MODULE - 7

DISTRIBUTION SYSTEM

7.1 CANAL SYSTEM:

• It has been stressed earlier that the direct irrigation theme employing a weir or a barrage, in addition because the storage irrigation scheme using a dam or a reservoir, need a network of irrigation channels. The whole network of irrigation channels is named canal system. The canal system, as explained earlier, consists of:

1.     Main canal

2.     Branch canals

3.     Distributaries

4.     Minors, and

5.     Watercourses

• In case of direct irrigation scheme, a weir or a barrage is built across the river, and water is headed abreast of the upstream side. The arrangement is thought as Head Works or Diversion Head Works, and will be explained in details, a litter later, in chapter. Water is diverted into the main canal by means of a diversion weir. A head regulator is provided at the head of the main canal, so as to regulate the flow of water into the main canal.

• In storage irrigation scheme, a dam is constructed across the river, thus forming a reservoir on the upstream side of the river. The water from this reservoir is taken into the main canal through the outlet sluices. There are generally two main canals, which off 'take from the reservoir, called the Left Bank Canal and the Right Bank Canal, as shown in figure.

• In certain storage irrigation schemes, commanded irrigation area may be far away from the dam site. In such cases, a separate head works consisting of a pickup weir, is constructed across the river on the downstream side of the main dam, at a point where the commanded area begins. The main canal, in such a case, will off 'take from the upstream side of the weir, just as in a normal diversion weir scheme.

• In both these irrigation scheme, when once the water reaches into the main canal, the problem left is to distribute this water into the fields. The aim is achieved through a network of channels, as delineated below:

(a)  Main Canal (Head reach):

• The canal head works are usually located during a} valley, and therefore the canal ought to mount the watershed within the shortest potential distance. The canal, during this reach, must be aligned very rigorously and must be generally excavated in deep cuttings below N.S.L. (natural surface level). Sometimes, it's to cross varied voidance lines. Many another times, straight alignment has to be sacrificed so as to realize an honest web site for cross drainage works.

b)   Main Canal (Portion below head reach):

• Attempts are made to align the canal along the watershed and somewhat central to the commanded area. Sometimes, water 'shed has to be sacrificed to bypass towns and villages, etc. Main canal is not required to do any irrigation.

(c)  Branch Canals:

• When a main canal leaves the high ground and must, therefore, bifurcate into branches, covering the whole tract required to be irrigated, the canals in such portions are called Branch Canals. Very little irrigation is done from the branch canals. Attempts are made to align them along subsidiary water sheds. Discharge in a branch channel, is generally, over thirty comics.

(d) Distributaries:

• Smaller channels that begin from the branch canals and distribute their offer through retailers into minors or water courses, are known as distributaries. They're aligned either as watershed channels or as aspect slope channels. Discharge in distributaries is mostly not up to 30 cumecs. Minors: Sometimes, the country is specified the space between the distributaries outlet and therefore the farmers field is extremely long; say a lot of called minors, are began from the distributaries, thus on supply water to the cultivators at the purpose nearer to their fields. Discharge in an exceedingly minor, is generally, less than 2.5 comics.

(e) Watercourses:

• These are not the government channels and belong to the cultivators. These are small channels, which are excavated by cultivators, to take water from the government ' owned outlet point provided in the distributaries or the minor.

7.2 ALIGNMENT OF CANAL:

• Irrigation canals can be aligned in any of the three ways:

1. As watershed canal

2. As contour canal; and

3. As side slope canal

1. Watershed Canal.

• The dividing line between the catchment region of two drains (streams) is called the watershed. Thus, between two major streams, there is the primary watershed which divides the drainage areas of the two. Similarly, between any tributary and the essential stream, and also between any two tributaries there, are subsidiary watersheds, dividing the drainage between the two streams on either side.

• For canal machine in undeniable areas, it is frequently indispensable as properly as fine to align all channels on the watersheds of the areas, they are designed to irrigate. The canal, which is aligned alongside any natural watershed, is called a watershed canal. From such canal irrigation, water is taken out by way of gravity on both side of the canal, directly or thru small irrigation channels.

• Moreover, cross 'drainage works are avoided, as the natural drainage can in no method go a watershed, thanks to the actual fact all the voidance flows aloof from the watershed. Sometimes, watershed may additionally got to be abandoned so as to skip localities settled on the watershed.

(2) Contour Canal:

• The higher than arrangement of providing the canals on the watershed is no longer possible in hill areas. Within the hills, the stream flows in the valley, while the watershed or the ridge line could also be hundred of meters above it. It becomes uneconomical to require the canal on pinnacle of such a ridge. The channel, in such cases, is generate enough waft velocities, are given to it.

• The most designed slope which will be provided in the canal barring generating undue velocities, is usually much not up to the obtainable u . s . Slope. The excellence is accommodated via providing canal falls at applicable places. A contour channel irrigates solely on one aspect, thanks to the actual fact the areas on the opposite side are higher.

• As the voidance go along with the flow is frequently at correct angles to the ground contours, such a channel would sincerely have to be compelled to move drainage lines. Appropriate go drainage works are then provided.

(3) aspect Slope Canal:

• A aspect slope channel is that that is aligned at proper angles to the contours, i.e. aboard the side slopes, as tested in figure.

• Such a channel is parallel to the flavoring drainage flow and hence, will no longer intercept move voidance, and consequently no pass drainage works are required.

7.3 ESTIMATION OF DESIGN DISCHARGE:

• The quantity of water required for the expansion of a crop within the course of its whole crop-growing period is understood because the water demand of the crop, and is measured in terms of depth of water adjoin the irrigated area. This requirement varies at one in all a form levels of the boom of the plant. The peak requirement ought to be got for the amount of the keenest demand. One in all the ways to see the water requirement is on the idea of displacement unit watering.

