This document discusses hydrographic surveying, which involves measuring physical features underwater. It begins by introducing hydrographic surveying and its main applications like nautical charting. It then discusses the preliminary steps, which include reconnaissance of the survey area and establishing horizontal and vertical control points. Next, it describes different methods for taking soundings, such as using sounding poles, lead lines, and fathometers. It also covers equipment like range markers and techniques like sounding by boat and using angles from shore. Finally, it discusses reducing soundings to a common datum and modern instruments like airborne lidar bathymetry and GPS.

1. Submitted by,
Shubham Bathwal
BE/10585/2017
Semester - VI
BIRLA INSTITUTE OF TECHNOLOGY
MESRA
SURVEYING – II CE 6005
HYDROGRAPHIC SURVEY

2. INTRODUCTION
 Hydrographic surveying or bathymetric surveying is the survey of physical features present
underwater. It is the science of measuring all factors beneath water that affect all the marine
activities like dredging, marine constructions, offshore drilling etc.
 Hydrographic surveying is mainly conducted under authority concerns. It is carried out by
means of sensors, sounding or electronic sensor system for shallow water.
The information obtained from hydrographic surveying is required to bring up nautical
charts which involves,
 Available depths
 Natural features of seabed
 Details of the coastline
 Breakwater
 The aids to navigation harbor facility
These survey also take part in necessary data collection relating to construction and
developments of port facilities, such as pier construction. This help in finding the loss in
capacity due to silt and many uncertainties.

3. APPLICATIONS OF HYDROGRAPHIC SURVEYING
• Water Power
• Flood Control
• Sewage Disposal
• Dock and Harbor Engineering
• Irrigation
• River Works
USES OF HYDROGRAPHIC SURVEYING
• Depth of the bed can be determined
• Shore lines can be determined
• Navigation Chart Preparation
• Locating mean sea level
• Scouring, silting and irregularities of the bed can be identified
• Tide measurement
• River and stream discharge measurement
• Massive structures like bridges, dams harbors are planned

4. PRELIMINARY STEPS IN HYDROGRAPHIC SURVEYING
The method starts by locating special control points along the shore line. The
sounding method is employed to determine the depth at various points by means of
stationary boats. Sounding locations can be either made from boat to the control
points or by fixing a point in the boat and taking sounding from the control point.
Before this procedure certain preliminary steps have to be made:
 Reconnaissance
 Locate Horizontal Control
 Locate vertical Control
As every project require a start-up plan to complete it effectively and economically,
reconnaissance has to be undergone. A complete reconnaissance of whole survey area to
choose the best way of performing the survey.
This would facilitate satisfactory completion of the survey in accordance with the
requirements and specifications governing such work. Aerial photographs would help this
study.
RECONNAISSANCE

5. LOCATING HORIZONTAL CONTROL
• For large areas – 2nd or 3rd order triangulation
• For smaller areas – transit tape traverse
• For small detached areas – stadia, graphical, plane table methods
• For long narrow river – traverse on one side
• For width < 1 km – traverse on both sides
Horizontal control surveys coordinate horizontal positional data. These positions can be referenced
by coordinate axes.
The horizontal control is necessary to locate all features of the land and marine in true relative
positions. Hence a series of lines is drawn whose lengths and azimuths are determined by means of
either triangulation or any other methods. The following guidelines may help in selection of the
type of control.
A number of benchmarks are established near the shore lines at close spacing to serve as
vertical control. The benchmarks are used for setting and checking the levels of gauge to which
the soundings refer to.
A vertical control survey determines elevation with respect to sea level. In a vertical control system,
at least two permanent benchmarks should be used, but more may be required depending upon
the needs and complexity of the project.
LOCATING VERTICAL CONTROL

6. SOUNDING IN HYDROGRAPHIC SURVEY
Sounding is the measurement of depth below the water surface. Sounding is most important
for any water body to improve its navigable properties, to know about silting and scouring etc.
The specific need for sounding are
1. Preparation of accurate charts for navigation.
2. Determination of the quantities of material to be dredged.
3. Location of the areas from where the material is to be dredged, and where to be dumped.
4. Obtaining information for the design of breakwaters, wharves, sea-wells, etc.

7. EQUIPMENT FOR SOUNDING
These are required to mark the range lines. A line perpendicular to shore line obtained by
line joining 2 or 3 signals in a straight line constitute the range line along which sounding
has to be performed. To make it visible from considerable distance in the sea it is made
highly conspicuous. Different range lines are distinguished by flags of different colours,
attached to the mast or pole of the signal.
A float made of light wood or air tight vessel which is weighted at bottom kept vertical by
anchoring with guywires are called buoys. In order to accommodate a flag a hole is
drilled. Under water deep, the range lines are marked by shore signals & the buoys.
SHORE SIGNAL AND BUOYS
Buoy

8. SOUNDING EQUIPMENT
 SOUNDING BOAT
 SOUNDING POLE OR ROD
 LEAD LINE
Sounding Equipment

9. A fathometer is an echo-sounding instrument used to determine the depth of oceans
indirectly, It works on the principle of recording time of travel by sound waves. Knowing the
time of travel from a point on the surface of the water to the bottom of the ocean and back,
and the velocity of sound waves, the depth can be calculated.
The fathometer gives truly vertical and accurate depth. It gives continuous profile by
recording the measurements on a drum. The soundings can be made with greater speed.
FATHOMETER
• Most common instruments are theodolite, prismatic compass, and sextant.
• The theodolite and prismatic compass are not suitable for angle measurements from
sounding boats due to instability of rowing boats.
• On the other hand, a sextant has been found to be most suitable for measuring angle
in any plane. Navigators and surveyors measures angles from a sounding boat by
sextant only.
• However, when the observations are made from the shore, theodolite and prismatic
compass are used.
ANGLE MEASURING INSTRUMENTS

