Unit - 1

Hydrology

Q1) Explain the steps of hydrological cycle?

A1)

First Step

• Due to picture graph voltaic radiation called as insulation i.e. in coming sun radiation.

• The oceanic and the water at the land floor get heated and get transformed into vapour.

Second step

• The vapour being lighter is lifted up withinside the ecosystem so the air have this vapour called as moisture starts cooling down and so its begin controlling.

• It reduces the sporting cap potential of air to maintain the moisture and it turns into moisture saturated i.e. no extra moisture it could maintain. This diploma is known as degree of condensation.

Third Step

• Due to the pushing of air from the earth floor, this saturated air continues to be driven withinside the upward path to make it although cooler and although greater compact to minimize its potential lesser than actuality accessible wetness. This additional moisture is reborn into tiny rain drops. That tempt the dirt particles to create it visible is understood as as clouds

Fourth step

• The moisture carrying clouds are carried by victimization the winds toward the land surface. If it's a craggy location the clouds are however raised up to extend the dimension of the raindrops and that they begin falling down spoken as rainfall.

Fifth step

• The fresh water obtained on the surface starts Moving towards the slopes, to form the strolling water or streams, which eventually meet the oceans. The rainwater noninheritable on the floor identical times percolates (it depends upon the type of rock, if it's porous the water percolates) to structure the bottom water. It in addition comes back on the ground within the structure of springs to structure a floor circulation to achieve the ocean.
• The rain water noninheritable on the surface, that is obvious and have non porous rock: forms lakes or tanks. The cycle is finished once the ocean or surface water comes back will the planet floor to start the primary stage of geophysics ice. It starts off evolved obtaining reworked from the liquid nation to the vaporific state.
• Once the water is obtained within the structure of sturdy kingdom i.e. snow, it in addition undergoes the equal cycle. When the system is fast the vapor directly gets reborn into strong snow particles.
• It's spoken as sublimation. This befell once the temperature of the wetness saturated air is a smaller amount than O Cie. Not up to the melting point temperature. Within the temperature and in the arctic zones on the planet it causes rainfall. 

• As noted on top of the hydro cycle is achieved in six states. Which may expressed via the usage of technical nomenclature these methods are as follows:

Fig.: Descriptive representation of hydrological cycle

Q2) What is Water budget equation?

A2)

For a given catchment during a amount ∆t, Inflow-Outflow = Storage [continuity equation]This continuity equation expressed in terms of variety section of hydrological cycle is named as water value vary equation/hydrological budget equation.

For Surface Flow

P+R1+Rg-R2-Es-Ts-I = ∆Ss (change in storage) ........... (1)

P = Ppt.

R1 =Surface water inflow

Rg=Ground water appearing as surface water.

R2 = Surface water outflow.

Es = Evaporation

Ts = Transpiration

I = Infiltration.

For Underground Flow

I+ G1- G2- Rg- Eg- Tg = ∆Sg.     (Storage change) ..........(2)

I = Infiltration

G1 =Ground water inflow

G2= Ground water outflow

Rg =Ground water appearing as surface water

Eg=Evaporation

Tg = Transpiration

Combined hydrological budget (water budget equation) is obtained by adding equation (1) and equation (2)

P-(R2 -R1 )- (Es + Eg)-(Ts + Tg )- (G2 - G1Z= ∆(Ss + Sg)

P-R-E-T-G = ∆S..........Water budget equation.

Where,

P = Precipitation

R = Net runoff

E =Net evaporation

T =Net transpiration

G = Net ground water flow

∆S = Net storage increase

Q3) What is Precipitation?

A3)

Precipitation:

• Precipitation is the fall of water in various forms on the earth from the clouds. The usual forms are rain, snow, sleet, glaze, hail, dew etc.

• Before studying the phenomenon of precipitation let us consider water vapours. Air in atmosphere can easily absorb moisture in the form water vapours. The amount of water vapours absorbed by air depends upon the temperature of air, the more is the temperature the more water vapours it can absorb.

• The water vapour exerts a partial pressure on the water surface called vapour pressure. The amount does water vapour present in air is indirectly expressed in terms of vapour pressure.

• If the evaporation continues, a state of equilibrium is reached when the air is fully saturated with vapour and therefore it cannot absorb more vapours. The vapours then exert a pressure which is known as saturation vapour pressure (es). es  increase with increase in temperature.

• Let us consider a of parcel of air as temperature T and a vapour pressure (ea) indicated by pt. A. The saturation vapour pressure at that temperature is indicated by pt. B. The intercept BA = (es-ea)is called saturation deficit.

• If vapours are added to the parcel of air, the pt. A will move to pt. B when air is fully saturated.

• If the parcel of air is cooled at constant pressure but without the addition of more vapours, the pt. Moves horizontally towards pt. D and the air would be saturated when pt. D is reached. At that stage, the air would have a temperature called dew point temperature (T). Cooling of air beyond this pt. Would result in condensation or formation of mint.

• If neither the temperature not the pressure remains constant, the water evaporates freely and the pt. Moves to pt. C. In this case, water vapor rises but temperature falls. The temperature at pt C. Is called wet bulb temperature (T). The saturation vapour pressure is indicated by ew.

