ASSIGNMENT TOPICS WITH MATERIALS UNIT: Ikgr.ac.in/beta/wp-content/uploads/2018/09/WRE-I-COURSE-FILE.pdf · ASSIGNMENT TOPICS WITH MATERIALS UNIT: I 1. Introduction to Engineering

JAGADISH S H, ASSISTANT PROFESSOR

ASSIGNMENT TOPICS WITH MATERIALS

UNIT: I

1. Introduction to Engineering Hydrology and Its Applications Hydrology: It is the science which deals with the occurrence, distribution and movement of

including that in the atmosphere and below the earth surface.

Water occurs in the atmosphere is in the form of vapour.

On the ground surface as water or ice.

Below the earth surface as ground water occupying all the voids with in the

geological stratum.

Hydrological Cycle and their Components Hydrological Cycle: Except for very deep ground waters, the total water supply of earth is in contact circulation

circulatory system is known as hydrological cycle. (Or) hydrological cycle is the process of

and evaporation of water back to the atmosphere.

Diagram Showing Hydrological Cycle 2. Hydrological cycle consists of the following Processes. 1. Evaporation and Transpiration (E)


The water from the surface of the ocean, rivers and also from the moist soil evaporates. The

vapours are carried over the land by air in the form of clouds. Transpiration is the process of

water being lost from the leaves of the plants from their pores. Total evaporation (E)

including transpiration consists of the following:

d. Surface evaporation: Evaporation from moist soil e. Water surface evaporation: Evaporation from river surface, from oceans f. Evaporation from plants and leaves ( Transpiration ) g. Atmospheric evaporation. 2. Precipitation (P)

s surface in any form. Precipitation may be two forms

Liquid Precipitation - rain

Frozen form consist of - Snow, Hail, sleet, freezing rain.,

3. Run off (R) Runoff is that portion of precipitation that is not evaporated. When moisture falls to the ground in the form of precipitation, a part of precipitation will be evaporated by means of soil surface, water surface and plants. The remaining part of precipitation is available as a runoff which ultimately reaches ocean through surface and sub surface streams. The run off may be classified as following:

Surface Run-off

Water flow over the land surface and First it reaches the streams and rivers ultimately

this quantity of water is discharged in oceans.

Inter flow (or) Sub-surface Run-off

depends on the geology of the basin, runs as a sub-surface flow ultimately reaches to oceans

through rivers and streams.


Ground Flow (or) Base flow Run-off:

It is also a portion of precipitation, which after infiltration, percolates down and Joins the ground water reservoir. This ultimately reaches the oceans. Precipitation = Evaporation + Run off 3.Measurement of Rain fall Rain fall is the main source of water used for various purposes. Knowledge of rain fall

quantity, intensity of rain fall & distribution of rain fall is extremely useful for irrigation

engineering. The amount of rain fall is measured in centimeters (inches).which is falls on a level

surface and is measured by rain gauges.

The intensity of rain fall is the rain fall per unit time. It is expressed as cm/hr. The following

are the main types of rain Gauges used for measurement of rain fall.

Non-automatic rain gauges

Non automatic rain gauges are non-recording type.

Eg: Symons rain gauge.

Automatic rain gauges.

Weighing bucket type rain gauge.

Tipping bucket type rain gauge.

Float type rain gauge. Symons rain gauge: Symons rain gauge is commonly non recording type rain gauge in India

and is used in meteorological department of government of India. It consists of cylindrical

vessel 127 mm (or 5") in diameter with a base enlarged to 210 mm (or 8") diameter. The top

section is a funnel provided with circular brass rim exactly 127 m (5") internal diameter. The

funnel shank is inserted. in the neck of a receiving bottle which is 75 to 100 mm ( 3 to 4")

diameter. A receiving bottle of rain-gauge has a capacity of about 75 to 100 mm of rainfall

and as during a heavy rainfall this quantity is frequently exceeded, the rain should be

measured 3 or 4 times in a day on day of heavy rainfall lest the receiver fill should overflow.

A cylindrical graduated measuring glass is furnished with each instrument, which reads to

0.2 mm. The rainfall should be estimated to the nearest 0.1 mm.


Weighing bucket type rain gauge: it is self recording type rain gauge this is used to

determine the rate of rainfall (or) intensity of rain fall over a short period of time. The

weighing bucket rain-gauge essentially consists of a receiver bucket supported by a spring or

lever balance or any other weighing mechanism. The movement of the bucket due to its

increasing weight is transmitted to a pen which traces the record on a clock-driven chart.

Tipping bucket type rain gauge: The tipping bucket type rain-gauge consists of 30 em

diameter sharp edge receiver. At the end of the receiver is provided a funnel. A pair of

buckets are pivoted under the funnel in such a way that when one bucket receives 0.25


(0.01 inch) of precipitation it tips, discharging its contents into a reservoir bringing

the other bucket under the funnel. Tipping of the bucket completes an electric circuit

causing the movement of pen to mark on clock driven revolving drum which carries a

record sheet.

Float Type Automatic Rain-gauge: The working of a float type rain-gauge is similar to the

weighing bucket type gauge. A funnel receives the rain water which is collected in a

rectangular container. A float is provided at the bottom of the container. The float is raised as

the water level rises in the container, its movement being recorded by a pen moving on a

recording drum actuated by a clock work. When the water level in the container rises so that the

float touches the top, the siphon comes into operation, and releases the water; thus all the water in the

box is drained out.


Site Selection For Rain Gauge:

The rain gauge should be installed on a plain surface.

The distance between rain gauge and nearest objective should be at least twice the height of the objective

The rain gauges should not be provided side and top of the hill. 4.Advantages of Recording type rain fall over non Recording type rain ruage:

Rain fall is recorded automatically and hence no attender is necessary.

By using automatic rain gauge records the intensity of rain fall, where as

in the case of non-automatic rain fall rain gauges, only rain fall depth is

inaccessible points also.

Human errors are avoided. Disadvantages

It is costly.

Fault may be developed in electric &mechanical mechanism for

recording the readings.


UNIT-II

1. Hydrograph Analysis

Hydrograph is a graph showing variations of discharge with time, at a particular point of a

stream. It shows the time distribution of total run-off at the point of measurement.as shown in

fig 1.1 Fig 1.1 Storm Hydrograph Component Parts of Storm Hydrograph A single peaked hydrograph resulting from a isolated storm is shown in Fig.1.2. A is the

point of rise, D is the peak and E is the point of inflection on the recession curve. As started

earlier, rain water, exclusive of the water withheld as basin recharge. May follow three paths

to stream:

Overland flow (surface run-off,

Interflow (influent stream), and

Ground water flow (effluent stream). Overland flow and interflow are frequently grouped together as direct run-off. Much of the

low water flow of streams is derived from ground water. In a storm hydrograph, the direct

run-off and the ground water run-off are separated by the following procedure. Extend the recession of the flow existing prior to the storm to a point under the peak (or crest) of the hydrograph (line AB). Select a point C on the recession limb of the hydrograph N days after the peak. Join point

Band C.


. Fig 1.2 Components of Single Peak hydrograph A rough selection of N

(in days) is given by

N= O.84A0.2 Where A = drainage area is sq. km.If the drainage area of the basin is expressed in sq. miles.

N= A10.2

Where A1= drainage area in sq. miles. Thus, ABC is the ground water divide line. Area ABCD gives volume of direct run-off. In

Fig.1.2, at any time instant t, the ordinate ab represents the flow due to ground water

storage or base flow and bd represents the flow due to both surface run-off as well as

influent stream.

Fig.1.2 also shows heytograph along with infiltration curve, at the top. It also shows the

following important time factors useful in hydrograph analysis.

Effective Duration: It is the time between which the rainfall rate is more than the

infiltration rate.

Basin Lag (tp): It is the time between the centroid of the net rainfall (Pnet) and the

peak of the hydrograph.

Recession Time (Tr): It is the duration of direct runoff after the end of effective

duration.


Time of Concentration (tc): Time of concentration is the time in hours taken by rain

water that falls at the farthest point to reach the outlet of a catchment. This is equal to the

time between point of inflexion and end of effective duration. Valley Storage: The discharge in a stream goes on increasing as water enters the stream, and

the levels go on increasing. The difference between the water level prior to the flood and the

flood water level indicates the volume of water that is temporarily stored.The water stored is

not standstill, but moves as sheet of water and is known as valley storage. Channel Storage:

If the flood water level is within the banks of the stream, the valley storage is known as

channel storage. Experience in America indicates that flow to the right side of the point of

inflexion of the falling side of the hydrograph above ground water line is due almost entirely

to channel storage.

Base flow or Depletion Curve: In Fig 1.2, ABC is the estimated or assumed base flow or

depletion curve. Actual contribution of ground water is shown by dotted lines in,,Fig. 1.3(b).

As shown in Fig. 1.3(a) when the water level before the storm is low, there is a flow from

ground water to stream. But as the water level in the stream is raised due to the storm, there

is flow from the stream to the ground water. As the flood level in the stream recedes, the

ground water again starts contributing to the stream. Thus ABC denotes the ground water

line only if there were no flood. However since the ground water contribution is small

percentage of the total flow, it is usually considered-justified that the flow above the line

ABC is due to direct run-off.

Hyetograph: Hyetograph is the graphical representation of average rainfall and rainfall

excess (i.e., rainfall minus infiltration) rates over specified area during successive unit time

intervals during a storm. Such hyetographs are plotted above the run-off hydrographs. Fig 1.3(a) Stages in storm before and after


(b) Actual base flow 2. Calculation of Direct Run-off for Rain-fall Excess From the Storm Hydrograph. Procedure (Refer Table 1.1). Table 1.1

Date and Time Ordinate of hydrograph Base flow Direct run-off (0)

(1) Total Q (cumecs) (4) . (cumecs) (2) (3)

14-8-65

0500 14 14 0

0800 25 12 13

1100 51 11 40

1400 65 10 55

1700 54 11 43

2000 28 13 15

2300 14 14 0

Q=166

Find the ordinates of storm hydrograph, representing total discharge Q at a

given time interval, say t hours.

Separate the ground water flow. Find the ordinates of the base flow at the same

time interval

Find the ordinates of direct run-off by subtracting the ordinates of base flow

from total discharge ordinates. .4. The direct run:-off in depth of water (in cm) is found from the expression Direct run-

off = Total volume of direct run-off /Area of basin

C. 0.36 (

Where t = Time interval between successive ordinates in hours A = Area of basin in sq. km.


