Introduction Irrigation Engineering

IRRIGATION ENGINEERING INTRODUCTION

Course Goals This course has two specific goals: (i) To introduce students to basic concepts of soil, water, plants, their interactions, as well as irrigation and drainage systems design, planning and management. (ii) To develop analytical skills relevant to the areas mentioned in (i) above, particularly the design of irrigation and drainage projects.

Course Outline • Basic Soil-Water Relations. • Irrigation Water Requirements, • Sources, quantity and quality of irrigation water: • Methods in Irrigation • Design of irrigation systems and structures.

Course Objectives On Completion of this course, students should be able to: (i) Understand the basic soil-plant-water parameters related to irrigation (ii)

Understand how to estimate the quantity of water required by crops.

(iii)

Be able to plan and design irrigation structures.

(iv)

Design channels and other irrigation structures required for irrigation, soil conservation, flood control and other watermanagement projects.

SYLLABUS Introduction Definition. Necessity of irrigation. Planning of irrigation projects. Scope of irrigation engineering. Benefits and ill effects of irrigation. Soil-Water Crop Relationship Soil and its physical and chemical properties. Root zone soil water. Crops of Pakistan and crop rotation. Methods of Irrigation Irrigation methods. Factors affecting irrigation methods. Surface methods. Sprinkler irrigation method and Sub-surface irrigation methods. Water Requirement of Crops Functions of irrigation water. Preparation of Irrigation land. Crop base period. Commanded areas. Intensity of irrigation. Duty and Delta of crop. Relationship between duty and delta. Factors on which duty depends, depth and frequencies of irrigation. Kharif-Rabi ratio, Optimization of irrigation water. Uniformity coefficient. Consumptive use of water. Estimation of consumptive use. Irrigation efficiencies. Net irrigation requirements.

Canal Irrigation System Alluvial and Non-alluvial canals. Alignment of canals. Distribution system for canal irrigation: basic definitions, determination of canal capacity, canal losses, empirical formula for channel losses and channel section for minimum seepage loss. Design of Irrigation Channels Design of stable channel. Regime channels. Kennedy's theory. Critical velocity ratio. Kutter's formula. Manning's formula. Lacey's theory. Design procedure for Lacey's theory. Estimation of transported sediment. Bed load equation. Meyer-Peter's and Einstein's formula. Design procedure for irrigation channel and maintenance of irrigation canals. Diversion Head Works Difference between a Weir and Barrage, layout of diversion head works. Diversion weir, types and components of diversion weir. Head regulator and cross regulator, canal regulation and silt control at the head works. Irrigation Outlets Definition. Essential requirements of an outlet. Types of outlets. Characteristics of outlets and description of each type of outlet.

Theories of Seepage and Design of Weir and Barrage Causes of failure by piping and direct uplift, safety against piping and uplift, Khosla's theory and concept of flow net, stream lines and equipotential lines, critical gradient, Khosla's method of independent variablies for determination of pressure and exit gradient below a weir or barrage, Khosla's simple standard profiles. Design examples of barrage, head regulator, cross regulator. River training works: Methods to control bank erosion Reservoir Planning and Dams in General Types of reservoirs, flood control reservoir, multipurpose reservoir. capacity of reservoirs. Storage zones of reservoirs. Reservoir yield. Distribution reservoir, Estimation of demands and optimal reservoir operation. Flood routing or flood adsorption, reservoir sedimentation, silt control in reservoir. Selection of suitable site for reservoir. Economic height of dam. Economics of combined project, cost benefit consideration and general principle of optimizing capital budget, various types of dam problems in dam construction. Factors governing the selection of particular type of dam, selection of darn site and environ mental impacts assessment of dams. Environmental Impact of Irrigation Engineering/Sea Water Intrusion Introduction to Related Soft wares

Books Recommended Irrigation Engineering and Hydraulic Structures Santosh Kumar Garg 12th edition or latest Khanna Publishers Irrigation and Water Power Engineering Dr. B. C. Punmia and Pande B. B. Lal 7th edition Standard Publishers, Delhi Irrigation and Hydraulic Structures: Theory, Design and Practice Dr. Iqbal Ali Institute of environmental Engineering Research, N.E.D. University, Karachi.

IRRIGATION ENGINEERING Irrigation is the application of water to the soil to supplement natural precipitation and provide an environment that is optimum for crop production.

