Lecture 7 ce1005 Irrigation and Flood control by Rabindra Ranjan Saha,PENG, WUB

Irrigation method-Check flooding, basin flooding, furrow irrigation, border irrigation method, sprinkler irrigation, trickle or drip irrigation method, sub surface irrigation method canal alignment, canal network system,

1. 1 (c) Check Flooding: In this method, relatively level plots are enclosed by small levees or embankments. Irrigation water enters the closed area and subsequently floods it. Check flooding method is very suitable for soils having high permeability. The reason is that the water quickly spreads over the entire area before it goes deep, below the root zone depths, into the ground and joins the water table. Thus, the water loss due to infiltration is prevented or reduced. It is best adopted for heavy soils also. In heavy soils water absorption rates are low. The land can be kept flooded for longer time till sufficient water infiltrates into the ground to fulfill soil-moisture deficiency. This method can be subdivided into two groups depending upon the mode of levee construction. The subdivisions are the following: ( i ) Rectangular Check (ii) Contour Check Lecture-7

2. 2 Ditch Openings Levees along the contours Connecting Figure: Plan view of Check flooding Otherwise the embankments or levees may put hindrance to farm machinery. This method is very useful in leaching the soil and reducing the salinity. It is generally used for grain and fodder crops. In check method 0.2 to 0.8 hectares area is better. The embankment should be about 25 to 30 cm high and the width at the base should not be more than 2.5 m. Lecture-7(contd.)

3. 3 Lecture-7(contd.) Photograph of Check irrigation

4. 4 Lecture-7(contd.) (d) Basin Flooding This method is special type of checking flooding and is adopted specially for orchard trees. One or more trees are generally placed in the basin, and the surface is flooded as in check method, by ditch water as shown the following figure. Tree Tree Tree Tree Tree Tree Basins Subsidiary ditches Entry water through a bank hole or by a hose Main ditch

5. 5 Photograph of basin flooding method

6. 6 Lecture-7(contd.) (e) Furrow irrigation Probably one of the oldest methods of irrigating fields is surface irrigation or furrow irrigation , where farmers flow water down small trenches running through their crops. Or it is a narrow field ditch excavated between two rows of plants and carry irrigation water through them. In furrow irrigation only one-fifth and one-half of the land surface is wetted. Results is less evaporation and permits cultivation sooner after irrigation. Figure-3 Furrow irrigation is conducted by creating small parallel channels along the field length in the direction of predominant slope. Water is applied to the top end of each furrow and flows down the field under the influence of gravity. At furrow irrigation, soil conditions, the land relief and slope, row-spacing width or interval between the furrows are taken into account.

7. 7 Figure 3 : Furrow irrigation Figure : Furrow Depth and width of irrigation furrows : According to depth, volume of filling and consequently hydraulic features furrows are of three types: ( i ) shallow furrows : 10…15 cm deep, 30…35 cm wide on the top (ii) medium-depth furrows : 15…20 cm deep and 40…45 cm wide on the top (iii) deep furrows are 20 to 30 cm deep and 50to 60 cm wide on the top. Lecture-7(contd.)

8. 8 2 . Sub Surface method Sub surface irrigation, also designated as sub irrigation. This method involves irrigation to crops by applying water from beneath the soil surface either by constructing trenches or installing underground perforated pipe lines or tile lines. Water is discharged into trenches and allowed to stand during the whole period of irrigation for lateral and upward movement of water by capillarity to the soil between trenches . Lecture-7(contd.) Photograph of sub surface irrigation method Water supply through pipe beneath the soil

9. 9 Lecture-7(contd.) 3. Sprinkler irrigation : is a method of applying irrigation water which is similar to natural rainfall. Water is distributed through a system of pipes usually by pumping. It is then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground. Figure : Sprinkler irrigation system. But this method is very costly. It can be applied for all kinds of soil and for widely different topographies and slopes. It can advantageously be used for many crops, because it fulfills the normal requirement of uniform distribution of water. This method possesses great potentialities for irrigating areas where other types of surface or sub surface irrigation are very difficult.

10. 10 Figure: Sprinkler irrigation system Lecture-7(contd.)

11. 11 Lecture-7(contd.) The 6 conditions favoring the adoption of this method are:   i . irregular land topography and unsuitable for surface irrigation ii. when the land gradient is steeper and soil is easily erodible iii. when the soil is highly impermeable. Field Sprinkler irrigation method

12. 12 iv. When the water table is high v. When the seasonable water requirement is low such as near the coasts vi When the crops 5equire humidity control, having shallow roots and crops requiring high and frequent irrigation Types of sprinkler systems: It is of three kinds, they are   1.Permanent system 2.Semi-permanent system and 3. Portable system Lecture-7(contd.)

13. 13 Lecture-7(contd.) 4. Drip / Trickle Irrigation method Drip irrigation is the latest field irrigation technique, and is meant for adoption at places where there exists acute scarcity of irrigation water and other salt problems. In this method, water is slowly and directly applied to the root zone of the plants, thereby maintaining the losses by evaporation and percolation . Drip irrigation is a form of irrigation that saves water and fertilizer by allowing water to drip slowly to the roots of many different plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters. It is done through narrow tubes that deliver water directly to the base of the plant. This method is also called trickle irrigation.