• Air in atmosphere can be cooled by many processes. However, adiabatic soling which occurs by a reduction of pressure through lifting of air masses is the main natural process.

Q4) Explain the types of precipitation?

A4)

Depending upon the factors responsible for lining and cooling of alit there is following types of precipitation:

(1) Convective precipitation:

• It occurs due to heating of air. The air close to the earth surface gets heated, and item density decreases.

• Consequently, the air rises upwards in the atmosphere and it gets cooled adiabatically to form a cloud, precipitation caused by such clouds is called convective precipitation.

(2) Orographic Precipitation:

• Orographic rainfall occurs due to ascent of air forced by mountain barriers.

• The mountain barriers lying across the direction of air flow forces the moisture laden air to rise along the mountain slope. It results in cooling, condensation and precipitation.

(3) Cyclonic Precipitation:

• A cyclone is a large zone of low pressure which is surrounded by circular wind motion.

• Air tends low pressure zone from and displaces low pressure cyclonic precipitation to move into the surrounding area air upwards. Thus, occurs due to displacement of air in upwards direction due to pressure difference.

(4) Frontal Precipitation:

• It is a type of cyclonic precipitation. When two contrasting air masses (cold polar air mass and warm westerly air mass) coming from opposite directions converge along a line, a front is formed. The warm wind is lifted upward along this front where as cold air being heavier settles downward.

• Because the two types of fronts (warm and old) have different temperature and density, frontal precipitation occurs when they clash with each other.

Q5) Explain the Evaporation process?

A5)

• The water is made up of a number of molecules. Each one of the molecules moves in different direction with different velocities. The velocity of the molecule depends upon the temperature.

• These molecules are attracted towards each other the force of attraction is proportionate to the mass and inversely proportionate to the distance square.

• If the mass is greater the point of attraction will be more and as the distance between two molecules goes on increasing the point of attraction goes on reducing. The molecules on the top are attracted by molecules below them.

• The molecules having more kinetic energy (through the heating process.) than the attraction in the down ward direction escape into the " atmosphere. This process is called as Evaporation.

• These escaped molecules while going up into the atmosphere carry some kinetic energy. So, evaporation is a cooling process.

• When molecules are pushed into the upward direction, some of them already in the air start coming down (decanting) and there is collision of these molecules moving in and out from the water surface.

• The evaporation is the net rate of movement of molecules to and from the water surface. When all t the rate of molecules coming towards the surface dive or water is more than the molecules moving from the water surface into the air, it is called as condensation.

• When the air near the water surface is very cool through the evaporation, the molecules are converted into solid form of snow.

• This process is called as sublimation. The evaporation is expressed in terms of the depth of the water per unit of area per unit of time. i.e.mm/m2/h.

Q6) Explain the Estimation & measurement techniques of Evaporation?

A6)

To estimate the rate of evaporation from the surface of the water body, following methods have been introduced.

A: Water Budget Method

• To calculate the rate of evaporation following equation is used:

Where,

E = Evaporation

P= Precipitation

I= Surface inflow

ui = Under-ground inflow of water into the surface water (Through springs)

uo =Under-ground out flow of water from the surface water (through percolation)

0= Out flow of water (through irrigation canal)

Ds =Change in the storage

• If all the numerical data (accurate) is available the loss of water through evaporation can be calculated.

B: Energy Budget Method

• In this method, for a specific period of time, how much energy is received from the sun by the water is calculated and how much energy is utilized for the evaporation is calculated to know the accurate evaporation. For this, the following equation is used.

Q₁ = QR ±Qs + QE

Where Q1= Total energy received from the solar radiation

QR= Total energy reflected by to the atmosphere through the reflection

Qs = Change in the energy in the stored water

QE = Energy required for evaporation

• In this QS, may be or - because in same case the energy may be added or may be reduced (through the utilization of energy).

• In this equation if all the figures are available QE i.e. energy required for evaporation can be calculated. The actual evaporation can be calculated if the following information is available.

1. Latent heat of evaporation
2. Temperature of water
3. Atmospheric pressure.

C: Mass Transfer Method

• This method is based on the determination of the mass of the water-vapour transferred from the water surface to the atmosphere. So, this method is also called as vapour flow approach or Aerodynamic approach.

• In this method, both the boundary layer theory and the continuous mixing theories have been used. It is assumed that the wind velocity in the upward direction is logarithmic and the atmosphere is adiabatic.

• This method is based on the determination of the mass of the water-vapour transferred from the water surface to the atmosphere. So, this method is also called as vapour flow approach or Aerodynamic approach.

• In this method, both the boundary layer theory and the continuous mixing theories have been used. It is assumed that the wind velocity in the upward direction is logarithmic and the atmosphere is adiabatic.

• The equation used to calculate the evaporation is as follows:

Where, E = Evaporation in mm/per hrs.

Z₁, Z₂ = Arbitrary levels above the mater surface levels in m.

e1,e2= The vapour pressure at Z1, Z2, in mm/of Hg

V₁, V₂ = Wind velocity at Z₁, Z2, in km/per hour

T= Average temperature in OC between Z₁, Z2

Q7) What is the necessity of irrigation?

A7)

• The irrigation water dissolves the nutrients in the soil, which are required for the plant growth through roots.

