Surveying Levelling & Contouring Unit 2 Notes updating.pptx (1).pdf

Department of Civil Engineering
Subject- Surveying (3CE4-05)
Semester/ Year – 3/ 2
By
Denis Jangeed

By :-Denis Jangeed
Department of Civil Engineering
GITS, Udaipur
Subject- Surveying
Topic:- Levelling & Contouring
Semester/ Year – 3/ 2

Subject Weightage (as per previous patterns)
Exam Marks Weightage
GATE 4-6 Marks out of 100
State JE/Aen 10% of total Weightage
SSC JE 10% of total Weightage
ESE/IES (Objective) 18-22 marks out of 300
ESE/IES (Conventional) 60-75 marks out of 600
Books
1 Surveying volume-I & II by Dr. B.C. Punmia
2 Surveying volume-I & II by S.K. Duggal
By :-Denis Jangeed

Flipped Classroom Pedagogy
Conducted Presentation activity for every student of 2nd year in
the classroom to enhance their Technical knowledge as well as
presentation skills form 25/8/2022 to 05/12/2022
Link-
Flipped Classroom Pedagogy

Some Glimpse of Flipped Classroom Pedagogy
● Topic Explanation on White-Board (as a Teacher)
● PPT Presentation
● Instrument Explanation

Innovation made in Teaching Pedagogy
Created a quiz on slido.com for 2nd year student and given a surprised gift to
winner on date 16 Dec 2022
(We can say Student Centric Activity)
Link-
Student Centric Activity

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Define levelling:-
▪ Levelling is a process of determining the height of
one level relative to another. It is used in surveying
to establish the elevation of a point relative to a
datum, or to establish a point at a given elevation
relative to a datum.
By :-Denis Jangeed

Definition and Terms used in levelling:-
▪ Reduced Level
▪ Absolute Level
▪ MSL
By :-Denis Jangeed
O
MSL
MSL
Earth
Earth
Center
RL
AL

By :-Denis Jangeed
FS

1. (BS- Back sight)
▪ It is the first staff reading taken by the surveyor after the levelling
instrument is set up and levelled.
▪ B.S is generally taken on the point of known (Elevation point)
reduced level as on the benchmark or a change point.
2. (FS- Fore sight)
▪ It is the last staff reading taken before changing the instrument to
the other position.
▪ It is the staff reading taken on point whose RL is to determined.
▪ This sight is considered as negative and deduced from Height of
Instrument to determine RL of the point.
By :-Denis Jangeed

5. (IS- Intermediate sight)
▪ All readings taken between backsight and foresight is called
Intermediate sight readings..
▪ These are the points whose RL is determined by the method
already mentioned above in FS.
4. (RL- Reduced Level)
▪ It is the height or depth of any survey points with reference to a
given assumed datum.
▪ The elevation is positive or negative according as point lies above
or below datum.
5. (B.M- BenchMark)
▪ Fixed reference point of known elevation with respect to which
RL of other points is determined.
By :-Denis Jangeed

▪ Benchmarks can be arbitrary or permanent, the former is used for
calculation of reduced levels for small survey works and the latter
is used to calculate the elevations of significantly important
locations and points.
▪ Arbitrary benchmarks are assumed to be equal to 100 meters
generally and then the elevations with respect to assumed
benchmark is determined. It is commonly practiced by engineering
students.
▪ For GTS surveys of the country, surveyors use permanent
benchmarks to calculate the elevations of different points.
6. Datum Surface:-
▪ It is Reference plane with respect to which RL of the other survey
points is determined.
▪ The datum surface may be real or imaginary location with a
nominated elevation of zero.
▪ The commonly used datum is mean sea level.
By :-Denis Jangeed

7. Levelling Staff:-
▪ A level staff, also called levelling rod, is a graduated wooden or aluminium
rod, used with a levelling instrument to determine the difference in height
between points or heights of points above a vertical datum.
▪ It cannot be used without a levelling instrument.
8. (HI- Height of instrument)-
The height of the line of sight of a levelling instrument above the adopted
datum
9. Change point (CP)
–Location of the staff when the level is moved
–Change points should be...•Stable •Well defined •Recoverable •e.g. sharp rock,
nail, change plate, etc...
By :-Denis Jangeed