Q = Discharge in cumecs.

O = Sum of discharge ordinates (direct run-off) in cumecs. For the above example, if area of the basin is 30 sq. km. . Directly run off = 0.36 (

0.36 166

3. Unit Hydrograph

A unit hydrograph is a hydro graph representing 1 cm (or 1 inch) of run off

from a rainfall of some unit duration and specific areal distribution.

Unit duration refers to the duration of a run-off producing rainfall-excess,

that results in a unit hydrograph.

For example, if a unit hydrograph results from a 3 hours unit rainfall duration,

it is known as a 3-hours unit hydrograph, meaning thereby a hydrograph produced

by surface run-off from a storm lasting for 3 hours and yielding rainfall excess of 1

cm.

The unit duration may vary from one day for large catchments to a few

hours for a small catchment. Experience has shown that best unit duration is

about one fourth of the basin lag, the time from the centre of mass of rainfall to

the peak of the hydro graph.

The basis of the unit hydrograph concept, first given by L.K.Sherman

(1932) is that if two identical rain storms could occur over a drainage basin with

identical conditions prior to the rain, the hydrographs of run-off from the two

storms would be expected to be the same.

The basic premise implies that the rainfall excess of n centimeters with in

the selected unit duration unit will give a run-off hydrograph having ordinates n

times as great as those of unit hydro graph of the same unit duration.


4. Assumptions of Unit Hydrograph Theory. The assumptions of unit hydrograph theory must be properly understood before applying it to

actual problems, as these assumptions impose certain limitations which must be carefully

noted. The various assumptions are given below.

The effective rainfall is uniformly distributed within its duration of specified

period of time.

The effective rainfall is uniformly distributed throughout the whole area of the

drainage basin.

The base or time duration of the hydrograph of direct run-off due to an effectiverainfall of unit duration is constant.

The ordinates of direct run-off of common base-time are directly proportional

to the total amount of direct run-off represented by each hydrograph.


UNIT-III

1. Types of geologic formations and Aquifers

There are basically 4 types of geological formations:

Aquifers

Aquiclude

Aquifuge

Aquitard

h. Aquifer: An aquifer is a water-bearing geologicfonnation which stores water and is

also capable of transmitting water through its pores at a relatively large rate which is

sufficient for economical extraction of ground water by wells. Thus an aquifer is a

saturated formation which not only stores water but also yields it in sufficient quantity

when extracted because of its high permeability.

There are two types of aquifers:

Unconfined aquifers

Confined aquifers

Unconfined aquifers: An unconfined aquifer is one in which a free surface (i.e. water

table) exists (as shown in figure 1.1(a)).The unconfined aquifer extends from the ground

surface upto the impervious stratum underneath. However, only the saturated zone of this

aquifer below the water table is of importance in ground water hydrology. A well drilled

into an unconfined aquifer indicates the water level corresponding to the water table at

that location. The unconfined aquifer is also called the water table aquifer, and a well

drilled in this type of aquifer is known as a water table well.

Confined aquifers: A confined aquifer is an aquifer which is sandwiched between

two impervious strata (or aquiciludes) (as shown in figure below 1.1 (b)). The water in a

confined aquifer is under pressure. The piezometric surface is much higher than the top

level of the aquifer at that point. The confined aquifer js also called the artesian aquifer.


Fig 1.1 (a) Unconfined aquifers (b) Confined aquifers

If the water level in the well drilled in a confined aquifer rises above the ground

surface, water flows out freely without any pump. Such a well is called as flowing

artesian well (as shown in figure 1.2). On the other hand, if the water level is below the

ground surface, the well water does not flow freely and the well is called a non-flowing

artesian well.

Fig 1.2 Artesian Well

Aquiclude: An aquiclude is a geologic formation which contains water but cannot

transmit it in sufficient quantity because of its low permeability. It is essentially a

geologic formation which is impermeable to the flow of water. Clay and shales are the

examples of aquicludes.


Aquifuge: An aquifuge is a geologic formation which does not have interconnected pores. It

is neither porous nor permeable. Thus it can neither store water nor transmit it. Examples of

aquifuge are rocks like basalt, granite, etc. without fissures.

D. Aquitard: An aquitard is a partly permeable geologic formation. It transmits water at

such a slow rate that the yield is insignificant. Pumping by wells is not possible. For

example, sand lenses in a clay formation will form an aquitard.

2. Darcy's Law

In 1856, Henry Darcy proposed a law for the velocity of flow through a porous

medium. According to Darcy's law, the velocity of flow in soil is proportional to. the

hydraulic gradient, and is given by

v= ki .

Where k is the coefficient of permeability and i is the hydraulic gradient.

As the hydraulic gradient is dimensionless, the unit of the coefficient of

permeability is the same as that of the velocity. The coefficient of permeability is also

called the hydraulic conductivity. The velocity v in the above equation is the discharge

velocity (or apparent velocity or superficial velocity) and is obtained as

v= Q/A .

Where Q is the discharge and A is the gross cross-sectional area of the soil mass,

including the area occupied by the solid particles.

Because the water can flow only through the pores of the soil mass and not through

the solid particles, the actual velocity (vs) through the pores is different from the apparent

velocity (v). The actual velocity of flow (based on macroscopic scale) through the pores is called the seepage velocity, and is given by

vs = v/n

Where Vs = actual velocity, v discharge velocity and n is the porosity.

As it is difficult to measure the seepage velocity, it is rarely used in ground water

hydrology. Discharge velocity (v) is commonly used in practice, and the velocity in

general means the discharge velocity, unless mentioned otherwise. The discharge can be

expressed as (Fig. 1.4).


Fig. 1.4 Darcy's Law

Q= (ki) A

Where A is the gross cross-sectional area of the porous medium (aquifer). The-hydraulic

gradient (i) is given by ( h/L), where h is the drop in head in a length L.

Range of validity of Darcy's law: Darcy's law is a particular case of the general

laminar flow. The upper limit for the validity of the law is usually taken as Reynolds number equal to unity, where Reynolds number is given by

Re =pvd/µ

Where Re = Reynolds number, v = discharge velocity (cmls), d is the effective diameter

(cm), which is taken as d10 size (i.e. 10% of the particles are finer than this size), p is the

mass density (g/ml), µ is the coefficient a) The flow in aquifers generally follows Darcy's law.

b) It has been found that Darcy's law can be applied even upto Re of 10 or so.

c) In aquifers with large fissures. coarse gravels. rockfills, etc.. the Reynolds

number is usually greater than 10, and therefore, Darcy's law is not strictly applicable.

3. Measurement of coefficient of permeability: In a laboratory, the coefficient of

permeability is determined with an instrument called permeameter. There are two

types of permeameters: (1) Constant-head permeameter. and (2) Falling-head

bpermeameter.


UNIT- IV

1. Necessity and Importance of Irrigation Definition

Irrigation may be defined as the process of artificially supplying water to soil for

raising crops. It is a science of planning and designing an efficient, low-cost, economic

irrigation system tailored to fit natural conditions. It is the engineering of controlling and

harnessing the various natural sources of water, by the construction of dams and

reservoirs, canals and headworks and finally distributing the water to the agricultural

fields. Irrigation engineering includes the study and design of works in connection with

river control, drainage of water-logged areas, and generation of hydroelectric power.

Necessity

India is basically an agricultural country, and all its resources depend on the

agricultural output.

Water is evidently the most vital element in the plant life. Water is normally

supplied to the plants by nature through rains.

However, the total rainfall in a particular area may be either insufficient, or

ill-timed. In order to get the maximum yield,

it is essential to supply the optimum quantity of water, and to maintain correct

timing of water.

This is possible only through a systematic irrigation system-by collecting water during

the periods of excess rainfall and releasing it to the crop as and when it is needed. Thus,

the necessity of irrigation can be summarised in the following four points:

i. Less Rainfall

When the total rainfall is less than needed for the crop, artificial supply is

necessary.

In such a case, irrigation work may be constructed at a place where more water is

available, and then to convey the water to the area where there is deficiency of

water.


3. Commercial Crops with Additional Water

The rainfall in a particular area may be sufficient to raise the usual crops, but more water

may be necessary for raising commercial and cash crops.

4. Controlled Water Supply

By the construction of proper distribution system, the yield of the crop may be increased.

Application of water to the soil by modern methods of irrigation serves the

following purposes:

It adds water to the soil to supply the moisture essential for the plant growth.

It saves the crops from drying during short duration droughts.

It cools the soil and the atmosphere, and thus makes more favourable

environment for healthy plant growth.

It washes out or dilutes salts in the soil.

It reduces the hazard of soil piping.

It softens the tillage pans.

2. Importance of Irrigation

The scope of irrigation is not limited to the application of water to the soil. It

deals with all aspects and problems extending from the watershed to the

agricultural farms.

It deals with the design and construction of all works, such as dams, weirs,

head regulators etc. in connection with the storage or diversion of water, as well

as the problems of subsoil drainage, soil reclamation and water-soil crop

relationships

An irrigation engineer is also required to have the knowledge of cultivation of

various crops, their maturing and protection from pests.

Briefly speaking, the scope of irrigation can be divided into two heads: Engineering aspect. Agricultural aspect. Engineering Aspect Storage, Diversion, or Lifting of. Water

This is the first phase of irrigation engineering. By the construction of a dam across

the river, a suitable reservoir can be created and water can be stored.


Alternatively,if river is perennial and carries sufficient discharge, suitable diversion

works, such as a weir, barrage and bandhara can be constructed across the river and water

can be diverted to the canal.

Places where ground water table is high, suitable wells can be dug and water can be

lifted and fed to small channels or pipes.

Conveyance of Water to the Agricultural Fields The stored or diverted water is conveyed to the agricultural fields through some

suitable distribution system.

If the project is big, the distribution system will consist of two or more main canals

and a number of distributaries, and minors.From the canal, the water is led to the field

through 'water course' or 'field channel'.These field channels take off from the distributaries

or minors through modular or non-modular outlets, so that water supply can be regulated.

Thus, this second phase includes the design and construction of suitable canal

system, along with various regulatory works such as head regulators, cross regulators, falls

etc. for the efficient working of the canal.

In addition to these, suitable cross drainage works, such as aqueducts, super

passages, level crossings, bridges etc. will have to be designed and constructed at the places

where the canal crosses a natural drain or a road.

