Hydrographic Survey Equipment & Methods Guide

CHAPTER 3 : HYDROGRAPHIC
SURVEY
Prepared By:
Asst. Prof. Pramesh Hada
MSC in Urban Planning
B.E In Civil
Asst. Professor, Civil Engineering Dept.
Nepal Engineering College

CONTENTS
3.1 Introduction, Definition of Basic Terms(pu08)
3.2 Vertical & Horizontal Controls
3.3 Equipment & Methods of
Sounding(pu06,07,09,10,11,14)
3.4 Measurement of Cross-Section
3.5 Measurement of Velocity & Flow (pu07,09)
Er.PrameshHada,Asst.Prof,civil
EngineeringDepartment,nec
3.5 Measurement of Velocity & Flow (pu07,09)
3.6 Instruction on Field Works

3.1 INTRODUCTION, DEFINITION OF BASIC TERMS
HYDROGRAPHY
Branch of science that deals with the
measurement of bodies of water.
Is the branch of applied sciences which
deals with the measurement and
description of the physical features of
oceans, seas, coastal areas, lakes and
rivers, as well as with the prediction of
rivers, as well as with the prediction of
their change over time, for the primary
purpose of safety of navigation and in
support of all other marine activities,
including economic development,
security and defence, scientific research,
and environmental protection.
Is a important tool for hydrologic
studies.

HYDROGRAPHY
Hydrographic surveying deals with the configuration
of the bottom and adjacent land areas of oceans,
lakes, rivers, harbors and other water forms on
Earth.
In strict sense, it is defined merely as the surveying
of a water area; however, in modern usage it may
include a wide variety of other objectives.
- such as measurements of tides, current, gravity, earth
magnetism, and determinations of the physical and
ada,Asst.Prof,civil
artment,nec
magnetism, and determinations of the physical and
chemical properties of water.
The principal objective of most hydrographic surveys,
is to obtain basic data for the compilation of nautical
charts with emphasis on the features that may affect safe
navigation.
Other objectives include acquiring the information
necessary for related marine navigational products and
for coastal zone management, engineering, and science
Er.Pramesh
Engineering

SIGNIFICANCE OF HYDROGRAPHIC SURVEY
PU 2006,2007,2008
The Purpose of hydrographic survey are as follows:
Used for controlling and planning of engineering projects
like bridge,dams,tunnels,reservoirs,harbours etc.
To determine mean sea level and observation of tides.
For the measurement of discharge of rivers.
For the measurement of areas subjected to scour or silting
ada,Asst.Prof,civil
artment,nec
For the measurement of areas subjected to scour or silting
and to ascertain the quantities of degraded material.
For the determination of shore lines.
For making subsequent investigation to secure information
needed for the construction, development & improvement
of port facilities.
Determination of coastal erosion, silting.
Determination of site of construction of harbours,
dockyards.
Er.Pramesh
Engineering

ada,Asst.Prof,civil
artment,nec
Er.Pramesh
Engineering

BASIC TERMS
Sounding : A Measurement of depth of water.
Harbour : A place where ships are parked for cargo
& others.
Reef : A submerged ridge of rock near the surface of
the water
M.S.L (Mean Sea level) : Average of Sea level,
Height according to mean sea level
Height according to mean sea level

3.2 VERTICAL & HORIZONTAL CONTROLS
Vertical control – Depth Calculated (R.l calculated)
Horizontal control – Northing and Easting calculated (X & Y)
The main objective in hydrographic surveying is to determine the
depth of water at a certain point.
Hence Sounding is the measurement of depth below the water
surface.
For Sounding, A vertical control is needed and to locate the
sounding, a horizontal control is needed.
Horizontal control may consist of either a triangulation or a
Horizontal control may consist of either a triangulation or a
traverse. Triangulation may have to be employed for horizontal
connection of widely seperated points.
Traverse may be done by chain,tape, plane tabling or by theodolite,
depending upon the stations.
Hence the underwater & near water points may be located with
reference to the traverse or triangulation.
Vertical connection may be affected by the determination of the
depth of the point below the water surface. Such determinations are
known as “Soundings”.

3.3 EQUIPMENTS NEEDED FOR SOUNDING (IMP)
Sounding Boat
Sounding Poles
Lead lines
Sounding Machine
Eco – Sounding (Fathometer)
Sounding Boat
Used for taking sounding.
Used for taking sounding.
should be sufficiently spacious and stable.
For quiet water. a flat bottom boat is more suitable, but
for rough water round-bottomed boat is more suitable.
For regular soundings, a row boat may be provided with
a well through which soundings are taken.
Should be extended far enough over the side to prevent
the line from striking the boat.