Bench Mark (B.M)
▪ It is a fixed reference point whose elevation with respect to some
datum is known.
▪ It is noted that any levelling work is first started from BM.
Types of Bench Mark
(a) GTS benchmark
(b) Permanent benchmark
(c) Arbitrary benchmark
(d) Temporary benchmark
(a) GTS benchmark (Great Trigonometric Survey)-
▪ GTS are established with the highest precision.
▪ This benchmark is established by the survey of India department at a
large interval (100 K.M.) all over the country with respect to the
MSL at Bombay Port as datum.
▪ The values of reduced level the relevant position and the number of the
benchmark are given in a catalogue (Known as GTS Maps) published
by this department. By :-Denis Jangeed

By :-Denis Jangeed
Permanent benchmark Temporary benchmark
Survey benchmark monuments
are brass or metal disks in the
ground that provide latitude,
longitude, or orthometric height.

(b) Permanent benchmark-
▪ This is a fixed point or mark established by different
government department like PWD, Railway platforms,
Irrigation etc.
▪ The RLs of this point is determined with reference to the
GTS benchmark and are kept on permanent point like the
plinth of a building, parapet of a bridge or culvert and so on.
(c) Arbitrary benchmark-
▪ when small ordinary levelling work is to be carried out or
when the permanent benchmark is not nearby the place
where the survey is to be carried out then to start the levelling
work any prominent object like plinth or step of building etc.
is chosen as the benchmark and its elevation is assumed
arbitrarily.
By :-Denis Jangeed

(d) Temporary benchmark-
▪ A temporary benchmark (TBM) is a point with a known
elevation used for level control during drainage
construction works of houses and surveys.
▪ For example, nails on road level or marks on drainage
channels are use as temporary benchmarks.
By :-Denis Jangeed

1. Level surface :(e.g. the geoid)
▪ A curved surface which at each point is perpendicular to the
direction of gravity at the point. The surface of a still water is a
truly level surface. Any surface parallel to the mean spheroid
surface of the earth is therefore a level surface.
▪ A water surface with no motion
▪ Gravity gradient is the normal to the level surface
▪ The Instrument’s Bubble is in the normal (!)
2. Level line :
▪ Normal to the plumb line at all points.
3. Horizontal line : Straight line tangential to the level at a point.
4. Vertical line : Line normal to the level line at a point.
By :-Denis Jangeed

By :-Denis Jangeed
5 Horizontal surface/Plane
● At the instruments axis,the horizontal surface is tangent to the level
surface
● Over short distances (<100 m) the horizontal surface and the level
surface will coincide
● For long leveling lines the effects of the gravity field must be
considered
6 Line of Collimation –
Imaginary line that passes through
leveling instrument at Cross Hairs

By :-Denis Jangeed
Barometric levelling:
● In barometric leveling, differences in height are determined by
measuring the differences in atmospheric pressure at various
elevations.
● Air pressure is measured by mercurial or aneroid barometer, or a
boiling point thermometer.
● It is a rough estimation and used rarely.

By :-Denis Jangeed
Trigonometric Leveling: In this method, trigonometric relations are
used to find the elevation of a point from angle and horizontal distance so, it
is called as trigonometric leveling. It is also called as indirect leveling.
The process of leveling in which the elevation of point or the difference
between points is measured from the observed horizontal distances and
vertical angles in the field is called trigonometric leveling.

By :-Denis Jangeed
Direct Leveling
It is the most commonly used method of leveling. In this method,
measurements are observed directly from leveling instrument. Based on the
observation points and instrument positions direct leveling is divided into
different types as follows:
● Simple leveling
● Differential leveling
● Fly leveling
● Profile leveling
● Precise leveling
● Reciprocal leveling

By :-Denis Jangeed
Simple Leveling
● It is a simple and basic form of leveling in which the leveling
instrument is placed between the points which elevation is to be
find. Leveling rods are placed at that points and sighted them
through leveling instrument. It is performed only when the
points are nearer to each other without any obstacles.

