CIVIL ENGINEERING

Tuesday, February 4, 2014

Tube Well Irrigation

Tube Well Irrigation

Occurrence of ground water:-During the rain or if water is collected on the surface of soil, then this water is goes downward till the hard strata is came. The moisture/water is then becomes static and collected in zones of soil which may be saturated or unsaturated zone .this water collected is then called occurrence of ground water in that zone.

Water table:-The upper most surface level of the zone of saturation is called a water table. When the rain water is collected in pound, then the water will goes downward due to seepage from unsaturated soil to saturated soil. This water is stopped by hard strata or rocks. So the seepage water is collected in saturated zone of soil layer. This water table is thus called underground water table.

Radius of influence:- The radial distance from the centre of a wellbore hole to the point where there is no lowering of the water table is known as the radius of influence.

Depression head:- When the water is pumped out from the wall, then the level of the well is reduced, then the difference in levels between original water level in the well is called depression head.

Cone of depression:-A cone of depression are occurs in aquifers when ground water is pumped out from a well. In the unconfined aquifers the cone of depression is a reduction in pressure head surrounding the pumped well.

Aquifers:-It is a wet underground layer of water bearing permeable rocks (gravels, silts or sand).these are saturated regions of the subsurface that produce economical quantity of water to lift irrigation by tube well or well.

Unconfined aquifers:- Those aquifers which contains water table in their upper boundaries. This area contains almost all the ground water table. These aquifers cannot contain by any impervious layer.

Confined aquifers:- It is the aquifer which is confined by an impervious stratum at the top. That the water is contained between the hard strata around it just like as water is flowing through pipe.

Yield of well:- When the water is lifted from the well contineously. Then the water level goes decreasing and there will be contribution of water from the surroundings layer into the well. If the lifting / water taken is increasing then the drawdown of water will be increasing and the fine silt /sand also entered into the well will started from the previous strata of the soil. At this stage water structure become unstable . due to this drawdown is always kept

Irrigation Engineering ] Water Logging and Drainage and Ground Water Re-charge

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Irrigation Engineering

Water Logging and Drainage and Ground Water Re-charge

Definition of water logging:-

The natural process of making saturation of soil and unproductive due to excessive in its pore is known as the water logging.

That area where it occurred is called water logging area.
Equation:-
I = O+S
Where,
I= inflow of water
O = outflow of water
S= storage of water
Cause of water logging:-
Topographic condition: - when the surface of soil is not uniform, then the rain water collects and make small pound. So due to permeability of soil, this water increases the water table, hence water logging occurred.
Inadequate drainage:-
If the drainage facility is not adequate then, it will increase the chance of water logging by increasing the water table.
Canal seepage:-
Seepage of water from the earthen canal also raises the water table and hence water logging occurred.
Over irrigation:-
Irrigation water if used in excess over the field’s .then it will raises the water table and hence water logging occurred.
Rainfall and flood:-
Excess rainfall or flood will also cause the increasing in water table. By which water logging occurred.
Effects of water logging:-
Anchorage problems of plants and trees:-

If the soil becomes saturated then, the plant roots become very shallow and are easily uprooted when wind blows.

Growth of water loving wild plants:-
When the soil is water- logged water loving plant grow up which are harmful to the crop growth.
Increase in harmful salts:-
When the water table rise, then the upward moment of water brings harmful salts in the crop root zone. After evaporation, the water leaves behind salt, which reduce the production of crops.
Lowering of soil temperature:-
If moisture is present in the soil pores, the temperature of soil lowers down. Then bacteria activity retarded, which affects growth of crops badly.
Reduction of time for maturity:-
When the underwater is logged, then the crop period shortens which reduces the crop’s maturity time.
Detection of water logged area:-

1. The water logged area can be easily detected by knowing the intensity of rainfall and the amount of runoff. So to calculate the quantity of rain water which infiltrate into the sub soil and help in raising the level of water table.

2. If the above information is no available then, a hole is made to be drilled to determine the level of underwater below the surface. If the water is available nearer to the root zone of the crops, then the area is called waterlogged area.