SOUNDING POLES/RODS
Is a pole of a sound straight-grained well
seasoned tough timber usually 5 to 8 cm in
diameter and 5 to 8 metre long.
Suitable for shallow and quiet waters.
An arrow or lead shoe of sufficient weight
is fitted at the end.
Helps in holding them upright in water.
Helps in holding them upright in water.
lead or weight should be of sufficient area
so that it may not sink in mud or sand.
Pole of 6 m can be used to depths upto 4
metres.

LEAD LINES
lead line or a sounding line is usually a length of a
such cord, or a brass chain with a sounding lead
attached to the end.
Due to prolonged use, a line of hemp or cotton is liable
to get stretched.
It should be soaked in water for about one hour before
it is used for taking soundings.
length of the line should be tested frequently with a
tape.
Er.PrameshHada
tape.
For regular sounding. a chain of brass, steel or iron is
preferred.
usually used for depths over about 6 metres.
Sounding lead is a weight (made of lead) attached
to the line.
weight is conical in shape and varies from 4 to 12 kg
depending upon the depth of water and the strength
of the current.
often has cup-shaped cavity at the bottom.
Hada,Asst.Prof,civil
Department,nec

SOUNDING MACHINE
Where much of sounding is to be done, a
sounding machine as very useful.
May either be hand driven or automatic. Fig.
1 shows a typical hand driven Weddele’s
sounding machine.
lead weight is carried at the end of a flexible
wire cord attached to the barrel and can be
lowered at any desired rate, the speed of the
drum being controlled by means of a brake.
drum being controlled by means of a brake.
Readings are indicated in two dials — the
outer dial showing the depth in feet and the
inner showing tenths of a foot.
Handle is used to raise the level which can be
suspended at any height.
Is mounted in a sounding boat and can be
used up to a maximum depth of 100 ft.

ECO – SOUNDING (FATHOMETER) (V.V.IMP)
Echo sounder is used for measuring depths of
large rivers, in excess of 10 m, and those of
seas.
Eco sounding is a technique of using sound
pulse to find the depth of water.
Is an electrical instrument, in which a sound
impulse from the surface of water is Sent
towards the bottom of the river or sea (Fig.
13.8).
Sound waves are reflected back From the
bed in the form of an echo which is arrested
Sound waves are reflected back From the
bed in the form of an echo which is arrested
by the receiver.
There is an automatic recording of the time
of onward and backward travel of the sound
wave.
Taking the velocity of sound in water to be
approximately 1470 m/s, the depth of water
can be computed.
Generally the echo sounder is placed just at
the water level to eliminate transmission loss
and obtain an accurate result.

ECO – SOUNDING (FATHOMETER)
Uses for Ocean sounding where depth is too
much.
It is adjusted to read depth in accordance with
the velocity of sound in the type of water in
which it is being used.
For Eco sounding Instrument called
“Fathometer” is used.
A fathometer may indicate the depth visually
or indicate graphically on a roll which
or indicate graphically on a roll which
continuously goes on revolving and provide a
virtual of the lake or sea.
The main parts of echo-sounding apparatus
are :
1. Transmitting and receiving oscillator.
2. Recorder Unit
3. Transmitter/Power unit

PRINCIPLE OF ECO SOUNDING
•Fig Below illustrates, the principle of
echo sounding.
•Consists in recording the interval of
time between the emission of a sound
impulse direct to the bottom of the sea
and the reception of the wave or echo
reflected from the bottom.
•If the speed of sound in that water is V
and time interval between the
and time interval between the
transmitter and receiver is t, then the
depth is given by , h = 1/2(Vt)
•Velocity varies with salinity & temp. of
sea water, so accoustic velocity in sea
water is -
S – in terms of per 1000.

ADVANTAGES OF ECO SOUNDING
It has the following advantages over the older method of lead
line and rod :
Used when a strong current is running and when the
weather is unsuitable for the soundings to be taken with the
lead line & other methods.
Is more accurate as a truly vertical sounding is obtained.
Under normal water conditions in ports and harbours an
accuracy of 7.5 cm may be obtained.
accuracy of 7.5 cm may be obtained.
Is more sensitive than the lead line.
Record of the depth is plotted immediately and provides a
continuous record of the bottom as the vessel moves forward.
Speed of sounding and plotting is increased.
Error due to estimation of water level in a choppy
sea(irregular) is reduced owing to the instability of the boat.