By :-Denis Jangeed
Differential Leveling
● Differential leveling is performed when the distance between
two points is more.
● In this process, number of inter stations are located and
instrument is shifted to each station and observed the elevation
of inter station points.
● Finally difference between original two points is determined.

By :-Denis Jangeed
Fly Leveling
● Fly leveling is conducted when the benchmark is very far from the
workstation.
● In such case, a temporary bench mark is located at the workstation
which is located based on the original benchmark. Even it is not
highly precise it is used for determining approximate level.

By :-Denis Jangeed
Profile Leveling
● Profile leveling is generally adopted to find elevation of points
along a line such as for road, rails or rivers etc.
● In this case, readings of intermediate stations are taken and
reduced level of each station is found. From this cross section of
the alignment is drawn.

By :-Denis Jangeed
Precise Leveling
● Precise leveling is similar to differential leveling but in this case
higher precise is wanted. To achieve high precise, serious observation
procedure is performed. The accuracy of 1 mm per 1 km is achieved.
Reciprocal Leveling
● When it is not possible to locate the leveling instrument in between
the inter visible points, reciprocal leveling is performed. This case
appears in case of ponds or rivers etc. in case of reciprocal leveling,
instrument is set nearer to 1st station and sighted towards 2nd station.

By :-Denis Jangeed
LEVELLING INSTRUMENTS:-
Following are Instruments commonly used in
direct levelling in surveying:-
(A). A Level:-
(B). A Levelling Staﬀ:-

By :-Denis Jangeed
(A) TYPES OF LEVELS:-
Following are the types of diﬀerent levels used for levelling in
surveying:-
(1). Dumpy Level:-
(2). Y Level:-
Y level or Wye-level consists y-shaped frames
which supports the telescope.
(3). Tilting Level
(4). Reversible Level
(5). Automatic Level

By :-Denis Jangeed
(1). The Dumpy Level:-
▪ The telescope of the dumpy level is rigidly ﬁxed to its supports.
▪ It cannot be removed from its supports nor can it be rotated about its
longitudinal axis.
▪ The instrument is stable and retains its permanent adjustment for a long
time.

By :-Denis Jangeed
(2). The Wye Level (Y-Level):-
▪ The telescope is held in two ‘Y’supports.
▪ It can be remove from supports and reversed from one end of the
telescope to the other end.
▪ The ‘Y’ supports consist of two curved clips which may be raised.
Those the telescope can be rotated about its longitudinal axis

By :-Denis Jangeed
(3). Reversible Level:-
▪ This is a Combination of the dumpy level and ‘Y’ level.
▪ It is supported by two rigid sockets.
▪ The telescope can be rotated about its longitudinal axis, withdrawn
from the socket and replaced from one end of the telescope to the other
end

By :-Denis Jangeed
(4). The Modern Tilting Level:-
▪ The telescope can be tilted slightly about its horizontal axis with the
help of its tilting screw.
▪ In this instrument the line of collimation is made horizontal for each
observation by means of the tilting screw.
▪ This is also known as the self-aligning level.
▪ This instrument levelled automatically within a certain tilt range by
means of a compensating device (the tilt compensator).

By :-Denis Jangeed
(5).The Automatic Level:-
▪ Automatic level is like the dumpy level.
▪ In this case the telescope is ﬁxed to its supports.
▪ Circular spirit can be attached to the side of the telescope for
approximate levelling.
▪ For more accurate levelling, compensator is attached inside the
telescope.

By :-Denis Jangeed
(5).The Automatic Level:-
1.Base Plate
2.Horizontal Circle
3.Eyepiece
4.Circular Bubble
5.Sighting Pointer
6.Objective Lens
7.Focusing Knob
8.Fine Motion Drive
9.Foot screw
10.Bubble Mirror

By :-Denis Jangeed
(B) Levelling Staff
▪ The levelling staff is a rectangular rod having graduations.
▪ The staff is provided with a metal shoes at its bottom to resist wear &
tear.
▪ The foot of the shoe represents zero reading.
▪ Levelling staff may be divided into two groups:
(i) Self reading staff
(ii)Target staff.