3. Types of Irrigation

Irrigation has the following main types or classes


Flow Irrigation

Flow irrigation is that type of irrigation in which the supply of irrigation water

available is at such a level that it is conveyed on to the land by the gravity flow. Flow

irrigation may further be divided into two classes:

(i) Perennial irrigation system (ii) Inundation or flood irrigation system.

Perennial Irrigation

In perennial irrigation system, the water required for irrigation is supplied in

accordance with the crop requirements throughout the crop period.

For such a system, therefore, some storage head works, such as dams and storage

weirs or barrages are required to store the excess water during floods and release

it to the crops as and when it is required.

Inundation Irrigation

Inundation irrigation is carried out by deep flooding and thorough saturation of

the land to be cultivated which is then drained off prior to the planting of the crop.

Depending up on the source from which the water is drawn, flow irrigation can be further

subdivided into three types:

Direct irrigation (River canal irrigation): know as Diversion scheme

Storage irrigation (Reservoir or tank irrigation): know as Storage scheme Combined storage and Diversion scheme.

Direct Irrigation or River Canal Irrigation

In this direct irrigation system, water is directly diverted to the canal

without attempting to store the water.


Fig1.1 Direct Irrigation Scheme

For such a system, a low diversion weir or diversion barrage is constructed

across the river. This raises the water level in the river and thus diverts the water

to the canal taking off upstream of the weir, as shown schematically in Fig. 1.1.

Generally, a direct irrigation scheme is of a smaller magnitude, since there are

no rigid controls over the supplies. One or two main canals may take off directly

from the river.

Cross-drainage works are constructed wherever natrual drains or distributary

streams cross the canals. In a bigger scheme, there may be branch canal taking off

from the main canal.


4. Choice between the Systems

Direct irrigation scheme is adopted in the circumstances where the river is

perennial and has a normal flow throughout the irrigation season, never less .at

any time than the requirements of the field.

On the contrary, storage irrigation system is adopted when the river flow is

either not perennial, or where flow is insufficient during certain parts of the crop

season for irrigation requirements.

In a multistage river -valley development, a combined storage-cum-diversion

scheme is more useful.

Lift Irrigation

Lift irrigation is practiced when the water-supply is at too low a level to run

by gravitation on to the land.

In such a circumstances water is lifted up by mechanical means. Irrigation

from wells is an example of lift irrigation, in which sub-soil water is lifted up to

the surface and is then conveyed to the agricultural fields.

5. Quality of Irrigation Water

Irrigation water usually contains some silt as well as certain dissolved salts. These

ingredients in the irrigation water may be useful for the crops if they supplement or

replenish the nutrients taken by the plants from the soil. On the other hand, some of

these ingredients may be injurious to the plant growth and may render the soil infertile.

The effects of silt and salts are separately discussed below:

2. Effect of silt in water The effect of silt on the quality of irrigation water depends

upon the type and amount of silt material as well as on the characteristics of the silt. If

the silt contains a large amount of nutrients required for the plants, it is quite useful,

especially for virgin soils of the agricultural land. Such soils usually have low content of

plant nutrients and a very low water-holding capacity. When the silty water is applied to

such soils, gradual accumulation of silt occurs and the fertility is improved. On the other

hand, the silt carried by the irrigation water may also be injurious to the land. This is

usually the case when the silt is not rich in plant nutrients and the land is already fertile.

Another disadvantage of the silt is that it may reduce the permeability of the soil and

make irrigation more difficult and time consuming.


2. Effect of salts in water The quality of irrigation water is mainly determined by

the concentration of the soluble salts such as chlorides, sulphates and borates of sodium

(Na), potassium (K),calcium (Ca) and magnesium (Mg). Salts of some heavy elements

such as lead, zinc, selenium, arsenic etc. are injurious to plants even when in small

quantities. Fortunately, under normal conditions, the solubility of heavy element salts is

quite low. Hence the concentration of such salts is usually much less than that which

may be injurious to plants. Thus the quality of irrigation is mainly controlled by salts of

sodium, potassi;-'m, calcium and magnesium.

In general, the irrigation water must have low concentration of salts. A high

concentration of dissolved salts affects the water intake of the plant. The plant may result

in dehydration or wilting due to high osmotic pressure. As such, water with a high

concentration of salt should not be used. However, the tolerable concentration of salts in

water will also depend upon the type of soil. The water with salts may however be

tolerable or even useful for irrigation on some types of soils. For example, heavy clayey

soil with a low permeability and plenty of soluble salts will not tolerate the water with a

concentration of salts, but light sandy soil may tolerate such water.

high concentration of a particular salt may destroy the soil structure due to

continuous exchange of ions between the irrigation water and the irrigated soil

For example, if the irrigation water contains a high concentration of sodium ions,

they may replace calcium and magnesium ions from the clayey soil.

Calcium and magnesium are beneficial for the soil because they keep it in a

coalgulated clod form.

This occurs because the silicates and aluminates of calcium and magnesium are

insoluble in water and they possess also cementing properties.

After the exchange of calcium and sodium ions by sodium ions of irrigation

water, soluble sodium silicates are formed which do not have cementing

properties.

The clods of the soil therefore crumble and fine silica grains are released which

clog the pores of the soil, resulting in the reduction of permeability and

destruction of the soil structure.

Exchangeable Sodium Ratio (ESR) The exchangeable sodium ratio (ESR) is equal to the

concentration of exchangeable sodium ions divided by the sum of the concentrations of


exchangeable ions of sodium, calcium, magnesium and potassium. Thus Classification of

Irrigation Water On the basis of suitability for irrigation, water may be classified into 3

classes as follows:

4. Class I water: This type of water is suitable for most crops under general growing

conditions. The water is rated to be excellent to good.

5. Class II water: This type of water is suitable only for sandy permeable soils and

for moderate leaching conditions. The water is rated to be good to injurious, depending

upon the type of soil.

6. Class III water: This type of water is unsuitable for most crops except a few more

tolerant crops. The water is rated to be injurious to unsatisfactory.

UNIT-V

1. Maximum probable flood and Design flood

Any flow which is relatively high and which overtops the natural or artifical

banks in any reach of a river may be called a flood. Floods are produced when the

capacity of the river channel is inadequate to carry off the abnormal quantity of water

arising from heavy rainfall causing the river to overflow its banks and inundate the

surrounding low-lying country.

Maximum probable flood

The maximum probable flood, abbreviated as MPF, has been defined as the flood that

may be expected from the most severe combination of critical meteorologic and

hydrologic conditions that are reasonably possible in the region. This is very large

flood indeed and is very rarely used in design except for reservoir spillways where

failure would lead to great damage and loss of life. The determination of the MPF

involves a detailed study of storm patterns, transposition of storms to a position that

will give maximum runoff and computation of maximum flood by the unit

hydrograph method.

Design flood

A design flood is the flood discharge adopted for the design of a structure after

careful consideration of economic and hydrologic factors. As the magnitude of the

design flood increases, the capital cost of the structure also increases but the

probability of annual damages will decrease.

The most economical design flood can be found after studying the various

alternatives. The design flood in many a case is less than the maximum probable flood

because the MPF is not economically practicable. Several design floods may be

adopted in a single structure, as for example the design flood for a spillway of a

reservoir may be much greater than the design flood adopted for temporary coffer

darns at the initial stages of the structure. Central water commission has given certain

recommendations regarding the design flood to be adopted with due consideration to

the size and importance of the project.

In general the methods used in the estimation of the design flood can be grouped as

under. Increasing the observed maximum flood by a certain percentage

Envelope curves

Empirical flood formulae

Rational Method

Unit hydrograph application

Frequency analysis (or Statistical methods).

For an economic design consistent with safety it is necessay to have the

complete design flood hydrograph rather than merely the value of flood peak.

Methods (i) to (iv) of the above list can give only the flood peak. Method (v) gives the

complete flood hydrograph but it cannot be used for very large areas. In method (vi)

the flood hydrograph may be constructed by making its peak discharge equal to the

estimated design flood, and other features to resemble the observed hydrographs in

the available record. The method to be adopted in any specific case is mostly decided

by the nature of data that is available.

2. Increasing the observed flood, Envelope Curves and Empirical

Formulae Increasing the observed Flood

When the flood data is not available, or when the available data is short, the

maximum flood that occurred during the past, and the number of years during which

this flood was the highest are found out by local enquiries or from the observation of

past records. This is then increased by a certain percentage and adopted as the design

flood. The percentage increase naturally depends on the number of years over which

the observed flood was maximum. If it is over a longer period the percentage increase

may be less and for shorter periods the increase may have to be more. This method is

adhoc in nature and has not much theoretical justification and should be resorted to

under helpless situations

Envelope Curves

When the observed peak floods in different catchments of a hydro

meteorologically homogeneous region are plotted against their respective areas on a

log-log sheet it will usually show that all the points lie below an enveloping curve

which can be drawn by eye. After the envelope curve is drawn the maximum flood for

the catchment under consideration can be read by entering the plot with the known

area of the catchment. Fig. 1.1shows the envelope curves for Indian Catchments,

presented by Kanwarsain and Karpov (1967). Baird and Mcilluraith (1951) gave the

following equation for the enveloping curve of maximum floods throughout the

world.

Q = 3010A

(277 + A) 0.78

where Q is in m3/s and A is in km2.

3. Probability Plotting Methods

In the probability plotting methods, the recurrence intervals are first computed

for various flood peaks.

A plot is then made between the flood discharge as ordinate and the recurrence

interval as abscissa.

For the computation of the recurrence intervals, the data are arranged in the

descending order of the magnitude.

The flood data are assigned the order or rank (m), depending upon the position

of a particular flood in the series.

Thus the highest observed flood is given the rank of 1, and the lowest observed

flood, the rank of n, where n is the number of years of record.

The recurrence interval (Tr) is usually computed by one of the following methods:

California formula

Hazen's formula

Gumbel's Distribution Method

Gumbel's distribution is perhaps the most widely used distribution for the estimation'

of floods of various recurrence intervals. Gumbel considered the annual flood series.

According to Gumbel, the probability of occurrence of an event X equal to or larger

than a value of Xo.

Flood routing

Flood routing may be defined as the procedure whereby the shape of a flood

hydrograph at a particular location on the stream is determined from the known or

assumed flood hydrograph at some other location upstream.

