Irrigation Engineering (Course Materials)

Short questions

Chapter 1(HYDROLOGY)

1. What do you mean by ‘hydrology’?

Ans- The different forms of water available above the earth surface or below the earth

surface is known as hydrology.

2. What do you mean by ‘hyetograph’?

Ans- The graphical representation of rainfall and run-off is known as hyetograph.

3. What do you mean by ‘unit hydrograph’?

Ans- A unit hydrograph may be defined as a hydrograph which is obtained fron one cm of

effective rainfall for unit duration.

4. What is a rain gauge?

Ans- The instrument which is used to measure the amount of rainfall is known as rain gauge.

5. What do you mean by “Catchment Area”?

Ans- Catchment area or drainage basin is an area of land, where the surface water from

rainfall, snowmelt, or ice flow into a lower elevation to form a single body of water, that may be

a lake or a river

6. Write down Dicken’s formula & and ryve’s formula for estimation of flood

discharge and explain the terms used thereon.

Ans- Dicken’s formula :-

Q=C X Q= Discharge in cumec; A= Catchment area in sq.km; C= A constant

Ryve’s formula

Q=C X Q= Discharge in cumec; A= Catchment area in sq.km; C= A constant

Long questions

1. Describe hydrological cycle with neat sketch.

Ans- diagram ( hand written notes)

The water of the universe always changes from one state to other under the effect of

the sun. The water from the surface sources likes lakes, rivers, oceans etc converts to

vapour by evaporation due to solar heat.

The vapour goes on accumulating continuosly in the atmosphere.

This vapour is again condensed due to sudden fall of temperature and pressure and

thus clouds are formed. These clouds again causes the precipitation(i.e rainfall)

Some of the vapour is converted to ice at the peak of the mountains. The ice again

melts is summer and flows as rivers to meet the sea or ocean.

These processes of evaporation, precipitation and melting of ice go on continuously

like an endless chain and thus balanced is maintained in the atmosphere.

This phenomenon is known as hydrological cycle.

2. Write short notes on Hydrograph.

Ans- Graph ( hand written notes)

The hydrograph is a graphical representation of the discharge of a river(in cumec)

against the time( in hr or days).

The discharge is plotted as ordinate (y- axis) and the time is plotted as abscissa (x-

axis).

During the dry season, there is only base flow(i.e ground water flow) but no surface

run off.

In rainy season, at the beginning of the rainfall there is only base flow.

After some period, when the initial losses ( like interception, evaporation, and

infiltration) are fulfilled, the surface runoff starts and hence the discharge of the river

goes on increasing. Hence the limb of the curve rises which is called the rising limb.

This line reaches to the peak at the value ‘C’. Again when the rain stops, the flow in

the river decreases and the limb of the curve declines. This limb is known as

recession limb.

The discharge at the point C indicates the maximum discharge.

The total area under the curve ABCDE indicates the total run off

3. Write short notes on Unit hydrograph.

Ans- Graph ( hand written notes)

A unit hydrograph may be defined as a hydrograph which is obtained from one cm of

effective rainfall for unit duration.

Here effective rainfall means the rainfall excess which flows directly to the river or

stream.

The unit duration is the period during which the effective rainfall is assumed to be

uniformly distributed.

The unit duration may be considered as 1hr, 2 hr, 3hr, 4hr…. etc.

For example, if a hydrograph is prepared for an effective rainfall of one cm lasting

for 2 hours, then it is known as 2 hr. unit hydrograph, for the duration of 3 hours it is

known as 3 hr unit hydrograph

4. What are the factors affecting run-off.

Ans- The factors affecting run-off.are:-

a. Intensity of rainfall: - If the intensity of rainfall is more, the corresponding run-off

will be more. Again the intensity of rainfall is low, the corresponding run-off will be

low.

b. Soil characterstics of catchment: - In the catchment area consisting of rockey or

clayey soil, the run off will be more. Again if the soil characterstics of the catchment

is sandy , the runoff will be low as the loss of infiltration is more.

c. Topography of the catchment: - If the ground slope of the catchment is steep, the

runoff will be more, If the ground slope is flat and consists of depressions, the runoff

will be low.

d. Shape and size of catchment: - If the catchment area is large and fan shaped, the

runoff will be more. If the catchment area is small and fern shaped, the runoff will be

low.

e. Geological condition:- If the catchment area consists of fissures, cracks etc, the

water losses will be more and the runoff will be low.

f. Weather condition: - If the temperature in the catchment area is high, the

evaporation loss will be more and hence run off will be less and vice versa.

g. Cultivation and vegetative cover in catchment area:- If the catchment area

consists of more cultivated area and forest areas, the run off will be low.

5. Describe briefly various types of rain gauges.

Ans- Types of rain gauges are-

A. Non- recording type rain gauge:-

Simon’s rain gauge is a non recording type of rain gauge which is most common

used.

It consists of metal casing of diameter 127 mm which is set on a concrete foundation.

A glass bottle of capacity about 100 mm of rainfall is placed with in the casting.

A funnel with brass rim is placed on the top of the bottle.

The arrangement is shown as below:-

The rain fall is recorded at every 24 hours, Generally, the measurement is taken at

8.30 a.m everyday. In case of heavy rainfall the measurement should be taken 2 or 3

times daily so that the bottle does not over flows. To measure the amount of rainfall

the glass bottle is taken off and the collected water is measured in a measuring glass

and it is recorded. When the glass bottle is taken off it is immediately replaced with a

new bottle of same capacity.

Diagram (hand written notes)

B. Recording type rain gauge:-

In this type of rain gauge, the amount of rainfall is automatically recorded on a graph

paper by some mechanical device.