By :-Denis Jangeed
(i) Self reading staff:-
▪ This staff reading is directly read by the
instrument man through telescope.
▪ In a metric system staff, one metre length is
divided into 200 subdivisions, each of uniform
thickness of 5 mm.
▪ All divisions are marked with black in a white
background. Metres and decimetres are written in
red colour.

By :-Denis Jangeed
The following three types of self reading staffs are available:-
(a) Solid staff:-
▪ It is a single piece of 3 m.
(b) Folding staff:-
▪ A staff of two pieces each of 2 m which can be folded one
over the other.
(c) Telescopic staff:-
▪ A staff of 3 pieces with upper one solid and lower two hollow.
▪ The upper part can slide into the central one and the central part can
go into the lower part.
▪ Each length can be pulled up and held in position by means of brass
spring. The total length may be 4 m or 5 m

By :-Denis Jangeed
(ii) Target staff:-
▪ If the sighting distance is more, instrument
man finds it difficult to read self reading staff.
▪ Target staff is similar to self reading staff,
but provided with a movable target. Target is a
circular or oval shape, painted red and white
in alternate quadrant.
▪ It is fitted with a vernier at the centre.
▪ The instrument man directs the person
holding target staff to move the target, till its
centre is in the horizontal line of sight. Then
target man reads the target and is recorded.

By :-Denis Jangeed
To obtain the reduced level of a point in the field from staff readings, we
have 2 methods:
1. Height of Instrument or Collimation method
2. Rise and fall method.

By :-Denis Jangeed
Height of Instrument (HI) method: consider the readings taken in the operation shown below:
Example
0.628m 1.564 1.00
2.259
0.991
1.210

By :-Denis Jangeed
Reduce level can be computed using the following expression:
RL of a point = HI – FS = ( RLBM +BS) – FS
Arithmetic check: ΣBS – ΣFS= Last RL – first R

By :-Denis Jangeed
Rise and fall (RF) method: the rise or fall of the ground between successive rod stations
is considered. For the same instrument set up,
If 2nd rod reading > first rod reading ⇒ fall
If 2nd rod reading < first rod reading ⇒ rise
Then RL of 2nd station = RL of first station – fall or RL of first station + rise

By :-Denis Jangeed
Errors and their effects
(many, but only a few addressed)
Errors in leveling, e.g.
•Collimation, Parallax
•Change point / staff instability
•Instrument or Benchmark instability
•Refraction
•Uncalibrated staff or levels
•Reading, booking, or computation errors
•Fore- and backsight distances different

By :-Denis Jangeed
Systematic and Random Errors
•Earth curvature
•Refraction
•Collimation errors

Effect of Earth Curvature
Distance (s) in m 10 20 50 100 1000
Effect (Dh) in mm 0,008 0,03 0,2 0,8 80

By :-Denis Jangeed
Mean Gradient: 0,2 °C / m
Refraction

By :-Denis Jangeed
Collimation error
•Occurs when the line of sight (as defined by the lens
axis and cross-hairs) is not horizontal
•Leads to an incorrect staff reading

By :-Denis Jangeed
Errors In Levelling
Errors can also be classified as:-
(1) Instrumental Errors
(2) Natural Errors
(3) Personal Errors
(a) Error Due to Imperfect Adjustment
(b) Error Due to Sluggish Bubble
(c) Error in the Movement of the Objective Slide
(d) Rod Not Standard Length

By :-Denis Jangeed
(2) Natural Errors
(a) Earth’s Curvature
(b) Atmospheric Refraction
(c) Settlement of Tripod or Turning Points
(d) Wind Vibrations
(3) Personal Errors
(a) Mistakes in Manipulation
(b) Mistake in Rod Handling
(c) Mistake in Reading the Rod
(d) Errors in Sighting
(e) Mistake in Recording

By :-Denis Jangeed
(a) Error Due to Imperfect Adjustment:-
● The essential adjustment of a level is the line of sight shall be
parallel to the axis of the bubble tube.
● If the instrument isn’t in this, adjustment, the line of sight will be
inclined upwards or downwards when the bubble is centered,
and the rod readings will be incorrect.
(b) Error Due to Sluggish Bubble:-
● When the bubble is sluggish, it will come to rest in the wrong
position, though it could creep back to the correct position
while the sight is being taken.
● Such a bubble is a constant source of delay and aggravation.

