Irrigation Engineering CHAPTER ONE 1.1. Definition and scope of irrigation 1.2. Need and purpose of irrigation 1.3. Merits and demerits of irrigation 1.4.

Irrigation Engineering

CHAPTER ONE

1.1. Definition and scope of irrigation1.2. Need and purpose of irrigation

1.3. Merits and demerits of irrigation1.4. Requirements for successful irrigation

1.5. Standards of irrigation water1.6. Irrigation History and Development

Introduction

1.1. Definition of irrigation• Irrigation is any process, other than natural

precipitation, which supplies water to crops for their successful growth.

• Irrigation is the artificial application of water to the soil to meet the crop water needs for its vegetative development and for production.

• Irrigation is the science of artificial application of water to the land, in accordance with the crop requirements throughout the crop period for full nourishment of the crops.

Definition of irrigation cont…• Irrigation is the application of water to the soil

to supplement natural precipitation and provide an environment that is optimum for crop production.

• Or in different words is a science of survival for mankind

• It is the Engineering of controlling and harnessing the various natural sources of water, by construction of dams & reservoirs, canals & head works and finally distributing the water to agricultural fields.

1.2. Need and purpose of Irrigation:• Irrigation is needed for a continuous and reliable

water supply to the different crops in accordance with their different needs

• When water supply is not sufficient and timely, crop yield reduced and consequently famines and disasters.

• Thus, irrigation may be supplementary irrigation or total irrigation based on rainfall availability.

• Irrigation is needed in:– Arid and semi-arid regions - natural rainfall does

not provide all the water needed, and therefore, irrigation can make up this deficiency.

– Humid regions – little doubt for the need but ideal rainfall patterns seldom occurs.

– The need of irrigation in humid regions is mainly to supplement the supply of water received from precipitation.

• Generally the following are some of the factors that necessitate irrigation. – inadequate rainfall

– uneven distribution of Rainfall

– increasing the yield of the crops

– growing a number of crops

– to insure against drought.

– to grow perennial crops.

Need and purpose of Irrigation cont…

purposes of Irrigation1. Add water to soil to supply the moisture

essential for plant growth.

2. Provide crop insurance against short duration droughts

3. Cool the soil and atmosphere, there by making more favorable environment for plant growth.

4. Reduce the hazard of frost

5. Wash out or dilutes salts in the soil

purposes of Irrigation cont…

6. Reduce the hazard of soil piping

7. Soften tillage pans and clods

9. To enhance fertilizer application- Fertigation

1.3. Merits and demerits of Irrigation:Various direct and indirect advantages of irrigation.

Merits:• Increase in crop production: irrigation helps in

increasing crop yield through controlled and timely supply of water to the crop

• Optimum benefits: Optimal utilization of water is made possible by irrigation

• optimum utilization of water, implies obtaining maximum crop yield with any amount of water.

• in other words yield will be smaller for any quantity lesser than or in excess of the optimal quantity

• irrigation helps to stabilize the farm economy• irrigation can improve the quality of crops

Merits cont…• Elimination of mixed cropping: in areas where irrigation

is not ensured, generally mixed cropping is adopted. • Mixed cropping is sowing /growing two or more crops

simultaneously in the same field. • If the weather condition is not suitable to one of the

crops it may be suitable for the other, and thus at least some yield is obtained.

• Mixed cropping can be adopted when irrigation facilities are not available, but if irrigation is assured it can be eliminated.

• Mixed cropping is generally not acceptable, because different crops require different types of field preparations and different types of manures, amount of water etc.

Merits cont…• Mixed cropping is thus necessary and

economical when irrigation facilities are lacking.

• But if irrigation is assured, mixed cropping can be eliminated or reduced through irrigation, the time of harvest can be more closely controlled with irrigation, fertilizers placed in the soil are available at once to plants

Merits cont…• irrigation protects certain high value crops

from frost damage/high temperature. • irrigation increases the survival of

transplanted crops• Conjunctive use of irrigation projects –

hydroelectric power, domestic water supply• General prosperity: Revenue returns are

sometimes quite high and helps in all round development of the country

Merits cont…• Generation of hydroelectric power: cheaper

power generation can be obtained on objects primarily designed for irrigation alone.