• When the plant is alone some centimeters high, it have to be compelled to be its initial watering, called the displacement unit watering, in a very confined length of your time that is recognised because the kor period.
• If the vegetation do now not acquire water throughout kor period, their growth is unintelligent and therefore the crop yield reduces considerably. The kor watering depth and the kor length vary relying upon the crop and the climatical factors of the region. In UP, the kor watering depth for depth for wheat is 13.5 cm and the kor length varies from eight weeks in north-east UP (a notably dry region) to three weeks within the hill neighbourhood (which is passing humid). For rice, the displacement unit watering depth one9|is nineteen} cm and therefore the kor amount varies from 2 to 3 weeks.

• If D represents the duty (measured in hectares/m3/s) then, by definition, 1 money supply/s of water flowing for b (i.e., base period in days irrigates D hectares.

• 1 m3/s of water flowing for 1 day (i.e., 86400 m3 of water) irrigates D/b hectares

• This amount (i.e., 86400 m3) of water adjoin D/b hectares provides the water depth, D

D = 86400 / (D/b) x 104 =8.64 b/D (metres)

• For the motive of coming up with on the idea of the keenest demand (i.e., the displacement unit amount requirement) the bottom period b and therefore the water depth Dare modified by suggests that of the kor length associate degreed kor water depth, respectively.

7.4 DESIGN OF CHANNEL:

• The style of a channel involves the choice of channel alignment, shape, size, and bottom slope and whether or not the channel ought to be lined to scale back ooze and/or to forestall the erosion of channel sides and bottom. Since a lined channel offers less resistance to flow than an unlined channel, the channel size needed to convey a mere flow at a particular slope is smaller for a lined channel than that if no lining were provided. Therefore, in some cases, a lined channel could also be a lot of economical than associate degree unlined channel.

• Procedures aren't presently obtainable for choosing optimum channel parameters directly. Every web site has distinctive options that need special considerations. Typically, the look of a channel is completed by trial and error. Channel parameters are selected and an analysis is done to verify that the operational needs are met with these parameters.

• A variety of alternatives are considered, and their prices are compared. Then, the foremost economical various that offers satisfactory performance is selected. During this process, it's necessary to incorporate the upkeep costs whereas scrutiny completely different alternatives. Similarly, the prices of energy needed if pumping is concerned and, for power canals, the number of revenues created by hydropower generation should be enclosed within the overall economic analysis.

• The channel style could also be divided into 2 categories, relying upon whether or not the channel boundary is erodible or non-erodible. For erodible channels, flow velocities are unbroken low so the channel bottom and sides aren't eroded. The minimum flow rate in flows carrying an oversized amount of sediment ought to be such the fabric being transported isn't deposited within the channel.

RIGID BOUNDARY CHANNEL:

• Rigid channels are those within which the boundary isn't deformable. The form and roughness magnitudes don't seem to be functions of flow parameters. For example, lined canals and non-erodible unlined canals.

• In Rigid channels the flow speed and shear stress distribution are going to be specified no major scouring, erosion or deposition can present itself within the channel and also the channel pure mathematics and roughness are basically constant with regard to time.

• When the boundary of the channel is mobile and flow carries appreciable amounts of sediment through suspension and is in touch with the bed. Such channels are classified as mobile channels.

• In the mobile channel, not only depth of flow but also bed width, longitudinal slope of channel may undergo changes with space and time depending on type of flow.

• The resistance to flow, quantity of sediment transported and channel geometry all depends on interaction of flow with channel boundaries.

• A general mobile boundary channel can be considered to have four degree of freedom. In rigid channel we have one degrees of freedom.

ALLUVIAL CHANNEL:

• If you were on a hike and came up to a 'Y' in the road, would you take the path that was nicely worn and smooth or would you take the rocky and uneven path? In different words, would you are taking the simple or the exhausting path?

• Well, if you were water, you'd take the trail of least resistance. In fact, water can withdraw of its thanks to take the easy path. This is often why some waterways appear to meander, twist and flow in wild ways. These patterns of flow are seen in deposit channels, that are water channels created from loose sediments. The various styles of alluvial channels and their distinctive characteristics are the main target of this lesson.

• Alluvial channels have the flexibility to regulate and shift. This is as a result of they contain loose substance materials called alluvium. If you walk up to a stream, reach in and pull up a couple of silt, sand, pebbles and different particles, you'd be holding alluvium.

• These particles are often picked up within the flow of the stream and deposited downstream. If the stream is moving fast, the water has additional force and causes erosion, or carrying away, of very little sediment chunks from the banks of the channel. Consequently, if the water flow is slow, we tend to see the subsidence of sediments, that could be a method referred to as deposition. This erosion and deposition explain how alluvial channels are able to change their shape or course over time.

KENNEDY'S AND LACEY'S THEORY OF REGIME CHANNEL:

KENNEDY'S SILT THEORY:

• Kennedy proposed his theory based on the charge and grade of silt present in the Upper Doab Canal (Punjab) and its distributaries. He observed that there is always one velocity for a given condition, called "critical velocity. Vo, which characterizes a non-silting and non-scouring channel in a steady regime. This velocity depends on the depth of water in the channel. He found that:

V0 = 0.546 D0.64

Where    V0 = velocity, m/s

D = depth of water, m   

This relation was applicable to the grade of silt present only in the Upper Doab Canal. He introduced a factor called the "critical velocity ratio, (CVR), m" in his equation to account for the varying grades of silt in other regions. Thus, he propounded

V = 0.546 D0.64

Where, m = V/V0 = CVR

Gives the values of m for various styles of silt.

Values of CVR for Various Types of Soils

NO.                       TYPE OF SLIT                                          VALUE OF m

1.Light sandy silt in the river of North India.                             1.00

2.        Rather coarser silt or debris of hard soils.                     1.30

3.        Somewhere coarse silt or debris of hard soil.               1.10

4.        Sandy loamy silt.                                                                  1.20

5.        Silt of river Indus in sand.                                                   0.70

• A value of 1.1 in the head reach, and O.85 towards the tail end of channels carrying appreciable heed and suspended loads, respectively, is recommended as the value of m for purposes of design.

