A hydrographic survey collects data on water safety and potential hazards, including tides, currents, waves, and the ocean floor. The survey is primarily safety-driven and follows certain conventions, with suggestions for areas to survey accepted from the public.
A hydrographic survey involves the collection of data about a particular area of water. This will usually be done to confirm that it is safe for the ships to sail and to identify any potential hazards. It is believed that the term can only apply to inland waters, such as rivers and lakes, but the phrase is commonly used in reference to the oceans.
Some of the measurements that will be taken in a hydrographic survey are tides, currents, and waves. These interact to create the overall pattern of water behavior. For example, waves are mainly affected by local wind patterns, although they can of course vary, while tides are regular and predictable. Currents are general patterns of movement in the oceans caused in part by winds and tides, but also by differences in temperature and salt levels in different areas of the ocean.
A hydrographic survey will also examine the land under the water, such as the river or ocean floor. This will involve measuring its depth at different points. The survey will also take into account natural features such as reefs and rocks that lie below the surface of the water.
Because a hydrographic survey is primarily safety driven, there are certain conventions that those conducting the surveys will follow. For example, where the depth of a section of water is variable, the survey will generally record the lowest depth possible rather than basing the figure on an average over time. This can be debated, as it can be argued that the graphs created by the survey are not a true representation of the waterbed as a whole; The counter argument is that it is better to err on the side of caution. In many cases, the people conducting the survey will take multiple measurements so that they can produce both safety-focused hydrographic results and a more precise measurement of the water bed known as a bathymetric table.
The relevant authorities will often accept suggestions from the public for areas that need a hydrographic survey but are not currently on the authority’s schedule. An example of a suitable case to suggest is when the pattern of use in an area has changed dramatically, for example if pleasure use of a stretch of water has increased. Someone might also suggest that an area be inspected if they believe an accident was caused by errors and omissions in the most recent previous survey.
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