RAMOGI INSTITUTE OF ADVANCED TECHNOLOGY (RIAT)
BUILDING & CIVIL DEPARTMENT
CERTIFICATE IN LAND SURVEY
TRADE PROJECT
FOR
INDIRECT CONTOURING
PRESENTED BY
: DENNIS DANIEL MOI
ADMISSION NO
: 14979
INDEX NO
: 73710101
PAPER NO
: 1308/316A
CENTRE NUMBER
: 737101
PRESENTED TO
KENYA NATIONAL EXAMINATION COUNCIL (KNEC) AS A REQUIREMENT IN
PARTIAL FULFILLMENT FOR THE AWARD OF CERTIFICATE IN LAND SURVEY
SUPERVISOR
:
EXAM SERIES
: JULY 2023
© 2023
ABSTRACT
Contouring is one of the methods used in topographical survey to give the heights of both the
physical and man-made features on the earth surface. It provides an accurate network of heights
spread all over the project area which are used to design engineering project and which
earthwork volumes can be determined.
RIAT college is rapidly expanding due to increase in student population. As a result of this
expansion there is need to come up with new football pitch at its extended compound plot to
control flooding. Contours will be generated to show the average elevation of all the physical
features on the ground to be used to generate the plan of the ground before designing.
The main objectives of this project are; to interpolate contours along the main playground of the
project area, to come up with a design level of the project area for use in future engineering
works of the area to control flooding.
The project area is located within Kisumu County in Kisumu West sub-county, approximately
1km from Riat junction off Kisumu-Kakamega road.
The approximate radius of the ground extension is 200m. The ground is gently sloping from
north to south.
The importance of project includes, to establish elevation of points on the ground, to establish/
interpolates contours and provide a vertical control of points to be in future as plans for
engineering construction projects and finally for future planning of engineering works.
The following tasks will be performed in order to achieve the above two stated object; they
include; theory of levelling, reconnaissance, planning for the project, carry out the field work,
computation for checks and drawing/ interpolating contours.
CHAPTER ONE
1.0 INTRODUCTION
Surveying is the science and art of making measurements of relative positions of natural and
manmade features or under the earth surface and presentation of this information graphically or
numerically. Based on the curvature of the earth, primary division of surveying includes plane
and geodetic survey. In plane survey, earth’s curvature is not taken into consideration while in
geodetic survey; earth curvature is taken into consideration because it’s carried over a larger
area.
Based on the purpose types of surveying includes survey control, Engineering survey, cadastral
survey, and topographical survey.
Contouring is one of the methods used in topographical survey to give the heights of both the
physical and man-made features on the earth surface. It provides an accurate network of heights
spread all over the project area which are used to design engineering project and which
earthwork volumes can be determined.
1.1 PROBLEM STATEMENT.
Due to the flooding of the football pitch at Ramogi playing ground when it rains, there is need to
come up with proper drainage system to control flooding also there is need to come up with new
playing ground at its extension plot. Contours will be generated to show the average elevation of
all the physical features on the ground to be used to generate the plan of the ground before
designing.
1.2 OBJECTIVES
The main objectives to this project are:
•
To interpolate contours along the main playground of the project area,
•
To come up with a design level of the project area for use in future engineering works of
the area to control flooding currently and in future and
1.3 SCOPE
1.3.1 Area of study
Contouring is to be done from control point within the institute. The ground is located in Kisumu
County.
1.3.2 Distance/ Radius
The approximate radius of the ground extension is 200m. The ground is gently sloping from
north to south toward Lake Victoria.
1.4 IMPORTANCE OF THE STUDY
•
To establish elevation of points on the ground
•
To establish/ interpolates contours and provide a vertical control of points to be in future
as plans for engineering construction projects.
•
For future planning of engineering works.
1.5 TASKS | DOCUMENTATION OF THE PROJECT
•
Theory of levelling
•
Reconnaissance
•
Planning for the project
•
Carry out the field work
•
Computation for checks
•
Drawing/ interpolating contours
CHAPTER TWO
2.0 LITERATURE REVIEW
Contouring is a survey exercise that is meant to establish contours either on the ground or map.
Contouring is one of the methods used in topographical survey to give the heights of both the
physical and man-made features on the earth surface. It provides an accurate network of heights
spread all over the project area or map. Contours provide important information for the purposes
of designing layout of roads, railways, drainage systems.
2.1 TERMS USED IN CONTOURING
Contour- is an imaginary line passing through points of equal’s elevation on the earth’s surface.
Horizontal equivalent-is the shortest horizontal distance between successive contours lines. It’s
different for different contours lines and is independent on slope of the ground surface.