• The irrigation water supplies moist to the soil. Which is required by the micro-life in the soil i.e., the de-composers in the eco-system.

• It helps to control the soil-temperature.

• It helps to soften the tillage pav i.e., the area to be irrigated.

• It provides a controlled and timely supply of water to be plant i.e., during sowing, growing and harvesting period.

Q8) What are the Advantages and Disadvantages of Irrigation?

A8)

Advantages of irrigation:

Following are the advantages of irrigation:

1. The water is made available, when even required for the crops.
2. It has the controlled supply of water.
3. It can help to have more cropping season i.e. the summer crops are possible only through irrigation.
4. It helps to go for commercial crops.

Disadvantages of irrigation:

Following are the disadvantages of irrigation:

1. Water logging.
2. Salinity and alkalinity of land.
3. Ill aeration of soil.
4. Pollution of underground water.
5. Results in less warm and damper weather inflicting outbreak of sicknesses like malaria.

Q9) Explain the Sprinkler method of irrigation?

A9)

• In this method the water is supplied to land by spraying it (like an artificial rainfall) As it comes from above, it is also known as overhead Irrigation.

• This method can be applied to any type, of crops except Rice and Jute as both need a standing water in the field. Rice is sown in the soil which is in a muddy form.

• This method is applied to almost all types soils except, clayey soils which are heavy and the rate of infiltration of this soil is very low. So, it is best suitable for the very light soils in which deep percolation losses are very low.

• As this method can be applied to a land which has rough topography, the levelling of land, before irrigation is not required.

Components of Sprinkler Irrigation System:

Following are the important components of the sprinkler irrigation system:

1. Main pipe lines (also called as mains).
2. Sub-main pipelines (also called as sub mains).
3. Lateral pipe line (or laterals).
4. Riser pipes (or Risers).
5. Sprinklers
6. Pumping unit

Working of sprinklers:

• The pump lift the water from the source ygion and it is supplied to the sprinklers. These sprinklers spray the water.

Merits of Sprinkler Irrigation:

• It can be applied in different topography, in different soils and for different crop.

• Due to reduction in the surface run off, the soil erosion is put under control.

• Uniform application of water is possible.

• By using this method, a controlled supply of water is possible and the discharge also is controlled mainly during the first few watering of crops after sowing and when the plants are still young.

• It needs less labour cost as the preparation of the field is not necessary.

• It does not require, the borders or field channels, so maximum land can be put to cultivation.

• In this method even a small stream of water can be used with maximum efficiency.

• The amounts of fertilizers to be used are also control in this method. (So, again, lesser inputs reduce the cost of production.)

• The crops are protected against frost as the ice (frost) gets melted when the drops of water from the sprinkler, touch the leaves. The areas having temperature as law as - 9°C the sprinklers can save the crops.

• In India except in the high-altitude regions of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh there no danger of prolonged frost in other states and except in Ladakh district of Jammu and Kashmir in no other areas such low temperatures are observed where agriculture is practiced.

• This method is good for the regions, like Rajasthan, south Punjab, Western U.P. Having arid and semi-arid climatic condition because by using this method about 80%, water application efficiency can be maintained.

• This method is good for humid regions also, because the atmospheric humidity is kept less.

• The pumping units can be used to drain out the excess water from the field to avoid the water logging conditions.

Limitations of Sprinkler Irrigation:

1. If the wind velocity increases, the pattern of sprinkler get distorted and creates non-uniformity in the application of irrigation water.
2. The initial cost of sprinkler system is very high.
3. The supply of water must be constant, if the system is to run economically.
4. The water to be sprinkled must be free from sand particles, to avoid clogging of the sprinklers.
5. Due to continuous pumping of water, the consumption of power is high (so the running cost also is high.)
6. If the soils are heavy e.g. Clayey soils, and have poor intake, this method cannot run efficiently.

Q10) Explain the methods of Sub surface irrigation?

A10)

The sub surface methods can be classified given below.

1. Natural Sub-irrigation.
2. Artificial Sub-irrigation.
3. Drip or Trickle irrigation.

Fig.: Sub-surface irrigation

Natural Sub-Irrigation:

• In this method the water is supplied to the crops by controlling the level of the water table.

• The method is called natural because, whatever water is received on the surface, gets percolated, through rivers, lakes streams drain and canals and reaches the water table which gets lifted upto the root zone of the crops and supplies the water for the growth of the plant. In this method to ensure the required supply of water for the growth of plants, the level of water table is required to be maintained by using artificial methods.

• For this a series of parallel channels with almost vertical sides are excavated in the fields which are to be irrigated.

• These channels are spaced about 15 to 100 metres from each after. This spacing depends upon the topography of the land and the permeability of the sub-soil. The depth of the channels varies between 0.3 and 1 metre and width between 0.25 and 0.5 metres. The beds of the channels are almost flat.

• The water is allowed to flow through these channels with very low velocity so, they always have enough water to get percolated in the sub soil and it helps to recipe the root zone of the crops.

• To prevent water logging conditions, it is necessary provide proper drainage to take out the excess amount of water. This can also be done by discontinuing the supply of water through the channels and by allowing the land to dry up, before harvesting.

