For diploma engineering students

1. Preparedby:-
Mr. Nirant J. Patel
Lecturer
TDEC, SURAT

2. • Levelling is defined as “an art of
determining the relative height of different
points on, above or below the surface”.
LEVELLING
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3. PRINCIPLE OF LEVELLING
• The principle of levelling is to obtain
horizontal line of sight with respect to
which vertical distances of the points above
or below this line of sight are found.
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4. 4• To determine the difference in levels of
points.
• To obtain contour map of an area.
• To obtain cross section of roads, canals, etc.
• To determine the depth cutting and filling in
engineering works.
• To establish points or construct building
component at a predetermined level.
APPLICATION OF LEVELLING

5. TERMS USED IN LEVELLING
Level surface:-
• It is the surface parallel to the mean
spheroidal surface of the earth.
Level line:-
• Line lying on level surface.
Horizontal plane:-
• Horizontal plane through a point is a plane
tangential to level surface.
Horizontal line:-
• It is a straight line tangential to level line.
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7. TERMS USED IN LEVELLING
• Datum:-
“It is an arbitrary level surface from which
elevation of points may be referred”. In India mean
sea level is considered as datum of zero elevation it
is situated at Karachi.
• Mean Sea Level:- It is the average height of sea
for all stages of tides it is derived by averaging
the hourly tide height over a period of 19 years.
• Elevation or Reduced level:-
It is height or depth of any point above or below
any datum. It is denoted as R.L.
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9. • Bench Mark (B.M.):-
It is a fixed reference point of known elevation with
respect to datum.
• Line of collimation:-
It is a line joining the intersection of cross hairs of
diaphragm to the optical centre of object glass and
its continuation. It is also known as line of sight.
• Height of instrument:-
It is the elevation of line of collimation with respect
to datum Back sight. It is a staff reading taken at a
known elevation. It is the first staff reading taken
after setup of instrument.
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10. • Fore sight( F.S.):-
It is the last staff reading taken denoting the
shifting of the instrument.
• Intermediate sight.(I.S.):-
It is staff reading taken on a point whose
elevation is to be determined. All staff reading
between B.S. and F.S. are Intermediate sight.
• Change Point (T.P) :-
It is a point on which both fore and back sight are
taken.
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12. INSTRUMENTS FOR LEVELLING
• The following instruments are essentially
required for levelling.
1. Level
2. Levelling Staff
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13. Types of Level :-
• Dumpy level
• Tilting level
• Wye level
• Automatic level
INSTRUMENTS FOR LEVELLING
• Level and types of level:-
• Level :- The instrument used to furnish
horizontal line of sight for observing staff readings
and determining R.L.s
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14. DUMPY LEVEL
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15. Dumpy level:-
• The Dumpy level is a simple, compact and stable
instrument. The telescope is rigidly fixed to its
supports. Hence it cannot be rotated about
horizontal axis.
• This are the basic levels used in construction
work.
• The telescope is attached to a single bubble and
the assembly is adjusted either by means of a
screwed ball-joint or by foot screws which are
adjusted first in one direction then at 90 degrees.
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BASIC COMPONENTS OF DUMPY LEVEL
1. Telescope – to provide a line of sight
2. Level Tube – to make line of sight horizontal
3. Leveling head – to bring the bubble of tube level at the
centre of its run.
4. Tripod – to support the above three parts of the level.
1. TELESCOPE : Telescope is an optical instrument used for
magnifying and viewing the images of distant objects. It
consists of two lenses. The lens fitted near the eye is called
the eye piece and the other fitted at the end near to the
object is called the objective lens.

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2.Level Tube : Also known as Bubble Tube consists
of a glass tube placed in a brass tube which is sealed
with plaster of Paris. Level tube is filled with either
or alcohol, the remaining space is occupied by an air
bubble. The centre of air bubble always rest at the
highest point of the tube.
The line tangential to the circular are at its highest
point i.e. the middle of tube is called the axis of
bubble tube. When the bubble is central the axis of
bubble becomes Horizontal.