10. METHODS OF LOCATING SOUNDINGS IN
HYDROGRAPHIC SURVEYING
The points where the sounding has been made in the water body, are required to be located for
plotting on the drawing sheet.
Depending upon the places of the observation points from where the location are made, the
methods may be classified as:
 Observation from the shore.
 Observation from the sounding boat
 Observation from both the shore and the sounding boat.
Depending upon the of instrument used, methods may be classified as:
• Conning the survey vessel
• Observations with theodolite or sextant
• Theodolite angles and EDM distances from the shore
• Microwave systems

11. SOUNDING BY CONNING THE SURVEY VESSEL
In this method, conning means keeping the boat at known course. This method is
suitable for rivers, open sea up to 5 km off shore. The markers are fixed on the shore
called as ranges along which vessel or boat is run. This method is again sub divided
into two types as follows.
 Location by cross rope
 Location by range and time interval
Location by Cross Rope
In this method, a wire or rope with markings or
tags at known distances is stretched across the
channel. The starting point of rope at the shore
is marked as reference point. Then using boat,
the sounding at different distances of wire are
determined by weighted pole. This method is
more accurate. This is most suitable for rivers,
narrow lakes and for harbors. This is also
suitable for knowing the amount of material
removed by dredging.
Location by Range and Time Interval
In this method, the boat is positioned in
range with two signals provided on the
shore. Then, the boat is rowed at
constant speed and time required to
reach the instant of sounding is
measured which gives the distance of
total point along the range. This method
is more suitable for less width channels
or rivers. It is not so much accurate.

12. BY RANGE AND ONE ANGLE FROM THE SHORE
In this method the shore line is divided by a number of range lines A’A,B’B,C’C, etc. at equal
intervals, and the instrument stations A, B, C etc., and the signal stations A’, B’, C’ etc., are fixed.
When the sounding is taken at a1, which is on the range line AA’, the angle is also observed from B
using a theodolite. Knowing the distance AB the distance Aa1 is calculated
In a similar manner the distances of points on other range lines be determined. The time of all
sounding are recorded. Every tenth sounding is usually located by observing angles and the
intermediate sounds are located by interpolation. The method is quiet convenient and gives
reasonable accuracy
Let AB = BC = CD = d then from the
right angled triangle BAa1,
we have, Aa1= dtanΘ
SOUNDING BY OBSERVATIONS WITH THEODOLITE OR SEXTANT

13. BY TWO ANGLES FROM THE SHORE
 In this method, two instrument stations are fixed
on the shore with proper distance. Two
instruments and two instrument men are
required to do this job. From the two instrument
stations, angular observations are made and a
point is located where sounding is measured.
 This method is used when it is not possible to
keep the sounding boat on a fixed range line or
where the shore topography does not permit
laying out system of intersecting lines. The
instrument stations A and B should be selected in
such a way that they provide good intervisibility
and intersections.
 Let the sounding boat be at P. When the
sounding is taken the boatman gives a signal to
the observers at A and B, and the angles a1 and
a2, are measured. If the distance AB is d, the
distances x and y for P can be computed from
the following equation
 This method gives good result if the angle of
intersection is nearly 90. The disadvantage of the
method is that it requires two instrument.

14. BY ONE ANGLE FROM THE SHORE AND ONE
ANGLE FROM BOAT
 This method also requires two instruments and two men to
operate. The method requires use of a theodolite for
measuring angle from the shore and a sextant for
measuring the angle from the boat. On the shore two
points A and B are selected. Let the point A be the
theodolite station and point B be the shore signal or any
other prominent point. The distance AB is measured, and
let it be d. To locate the sounding point P, the angles a and
B are measured with the theodolite with the sextant at P,
respectively. The coordinates x and y of P are computed
from the following relations

15. • In tidal rivers and oceans, an appropriate safe route is required for navigation of vessels
during low tide. For this a common datum of reduction of soundings, mean low water of
spring tides (M.L.W.S. or L.W.O.S.T) is commonly adopted.
• M.L.W.S. or L.W.O.S.T is the lowest level of water in tidal areas. Since the soundings refer to
existing water level at the time of observations, they are required to be reduced to the
assumed datum, i.e., M.L.W.S.
• This is made possible by taking gauge reading the time of soundings. The tidal gauge
readings are recorded at every 5 minutes. For any sounding between five minutes of time,
gauge readings can be obtained by interpolation.
• The soundings are reduced to M.L.W.S. by applying corrections to the soundings. The
difference of levels between the gauge reading, i.e., actual water level the time of soundings
and M.L.W.S., is the required correction to be applied to the soundings.
REDUCTION OF SOUNDINGS

16. AIRBORNE LIDAR BATHYMETRY (ALB) - It is used to measure water depth
by aircraft equipped with laser ranging system instead of survey vessel with
systems that produce acoustic waves.
The ALB principle is to generally transmit two types of lasers, a green laser and an
infrared laser. The green laser can measure the distance between the aircraft and the
sea bottom, while the infrared laser, which is absorbed by water, measures the distance
between the aircraft and sea surface.
GLOBAL POSITIONING SYSTEM (GPS)
The principle behind GPS positioning is similar to that of radio navigation.
• GPS satellites are equipped with very accurate clocks and the signal transmitter, and
GPS receivers on ship can receive the signal transmitted from GPS satellites.
• The distance between a GPS satellite and a receiver can be determine by timing the
difference between transmitted and receive times.
• The receiver position can be determined by computing the geometric relation
among the multiple GPS satellites and the receiver at the same time.
MODERN INSTRUMENTS

17. THANK YOU!!!