Er.PrameshHada
Shorelines are where oceans and seas meet land.
The change is abrupt and sudden.
Department,nec

METHODS OF LOCATING SOUNDING
Soundings are located with reference to the shore traverse
by observations made
(I) entirely from the boat, (ii) entirely from the shore or (iii)
from both,
The following are the methods of location
1. By cross rope
2. By range and time intervals
2. By range and time intervals
3. By range and one angle from the shore
4. By range and one angle from the boat
5. By two angles from the shore
6. By two angles from the boat
7. By one angle from shore and one from boat
8. By Intersecting ranges
9. By tacheometric Observation

1. Location by Cross Rope
most accurate method of locating the soundings and may be used for
rivers, narrow lakes and for harbors.
Used to determine the quantity of materials removed by dredging,
the soundings being taken before and after the dredging work is
done. (dredging - Remove with a power shovel, usually from a bottom of a body of
water)
Single wire or rope is stretched across the channel and is marked by
metal tags at appropriate known distance along the wire from a
reference point or zero station on shore.
Er.PrameshHada,A
EngineeringDepartm
Methods of Locating Sounding
reference point or zero station on shore.
The soundings are then taken by a weighted pole.
The position of the pole during a Sounding is given by the
graduated rope or line.
,Asst.Prof,civil
rtment,nec

2) Location by range and time interval :
Method used when the width of channel is small and when
great degree of accuracy is not required.
In this method, boat is kept in range with the two signals on
the shore and is rowed along it at constant speed.
soundings are taken at different time intervals, knowing the
constant speed and the total time elapsed at the instant of
sounding.
Distance of the total point can be known along the range.
3. By range and one angle from the shore
Boat is ranged in line with the two shore signals and rowed
along the ranges.
Point where sounding is taken is fixed on the range by
observation of the angle from the shore.
As the boat proceeds along the shore, other soundings are
also fixed by the observation of angles from the shore.
contd……..

•Let “B” is the instrument station, A1-A2 is the
range along which the boat is rowed and α1, α2, α3
etc. are the angles measured at B to points 1, 2, 3
etc.
•This method is very accurate and very convenient
for plotting.
•If the angle at the sounding point is less than 30°,
a new instrument station must be chosen.
By range and one angle from the shore
a new instrument station must be chosen.
•After first and last soundings & every tenth
soundings are fixed by angular observations and
intermediate points are fixed by time interval.

4. Location by range and one angle
from the boat
Is similar to the previous one except that the
angular fix is made by angular observation from
the boat.
Boat is kept in range with the two shore signals
and is rowed along it.
At the instant the sounding is taken, the angle
subtended at the point between the range and
some prominent point B on the shore is
measured.
some prominent point B on the shore is
measured.
This method has the following advantages :
Since all the observations are taken from the boat,
the surveyor has better control over the operations.
Mistakes are reduced since the recorder books the
readings directly.
On important fixes, check may be obtained by
measuring a second angle towards some other signal
on the shore.
To obtain good intersections throughout, different
shore objects may be used for reference to measure
the angles.

5) Location by two angles from the shore
In this method, a point is fixed independent of the
range by angular observations from two points on
the shore.
Used to locate some isolated points.
Two instruments & two surveyor are required &
instrument is selected with accuracy.
If A & B are two instrument station and ‘d’ is
measured accurately.
Instrument stations A and B are precisely connected
to the ground and their positions on plan are known.
to the ground and their positions on plan are known.
Surveyor on the boat holds a flag for a few seconds,
and on the fall of the flag the sounding and the
angles are observed Simultaneously.
co-ordinates of the position P of the sounding may be
computed from the relations :
Method has the following advantages
Preliminary work of setting out and erecting range
signals is eliminated..
Suitable for strong current of water due to which it
is difficult to row the boat a1on the range line.

6. LOCATION BY TWO ANGLES FROM THE BOAT
In this method, the position of the boat can be
located by the solution of the three-point
problem by observing the two angles
subtended at the boat by three suitable shore
objects of known position.
Three-shore points should be well-defined and
clearly visible.
Prominent natural objects such as church
spire, lighthouse, flagstaff, buoys etc. are
selected for this purpose.
spire, lighthouse, flagstaff, buoys etc. are
selected for this purpose.
Let A, B and C are the shore objects and P is
the position of the boat from which the angles
α and β are measured.
Both the angles should be observed
simultaneously with the help of two sextants,
at the instant the sounding is taken.
The method is used to take the soundings at
isolated points.

