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It is the branch of surveying which deals with waterbodies e.g. Lake, river etc

The usual fundamental principles of surveying and leveling are adopted for acquiring data for determination of :

PURPOSE OF HYDROGRAPHIC SURVEYING

WHAT IS HYDROGRAPHY

WHAT IS SOUNDING

the process of making measurements in streams and rivers for the purpose of predicting the rate of discharge at various water levels or stages

the process of measuring the depth of a body of water at a particular point.

the process of measuring the depth of a body of water at a particular point.

a map or chart used in navigation. It is basically similar to topographic map except that water depths, navigational markers, and the character of underwater surface are indicated.

are specific tide levels which are used as surfaces of reference for depth measurements in the sea and as a base for the determination of elevation on land

the volume of water flowing past a section of a stream, canal, flume, and other waterways. It is usually expressed in cubic feet per second or cubic meters per second.

a current or steady flow of water running along the earth’s surface.

the process of scooping or sucking up mud, sand, rocks and other materials underwater for the purpose of enlarging, deepening or clearing channels, harbors, rivers, and other bodies of water.

an imaginary line on the surface of the earth found underwater, all points of which are of the same elevation. They are sometimes known as depth curves or bathymetric contour

various types are used for hydrographic surveys. These includes rowboats, motor launches, and small vessels.

a graduated and rounded piece of lumber, about 3 meters long, used for taking soundings. It is suitable for use where the water depth does not exceed 2 ½ meters.

a leadline or sounding line is usually a length of sash or hemp cord, braided flax, or nylon cord, with sounding lead attached to one end

a simple device in which piano or stranded wire is used and wound on areel mounted on a stand

a measuring device which automatically records soundings taken on a moving vessel

signal are constructed In a variety of ways but they should be seen and easily distinguished from each other.

are instruments for measuring the height of the tide (non-recording gages & automatic or self registering gages)

a portable device and hand-held instrument used for measuring horizontal and vertical angels.

the half-daily cycle of rhythmic rise and fall of the surface of oceans, seas, lakes, bays, rivers, and other bodies of water connected with them due to the gravitational attraction of the sun and moon acting upon the rotating earth

GIVE THE 6 HYDROGRAPHIC SURVEY

the horizontal movement of water accompanying tides and which is produced by the combined action of astronomical, hydrological, and meteorological factors.

the period within which the water surface is rising and moving toward the shore.

the period within which the water surface is falling and moving seaward.

the instant at which the tidal current is changing direction and flows neither in or out.

refers to the direction of current flow

refers to the speed of current flow

refers to the maximum height to which the water surface rises above the standard datum plane during a given period. It is also known as “HIGH TIDE”.

or “LOW TIDE” refers to the greatest depression of the water surface below the standard datum plane during a given period. Tide Range – the difference between the high and low tide at a certain location on a given

consist of an idealized average period of 24 hours and 50 minutes between the occurrence of two successive high tides of the same type at the same location.

is the period around which the greatest peak or depression of the tides is reached and during which any change in height of the tide is scarcely noticeable

consist of a large head or front of water generated at the surface of the ocean by force winds of hurricanes or typhoons, or by isostatic adjustment of the ocean floor accompanying a submarine earthquake

Are specific tide levels which are used as surfaces of reference for depth measurements in the sea and as a base for the determination of elevation on land. The height of these surfaces will depend on local conditions and therefore it cannot be transferred from some other locality by levels or computed from geodetic mean sea level

are those characterized by two high and two low waters each tidal day

are those which, in the long run, display but one high and low water each day.

a type of tide which has two high waters and has two low water each day

These are used to determine the exact water surface level ➢ The movement of tides during the time soundings are made. ➢ The gauges are read at regular intervals, varying from 10m to 30 min

Simplest type of gauge. ➢ It consists of a graduated board, 150 to 250 mm wide and 100 mm thick, fixed in vertical position

➢ The float gauge is designed to overcome the difficulty in reading a staff gauge when the intensity of tides is high and the variations of water level is more. ➢ It consists of a float to which a graduated vertical staff is attached.