• As the movement of water is always on upward side the water which comes up also brings salts and makes the soils saline and us less for cultivation, if it continues. So, there is need to have periodic leaching of soil, by applying more amount of water to get it percolated along the salts which have been brought up through the capillary actions.

Conditions Required to Apply Natural Sub Irrigation:

• The soil in the root zone must be loamy or sand-loam having maximum permeability.

• Below the surface at the depth of 2 to 3 metres there must be a free water table (developed, due to impermeable sub stratum.)

• The topographical conditions of the land to be irrigated must be uniform, with a flat surface.

• The water supply must be abundant and free from salts.

• It needs to have unusual natural conditions, so it is tried under different conditions', it may create unsafe conditions for the growth of the plants.

Artificial Sub-Irrigation:

• In this method, the water is applied beneath the land surface, by a network of buried perforated pipes. The water under pressure is allowed to percolate into the soil, to reach in the root zone of the plant and to provide the irrigation water for the growth.

• The functioning of this method can be effective if the soil in the root zone has high horizontal permeability to permit free lateral movement of water and low vertical permeability to prevent deep percolation of water.

• To have uniform distribution of water which percolates in the soil the pipes are required to be very closely spaced (up to 0.45 metres space between two pipes).

• To avoid interference with the crops these pipes are buried at least 0.4 metres below the surface of the ground. The method is not commonly used due to the following limitations.

1. It is very expensive due high cost of pipes and the high installation charges as a skilled labour is required to lay down these pipes at a given depth.

II.            As the rootlets tend to grow close to the outlets of the pipes, they clog the openings of the pipes and thus reduce the expected destruction of water and the performance of the pipe become very poor.

• To overcome these difficulties, mainly to avoid clogging of the small perforations, the water must be free from any type of silt sand or debris. The salinity of the water must be very low to avoid salinization of soil as in this method no lacking is possible (to reduce the salinity of the soil.)

Drip or Trickle irrigation/Micro irrigation:

• This is one of the latest methods of irrigation and also a very popular method among the actual users of irrigation farming.

• In this method small diameter plastic pipes are used together with drip nozzles which are known as Emitters or Drippers. They deliver water to the land surface, near the base of the plant.

• In this method the application of water is at very low rate which varies between 2 and 10 lit/per hrs. This keeps the soil moisture within the desired range for growth of the plant.

Q11) What is the Water requirement of Crops?

A11)

• The total amount of water needed by a crop from the time of its sowing, up to the period of harvesting. If put together, the-sum total of water is known as "The water requirement of crop'.

• This quantity of water required by the crop varies from crop to crop, also varies from sowing harvesting period i.e., summer crops, winter crops, rainy season crops and naturally varies from soil to soil, depending upon the capacity of soil to retain the water i.e., higher the retentivity less will be the amount of water needed to be supplied to the crop in that soil.

• For any crop, it is also necessary to maintain the quantity of readily available moisture in soil, by irrigation and so it is necessary to distribute the total amount of water required by any crop, in such a way that a part of it supplied at each irrigation, must be sufficient to meet the need of the crop, for a period in between two successive irrigation and is stored in the soil.

• So, together with the quantity of water required by the crop, it is necessary to calculate, the required frequency of irrigation and also the total quantity of water to be irrigated during each application. All these points (qualitative information) are based on the soil moisture conditions. Let us see what makes the conditions to retain the soil moisture.

Q12) Explain the Duty and Delta relationship?

A12)

• It is defined as, "it is the period to which the stated duty of water has reference." The total quantity of water is supplied to a crop, through a no. Of devices at central interval. The quantity of water to be given to a crop, during each watering. Varies and it is to be given a specific duration.

• So, the term "Duty of water" is used to indicate the quantity of water required to be given during each watering and it is referred to a specific period when the water is applied, so it is called as the base of the duty of water. When the duty of water is stated for each watering, its base also needs to be stated.

• The duty of water, expressed for each watering, also gives information about the actual rate at which is given to the crop on any day; or a number of days. But such information is not given, by the duty of water which is expressed for the entire base period of a crop, as it gives only the average rate of water application during that period. In fact, when the base is not mentioned, it is assumed that the duty of water refers to the entire base period.

• Delta (): "It is total depth of water required by a crop to came to maturity is called as Delta". It is measured in meters or centimeters.

Duty Hectares / Cumecs CD,

Delta A meters Base Period = 'B' day

One cumec of water flowing continuously for 'B' days; would give the depth of water 'A', over an area of 'D' hectares. The volume of water @ 1m3 sec in one day.

= 1x24x60x60 = 86400 m²

The volume of water @ 1 m³ sec 'B' days

= 1×24×60×60 = 86400 B m3

= 86400 m² m.    … (1)

As 1 hectare = 10,000 m², 1 m² = 1104 N

Then the equation becomes,

Volume of water @ 1 m³ sec in B days

= 86400 B m3

= 86400 B 1104 H-m volume of water @ 1 m³ sec in B days

= 864 x B H-m     …. (2)

The depth of water required by crop,

A = Volume of area A

= 8.64 x B H-m DHA

= 8.64 BDM (in F.P.S. System)

Let, Duty = D (Acres/cusecs)

Delta =A feat base period

= B days (by definition)

One cusec of water flowing continuously for B days, would give the depth of water 'A' over an area of 'D' acres.