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3) Leveling head : Leveling head generally
consists of two parallel plates with 3 foot screws.
Upper plate is known as Tribrach and lower plate is
trivet which can be screwed on to the tripod.
Leveling head has to perform 3 distant functions :
i) to support the telescope
ii) to attach the level to the tripod
iii) to provide a means for level (foot screws)

21. LEVELLING STAFFS
• Levelling staffs are scales on which these
distances are measured.
• Levelling staffs are of two types
1. Self Reading staff
2. Target staff
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23. Self Reading Staff
• The self reading staff can be read directly by
the level man looking through the telescope.
• Common types of self reading staffs
1. Ordinary staff
2. Sop-with telescopic staff
3. Folding Staff
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24. Ordinary Staff
• The one length staff, is
solid and made of seasoned
wood, it is 3 m long and
graduated in the same way as
the telescopic staff
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25. Folding Staff
• The folding staff is made up of well seasoned
timber such as Cyprus. It consists of two 2 m
wooden pieces with a joint assembly. Each piece of
the staff is made of one longitudinal strip without
any joint. The folding joint is of the detachable
type with a locking device at the back. The staff is
joined together in such a way that the staff may be
folded from one another when required.
• The staff has brass cap at the bottom. It has two
folding handles, with spring action. It is provided
with a circular bubble fitted at the back.
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27. Sop-with Telescopic Staff
• Such a staff is arranged in three lengths placed
one into the other. It can be extended to its full
length by pulling. The top portion is solid and
the central box is hollow the total length of staff
is 4 m.
• The staff is graduated in such a way that
smallest division is of 5 mm. the value in m are
marked in red on the left and those in decimetre
are in black on the right.
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29. Target Staff
• For very precise works and sight target staff are
used. A movable target is provided in this staff.
• A vernier is provided on target to give precise
reading. In target staff level man directs the staff
man to move the target up and down until it
bisects by the line of sight. The staff man observe
the staff reading.
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Temporary Adjustments of a level
• These adjustments are performed at every
setup of instrument.
• Setting up of level
• Levelling of telescope
• Focusing of the eye peace
• Focusing of object glass

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• Temporary Adjustments of a level Setting up the
level This includes ..
• A) Fixing the instrument on tripod
• B) Levelling the instrument approximately by
Tripod

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•Levelling is done with the help of foot screws.
The purpose of levelling is to make vertical axis
truly vertical. It is done with the help of foot
screws.
• A) Place the telescope parallel to a pair of foot
screw then hold the foot screws between thumb
and first finger and turn them either inward or
outward until the longitudinal bubble comes in
the centre.
• B)Turn the telescope through 90º so that it lies
parallel to third foot screw, turn the screw until
the bubble comes in the centre.

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Temporary Adjustments of a level Focusing the
eye piece:-
• To focus the eye piece, hold a white paper in
front of object glass, and move the eye piece in or
out till the cross hair are distinctly seen.
•Focusing of object glass Direct the telescope to
the levelling staff and on looking through the
telescope, turn the focusing screw till the image
appears clear and sharp.

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1. Precise Levelling
2. Trigonometric Levelling
3. Barometric Levelling
4. Hypersometric Levelling
Methods of levelling

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Classification of Levelling
1. • Simple Levelling
2. • Differential Levelling
3. • Fly Levelling
4. • Check Levelling
5. • Profile Levelling
6. • Cross Levelling
7. • Reciprocal Levelling

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Simple Levelling
• It is the simplest method used, when it is
required to find the difference in elevation
between 2 points.

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Differential Levelling
• This method is used to find the difference in the
elevation between points if they are too far apart
or the difference in elevation between them is too
much.

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Fly Levelling
• Fly levelling is just like differential levelling
carried out to check the accuracy of levelling work.
In fly levelling only B.S. and F.S. are taken.

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Check levelling
• This kind of levelling is carried out to check the
accuracy of work. It is done at the end of the days
work in the form of fly levelling to connect the
finishing point and starting point.
Profile levelling or L-Section
• This method is used for taking levels along the
centre line of any alignment like road, railway
canal etc. The object is to determine the
undulations of the ground surface along the
alignment.

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Cross-Sectioning
• This operation is carried out perpendicular to
alignment at an interval of 10, 20 ,30, 40 m. The
idea is to make an estimate of earthwork.

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• Reciprocal Levelling:-
• This method is adopted to accurately determine the
difference of level between two points which are far
apart. It is also used when it is not possible to setup
level in midway between two points.
• Let A and B be the two points on opposite banks of a
river. It is required to find out the level difference
between A&B.
• Setup the level very near to A and take the reading
at A and B let the reading be a1 and b1.
• Shift the level and setup very near to B and observe
A and B to get reading a2 and b2.

