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Comprehensive Guide to Hydrographic Surveying Credits: 5 PDH

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Comprehensive Guide to Hydrographic Surveying Credits: 5 PDH Comprehensive Guide to Hydrographic Surveying Credits: 5 PDH Course Description Hydrography is the science of measuring and describing the topographical features and the entire aquatic environment as a whole, beneath the surface of water bodies. These subsurface features affect bridge scour, flood mitigation, erosion control and siltation transport, maritime navigation, marine construction, dredging, offshore oil exploration and offshore oil drilling, among many other activities. Hydrographic surveying does not strictly apply to coastal and oceanic regions of the US. Hydrographic surveying has many applications inland. Many environmental and civil engineering project in and around bodies and channels of water (streams and rivers, lakes and ponds, wetlands) can all benefit from hydrographic surveys and analysis. Topics Intro and overview of hydrographic surveying History and early methods of measurement Sounding poles, lead lines, wire drags Echo sounders and fathometers Agencies which perform hydrographic surveys: office of coast survey, NOAA, USGS, COE, IHO, NOO Marine magnetometry DC resistivity imaging Radar altimetry GPR for marine applications SONAR devices: side scan, single beam, multi beam sonar Light Pulse (LIDAR) devices US maritime limits and boundaries Sources of existing bathymetric datasets Types of tidal datums (sounding and chart) and tidal cycles Online-PDH 1265 San Juan Dr. AUV, ROV and UAS technologies Merritt island, FL 32952 Crowdsourced bathymetric surveying Fisheries acoustics Original Courseware by: Donald W. Parnell, PE All rights reserved Chapter 1: Introduction Hydrographic Surveys for Safe Navigation There are numerous reasons to conduct a hydrographic survey, but the most common Page 1: Hydrographic Surveying objective is for compiling nautical data along What is Hydrography? navigational channels, with an emphasis on the Hydrography is a branch of physical oceanography measurement and profiling of the subsurface or applied science which deals with the measuring physical features that may affect safe navigation and description of the configuration of the bottoms and travel by marine vessels. and adjacent land areas of oceans, lakes, rivers, harbors, and other water forms. What are Hydrographic Surveys? A hydrographic survey deals with measuring and description of features of a water area and the bed configuration; however, it may also encompass a wide variety of other objectives such as the measuring of tides, currents, gravity, Earth magnetism, and for determining the physical and chemical properties of water. The image above shows a dredging operation Bathymetric Surveying consisting of a clamshell bucket dredge on a barge The label of hydrographic surveying is often synonymously applied to bathymetric surveying. Documenting the Geomorphic Changes However, the Routine hydrographic surveys are essential to latter actually documenting the transportation of silt and Bathymetry refers to the sedimentation, in order to unsure safe lanes of The term "bathymetry," originally study and shipping in rivers and along coastlines. nautical in origin, referred to the ocean's depth relative to the sea measurement of level (free surface), although it the bottom or Natural currents and storm events such as has since come to refer to the “bed” of a hurricanes tends to shift the silt on the sea or river “submarine topography,” or the navigable water beds, potentially accumulating in previously depths and shapes of the body (whether it dredged channels, causing dangerous conditions or underwater earthen terrain. is an ocean, river, obstructions. lake or other body or channel of water.) In other Locating Submerged Obstacles words it deals with the topography of the solid In addition to the surveying of geomorphic earth, beneath a body of water. changes, hydrographic surveys may be utilized to locate submerged vessels and other hazardous Below are various types of hydrographic surveying debris along river and sea beds. methods. A hydrographic survey can be used to facilitate offshore oil and gas exploration, drilling operations, marine construction, dredging, installation of subsea cables and more. Other Applications Other applications for hydrographic surveying: to generate the data needed to create and update nautical charts to verify that navigational channels are This agency was established when then President, clear and accurate Thomas Jefferson and Congress authorized a port and harbor maintenance (dredging), survey to be taken of coasts of the newly formed expansion, and re-design “United States of America." coastal engineering and geomorphological First Head of the US Coast Survey