The volume of water @ 1 ft3 sec. In one day

= 1x24 x 60 x 60 = 86400 ft3

The volume of water @ 1 ft2 sec for 'B' days

= 1×24×60×60 = 86400 B ft³

=86400 ft² ft

As 1 Acre = 43560 ft², 1 ft2=143560 Acres,

Then the equation becomes, volume of water @ lft3 sec, in 'B' days = 86400 ft3 = 86400 B × 143560 Acre-ft, volume of water @ 1 ft3 sec. In B days

= 1.983 B Acre-it      … (3)

The depth of water required by a crop.

'A' = Volume of Area 'A'

= 1.983 B Acre ft D Acre A = 1.983 x BD ft.

Q13) Explain the Irrigation frequency?

A13)

• It is necessary that the amount of water to be applied to the soil, should be such that the moisture content of the soil is lifted up (raised up) to its field capacity. When the supply of water is stopped the moisture content of soil is reduced due to evaporation from soil and also due to transpiration.

• The total water (moisture) lost by either evaporation or transpiration is known as Evapo- transpiration or the consumptive use of water.

• This reduction of soil moisture content should be allowed to go below the readily available moisture i.e., if and when the soil moisture content reaches the lower limit of the readily available moisture, it must be immediately, replenished by irrigation and the field capacity of soil should reached (as shown in the Fig.). The minimum depth of water dw, is to be applied, during irrigation dw can be calculated by following formula.

Dw =

Or dw=Depth of the readily available moisture in the root zone of soil.

ws = Specific weight of soil,

W = Specific weight of water

d = Depth of root zone of soil

Fig.: Frequency of irrigation

• The frequency of irrigation, [the time interval between any two successive irrigations to the same soil] depends upon the amount of readily available moisture in the root zone of the soil and rate of the consumptive use, through the evapo-transpiration.

So, if C= The consumptive use expressed in terms of depth of moisture lost from the soil per day.

Then the frequency of irrigation (fw) can be calculated by,

Fw= dw/ Cu x number of days.

Where, fw= Frequency of Irrigation

Dw = The minimum depth of water

Cu = Consumptive use

Q14) What are the irrigation efficiencies?

A14)

• Irrigation efficiency (n.) is the optimum use of the water applied, for the growth of the plant. But it is fact that even with the best method of irrigation, there are always some losses through seepage, percolation and evaporation from the canals and also from the field.

• The ratio of, water available for use to the water applied can be defined as the efficiency of irrigation (Theoretically the ratio should be 1:1, to indicate optimum efficiency, but it never observed in reality.) Generally, the well irrigation has maximum efficiency as, the transit losses are almost nil as the well water is directly applied to the field (No chance of losses through seepage or percolation).

• Various methods are used to calculate various types of irrigation efficiencies which are expressed as below.

Water Conveyance Efficiency (nc)

• It is a ratio of the quantity of water delivered to the field (or to the irrigated land) to the quantity of water diverted into the canal system from the river or reservoir it is expressed in the following equation,

Where,

nc = water conveyance efficiency.

Wf = Quantity of water delivered to the field.

Wr= Quantity of water diverted into the canal system from the river or reservoir.

• So, this efficiency accounts for the losses of water, which occur in conveyance from the point of diversion into canal system to the field.

Water Application Efficiency (na)

• It can be defined as, "The ratio of quantity of water stored in the root zone of the plant, to the quantity of water delivered into the field". This ratio is expressed in the following equation.

Where,

= Water application efficiency.

Ws = The quantity of water stored in the root zone.

Wf = The quantity of water delivered into the field.

• So, this efficiency accounts for the losses of water, during the application of irrigation water to the field. The common losses during this process are from the surface runoff and from the deep percolation. So if R, is the quantity of water lost due to surface runoff from the field and D, is the quantity of water lost due to deep percolation (which far below the root zone and so use less for the growth of plant).

∴

• This application efficiency varies as the methods of irrigation vary e.g. If the sprinklers are used for the irrigation of plants its efficiency is upto 80%, of the total quantity of water delivered to the field and in case of surface irrigation (canal or well) the efficiency never goes above 60% of the total quantity of water delivered to the field.

Water Use Efficiency (nu)

• It is the quantity of water used, beneficially, including the water required for leaching, to the quantity of water delivered. This ratio is expressed in the following equation.

Where,

= The water use efficiency,

Wu = The quantity of water used beneficially

Wf= The quantity of water delivered to the field.

Water Storage Efficiency (ns)

• It is the ratio of the quantity of water stored in the root zone (during the irrigation) to the total quantity of water needed to bring the moisture content of the soil to its field capacity. It is expressed in the following equation.

Where,

= Water storage efficiency.

Ws= Quantity of water stored in the root zone.

Wn = Quantity of water needed to bring the moisture content of the soil to the field capacity (Wn= field capacity available moisture in the soil, before irrigation).

Water Distribution Efficiency (nd):

• It is measure used to compare different methods of irrigation i.e. surface irrigation to sprinkler in irrigation methods. For that the following v equation is used:

Where,

= Water distribution efficiency.

y = The average numerical deviation in depth of water stored from the average depth of water.

d = The water stored in the root zone during irrigation.