50. 50• Let d is the true difference of level between A
and B, and e=error due to curvature, refraction
and imperfect adjustment.

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Reciprocal Levelling
• Thus to eliminate the error take an average of
the difference in elevation taken from 2 points.
• i.e. from A the true difference will be d= (b 1-
a1)-e
• From B the difference will be d= (b2-a2)+ e
• Adding these two eqn to eliminate e, we get
• Therefore d={(b1-a1)+ (b2-a2)}/2

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55. Bench Marks
Bench mark is a point of known elevation. There
are 4 kinds of bench marks.
• GTS (Great trigonometrically survey bench
mark)
• Permanent bench mark
• Arbitrary bench mark
• Temporary bench mark
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56. GTS Bench Mark
• They are the bench marks established with very
high degree of precision at regular intervals by
the survey of India Department all over the
country Their position and R.Ls values above
mean seal level which was earlier located at
Karachi and now it is taken at Bombay High,
Mumbai and is given in catalogue formed by the
department.
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58. Permanent Bench Mark
• Permanent bench marks are fixed in between
GTS benchmarks by govt. agencies such as
railways, PWD, etc. This benchmarks are written
on permanent objects such as milestones,
culverts, bridges etc their value are clearly
written and their position are recorded for future
reference.
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60. Arbitrary Bench Marks
• These are reference points whose R.L.s are
arbitrarily assumed. They are used in small works
such bench mark may be assumed as 100 or 50 m.
Temporary Bench Marks
• They are the reference points established
during the levelling operations when there is a
break in work, or at the end of day’s work the
value of reduced levels are marked on some
permanent objects such as stones, trees etc.
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Methods of Reducing Levels
Height of Instrument Method:-
• This method consist of finding H.I. for every
setup of instrument, and then obtaining the R.L.
of point of reference with respect to H.I.

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Rise and Fall Method:-
• This method consist of determining the
difference of level between consecutive points
by comparing each point with immediate
preceding point.

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Errors in Levelling
The following are the different sources of Errors.
• Personal Error
• The Instruments may not be levelled
• The focusing of eye piece and objective glass may not
be perfect
• The parallax may not be eliminated
• The position of staff may have changed
• Entry and recording in the field book may not be
correct
• The staff may not be fully extended, may not be held
vertical.

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Errors in Levelling Instrumental Error :-
• The Permanent adjustment of the instrument may
not be perfect. That is the line of collimation may
not be horizontal line.
• The internal arrangement of focusing tube may
not be correct
• The graduation of the staff may not be perfect
• Defective bubble tube, if the bubble tube is
sluggish, it may apparently be in the mid-position
even though the bubble line is not horizontal.

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Errors in Levelling Errors due to Natural Causes
• The Curvature of the Earth may affect the staff
readings when the distance of sight is long.
• The effect of refraction may cause a wrong staff
reading
• There are some errors in staff readings due to
high velocity wind

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Common errors in Leveling
• Foresight and back sight not being taken on
exactly the same point
• Reading the staff upward instead of downward
• Reading of wrong number of metre and decimeter
• Entering backsight in F.S and vice versa
• The leveling staff not being fully extended.

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Curvature Correction
• For long sights the curvature of earth can effect
staff readings. The line of sight is horizontal but the
level line is curved and parallel to the mean
spheroidal surface of the earth.
• The vertical distance between the line of sight and
level line at particular place is called the curvature
correction.
• The effect of curvature is to cause the object
sighted to appear lower than they really are.
• Curvature correction is always Subtractive(-)

72. 72True staff reading=(Observed staff reading-
0.0785D2)m
• Where D= distance in Km

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Refraction
• The ray of light pass through layers of air of
different densities and refractor bent down. The
effect of refraction is to make the object appear
higher then they really are. Refraction varies
considerably with climate conditions. However it is
taken as,
• Cr=0.0112 D2m(+)
• Refraction is always additive
• True staff reading =Observed staff Reading+
Refraction correction.

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CONTOURING

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Contour Line
• A contour line may be defined as “An imaginary
line passing through points of equal reduced
levels”. A contour line may also be defined “as the
intersection of a level surface with the surface of
the earth”. Thus, contour lines on a plan illustrates
the topography of the area.
• For ex a contour of 90 m indicates that all the
points on this line have RL of 90 m. Similarly, in a
contour of 89 m all the points have RL of 89 m and
so on.