evaluations The first person to officially head the US Coast beach erosion and replenishment studies Survey was Ferdinand Rudolph Hassler, who coastal zone management assembled a number of skilled professionals from offshore resources development various scientific communities, to survey and chart oil and gas exploration out the coastlines of the US. volumetric studies erosion and siltation studies pre- and post-dredge evaluations Types of Professionals at river crossing profiles and evaluations the USCS aquatic vegetation design mathematicians cartographers flood studies geodesists to locate and verify the integrity of meteorologists submerged cabling and piping hydrographers for determining fisheries habitat and topographers understanding marine geologic processes sailors and laborers administrators to determine seabed and riverbed materials (i.e. sand, mud, rock) preliminary bed analysis for anchoring, The first official US survey - 1834 construction of marine structures, and The first official hydrographic survey performed in pipeline and cable routing the US was conducted along the southern shore of Long Island in 1834. disaster response following storm events; looking for changes in depth or debris in The first official US nautical chart – 1839 navigational channels In 1839, the US government produced its first nautical chart. However, many privately commissioned charts of the Americas were known Page 3: History of Hydrographic Surveying to exist prior to this date. Origins The history of hydrographic and bathymetric surveying likely dates back to the origins of sailing. As long as people have sailed the oceans, there has been the need to chart pathways for safe travel to avoid vessel groundings, and to document regional and seasonal oceanic currents and meteorological patterns. US Coast Survey Establishment of the US Coast Survey – 1807 Navigational chart of the Potomac estuary In the US, the first officially sanctioned (created in 1838 by the Alex’a Canal Company) hydrographic surveying office began in 1807, with the establishment of the “US Coast Survey”, which is one of the oldest scientific agencies in the US. Page 4: Early Hydrographic Surveying and other bathymetric methodologies, they are still Methods – Sounding Poles and Lead Lines sold by some “Mark Twain” survey supply Prior to 1900s – Poles and Lines In modern literature, Samuel companies, and Shallow water surveys – In early hydrographic Clemens took his pen name from may be used in practice, shallow water surveys consisted of depth his early employment as a areas where leadsman on the Mississippi River. measurements conducted by use of sounding The leadsman was the person large amounts of poles. who used a sounding pole or lead vegetation or line to measure the river depths thick mud would Deep water surveys – Sounding Lines to ensure the boat was staying tend to distort In greater depths, a sounding line (or lead line) was away from the shallow banks. To the electronic "mark twain" referred to marking used to make measurements of river channel, returns of estuarial and oceanic navigational pathways. a depth of the water of two fathoms, or 12 feet. modern Positions were determined by three-point sextant equipment. fixes to mapped reference points. A more sophisticated means of measuring deep water at Lead Lines this time was through the use of sounding Lead line systems consisted of ropes or lines, with machines, which were simply reel or drum based depth markings and line devices. lead weights attached (see image). The lead Sounding poles weights were usually A sounding pole (see image below) is simply a long conical in shape, rod, (usually made of wood, or aluminum in weighing around 12- present day use), that is used to measure 14 lbs., and navigational channel depths. Though mainly used occasionally had a to measure water depth, they may be used to small amount of wax measure the depths of boreholes, snow piles, or or lard on the base to loose soil stockpiles as well. collect a small sample of the surface sedimentary deposits. This A typical length of a sounding pole is about 20 feet, rudimentary but effective system could reportedly marked in one inch increments. They might have a provide reliable soil samples to depths of 100 circular plate at one end to ensure that the location fathoms or 600 ft. being measured is somewhat level and normalized, The “Fathom” and to prevent inaccuracies due to the pole sinking The line was lowered too deep into the In the early days of until it hit bottom, hydrographic surveying, a muck or silt bottom. then read manually in fathom was used to The pole technician a tedious, painstaking measure water depth. A would drop the pole process. These initial fathom is a linear unit of until there is adequate measurement, equal to 6 depth soundings were feet. resistance at the soil
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