• Kennedy's equation in the general form can be written as:

V0 = KDn

• Various investigators have reported that K and n both vary with the silt grade.

• Gives the relations for other regions.

Kennedy's Relations for Various Regions

NO.              RELATION                             REGION

1.                 V = 0.391 D0.55.                               Godavari delta

2.                V = 0.530 D0.52.                              Krishna wester delta

3.                V = 0.567 D0.57                               Lower Chenab delta

4.                V = 0.283 D0.75                                                  Egyptian canals

LACEY'S SILT THEORY:

• Lacey stated that a channel flowing in incoherent alluvium of infinite depth of the same grade as the material carried by it would reach final stability or [final regime conditions, if the low is continuous, that is both the discharge and silt remain constant over a reasonably long period

• A channel attains regime conditions when silting and scouring are in equilibrium and a dynamic balance exists between the forces generating and maintaining the channel cross section and gradient. These ideal conditions, though rarely achieved in nature, are termed as rue regime conditions.

• A particular grade of silt can be carried by a given discharge through a channel of a selected section and a particular slope. Possibilities transporting natural silt have a bent to realize a semi-elliptical section. If the silt is coarsest, the main axis of the conic section is horizontal and if it's terribly fine, this axis is vertical.

• A channel designed with an area that's too little and also the slope vessel than needed for a given discharge can get worn until acceptable regime conditions are attained. Wherever a channel is meant with a section that is overlarge and the scope blandish than required for a given discharge the channel will deposit silt till final regime conditions are reached.

• Lacey's formulaic hold for regime conditions, i.e., constant discharge and silt grade, and are, hence, called "regime formulae. The discharge and silt factor determine the final regime velocity. Knowing the discharge and silt factor. f, regime velocity, V can be determined from which A and R can be calculated. If the shape of the channel is defined, the bed width and depth can be computed. It is usual to excavate channels with 1:1 side slopes which after silting will attain side slopes of0.5: 1 (H: V).

Lacey's Regime Equations

• Actual observations were plotted by Lacey and he proposed two relations in the first instance, such as:

V = √ (2fR/5) = 0.632√(fR)

Af2 = 140 V5

• Where, V = velocity, ms

S = silt factor,

R = hydraulic mean radius, m, and

A = area, m2

• By combining the two relations, be got the "Perimeter - Discharge" or "P-Q relation" as :

P = 4.75 √Q

Where, P = wetted perimeter, m and

Q = discharge, cumec

Further bhe arrived at "V-Q-f relation" as given below:

V = (Qf2/140)1/6

His "regime flow relations" are given as under:

V = 35.5 √(R/V).√(RS)

Or.   V = 10.8 R3/4 S1/3

And, "non-regime flow relation" is written as

V = k1 R3/4 S1/2/Na

Where, Na = Lacey’s absolute rigidity coefficient.

And K1 is a constant

The values of Na, depending on the type of material,

Values of Na for Various Materials

NO.                   MATERIAL OF CHANNEL                                Na.

1.                      Ashlars and good brickwork.                             0.013

2.                     Cement plaster.                                                      0.010

3.                     Earthen channel in bad order.                             0.0275

4.                     Earthen channel in excellent order.                   0.020

5.                     Earthen channel in moderate order.                  0.0225

6.                     Earthen channel in poor order.                              0.025

7.                    Earthen channel in very bad order.                     0.030

8.                   Rough brickwork or good stonework.                 0.015

9.                  Stonework in poor condition.                                  0.018

• The absolute rigidity coefficient is a function of the grade and density of the boundary material and does not depend on the channel conditions. Furthermore, other unseen relations are given below

"Na f relation

Na = 0.0225 f1/4

"Regime scours depth relation"

R = 0.47 (Q/f)1/3

"Regime slope equation"

S = f5/3 / 3340 Q1/6

Or. S = 0.0003 f5/3 / Q1/6

"Sills factor grain size relation"

f = 1.76 √mr

Where, m, = average particle size, mm (the average size hewing 0.323 mm)

Gives values of m, and for different materials

Lacey's Silt Factor

NO.        TYPE OF MATERIAL.             GRAIN SIZE mr mm.     SILT FACTOR ,f

1.           Bajri

Coarse.                  2.422.                2.74

Medium.               1.290.                2.00

Fine.                     0.888.                1.66

2.        Boulders

Large.                   188.800.                24.18

Medium.                72.500.               15.00

Small.                    50.100.               12.46

3.       Gravel

Heavy.                  26.100.              9.00

Medium.                 7.28.                  4.75

4.     Sand

Coarse.                 0.725.                 1.50

Medium.                0.505.                  1.25

5.     Silt

Very fine.               0.052.                 0.40

Fine.                     0.120.                0.60

Medium.                 0.158.    0.70

Standard.               0.323.                  1.00

7.5 CANAL OUTLETS:

• Canal retailers are of the subsequent 3 types: 1. Non-Modular shops a pair of Semi-Modular shops three standard Outlets.

Type 1. Non-Modular Outlets:

• In non-modular canal outlets, discharge potential depends upon on the distinction of water stages within the branch and also the watercourse. The discharge through non- modular retailers fluctuates over an outsized vary with versions in the water levels of each the distributary or the watercourse. The non-modular canal outlet is managed through a shutter at its upstream end. Loss of head in non-modular outlet is far not up to that in an exceedingly} modular outlet.

• Hence, non-modular canal retailers are very applicable for low head conditions. However, in non-modular canal outlets, the dis­charge also can fluctuate even once the water stage within the branch remains constant. Hence, it's terribly troublesome to create sure evenhanded distribution of water in any respect retailers at instances of eager demand of water.