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Contour Interval
• The vertical distance between two consecutive
contours is known as a contour interval.
• For ex, a map indicates contour lines of 90 m, 89
m, 88 m and so on, the contour interval is 1m.
• This interval depends upon the following factors:
• The nature of the ground (i.e. . Whether flat or
steep) • The scale of the map, and The purpose of
the survey.

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Contour Interval
• Contour intervals for flat ground are generally
small, e.g.. 0.25 m, 0.5 m, 0.75 m
• The contour interval for a steep slope in a hilly
area is generally greater, e.g.. 5 m, 10 m, 15 m, etc.
• Again, for a small scale map, the interval may be
of 1 m, 2 m, 3 m, etc.
• Contour interval is kept large up to 2 m for
projects such as highways and railways, whereas it is
kept as small as 0.5 m for measurement of
earthwork, building sites, dams, etc.

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Horizontal Equivalent
• The horizontal distance between any two
consecutive contours is known as horizontal
equivalent. It is not constant. It varies from point
to point depending upon the steepness of the
ground. Steeper the ground, lesser is the
horizontal equivalent.

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Use of Contour Map
• Contour maps provide valuable information about
the topography of the area, whether it is flat,
undulating or mountainous. The nature of the ground
surface of an area can be understood by studying a
contour map.
• The following are the specific uses of the contour
map.
• To select sites for engineering projects such as
roads, canals, railways.
• To find the possible route of communication
between different places.

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• To ascertain the indivisibility of stations.
• To ascertain the profile of the ground surface along
any direction.
• A suitable route for given gradient can be marked
on the map. To estimate the quantity of cutting,
filling, etc.
• To know the drainage characteristics of the area.
It helps to select sites for culverts, bridges, drainage
system.
•The capacity of a reservoir and the area of
submergence can be computed.

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Characteristics of Contours
• Since every point on a contour line has the same
elevation, a contour map with a constant interval
portrays the conformation of the ground in a
characteristics manner.
• The knowledge of contour characteristics helps in
identifying the natural features of the area from
the given map and in avoiding mistakes in plotting
the contours correctly.

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Characteristics of Contours
• The following characteristics help in plotting
or reading a constant map.
• All the points on a contour line have the same
elevation. The elevations of the contour are indicated
either by inserting the figure in a break in respective
contour or printed close to the contour.
• Two contour lines do not intersect with each other.
• Contour lines always from a closed circuit. But these
lines may be within or outside the limit of the map.
• Contour do not have sharp turning.

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Characteristics of Contours
• The contour lines are closer near the top of a hill
or high ground and wide apart near the foot. This
indicates a very steep slope towards the peak and a
flatter slope towards the foot.
• The contour lines are closer near the bank of a
pond or depression and wide towards the centre.
This indicates a steep slope near the bank and a
flatter slope at the centre.
• Uniformly spaced contour lines indicate a uniform
slope.

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Characteristics of Contours
• A series of closed contour always indicates a
depression or summit. The lower values being inside
the loop indicates a depression and the higher values
being inside the loop indicates a summit. (Hillock)
• Contour deflect uphill at valley lines and downhill
at the ridge lines. Contour lines in U-shape cross a
ridge and V- shape cross a valley at ridge angles. The
concavity in contour lines is towards higher ground in
the case of ridge and towards lower ground in the
case of valley.

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• Contour lines meeting at a point indicate a
vertical cliff.
• Contour lines cannot cross one another, except
in the case of an overhanging cliff. But the
overhanging portion must be shown by a dotted
line.

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97. 97Methods of Contouring
• Contouring requires the planimetric position of the
points whose elevation have been determined by
levelling.
• The methods of locating contours, therefore depending
upon the instruments used to determine the horizontal
as well as vertical position of several points in the area.

98. 98Methods of Contouring
• Broadly, the method can be divided into
the following two classes.
1. Direct methods
2. Indirect methods

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Direct Method
• In the direct method of contouring, the reduced level
of various selected points on a contour line are obtained
and their positions are located. The contours are then
drawn by joining these points. It is a very accurate method but it
is slow and tedious.
• This method is employed only for small area where superior
accuracy is demanded. The method of locating contours directly
consists of horizontal and vertical control. The horizontal control
for a small area can be exercised by a chain or tape and a large
area by compass, theodolite or plane table. For vertical control
either a level and staff or a hand level may be used.