Preventive measures:-

1. Controlling seepage from the canals: -

By following measures should be adopted to reduce seepage from the canals.

a) By lowering the F.S.L of the canal:-

When the full supply level of canal is lowered then the loss of water’s seepage loss is reduced, and hence water logging is also reduced.

b) By lining of canal :-

The bed and sides of the canal should be lined by protective materials so that seepage loss is reduced and hence water logging is also reduced.

Disposal of rain water:-
Rain water as soon as, it falls on the earth’s surface should be disposed of as soon as possible otherwise it will increase water logging.
Reducing the intensity of irrigation:-
The intensity should be reduced in this area where water logging occurred. Irrigation should be done rotation wise in different seasons.
REMEDIAL MEASURES:-
The followings methods are adopted to reclaim the water logged areas.

Installation of lift irrigation system:-

When a tube well systems are introduce, then the level of underground water goes down and hence water logging is reduced.

Implementation of drainage scheme:-

Area is reclaimed by introducing overland and subsurface drainage schemes. Surface drainage may be of:-

1) Providing seepage drain

2) By providing storm water or surface drain.

3) By providing lining of canal.

4) Implementation of tube well in fields or water logging area.

Surface drain: -
Surface drains are that construction may be natural of artificial which remove surplus water from any area and placed over the surface of the soil. While aligning surface drains followings points which are given below, should be considered.
1)      Drain should follow lowest contour in a natural drainage line.
2)      The total alignment of drain should be straight, so that length of the drain is reduced and all this reduces the cost of construction of that drain.
3)      The drain should not pass through any ponds and it also should not cross irrigation canals
Sub surface drains:-
When the depth of the surface drain increases, then the drain scheme becomes uneconomical. In this situation subsurface drain is used. Subsurface drain is pipe drain laid in permeable stratum below a ground water table. These drains are circular pipes made of vitrified clay. The trench is excavated in the ground up to the required depth and tile line is laid on 15 cm sand bed.

Ground water recharge:-

It is a process where water moves downward from surface water to ground water. This process usually below plant root. The water table recharge occurs naturally of artificially.
Natural Ground water is recharge by rain water, by melting of snow, by river and lake through permeability of soil
Artificial ground water is recharge by making a pond, reservoirs and by storing rain watered.

[INTRODUCTION ] IRRIGATION

(IRRIGATION) [CIVIL ENGINEERING]

INTRODUCTION

IRRIGATION:- The art, science and practice of supplying water artificially to land for producing crops is called Irrigation.

NECESSITY OF IRRIGATION:-

1) Non uniformity of rainfall:-
Rainfall varies place to place as Punjab, Rajasthan, etc. rainfall is not same. Therefore in order to meet the water requirements of crop, it is very essential to provide facilities for irrigation.

2) Crop requirement:-

The requirement also depends upon the type of crop, its depends upon the time of sowing & the period of maturity.

3) Economical use of water:-

The crop production can be increased by supplying of proper quantity of water at proper time.

TYPES OF IRRIGATION:-

Artificial Irrigation:-
The process of supplying water artificially for the purpose of irrigation the field.

The irrigation done by construction headwork sand canal is also referred as direct irrigation or river canal irrigation.

Types of Artificial Irrigation

1) Lift Irrigation :-

The process of supplying water to the field for crop production by lifting it from its sources is called Lift Irrigation.

e.g. by wells, tube wells

2) Flow Irrigation :-

The process of supplying water to the by flowing water by gravity is called flow Irrigation also called canal Irrigation.

3) Sprinkler Irrigation :-

The process of irrigation in which water is applied to the land through a system of pipe network connected to fine spray nozzles is called Sprinkler Irrigation.

METHODS OF IRRIGATION

1) Free Flooding :-

In this method, water is supplied through ditches. It flows across the field. This method is mostly used in India, U.S.A., Egypt etc.

2) Border Flooding:-

In this farm id divided into no. of strips. The width & length of each strip should not exceed 9-18 m & 100 – 400 m respectively.