• The non-modular canal outlet is usually in the structure of a submerged pipe outlet or a masonry sluice that is constant in the canal establishment at correct perspective to the course of float in the distributary. The diameter of the pipe varies from ten to thirty cm. The pipe is ordered on a gentle concrete basis to avoid uneven settlement of the pipe and resulting outflow problems.

• The pipe recess is generally saved regarding twenty five cm below the water level within the branch. Once vast fluctuation in the distributary water stage is anticipated, the inlet is therefore mounted that it's below the negligible water stage in the distributary. Figure 7.9 indicates a pipe outlet.

• Obviously, the discharge via non-modular shops varies with water ranges in the distributary and also the watercourse. Just in case of fields positioned at high elevations, the watercourse degree is high and, hence, the discharge is very small. However, in case of fields positioned at low elevations, the discharge is fairly larger thanks to decrease water direction levels.

• Further, relying upon the number of withdrawals of water within the head reaches, the tail reach could to boot be positively dry or get flooded. The discharge via pipe stores are often increased via deepening the watercourse and thereby decreasing the water level in it. The discharge varies from outlet to outlet attributable to waft conditions and additionally at one in all a form instances on the equal outlet due to sediment discharge in the dis­tributary channel.

• As such, correct and evenhanded distribution of water is extremely difficult. These are serious drawbacks of pipe shops. The non-modular retailers can, however, work nicely for low heads too and this can be their chief merit. Pipe outlets are adopted within the initial degrees of distribution or for added irrigation in an exceedingly season once excess give is available.

Type 2 Semi-Modular Outlets:

• The discharge through a semi-modular canal outlet (or semi-module or versatile outlet) depends solely on the water degree in the distributary, and is unaffected via the water level in the watercourse equipped a negligible operating head needed for its working is available.

• A semi-module is larger applicable for attaining evenhanded distribution of water in any respect retailers of a distributary. The only disad­vantage of a semi-modular canal outlet is that involves comparatively larger loss of head.

• The easiest kind of semi-modular canal outlet is a pipe outlet discharging freely into the atmosphere. The pipe outlet described as non-modular outlet works as semi-module when it discharges freely into the watercourse. The exit stop of the pipe is positioned higher than the water degree in the watercourse.

• In this case, working head H is the difference between water degree in the distributary and the centre of the pipe outlet. The discharge via the pipe outlet can't be expanded through the cultivator with the help of dig the watercourse associate degrees, thus, decreasing the water level of the watercourse. Alternative kinds of versatile shops embrace Kennedys gauge outlet, open flume outlet and opening semi-modules.

(i) Kennedys Gauge Outlet:

• This outlet wont to be developed via R.G. Kennedy in 1906. It unremarkably consists of an orifice with bellmouth entry, a long-expanding delivery pipe and an interven­ing vertical air column on top of the throat. The air vent pipe permits free circulation of air round the jet.

• This association makes the discharge via the outlet freelance of the water stage within the watercourse. The water jet enters the solid iron increasing pipe that could be about 3 m prolonged and at the stop of which a cement concrete pipe extension is usually provided. Water is then discharged to the watercourse.

• This outlet are often competently tampered with through the cultivator who blocks the air vent pipe to enlarge the discharge through the outlet. Due to this disadvantage and its high cost, Kennedys gauge outlet is often not used.

(ii) Open Flume Outlet:

• An open flume outlet is a weir with sufficiently constricted throat to confirm critical flow, ANd prolonged enough to create sure that the dominant section stays within the throat the least bit discharges up to the maximum. A gradual enlargement is provided downstream of the throat. The total form is made in brick masonry, but the controlling half is often furnished cast-iron or steel pad and check plates.

• This arrangement ensures the formation of hydraulic bounce and consequently the outlet discharge remains freelance of the water level within the watercourse. Figure 7.11 suggests an open flume outlet that is normally employed in Punjab. The discharge through the canal outlet is proportional to H3/2.

(iii) opening Semi-Modules:

• An orifice semi-module consists of AN orifice followed by a step by step expand­ing flume on the downstream facet (Fig. 7.12). Critical flow through the orifice causes the formation of hydraulic jump within the increasing flume and, hence, the outlet discharge remains freelance of the water level in the watercourse.

• The roof block is appropriately formed to confirm joining stream­lines in order that the discharge constant doesn't terribly much. The roof block is fastened in its place by means that of 2 bolts that are embedded in a very masonry key. For adjustment, this masonry are often destroyed and the roof block is appropriately adjusted.

• After this, the masonry secret is rebuilt. Thus, the adjustment are often created at alittle cost. However, change of state with the outlet by the cultivators would be simply noticed through the harm to the masonry key. This is often the chief advantage of this outlet.

Type  3. Standard Outlets:

• In modular canal shops, the discharge is freelance of the water levels within the branch and therefore the watercourse, at intervals cheap operating limits. These outlets could have moving elements or is also while not moving parts. Within the latter case, these are referred to as rigid modules. The modular canal outlets with moving elements don't seem to be straightforward to style and construct and are, hence, expensive.

• A standard canal outlet provides fastened discharge and, therefore, allows the farmer to set up his irrigation accordingly. However, just in case of excess or deficient supplies within the branch, the tail-end reach of the distributary could either get flooded or be deprived of water. This is often because of the explanation that the modular outlet wouldn't alter its discharge in keeping with the amount in the distributary.

• But, if an outlet is to be provided in a very branch canal that is probably going to run with massive fluctuations in discharge, a modular outlet would be a perfect choice. The outlet would be set at grade low enough to allow it to draw its due share once the branch is running with low provides.

• When the branch needs to carry excess supplies to fulfill the stress of the distributaries, the discharge through the standard outlet wouldn't be affected, and therefore the excess supplies would reach up to the specified distributaries.

• Similarly, if AN outlet is desired to be placed upstream of a regulator or a raised crest fall, a modular outlet would be an appropriate choice. Most of the modular shops have moving elements that make them pricey to put in additionally as maintain.