The weight gauge consists a weight attached to brass chain or wire. ➢ The chain passes over a pulley, and is laid horizontal along the side of a graduated scale. ➢ The weight is lowered to touch the water surface, and the reading is taken on the graduated scale against an index attached to the chain

Weight gauges

When locating sounding for a hydrographic survey, the composition of the boat party will depend upon the survey method used. Usually the following personnel will form the boat party

Person who directs all survey operation of the party, he is responsible for the accurate gathering of the required survey data which will be needed in the preparation and compilation of the hydrographic chart.

Person who is responsible for setting up the different instruments to be used in hydrographic survey

Person whose task us to record all the survey data gathered

Handles the leadline or the sounding rod, he also serves as a lookout

Responsible for steering the boat on selected compass bearing or ranges

In waters where there are expected dangers to navigation a lookout is employed. He is stationed at the most suitable elevated position in the boat. He should report all possible hazards so that proper action can be taken

Person who alerts the shore party that sounding is about to begin. He is equipped with a set of colored flag

In deep water surveys where a fathometer is employed, the attendant focus full attention on this instrument.

Are well-defined lines on courses whose position are known and along which sounding are taken.

Buoy is a floating object anchored in place in a body of water by a heavy weight to which buoy is attached by a rope or chain.

Is generally used when the required accuracy of the survey is not high. This Method is simple and economical to undertake.

Is Commonly used on small lakes or range lines extend only to relatively short distances towards the water from the shore area

The fixed range lines are located on shore and so laid out to intersect at approximately right angles. Signals are used to mark each range line. The boar proceeds to the intersection of any two range lines and sounding are taken.

Is performed in a manner similar to that of stadia surveying. It is convenient for surveys of small bodies of water.

A common method of locating sounding is to direction to the boat simultaneously from to instrument station. This method is adapted when it is difficult to establish range signals on shore

In order that the position of the boat used in sounding could be located and plotted on a map, to angles need to be simultaneously observed from the boat to three fixed points on shore. This method of locating sounding is an application of the three point problem

Locating sounding by stretching a graduated wire or cross rope across a narrow stream is

A convenient method of locating sounding where there is a cliff or high bluff is by observing vertical (depression) angles with a transit or a theodolite. ➢ This method, which is also known as the "Norwegian Method" is particularly useful when the instrument used can be set up at stations having a commanding view of the lake

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Different in elevation between the horizontal axis of the instrument and the target sighted on the boat

Height of the instrument

Horizontal distance from the instrument to the boat.

Designed to measure the time of transit or difference in transit times of electromagnetic waves in the atmosphere. ➢ A typical system consists essentially of transmitting on a fixed frequency, an unmodulated radio wave from the ship to the three triangulation stations of known position. ➢ Requires a relay unit on shore which must be equipped with a transmitter, receiver and an amplifier

➢ Originally developed for blind bombing by military aircraft and aerial photographic reconnaissance. ➢ Usually employed when a rapid determination of position is required even under adverse weather conditions. ➢ Widely used now often in most offshore measurements and in establishing triangulation stations for horizontal control networks. ➢ range of from about 80 to 120 kilometers depending largely on the height of antennas used

Principle employed is similar to Shoran except for the use and transmission of high pules of electromagnetic energy. ➢ High frequency waves are employed in the Loran method since these waves allow the measurement of greater distances.

➢ Combines some of the principles and techniques used in long-range and shortrange navigation. ➢ US Coast and Geodetic Surveys developed this system in order to increase the measuring capability of the two systems developed earlier while still maintaining a comparable degree of accuracy

➢ Another method of control used in hydrographic surveying used to determine the position of a survey vessel. ➢ It's functional during night

➢ Method of measuring the depth of water by determining the time required for sound waves to travel from a point near the surface of the water to the bottom and back

➢ Mounted on a small boat or suspended over the side. ➢ Operated by dry batteries and can be easily shifted from one boat to another. ➢ Read by means of a meter or a scale since they do not have the capability to move and mark a paper strip.