The Recording type rain gauge may be of 3 types:-

a) Weighing Bucket Rain gauge

This type of rain gauge consists of receiving bucket which is placed on pan. The pan is again

filled with some weighing mechanism. A pencil arm is pivoted with the weighing mechanism in

such a way that the movement of the bucket can be traced by a pencil on the moving recording

drum. So when the water is collected in the bucket the increasing weight of water is transmitted

through the pencil which traces a curve on the recording drum. The rain gauge produces a graph

a cumulative rainfall versus time and hence it is sometimes called integrating rain gauge

Diagram (hand written notes)

b) Tripping Bucket Rain gauge

I t consists of a circular collector of diameter 30 cm in which the rain water in initially collected.

The rain water then passes through a funnel fitted to the circular collector and gets collected in 2

compartments tipping buckets pivoted below the funnel.

Diagram (hand written notes)

6. Describe the different types of precipitation?

Ans- The different types of precipitation are:-

1. Cyclonic Precipitation:- This type of precipitation is caused by the difference of

pressure with in the air mass on the surface of the earth. If low pressure is generated at

some place the warm moist air from the surrounding area rushes to the one low pressure

with violent force. The warm moist air rises up with whirling motion and gets condensed

at higher altitude and ultimately heavy rain fall occurs. There are2 types-

(a) Frontal Precipitation-

When the moving warm moist air mass is obstructed by the zone of cold air mass, the

warm moist air rises up to higher altitude where its gets condensed and heavy rainfall

occurs. This is known as frontal precipitation.

(b) Non Frontal Precipitation-

When the warm moist air mass rushes to the zone of low pressure from the

surrounding area, a pocket is formed and the warm moist air rises up like a chimney

towards higher altitude. At higher altitude this air mass gets condensed and heavy

rainfall occurs. This is known as non frontal precipitation.

2. Convective precipitation: In tropical countries when on a particular hot day the ground

surface gets heated unequally, the warm air is lifted to higher altitude and the cooler air

takes its place with high velocity. Thus the warm moist air mass is condensed at the high

altitude causing heavy rainfall. This is known as convective Precipitation.

Chapter 2 (WATER REQUIREMENT OF CROPS)

Short questions

1. Define the term irrigation.

A- The process of artificial application of water to the soil for the growth of agricultural

crops is termed as irrigation.

3. What is lift Irrigation?

A- When water is lifted from surface sources or underground sources by man, animal power,

mechanical or electrical power and directly supplied to the agricultural land then it is known as

lift irrigation.

4. Write down three techniques of water distribution in the farm.

A- (i) Surface method

(ii) Sub- Surface method

(iii) Sprinkler method

5.What is sub-surface irrigation?

A- Subsurface or drip irrigation is defined as the uniform application of small

quantities of water at frequent intervals below the soil surface from discrete emission

points or line sources

6. Define “Duty”.

A- The duty of water is defined as the no. of hectares that can be irrigated by constant supply of

water at the rate of one cumec throughout the base period. It is expressed in hectares/ cumec and

is denoted by ‘D’.

7.Define base period for a crop.

A- The base is defined as the period from the first to the last watering of the crop just

before its maturity. It is also known as base period. It is denoted by ‘B’ and expressed in

no. of days.

8.Define crop season.

A- The period during which some particular types of crops can be grown every year on

the same land is known as crop season. The main crop season are Khraif Season and Rabi

Season.

9.Differentiate between ‘GCA’and ‘CCA’.

A-

GCA CCA

1. GCA is known as Gross command

area

2. The whole area enclosed between an

imaginary boundary line which can

be included in an irrigation project

for supplying water to agricultural

land by the network of canals is

known as Gross Command Area.

3. It includes both the culturable and

unculturable areas.

1. CCA is known as Culturable

command area.

2. The total area with in an

irrigation project where the

cultivation can be done and crops

can be grown is known as

Culturable command area.

3. It includes both the culturable

cultivated area and culturable

uncultivated areas.

10. Define CCA & intensity of irrigation.

A- CCA - The total area with in an irrigation project where the cultivation can be done and crops

can be grown is known as Culturable command area.

Intensity of irrigation- The intensity of irrigation may be defined as a ratio of cultivated land for

a particular crop to the total culturable command area. It is expressed as a percentage of CCA.

11. Define crop ratio.

A- It is defined as the ratio of the areas of the two main crop seasons.

E.g- Kharif crops and rabi crops

12.Define crop rotation.

A- The process of changing the type of crop for the cultivation on the same land is

known as crop rotation.

Few crop rotation possible are

(i) Rice-Gram

(ii) Wheat- Millet- Gram

(iii) Rice-Gram-Wheat

13. Define crop period.

A- The crop period is defined as the total period from the time of sowing a crop to the

time of harvesting it. That means, it is the period in which the crop remains in the field.

Long questions

1. Describe the necessity of irrigation.

A- The necessity of irrigation are

(a) Insufficient Rainfall:- When the seasonal rainfall is less than the minimum

requirement for the satisfactory growth of crops, the irrigation system is essential.

(b) Uneven Distribution of Rainfall:- When the rainfall is not evenly distributed during

the crop period or throughout the culturable area, the irrigation is extremely

necessary.

(c) Improvement of perennial crops:- Some perennial crops like sugarcane , cotton, etc

require water throughout the major part of the year. But the rainfall may fulfill the

water requirement in rainy season. So for the remaining part of the year, irrigation

becomes necessary.

(d) Development of agriculture in Desert area:- In desert area where the rainfall is very

scanty, irrigation is required for the development of agriculture.

2. Write short notes on Inundation irrigation system.

A-

In this system , a canal is excavated from the bank of the inundation river (i.e. the river

which overflows in rainy season but nearly dried up in summer and winter)

In this case water flows to the agricultural land in rainy season only. There is no regulator

at the head of the canal to control the flow of water. The bed level of the canal is fixed at

such level that the water can flow through the canal oly when the water level of the river

rises above the canal bed.

Again, the flow of water through the canal stops automatically when the water level of the

river falls below the canal bed.

So this system of irrigation depends completely on the water level of the river. As there

there is no regulator at the head of the canal, over irrigation is possible resulting in

damaging the crops.