• Following 2 kinds of standard retailers (also called rigid modules), however, don't have associate moving part:

(i) Khannas rigid module

(ii) Gibbs Rigid Module:

(ii) Gibbs Rigid Module:

(I)  Gibbs Rigid Module

• This module has an water pipe below the branch bank. This pipe takes water from distributary to a rising spiral pipe that joins the eddy chamber (Fig. 7.13). This arrangement leads to free vortex motion. Thanks to this free vortex motion, there's heading from water (due to smaller speed at larger radiusa characteristic of vortex motion) close to the outer wall of the rising pipe. The water surface, thus, slopes towards the inner wall.

• A range of baffle plates of appropriate size are suspended from the roof of the eddy chamber specified the lower ends of those plates slope against the flow direction.

• With the rise in head, the wafer bank up at the outer wall of the eddy chamber associated impinges against the baffles and spins spherical within the compartment between 2 ordered baffle plates. This causes dissipation of excess energy and leads to constant discharge. The outlet is comparatively a lot of pricey and its sediment withdrawal is additionally not good.

(ii) Khannas Rigid passageway Module:

• This canal outlet is analogous to an orifice semi-module. However it has, in addition, sloping shoots fastened within the roof block (Fig. 7.14). These shoots cause back flow associated, thus, keep the outlet discharge constant.

• If the water level in the branch is at or below its traditional level, the outlet behaves like an passageway semi-module. However once the water level in the parent channel is higher than its normal level, water level rises in chamber A and enters the primary sloping shoot. This causes back flow and dissipates extra energy.

• The water table doesn't stay constant. There shall be seasonal fluctuations, thanks to variation in rainfall.

7.6 CAUSES OF WATER LOGGING :

• Following is also the causes of rise in water level that ultimately results in water logging of the area:

1. Over and Intensive Irrigation:

• When a coverage of intensive irrigation is adopted, then, most irrigable water is provided to bound region. This leads to serious percolation and ulterior upward jab of water table. For this reason, to avoid water logging, a coverage of large irrigation (on larger area) should be most popular from the policy of intensive irrigation (more water on tiny area).

• In transient irrigation water used to the fields is larger than the necessities of crop and this lead to deep percolation. Percolated water augments the ground water storage and motives upward shove in water table.

2. Flowing of Water from abutting High Lands:

• The water from adjacent high lands can even flow into the sub-soil of the affected land and may also purpose upward jab in water table.

3. Flowing of Water via the Canals:

• In nature the water table is usually during a kingdom of equilibrium. In several words quantity of flow is much capable the number of outflow. Thanks to building of canal, the flowing via pad ANd aspects of the canal takes place. This can increase the influx into the ground water and consequently upward shove in water table occurs.

• The upward thrust in water level takes space up to the amount once the increased influx is another time balanced by means that of the extended outflow via means of improved soil evaporation, extended transpiration and expanded discharge into seepage drains.

4. Moth-resistant Obstruction:

• Seeping water below the soil strikes horizontally. If this waft finds an tightly closed obstruction, upward shove in water table happens on the U/S aspect of the obstruction. On the identical ground if AN entrenched stratum happens at a lower place the highest layer of receptive soil, oozing water will not be during a position to travel deep and this to boot motives speedy upward jostle in water table.

5. Inadequate Natural Drainage:

• Soils having less pervious substrata (such clay) below the head layers of pervious soils, won't be capable to empty water deep into the ground. This can reason upward jostle in water level.

6. Inadequate Surface Drainage:

• If the world isn't any longer acceptable drained, the storm water will accumulate into the depressions within the area. This increased water remains percolating and reasons upward jostle within the water table. If natural drains of the neighborhood are occluded with the help of railway or throughway embankments, the water can get collected and for that reason causes water work.

7. Excessive Rains:

• Excessive precipitation may cause transient water logged conditions. If the region isn't smart drained, the vicinity may also be subjected to endured water logging.

8. Immersion thanks to Floods:

• If a land is regularly subjected to submergence by floods, water infatuated flowers may additionally grow in abundance. The weed increase will hinder the natural surface evacuation of the soil and chances of water logging get increased.

9. Irregular or Flat Topography:

• The water is instantly drained from everyday steeply slanted area. If the place is flat and irregular, the evacuation of the place is poor. This causes detention of water on the ground for extended periods, longer water table may to boot rise.

10. Inadequate capability of blood vessel Drains:

• If the capacity of the drains managing flood water is smaller than the desired size, the flood water of neighborhood drains will meet u . s . Aspect for days. This can reason serious percolation of water and should additionally after cause water logging.

11. Construction of Reservoirs:

• Seepage from reservoirs, canals, can even motive water work of the abutting spaces.

Ill Effects of Water Logging:

• The ill-effects of water logged soils are the following:

• Water logged fields normally keep wet and their tillage becomes difficult.

• Sowing of the crops is often delayed thanks to the actual fact plowing and mulching of fields is delayed in water logged areas.

• The climate of the water logged area can become damp. Standing water in pools will become stagnant. The stagnant pools of water become glorious breeding locations for mosquitoes. All these, outcomes sooner or later cause conditions damaging to the fitness of the community.

• Growth of untamed Weeds: Weed growth in water logged areas is sometimes terribly intensive. This reduces the provision of meals to the crops, as weed shares the food. Farmers need to do heap of labor to clear the fields from weeds in order that might} even have high producing of crops.

• If water logged region has canal system of irrigation, the canal water are going to be used little or no in and of itself areas need very little irrigation. This issue may to boot cause wastage of canal water, that stays crammed up in low areas and may also purpose water work of larger areas.

• Inadequate Circulation of Air in Root Zone: In water logged spaces, air circulation within the root area can become inadequate, thanks to that enterprise of microorganism and resultant growth of the plants is affected.