7. Location by one angle from shore and
one from boat
This method is used to locate the isolated
points where soundings are taken.
Let two points A and B are chosen on the
shore, one of the points (say A) is the
instrument station where a theodolite is set
up, and the other (say B) is a shore signal or
any other prominent object.
any other prominent object.
Sounding is taken at P, the angle α at A is
measured with a theodolite while the angle β
at the boat is measured with the help of a
sextant.
Knowing distance d between the two points A
and B by ground survey, the position of P can
be located by calculating the two co-ordinates
x and y.

8. Location by Intersecting Ranges
Method is used when it is required to
determine by periodical sounding at the
same points, the rate at which silting or
scouring is taking place.
This is very essential on the harbors
and reservoirs.
The position of sounding is located by
The position of sounding is located by
the intersection of two ranges, thus
completely avoiding the angular
observations.
Suitable signals are erected at the shore.
The boat is rowed along a range
perpendicular to the shore and
soundings are taken at the points in
which inclined ranges intersect the
range.

9. Location by Tacheometric Observations
Method is very much useful in smooth
waters.
Position of the boat is located by
tachometric observations from the shore
on a staff kept vertically on the boat.
Observing the staff intercepts at the
instant the sounding is taken, the
horizontal distance between the
horizontal distance between the
instrument stations and the boat is
calculated by :
Direction of the boat (P) is established by
observing the angle (α) at the instrument
station B with reference to any prominent
object A.

3.4 MEASUREMENT OF CROSS-SECTION
Case I – When the River is small
Two poles are fixed on both banks of the river & a rope is
stretched between them.
The water width of the river is divided into several
compartments of equal width (say b) and the points are
marked by hanging tags or pendants.
Depth of water corresponding to each pendant is measured
by a sounding rod or sounding cable.
Let the depths of water be d0,d1,d2…..Considering the end
compartments as traing1es and other compartments as
compartments as traing1es and other compartments as
trapeziums, the area is calculated as follows.

CASE II – WHEN THE AREA IS LARGE
Two centre line AB is taken perpendicular to
the river.
Two stout pegs T1,T2 are fixed on AB.
Then following procedure is adopted:
1. At station A, a theodolite is set up and the
line is ranged properly. The width of the
river is measured by stadia method.
2. The width is divided into equal parts, and
the widths of these compartments are fixed.
Thus the distances AP1, P1P2, P2P3,... are
fixed.
3. Another theodolite is set up at C, so that
3. Another theodolite is set up at C, so that
AC is perpendicular to AB. The distance AC
is measured (say it is equal to D).
4. Then the angles ( α1, α2… are calculated,
in the following manner.
5. The calculated angles α1, α2, ... arc set out from the theodolite at C.
Thus, the line of sight of the theodolite at A and that of the theodolite at C
coincide at the points P1, P2, P3, ... which are the points along the cross
section where soundings are to be taken.
6. The depths of water at these points arc measured by a sounding cable or
echo—sounder mounted on a boat.
7. Then the cross—sectional area of the water section is calculated in the
usual manner.

MEASUREMENT OF VELOCITY
Measurement of velocity is an important aspect of many direct
stream flow measurement techniques.
Different methods used for the measurement of velocity:
1. Surface float method
2. Sub-surface float method
3. Velocity rod method
4. Pitot tube method
5. Current meter method
1. Surface float method
Surface floats are made of cork. and can easily float on water.
Are generally in the form of 10 cm cubes.
The floats are painted red or white and have a small flag
attached on top [Fig. (a)].
(cork –cap or Outer bark of the cork oak; used for stoppers for bottles etc)

1. SURFACE FLOAT METHOD
Velocity is measured in the following way:
(a) At the discharge site, a rope is stretched
between two poles fixed on both banks of
the river and the water section is divide d
into several compartments by hanging tags
from a rope [Fig. 13.9(b)].
b)velocity of each compartment is
measured by the float, which is released
slightly ahead of C/S-1. When the float
just crosses the section, the stop watch is
just crosses the section, the stop watch is
started. When it just crosses C/S-2, the
stopwatch is closed. The time taken by
the float to cover the ‘run’ (known
distance) is noted, and from this the
velocity is calculated [Fig. I3.9(c)j.