• Also falls on irrigation channels can be utilized to generate electricity which may help in industrializing the rural area and so in solving the problem of fuel shortage.

• Domestic water supply:- irrigation helps in augmenting the town water supply where water is available with great difficulty.

• It also provides water for swimming bathing, cattle drinking etc.

Merits cont…• Facilities of communication: Irrigation

channels are generally provided with embankments and inspection roads.

• These inspection paths provide a good road way to the villagers for walking, cycling or even motoring.

• In land navigation

ILL-effects /demerits of irrigation • ILL-effects of irrigation occur only when the

scheme is not properly designed and implemented.

• if not properly managed, irrigation may result in the outbreak of water borne diseases and Salinity problem

• Most of these are due to excess irrigation water application.

• Some of the common ill-effects are:

ILL-effects /demerits of irrigation cont..1.Waterlogging when cultivators apply more water

than actually required by the crops, excess water percolates in to the ground and raises the water table.

• Water logging occurs when the water table reaches near the root zones of the crops.

• The soil pores become fully saturated and the normal circulation of air in the root zones of the crop is stopped and the growth of the crops is decreased.

• Thus crop yield considerably reduces.• When the water table reaches the ground surface,

the land becomes saline.

ILL-effects /demerits of irrigation cont..• Ground water pollution through leaching of

fertilizers• Irrigation is relatively expensive and the

management is difficult.• Long term application of pesticides under large

scale irrigation system might have a negative influence on soil microbial activities, on the quality of surface and sub surface water resources and the survival of the surrounding vegetation.

• Irrigation may contribute in various ways to the problem of pollution.

• One of these is the seepage in to the ground of the nitrates that has been applied to the soil as fertilizer.

ILL-effects /demerits of irrigation cont..• Sometimes up to 50% of the nitrates applied

to the soil sink in to the underground reservoir.

• The under ground water thus get polluted. • Irrigation may result in hot and damper

climate causing outbreak of disease like malaria.

• Irrigation is complex and expensive in itself. • Some times cheaper water is to be provided

at the cost of the government and revenue returns are low.

1.4 Requirements for successful irrigation:a) Land Capability

Irrigation should be confined to soils that are capable of producing sustained high yields of adapted crops

b) Adequate Water Supply A supply of water adequate to meet the needs of the crops being irrigated must be available when needed.

c) Adequate Labor Irrigation requires more labor than rain-fed agriculture.

d) ClimateThe climate is a very important factor in any sort of cultivation

e) Adequate CapitalEnough initial capital to install, operate and maintain irrigation project is required.

f) Others: Effective management of soil and water

1.5. standards of irrigation water• Every water is not suitable for irrigation.

• The quality of irrigation water is very much influenced by:– the continents of the soil, which is to be irrigated– particular water may be harmful for irrigation on

a particular soil – But the same water may be tolerable or – even useful on some other soil.

1.5. standards of irrigation water cont..• Irrigation water may be said to be

unsatisfactory for its intended use if it contains: – Chemicals toxic to plants or the persons using

plant as food – chemicals that react with the soil to produce

unsatisfactory moisture characteristics – Bacteria injurious to persons or animals eating

plants irrigated with water.

Irrigation water unsuitability suitability • Sediment: its effect depends upon the type of

irrigated land when fine sediment from water is deposited on sandy soils the fertility is improved on the other hand if the sediment has been derived from the eroded areas it may reduce the fertility or decrease the soil permeability.

• Sediment water creates troubles in irrigation canals as it increases their siltation and maintenance costs.

• In general ground water or surface water from reservoirs, etc does not have sufficient sediment to cause any serious problems in irrigation.

Irrigation water unsatisfactory / Unsuitability cont.