• Water work Causes Salinity of the Soil: The water that has up up perpetually evaporates by suggests that of capillary action. This establishes non-stop upward flow of water from the formation to the land surface. With this upward flow, the salts which are current in water and in addition in lower layers of soil rise towards the surface, leading to the deposition of salts in the root zone of crops.

• The attention of those salts (which are unremarkably alkaline) contains a erosion impact on the roots, that reduces the diffusion diversion of the vegetation and reduces their growth. Such soils which contain large concentrations of venturesome salt within the root region are recognised as saline soils. From this it is simply declared that at anywhere there's water logging, salinity could be a must.

• In wet areas, temperature of the soil is mostly low. Lower temperature will no longer allow microorganism to feature fascinating and intrinsically provide of food to the flowers is reduced.

7.7 REMEDIAL MEASURES OF CONTROLLING WATER LOGGING:

• It is obvious that water-logging is controlled provided that the extent of water entering into the soil is checked and reduced. To achieve this, the flow of water into the ground water reservoir have to be compelled to be shrivelled and therefore the outflow from this reservoir ought to be increased.

• Following are a number of the lives which may be adopted for dominant water logging:

• All the canals and water courses, used for irrigation and alternative purposes, need to be lined. It's thought to be one amongst the foremost very good measure of controlling water logging.

• Intensity of irrigation within the section probably to be water logged got to be reduced. In areas wherever water story is incredibly high, irrigation throughout Kharif season could in addition solely be allowed. Throughout Rabi season, the cultivators also can he asked to irrigate from wells.

• Cultivators may additionally be arch for monetary use of water. They have to be compelled to be created to know the importance of irrigation water. They have to be asked to divide fields into tiny Kiaries in order that deep percolations do now not occur.

• In order to limit ooze from Kucha canals, they ought to be designed with lesser depth of water. Lesser depth can induce lesser head for seepage losses.

• Certain crops need bigger water than others. If a particular subject is often planted with a crop requiring a lot of water the probabilities of water-logging are more. So as to avoid this, vegetation requiring lesser, and additional volume of water, have to be compelled to be sown alternately within the fields.

• Optimum Use of Water: bound mounted volume of water for a singular crop offers fine results. Under that and quite that reduces the yield. However, most of our farmers are unaware of this fact. They perpetually suppose that greater the waterings you apply, to the field, the upper goes to be the yield and thus they struggle to use bigger and a lot of water. This may be checked via instructing the farmers.

• Revenue got to be charged on the groundwork of extent of water utilized and now not in accordance to the place irrigated. This live has its own sensible drawbacks but in theory the cultivator would be tempted to irrigate greater region with same amount of water.
• Providing Intercepting Drains: Intercepting drains on the canals, specifically in high hill reaches need to be constructed. These drains intercept ooze and percolation from the canals. They have to be compelled to not be ordered terribly shut to canals, due to the actual fact then they'd be drawing water from the canals directly.
• Introduction of raise Irrigation (Well Irrigation): Well irrigation utilizes the underground water for irrigation. Thus the areas that are probably to be water logged in getting ready to future have to be compelled to be irrigated from wells and depth of irrigation from canals need to be shriveled considerably. Well irrigation would lower the bottom water-table and possibilities of land changing into water-logged are eliminated.

• Improving the Natural voidance of the Area: The natural system of the placement ought to be such no water is allowed to face for extended period and as quickly as rain water drops on the bottom it should be instantly diode to empty. For this favorer drains got to be maintained clear from weed growth ANd any obstructions be removed. Natural slopes of drains must be maintained via clearing silt from time to time.

• Provision of an economical avoidance System: AN atmosphere friendly system have to be compelled to be provided to drain away the storm water. a real drainage widget could encompass floor drains further as sub-surface drains. If region is incredibly intensively water- logged and soil is of poor drain ability, underground porous, or tile drains have to be ordered to expeditiously decrease down the water able.

• Adoption of mechanical device methodology for Irrigation: this system virtually utterly eliminates the percolation losses from water courses. Most share of this water is used in structure of consumptive use and losses are shriveled to minimum.

7.8 LINING OF CANALS :

• Principle of conservation needs that full use of obtainable water be created by manner of minimizing the water loss thanks to ooze within the course of conveyance in the canals.

• Canal lining presents the answer due to the actual fact it helps conserve the expensive impounded water in the other case misplaced at some purpose of conveyance thanks to excessive ooze losses in unlined section.

Objectives of Canal Lining

• Following are the goals of canal lining:-

• To minimize the losses because of flowing

• To defend the locality prone to water work due to upward thrust in water table

• To increase the discharge potential of the canal

• Improvement of command and bigger operating head for power generation

Advantages of Canal Lining

• Following are the advantages of canal lining:

• Reduction in seepage losses

• Low maintenance cost

• Minimizes the likelihood of breaching of canals

• Prevents weed growth

• Improved hydraulic effectuality of canals

• Reduces move sectional dimensions of canal

• Improvement in command

Disadvantages of Canal Lining

• Higher initial investment

• Repair is costly

• Shifting of outlet is expensive as a result of it contain activity and relaying of lining.

• Longer construction period

• Sophisticated development tools and labor is needed.

7.9 Types of Canal Lining

• Following are the twelve common varieties of Canal lining.

• Reinforced Concrete Lining

• Plain Cement Concrete Lining

• Prefabricated Cement Concrete Lining

• Shotcrete Lining

• Brick or Tile Lining

• Asphalt Concrete Lining

• Stone Lining

• Soil Cement Lining

• Compacted / stable Earth Lining

• Membrane Lining

• Exposed Membrane

• Burried Membrane

• Brick Lining in Canal

• Brick Lining in Canal

• Selection of appropriate sort of Lining

1. Imperviousness:

• To  save flowing losses and as a very important anti water-logging measure, it ought to guarantee most degree of water-tightness. Cement and concrete lining is a lot of fast than tile lining.