Diagram (hand written notes)

3. Mention the types of irrigation followed in India.

A- types of irrigation followed in India are:-

(i)Lift irrigation

(ii)Flow irrigation

Lift irrigation:- When water is lifted from surface sources or underground sources by man,

animal power, mechanical or electrical power and directly supplied to the agricultural land then

it is known as lift irrigation.

Flow irrigation:- When water flows under gravitational pull through the rtifical canal towards

the agricultural land, it is termed as flow irrigation.the different systems of flow irrigation are:0

(a) Inundation irrigation system

(b) Perennial system of irrigation

Inundation irrigation system:- In this system , a canal is excavated from the bank of the

inundation river (i.e. the river which overflows in rainy season but nearly dried up in

summer and winter)

In this case water flows to the agricultural land in rainy season only. There is no regulator

at the head of the canal to control the flow of water. The bed level of the canal is fixed at

such level that the water can flow through the canal oly when the water level of the river

rises above the canal bed.

Again, the flow of water through the canal stops automatically when the water level of the

river falls below the canal bed.

So this system of irrigation depends completely on the water level of the river. As there

there is no regulator at the head of the canal, over irrigation is possible resulting in

damaging the crops.

4. Derive a relationship between duty, delta and base period.

A- handwritten notes

5.. What are the various methods of improving duty?

A- The methods are:-

Proper Ploughing:

Ploughing should be done properly and deeply so that the moisture retaining capacity of

soil is increased.

Methods of supplying water:

The method of supplying water to the agriculture land should be decided according to the

field and soil conditions. For example,

Furrow method For crops sown ion rows

Contour method For hilly areas

Basin For orchards

Flooding For plain lands

Canal Lining:

It is provided to reduce percolation loss and evaporation loss due to high velocity.

Minimum idle length of irrigation Canals:

The canal should be nearest to the command area so that idle length of the canal is

minimum and hence reduced transmission losses.

Quality of water:

Good quality of water should be used for irrigation. Pollution en route the canal should be

avoided.

Crop rotation:

The principle of crop rotation should be adopted to increase the moisture retaining

capacity and fertility of the soil.

6. Discuss briefly the factors on which duty depend.

A- The factors on which duty depend are:-

Soil Characteristics:

If the soil of the canal bed is porous and coarse grained, it leads to more seepage loss and

consequently low duty. If it consists of alluvial soil, the percolation loss will be less and

the soil retains the moisture for longer period and consequently the duty will be high.

Climatic Condition:

When the temperature of the command area is high the evaporation loss is more and the

duty becomes low and vice versa.

Rainfall:

If rainfall is sufficient during the crop period, the duty will be more and vice versa.

Base Period:

When the base period is longer, the water requirement will be more and the duty will be low and

vice versa.

Type of Crop:

The water requirement for various crops is different. So the duty varies from crop to crop.

Topography of Agricultural Land:

If the land is uneven the duty will be low. As the ground slope increases the duty decreases

because there is wastage of water.

Method of Ploughing:

Proper deep ploughing which is done by tractors requires overall less quantity of water and

hence the duty is high.

Methods of Irrigation:

The duty of water is high in case of perennial irrigation system as compared to that in inundation

irrigation system.

Water Tax:

If some tax is imposed the farmer will use the water economically thus increasing the duty.

7. What are the points to be remembered while ascertaining the water requirement for

crop?

A-

Climate

In hot climate the evaporation loss is more and hence the water requirement will be more and

vice versa.

Water Table

If the water table is nearer to the ground surface, the water requirement will be less. If it is much

below the ground surface , the water requirement will be more.

Ground Slope:

If the slope of the ground is steep the water requirement will be more due to less absorption time

for the soil.

Intensity of Irrigation:

It is directly related to water requirement, the more the intensity greater will be the water

required for a particular crop.

Method of Application of water:

In sprinkler method less water is required as it just moist the soil like rainwater whereas in flood

more water is required.

Method of Ploughing:

In deep ploughing less water is required and vice versa.

8. Describe briefly about the flooding method.

A- This method is suitable for the agricultural land which exists in flat topography. In

this method, the field is flooded with water with the help of field channels. The flooding

method is of 2 types:-

i. Uncontrolled flooding- This methos is applicable in indunation irrigation system.

Here , the land is flooded with water by indunation canal. As tgere is no controlling

system in inundation canal, this type of distribution of water is known as

uncontrolled flooding. This method results in watage of water and over irrigation.

ii. controlled flooding- This method is applicable in perennial irrigation system. In this

method, the agricultural area ais flooded with water through the canals which are

provided with the regulators. It is again subdivided in to following types:-

a. Free flooding

b. Basin method

c. Check flooding

d. Border flooding

e. Zig-zag method

9. What is lift irrigation? Give the advantages and disadvantages of lift irrigation

A- When water is lifted from surface sources or underground sources by man, animal power,

mechanical or electrical power and directly supplied to the agricultural land then it is known

as lift irrigation.

Advantages

i. Irrigation helps to maintain the condensation of the loam.

ii. It provides mineral as well as other nutrition by the assimilation from the mold.

iii. Irrigation is one of the most feasible ways to grow cash crops like sugarcane, tobacco, etc.

iv. As people are dependant on irrigation channels, there is now an extensive irrigation system

which people are using as a mean of their communication

v. It helps to preserve the structure of the topsoil

vi. By eliminating the deficiency of water, Irrigation manages to give fast manufacturing

vii. The more production rate intensifies, the more living standard of the farmer increases

viii. At many places, the irrigation serves as the only water source.

ix. Irrigation helps to make the cash flow of a country profound with the massive production

of crops

Disadvantages

i. Irrigation sometimes creates unrestrained excretion and percolation of water throughout

the whole passage.

ii. The overflowing irrigated water gives insects a place to make their habitat which is

harmful to surroundings giving rise to various diseases.

iii. As irrigated water helps to lessen the inversion, sometimes it turns the area into a wet and

sweaty surface. Immoderate irrigation clogs specific area by raising the water.

iv. While constructing the colossal irrigation waterways, people lose their residential and

commercial lands.

v. Not every time irrigation is affordable. The embryonic value of irrigation is quite

inflated, and people end up paying a lot of imposed taxes.

vi. Irrigation becomes an obstacle in the path of free devours during the rainy season.

vii. Careless and over-irrigation can lead to salt efflorescence.