Types of Irrigation Supplementary irrigation: in areas with rainfall for a part of the season or year Total irrigation: in areas of no rainfall

Necessity of Irrigation

1.Less rainfall 2.Non-uniform rainfall 3.Commercial crops with additional water 4.Controlled water supply

Scope of Irrigation Science a) Engineering Aspect: 1.Storage, Diversion or Lifting of water 2.Conveyance of water to agricultural fields 3.Application of water to agricultural fields 4.Drainage and relieving water logging 5.Development of water power b) Agricultural Aspect: 1.Depth of water 2.Distribution of water 3.Capacity of soil and flow of water 4.Reclamation of lands

Multipurpose River Valley Project 1.Irrigation 2.Public health and sanitation 3.Hydroelectric power development 4.Flood control and river training 5.Soil conservation 6.Inland navigation 7.Fish culture

Advantages of Irrigation

(1)Increase in Food Production

(2)Optimum Benefits (3)Elimination of Mixed Cropping. (4)Facilities of Communications. (5)Generation of Hydro-electric power. (6)Domestic Water Supply. (7)Facilities of Communications. (8)Inland Navigation. (9)Afforestation.

Disadvantages and Ill-Effects of Irrigation (1) Water pollution: seepage of nitrates (when applied as fertilizer) into the ground water – groundwater polluted – causes anemia disease (when consumed by people through wells ). May affect the fishing, as the tides carry the polluted water out into the ocean. (2) Colder and damper climate: causing outbreak of diseases like malaria. (3)

Water-logging: due to over-irrigation - reduces crop yields.

(4) Complex and expensive to government: provision of cheaper water vs. low revenue returns

PLANNING OF IRRIGATION PROJECTS

Agricultural establishments capable of applying controlled amounts of water to lands to produce crops are termed irrigation projects. These projects mainly consist of engineering (or hydraulic) structures which collect, convey and deliver water to areas on which crops are grown. Irrigation projects may range from a small farm unit to those serving extensive areas of millions of hectares.

A small irrigation project may consist of a low diversion weir or an inexpensive pumping plant along with small ditches (channels) and some minor control structures. A large irrigation project includes a large storage reservoir, a huge dam, hundreds of kilo metres of canals, branches and distributaries, control structures and other works.

Irrigation project mainly includes the following works: (i) Storage (or intake) and diversion works, (ii) Conveyance and distribution channels, (iii) Control and other hydraulic structures, (iv) Farm distribution, and (v) Drainage works. Every irrigation project undergo following stages: 1.Development of an Irrigation Project 2.Feasibility of an Irrigation Project 3.Planning of an Irrigation Project

1. Development of an Irrigation Project A small irrigation project can be developed in a relatively short time. Farmers having land suitable for agriculture, source of adequate water supply, and necessary finance can plan their own irrigation system and get the engineering works constructed without any delay. On the other hand, development of a large irrigation project is more complicated and time-consuming. Complexity and the time required for completion of a large project increase with the size of the project. This is due to the organizational, legal, financial, administrative, environmental and engineering problems; all of which must be given detailed consideration prior to the construction of the irrigation works. The principal stages of a large irrigation project are: 1.Promotional stage, 2.Planning stage, 3.Construction stage, and 4.Settlement stage.

The planning stage itself consists of three sub stages: (i) preliminary planning including feasibility studies, (ii) detailed planning of water and land use, and (iii) the design of irrigation structures and canals.

2. Feasibility of an Irrigation Project A proposed irrigation project is considered feasible only when the total estimated benefits of the project exceed its total estimated cost. However, from the farmer's viewpoint, an irrigation project is feasible only if his annual returns exceed his annual costs by sufficient amount. The feasibility of an irrigation project is determined on the basis of: •preliminary estimates of area of land suitable for irrigation, •water requirements, •available water supplies, •productivity of irrigated land, and •required engineering works.

3. Planning of an Irrigation Project Once the project is considered feasible, the process of planning starts. Sufficient planning of all aspects (organizational, technical, agricultural, legal, environmental and financial) is essential in all irrigation projects. The process of planning of an irrigation project can be divided into the following two stages: (i) Preliminary planning, and (ii) Detailed planning.

The following are the main factors which must be determined accurately during the planning stage of an irrigation project: (i) Type of project and general plan of irrigation works, (ii) Location, extent and type of irrigable lands, (iii) Irrigation requirements for profitable crop production, (iv) Available water supplies for the project, (v) Irrigable areas which can be economically supplied with water, (vi) Types and locations of necessary engineering works, (vii) Needs for immediate and future drainage, (viii) Feasibility of hydroelectric power development, (ix) Cost of storage, irrigation, power and drainage features, (x) Evaluation of probable power, income and indirect benefits, (xi) Method of financing the project construction, (xii) Desirable type of construction and development, (xiii) Probable annual cost of water to the farmers,

(xiv) Cost of land preparations and farm distribution systems, and (xv) Feasible crops, costs of crop production, and probable crop returns.