WHAT IS TWO TYPES OF ECHO SOUNDERS

➢ Considered part of the navigation equipment of the sounding vessel or survey ➢ Designed to measure sounding to depths of over 60 meters to an accuracy of about ½ centimeter. ➢ These fathometers are very sensitive and have the capability to record reflections from layers of different density. ➢ Depths up to about 60 meters can be determined by use of portable fathometers

CONDITIONS INFLUENCING ECHO SOUNDINGS

➢ Recently copied by echo sounders to provide an intermediate printout of sounding depths and their related positions.

➢ Developed to allow interpolation between plotted depths and plotters are utilized to draw the depth (bathymetric) contours automatically just as in automated plotting for topographic surveys.

➢ Employs lasers, offers high accuracies but is applicable only to depths less than 50m,

➢ Soon expected to replace conventional hydrographic survey methods performed on board sounding vessels.

➢ An air bome lasers system. a pulse type laser is used to emit a burst of light which is reflected at the water surface and at the bottom of the body of water

➢ Allow remote measurements of water depths. •Systems are based on the principle that less energy is returned from deep waters than from shallow waters, calibration of such a system is done by comparing returned energy with known water depths.

➢ Another type of airborne hydrographic system being developed, in this method, an aerial camera is used to photograph the water areas using standard techniques of photogrammetry. Natural color film is used in photography. ➢ Has been found to be accurate in locating depths up to 20m in clear water.

➢ The interpretation of multispectral imagery is primarily based on the tones of the objects viewed. Depending upon the spectral reflectance of the object, tone varies with the wavelength. Any surface that reflects strongly in a certain band of the spectrum is said to have a high response in that band.

Launched by the United States of America in ____________________ into a sun-synchronous orbit around the Earth at an altitude of ____________.

__________________ observatory weighing _____________ which circled the Earth the Earth _________________________

The spacecraft was equipped with a multispectral scanner which had the capability to view a __________ of the Earth's surface on an ___________________.

In ___________, it was decided to rename ERTS to __________________.

Four bands of the spectrum-________, _________ and ____________.

_______________- unit used in remote sensing to express the wavelength of an electromagnetic spectrum.

➢ Wavelengths range from 500-600nm. ➢ Water is quite transparent in this band and it tends to enhance features such as sediment with water.

➢ Wavelengths ranges from 600-700nm. ➢ Show good contrast between natural surface cover and man-made structures. ➢ Artificial structures appear very bright against the dark appearance of vegetation

➢ method of taking leadline sounding at cettain interval will usually give a satinfuctorul representation of the shape of the bottom of a body of water which is uniporm and without abrupt changes

➢ this device congist of a horizontal bottom wire of suitable length which may be set at any deaited depth it in used to locate under water water obstraction. The" wire 19 supported at regular intervals by adjustable upright cables which are suspended from qurface buoys.

➢ The length of the vertical cables supporting the bottom wite cannot be adjusted, and these cables are positioned much farther apart. Alau imo intermediate ploata are Faatened to the write such as that there are no provision for representing the sag of the wire between cables.

➢ is to determine minimum clear depths. They locate obstruction and navigation danger in confine areas such ag shwals. rock pinnades, refers, or wreck. The sweep bar is a heavy section. of tail road, steel pipe, or a atructural ateel section. it is held by two vertical calde.

➢ Dredring in the process of widening, enlarging, cleaning or deepening of channel in harborn, rivers and canals.

➢ use when the excavation material are loaded into rows which are towed to a deep water dumping aite.