CHAPTER 3 (FLOW IRRIGATION)

Short questions

1. What is “Dowla”?

A- The protective small embankment which is provided on the canal side of the service road for

the safety of the vehicles plying on it is known as dowel or dowla. It is provided above the F.S.L

with a provision of freeboard. The top width is generally 0.5m and the ht. above the road level is

about 0.5m.The side slope is similar to the slope of the bank.

2. Name the classification of canals according to their alignment.

A- Classification of canals according to their alignment are:-

(a) Ridge or watershed canal

(b) Contour canal

(c) Side slope canal

3. Define the term Berm.

A- The distance between the toe of the bank and the topedge of cutting is termed as

berm. The berm is provided for the following reasons:-

i. To protect the bank from erosion.

ii. To protect the bank from sliding down towards the cnal section.

iii. To provide a space for widening the canal section.

4. What do you mean by ‘Free board’?

A- It is the distance between the full supply level and the top of the bank.

It is provided for the following reasons:-

To keep sufficient margin so that the canal water does not over top the bank in

case of heavy rainfall or fluctuation in water supply.

5. What do you mean by Inundation River?

A- The canal which is excavated from the banks of the indundation river to carry water to the

agricultural land in rainy season only when the river flow to it full capacity known as

indundation canal.

6. What is a feeder canal?

A- The canal which is constructed to feed another canal or river for the purpose of irrigation or

navigation is known as feeder canal.

Long Questions

1. Give neat sketches of various canal cross-sections showing different parts of canal

thereon.

A- Diagram is done is notes copy.

different parts of canal are-

Canal Bank- The canal bank is necessary to retain water in the canal to the full

supply level . But the section of the canal bank is different from different site

conditions are-

(a) When the canal fully in cutting

In this case, the banks are constructed on both the sides of the canal to provide only a

inspection road. Here the hydraulic gradient has no function.

(b) When the canal fully in partial cutting and banking

In this case, the banks are constructed on sides of the canal to retain water. The height

of the bank depends on the fully supply level of the canal. Thhe section of the canal

depends on the hydraulic gradient.

(c) When the canal in full banking

In this case the canal and the both of the canal banks are constructed above the

ground level.

Berm- The distance between the toe of the bank and the top edge of cutting is termed

as berm. The berm is provided for the following reasons:-

iv. To protect the bank from erosion.

v. To protect the bank from sliding down towards the canal section.

vi. To provide a space for widening the canal section.

Dowla- The protective small embankment which is provided on the canal side of the

service road for the safety of the vehicles plying on it is known as dowel or dowla. It is

provided above the F.S.L with a provision of freeboard. The top width is generally 0.5m

and the ht. above the road level is about 0.5m.The side slope is similar to the slope of the

bank.

Free board- It is the distance between the full supply level and the top of the bank.

It is provided for the following reasons:-

To keep sufficient margin so that the canal water does not over top the bank in

case of heavy rainfall or fluctuation in water supply.

Hydraulic Gradient- When the water is retained by the canal bank, the seepage occurs

through the body of the bank. Due to resistance of the soil, the saturation line forms a sloping

line which may pass through the bank. This sloping line is known as hydraulic gradient line.

Counter berm- When the water is retained by a canal bank the hydraulic gradient line passes

through the body of the bank. Some times it may occur that the hydraulic line intersects the outer

side of the bank.

Service Road- The road way which is provided on the top of the canal bank for inspection and

maintainance works is known as the service road.

Spoil Bank- When the canal is constructed in full cutting , the excavated earth may not be

completely required for forming the bank. The spoil banks are provided on one side or both the

sides of the canal bank.

Borrow Pit- When the canal is constructed in partial cutting and partial banking , the excavated

earth may not be sufficient for forming the required bank.

In such a case, the extra earth required for the construction of banks is taken from some pits

which are known as borrow pits.

2. What is canal lining? Write the different types of canal linings.

A- canal lining-It means the earthen surface of the channel is lined with a stable lining

surface such as concrete, tiles etc

The different types of canal linings

i. Cast in situ or Cement Concrete lining

ii. Shotcrete or Plaster lining

iii. Cement Concrete tile lining or Brick lining

iv. Asphaltic Concrete lining

v. Boulder lining

vi. Soil cement lining

Cast insitu or Cement Concrete lining - Cement concrete lining made from MIS cement

concrete mix (1:2:4) is considered a good quality type of lining.

Preparations of Sub-grade

Cement concrete linings are best suited for main canals which have to' carry huge flows and at

higher velocities. If the subgrade becomes too dry, it should be thoroughly wetted several hours

before the lining is placed, so that the subgrade will be moist but not muddy at that time. Highly

expensive soils like black cotton soils, need special treatment in the form of laying a layer of

CNS (Cohesive non-swelling soil) material like murum, etc. in depth of about 300-1000 mm

over the given soil surface before laying the lining.

Laying of Concrete

The leveled and dressed sub-grade soil surface shall be moistened thoroughly before laying

cement concrete, so that the moisture is not withdrawn by the sub grade from the cement

concrete..

Shotcrete or Plaster lining

Shotcrete is a technical term used to designate cement mortar applied under pressure through a

nozzle on the surface of the channel. It consists of a mixture of cement and sand (generally in the

ratio of I :4). Sand is having a maximum size of 0.5 cm. Shotcrete lining is generally laid in a

thickness of about 3.5 cm. Excavation, compaction, curing etc. for a shotcrete lining are the same

as those required for a cement concrete lining.

