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
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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.