IRRIGATION ENGINEERING UNIT 5:INTRODUCTION

1. IRRIGATION ENGINEERING UNIT 5:INTRODUCTION

2. Introduction • Need for irrigation • Advantages & disadvantages • Environmental impact • Systems of irrigation • Gravity Irrigation • Lift Irrigation • Well Irrigation • Tube well irrigation • Infiltration Galleries • Sewage irrigation • Supplemental Irrigation

3. Irrigation is defined as the artificial application of water to arid land for growing crops.

4. Need for Irrigation • Deficient rain fall • Non uniformity of rain fall • Augmentation of crop yields • Exacting water requirement • Cash crop cultivation • Assured water supply

5. Scope of Irrigation Science. • Engineering Aspect • Agricultural Aspect

6. Engineering aspect: • Storage, Diversion or lifting water • Conveyance of water to the fields. • Application of water to Agricultural fields • Drainage & relieving water logging. • Development of power.

7. Agricultural Aspect • Water depth necessary in single application for various crops • Distribution of water uniformly and periodically • Capacities of different soil for irrigation water & the flow of water in soils. • Reclamation of waste & alkaline lands.

8. Benefits of Irrigation: • Increase in food production • Protection from famine • Cultivation of cash crops.(sugar cane,tobacco,cotton etc.) • Addition to the wealth of the country • Increase in prosperity of people • Generation of hydro power • Domestic & industrial water supply • Inland navigation • General development of country

9. Dis Advantages: • Breeding place for mosquitoes • Water logging • Damp climate

10. Irrigation Systems • Gravity Irrigation • Lift Irrigation • Infiltration Irrigation • Sewage Irrigation • Supplemental Irrigation

15. Lift Irrigation • Used for lands which are not commanded by gravity flow. • Water is lifted from a river or a canal to the bank . Well Irrigation: • Water is extracted from the ground water reservoir • Open well is essentially a vertical hole of 2 to 6m diameter & of shallow depth • Small discharge capacity • Depends on local ground conditions

16. Classification of wells • Unlined well • Pervious lined well • Impervious lined well • Shallow well • Deep well • Gravity well • Pressure well

17. Tube well irrigation • A tube well is a smaller dia. but large discharging well and draws water from under ground reservoir. • Capacity of tube well is 0.042 cumec , may reach optimum value of 0.07 cumec. Types: • Strainer type • Tube well in unconfined aquifer • Cavity type • Artesian Type

18. Infiltration Galleries These are the horizontal or nearly horizontal small tunnels circular in section or consist of pipes constructed through water bearing strata parallel to a river bank for the collection of inflow of ground water to the river.

19. Sewage Irrigation • Sewage is a water borne waste from community, residences,institutions,offices,commercial and industrial establishments . • Sewage water can be recycled for agriculture • Sewage effluent has to be managed in a sanitary manner without polluting the soil or contaminating crops raised on the sewage farm. • In India raw sewage, settled sewage as well as treated sewage is used for sewage farming both by gravity and lifting. • Command area for effluent irrigation shall not be located within 300 m from the residential area & 1000m from the city water works or in close proximity of water bearing aquifers.

20. Recommended standards (IS:3307-1977): • Total concentration of solids(inorganic) ≤ 200mg/l • Percentage of sodium with respect to total content of Na,Ca,Mg & P ≤ 60mg/l • Boron ≤ 2mg/l • PH. Of Sewage ≤ 5.5 to 9 • BOD ≤ 500

21. Supplemental irrigation • In humid areas normally artificial means of irrigation are not required. • But to take care of water requirement of crops during seed germination or other critical periods in plant growth in the serious drought periods extending to several days , supplemental irrigation is needed. • Sprinkler irrigation with perforated pipes instead of ditches is usually adopted.

22. Methods of Field Water Application • Surface irrigation method • • Subsurface irrigation method • • Sprinkler irrigation system • • Drip irrigation system

23. Surface Irrigation Methods Border irrigation

24. Contour border method

25. Check basin method

26. Ring basin method

27. Furrow Irrigation

28. Subsurface irrigation methods • As suggested by the name, the application of water to fields in this type of irrigation system is below the ground surface so that it is supplied directly to the root zone of the plants. • The main advantages of these types of irrigation is reduction of evaporation losses and less hindrance to cultivation works which takes place on the surface.

29. Types of sub surface irrigation Natural sub-surface irrigation method • The soil in the root zone should be quite permeable • There should be an impermeable substratum below the water table to prevent deep percolation of water. • There must be abundant supply of quality water that is one which is salt free, otherwise there are chances of upward movement of these salts along with the moisture likely to lead the conditions of salt incrustation on the surface.