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By Level and Staff
• The method consists of locating a series of points
on the ground having the same elevation by using a
level and leveling staff. Instrument is setup in such a way that
number of readings can be taken from the area to be surveyed.
• The instrument is set up and RL of HI is determined from the
nearest benchmark. For a particular contour value, the staff
reading is worked out. A series of points having the same staff
reading is worked out, and thus the same elevations are plotted
and joined by a smooth curve.

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103. 103By Hand Level
• The principle used is the same as that used in the
method using a level and staff. Instead of the hand level,
an abbey level may also be used. However this method is
very rapid and is preferred for certain works.

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Indirect Methods
• Indirect methods are less expensive, less time
consuming and less tedious as compared with the direct
methods. These methods are commonly employed in
small scale survey of large areas.

106. 106Methods of Contouring
• There are three different ways of employing the indirect
methods of contouring .
• (i) Grid Method
• (ii) Cross-Sectional Method
• (iii) Radial line method or Tachometric method

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Grid Method
• If the area is not large, it is divided into a grid or
series of squares. The grid size may vary from 5m x 5 m
to 25 m x 25 m depending upon the nature of the ground, the
contour interval and the scale of the map. The grid corner are
marked on the ground and spot levels of these corners are then
determined by normal method of leveling using a level.
• The grid is plotted to the scale of the map and the spot levels
of the grid corners are entered, the contours of desired values
are then locked by interpolation. This method is very suitable
for a small open area where contour are required at a closed
vertical interval.

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Cross-Sectioning Method
• In this method, suitable spaced cross –sections
are projected on either side of the centre line of
the area. Several points are chosen at reasonable distances
on either sides. The observations are made in the usual
manner with a level.
• The cross- section lines are plotted to the scale, the points
on these lines are marked and reduced levels are entered.
The contours of desired values are then located by
interpolation. This method is suitable for road, railway and
canal survey.

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Radial Line Method or Tachometric Method
• In this method, a number of radial lines are set out
at known angular interval (i.e. 15 0 or 30 0) at each station.
The point are selected on a line depend on the nature of the
ground surface. Instead of the level, a tachometer may be
used.
•The observations are taken on the staff stations and elevations
and distances are then calculated. A traverse and radial lines
are plotted to the scale RLs of the point entered. The contour
of desired values are then located by interpolation . This
method is convenient in hilly area.

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Comparison of direct and Indirect methods of
contouring
Direct Method Indirect Method
Most accurate but slow
and tedious
Not so accurate but
rapid and less tedious
Expensive Cheaper
Not suitable for hilly
area
Suitable for hilly area
During the work
calculations can be done
Calculations are not
required in the field
Calculation can not be
checked after contouring
Calculation can be
checked as and when
required

114. 114Interpolation of Contours
• The process of locating the contours proportionately
between the plotted point is termed interpolation may be
done by:
1. Estimation
2. Arithmetical Calculation
3. Graphical Method

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Estimation
• The points on the required contour are located
by eye judgment or estimation between points
whose elevations are already known.
•This method is good for small scale maps. It is
assumed that slope between the ground points is
uniform.

116. 116Arithmetic Calculations
• This methods is used when high accuracy is required and
scale of the map is of intermediate or large.
• In this method the distances between two points of
known elevation are accurately measured. Then with the
help of arithmetic calculations, the positions of the
required elevation points are computed.

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Graphical Method
• When high accuracy is required and many interpolation
are to be made, this method of plotting contours proves
to be most rapid and convenient. For this purpose tracing
paper is used.

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Plotting of a Contour Map
• Before plotting the contour map, suitable scale is
selected.
• e.g. 1 cm = 1 m, 1 cm = 2 m, 1 cm = 2.5 m, 1 cm =
4 m or 1 cm = 5 m etc. Here 1 cm = 2m is selected.
• A horizontal line is drawn as the centre line
• The chainages are marked along the horizontal
line according to the scale.
• Ground levels are written from the level book
according to the chainage.

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• The cross-section (L/s and R/S) are also plotted
(perpendicular lines) at each of the chainage.
• By interpolation contours are joined by smooth curves
keeping in mind the characteristics of contour.
• First find out maximum and minimum RL values and then
first plot full values contour lines i.e.. 47 , 48, 49 etc.
Contour interval is 1 m. After plotting these contour lines
reduces contour interval and it is taken 0.5 m and contour
lines i.e. 47.5, 48.5, 49.5 etc are plotted.
Contour lines are then inked.

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