Cement Concrete tile lining or Brick lining

The top layer of tiles is generally laid in 1 : 3 cement mortar over 15 mm thick layer of plaster in

1 : 3 cement plaster.

Asphaltic Concrete lining

Asphalt has been used as a lining material at a very few places. Asphaltic concrete is a carefully

controlled mixture of asphalt and graded stone aggregate, mixed and placed under elevated

temperature. It provides a fairly cheap lining, especially where the asphalt is available within the

country. It is flexible and readily confirms to the subgrade.

Boulder Lining

Boulder lining, also called dry stone lining or stone pitching, consists of lining the side slopes' of

on earthen canal by proper placement & packing of stones, either after laying a filter layer over

the soil surface, or without any such filter, depending upon the site requirement. Such a lining

does not prevent seepage of canal water, though helps in retaining the shape of canal section,

thereby reducing maintenance cost. The stones to be used for lining are rounded or sub-angular

river cobbles, or blasted rock pieces with sufficient base area, so as to remain stable in their

position.

Soil cement lining

Portland cement up to the extent of 2 to 8% is added to the soil having a high percentage of fines.

The mixture is first mixed dry. Water is then added so as to bring the soil to its optimum

moisture content, and again mixed thoroughly. Material is then placed at site and compacted.

Curing is then required for at least seven days by covering with wet sand, etc.

3.What are the advantages and disadvantages of canal lining?

Advantages of canal lining-

i. It reduces the loss of water due to seepage and hence the duty is enhanced.

ii. It controls the water logging and hence the bad effects of water logging are eliminated.

iii. It provides smooth surface and hence the velocity of flow can be increased.

iv. Due to the increased velocity, the evaporation loss also be reduced.

v. It provides the stable section of the canal.

vi. It reduces the maintenance cost for the canal.

Disadvantages of canal lining-

i. The initial cost of the canal lining is very high, so it makes the project very expensive

with respect to the output.

ii. It involves many difficulties for repairing the damaged section of the lining.

iii. It takes too much time to complete the project work.

iv. It becomes difficult , if the outlets are required to be shifted or new outlets are required to

be provided, because the dismantling of the lined section is difficult.

v.

Chapter 4 (Water logging and drainage)

Short questions

1. Define salinization.

A-

Due to water logging, the dissolved salts like sodium carbonate, sodium

chloride and sodium sulphate come to the surface of the soil. When the water

evaporates from the surface, the salts are deposited there. This process is

known as salinization of soil.

Excessive concentration of salt makes the land alkaline. It does not allow the

plants to grow and thus the yield of crop is reduced.

2. Define leaching.

A-

It is the process for reclamation of the saline soil. In this process, the agricultural land is

flooded with water to a depth of about 20-30 cm

The salt deposits on the surface are dissolved some portion of salt is then drained off

through the sub soil drainage system and some portion is removed by surface drainage

system. This operation is repeated several times at regular intervals.

3. Define water logging.

A-

In agricultural land , when the soi pores with in the root zone of the crops gets saturated

with the subsoil water, the air circulation with is the soil pores gets totally stopped, This

phenomenon is termed as water logging.

The water logging makes the soil alkaline in character and the flexibility of the land is

totally destroyed and the yield of crop is reduced.

Long Questions

1. Write down any causes of water logging?

A- causes of water logging are:-

(i) Over irrigation-

In inundation irrigation, since there is no controlling system of water supply, it

may cause over irrigation. The excess water percolates and remains stored with in

the root zone of the crops.

In perennial irrigation, if water is supplied more than what is required. the

excess of water is responsible for water logging.

(ii) Inadequate surface drainage-

When the rainfall is heavy and there is no proper provision for surface drainage

the water gets collected and submerges vast area, When this condition

continues for a long period, the water is raised.

(iii)Seepage of Water through the Canals-

Water may seep through the beds and sides of the adjoining canals, reservoirs, etc.,

situated at a higher level than the affected land; resulting in high water table. This

seepage is excessive, when soil at the site of canals, reservoirs, etc. is very pervious.

(iv) Excessive Rains-

Excessive rainfall may create temporary water-logging, and in. the absence of good

drainage, it may lead to continued water-logging.

(v) Impervious Obstruction-

Water seeping below the soil moves horizontally (i.e. laterally) but may find an

impervious obstruction, causing the rise of watertable on the upstream side of the

obstruction. Similarly, an impervious stratum may occur below the top layers of

pervious soils. In such cases, water seeping through the pervious soils will not be able

to go deep, and hence, quickly resulting in high watertable.

2. Describe the method of controlling water logging.

A-

i. Lining of Canals and Water Courses-

Attempts should be made to reduce the seepage of water from the canals and water

courses. This can be achieved by lining them. It is a very effective method to control

water-logging.

ii. Reducing the Intensity of Irrigation-

In areas where there is a possibility of water-logging, intensity of irrigation should be

reduced. Only a small. portion of irrigable land should receive canal water in one particular

season. The remaining areas can receive water in the next season, by rotation.

iii. By Provision of an Efficient Drainage System-

An efficient drainage system should be provided in order to drain away the storm water and

the excess irrigation water. A good drainage systern consists of surface drains as well as sub-

surface drains.

iv. By Improving the Natural Drainage of the Area.

To reduce the percolation, the water should not be allowed to stand for a longer period. Some

relief in this direction can be obtained by removing the obstructions from the path of natural

flow. This can be achieved by removing bushes, jungles etc. for improving the-slopes of the

natural drainage lines.

v. By Introducing Crop-rotation-

Certain crops require more water and others require less water. If a field is always sown with

a crop requiring more water, the chances of water-logging are more. In order to avoid this, a

high water requiring crop should be followed by one requiring less water, and then by one

requiring almost no water. Rice may be followed by wheat, and wheat may be followed by a

dry crop such as cotton.

3. What are the two principal types of drainage systems necessary for draining

irrigated tracts to avoid their water logging?