30. Artificial sub-surface irrigation method • The concept of maintaining a suitable water table just below the root zone is obtained by providing perforated pipes laid in a network pattern below the soil surface at a desired depth. • For uniform distribution of water percolating into the soil, the pipes are required to be very closely spaced, say at about 0.5m. • Further, in order to avoid interference with cultivation the pipes have to be buried not less than about 0.4m below the ground surface. • This method of irrigation is not very popular because of the high expenses involved, unsuitable distribution of subsurface moisture in may cases, and possibility of clogging of the perforation of the pipes

31. Sprinkler Irrigation System • Sprinkler irrigation is a method of applying water which is similar to natural rainfall but spread uniformly over the land surface just when needed and at a rate less than the infiltration rate of the soil so as to avoid surface runoff from irrigation. • The system of irrigation is suitable for undulating lands, with poor water availability, sandy or shallow soils, or where uniform application of water is desired. • The water that is pumped through the pump pipe sprinkler system must be free of suspended sediments. As otherwise there would be chances of blockage of the sprinkler nozzles.

33. Drip Irrigation System • Drip Irrigation system is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 litres per hour) from a system of small diameter plastic pipes filled with outlets called emitters or drippers. • With drip irrigation water, applications are more frequent than with other methods and this provides a very favourable high moisture level in the soil in which plants can flourish

35. Environmental impact of irrigation • Environmental impacts of irrigation are the changes in quantity and quality of soil and water as a result of irrigation and the effects on natural and social conditions at the tail-end and downstream of the irrigation scheme. Direct Impacts • Downstream riverdischarge is reduced • The evaporation in the scheme is increased • the groundwater recharge in the scheme is increased • Level of the water table rises • Drainage flow is increased

36. Indirect Impacts • waterlogging • soil salination • land/soil subsidence, • along the coast, saltwater intrusion.

38. For the formation of clouds and subsequent precipitation: • Atmosphere must have moisture. • Sufficient nuclei present to aid condensation. • Weather condition must be good for condensation • Product of condensation must reach the earth.

39. Forms of precipitation:

40. Forms of precipitation contd….. Rain: • It is the term used to describe the precipitation in the form of water drops of sizes larger than 0.5mm. • It is the principal form of precipitation in India. • Maximum size of a rain drop is about 6mm.

41. Snow: • It consists of ice crystals which usually combine to form flakes. • Density varies from 0.06 to 0.15 g/cm3 . • Avg.density = 0.1 g/cm3 . • In India, snow occurs only in the Himalayan regions. Drizzle: • A fine sprinkle of numerous water droplets of size less than 0.5mm & intensity less than 1mm/h. • Drops are so small that they appear to float in air.

42. Glaze: When rain or drizzle comes in contact with cold ground at around 0◦C , the water drops freeze to form an ice coating called glaze or freezing rain. Sleet: • It is frozen rain drops of transparent grains which form when rain falls through air at subfreezing temperature. • In Britain, Sleet denotes precipitation of snow and rain simultaneously.

43. Hail: • It is a showery precipitation in the form of irregular pellets or lumps of ice of size more than 8mm. • It occur in violent thunderstorms in which vertical currents are very strong.

44. Types of precipitation: • Frontal precipitation • Convective precipitation • Orographic precipitation • Cyclonic precipitation

45. Frontal precipitation This is the precipitation that is caused by the expansion of air on ascent along or near a frontal surface.

46. Convective precipitation • Precipitation caused by the upward movement of air which is warmer than its surroundings. • This precipitation is generally showery nature with rapid changes of intensities.

47. Orographic precipitation • Precipitation caused by the air masses which strike the mountain barriers and rise up, causing condensation and precipitation. • The greatest amount of precipitation will fall on the windward side of the barrier and little amount of precipitation will fall on leave ward side.

48. Measurement of Precipitation • It is commonly used to estimate the amount of water falling over the land surface. • It is collected and measured in a Rain Gauge. • Pluviometer,Ombrometer,Hyetometer –terms used to designate a raingauge. • A raingauge consists of a cylindrical vessel assembly kept open to collect rain. • It is measured in depth units.(i.e.cm)

49. Important Considerations for Raingauge: • The ground must be level & the instrument must present a horizontal catch surface. • The gauge must be set as near the ground as possible to reduce wind effects. • But it must be sufficiently high to prevent splashing,flooding,etc. • The instrument must be surrounded by an open fenced area of at least 5.5m x 5.5m. • No object should be nearer to the instrument than 30m or twice the height of the obstruction.

50. Raingauge Classification • Non recording raingauges Symon’s rain gauge • Recording raingaugs Weighing bucket type Tipping bucket type Float type ( Syphon Type)