• This efficiency evaluates, the degree, to which, the water is uniformly distributed throughout the root zone, during irrigation so, it is also called as "Uniformity coefficient".

• If the value of n, is higher, more will be the uniformity, which helps to get better crop response e.g. If n=80% means that, as compared to average depth of water application 10%, is the excess depth of water applied and 10% is the deficient depth of water applied.

Consumptive Use Efficiency (new)

• It is a ratio of normal consumptive use of water, to the net amount of water depleted from the root zone. The consumptive use efficiency can be calculated by using the following equation,

Where, = The consumptive use efficiency.

=We The normal consumptive use of water  or evapotranspiration.

Wd = The net amount of water depleted from the root zone.

• So accounts for the loss of water by deep percolation any type of excessive evaporation, after the irrigation.

Q15) What are the Principal crops?

A15)

• The crops of any country depend upon various physical and climatic factors i.e. The types of soil, depth of soil, General slope of the region, Availability of water. Temperature condition and type of rainfall average rainfall, rainfall season etc.

• The type of crops also depends upon the economic conditions i.e., capacity to invest, need of the crops, transport facilities, market conditions etc. A country having a vast population to serve, needs to have food grains as a top, crop to be cultivated.

• India, we have a vast variation in all the physical and climatic factors e.g., south India has a tropical not and humid climate while in North India, it is sub-tropical, to temperature climate which is humid and cool. In Rajasthan and in Run of Kuch. It is dry climatic while in Assam, Meghalaya it is very humid climate.

• We receive the monsoonal type rainfall mainly due to south-west monsoons, which also have a huge regional variation i.e., coastal areas and states in the North-East directions observe heavy seasonal rainfall, while in the interior states and in western states rainfall is very low.

• The irrigational facilities also, make an impact on the selection of crops i.e., Uttar Pradesh, Bihar, Punjab, Haryana etc. states have good canal irrigation. So, the crops like wheat, Sugar cane cotton, oil seeds etc. are developed while in hot, dry region have lesser irrigation facilities, have dry non-irrigated crops mainly the food crops like, Jowar, Bajra, Rai, Pulses etc. Rice is cultivated in the stages having heavy rainfall. So west-Bengal, Odisha, Andhra Pradesh and Tamil Nādu have maximum are under Rice cultivation.

• So, India in general have high variation in the types of crops and also in cropping seasons i.e., Kharif and Rabi seasons the regions having good supply of irrigation water enjoy the third cropping season called as summer crops.

Q16) What is Crop rotation? Explain its advantages and disadvantages?

A16)

"The rotation of crop is method of growing a different types of crops in different season, in the same field"

Advantages of Rotation of Crops:

1. It helps to make the best use of the soil.
2. It helps to central pest generation.
3. It helps to reduces the growth of weeds.
4. It helps to improve the soil structure and fertility.
5. It helps to make the best use of available irrigation water.
6. Due to the rainfall variation, it can help to reduce the changes of total economic loss,due to crop failure.

Disadvantages of Rotation of Crops:

1. It has less profitability.
2. It needs different machinery for different crops.
3. It reduces the crop flexibility.
4. It needs to have a high initial capital investment.

The crop rotation chart:

• There are many ways to rotate the crops in a given area. One of the easiest ways is to plan the rotation, to get maximum benefit with minimum losses.

• The types of crops to be rotated would vary from region to region, depending upon the relief climatic conditions and the capacity of the farmer to invest, the following Fig. Explains the four year rotation of crop.

• To follow the rotation of crop method one has the assume the following:

1. The field size is moderate to large i.e. 5 ha to 10 ha.
2. The irrigation water is available throughout the year.
3. The purpose of farming is commercial.
4. The market is available with all weather roads for transportation.
5. The farmer has the capacity to have a large capital investment.

Q17) Explain Classification of canals based on alignment?

A17)

1. Contour canals
2. Ridge canal/Ridge alignment
3. Side slope
4. Canal network

The canals classification based on alignment are as follows:

1.Contour canals

• When canals are to be aligned in hilly area's it is not possible to align along areas which is at top of the hill. In such cases canals are aligned generally along contours. The canal taking off from reservoir follows contour alignment such canal which is aligned parallel to the contours of area is known as contour canals.

Fig.: Cross Drainage work

• Contour canals have large number of cross drainage work but no falls.

• A contour canal can irrigate only one side as ground level as other side is quite high.

• Contour canals need not to follow same contour along its length.

• To contour canals longitudinal slope is given to enable the water to flow by gravity.

2. Ridge canal / Ridge alignment

• It is also called as watershed canal. These types of canals are generally laid along ridge or natural watershed line as canal runs on watershed it can irrigate on both sides and thus irrigates area on both sides.

• These canals are very economical. No cross drainage work is required.

Fig.: Ridge canal

3. Side slope canal

• In this type of alignment canal is not aligned along either ridge or contour but it is aligned across contour.

• These canals run nearly parallel to natural drain similar to contour canal. It also irrigates areas on only one side.

• These types of canals are not intercepted by cross drainage work.

4.Canal network

Fig.: Canal Network

Q18) Explain Classification of canals based on the Nature of water source?

