Lesson Note On Hydrographic Surveying

Hydrographic Surveying
	Definition: It is the branch of surveying which deals with any body of still or running water such as a lake, harbor, stream or river. Hydrographic surveys are used to define shore line and under water features. Objects of Hydrographic Surveying: Hydrographic surveying are carried out for one or more of the following activities. Measurement of tides for sea coast work E.g. construction of sea defense works, harbors etc, for the establishment of leveling datam and for reducing sounding. Determination of bed depth, by soundings For navigation Location of rocks, sand bars, navigation light. Fro location of under water works volumes of under water excavation etc. In connection with irrigation and land drainage schemes.
Determination of direction of current in connection with The location of sewer any pipe or channel that carry waste water out falls.   Determination of area subject to silt and seour the eating of the place. Fornication purposes. Measuremenment of quantity of water and flow of water in connection of water schemes, Power scheme and flood controls. Why we need Hydrographic Surveys - Uses & Applications of Hydrographic Survey Offshore engineering and the shipping industry have continued to expand. Drilling rigs (extracting oil, gas etc from deep sea) locating up to 125miles offshore, search for resources particularly oil and gas. Offshore islands are constructed of dredged material (to bring material form some where and dump there) to support marine structure. Harbor depth up to 80 is required to accommodate larger ships and tankers. Containerization has become an efficient and preferred method of cargo handling. The demand for recreational transportation ranges form large pleasure cruise ships to small sail bonds. Cruise ships to small sail bonds. Hydrographic surveys are made to a quire and present data on oceans, lakes and harbors. It comprises all surveys made for The determination of shore lines, soundings (measurement of depth below the water level) characteristics of bottoms, areas subjected to Suring and silting, depth available for navigation and velocity as well as characteristics of flow of water. The location of lights rocks sand balls, buoys ( anything that floats on the surface of water) Establishing Horizontal and Vertical Controls (Click Here) The first step in making a hydrographic survey is to control both horizontal and vertical. Horizontal Controls: In an extensive survey, the primary horizontal control is established primarily by running theodolite and tape traverse before the triangulation station. Tthe traverse lines being run to following the shore lines approximately. In survey of less extent the primary horizontal control only is required and is established by running a theodolite and tape traverse sufficiently close to shore line. For rough work, the control may be established by running a theodolite and staid traverse or plane table trader. Vertical Controls: These are based upon a series of bench marks established near the shore line by spirit leveling and these serve for setting and checking tide gages etc to which the sounding are referred. River Surveying The survey of the shore line of a river is made by running a theologize and tape traverse on a shore at a convenient distance form the edge of the water. If the river is narrow, a single theologize and tape traverse is on one bank and both banks. Located by staid or plane table methods. Sounding Surveying The measurements of depths below the water surface is called Sounding. The object of making soundings is to determine the configuration of the bottom of the body of water. This is done by measuring form the boat, the depth of water at various points