As the discharge in a stream increases stage also increases and with it the volume of

water in temporary storage in the channel. When the flood wave recedes water is

depleted from the channel storage as the stage in the stream falls. As a result, a flood

wave moving down a channel lengthens its base time and consequently its peak gets

reduced. The flood wave is then said to be attenuated. The effect of reservoir storage

or lake storage is also similar. Flood routing is the technique in hydrology to compute

the effect of storage on the shape and movement of the flood wave, Flood routing is

used in establishing the height of a flood peak ata downstream location in short term

flood forecasting, estimating the protection that would result from construction of a

reservoir, determining required levee heights for flood protection, determining the

adequacy of spillways, predicting the behavior of a river after a change in channel

conditions and in the derivation of synthetic unit graphs.

Flood routing may be divided into two basic types namely

The reservoir routing and

The channel routing or the stream flow routing.

The reservoir routing analyses the effect of reservoir storage on the flood

hydrograph, while the channel routing analyses the effect of storage of a specified

channel reach on the flood hydrograph.

Reservoir routing

Letting I and Q to denote the inflow into and outflow from a reservoir, and S the

storage in the reservoir, the continuity equation in the differential form for the

reservoir is given by

I-Q = ds

Alternatively, the same can be written as

O is the average outflow rate in the same time interval and

time interval.

If suffixes 1 and 2 are used to denote a given quantity at the beginning and the end of the time interval and if the inflow and outflow have straight line variation within the time interval, the above equation can be written as

(I1 + I2/ (O1 + O2 2 S1

Proper units must be chosen for storage to maintain compatibility in the above

equation For example, if / and Q are express

must be expressed in cumec-days.

the first term on left hand side represents the volume of water entering the storage,

(I1 + I2/

the second term represents the volume of water leaving the storage and

(O1 + O2

the term on the right hand side represents the change in storage,

S2 S1

which can be either Positive or negative depending on whether 1 is more than or less

than O. if I> O Positive storage

. if I< O Negative storage

In the above equation I1 and I2 are known from the given inflow hydrograph to be

routed through the reservoir, O1 and S1 are the initial outflow from the reservoir and

the initial storage in the reservoir which are either known or assumed and O2 and S2

are the two unknown quantities which must be determined. Thus to solve for O2 and

S2 one mor.e relation is needed.

In reservoirs the water surface is level (or horizontal) and it can be assumed that the storage in the reservoir is independent of inflow and the outflow is dependent onJy on storage. And it is this relation between storage and outflow which provides the

additional relationship required for the solution of S2 and O2.. For this reason, the

reservoir routing is also caIJed level pool routing. All the reservoir routing methods will make use of this storage discharge relation in some convenient form or other.

4. Storage Discharge Relation

Before we discuss the routing methods, we describe how the storage discharge

relation can be obtained from the topographical data of the reservoir site and the

discharge characteristics of the reservoir outlets such as spillways and sluices.

Establishing Storage-Discharge Relationship

The area at the reservoir site is surveyed in detail and a contour map is

prepared with a contour interval of 2 to 3 m depending on the size of the

reservoir.

From this map the areas enclosed by various contours are .planimetered and a

curve of elevation versus area is prepared.

Such a curve is very useful in estimating the evaporation losses from the

reservoir since the area enclosed by any contour will also represent the water

spread area

if the water is stored in the reservoir up to that contour' elevation, though it is

not directly useful in the routing procedure.

Once the areas enclosed by contours are known the incremental volumes of

water stored between any two successive contours can be determined using

one of the following equations.

16). UNIT WISE-QUESTION BANK

UNIT-I

TWO MARKS QUESTION WITH ANSWERS

1. Draw the hydrological cycle.

2. Name the types of rain gauges?

Types of Rain Gauges

There are two types of rain gauges:

1) Non-recording type

2) Recording type

a) Weighing bucket type

b) Tipping bucket type

c) Floating or natural syphon type rain gauge

3. What do mean by term HYDROLOGY?

The sequence of conditions through which water passes from vapor in the atmosphere

through precipitation upon land or water surfaces and ultimately back into the atmosphere as

a result of evaporation and transpiration called also hydrological cycle

4. Define readily available soil moisture

Readily available water (RAW) is the water that a plant can easily extract from the soil.

RAW is the soil moisture held between field capacity and a nominated refill point for

unrestricted growth

5. Define permanent wilting point.

Permanent wilting point (PWP) or wilting point (WP) is defined as the minimal point of soil

moisture the plant requires not to wilt. If moisture decreases to this or any lower point a plant

wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12

hours.

THREE MARKS QUESTIONS WITH ANSWERS

1. Define rainfall double mass curve.

Double-Mass Curves. ...

The double-mass curve can be used to adjust inconsistent precipitation data. The graph of the

cumulative data of one variable versus the cumulative data of a related variable is a straight

line so long as the relation between the variables is a fixed ratio.

2. How can you measure the infiltration?

The infiltration rate is the velocity or speed at which water enters into the soil. It is

usually measured by the depth (in mm) of the water layer that can enter the soil in one hour.

An infiltration rate of 15 mm/hour means that a water layer of 15 mm on the soil surface will

take one hour to infiltrate.

3. What is transpiration?

Transpiration is the process where plants absorb water through the roots and then give off

water vapour through pores in their leaves. An example of transpiration is when a plant

absorbs water in its roots.

4. How will you measure flow in stream and rainfall?

Stream flow, or channel runoff, is the flow of water in streams, rivers, and other channels,

and is a major element of the water cycle. ... The discharge of water flowing in a channel

is measured using stream gauges or can be estimated by the Manning equation. The record

of flow over time is called a hydrograph.

5. What are infiltration indices?

Infiltration Index is a method used for Measurement of Infiltration. It represents average rate

of infiltration. There are two types of infiltration index: - - Index It represents

average infiltration rate during the period of rainfall excess.

FIVE MARKS QUESTIONS WITH ANSWERS

1. Explain the balanced equation for precipitation.

The precipitation reaction is defined as the Chemical reaction occurring in aqueous

solutions where two ionic bonds combine forming up insoluble salts. The salts formed are

precipitates and are the products of precipitation reaction.

The precipitation reaction is the double displacement reactions involving the production of a

solid form residue called the precipitate. The reaction also occurs when two or more solutions

with different salts are combined, resulting in the formation of insoluble salts that precipitates

out of the solution.

One of the best examples of precipitation reactions is the chemical reaction between

potassium chloride and silver nitrate, and solid silver chloride is the precipitate or the

insoluble salt formed as a product of the reaction. The chemical equation for this

precipitation reaction is as below-

AgNO3(aqueous) + KCl(aqueous) AgCl(precipitate) + KNO3(aqueous)

In the above reaction, a white precipitate called as silver chloride or AgCl is formed which

is in a solid state. This solid silver chloride is insoluble in water. Precipitation reactions

help in determining the presence of different ions present in a particular solution.

The other example of a precipitation reaction is the reaction between calcium chloride and

potassium hydroxide, resulting in the formation of an insoluble salt Called calcium

hydroxide. The chemical equation for this reaction is below-

2KOH(aqueous) + CaCl2(aqueous) -Ca(OH)2(aqueous) + 2KCl(aqueous)

Some more examples of chemical equations of on precipitation reaction are as below-

AgNO3(aqueous) + NaCl(aqueous) - (aqueous)

Mg(OH)2(s) + 2HCl (aqueous) MgCl2(aqueous) + 2H2O(l)

2. Discuss the factors affecting evaporation.

The turning of any liquid into vapour is called Evaporation. The factors affecting the

evaporation are:

Temperature. As the temperature increases, the rate of evaporation also increases.

Surface Area. As the Surface area increases, the rate of evaporation increases.

Density. As the density increases, the rate of evaporation decreases.

Wind Velocity. The velocity of the wind also affects the rate of evaporation. As the

velocity of wind increases, the rate of evaporation increases.

3. Explain the following in brief.

(a) Probable maximum precipitation

(b) Rain gauge density

(a) Probable maximum precipitation:-

Probable Maximum Precipitation (PMP) is defined by the Manual for Estimation of Probable

Maximum Precipitation (WMO,2009) as: "...the theoretical maximum precipitation for a

given duration under modern meteorological conditions."

(b) Rain gauge density:-

Rainfall is an extremely variable parameter in both space and time. Rain gauge density is

very crucial in order to quantify the rainfall amount over a region. The level

of rainfall accuracy is highly dependent on density and distribution of rain gauge stations

over a region

4. Describe the terms

i) Interception and

ii) Depression storage.

i) Interception:-

Interception refers to precipitation that does not reach the soil, but is instead intercepted by

the leaves, branches of plants and the forest floor. It occurs in the canopy (i.e. canopy

interception), and in the forest floor or litter layer (i.e. forest floor interception . Because

of evaporation, interception of liquid water generally leads to loss of that precipitation for

the drainage basin, except for cases such as fog interception, but increase flood protection

dramatically, Alila et al., (2009).

5. Definition of canopy and forest floor interception

Intercepted snowfall does not result in any notable amount of evaporation, and most of the

snow falls off the tree by wind or melts. However, intercepted snow can more easily drift

with the wind, out of the watershed. Conifers have a greater interception capacity

than hardwoods. Their needles gives them more surface area for droplets to adhere to, and

they have foliage in spring and fall, therefore interception also depends on the type of

vegetation in a wooded area.

Mitscherlich in 1971 calculated the water storage potential as interception values for different

species and stand densities. A storm event might produce 50 - 100 mm of rainfall and 4 mm

might be the maximum intercepted in this way. Grah and Wilson in 1944 did sprinkling

experiments where they watered plants to see how much of the intercepted is kept after

watering stops.

ii) Depression storage:-

Depression storage capacity, in soil science, is the ability of a particular area of land to

retain water in its pits and depressions, thus preventing it from flowing. Depression

storage capacity, along with infiltration capacity, is one of the main factors involved

in Horton overland flow, whereby water volume surpasses both infiltration and depression

storage capacity and begins to flow horizontally across land, possibly leading

to flooding and soil erosion. The study of land's depression storage capacity is important in

the fields of geology, ecology, and especially hydrology.

5. Write short notes on:

(i) Double-mass curve

(ii) Cold and warm fronts

(iii) Cyclones and anticyclones.

(i) Double-mass curve:-

Double mass analysis is a commonly used data analysis approach for investigating the

behaviour of records made of hydrological or meteorological data at a number of locations. It

is used to determine whether there is a need for corrections to the data - to account for

changes in data collection procedures or other local conditions. Such changes may result from

a variety of things including changes in instrumentation, changes in observation procedures,

or changes in gauge location or surrounding conditions. Double mass analysis for checking

consistency of a hydrological or meteorological record is considered to be an essential tool

before taking it for analysis purpose. This method is based on the hypothesis that each item of

the recorded data of a population is consistent.