2. SUB-SURFACE FLOAT METHOD
Sub-surface float is a hollow cylinder which is attached
by a cord to a surface float.
Position of the sub-surface float is adjusted according to
the depth of the river. Generally, it is kept 0.2D meters
above the bottom.
In this case, the measured velocity is equal to the mean
velocity.
The procedure of measurement is the same as that in the
The procedure of measurement is the same as that in the
surface float method (Fig. 13.10). Here, D is the depth of
water.

3. VELOCITY ROD METHOD
Er.PrameshHada
Velocity rod made of hollow metal or wood. Its
diameter is about 2.5 to 5 cm.
Weight provided at the bottom of the rod to keep it
vertical. length of the rod is adjustable.
Rod is generally submerged to the extent of O.6D.
The procedure of measurement is exactly similar to
that in the surface float method (Fig. 13.11).
Department,nec
that in the surface float method (Fig. 13.11).

4. THE PITOT TUBE
Pitot tube is a glass tube bent at an
angle of 90° at the lower end.
Upper end is open and kept above the
water level. The lower end is in the
form of a nozzle, and is directed
upstream.
Due to the velocity of water, the
water column rises in the right limb
(Fig. 13.12). Let the rise in water
Er.PrameshHada
(Fig. 13.12). Let the rise in water
level be h. Then applying Bernoulli’s
theorem between points A and B.
Measuring the rise of water column
the velocity can be calculated.
Department,nec

5. CURRENT METER METHOD
Commonly used for measuring the velocity of water.
It consists of the following components.
(a) A tail which keeps the meter in the direction of
alignment,
(b) A system of conical buckets fitted to a spindle
which rotates due to current,
(c) A counterweight which keeps the meter vertical,
and
(d) A headphone for registering the sound produced
by the spindle at every revolution.
Current meter is lowered to a depth of 0.6 D (DCurrent meter is lowered to a depth of 0.6 D (D
being the depth of water) by a suspension cable.
Conical buckets is kept on the upstream side and
the tail on the downstream side.
Due to the velocity of water, the system of conical
buckets rotates about the spindle and a ‘tick’ sound
is emitted once for every revolution. Thus, a
continuous “tick-tick” sound is heard through the
headphone. The number of revolutions per minute
15 counted with the help of a stopwatch.
velocity can be ascertained from the rating table
(supplied by the manufacturer with the meter). This
velocity gives the mean velocity of flow.

Current meter Method

Different structures like notch,weirs,sluice gates are used for
measuring flow or discharge.
Notch – device used for measuring the rate of flow of liquid
through a small channel or a tank.
Weir – concrete or masonary structure placed in an open channel
over which the flow occurs.
A/c to the shape of the opening, it is classified as:
Rectangular weir or notch
3.4 Measurement of Flow
Rectangular weir or notch
Triangular weir or notch
Trapezoidal weir or notch
Broad crested weir
Discharge over a Rectangular weir or notch
Discharge through a Triangular weir or notch
Discharge through a Trapezoidal weir or notch
Discharge through a Broad crested weir

Discharge through a Triangular or V-notch
dh
h

Discharge through a Trapezoidal notch or weir

Discharge through a Broad - Crested weir

TUTORIAL 1 – HYDROGRAPHIC SURVEY(IMP PU QUESTIONS)
What is Sounding? Explain two most accurate methods of locating sounding
Position. (7)
What is the significance of underwater mapping in hydrographic survey?
Explain Rectangular weir & V-notch methods to find the volume of water in
the river?(8)
Write the purposes of hydrographic survey & Explain the methods of locating
sounding positions.(9)
Explain the terms i)Sounding ii)Echo-sounding iii)sextant (6)
Explain various methods used in the measurement of flow.(6)
Er.PrameshHada
Explain various methods used in the measurement of flow.(6)
What is Echo sounding? Enlist the advantages of Echo Sounding.(7)
What is Sounding ? Explain any three methods of sounding.(7)
Define hydrographic survey. Write the purpose of hydrographic survey . (8)
How do you find the discharge of a river in Hydrographic survey. Describe at
least two methods.(8)
What is Eco-sounding? How it measures the depth of water bodies?
Discuss. (7)
Department,nec

Hydrographic Survey Equipment & Methods Guide

Hydrographic Survey Equipment & Methods Guide

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