Vertical interval-is the difference in height between successive contours lines and is constants
on any one drawing. Its depend on the scale of the plan, the purpose for the plan, nature of the
ground and time and expenses of the field work.
Spot height- is points distributed randomly over a site whose elevation has been determined
accurately by leveling.
Gradients- are the slope of the ground which is expressed by the ratio of height risen in a given
horizontal distance travelled.
2.2 CHARACTERISTICS OF CONTOURS
a) The ground slope between contour lines is assumed to be uniform
b) The direction of the steepest slope on a contour line is at right angles to the contours.
c) Closely spaced contours indicate steep slope
d) Widely spaced contours indicate moderate slope
e) Equally spaced contours depict a uniform slope.
f) Contours are not shown going through a building.
g) Contours crossing a man-made horizontal surfaces (roads) will be straight lines as they
cross the surfaces.
h) Contours of different elevation cannot cross each other since contours joins points of equal
elevation (except in caves and overhanging cliffs.
i) Contours of different elevation cannot unite to form one Contour (except in a vertical cliff)
j) Contours cannot begin or ends on the same plan.
k) The same contours must appear on both sides of a ridge or valley.
2.3 METHODS OF CONTOURING
2.3.1 Direct method
The contours to be plotted are actually traced on the ground. Only those points surveyed which
happen to fall on a particular contour are plotted and joined. The method of locating contours
directly consists of providing vertical control for location of points on the contours and
horizontal control for plotting the located points. The direct method of contouring can be
employed in the following two ways:
-Vertical control- instrument used are a level, leveling staff and a plane table with
accessories.
-Horizontal control- this is generally provided using a plane table with accessories such
as tape, ranging rod etc. in case of a small areas, the location of the points on each
contour are plotted on the plane table section by method.
2.3.2 Indirect method
Sufficient number of points are located and given spot levels. The locations of all such point are
easily plotted on a plane table sections as the points are generally well-shaped geometrical
figures such squires, rectangles and triangles. There are three different ways of employing the
indirect method of contouring:
Grid method – if the area is large, it’s divided into grids or series squares. The grid size may
vary from 5m by 5m to 25m by 25m depending upon the nature of the ground, the contour
interval and the scale of the map.
Cross- section method – in this method, suitably spaced cross section are projected on either
sides of the center line of the area. Several points are chosen at reasonable distances on either
side. The spot level is given to those points by normal leveling methods. The cross- section
lines are plotted to the scale, the points on these lines are marked and spot level is entered.
The points on the chosen contours are interpolated assuming uniform slope between adjusted
points and joined by a smooth curve.
Radial line method or tachometric method- a number of radial lines are set out at known
angular interval at each station and points are fixed at a convenient constants distance apart
on the rays that are set by compass or for greater accuracy by theodolite.
2.4 COMPARISONS BETWEEN DIRECT AND INDIRECT METHODS OF
CONTOURING
Direct method
Indirect method
1.Expensive
Very cheap
2. Very accurate but
slow and tedious
Not very accurate but
quicker and less tedious
3. Used for small
projects requiring higher
accuracy e.g. layout of
buildings, factory etc.
Used for large project
requiring g lower
accuracy e.g. layout of
highways, railways,
canals etc.
4. Unsuitable for hilly
areas
Suitable for hilly terrain
using tacheometry
5.Calculations to be
done in the field
Calculations in the field
not required
6.After contouring,
calculations cannot be
checked
Calculation can be
checked and when
needed
2.5 CONTOUR GRADIENT
Is the imaginary line on the surface of the earth having a constant inclination (slope) to the
horizontal. The inclination of a contour gradient is generally either given as a rising or falling
gradient, and is either expressed as a ratio of the vertical height to a specified horizontal distance.
If the inclination of a contour is 1 in 50, means that for every 50m horizontal distance there is
rise or fall of 1m. When the inclination of a contour gradient is given, its direction from appoint
may be easily located either on a map or on the ground by methods below.
2.6 USES OF CONTOUR MAPS
a) Cross-section- a section along any line, say PQ, can be drawn from contours. The
horizontal locations at different elevations of the contours are projected and joined smoothly
to give the configurations of the ground surface along PQ.
b) Canal alignment- canals have down slope to allow water to flow under gravity.