An example of a double mass analysis is a "double mass plot", or "double mass curve".[2] For

this, points and/or a joining line are plotted where the x- and y- coordinates are determined by

the running totals of the values observed at two stations. If both stations are affected to the

same extent by the same trends then a double mass curve should follow a straight line. A

break in the slope of the curve would indicate that conditions have changed at one location

but not at another. This technique is based on the principle that when each recorded data

comes from the same parent population, they are consistent.

(ii) Cold and warm fronts:-

A cold weather front is defined as the changeover region where a cold air mass is replacing a

warmer air mass. Cold weather fronts usually move from northwest to southeast. The air

behind a cold front is colder and drier than the air in front. When a cold front passes through,

temperatures can drop more than 15 degrees within an hour.

On a weather forecast map, a cold front is represented by a solid line with blue triangles along

the front pointing towards the warmer air and in the direction of movement.

There is usually an obvious temperature change from one side of a cold front to the other. It

has been known that temperatures east of a cold front could be approximately 55 degrees

Fahrenheit while a short distance behind the cold front, the temperature can go down to 38

degrees. An abrupt temperature change over a short distance is a good indicator that a front is

located somewhere in between.

A warm weather front is defined as the changeover region where a warm air mass is replacing

a cold air mass. Warm fronts usually move from southwest to northeast and the air behind a

warm front is warmer and moister than the air ahead of it. When a warm front passes, the air

becomes noticeably warmer and more humid than it was before.

On a weather forecast map, a warm front is represented by a solid line with red semicircles

pointing towards the colder air and in the direction of movement.

Again, there is typically a noticeable temperature change from one side of the warm front to

the other, much the same as a cold front.

If colder air is replacing warmer air, it is a cold front, if warmer air is replacing cold air, then

it is a warm front.

(iii) Cyclones and anticyclones:-

A cyclone is a storm or system of winds that rotates around a center of low atmospheric

pressure. An anticyclone is a system of winds that rotates around a center of high atmospheric

pressure. Distinctive weather patterns tend to be associated with both cyclones and

anticyclones. Cyclones (commonly known as lows) generally are indicators of rain, clouds,

and other forms of bad weather. Anticyclones (commonly known as highs) are predictors of

fair weather.

Winds in a cyclone blow counterclockwise in the Northern Hemisphere and clockwise in the

Southern Hemisphere. Winds in an anticyclone blow just the opposite. Vertical air

movements are associated with both cyclones and anticyclones. In cyclones, air close to the

ground is forced inward toward the center of the cyclone, where pressure is lowest. It then

begins to rise upward, expanding and cooling in the process. This cooling increases the

humidity of the rising air, which results in cloudiness and high humidity in the cyclone.

In anticyclones, the situation is reversed. Air at the center of an anticyclone is forced away

from the high pressure that occurs there. That air is replaced in the center by a downward

draft of air from higher altitudes. As this air moves downward, it is compressed and warmed.

OBJECTIVE QUESTIONS WITH ANSWERS

1) which of the followings methods of applying water may be used rolling land?

a) boarder flooding

b) check flooding

c) furrow flooding

d) free flooding

2) The value of sodium absorption ratio for high sodium water lies between

a) 0 to 10

b) 10 to 18

c) 18 to 26

d) 26 to 34

3) Irrigation water having concentration of Na++, Ca++, and Mg++ as 20, 3 and 1 milli

equivalent per litere respectively

a) sodium water

b) medium sodium water

c) high sodim water

d) very high sodium water

4) The duty is largest

a) At the head if water course

b) On the field

c) At the head of main canal

d) Same at all places

5) The outlet discharge factor is the duty at the head of

a) Main canal

b) Branch canal

c) Water house

d) distributory

6) The water utilized by plant is available in soil mainly in the form of

a) Gravity water

b) Capillary water

c) Hydroscopic water

d) Chemical water

7) Hydrograph is the graphical representation of

a) Runoff & time

b) Surface runoff & time

c) Ground water flow & time

d) Rainfall & time

8) Infiltration rate is always

a) more than the infiltration capacity

b) less than the infiltration capacity

c) Equal to or less than the infiltration capacity

d) Equal to or more than the infiltration capacity

9) Infiltration is the

a) Movement of water through

b) Absorption of water by soil surface

c) Both (a) and (b)

d) None of the above

10) Which of the following is non-recording rain gauge?

a) Tipping bucket type rain gauge

b) rain gauge

c) weighing type rain gauge

d) Floating type rain gauge

KEY ANSWERS

Question no Answers 1 Boarder flooding 2 18 to 26 3 Medium sodium water 4 On the field 5 distributary 6 Capillary water 7 Runoff & time 8 Equal to or less than the

infiltration capacity 9 Movement of water through 10

FILL IN THE BLANKS WITH ANSWERS

1

2 the head of.

3.

4.

5 is the movement of water through the soil.

KEY ANSWERS

Question no Answers 1 Boarder Flooding

2 Watercourse

3 Capillary water

4 Runoff and time

5 Infiltration

UNIT - II

TWO MARKS QUESTIONS WITH ANSWERS

1) Explain Hydrograph analysis?

A hydrograph is a continuous plot of instantaneous discharge v/s time. It results from a

combination of physiographic and meteorological conditions in a watershed and represents

the integrated effects of climate, hydrologic losses, surface runoff, interflow, and ground

water flow.

2. What do you mean by Base flow?

Base flow (also called drought flow, groundwater recession flow, low flow, low-water flow,

low-water discharge and sustained or fair-weather runoff) is the portion of stream flow that

comes from "the sum of deep subsurface flow and delayed shallow subsurface flow"

3. Define unit hydrograph

It can be defined as the direct runoff hydrograph(DRH) resulting from one unit (e.g., one cm or

one inch) of effective rainfall occurring uniformly over that watershed at a uniform rate over

a unit period of time

4. Define design flood?

Definition of Design Flood: Design flood is the value of the instantaneous peak discharge

adopted for the design of a particular project or any of its structures.

5. Define annual series?

The equivalent annual cost (EAC) is the annual cost of owning, operating and maintaining an

asset over its entire life. EAC is often used by firms for


1) Define partial series?

Let us define things a little better now: A Sequence is a set of things (usually numbers) that

are in order. A Partial Sum is the sum of part of the sequence. The sum of infinite terms is an

Infinite Series. And Partial Sums are sometimes called "Finite Series.

2) Write the formulae used to calculate unit hydrograph.

The instantaneous unit hydrograph is defined as a unit hydrograph produced by an effective

rainfall of 1 mm and having an infinitesimal reference duration (in other words the duration

tends towards zero).

3) What is recession time?

A recession is a decline of economic activity, more specifically, a decline in gross domestic

product (GDP) for two or more consecutive quarters. GDP is the market value of all goods

and services produced within a country in a given period of time.

4) What is flood frequency?

Flood frequency analysis is a technique used by hydrologists to predict flow values

corresponding to specific return periods or probabilities along a river. The application of

statisticalfrequency curves to floods was first introduced by Gumbel

5) Write dickens formula for flood discharge

DICKENS FORMULA (1865) Qp = CD A 3/4

whereQp = maximum flood discharge (m3 /s) A = catchment area (km2)

CD = Dickens constant with value between 6 to 30 .The following are some guidelines in

selecting the value of CD:

RYVESFORMULA (J884)

Qp = CR 2/3

where Q = maximum flood discharge (m3 /s) A = catchment area (km2) and CR = Ryves

coefficient This formula originally developed for the Tamil Nadu region, is in use in Tamil

Nadu and parts of Karnataka and Andhra Pradesh. The values of CRrecommended by Ryves

for use are:

CR = 6.8 for areas within 80 km from the east coast

=8.5 for areas which are 80 -160 km from the east coast.


1) Explain the terms:

(i). Recurrence interval

(ii). Probable maximum precipitation

(i). Recurrence interval:-

A return period, also known as a recurrence interval (sometimes repeat interval) is an

estimate of the likelihood of an event, such as an earthquake, flood, landslide, or a river

discharge flow to occur.

It is a statistical measurement typically based on historic data denoting the average recurrence

interval over an extended period of time, and is usually used for risk analysis (e.g. to decide

whether a project should be allowed to go forward in a zone of a certain risk, or to design

structures to withstand an event with a certain return period). The following analysis assumes

that the probability of the event occurring does not vary over time and is independent of past

events.

1. What are the limitations of unit hydrograph?

Limitations of the Unit Hydrograph

intensity during the duration of rainfall excess. In practice, these two conditions are never

satisfied.

-uniform areal distribution and variation of in intensity, the unit

hydrograph theory can still be used if the areal distribution is consistent between different

storms.

theory (because the centre of the storm can vary from storm to storm and each of these storms

can give a different DRH under otherwise identical conditions in very large basins).

2

basins, the flood hydrographs can be studied by dividing it into a

number of smaller sub-basins, developing DRHs for these sub-basins by the UH method, and

then routing these DRHs through their respective channels to obtain the composite DRH at

the catchment outlet.

2.

Barlow, the first Chief Engineer of the Hydro-Electric Survey of India (1915) on the basis of

his study in small catchments (area ~ 130 km2) in Uttar Pradesh expressed runoff R a shown

in (19.1)

Where Kb is the runoff coefficient which depends upon the type of catchment and nature of

monsoon and P is the rainfall.

Table 19.1. b in percentage

(Developed for use in UP) (Source: Subramanya, 2008)

Class Description of catchment

Kb (percentage)

Season I Season II Season III

A Flat, cultivated, and absorbent soil 7 10 15

B Flat, partly cultivated, and stiff soil 12 15 18

C Average catchment 16 20 32

D Hills and plains with little cultivation 28 35 60

E Very hilly, steep and no cultivation 36 45 81

Season I: Light rain, no heavy downpour

Season II: Average or varying rainfall, no continuous downpour

Season III: Continuous downpours

Strange (1892) studied the available rainfall and runoff in the border areas of present-day

Maharashtra and Karnataka and has obtained yield ratios as functions of indicators

representing catchment characteristics. Catchments lie classified as good, average and bad

according to the relative magnitudes of yield they give. Two methods using tables for

estimating the runoff volume in a season are given.