By :-Denis Jangeed
(c) Error in the Movement of the Objective Slide:-
● In the case of external focusing instruments, if the objective
slide is slightly worn out, it may not move in a truly horizontal
direction.
● From the short sights, the objective slide is moved out nearly
its entire length, and the error is, thus, more.
(d) Rod Not Standard Length:-
● Incorrect lengths of divisions on a rod cause errors similar to
those resulting from the incorrect marking on a tape.
● The error is systematic and can be directly proportional to this
difference in elevation.
● When the rod is too long, the correction is added to a
measured difference in elevation; when the rod is too short,
then the correction is subtracted.

By :-Denis Jangeed
(2) Natural Errors
(a) Earth’s Curvature
● The effect of curvature is to increase the rod readings.
● If the distances are small that the error is negligible, but for
greater distances, once the back and foresight aren’t balanced,
then a systematic error of considerable magnitude is produced.

By :-Denis Jangeed
(b) Atmospheric Refraction
● Because of refraction, the ray of light bends downwards in the
form of the curve with its concavity towards the earth surface,
thus decreasing the staff readings.
(c) Settlement of Tripod or Turning Points
● If the tripod settles at the interval that elapses between taking
a back sight and the following foresight, the observed foresight
will be too small and the elevation of this turning point will be
too great.
● Similarly, if a turning point settles from the interval that elapses
between taking the foresight and the following back sight at the
next set up, the observed back sight will be too great and H.I.
calculated will be too great.
● Thus, whether the tripod settles or the turning point settles, the
error is always systematic and the resulting elevation will

By :-Denis Jangeed
(d) Wind Vibrations
● High wind shakes the instrument and thus disturbs the bubble
and the rod.
● Precise levelling work should never be done in high wind.
(3) Personal Errors
(a) Mistakes in Manipulation
● These include mistakes in setting up the level, imperfect
focusing of the eye-piece and of objective, errors in centering
the bubble and failure to watch it after each sight, and errors
because of resting the hands-on tripods or telescope.
● Parallax caused by an improper focusing results in incorrect
rod readings it produces an accidental error and can be
eliminated by carefully focusing.

By :-Denis Jangeed
(b) Mistake in Rod Handling
● If the rod isn’t in plumb, the reading taken will be too great. The
error varies directly with the magnitude of the rod reading and
directly as the square of the inclination.
● The error can be minimized by carefully plumbing the rod either
by eye estimation or from using, a rod level, a special
attachment devised for plumbing the rod or by waving the level
rod slowly towards or away in the level thereby taking the
minimum rod reading.
(c) Mistake in Reading the Rod
The common mistakes in reading the rod are:
● Reading upwards, instead of downwards.
● Reading downwards, instead of upwards when the staff is
inverted.

By :-Denis Jangeed
● Reading the wrong meter mark when the staff, is near the level
and only one-meter mark is visible through the telescope.
● To omit a zero or even two zeros from a reading. For example,
1.28 instead of 1.028 or 1,06 instead of 1.006.
(d) Errors in Sighting
● The error is caused when’ it is difficult to tell when the
crosshair coincides with the center of the target in a target rod
and to determine the exact reading that the cross-hair appears
to cover in the case of this self-reading rod.
● This is an accidental error the magnitude of which depends
upon the coarseness of this cross-hair, the type of rod, the
form of target., atmospheric conditions, length of sight and the
observer.