Functions of Irrigation Water Soil furnishes the following for the plant life: 1.To supply water partially or totally for crop need 2.To cool both the soil and the plant 3.Provides water for its transpiration. 4.Dissolves minerals for its nutrition. 5.Provides Oxygen for its metabolism. 6.Serves as anchor for its roots. 7.To enhance fertilizer application- fertigation 8.To Leach Excess Salts 9.To improve Groundwater storage 10.To Facilitate continuous cropping

TYPES OF IRRGATION PROJECTS/SCHEMES

Direct irrigation project

Storage irrigation project

Types of Irrigation w.r.to Source Irrigation may broadly be classified into : 1.Surface irrigation [(a) Flow irrigation; and (b) Lift irrigation.] 2.Sub-surface irrigation

When the water is available at a higher level, and it is supplied to lower level, by the mere action of gravity, then it is called Flow Irrigation. But, if the water is lifted up by some mechanical or manual means, such as pumps, etc. and then supplied for irrigation, then it is called Lift Irrigation.

Types of Flow irrigation (i) Perennial irrigation, and (ii) Flood irrigation.

(i) Perennial Irrigation. In perennial system of irrigation, constant and continuous water supply is assured to the crops in accordance with the requirements of the crop, throughout the crop period. In this system of irrigation, water is supplied through storage canal head works and canal distribution system. When the water is directed into the canal by constructing a weir or a barrage across the river, it is called Direct Irrigation. But, if a dam is constructed across a river to store water during monsoons, so as to supply water in the off-taking channels during periods of low flow, then it is termed as Storage Irrigation. This perennial system of irrigation, is most important and is mostly practiced in Pakistan.

(ii) Flood Irrigation. This kind of irrigation, is sometimes called as inundation irrigation. In this method of irrigation, soil is kept submerged and thoroughly flooded with water, so as to cause thorough saturation of the land.

Soil Constituents • Mineral Material: Sand, clay and silt • Organic matter • Water • Air

Proportions of Soil Constituents

20% 45%

30% 5%

MINERALS OM Water Air

Mineral Components • Except in the case of organic soils, most of a soil’s solid framework consists of mineral particles. • They are variable in size and composition. They can vary from small rock particles to colloids. • The mineral can be raw quartz and other primary materials – coarse fractions which have not changed from parent material) • They can also be silicate clays and iron oxides formed by the breakdown and weathering of less resistant minerals as soil formation progressed. These are called secondary minerals.

Mineral Constituents

ROCKS SAND SILT

CLAY

USDA

ISSS

> 2 mm

> 2 mm

0.05 to 2 mm

0.02 to 2 mm

0.002 to 0.05 mm

0.002 to 0.02 mm

< 0.002 mm

< 0.002 mm

Sand Component Visible to the Naked Eye and Vary in Size. They are Gritty when rubbed between Fingers. Sand Particles do not Adhere to one another and are therefore not Sticky.

Silt and Clay Components Silt Particles are smaller than sand. The silt particles are too small to be seen without a microscope. It feels smooth but not sticky, even when wet. Clays are the smallest class of mineral particles. They adhere together to form a sticky mass when wet and form hard clods when dry.

Colloidal Material The smaller particles (< 0.001 mm) of clay and similar sized organic particles) have colloidal properties and can be seen with an electronic microscope. The colloidal particles have a very large area per unit weight so there are enough surface charges to which water and ions can be attracted. These charges make them adhere together. Humus improves the water holding capacity of the soil.

Soil Water Quantity of water in a soil as determined by its moisture content does not give a true indication of the soil ‘wetness’. A clay soil, which on handling feels dry, can be at the same moisture content as a sandy soil, which feels wet. A plant will have less difficulty extracting water from a sandy soil than from a clay soil at the same moisture content. There is need for a soil ‘wetness’ which reflects the ease or difficulty of extraction of water from the soil by the plant. The Concept of Soil Water Potential is therefore used in Soil/Plant/Water Relations.

Mechanism of Soil Water Movement The flow of water in any hydraulic system, including the soilplant-water system, takes place from a state of higher to one of lower potential energy. The steepness of the potential gradient from one point in the system reflects the ease with which water will flow down the potential gradient between the points. Soil-water system is mainly made up of three components:

i) Gravitational Potential: Reflects gravitational forces on the soil water. ii) Pressure Potential: This is positive when greater than atmospheric pressure, and negative when below atmospheric. A negative pressure potential (or tension, or suction) is also known as the matric potential. It is characteristic of soil water above a free water surface. iii) Osmotic Potential: reflects the effect of solutes in soil water, in the presence of a semi-permeable membrane The total potential of soil water at a point is the sum of all the components of potential, which are acting. Note that the movement of water in the soil is slow, so kinetic energy is neglected.