2. Hydraulic Efficiency:

• The carrying capability of a channel varies reciprocally with the worth of constant of roughness of the lined surface. The constant of roughness will increase with the deterioration of lined surface with the passage of time. Concrete and tile linings are hydraulicly most efficient.

• Canal lining offers the answer as a result of it helps conserve the pricey impounded water otherwise lost throughout conveyance because of high flowing losses

3. Durability:

• The lining ought to be sturdy and durable. It should be immune to wearing, weathering, natural action of salts gift in soil, thermal and wet changes.

4. Structural Stability:

• The lining should be fairly stable to face up to the differential undersoil water pressure due to subsoil water and backfill obtaining saturated through seepage or due to fulminant draw down.

5. Economy:

• The lining is even just in case the advantages occurring from it offset the primary value and sequent maintenance and provides an affordable come on the capital investment. The liner ought to be economical in initial cost, repair and maintenance.

6. High Velocity:

• Lining is meant to face up to most rate of flow in order that the section is that the minimum possible.

7. Life:

• Channel Lining in Progress

• The lifetime of lining should be as intended. Cement concrete lining has the longest established life (over sixty years) with least maintenance.

8. Weed Growth:

• The lining should be in-penetrable to root of plants, entirely eliminating the likelihood of weed growth to stay the flow smooth, clear and perfect.

9. Handiness of construction material:

• The economical lining is that the one that makes use of the offered construction material at or close to the site.

10. Labor Strength Available:

• The optimum utilization of the sort and strength of labor available for work ought to be potential with the type of lining chosen.

11. Operation and maintenance charges:

• The lining selected should need least operation and maintenance charges; simple reparability and at economical value as just in case of tile brick and formed concrete lining compared to incite concrete lining.

12. Sub-grade:

• Adaptability of the type of lining selected to the given sub-grade is of preponderating importance.

13. Resistance to abrasion:

• Sediment carried by canal water damages the liner by abrasion. Concrete and boulder lining are most resistance to abrasion compared to alternative linings.

Types of Canal Lining

Reinforced Cement Concrete lining:

• Most concrete linings put in in older irrigation channels were bolstered. Throughout recent years reinforcement has been omitted where doable to scale back construction cost.

• Unreinforced concrete linings are to some extent liable to harm by fluid mechanics or alternative pressure underneath the liner than ferroconcrete linings. Wherever surprising hydrostatic pressures are encountered under the lining, unreinforced concrete ruptures additional without delay than the reinforced concrete.

• The reinforced concrete lining may be even under uncommon conditions, comparable to high back pressures, high flow velocities within the canal, unstable sub-grade and in reaches where failure would endanger life and property outside the canal.

• The main perform of reinforcement is to attenuate the tendency and severity of cracking and forestall separation of many elements of the concrete slab. Power channel of Ghazi Brotha Hydropower Project is RCC lined canal.

Plain Cement Concrete Lining:

• Concrete linings in all probability represent the simplest kind wherever advantages justify their high cost.  Properly designed, made and maintained concrete linings ought to have a median serviceable lifetime of over forty years. Some linings still in physical fitness are fifty to sixty years old.

• Concrete linings are appropriate for giant and tiny canals, and for each high and low velocities. They fulfill much each purpose of lining.

• They are typically subject to some cracking, however cracks which enable considerable escape may be sealed with asphalted compounds. Expensive maintenance is rarely necessary.

• These are made by well-designed premixed cement concrete combineture of chosen aggregates, Portland cement and water. The concrete mix ought to have enough physical property for thorough consolidation. At a similar time, it can be set manually or by mechanical means. Hand putting is feasible solely in little canals and distributaries.

• Concrete linings usually accommodates a pair of to six inches thick slabs placed on well ready canal sub-grade.

Prefabricated Cement Concrete Lining:

• Canal lining with prefab cement concrete slabs is more appropriate at places wherever low cost labour, combination and transport are simply available. This kind of lining is most popular over the insitu concrete lining due to higher management over mixing, moulding and action which may be achieved in an exceedingly controlled casting yard.

• Prefabricated slabs are straightforward to position on steep side-slopes as compared to birthing of cement concrete at website in similar conditions.

• This takes lesser time for construction than that of unchanged concrete. Nominal reinforcement is needed to avoid breakage throughout haulage. Operation and maintenance cost is low with a median lifetime of fifty years.A combination of in-situ concrete within the bed and formed block on the edges can even be adopted with advantage. Thickness of precast slabs could vary from a pair of to 2.75 inches or additional.

Shotcrete Lining:

• Shotcrete could be a term adopted for applying cement-sand mortar underneath gas (air) pressure.  If shotcrete is employed in skinny layers of 1/4″ to 1/2″ on soil, it usually offers trouble. A thick coat of 1.0 to 1.5 inches is sturdy however it's more expensive than a cement concrete layer of equal thickness. Use of shotcrete on rigid but porous or deteriorated surfaces is incredibly useful. Geocomposite liner with a 3-inch shotcrete cowl is used for lining choice in playwright CANAL, in Wenatchee depression Washington.

Brick or Tile Lining:

• This kind is usually used if smart quality tiles or bricks and low cost labor are available. The tiles/bricks ought to be factory-made from the soil having a clay content ten to twenty p.c and salt content of less than 0.3 percent.

• Clay tiles are terribly porous and aren't a lot of effective in preventing ooze losses.  Brick/tiles linings are tried on numerous canals within the sub-continent. The most benefits of brick/tile lining are that the bricks/tiles may be manufactured in the neck of the woods of the work.

• No contraction and enlargement joints are needed and these are straightforward to put and maintain. The most downside within the manufacture of bricks/tiles is that the downside of non-availability of appropriate soil as most of the soils in West Pakistan contain salt considerably above the prescribed limit. Mohajir Branch (of Thal Canal), BRBD, city Branch etc are brick lined.