3) Check Flooding :-

In this case, farm is divided into small check areas. These are surrounded on all sides by low, flat ridges.

4) Basin Flooding :-

It is same as check except that it is applied to orchard.

5) Furrow Method :-

In this case crops are grown by supplying water b/w crops rows. This method consists in Appling water to the field by furrow supplying 8 – 24 cm per 100 m.

DESIGN OF IRRIGATION CANALS

Irrigation Canals:-

The canals used for irrigation purpose are called irrigation canals. Canals may be defined as artificial channels constructed on the ground to carry water from one place to the other. The canals may be classified as an alluvial or non alluvial canal which is based on the nature of source of supply. It may be termed as inundation or a permanent canal. Depending on how the water is fed from one system to another.

Classification of canal:-

1. Alluvial Canal:-

A canal flowing through alluvium soil (silt, sand and gravel) is called an alluvial canal. A canal flowing through such sediments transports some of this material along with the flowing water. These canals take supplies from rivers which always carry sediments rolling on the bed or held in suspension , which is passed on to the offtaking canals . If the velocity in a canal is very high, the suspension particles are not deposited, but if the velocity is very low, the sediment held in suspension will get deposited.

2. Non Alluvial Canal:-

Non alluvial canals are those that have been lined with some suitable material to provide a rigid bed banks so as to avoid the problems with alluvial sides (boundaries) of a canal.

3. Inundations canal :-

Those canals which depend for their supply on the periodical rise in the water level of the river from which they are taken off. The supplies of these canals are not always of the desired level .these canals are fill with water in Rainey season or in monsoon.

4. Permanent canal:-

A canal is said to be permanent when its source of supply is sufficiently well assured so as to warrant the construction of a regular grade channel supplied for regulation and distribution. These canals are provided with permanent masonry head works, regulator and distribution works and are constructed with engg. skills. The lining of the irrigation canal is also a protective work as it helps in minimizing the chances of water- logging.

5. Productive Canals:-

The canals, which indicate at the time of design and planning, that the total income will exceed the annual maintenance charges, are called productive canals.

6. Feeder or Link canal:-

Link canals supply water from a reservoir to another place wherefrom a given irrigation canal system is fed. These canals are used for diverting surplus water from one source to another.

Design of irrigation canals –

Chezy’s formula:-

Chegy ‘s formula for the velocity of uniform flow in an open channel is given by the relation:-

V=C √ ( RS )

Where,

V = velocity of flow in m/s

S = bed slope of the channel

C = Chezy’s coefficient

C= 23+(1/N)+(0.00155/S) / 1+[ 23+(0.00155/S] (N/ √ R)

C = 87 / 1+(K / √ R)

N= rugosity coefficient depending upon the nature of the bed and sides of the channel.

R = hydraulic mean radius

R = area of cross section of flow / wetted perimeter

Manning’s formula:-

The mean velocity for a uniform flow as given by Mannings is given by

V= (1/n) R^2/3S1^/2

The value of n depends upon the bed and side material of the channel.

Kennedy’s theory:-

Sediment in flowing canal is kept in suspension solely by the vertical components of the constant eddies (opposing forces by bed of canal) .In order to obtain an expression for the silt supporting power of a stream, it may be safely assumed that the quantity of silt supported power is proportional to the width of the bed, all other conditions remaining the same. Hence the amount of silt supported in a stream may be expressed by A.B V₀^n-1.

Where,

A= some constant

B= bed width

V_{0 =} velocity in stable state.

n= some index. It is depends on the type of silt.

Design of irrigation canal using Kennedy’s theory:-

When an irradiation canal is to be designed by the Kennedy’s theory it is essential to know ,F.S.D (Full supply discharge ,Q ) , coefficient of rugosity (N) ,C.V.R (m) critical velocity ratio & longitudinal slope of channel (s) . By making use of the following three equations a canal section can be designed by trials.