A18)

Classification of canals based on the Nature of water source are a s follows:

1. Permanent canals
2. Inundation canals

I: Permanent canals

• It is the canal, getting perennial supply of water from its source. It is a well-graded canal and has permanent regulation and distribution work. These canals can be further divided into two as,

• Perennial canals: They get continuous supply of water, around the year. They are constructed on a river which is perennial like River Ganga, River Indus and its tributaries (Sutlej, Ravi, Jhelum etc.) and River Yamuna in the Ganga plains in North India.

• Non-perennial canals: These canals are constructed on the river which are non-perennial and so during the cropping season only, they are used for irrigation purpose (they do not have water round the year).

II: Inundation canals

• It is a canal which get water at the time of floods only when the water level, in the river (on which the canal has been constructed) rise above the average.

• These canals do not have any head works for the purpose of diversion of the river water. They get water through the open cuts in the bank of the river. They are called as heads. In the downstream of canal at about the distance of five to six kms, the regulator is provided from the points of heads, to control the water supply.

• So, by its nature itself, it is clear that inundation canals are non-perennial and they can supply the water when the level of the water in the river (its source) rises above the average (during the flooding seasons).

Q19) Explain Classification of canals based on the function of the canals?

A19)

Classification of canals based on the function of the canals are as follows:

1. Feeders or feeder canals
2. Carrier canals

I: Feeders or feeder canals

• This type of canal is constructed with the only purpose to supply water to another canal. e.g. The canal known as Indira Gandhi Canal in Rajasthan is a feeder canal. It gets water from the Harike Barrage in Punjab state from the ri er Sutlej. (the total length of the feeder canal is about 216 km).

II: Carrier canals

• These canals serve both the purpose i.e. They supply the water directly for the irrigation purpose and also make supply of water to another canal. Such type of canal has been constructed in western parts of Punjab (in Pakistan) on the river channels. It is known as upper channel canal.

Q20) Explain Classification of canals based on discharge?

A20)

Classification of canals based on discharge are as follows:

1. Main canal
2. Branch canal
3. Major distributaries
4. Minor distributaries
5. Field canals

I: Main canal

• It is a large capacity canal getting the supply of water directly from the river or from the reservoir. It has a large capacity to supply water to the major distributaries and the branch canals. They are generally not used to make direct supply of water to the agricultural fields.

II: Branch canal

• They are also called as "Branches." They are constructed on both the sides of the main canal (called as left and right canal). They are generally used to collect water from the main canal and supply it to the major or the minor distributaries. In case of small branch canals they are also used to the provide water directly to the agricultural fields. Their discharge is above 5 cumec.

III: Major distributaries

• These distributaries receive water either from the main canal or from the branch canal. Their discharge of water vary between 0.15 and 5 cumeè. They are used to supply water from the out lets to the agricultural fielders some of them are also used to supply water to the minor distributaries.

IV: Minor distributaries

• They get the water supply either from the major distributaries or fro branch canal. Their carrying capacity is less than 0.25 cumec. They make supply of water to the agricultural fields.

V: Field canals

• They are also called as water courses. They collect water from a outlet of a major or a minor or a branch canal and carry water to the agricultural fields. The field canals are constructed controlled and maintained by the actual users. i.e. farmers who are the owners of these field canals. The main branch major and minor canals are constructed, maintained and controlled by government as they are owned by the government. Recently under the Command Area Development (CAD) program the water courses are constructed by the government but they are regulated and maintained by the farmers only.

Q21) Explain Classification of canals based on financial output?

A21)

1. Productive canals
2. Production canals

I: Productive canals

• Definition: In case of canals getting full yields (revenue) to cover up not only the running cost but also about 6% of the capital investment as the savings (profit) so it is called as productive canal,

II: Production canals

• In this type of canal there is no profit making infact it does not cover the running cost even and there is no chance to repay the initial capital expenditure. These canals are not constructed to gain profit but to give protection to the famine affected areas by generating employment through such relief work. This helps to provide water for cultivation in future and reduce the danger of total famine.

• In fact they cannot be compared with profit working productive canal, as it is a social cost, the government must accept.

Q22) Explain Classification based on lining provided or not provided (unlined) to canals?

A22)

1. Unlined canals
2. Lined canals

I: Unlined canals

• These are the canals which are made up of natural soil and no lining of impervious material is provided.

• The velocity of flow is always kept low, to provide protection to the bed and banks.

• As these canals have high seepages and water losses are high. If the length of such canals is high the water losses go on increasing.

II: Lined canals

• These canals have been provided with a lining of impervious material on its banks and bed. This helps to prevent the seepage of water.

• As the velocity of flows can be kept greater the cross-section area can be reduced.

Q23) What is the Alignment of canal?

A23)

The following points should be considered while fixing alignment of canal:

1. The alignment should not made in a rocky cracked strata.
2. The number of curves should be minimum.
3. There should be minimum number of crossing with natural drain.
4. The length of main canal should be minimum.
5. Command area should be at higher level.
6. The alignment should be such that most economical section should be achieved.

Q24) Explain the parts of canal system?

A24)

Component parts of Canal System are as follows:

1. Main canal
2. Branch canal
3. Major distributor
4. Minor distributor
5. Water course
6. Head work

Main canal

• Definition: The canal taking off from a river or reservoir i.e., from source is called as main canal.

