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What is a Hydrographic Survey?
A hydrographic survey involves the gathering of data about a particular area of water. This will usually be carried out to confirm that it is safe for boats to navigate and to identify any potential dangers. There is a school of thought that the term can only apply to inland waters such as rivers and lakes, but the phrase is commonly used in reference to oceans.
Some of the measurements which will be taken in a hydrographic survey are tides, currents and waves. These interact to create the overall pattern of the water’s behavior. For example, waves are affected mainly by local wind patterns, though of course these can vary, while tides are regular and predictable. Currents are overall patterns of movement in the oceans caused partly by both winds and tides, but also by the differences in temperature and salt levels in different areas of the ocean.
A hydrographic survey will also look the land beneath the water such as the river or ocean bed. This will involve measuring its depth at different points. The survey will also take into account natural features such as reefs and rocks which lay below the water surface.
Because a hydrographic survey is primarily driven by safety, there are certain conventions which those carrying out the surveys will follow. For example, where the depth of a section of water is variable, the survey will usually record the lowest depth which is possible rather then base the figure on an average over time. This can cause debate since it can be argued that the charts 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 carrying out the survey will take multiple measurements so that they can produce both the safety-focused hydrographic results and a more accurate measure of the water bed known as a bathymetric chart.
The relevant authorities will often accept suggestions from the public for areas which need a hydrographic survey but are not currently on the authority’s schedule. One example of a suitable case for suggestion is when the pattern of use in an area has dramatically changed, for example if leisure use of a stretch of water has increased. Somebody could also suggest an area is surveyed if they believe an accident has been caused by errors and omissions in the most recent previous survey.
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![Measurements of waves, tides, and currents are taken during a hydrographic survey.]()
By: EpicStockMediaMeasurements of waves, tides, and currents are taken during a hydrographic survey. -
![During the Age of Sail, many shipwrecks were caused by the use of navigational charts that lacked information on submerged dangers like reefs and sandbars.]()
By: James SteidlDuring the Age of Sail, many shipwrecks were caused by the use of navigational charts that lacked information on submerged dangers like reefs and sandbars.
Discussion Comments
@David09 - I believe that after the terrible Indonesian tsunami of 2004, vast stretches of the coast line and the ocean bed in different islands had changed dramatically.
I remember seeing the before and after satellite images of these changes. I think in that situation, you should definitely have new hydrographic surveys. Areas that you once thought were safe may no longer be safe anymore, and vice versa.
@NathanG - My parents live in Florida and sometimes I go deep sea fishing with them off the Gulf coast.
I have to admit, we go pretty far out at times, looking for the fish. We use the so called “fish finder” equipment on the boat which shows us where the schools of fish are.
While the area seems to be safe, I do wonder about those deep waters. Sometimes it seems that the boat rocks a little too much with the shaking of the currents, and I have this brief fear of a “killer wave” suddenly emerging from the distance and engulfing us.
It’s not just a vivid imagination that I have; I saw something on television about killer waves, and they tend to be unexpected. This fear gets worse when it seems like we’re the only ones out at sea. However, now and then we see a helicopter overhead, so that tells me that all is clear.
@David09 - Actually, I think the article does allude to that possibility, it just doesn’t say it outright.
I believe that when the surveyors look at the ocean bed, they are taking the possibility of an earthquake into their analysis.
There are full time scientists, however, whose job it is to constantly monitor the ocean floor for seismic activity such as earthquakes. I think that they would mainly do that job rather than leave it to the surveyors.
I believe that a hydrographic analysis is a fairly cursory investigation of the area, whereas the seismic geologists are using computers and special equipment to monitor the area twenty four hours a day.
The article talks about many factors that are taken into account when doing a hydrographic survey.
However, I think that one of the most important factors is whether the ocean is sitting on a seabed that has had fault activity, which would make it a prime location for a possible tsunami in the event of an earthquake.
In my opinion, this is the most important criteria. I realize that earthquakes are difficult to predict, but there should be some evidence in the ocean floor that would indicate recent earthquake activity.
Perhaps fault lines with unusually large fissures would be a cause for concern. I definitely think that these should be part of the hydrographic analysis, rather than just the ebb and flow of tides.
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