A- two principal types of drainage systems are-

(a) Surface Drainage –

Surface drainage is the removal of excess rain water falling on the fields or the excess

irrigation water applied to the fields, by constructing open ditches, field drains, and other

related structures. The land is sloped towards these ditches or drains, as to make the

excess water flow in to these drains.

(b) Sub-surface Drainage –

Plants need air as well as moisture. in their root zones for their survival. Excess irrigation

farm water is free to move into the underground tile drains. This water, if not removed,

retards the plant growth, because it fills the soil voids and restricts proper aeration.

Subsurface drains are required for soils with poor internal drainage and a high watertable.

If no impervious layer occurs below the farm land and the watertable is low (lower than

about 3m from the ground), internal soil drainage may be sufficient.

Chapter 5 (Diversion head work and regulatory Structures)

Short questions

1. Define diversion head works.

A- When a weir or barrage is constructed across a perennial river to raise the water level

and to divert the water to the canal then it is known as diversion headwork.

The flow of water in the canal is controlled by head regulator.

2. Write down the names of various types of Diversion headwork?

A- (i) Weir and barrage

(ii)Divide wall

(vi) Fish ladder

(vii) Canal head regulators

(viii) Guide bank

(ix) Marginal Embankment

3. Why a divide wall is constructed?

A-

The divide wall is a long wall constructed at right angles to the weir or barrage.

It may be constructed with stone masonry or cement concrete.

4. Why a fish ladder is provided?

A-

The fish ladder is provided just by the side of the divide wall for the free movement of

fishes.

Rivers are important sources of fishes. There are various types of fish in the river.

In general, the tendency of fish is to move from downstream to upstream in monsoons.

Due to construction pg weir or barrage, this movement gets obstructed.

In the fish ladder, the baffle walls are constructed in a zig-zag manner so that the velocity

of flow within the ladder does not exceed 3m/sec

5. What is the purpose of providing a silt excluder?

A-

When silt water pocket is formed in front of the canal head by constructing the divide wall,

then it is found that the lower layer of water contains heavy silt and the upper layer

contains very fine silt. The fine silt is very fertile and may be allowed to enter rhe canal.

But the heavy silt causes sedimentation in the pocket. To eliminate the suspended heavy

silt, the silt excluder is provided.

6. What is the function of head regulator?

A-

To regulate all control the supply of water to the canal.

To control the silt entering to the canal

7. Define weir and barrage.

A- Weir-

Weir is constructed across the river to raise the water level. Hence the water

can be easily diverted to the canal.

The weir may be constructed with masonry or concrete.

Barrage

When the water level on the upstream of the weir is required to be raised to

different levels at different time, then the barrage is constructed.

A barrage is an arrangement of adjustable gates or shutters at different tiers

over the weir.

8. Write any 2 functions of regulatory structures?

[2019S]

A-

To regulate all control the supply of water to the canal.

To control the silt entering to the canal

To effective control the entire canal of the irrigation system.

They help in closing the supply to the main channel for the purpose of repair and

reconstruction work.

Long questions

1. Enumerate the points to be considered while selecting the site for diversion head

works.

A-

i. At the site , the river should be straight and narrow.

ii. The river banks should be well defined.

iii. The valuable lands should not be submerged when the weir or barrage is constructed.

iv. The elevation of the site should be much higher than the area to be irrigated.

v. The site should easily accessible by roads and railways.

2. Write the components parts of diversion headwork.

A- Diagram is in notes

i. Weir and Barrage

In general, the above purpose can be constructing a barrier across the river, so as to raise

the water level on the upstream side of the obstruction, and thus, to feed the main canals

taking off from its upstream side at one or both of its banks. If the major part or the entire

ponding of water is achieved by a raised crest and a smaller part of nil part of it is

achieved by the shutters, then this barrier is known as a weir

On the other hand, if most of the ponding is done by gates and a smaller or nil part of it is

done by the raised crest. then the barrier is known as a Barrage.

ii. Under-Sluices or Scouring Sluices.

A comparatively less turbulent pocket of water is created near the canal head regulator by

constructing under-sluice portion of the weir. A divide wall separates the main weir

portion from the under-sluice portion of the weir. The crest of the under-sluice portion of

the weir is kept at a lower level than the crest of the normal portion of the weir.

The discharging capacity of under-sluices may be selected as follows :

(i) They should be able to ensure sufficient scouring capacity, for which the

discharging capacity should be atleast twice the full supply discharge of the main

canal at its head.

(ii) They should be able to pass the dry weather-flow and low floods during the

months

(iii) They should be able to dispose of 10 to 15% of the high flood discharge during

severe floods.

iii. Divide Wall

The 'divide wall' is a masonry or a concrete wall constructed at right angle to the axis of the

weir, and separates the weir proper from the under-sluices. The divide wall extends on the

upstream side beyond the beginning of the canal head regulator; and on the downstream side,

it extends up to the end of loose protection of the undersluices The top width of divide wall is

about 1.5 to 2.5 metres.

The main functions served by the divide wall are :

(a) It separates the under-sluices from the weir proper. Since the crest level of the under-

sluices is lower than that of the weir proper, the two must be separated, and this is being done

by the Divide wall.

(b) It helps in providing a comparatively less turbulent pocket near the canal head regulator,

resulting in deposition of silt in this pocket and, thus, to help in the entry of silt-free water

into the canal.

iv. Fish Ladder

Large rivers are generally inhabited by several types of fish, many of which are migrated and

move from one part of the river to another part, according to the season. A structure which

enables the fish to pass upstream is called a 'fish ladder'. It is a device by which the flow energy

can be dissipated in such a manner as to provide smooth flow at sufficiently low velocity, not

exceeding 3 to 3.5 m/sec. This object is generally accomplished by providing a narrow opening

adjacent to the divide wall and provide suitable baffles or staggering devices in it, so as to

control the flow velocity.

v. Canal Head Regulator-

A canal head regulator is provided at the head of the off-taking canal, and serves the following

functions (i) It regulates the supply of water entering the canal.