(I) Runoff Volume from Total Monsoon Season Rainfall

A table giving the runoff volumes for the monsoon period (i.e. yield during monsoon season)

for different total monsoon rainfall values and for the three classes of catchments (viz. good,

average and bad) is given in Table 19.2a. The correlation equations of best fitt.ing lines

relating percentage yield ratio (Y)to precipitation (P)could be expressed as

Table 19.2a.Strange's Table of Total Monsoon Rainfall and estimated Runoff(Source:

Subramanya, 2008)

Since there is no appreciable runoff due to the rains in the dry (non-monsoon) period, the

monsoon season runoff volume is recommended to be taken as annual yield of the catchment.

This table could be used to estimate the monthly yields also in the monsoon season.

However, it is to be used with the understanding that the table indicates relationship between

cumulative monthly rainfall starting at the beginning of the season and cumulative runoff, i.e.

a double mass curve relationship.

3. Explain in detail about synthetic unit hydrograph?

Snyder's synthetic unit hydrograph

A synthetic unit hydrograph retains all the features of the unit hydrograph, but does not

require rainfall-runoff data. A synthetic unit hydrograph is derived from theory and

experience, and its purpose is to simulate basin diffusion by estimating the basin lag based on

a certain formula or procedure.

The first synthetic unit hydrograph was developed by Snyder in 1938.1 In order to provide

sufficient flexibility for simulating a wide range of diffusion amounts, Snyder devised two

parameters: (1) a time parameter Ct, and (2) a peak parameter Cp. A larger Ct meant a greater

basin lag and, consequently, greater diffusion. A larger Cp meant a greater peak flow and,

consequently, less diffusion.

4. What are the applications of unit hydrograph?

The Unit Hydrograph (UH) technique is widely used for runoff estimation, especially for

determining peak discharges. In this paper, a geomorphological based UH has been applied.

Its most remarkable characteristic is that it includes the watershed structure in its formulation.

This is defined from the drainage network, each sub watershed being considered as a linear

reservoir. In this method, the fact of considering this reservoir sequence according to the

drainage network leads to the formulation of the model only depending on a single parameter.

The Geomorphological Unit Hydrograph of Reservoirs (GUHR), proposed in this paper, is

compared with Nash's Instantaneous Unit Hydrograph (Nash's IUH), by applying the two

methods to the Aixola watershed. This 4.7-km2 watershed is located in Gipuzkoa (Northern

Spain). It is characteristic of the headwaters watersheds of the area. Most of them are forested

and have steep slopes. Annual rainfall is over 1500 mm and many intense rainfall events are

observed, among which 18 were selected for this study. Both UH techniques were applied to

the rainstorms. The resulting hydrographs were plotted against registered data and the best

fits were determined. According to these results, the GUHR model behaved similarly to

Nash's IUH. However, the GUHR method seemed able to reproduce a wider range of

rainstorms than Nash's IUH. While analyzing the UHs calculated, seasonal behavior was

observed in runoff generation, and different average UHs were proposed for two different

periods. This variability was also observed in values adopted by the GUHR model parameter,

providing some information about the watershed time response. The dynamic character of the

only uncertain parameter, and the model formulation, in which the watershed morphology is

reflected, together with the model's simplicity, leads us to consider GUHR as being a

promising UH model.


1. Water contains

a) One hydrogen atom and one oxygen atom

b) Two hydrogen atoms and one oxygen atom

c) One hydrogen atom and two oxygen atoms

d) Three hydrogen atoms and two oxygen atoms

2. Unit Hydrograph theory was enunciated by

a) Merril Bernard,

b) W.W. Horner,

c) Le-Roy K. Shermen,

d) Robert E. Horte

3. Hydrology helps in

a) Predicting maximum flows,

b) Deciding the minimum reservoir capacity,

c) Forecasting the availability of quantity of water at reservoir site,

d) All the above.

4. The surface Run-off is the quantity of water,

a) Absorbed by soil,

b) Intercepted by buildings and vegetative cover,

c) Required to fill surface depressions,

d) That reaches the stream channels.

5. Pick up the correct equation from the following :

a) Run off = Surface run off + Ground water flow,

b) Run off = Surface run off - Ground water flow,

c) Run off = Surface run off / Ground water flow,

d) Run off = Surface run off x Ground water flow.

KEY ANSWERS Question no Answers

1 Two hydrogen atoms and one oxygen atom

2 Le-Roy K. Shermen,

3 All the above.

4 That reaches the stream channels.

5 Run off = Surface run off + Ground water flow


1.

2.

3.

4.

5. is used for measuring rain in remote hilly inaccessible.

KEY ANSWERS

Question no Answers

1 In an open space

2 Rain deficiency of 30%

3 Cubic meter/sec

4 Increase in intensity of rain

5 Tipping bucket type

UNIT-III

TWO MARKS QUESTIONS WITH ANSWERS

1. Define Aquifer?

A body of permeable rock which can contain or transmit groundwater

.

2. What are different types of aquifer?

Aquifers come in two types which are shown below: unconfined and confined. Unconfined

aquifers are those into which water seeps from the ground surface directly above the aquifer

3. Define Specific yield?

Specific yield is defined as the volume of water released from storage by an unconfined

aquifer per unit surface area of aquifer per unit decline of the water table.

4. Define specific retention?

Definition of specific retention.The ratio of the volume of water that a given body of rock or

soil will hold against the pull of gravity to the volume of the body itself. It is usually expressed

as a percentage.

5. Define permeability?

The ability of a substance to allow another substance to pass through it, especially the ability

of a porous rock, sediment, or soil to transmit fluid through pores and crack.


1. Define porosity?

Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the

volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and

100%

2. Define transmissibility?

Transmissibility is the ratio of output to input. Transmissibility (T) = output/input. T>1

means amplification and maximum amplification occurs when forcing frequency (ff) and

natural frequency (fn) of the system coincide

3. Define storage coefficient?

Storability or the storage coefficient is the volume of water released from storage per unit

decline in hydraulic head in the aquifer, per unit area of the aquifer. Storability is a

dimensionless quantity, and ranges between 0 and the effective porosity of the aquifer.

4. What are the types of wells?

There are three types of private drinking water wells.

Dug/Bored wells are holes in the ground dug by shovel or backhoe. ...

Driven wells are constructed by driving pipe into the ground. ...

Drilled wells are constructed by percussion or rotary-drilling machines.

5. Define well development?

Well development of drilled wells is a part of normal well drilling procedure after the

completion of the well and before the final disinfection. ... It refers to the cleaning of oil wells

to improve performance and requires utterly differing methods than the rehabilitation of

water wells.


1. Write short notes on:

(a) Specific capacity of a well

(b) Specific yield of an aquifer

(c) Aquifer and aquiclude .

(d) Specific capacity of a well

200 gpm.The maximum pumping rate of a well can be estimated using the initial Specific

Capacity. The maximum pumping rate is calculated as the Specific Capacity times the

maximum available drawdown. For example, with a well that has 40 feet of drawdown and is

pumping 200 gpm has a Specific Capacity of 4.9.

(e) Specific yield of an aquifer-

Specific yield is defined as the volume of water released from storage by an

unconfined aquifer per unit surface area of aquifer per unit decline of the water table. ...

Thus,specific yield, which is sometimes called effective porosity, is less than the total

porosity of an unconfined aquifer (Bear 1979).

(f) Aquifer and aquiclude

Porous water-bearing formation capable of yielding exploitable quantities of water. (WMO,

2006)A formation, group of formations, or part of a formation that contains sufficient

saturated permeable material to yield significant quantities of water to wells and springs

(LOHMANN, 1972)

Aquitard

A confining bed that retards but does not prevent the flow of water to or from an adjacent

aquifer; a leaky confining bed.It does not readily yield water to wells or springs, but may

serve as a storage unit for ground water.

Aquiclude

A hydrogeologic unit which, although porous and capable of storing water, does not transmit

it at rates sufficient to furnish an appreciable supply for a well or spring (WMO, 1974)

2) Distinguish between Groundwater and Perched groundwater.

Water table:

Water table is a free water surface in an unconfined aquifer.

A well driven into an unconfined aquifer will indicate a static water level. This water level is

corresponding to the water table level at that location. It is constantly in motion adjusting its

surface to achieve a balance between the recharge and outflow.

Fluctuations in water table level

Fluctuations in water level occur due to:

Lowering of ground water due to heavy pumping of the wells.

Rise in the water of an irrigated area with poor drainage.

During various seasons of the year.

3. Distinguish between Open wells and tube wells.

Water wells can be classified either open wells or tube wells. Open wells have relatively large

diameter (generally 1 to 5 m) and low yields (generally less than 30 m3/hr), and are not very

deep (generally 3 to 15 m). Since these wells are constructed by digging, they are also known

as dug wells. The walls of an open well may be of either brick (or stone) masonry or precast

concrete rings.

Open wells can be either shallow open wells or deep open wells. A shallow open well drains

its supplies only from the top upper aquifer. But deep open wells are those which rest on an

impervious stratum and draw their supplies from the previous water-bearing stratum lying

below the impervious stratum through a bore hole made in the impervious stratum. As shown

in Fig. 4.4, a deep open well can have its depth smaller than a shallow open well in the

vicinity. A tube well is in the form of a long pipe with holes (or slots) at suitable locations

and which is sunk into the ground intercepting one or more aquifers. The diameter of a tube

well is usually in the range of about 8 to 60 cm. The depth of a shallow tube well is usually

limited to about 30 m. A deep tube well can have depths up to about 600 m.

4. Distinguish between Water table and artesian aquifers.

The Water Table

The water table is the upper most section of the saturation zone in the ground. The saturation

zone is the area of ground in which water has penetrated and fills all the gaps in the ground,

completely saturating it. As time progresses, the saturation zone may raise or lower

depending on levels of precipitation. As the saturation zone changes, so does the water table

level. For example, if the weather is dry, the water table may become deeper as less water is

available. An aquifer is the water beneath the water table.

Aquifer

An aquifer is a body of saturated rock through which water can easily move, according to the

Idaho Museum of Natural History. Water moves through the pores of the rock. The pores act

as a natural filtration system, removing even viruses and bacteria from the water. Aquifers

can be considered unconfined or confined. An unconfined aquifer's bottom is a layer of

nonporous rock, which restricts water flow, creating a barrier to the aquifer. The water table

is the top layer of the unconfined aquifer. A confined aquifer sits below a unconfined aquifer

and layer of nonporous roc

5) Distinguish between Confined aquifer and water table aquifer

A confined aquifer is an aquifer below the land surface that is saturated with water. Layers of

impermeable material are both above and below the aquifer, causing it to be under pressure

so that when the aquifer is penetrated by a well, the water will rise above the top of the

aquifer.