By :-Denis Jangeed
(e) Mistake in Recording
The common mistakes are:-
● Entering the reading with digits interchanged i.e., 1.242 Stead
of 1.422.
● Entering back sights and foresight in the wrong column.
● Mistaking the numerical value of reading called out by the level
man.
● Omitting the entry.
● Entering the wrong remark- against a reading.
● Adding a foresight instead of subtracting it and/or subtracting a
back sight reading instead of adding it.
● Ordinary arithmetical mistakes.

By :-Denis Jangeed
Contouring (also Isoline, Isopleth, Isoquant or Isarithm)
▪ Earth's surface has many different kinds of landforms
that vary widely in height and elevation.
▪ Contour maps show the elevations of these surface
features, which allows you to look at a
two-dimensional map to visualize the Earth in three
dimensions.

By :-Denis Jangeed
Contouring
Definition of Contour:-
▪ A Contour or a contour line is an imaginary line on
the ground which meets the point of equal or same
elevation.
▪ The space between the lines indicates the slope of the
land.

By :-Denis Jangeed
Uses of contours maps
▪ Contours provide valuable information about the
nature of terrain. ...
▪ Nature of Ground. To visualize the nature of ground
along a cross section of interest,
▪ Locate water sources
▪ Identify areas that may be prone to flooding or
landslides.
▪ To Locate Route. ...
▪ Intervisibility between Stations. ...
▪ To Determine Catchment Area or Drainage Area. ...
▪ Storage capacity of a Reservoir.

Contouring
Basic terms in Contour:-
Contour Interval and Horizontal Equivalent:-
▪ The constant vertical distance between two consecutive
contours is called the Contour Interval.
▪ The horizontal distance between any two adjacent contours
is termed as the horizontal equivalent. The horizontal
equivalent depends upon the slope of the ground.

The contour interval depends upon the following factors:-
(i) The nature of the ground:-
▪ In flat and uniformly sloping country, the contour interval is
small, but in broken and mountainous region, the contour
interval should be large otherwise the contours will come
too close to each other.
(ii) The purpose and extent of the survey:-
▪ Contours interval is small if the area to be surveyed is small
and the maps are required to be used for the design work or
for determining the quantities of earth work etc., while
wider interval shall have to be kept for large areas and
comparatively less important works.
(iii) The scale of the map:-
▪ The contour interval should be in the inverse ratio to the
scale of i.e. the smaller the scale, the greater the contour
interval.

Characteristic of Contours:-
1. All points in a contour line have the same elevation.
2.Flat ground is indicated where the contour are widely separated and
the steep ground where they run close together.
3.A uniform slope is indicated when the contour lines are uniformly
spaced and a plane surface when they are straight, parallel and
equally spaced.

4.A series of closed contour lines on the map represent a hill, if the
higher values are inside.(Fig- 8.1)
5.A series of closed contours on the map indicate a depression, if the
higher values are outside. (Fig- 8.2)

6. Contour lines across ridge or valley lines at right angles. If the
higher values are inside the bend or loop in the contour, it
indicates a “Ridge”. (Fig. 8.3).
And if the higher values are outside the bend, it represents
a “Valley” (Fig. 8.4).

7. Contour lines cannot end anywhere but close on themselves
elders within or outside the limits of the map.
8. Contour lines cannot merge or cross one another on map except
in the case of an overhanging cliff. (Fig. 8.5).

9. Contours never run into one another except in the case of a
vertical cliff (Fig. 8.6). In this case, several contours coincide
and the horizontal equivalent becomes zero.

10.Depression between summits is called a saddle. It is
represented by four sets of contours as shown in Fig. 8.7. It
represents a dip in a ridge or the junction of two ridges. And in
the case of a mountain range, it takes the form of a pass. Line
passing through the saddles and summits gives water shed line.

By :-Denis Jangeed
History
▪ The idea of lines that join points of equal value w
rediscovered several times. The oldest known isoba
(contour line of constant depth) is found on a map dat
1584 of the river Spaarne, near Haarlem, by Dutchma
Pieter Bruinsz
• The lines are usually drawn at regular intervals, such
every 10 meters or every 100 feet.

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