate the water at different branches of canals. To get the total control over the supply of water there should have the provision of water measurement at the critical points in irrigation systems. Units of Measurement Water is measured at rest or in motion. The water of reservoir, ponds, tanks, etc. at rest is measured in volumetric unit as liter, cubic meter, hectare-meter and hectare-centimeter. Water flowing in rivers, canals, channel, etc. is measured in liter/s, liter per hour, meter per second and hectare-meter per hour or day.

3. 1 Introduction Irrigation efficiency evaluates how effectively the water has been distributed for the purpose of crop production. Water is conveyed to crop field through canal water courses and channels. During this process considerable amounts of water get lost through run off, deep percolation, evaporation, etc. The losses of water greatly depend on the skill of the irrigator, degree of land preparation, and design and planning of the system. The extent of water losses starting to diversion of water from its source to crop field though conveyance and ultimate application and distribution of water in crop field which can be estimated separately. The estimation of these efficiencies enables one to identify the step(s) where improvement is required. The method of measurement and evaluation for its efficiency is prerequisite for proper use of water. Irrigation efficiency in developing countries in general is poor particularly in gravity irrigation methods. However, water is become more and more scarce. Due to pressing need of it judicious and efficient management is one of the vital issues to be solved on priority basis.

Scheduling irrigation is the process of determining when to irrigate and how much to irrigate. Selecting the appropriate time span in between two irrigation and applying the required volume of water in each irrigation, ensures saving of water, minimize energy use, higher crop yield and lower production costs. Irrigation applied earlier than due date causes loss of water through evaporation or deep percolation and later causes water stress to plants and thereby affects the growth and yield of the plants. Scheduling of irrigation may be required in two field conditions: (i) when availability of water is adequate, (ii) when availability of water is limited. In the places where water is adequate scheduling of irrigation follows full irrigation with time sequence of minimum number of irrigation to ensure maximum yield and high water use efficiency. When water is limited its use is rationalized by using at the sensitive stages of the plants and withholding irrigation at other stages. The sensitive stages so selected that by using the available water provides possible maximum yield.

5. 1 Irrigation Channels Canal or channel is an artificially made conduit through which water is supplied to the field from river, tank, reservoir or wells. The open channel is the most common type of water conveyance system. If the pipes and drains are partially full behave like open channel. The irrigation channel may be lined or unlined and the flow is either uniform or varied. The canal may be classified in following ways. (a) Classification based on the source of supply (i) Permanent or perennial canal (ii) Inundation canal

The plants collect water by its root system available in the soil medium. A soil rich in nutrients cannot ensure success of crops unless the presence of satisfactory state of water and air, mechanical attributes and thermal regime. The physical properties of soil and plants greatly influence the movement, retention and use of water. The soil should provide sufficient pore spaces and size distribution and decomposition of rocks and for the movement and retention of water for plant needs. Rainwater, irrigation, groundwater, seepage, etc. , contribute in replenishing the water in dried up soils. In all the cases thorough understanding of behavior of water is required to ensure the need of water to plants and optimize the use of irrigation water.

7. 1 General The major portion of water in a crop field gets lost through evaporation and transpiration. Evaporation is the process by which water is changed from the liquid state to vapor state. It takes place from the adjacent soil, water surface or from the surfaces of leaves of the plants. Transpiration is the removal of water vapour through plant body. Evapotranspiration (ET) is the sum of evaporation and transpiration. The process of evaporation and transpiration goes on simultaneously and difficult to separate them in a crop field. The term consumptive use is used to refer evapotranspiration together with the water used in the metabolic activities of the crop plants. The actual amount of water used in metabolic activities is insignificant (less then 1% to ET). Therefore, the consumptive use and evapotranspiration are often used as synonymous term. It includes the water consumed by the plants for metabolic activities or transpiration plus the water evaporated from the land and water surfaces of the cropped area. The factors affecting the rate of evaporation are the vapour pressure at the water surface and air above, air and water temperatures, wind speed, atmosphere pressure and size of the water body. Other factors remaining same, the rate of evaporation increases with an increase in the water temperature. Higher wind velocity causes greater scope for evaporation. Decrease in atmospheric pressure increases evaporation. The solute dissolved in water causes reduction in the rate of evaporation than that of pure water. The evaporation from soil surface occurs in same way to free water surface when the soil particles are surrounded by thin film of water and pore spaces are partially filled. However, in such situation greater resistance has to overcome for evaporation from the soil particles than while evaporating from a free water surface. The evaporation process practically stops when the moisture content in soil goes below a threshold value.