(ii) It controls the entry of silt in the canal.

(iii) It prevents the river floods from entering the canal.

vi. silt excluder

When silt water pocket is formed in front of the canal head by constructing the divide wall,

then it is found that the lower layer of water contains heavy silt and the upper layer contains

very fine silt. The fine silt is very fertile and may be allowed to enter the canal. But the heavy

silt causes sedimentation in the pocket. To eliminate the suspended heavy silt, the silt

excluder is provided.

Chapter 6 (Cross Drainage Works)

Short questions

1. Name the cross drainage work recommended when a natural drain passes below a

canal. [2009]

A- cross drainage work are:-

(i) Aqueduct

(ii) Siphon Aqueduct

2. What is a cross drainage work?

A-

In an irrigation project, when the networks of main canals, branch canals, distributoriesetc

are provided, then theses canals may have to cross the natural draiangs like rivers,

streams, nallabs etc. at different points with in the command area of the projects.

The crossing of the canals with such obstacles cannot be avoided. So suitable structures

must be constructed at the crossing point for the easy flow of water of the canal and

drainage in the respective directions. These structures are known as cross drainage works.

3. What is level crossing?

A- When the beds of the drainage and canal are practically at the same level, then a

hydraulic structure is constructed which is known as level crossing. This is suitable

for the crossing of large drainage with the main canal.

4. What do you mean by aqueduct and super passage?

A- Aqueduct- The hydraulic structure in which the irrigation canal is taken over the

drainage (such river, streams etc) is known as aqueduct.

Super passage- The hydraulic structure in which the drainage is taken over the

irrigation canals is known as super passage.

Long questions

1. Describe with sketches different types of cross drainage work.

A- Types of cross drainage works are-

Type 1 – Irrigation canal passes over the Drainage

Aqueduct

In these works, the canal is taken over the natural drain, such that the drainage water runs below

the canal either freely or under syphoning pressure. When the HFL of the drain is sufficiently

below the bottom of the canal, so that the drainage water flows freely under gravity, the structure

is known as an Aqueduct. In this type of works, the canal water is taken across the drainage in a

trough supported on piers An inspection road is provided along with the trough. An aqueduct is

just like a bridge except that instead of carrying a road or a railway, it carries a canal on its top.

An aqueduct is provided when sufficient level difference is available between the canal and the

natural drainage, and canal bed level is sufficiently higher than the torrent level.

Siphon Aqueduct

In these works, the canal is taken over the natural drain, such that the drainage water runs below

the canal either freely or under syphoning pressure if the HFL of the drain is higher than the

canal bed and the water passes through the aqueduct barrels under syphonic action, the structure

is known as Syphon Aqueduct. In the case of a syphon aqueduct, the drain bed is generally

depressed and provided with pucca floor. On the upstream side, the drainage bed may be joined

to the pucca floor either by a vertical drop or by a glacis of 3 : l. The downstream rising slope

should not be steeper than 5 : 1.

Type 2 – Drainage passes over the Irrigation canal

Super-passage

In these works, the drain is taken over the canal such that the canal water runs below the drain

either freely or under syphoning pressure. When the FSL of the canal is sufficiently below the

bottom of the drain trough, so that the canal water flows freely under gravity, the structure is

known as a Super passage. A super passage is thus the reverse of an aqueduct, and similarly,

However, in this type of cross-drainage works, the inspection road cannot be provided along

HFL, the canal and a separate bridge is required for the road-way.

Siphon Super-passage

In these works, the drain is taken over the canal such that the canal water runs below the drain

either freely or under syphoning pressure, then the FSL of the canal is sufficiently above the bed

level of the drainage trough, , the structure is known as a canal siphon or a Siphon Super-

passage. A siphon Super-passage is a reverse of an aqueduct siphon. However, in this type of

cross-drainage works, the inspection road cannot be provided along HFL, the canal and a

separate bridge is required for the road-way.

(NEAT SKECTHES IS DONE IN NOTES)

2. Explain the level crossing system with neat sketch.

A- level crossing - In this type of cross-drainage work, the canal water and drain water are

allowed to intermediate with each other. A level crossing is generally provided when a large

canal and a huge drainage (such as a stream or a river) approach each other practically at the

same level. A regulator is provided across the drainage just on the downstream side of the

crossing so as to control the discharge passing into the drain.

During dry season, when there are no floods, the regulator is generally kept closed and the

outgoing canal regulator is kept fully open, so that the canal flows without any interruption.

During floods, however, the regulator is opened so as to pass the flood discharge.

(NEAT SKECTHES IS DONE IN NOTES)

Chapter 7 (Dams)

Short questions

1. What do you mean by gravity dam?

A-

The solid gravity dam may be constructed with rubble masonry or concrete.

The rubble masonry is dine according to the shape of the dam with rich cement mortar.

The upstream and downstream faces are finished with rich cement mortar.

Concrete gravity dams are preferred because they can be easily constructed by laying

concrete, layer by layer with construction joints.

2. Name the different forces which act on a gravity dam

A-

(i) Weight Of The Dam

(ii) Water Pressure

(iii) Uplift Pressure

(iv) Sesmic Force

(v) Silt Pressure

(vi) Wave Pressure

(vii) Ice Pressure

(viii) Wind Pressure

3. What is the purpose of providing a spillway in dam?

A-

The height of the dam is always fixed accordingly to the maximum reservoir capacity.

The top of the dam is generally utilized by making road. The surplus water in not be

allowed to over top the dam, so to stop the over topping by the surplus water. The

spillways become extremely essential.

To protect the downstream base and floor of the dam from the effect of scouring and

erosion, the spillways are provided so that the excess water flows smoothly.

4. What is a dam?

A- An impervious high barrier which is constructed across a river valley to form a deep

storage reservoir is known as dam. It is suitable in hilly region where a deep gorge

section is available for the storage reservoir.