• Irrigation water Salinity

• Two main causes of salinity:

• Salinity caused by the supply of irrigation water

• Salinity caused by the upward movement of water and salts, related to high water tables and lack of drainage; it is only indirectly related to salts in the irrigation water

Irrigation water unsuitability / suitability cont…• The general solution to these problems is to remove

the salts from the soil by providing extra water, which dissolves the salts and percolates to the saturated zone.

• This process is called leaching.

• Where it is removed by drainage.

• This is one of the reasons why irrigation systems also require drainage systems.

Irrigation water unsuitability / suitability cont…• Total concentration of soluble salts: • Salts, when present in excessive quantities,

– reduce osmotic activities of the plants and may prevent adequate aeration causing injuries to plant growth.

• The effect of salts on plant growth depends largely upon the total amount of salts in the soil solution.

• The salinity concentration of the soil solution (Cs) after the consumptive use (Cu) has been extracted from the soil is given by :

where, Q is quantity of water applied

Cu is consumptive use of water i.e. the total amount of water used up by the plant for its growth.

Peff is useful rainfall Cu-Peff is used up irrigation water

C concentration of salt in irrigation water C*Q is the total salt applied to the soil with Q amount

of water

salinity concentration• Concentration of salt is measured in PPM (mg/l). • Concentration of salt above 2000 PPM is generally

harmful for almost all crops. • Salt concentration is measured by determining

electrical conductivity. • Low Conductivity (low salinity)100-250

micromhos /cm • Medium conductivity 250-750 micromhos/cm • High conductivity 750-2250 micromhos/cm • Very high conductivity >2250 micromhos at 250C

Proportion of sodium ions to other cations• small quantities of sodium ions are present in most

soils relative to other cations. • If its percentage increases it has an influence on

the aggregation of soil grains i.e. breaks down. • The soil becomes less permeable and of poorer

tilth. • It starts crusting when dry and its PH increases

towards that of an alkaline soil.• High sodium soils are therefore, plastic, sticky

when wet, and are prone to form clods and they crust on drying.

Sodium adsorption • The proportion of sodium ions present in the soil is

generally measured by a factor called sodium-absorption ratio (SAR) and represents the sodium hazards of water.

• SAR is defined as:

• Where the concentration of the ions is expressed in equivalent per million (epm).

• epm is obtained by dividing the concentration of salt in mg/l or PPM by its combining weight (i.e. atomic weight valence)

Sodium adsorption cont…• When SAR between 0-10 it is low sodium water • 10-18 medium ,, • 18-26 High ,, • >26 very high ,, • Low sodium water is suitable for irrigation except in

crops, which are sensitive to sodium like fruit trees, avocados etc

• where as medium sodium water is hazardous in fine textured soils.

• Very high sodium water is generally not suitable for irrigation.

• SAR value can be reduced by adding gypsum (CaSO4)

Potentially toxic elements:• Elements like Boron, Selenium, etc may be toxic

to plants. • Concentration of Boron exceeding 0.3 PPM may be

toxic to certain plants. • >0.5 PPM dangerous to nuts, citrus fruits. • Dates, Beets, asparagus are quite tolerant. • Even for the most tolerant crops its concentration

should not exceed 4 PPM . • Boron is present in various soaps. • Wastewater containing soap, etc should be used

with great care in irrigation. • Guidelines for the interpretation of water quality for

irrigation water (FAO,1976)

Irrigation problem No problem medium problem severe

Salinity(affects water uptakeEcw (mmhose /cm)

< 0.75 0.75 to 3.0 >3.0

Permeability (affects water infiltration and availability(Ecw (mmhose /cm > 0.5 0.5 - 0.2 < 0.2

Adj. SARMontimorilonite- HliteVermiculiteKaolinite- sesquixides

< 6< 8< 10

6 - 98 - 1616 - 24

> 9> 16> 24

Specific ion toxicity(affects sensitive crops) Sodium (Adj.SAR)Chloride (meq./l)Boron (mg/l)

< 3< 40.75

3 - 94 - 100.75 - 12

>9> 10> 12

Miscellaneous effects (affects susceptible crops) NO3-N or NH4-N (mg/l)HCO3 (meq./l)PH

< 5< 1.5

5 - 301.5 - 8.5Normal range

30>8.56.5 to 8.4

Problems in Irrigation Development

Irrigation plays a significant role in the agricultural development of the country but there are still enormous constraints in its development.