Therefore, the canal alignment should be below the reservoir level.
c) Contour gradient- on a contour map, the alignment of a proposed road or railway for
given contour gradient can be easily be marked.
d) Intervisibility of points-some time the intervisibility between the two points can be
ascertained by inspection of the area on the map. When the intervening ground does not have
contours of higher value than elevation of the two points, the points will be intervisible.
e) Catchment area or drainage area- is the tract of land which distributes water flow over
the surface of the ground into river or stream at any point. The limits of the catchment area
can be delineated sufficiently accurate on a contour map. The line forming the limits,
separating the catchment area of a river from the rest of the area is called the water shed line.
f) Storage capacity of the reservoir- contour line indicating the full reservoir level (F.R.L)
is drawn on the contour map. The FRL begins and ends at the dam. The volume of water
between this line and the river bed is estimated by measuring the area enclosed by all
contours lying between the river bed and FRL contour.
CHAPTER THREE
3.0 METHODOLOGY
3.1 INTRODUCTION
This chapter basically explains the statistical techniques and methods used in collecting and
presentation of data. The chapter also state the purpose of data collected.
3.1.1Instrumentation
These are instruments and equipment that were used to collect data. These include:
•
Automatic level
•
Levelling staves {2}
•
A linen tape {100 m]
•
Nails
•
Hammer
3.2 LEVELING AND CONTOURING TEAM
These are the people involved in the levelling practice during the execution of this project.
•
Observers
His job was to level the instrument, making the observations and reading them out to the booker.
•
Booker
His job was to book the readings in their respective column.
•
Staff man
Their job was to hold staves at the stations point along the project area.
•
Other staff man
They measured distances using the linen tape. Held either back sight or foresight.
3.3 FIELD WORK
3.3.1 Reconnaissance
Prior to the actual field work, a reconnaissance was conducted to familiarize with the project
area. During the visit an opening TBM1 (temporary bench mark) of Reduced level 1366.540 m
was established at within Kisumu National Polytechnic gate and a closing TBM2 of RL 1370.
295Mm. The nature of the terrain was also inspected to determine the appropriate techniques to
be used during the levelling and contouring process. An area of approximately 120 by 120
meters was identified and pegs were driven at interval of 40 meters at each corner to give a
geometrical figure of a square of size 40 by 40 meters. A total of 9 squares was obtained. The
appropriate route for the levelling process and indivisibility between the stations were considered
for the effective contours lines to be traced, to manage time, the cost of the work and to
minimize the effect of errors that might arise due to physical phenomenal. The figure 1 below
shows how the ground was marked using pegs at each corner as A, B, C, D, E, F, G, H, I, J, K, L,
M, N, O, and P.
3.3.2 Testing of the Instrument [The two peg test]
Before the actual surveying, the geometrical setting of the instruments was tested by the two peg
test method. Two staves were held on two station point apart for the instance A and B. The
instrument was then set up and levelled exactly at the midpoint between the two points. Reading
on both staves were taken and recorded and their differences calculated.
The instrument was moved onto appoint close to one of the staves and the readings of the staves
stations taken. The difference between the two staves readings was again calculated and the two
differences computed to check whether the instrument was out of calibration.
3.3.3 The Actual Survey
During the actual survey process, the following instruments were used in carrying out the
project:
•
A tripod
•
Telescopic staves
•
A tape
•
Scale rule
The levelling network was opened at known reference point i.e. TBM. 1.
At the first instrument, station a back sight-reading on the staff placed on known Benchmark was
taken and a foresight on staff held on a change plate was taken.
The staff readings and distances between the stations readings were recorded on the booking
sheet by the booker. The following procedures were systematically followed in the field during
contouring;
•
A bench mark of known elevation was established.
•
Project area of 50m by 50m near the BM was determined and subdivided into squares
and the elevations of their corners accurately determined by ordinary levelling and noted
down.
•
Contour interval of 2m was chosen
•
The level is set up at any commanding position A and a back sight is taken on the
TBM1.
•
The height of the instrument was calculated and noted down.
•
To locate the contours of a certain value, the staff man is directed to occupy the position
on the ground where the staff reading will be height of instrument minus contour value
to be located on the ground.
•
Mark all the stations on the ground where the staff reading will be equal to computed
staff reading in (IV) above by inserting wooden pegs.
•
Contour interpolations.