• The main function of such canal is to carry the total irrigation water and to distribute it to canal system.

• It is the largest canal in system and no direct irrigation is normally done from main canal.

Fig.: Canal distribution system

Branch canal

• It is canal takes off from main canal on either side. Very little direct irrigation is done from them.

• These canals act as a feeder canal for major or minor distributor. The discharge capacity of branch canal is usually varying from 5 to 25 cumec.

• It helps to make irrigation water available in different parts for distribution.

Major distributor (Rajbaha)

• It generally takes off from main canal which supplies water to other distributaries.

• The discharge capacity of major distributaries varies from 0.25 to 5 cumec in some cases it may be 10 cumecs.

• These are generally used for direct irrigation and their main function is to distribute water to water courses.

Minor distributor /Minor

• Minor distributor generally takes off from major distributors or from main canals or another distributor and supplies water to water course.

• Its discharge capacity is less than 0.25 cumecs. These are also used for direct irrigation.

Water courses / Field channels

• These are small channels ich take water from the outlet of distributor or minor distributor and supply it to the agricultural fields.

• These are owned constructed controlled and maintained by cultivators.

• Sometimes these are constructed, by government on behalf of irrigators but its maintenance is carried out by irrigators only.

Fig.: Water course

Head work

• The works those are constructed to store, divert and control the river water and regulate the supplied into the canal.

Q25) What is Command area?

A25)

The location over which canal irrigation water flows with the aid of using gravity is referred to as the command location in irrigation. Following are the kinds of command regions:

Types of Command Area in Irrigation:

1. Gross Command Area:

• Gross Command Area is the overall location that may be economically irrigated from an irrigation scheme without thinking about the restrictions of water.

• It is denoted with the aid of using GCA. It consists of cultivating land in addition to roads, wastelands, forests, barren lands, and so forth.

• GCA = CCA + Uncultivable location

2. Culturable Command Area:

• Culturable Command Area is the location wherein a crop is grown at a selected time or crop season. It is denoted with the aid of using CCA.

• Uncultivable regions are excluded from GCA to reap CCA. The uncultivable location consists of barren lands, forests, and so forth.

• CCA=GCA – Uncultivable location

• The culturable Command Area may be of types. They are:

a. Culturable Cultivable Area:

• It is the location in the culturable command location wherein cultivation is really accomplished at present.

b. Culturable Uncultivable Area:

• It is the location in the culturable command location wherein the cultivation is viable however now no longer accomplished at present.

3. Net Command Area:

• It is the Culturable Command Area received after the deduction of canal networks, deliver ditches, and so forth built withinside the field.

• It is denoted with the aid of using NCA.

• NCA=CCA – the location occupied with the aid of using canals, canals network, and ditches.

Q26) Explain the types of channel losses?

A26)

Basic types of water losses are:

1. Losses due to Evaporation
2. Losses due to Percolation
3. Losses due to Transpiration

(A) Losses due to evaporation

• The loss of water through evaporation depends upon various factors like temperature. Surface are of the water bodies, relative humidity (if relative humidity is 100%. i.e. the air is totally saturated with moisture there will be almost no evaporation if the air is totally dry i.e. there is no moisture the rate of evaporation will be maximum), velocity of wind, cloudiness etc. In the summer season i.e. in the months of March, April and May in India as the duration of the day is higher the in coming solar radiation, through short waves, is more and, so during these months the rate of evaporation is more. In winter due to less temperature and during rainy season due to high relative humidity and over cast conditions (i.e. cloudiness) the rate of evaporation is less.

• For these losses no special consideration is made while designing an irrigation channel.

(B) The losses due to percolation

• This type of loss of water is also known as seepage loss. The percolation losses depends upon the following conditions,

1. Permeability of the soil in the bed and on the banks of the channel: If the soils are highly permeable the water losses will be very high.
2. The depth of the water in the channel: If the depth is higher, higher will be the water losses, through percolation.
3. Velocity of the flow: If the velocity of the water is high, the rate of percolation will be less.
4. Amount of silt in the water: If the water has more silt in suspension, the rate of percolation will be less.
5. Temperature of water: If the temperature of flowing water is high, the losses through percolations are high.
6. Age of the channel: As the channel becomes old, the fine silt gets deposited on the bed of the channel and block the holes through which the water gets percolated and it reduces the speed of loss of water through percolation. In case of new channel, the holes in the bed are still open and it has less siltation, so the rate of percolation is always greater.
7. The depth of the ground water: If the ground water level is just below the surface the rate of percolation is less.

(C) Losses through transpiration

• There is a little loss of water through the plants, vegetation and weeds on the banks of the channel due to transportation. This can be controlled by keeping the banks clean from the growth of vegetation and weeds.

Q27) A duty for a crop is 1152 hectares/cumec on the field, the base period of this crop is 120 days.

A27)

Duty D= 1152 hectares/cumec

Base period B=120 days

Delta=0.9m

Q28) A crop required 1080 mm of water for a base period of 125 days. Find the duty of water.

A28)

Given:

Delta

Base period B=125 days

To find: Duty D=?

Duty D=