Lack of mapping data: Mapping information not available at a scale suitable for detailed

studies of irrigation areas, dam sites, etc. Similarly, data related to soils are not found in sufficient detail to all

potential areas.Lack of Hydrologic Data: The collection of hydro meteorological information are not adequate. River gauges are mostly available for major rivers and bigger

tributaries.

Lack of resources: The level of skilled manpower available in the country is not adequate

to carry out the number of projects being demanded by the regions. Inadequacy in construction capability due to inadequate machinery,

equipment and spare parts.

..Lack of Finance: Despite ambition plan of the government, sources

of finance for implementing the planned irrigation projects is expected from foreign aid and loans.

Inadequate research undertakings in the area:So far, little emphasis for irrigation in agricultural research.

Operation and Maintenance: Institutional water operation and management is in

a very poor condition with regard to the administration of supply, maintenance and repair of the networks due to lack of trained manpower, sufficient maintenance tools and equipment.

Problems in Irrigation Development

Irrigation engineering • Irrigation Engineering is a broad-based

science which deals not only with the application of water to the land but also with the planning and design of various structures required for an irrigation system

• Irrigation Engineering is not only confined to the application of water to the land for raising crops.

• It includes all aspects and problems extending from the watershed to the agricultural fields.

irrigation engineering cont…• It deals with:

– hydrology, – river Engineering, – the design and construction of dams, weirs,

canals and various other hydraulic and irrigation structures.

• It also deals with:– surface and sub surface drainage system, – soil reclamation, – water-soil –crop relationships.

irrigation engineering cont… • It deals with the Harnessing of various natural

water resources for irrigation and all aspects and problems starting

• from the watershed to the agricultural fields/ command areas

• Other allied sciences such as:– flood control, – hydropower, and – inland navigation are also studied in IRRIGATION

Engineering.

Various aspects of irrigation Engineering A) Water resources and hydrology aspect

– to locate various water sources and to study the hydrology of the region.

• This includes study of :– meteorology, – precipitation, – stream flow, – floods, – river engineering, – reservoirs and flood control.

Aspects of irrigation Engineering cont…• Information required while designing

various irrigation structures are as follows

• The quantity of water that will be available at a reservoir site for storage. – Maximum discharge at a river site.

– Reservoir capacity that ensures adequate Quantity of water for various purposes.

– Quantity of ground water which can be economically exploited

Aspects of irrigation Engineering cont…B) Engineering Aspect - involves the

development of a source of water for irrigation and construction of various irrigation structures. – Dams and water power Engineering

– Diversion and Distribution structures

– Minor irrigation schemes • (well, Tank / Pond, inundation Irrigation).

Aspects of irrigation Engineering cont…C) Agricultural aspect – • Involves irrigation practice • the study of agricultural Characteristics of

the land.• Crops• Soils

D) Management Aspect- • deals with successful implementation and

efficient management of engineering aspects and agricultural works

Scope of Irrigation Engineering

IRRIGATION ENGINEERING: involves – Conception,

– Planning,

– Design,

– Construction,

– Operation and Management of an irrigation system.

Scope of Irrigation Engineering cont….• An irrigation engineer is one who has a long

theoretical and practical training in:

– planning,

– design,

– construction,

– operation and management of irrigation systems.

To Understand Irrigation, One Needs Knowledge of:

• Basic Soil Science/Physics• Plants• Water• Plant/Soil/Water Relations• Hydraulics• Hydrology• General Engineering Principles

Assignment-I

Irrigation History and Development