5. In which condition earth dam is constructed.

A- Earthen dams are constructed purely by earth work in trapezoidal section. These are

most economical and suitable for weak foundation.

6. Define spillway.

A- The spillways are openings provided at the body of the dam to discharge safely the

excess water or flood water when the water level rises above the normal pool level.

7. Define ogee spillway

A-

The ogee spillway is a modified form of drop spill way.

Here the downstream profile of the spillway is made to coincide with the shape of the

lower nappe of the free falling water jet from a sharp crested weir.

In this case, the shape of the lower nappe is similar to a projectile and hence downstream

surface of the ogee spillway will follow the parabolic path where 0 is the origin of the

parabola.

Thus the spillway takes the shape of letter S. Hence the spill way is termed as Ogee

Spillway.

8. What is meant by rock-fill dam?

A-

This type of dam is constructed by dumping stones(i.e boulders) in a trapezoidal section.

No mortar is used while dumping the stones.

The stones are dropped from some height so that the edges of the stones are broken and

they are well set with each other.

Rubble masonry is done on the upstream side which is grouted by cement.

This type of dam is suitable when plenty of stones are available from a nearby quarry.

Long questions

1. Write the classification of dams?

A- Based on materials of construction

A- (i) Rigid Dams-- It is constructed with rigid materials like masonry, concrete , steel

or timber. It is designated as (a) masonry dam (b) concrete dam (c) steel dam (d) timber

dam.

(ii) Non-rigid Dams- - It is constructed with non rigid materials such as earth, clay, rock

materials etc. It is designated as (a) earthen dams (b) rock-fill dams (c) composite dam

Based on functions-

(i) Storage Dams-They are constructed in order to store water during the periods of surplus

water supply, to be used later during the periods of deficient supply. The stored water may be

used in different seasons and for different uses. They may be further classified depending upon

the specific use of this water, such as navigation, recreation, water supply, fish, electricity, etc.

(il) Diversion Dams. These small dams are used to raise the river water level, in order to feed an

off-taking canal and or some other conveyance systems. They are very useful as irrigation

development works. A diversion dam generally called a weir or a barrage.

(iii) Detention Dams. They detain food-waters temporarily so as to retard flood runoff and thus

minimise the bad effects of sudden flood. Detention dams are sometimes constructed to trap

sediment They are often called debris dams.

Based on hydraulic Behaviour-

(i) Overflow Dams- They are designed to pass the surplus water over their crest. They are often

called Spillways. They should be made of materials which will not be eroded by such discharges.

(ii) Non-overflow Dams. They are those which are not designed to be overtopped. This type of

design gives us wider choice of materials including earthfill and rockfill dams.

2. Describe briefly the causes of failure in earthen dams

A- causes of failure in earthen dams are-

Hydraulic failure

(a) Overtopping- If the actual flood discharge is much more than the estimated flood

discharge or the freeboard is kept insufficient or there is settlement of the dam or the

capacity of spillway is insufficient, then results in the overtopping of the dam.

(b) Erosion- If the stone projection of the upstream side is insufficient, and then the

upstream face may be damaged by erosion due to wave action. The downstream side also

may be damaged by tail water, rainwater etc.

Seepage failure

(a) Piping or undermining- Due to the continuous seepage flow through the body of the

dam and through the subsoil below the dam, the downstream side gets eroded or washed

out and a hollow pipe like groove is formed which extends gradually towards the

upstream through the base of the dam. This phenomenon is known as Piping or

undermining

(b) Sloughing- The crumbling of the toe of the dam is known as sloghing. When the

reservoir runs full, for a longer time, the downstream base of the dam remains saturated.

Due to the force of the seepage water the toe of the dam goes on crumbling gradually.

The base of the dam collapses.

Structural failures

Slide in. Embankments- When the embankment slopes are too steep for the strength of the

soil, they may slide causing dam failure. The most critical condition of the slide of the u/s

slope is the sudden drawdown of the reservoir and the d/s slope is most likely to slide, when

the reservoir is full. The u/s slope failures leads to catastrophic failures, but the d/s slope

failures are very serious. These failures, generally occur due to development of excessive

unaccounted pore pressures which may reduce the shearing strength of the soils. Many

embankments may fail during the process of consolidation, at the time of construction or

after the construction.

3. Describe the types of spillway with neat sketches

A- types of spillway are-

Drop Spillway-

This is the simplest type of spillway and may be constructed on smal1 bunds or on thin arch

dams, etc. It is a low weir and simple vertical fall type structure.

The downstream face of the structure may be kept vertical or slightly inclined. The crest is

sometimes extended in the form of an overhanging lip, which keeps small discharges away from

the face of the over fall section.

The water falls freely from the crest under the action of gravity. Since vacuum gets created in the

underside portion of the falling jet sufficient ventilation of the nappe is required in order to avoid

pulsating and fluctuating effects of the jet.

Sometimes, a secondary dam of low height is constructed on the downstream side to create an

artificial pool of water so as to dissipate the energy of the falling water.

Ogee Spillway-

Ogee spillway is an improvement upon the free overfall spillway, and is widely used with

concrete, masonry, arch and buttress dams.

Such a spillway can be easily used on valleys where the width of the river is sufficient to provide

the required crest length and the river bed below can be protected from scour at moderate costs.

The shape of the lower nappe of freely falling jet over a sharp crested weir can be determined by

the principle of projectile. It generally rises slightly (to point C) as it originates from the crest (

0) of a sharp crested weir and then falls to make a parabolic form.

Now, if the space between the sharp crested weir and the lower nappe is filled with concrete or

masonry, the weir so formed will have a profile similar to an 'ogee' and hence called an 'ogee

weir' or an 'ogee spillway'.

This lower nappe, will then become the crest of the spillway. Since the lower nappe of the free

falling jet will be different for different heads over the crest of the sharp crested weir, the profile

of the ogee weir is generally confined to the lower nappe that would be obtained for maximum

head over the spillway

(NEAT SKECTHES IS DONE IN NOTES)