Asphalt Concrete Lining:

• Asphalt mixed with sand and gravel, is employed as a lining mixture in the same manner as concrete made up of Portland cement. Asphalt concrete linings once properly made are reminiscent of portland cement concrete linings in several respects.

• The thickness of lining varies from a pair of to 4 inches. The serviceable life varies from fifteen to twenty years

• The benefits as compared with Portland cement concrete linings embrace the likelihood of placement even throughout phase transition temperatures. It's higher adjustment to sub-grade changes and possibility to use slightly poorer quality of aggregate. Initial value of this kind of lining is incredibly low on account of extended worth distinction between asphalt and portland cement.  ooze losses may be reduced to as low as within the case of portland cement concrete lining however these can increase significantly once the weed growth over the time with cracks development.

Stone Lining:

• Lining of stone masonry may be applied in areas wherever appropriate materials, comparable to stone are available. The development of this kind is comparatively slow and therefore the value of labour is that the major expense. Ooze losses is also terribly high if the stones aren't set in mortar. This kind is additional suitable for main canals underneath scouring action or in locations where there's movement of gravel on the bed.

Soil-Cement Lining:

• Soil-cement linings are made with mixture of sandy soil, Portland cement and water. This mixture hardens to a concrete like material. The lifetime of this type of lining varies from ten to 12 years however if correctly made and maintained then it should dish to twenty years or so. The thickness of lining varies from four to six inch. Initial value of soil cement lining is low as compared to others.

• It is appropriate for the areas wherever smart sandy soils are out there inside or within the neck of the woods of the project area. The ooze losses may be reduced thereto of the cement concrete lining, if proper mixture and compaction is done. It but affords less structural stability.

Compacted / stable Earth Lining:

• Earth lining consists of compacted earth, mixed with some chemicals which improve the stabilization of the earth. This is often relatively the most affordable type.

• Thickness of lining varies from twelve to twenty four inches for bed and even additional for steep slopes.Seepage losses are more and therefore the structural strength is additionally poor. It's resistive to weed growth. Deep cracks develop on the surface, if the canal is dry. It needs top-most quality of compaction in order that wetness content might not increase or decrease. The common lifetime of this kind of lining is concerning ten years.

Exposed Membrane Lining:

• Exposed membranes embrace skinny membranes of asphalt, plastics and artificial rubber. They possess low permeability, however haven't any structural strength. Ooze losses principally depend on weed growth and different mechanical damages furthermore as weathering. The lifetime of this kind is just many irrigation seasons.

• Due to shorter life the economic use of exposed membrane lining is restricted to special cases, adore temporary emergency linings, short sections less susceptible to damages etc.

Buried Membrane Lining:

• A buried membrane canal lining consists of a comparatively thin and fast water barrier lined by a protecting layer that forms the water-carrying prism. The asphalt spray, plastic film, clay and prefab asphalt are used as construction material for membranes. Since the protective covering doesn't get properly connected with the plastic sheet, organic process and slippy of earth on facets sometimes take place. The minimum side slope suggested is 2:1.

• The lifetime of the liner depends for the most part on erosion resistance of canopy material. Practiced personnel are required; it is transported simply on the canal. Suitableness of excavated soil as cover material is very important for economic reasons.

7.10 DRAINAGE OF IRRIGATION LANDS :

• Improves soil structure and will increase the soil productivity,

• Facilitates early plowing and planting,

• Increases the depth of root zone thereby increasing the on the market soil wetness and plant food,

• Increases soil ventilation,

• Increases water infiltration into the bottom thereby decreasing eating away on the surface,

• Creates favourable conditions for growth of soil bacteria,

• Leaches excess salts from soil,

Maintains favourable soil temperature, and

• Improves sanitary and health conditions for the residents of the area.

• Water table is down by eliminating or dominant sources of excess water. Improvement in natural system and provision of artificial drain system will be of appreciable facilitate in lowering the water table. Natural drainage systems can be properly maintained at low prices and are possible suggests that to safeguard irrigated lands from excessive percolation.

7.11 NECESSITY METHOD:

• During rain or irrigation, the fields become wet. The water infiltrates into the soil and is keep in its pores. Once all the pores are stuffed with water, the soil is alleged to be saturated and no additional water is absorbed; when rain or irrigation continues, pools could type on the soil surface.

• During significant rain the higher soil layers become saturated and pools may form. Water percolates to deeper layers and infiltrates from the pools.

• Part of the water gift within the saturated upper soil layers flows downward into deeper layers and is replaced by water infiltrating from the surface pools.

• When there is no more water left on the soil surface, the downward flow continues for a while and air re-enters in the pores of the soil. This soil is not saturated anymore.

• However, saturation may have lasted too long for the plants' health. Plant roots require air as well as water and most plants cannot withstand saturated soil for long periods (rice is an exception).

• Besides damage to the crop, a very wet soil makes the use of machinery difficult, if not impossible.

• The water flowing from the saturated soil downward to deeper layers, feeds the groundwater reservoir. As a result, the formation (often called groundwater table or just water table) rises. Following significant rain or continuous over-irrigation, the bottomwater table may even reach and saturate a part of the basis zone (see Fig. 97). Again, if this example lasts too long, the plants may suffer. Measures to manage the increase of the water table are therefore necessary.

• The removal of excess water either from the ground surface or from the root zone is named drainage.

• Excess water is also caused by rainfall or by victimization an excessive amount of irrigation water, however may additionally produce other origins adore canal seepage or floods.

• In terribly dry areas there's often accumulation of salts within the soil. Most crops don't grow well on salty soil. Salts is washed out by percolating irrigation water through the rootzone of the crops. To realize adequate percolation, farmers can apply additional water to the sector than the crops need. However the salty percolation water will cause the water level to rise. Drain to manage the water table, therefore, conjointly serves to control the salinity of the soil.