3.3.4 Reduction of observation by height of instrument method
Back
sight
1.900
Intersight
Foresight
Height of
instrument
1368. 440
1.233
8.870
1.737
0.475
1369. 702
1.150
1370. 308
1.187
1371. 428
1.063
0.354
1.756
1.560
1.474
1.470
1.457
1.367
2.307
2.106
1.744
1.374
0.936
0.236
0.030
1.144
1.603
A
H
Reduce level
1366. 540
1367. 210
1359. 570
1367. 965
1368. 639
1369. 348
1368. 552
1368.748
1368. 834
1368. 838
1368. 851
1368. 941
1369. 121
1369. 322
1369. 684
1370. 054
1370. 492
1371. 192
1371. 398
1370. 284
1369. 825
B
G
chainages
C
F
Remark
TBM1
A
B
CP1
C
D
CP2
E
F
G
H
I
CP3
J
K
L
M
N
O
P
TBM2
D
E
I
J
P
K
O
L
N
M
3.4 CONTOURS INTERPOLATIONS
Is a process of drawing contours between plotted ground points of known elevations by
proportions assuming uniform elevations by two points or in between plotted contours. It can be
done by one of the following methods;
•
Estimation- the points on the required contour are located by eye judgement or
estimation between points whose elevation are already known. This method is good for
small scale maps and locating contours between two already plotted contours
•
Arithmetic calculation- the positions of points on the required contour between two
points of known elevation is determined by linear interpolations on the basis of
assumption of uniform slope between the two points.
Points A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, and P were the sixteen points of known
elevations as 1367. 210, 1359. 570, 1368. 639, 1369. 348, 1368. 748, 1368. 834, 1368.
838, 1368. 851, 1368. 941, 1369. 322, 1369. 684, 1370. 054, 1370. 492, 1371. 192, 1371.
398 and 1370. 284 meters, respectively with contour interval of 1m. These points lie on
the corner of the four grid of size 40 m by 40 m.
The points of minimum elevation B having elevation of 1359. 570 m and the point of
maximum elevation is O having elevations 1371. 398 m. Therefore, the contour which
will pass over the grid are 1360.000, 1361. 000, 1362. 000, 1363. 000, 1364.000,
1365.000, 1366. 000, 1367. 000, 1368. 000, 1369. 000, 1370. 000, and 1371. 000. The
points are located on the lines AB, BC, CD, DE, EF, FG, GH, HA, GJ, JI, IH, FK, KJ,
EL, LK, LM, MN, NK, NO, OJ, OP and PI as explained below. e.g.
For rectangle ABGHA, interpolation along AB,
Difference of elevation between A and B in a distance of 40 m
1367. 210-1359. 570 m = 7.640 m
Difference in elevation between B and 1360.000 m contour point
1360-1359. 570 = 7. 210
The distance of 1360.000 contour from B= 40× (7. 210÷7.640) =38 m
The 1360.000 m contour will lie on BA at 1AB, 38 m from B.
CHAPTER FOUR
4.0 DATA ANALYSIS
The entire levelling network was done on a radius of 120m by 120m. The reduction of the
observations was done to obtain the reduced level of the corners of plot.
CORNER POINT REDUCED LEVEL
A
1367. 210
B
1359. 570
C
1368. 639
D
1369. 348
E
1368. 748
F
1368. 834
G
1368. 838
H
1368. 851
I
1368. 941
J
1369. 322
K
1369. 684
L
1370. 054
M
1370. 492
N
1371. 192
O
1371. 398
P
1370. 284
4.1 ANALYSIS OF TIME AND ECONOMY
During the fieldwork, it took two days for data collection, one day in fieldwork and two days on
field data reduction and interpolations of contours.
It was therefore noted that contours interpolations are very accurate and economical in providing
vertical control and also cost effective.
4.2 CONCLUSION
The main objective of this project has been achieved with acceptable accuracy.
Interpolations of contours were done at a scale of 1: 500 of the project area as plotted.
This project data is therefore available for the engineer to be used in designing suitable levels for
sewer lines and drainage channels along the project area.
Despite the following challenges experienced during the fieldwork for instance obstruction by
trees branches and Steepness of the ground and sunny weather conditions certain precautions
were taken to overcome them to ensure integrity of the project.
With effective planning, contouring is an effective method of data collection and economical in
terms of labour requirements.
Contouring is also fastest in gradually sloping ground as compared to steep ground due the
difference in the nature of terrain.
4.3 RECOMMENDATIONS
From this contouring project, the following recommendations were perceived to be essential for
future related projects. Contouring is most effective method of topographical survey if carried
out by direct method.
•
Surveyors, umbrella should be used during sunny conditions to overcome the differential
heating of the instrument.
•
Great care should be taken when interpolating contours to avoid joining contour line of
different elevation on the same contour map.
REFERENCES
Surveying sixth edition by A. BANNISTER
Surveying sixth edition by S. RAYMOND
Practical field Surveying and Computation by: ALLAN HOLLYWAY & MAYNESS
Lectures notes
APPENDICES
A sketch of Contour map