8. 1 Introduction Water is a precious commodity. Necessity of conservation of water supply is increasingly felt all over the world as the demand of it continues to increase when the sources of supply are increasingly scarce. The conveyance and proportional distribution of water is one of the most important part of any irrigation project. Water available in the stream, reservoirs or wells is carried to the field of use through canals. The economy of any irrigation project largely depends on how efficiently the water is being transported and distributed in respect to water losses and cost. Water losses in irrigation channels are mainly due to evaporation from the water surface and seepage from the bed and side of the channels. Seepage losses some time become the single important factor which causes unavailability of water particularly in downstream of the channel in canal irrigation system and excess pumping of water in tube wells and river lift irrigation system. Lining irrigation channels means to cover the channel earthen surface by any substance, which can considerably reduce the seepage loss. The concrete, brick, stone, natural clay of low permeability, bituminous material, plastic compounds, etc. , are used for channel lining.

Poor quality of water is one of the important factors causes gradual accumulation of salts on the ground or in the root zone of crops leads to saline and alkaline condition. This results in loss of permeability, toxicity and anaerobic conditions. In salt affected soils plants face constraint to derive their nutrients at the required rate due to high soil moisture tension, which affects adversely the crop growth and productivity.

10. 1 Land and Water Resource India has got the world’s 2. 45% area and 16. 87% of population with only the 4% of available fresh water (Table 10. 1). This indicates the necessity of development of water resources and optimal use of it. India at macro level does not have short of water. But the shortage of water is due if not properly managed by conservation and sector wise utilization.

11. 1 Introduction Agricultural drainage is the removal of excess water from the farmland for the purpose of providing favorable soil air environment for plant growth. Removal of water may take place form the surface or below the surface of the land. The practice of lowering ground water table below the root zone depth to improve the plant growth or to reduce the accumulation of salts in soil is also called as drainage. Drainage system is broadly classified as surface and subsurface drainage. Removal of excess water over the land surface is known as surface drainage and that of removing water below the surface is known as subsurface drainage. The flow of water in the form of evaporation or evapotranspiration also play important role in improving drainage situation. It gives the idea of the time required to get the wetland workable though it is not called a type of drainage as because this is very slow process and cannot be controlled by the human activities. However, using of certain tree plants e. g. , Eucalytus, Poplar, Casurina or similar species in wet fields, which transpires at high rate and improves the drainage problem by lowering the shallow water table is the new idea known as bio-drainage.

The purpose of a sub-surface drainage system is to lower the ground water table and removal of salts beyond the crop root zone. The ground water table may rise due to commonly practiced flood irrigation method, seepage from unlined channels, percolation of rain and runoff water and sub-surface flow from higher areas. Sub-surface drainage consists of drains laid at a specified depth, spacing and grade below the ground surface. The size, spacing and depth of drains depend largely on the soil-water properties viz. , infiltration, saturated hydraulic conductivity, drainable porosity; and the requirement of removal of water through drains in certain time period fixed on the basis of rainfall and crop cultivated. The drains are usually placed in a pervious stratum. Suitable filter of coarse sand and gravel may be used when it is placed in a low permeable stratum. Sub-surface drainage serves the important job of removal of concentrated salt solution from the crop root zone particularly in arid and semi-arid region.