A water-table, or unconfined, aquifer is an aquifer whose upper water surface (water table) is

at atmospheric pressure, and thus is able to rise and fall. Water-table aquifers are usually

closer to the Earth's surface than confined aquifers are, and as such are impacted by drought

conditions sooner than confined aquifers.


1. Infiltration capacity of soil depends upon,

a. Number of voids present in the soil,

b. Shape and size of soil particles,

c. Arrangement of soil particles,

d. All the above.

2. The main factor which affects the infiltration capacity is

a. Thickness of saturated layer,

b. Depth of surface detention,

c. Soil moisture,

d. All the above.

3. According to Robert E. Horton, the equation of infiltration capacity curve is

(where letters carry their usual meanings),

a. F = fc (fo - fc) ekt,

b. F = ft - (fo - fc) e-kt,

c. F = ft + (fo - fc) e-kt,

d. F = f + (fo - fc) ekt.

4. Absolute humidity in air,

a. Decreases at higher altitudes,

b. Increases at higher altitudes,

c. Remains constant at all altitudes,

d. None of these.

5. Precipitation caused by lifting of an air mass due to the pressure difference, is

called,

a. Cyclonic precipitation,

b. Convective precipitation,

c. Orographic precipitation,

d. None of these.

e.


1 All the above.

2 All the above

3 F = ft + (fo - fc) e-kt,

4 Decreases at higher altitudes,

5 Cyclonic precipitation,


1.

2. The

3. A

4.

5. -recoding rain gauge.


1 Velocity of flow of water

2 One fourth of basin lag

3 Deep well

4 Infiltration

5

UNIT-IV TWO MARKS QUESTIONS WITH ANSWERS

1. Define irrigation.

Irrigation is the application of controlled amounts of water to plants at needed intervals.

Irrigation helps grow agricultural crops, maintain landscapes, and revegetate disturbed soils

in dry areas and during periods of less than average rainfall.

2. What are different types of soils

There are six main soil types:

Clay.

Sandy.

Silty.

Peaty.

Chalky.

Loamy.

3. Define water logging

In agriculture, various crops need air (specifically, oxygen) to a greater or lesser depth in the

soil. ... In irrigated agricultural land, waterlogging is often accompanied by soil salinity

as waterlogged soils prevent leaching of the salts imported by the irrigation water.

4. Define field capacity. Field Capacity is the amount of soil moisture or water content held

in the soil after excess water has drained away and the rate of downward movement has

decreased. This usually takes place 2 3 days after rain or irrigation in pervious soils of

uniform structure and texture.

5. Define soil fertility

Soil fertility refers to the ability of a soil to sustain agricultural plant growth, i.e. to

provide plant habitat and result in sustained and consistent yields of high quality. A fertile

soil has the following properties: ... The absence of toxic substances which may inhibit plant

growth.


1. What you mean by irrigation efficiency?

Definition of irrigation efficiency. : The ratio between irrigation water actually utilized by

growing crops and water diverted from a source (as a stream) in order to supply

such irrigation water

2. What course ?

A watercourse is the channel that a flowing body of water follows. ... In some jurisdictions,

owners of land over which the water flows may have rights to some or much of the water in

a legal sense. These include estuaries, rivers, streams, anabranches and canal

3. What do mean by artificial irrigation, give example

Irrigation can be defined as the science of artificial application of water to the land in order

to fulfill the water requirements of the crops throughout the crop period for the full

nourishment of the crops. ... Irrigation Supplying of water artificially to the crop for their

proper growth at required time.

4. What is consumptive use?

Consumptive water use is water removed from available supplies without return to a water

resource system (e.g., water used in manufacturing, agriculture, and food preparation that is

not returned to a stream, river, or water treatment plant).

5. When do you consider the land for crop rotation?

The non-natural or man-made provision of water to plants or crops that fulfill profit or food

requirements of people near or far away from the area to help them grow properly without

diminishing the their growth or productivity can be defined as irrigation.


1. Discuss various methods of irrigation and state the advantages of each method.

Traditional method of irrigation

The various traditional method of irrigation are

1)Moat(pulley system)

2)Chain pump

3)Dhekli

4)Rahat(lever system)

Traditional method of irrigation are cheaper but less efficient.Pumps are commonly used for

lifting water.These pumps run by electricity,diesel,biogas or solar energy.

When a pump is used to draw out water from a narrow well,it is called tube-well.They are

used increasingly for lifting underground water to be used for irrigation in agriculture.

Modern methods of irrigation

The two main modern methods of irrigation are:

1) Sprinkler system: A main pipeline is laid in the field. Perpendicular pipes having rotating

nozzles at the top are joined to the main pipelines at regular intervals. When water from a

tube-well is allowed to flow through the main pipelines under pressure with the help of a

pump, it escapes from the rotating nozzles. This water gets sprinkled on the crop plants as if

it is raining.

Advantages

1) It is more useful for the uneven land where sufficient water is not available.

2) It is very useful for sandy soil.

2. Describe the step by step procedure for preparation of land for irrigation

When establishing a new date plantation, certain actions need to be implemented to ensure

the long term success of the plantation. One of these actions involves the initial land

preparation which should be done prior to transplanting of the plant material (offshoots or

tissue culture-derived plants).

The purpose of land preparation is to provide the necessary soil conditions which will

enhance the successful establishment of the young offshoots or the tissue culture plants

received from the nursery. Considering the nature of the date palm, one cannot "save" on this

operation and hope for long term sustainability of the plantation.

The aim is to enable the date grower to plan and structure the implementation process in

advance, ensuring the successful establishment of the date plantation. Planning forms part of

the initial preparation and will help to limiting unnecessary stoppages during the

implementation phase.

Critical factors to consider during this planning exercise are summarised as follows:

- Availability and quality of irrigation water;

- Field selection;

- Mechanical actions to be implemented;

- Chemical needs for pre-plant soil improvement;

- Tools and equipment needed for date cultivation;

- Labour needs;

- Irrigation design and installation;

- Leaching schedule;

- Hole preparation;

- Financial requirements and

- Time schedule.

3. Discuss in brief various methods of surface irrigation?

Basin irrigation

Level basin flood irrigation on wheat

Residential flood irrigation in the Southwest, United States of America.

Level basin irrigation has historically been used in small areas having level surfaces that are

surrounded by earth banks. The water is applied rapidly to the entire basin and is allowed to

infiltrate. In traditional basins no water is permitted to drain from the field once it is irrigated.

Basin irrigation is favoured in soils with relatively low infiltration rates(Walker and

Skogerboe 1987). This is also a method of surface irrigation. Fields are typically set up to

follow the natural contours of the land but the introduction of laser levelling and land grading

has permitted the construction of large rectangular basins that are more appropriate for

mechanisedbroadacre cropping.

Drainback Level Basins

Drain back level basins (DBLB) or contour basins are a variant of basin irrigation where the

field is divided into a number of terraced rectangular bays which are graded level or have no

significant slope. Water is applied to the first bay (usually the highest in elevation) and when

the desired depth is applied water is permitted to drain back off that bay and flow to the next

bay which is at a lower elevation than the first. Each bay is irrigated in turn using a

combination of drainage water from the previous bay and continuing inflow from the supply

channel. Successful operation of these systems is reliant on a sufficient elevation drop

between successive bays. These systems are commonly used in Australia

where rice and wheat are grown in rotation.

Furrow irrigation

Furrow irrigation is conducted by creating small parallel channels along the field length in the

direction of predominant slope. Water is applied to the top end of each furrow and flows

down the field under the influence of gravity. Water may be supplied using gated pipe,

siphon and head ditch, or bankless systems. The speed of water movement is determined by

many factors such as slope, surface roughness and furrow shape but most importantly by the

inflow rate and soil infiltration rate. The spacing between adjacent furrows is governed by the

crop species, common spacings typically range from 0.75 to 2 metres. The crop is planted on

the ridge between furrows which may contain a single row of plants or several rows in the

case of a bed type system. Furrows may range anywhere from less than 100 m to 2000 m

long depending on the soil type, location and crop type. Shorter furrows are commonly

associated with higher uniformity of application but result in increasing potential for runoff

losses. Furrow irrigation is particularly suited to broad-acre row crops such

as cotton, maize and sugar cane. It is also practiced in various horticultural industries such

as citrus, stone fruit and tomatoes.

The water can take a considerable period of time to reach the other end, meaning water has

been infiltrating for a longer period of time at the top end of the field. This results in poor

uniformity with high application at the top end with lower application at the bottom end. In

most cases the performance of furrow irrigation can be improved through increasing the

speed at which water moves along the field (the advance rate). This can be achieved through

increasing flow rates or through the practice of surge irrigation. Increasing the advance rate

not only improves the uniformity but also reduces the total volume of water required to

complete the irrigation.

Surge irrigation

Surge Irrigation is a variant of furrow irrigation where the water supply is pulsed on and off

in planned time periods (e.g. on for 1 hour off for 1½ hour). The wetting and drying cycles

reduce infiltration rates resulting in faster advance rates and higher uniformities than

continuous flow. The reduction in infiltration is a result of surface consolidation, filling of

cracks and micro pores and the disintegration of soil particles during rapid wetting and

consequent surface sealing during each drying phase. On those soils where surging is

effective it has been reported to allow completion of the irrigation with a lower overall water

usage and therefore higher efficiency and potentially offer the ability to practice deficit

irrigation. The effectiveness of surge irrigation is soil type dependent; for example, many

clay soils experience a rapid sealing behaviour under continuous flow and therefore surge

irrigation offers little benefit.

Bay/border strip irrigation

Border strip, otherwise known as border check or bay irrigation could be considered as a

hybrid of level basin and furrow irrigation. The field is divided into a number of bays or

strips, each bay is separated by raised earth check banks (borders). The bays are typically

longer and narrower compared to basin irrigation and are orientated to align lengthwise with

the slope of the field. Typical bay dimensions are between 10-70m wide and 100-700m long.

The water is applied to the top end of the bay, which is usually constructed to facilitate free-

flowing conditions at the downstream end. One common use of this technique includes the

irrigation of pasture for dairy production.

4) Explain in detail about the ill effects of irrigation?