1. V =0.546 MD^0.64

2. Q = A.V

3. V=C √ ( RS )

R = Hydraulic mean Radius

S = bed slope

Procedure:-

1. Assume a reasonable full supply depth D.

2. Using equation 1 find out the value of V.

3. With this value of V, using equation 2 & find out the value of A.

4. Assuming side slopes & from the knowledge of A & D, find out bed width B.

5. Calculate R, which is ratio of area & wetted perimeter.

6. Using equation 3 , find out the value of actual velocity V.

When the assumed value of D is correct, the value of V in step no 6 will be same as V calculated in step no 2. If not another suitable value of velocity come out to be the same.

Lacey‘s theory:-

According to lacey the dimensions, i.e width, depths and slope of a regime channel to carry a given discharge & given silt charge are fixed by nature.

Regime channel:-

A channel will be regime if it flows in incoherent unlimited alluvium of the same character as that transported & the silt grade charge are all constant, a channel is said to be in regime when

1. The discharge of the channel is constant.

2. The silt grade & silt charge are constant.

3. The channel is flowing in unlimited in coherent.

4. The channel has freedom to form its own section alluvium of the same character as that transported.

Incoherent alluvium:-

Soil composed of loose granular grade material which can be scoured with the same case with which it is deposited.

These conditions are very rarely achieved & very difficult to maintain in practice.

Hence according to Lacey’s conception regime conditions may be subdivided as initial and final.

Fig 1

Initial Regime:-

If a channel is excavated initially with some defective slope & somewhat narrow section ,it is free immediately to throw down the incoherent silt on the bed there by increasing its bed slope & generating the increased velocity to achieve a non silting regime.

Final Regime:-

A channel which has formed its shape & slope in its own silt finally is said to be in final regime.

Design of irrigation canal making use of the Lacey theory:-

When Q & f = m² are known, design can be done in the following ways.

1. Find out the value of V by using equation V = 0.4382 (Q.f^2)1/6.

2. Calculate the value of R using equation R =4.825 Q^1/2.

3. Calculate wetted perimeter (the area which covered with water) Pw using equation Pw = 4.825 Q^1/2.

4. Calculate cross sectional area A , using equation Q = A.V

5. Assuming side slopes , calculate the full supply depth from A , Pw & R using equations a) A = BD+ D² /2 OR b) Pw = B + √ 5 D

Where B = width of canal

6. Calculate longitudinal slope of the canal using equation = f^5/3 / 3316 Q^1/6

Comparison between Kennedy’s and Lacey’s theories:-

1. The basic concept regarding silt transportation is the same in both.

2. Kennedy assumes that the eddies are produced on the bed of canal only but Lacey proposed that eddies are produced along complete wetted perimeter.

3. Lacey states that as the shape of an irrigation canal is fixed to particular geometrical figure, it cannot achieve final regime conditions and hence may be said to achieve initial regime only. Kennedy assumes that when there is neither silting nor scouring the channel is in its regime condition.

4. Kennedy selects Kutter’s formula for designing irrigation canal. But in Kutter’s formula value of N is fixed.

5. Kennedy use term C.V.R (m) but he did not give any basis for calculating m. He simply states that it depends on the silt change & silt grade flowing in canal. But lacey has introduced silt factor f. He related f to mean diameter of the bed material & given basis to calculate f. The formula is f = 1.76 √ mr

6. Kennedy gives no idea for calculating longitudinal regime slope . but lacey gives a regime slope formula.

7. Design based on kennedy’s theory can only be achieved by making trials . lacey gave important wetted regime perimeter equation

Pw = 4.825 Q^1/2

Canal lining :-

The impervious layer which protects the bed and sides of the canal from seepage is called canal lining.

Advantages of lining :-

1. To save water for irrigation.

2. To maintain the stability of section which reduces the change of shifting of outlets.

3. To minimize the costs of maintenances.

4. To carry water at higher velocities.

5. To prevent canal’s bank erosion.

6. To increase in canal capacity.

7. Removal of silt & plants from the sides of beds.

8. Minimizing of flood dangers.

Disadvantage:-

The cost are increased.

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