14. 14 Lecture-7(contd.) Figure: Drip System Photograph: A vineyard with a drip irrigation system running along the bottom of the vines

15. 15 Lecture-7(contd.) 2. No water logging and rise of water table 3. No salinity problems caused by this irrigation type is almost nil. 4. Uniform distribution of water. 5. Good water management. 6. Economical use of labor . Advantages 1. No loss of water because all water drops at root zone. Image: Drip watering system Water drops falli ng

16. 16 Lecture-7(contd.) Canal irrigation system An open canal , channel, or ditch, is an open waterway whose purpose is to carry water from one place to another. Channels and canals refer to main waterways supplying water to one or more farms. Field ditches have smaller dimensions and convey water from the farm entrance to the irrigated fields.   These canals have to be excavated either in alluvial soil or non-alluvial soils; depending upon which they are called alluvial or non-alluvial canals. Alluvial soils : The soil which is formed by transportation and deposition of silt through the agency of water, over a course of time, is called alluvial soil.   Non-alluvial soils: Mountainous regions may go on disintegrating over a period of time, resulting in the formation of a rocky plain area, is called non-alluvial area. It is an uneven topography, and hard foundations are generally available.

17. 17 Canal Alignment Lecture-7(contd.) Irrigation canals can be aligned in any of the following three ways:   a. watershed canal or ridge canal b. contour canal; and c. side slope canal River River Watershed/Ridge line P Q Rl.3.5m A Rl . 3.0 m Ridge line B ( Rl . 2.0 m Canal L 1 L 2 L 3 L 1 Canal a. Watershed canal The dividing ridge line between the catchment areas ( the area from which rain water flows into a drain or a stream, is known as its catchment area) of two streams (drains) is called the water –shed, or the ridge.

18. 18 Thus, between two major streams, there is main water –shed line which divides the drainage area of two streams as shown in the previous figure. Similarly, between a main stream and any of its tributary, there are subsidiary watersheds (ridge line) dividing drainage between the two streams on either side. Lecture-7(contd.)

19. 19 Lecture-7(contd.) Example of Watershed canal

20. 20 Side Slopes canal 3.0 m 2.0 m 1.5 m  Ground contours   F igure: Alignment of side slope canal b. Side Slope Canal This canal aligned roughly perpendicular to contour of the contour. Since it is perpendicular to the contour, construction of cross Drainages Works (CDWs) does not arise. Since constructed along the falling contour, slope of this canal is steep, which is not essential for unlined canal. It irrigates only on one side just like contour canal. Lecture-7(contd.) Side slope irrigation canal

21. 21 Lecture-7(contd.) c. Contour canal : The canal constructed along the ridge line are called contour canal. It is uneconomical in hill areas since the conditions in hills are vastly different compared to those of plain lands.

22. 22 In hills , the river flows in the valley well below the water – shed. In fact the ridge line is 100 meters above the river which is generally impossible to take the canal on top of such a higher ridge line. In such conditions, contour canals (as shown the figure-2) are usually constructed. A contour canal irrigates only one side because the area on the side is higher. As the drainage flow is always at right angles to the ground contours, such channel would definitely have no cross natural drains and streams, necessitating of cross-drainage structures. Distribution system of canal irrigation Direct irrigation scheme using a weir or a barrage, as well as storage irrigation scheme using a dam or a reservoir, requires a network of irrigation canals of different sizes and capacities. Lecture-7(contd.)

23. 23 Lecture-7(contd.) The entire network of irrigation channels (Figure 8-6 ) is called the distribution system of canal irrigation.

24. 24 The canal system consists of   Main canal Branch canals Distributaries also called major distributaries Minors Water courses 1.Main canal: The canal constructed or aligned along the ridge and some what central to the command area receiving water from reservoir or river is called main canal. Main canal is not required to do any irrigation.. The canal must, therefore, be aligned very carefully, and has to be generally excavated in deep cuttings below NSL(Natural surface level). Sometimes, it has to cross various drainage lines.     Lecture-7(contd.)

25. 25 Lecture-7(contd.) 2.Branch canal: Branch canals are taken off from the main canal on either side to take irrigation water to the whole tract required to be irrigated 3 . Distributaries: Small channels which take off from the branch canals and distribute their supply through outlets into minors or water courses, are called distributaries. They are aligned either as ridge canals or as cotor canals. Photograph :Distributaries

26. 26 4. Minor : Sometimes distributaries outlet and the farmer’s field is very long, say more than 3 km or so on. In such a case, small channels called minors are taken off from distributaries, so as to supply water to the cultivators. 5. Water courses : The small c hannels, which are excavated and maintained by the cultivators, at their own costs, to take water from the government-owned outlet points, provided in the distributaries or the minor. Lecture-7(contd.) Photograph: water distribution by artificial canal system