Ill-effects of Irrigation

The uses of irrigated agriculture have the following ill effects if not properly managed:

Dampness of weather

Loss of soil fertility

Soil erosion

Production of harmful gases

Loss of valuable lands

5. Define the terms Duty, Delta and base period and also derive the relation between

them

Duty and Delta are very basic definitions used in the calculation of irrigation water demand

of the crops.

To put it simple, Duty is the area of land that can be irrigated with a unit volume of water

supplied across the base period where as delta is the depth of water required to raise a crop

over a unit area.

As the quantity of irrigation water required changes for each crop, the duty and delta values

also change. For example, the delta value for Rice (around 1500 mm) is more than Wheat

(around 500 mm) . They are dependent on the type of soil , type of crop , cultivation method

etc.,

The relationship between duty and delta is very easy to establish and is as follows :

Consider B is the base period of the crop , flow into the filed is in cumecs, then volume of

water supplied during the base period , V can be expressed as

V (cubic meters) = B(days) * 24(hours) * 60(minutes) * 60(seconds)

V= 86400 * B cubic meters

If area of D hectares is irrigated ,

Area of the crop irrigated = D * 10000 square meters ( As 1 hectare = 10000 square meters)

Now, depth of water required raise a crop in unit area (Delta) = volume of water supplied

during the base period / Area of crop irrigated

Delta = 86400 * B / D * 10000 = 8.64 B/ D


1. The standard height of a standard rain gauge is

a) 10 cm,

b) 20 cm,

c) 30 cm,

d) 50 cm.

2. In India, rain fall is generally recorded at,

a) 8 A.M.

b) 12 Noon

c) 4 P.M.

d) 8 P.M.

3. In India the recording type rain gauge generally used,

a) Is weighing type,

b) Tipping type,

c) Float recording type,

d) None of these.

4. The best unit period of a unit hydrograph, is equal to basin lag divided by,

a) 2,

b) 3,

c) 4,

d) 5.

5. The deficiency in rain catch due to vertical acceleration of air forced upward

over the gauge is

a) Greater for heavy rain,

b) Greater for lighter rain,

c) Greater for large drops,

d) Lesser for small rain drops.


1 30 cm

2 8 A.M.

3 Float recording type,

4 4

5 Greater for lighter rain,


1.

2.

3.

4. Seepage through embankments in an earthen dam is

5.

KEY ANSWERS

Question no Answers 1 Hydrodynamic pressure

2 Self-weight of dam

3 Decrease the principal stress

4 Drain trenches

5 Super critical

UNIT-V TWO MARKS QUESTIONS WITH ANSWERS

1. What is different between a lake and a canal?

A lake is a still water body surrounded by land from all sides except a side where it is fed by

a river, stream or any other moving body of water. Lakes are far away from oceans and seas,

and they are inland water bodies that are larger and deeper than similar water bodies called

ponds.

2. What do you understand about SCS CURVE?

The runoff curve number is an empirical parameter used in hydrology for predicting

direct runoff ... Ascan be seen in the curve number equation, runoff cannot begin until the

initial abstraction has been met. ... The NRCS curve number is related to soil type, soil

infiltration capability, land use, and the depth of the seasonal...

3. What is meant by depression storage?

Depression storage refers to small low points in undulating terrain that can store precipitation

that otherwise would become runoff. The precipitation stored in these depressions is then

either removed through infiltration into the ground or by evaporation

4. What do you know about Gumbels method of flood frequency analysis?

Flood frequency analysis is a technique used by hydrologists to predict flow values

corresponding to specific return periods or probabilities along a river. The application of

statistical frequency curves to floods was first introduced by Gumbel

5. What is meant by detention storage?

The temporary storage of surface water in low areas such as puddles, bogs, ponds, and

wetlands, from which it evaporates or flows overland towards a stream channel. Also known

as depression storage.


1. What is

theory

1. The flowing water has to be counter act some amount of friction against the bed of the

channel. By the result of that eddies are formed. These eddies are responsible to keep the silt

in suspension without scouring.

2. Kennedy defines the critical velocity which is the mean velocity which will just keep the

channel without silting and scouring.

3. Kennedy gave the equation for the determination of critical velocity.

2. Why is the stream gauging used?

Stream gauging is the process of measuring the water discharge or flow at a particular point

on a stream or river. ... The stream gauging instruments used by water professionals don't

actually measure the flow of the stream, because making a direct measurement of flow is

challenging.

3. What do you mean by reservoir?

A natural or artificial place where water is collected and stored for use, especially water for

supplying a community, irrigating land, furnishing power, etc

4. What are the types of canals ?

Types of canals:

There are two broad types of canal: Waterways: canals and navigations used for carrying

vessels transporting goods and people

5. Name the methods used for design of irrigation canals.

Design of Canals Many procedures have been developed over the years for the hydraulic

design of open channel sections. The complexity of these procedures vary according to flow

conditions as well as the level of assumption implied while developing the given equation.

The Chezy equation is one of the procedures that was developed by a French engineer in

1768 (Henderson, 1966). The development of this equation was based on the dimensional

analysis of the friction equation under the assumption that the condition of flow is uniform.


1. Write down the classification of canals and write down canal alignment.

Classification of canals based on the function of canal

Classifications of canals on the basis of their functions are given below:

1. Irrigation canal.

2. Navigation canal.

3. Power canal.

4. Carrier canal.

5. Link canal.

6. Feeder canal.

Irrigation canals these are the canals which carry water to the fields. The canals having

outlets are called irrigation canals.

2. What do you understand by initial and final regime of canals?

Initial Regime - When a channel is first put into service, then the channel tries to attain its

"intial regime" condition. When the channel is excavated with small width and flatter slope,

then the bed slope gets increased due to deposition of sediment, in order to develop increased

flow velocity. The increased velocity enables the discharge to pass through the channel

having small width.

Here with the increased bed slope the depth of the channel also varies, however the width of

the channel does not vary and remains constant. So keeping constant discharge, constant

width, constant silt charge and constant silt grade and only by varying bed slope and depth of

channel, the channel attain stability; such a condition is known as initial regime condition.

Final Regime: - This is the ultimate regime condition attained by the channel when, in

addition to varying bed slope and depth of the channel, the width of the channel is also

allowed to vary.

What happen exactly is that with the passage of time, the resistance offered by the sides of

the channel against erosion comes to an end due to continuous action of water, so the channel

adjusts its bed slope, depth and width in order to attain stability. Such a condition is known

as final regime condition.

Such a channel where all the parameters such as width, depth and bed slope are allowed to

vary freely has the tendency to attain a semi-elliptical shape. So coarser the silt, flatter would

be the semi-ellipse and finer the silt, the shape would be more or less of a semi-circle.

3. Why

Taking lead from the Kennedy theory Mr. Gerald Lacey undertook detailed study to evolve

more scientific method of designing irrigation channels on alluvial soils. He presented

revised version of

theory, Lacey described in detail concept of regime conditions and rugosity coefficient. The

definitions of these terms are already given.

It may be seen that for a channel to achieve regime condition following three conditions have

tobefulfilled:

that transported by the water;

ii. Silt grade and silt charge should be constant; and

iii. Discharge should be constant.

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

final. The definitions of these two terms are already given earlier.

4. What

From observation of Siphons designed on Bligh's theory, by actual measurement of

pressure, with the help of pipes inserted in the floor of two of the siphons?

Does not show any relationship with pressure calculated on Bligh's theory. This led to

the following provisional conclusions:

Outer faces of end sheet piles were much more effective than the inner ones and the

horizontal length of the floor.

Intermediated piles of smaller length were ineffective except for local redistribution

of pressure.

Undermining of floor started from tail end.

It was absolutely essential to have a reasonably deep vertical cut off at the

downstream end to prevent undermining.

Khosla and his associates took into account the flow pattern below the impermeable

base of hydraulic structure to calculate uplift pressure and exit gradient.

Starting with a simple case of horizontal flow with negligibly small thickness.

(various cases were analyzed mathematically.)

Seeping water below a hydraulic structure does not follow the bottom profile of the

impervious floor as stated by Bligh but each particle traces its path along a series of

streamlines.

5. Explain

Bligh's theory

Bligh's theory states that water creeps along the bottom contour of the structure. The length

of creep refers to the length of the path of water. The loss of head is proportional to the

length. The hydraulic gradient or the loss of head per unit of creep length is HL / L where HL

is the total head loss between upstream and downstream and L is the length. This theory does

not discriminate between horizontal and vertical creeps.

Khosla's theory

According to this theory the seepage water does not creep along the bottom contour as stated

by Bligh. It moves along a set of stream-lines. In order to calculate the uplift pressure and

exit gradient the theory takes into account the flow pattern below the impermeable base of

hydraulic structures.


1. For determination of average annual precipitation in a catchment basin,

a) The best method is Arithmetical method,

b) Thiessen's mean method,

c) Isohyetal method,

d) None of these.

2. Consumptive use of a crop during growth is the amount of

a) Interception

b) Transpiration

c) Evaporation

d) All the above.

3. The run off a drainage basin is

a) Initial recharge + ground water accretion + precipitation,

b) Precipitation + ground water accretion + initial recharge,

c) Precipitation - ground water accretion + initial recharge,

d) Precipitation - ground water accretion - initial recharge.

4. Discharge curve may be extended by logarithmic method if,

a) Cross section of river is uniform,

b) River is broader and shallower,

c) River is of any type,

d) None of these.

5. The best instrument for measuring the velocity of a stream flow is,

a. Pitot tube,

b. Price's current meter,

c. Surface float,

d. Sub-surface float

KEY ANSWERS

Question no Answers 1 Isohyetal method

2 All the above

3 Precipitation - ground water accretion

- initial recharge

4 Cross section of river is uniform

5 Price's current meter


1.

2.

3. Canal structure is used to remove surplus water from an irrigation channel

in to a natural drain?

4.

5.


1 Separate the under sluices from weir

proper

2 Directly proportional to square root of

average particle size

3 Canal escape

4 1

5 Zero

17) BEYOND SYLLABUS TOPICS

WITH MATERIALS

18)RESULTANALYSISREMEDIAL

/CORRECTIVE ACTION

19) RECORD OF TUTORIAL

CLASSES

20) RECORD OF REMEDIAL

CLASSES

21) RECORD OF GUEST LECTURES

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ASSIGNMENT TOPICS WITH MATERIALS UNIT: Ikgr.ac.in/beta/wp-content/uploads/2018/09/WRE-I-COURSE-FILE.pdf · ASSIGNMENT TOPICS WITH MATERIALS UNIT: I 1. Introduction to Engineering