➢ pumps the material to low lying areas ashore where it is ble al fill auch as in reclamation projects

➢ an a process, ig used to tomove the deposita percolated underwater for the purpose of elearing the water pathway for ship to pass to create bridges, dy leg and damne

➢ dredging process mainly involves carrying out excavation of either naturally. deposited sediment of manmade deleria such as rocks.

OLDEST KNOWN DREGING ACTIVITIES

AKA. Clamshell dredger a stationary dredger which has a grab an a dredging tool.

Excavation, transportation of excavated material and then usage or proper disposal of dredged material

In __________ increase in trade at seas necessitated the development of some bed scratcher such as _______________, which was a primitive bed leveller

__________ were developed around _________, these were a sort of dredging equipment which was primarily employed for digging in ports. Mills had a rotating chain connected with wooden boards, these wooden boards dig up the mud.

In _______ there came a revolutionary development with the evolution of the design of suction dredger by a French engineer. He used successfully this suction dredger in dredging the _________. From then on, dredging by suction became more and more common.

➢ is the process which sediments are picked up using mechanical tools such as bucket, grabs etc.

➢ in this process of removing sediment from the dreged site by using pumps usually centrifugal pumps. sucked into pipe used to transport the sediments

ADVANTAGES OF DREDGING

➢ Reduces capital cost ➢ Safe and efficient ➢ Reduces use of equipment and transportation ➢ Hydrodynamic Dredging ➢ reduces energy and emissions compared to mechanical dredging process

BUCKET DREDGERS

➢ AKA. FIXED ARM DREDGER it's a stationary dredger which usually mounted on a barge of

➢ It is a stationary dredger normally used for mining sand. The suction pipe of this dredger is inserted into the sand deposit and water jets are used to bring the sand up from the excavation site. The sediment can be pumped by sucking the sediments into the pipeline and transferring it to the reclamation site or loaded into barges, depending upon the location and available transfer arrangement.

➢ It is another stationary dredger with a cutter head as a dredging equipment to loosen the base which is to be dredged. Similar to the suction dredger, the sediments are sucked and pumped via a pipeline ashore or into barges. The cutter head can be of different designs and materials, depending upon the properties of the surface to be dredged

➢ This is a self-propelled ship carrying the dredger equipment having a hold or hopper arrangement to fill it with excavated material while following a pre-set dredging operation. This type of dredger has an arrangement to open the bottom of the hold to unload the dredged material into the designated site. This kind of dredger is mainly used in open water such as canals, rivers, estuaries etc

➢ This is actually an assisting equipment in the dredging operation and not a dredger itself. It is used to empty the hopper barges sediments using suction pipe which can be lowered in the hopper barge hold. Additional

➢ These ships have the unique constructional feature of working out of the water surface using long legs as their base. They can be equipped with grabs, buckets or a shovel installation

➢ This dredger uses high pressure air jets instead of water jets for material flow at the mouth of the suction pipe.

➢ This type is used to level the bed surface which has recently been dredged. It consists of a long flat blade or heavy bar which is connected to a tugboat at the end and when it is pulled, it will level the surface on the dredged surface over short distances.

➢ The quantity of material dredged from anybody of water can be determined either by sounding or scow measurements. Depth measurement are obtained before and after when soundings are used. The spacing of the soundings will depend upon the smoothness or irregularity of the bottom and upon the difficulty of excavating material. Soundings taken in tidal waters or in rivers at different stages of the stream must be reduced to a common datum

➢ The constructions of dams and reservoir require extensive topographic and hydrographic surveys. Dams are barriers which are built to hold back or impound water. The impounded water forms an artificial lake or pond, called reservoir, in which water is collected and stored usually for purpose of irrigation, water supply, and hydroelectric power production wand transmission.

➢ The involvement of a civil engineer during the early stages in the planning and development of ports, wharves harbors, and other marine structure is highly essential. His task usually includes the preparation of plans and design, supervision of all new marine construction, the execution of related hydrographic survey, and the subsequent maintenance of existing marine structure.

Reasons if the discrepancy is unreasonably large: