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A Glance at Hydrographic Survey

If you are going to build any type of structure in or near a waterfront area, you are going to need a hydrographic survey.  Hydrographic Surveys are performed in locations such as ponds, rivers, lakes, reservoirs, and ocean environments, and are often conducted in conjunction with land-based surveys in support of waterfront construction including piers, docks, seawalls, beach nourishment, and dredging projects for both private and public entities.

Historically, depth measurements below mean sea level were performed using mechanical means.  The distance to the bottom was manually measured by hand using sounding poles and lead lines lowered from the water surface to the bottom. The development of SONAR (sound navigation and ranging) in the early 1900’s began  the basis for development of state of the art equipment used for surveying water depths.

The basic principle of SONAR is that a pulse of sound (ping) is emitted from a device called a transducer which then receives the reflected pulse (echo) when it reflects off the bottom.  A distance measurement from the origin of the pulse (transducer) to the bottom surface is then calculated based on the velocity of sound and the travel time of the acoustic pulse.  SONAR is widely used by recreational organizations for determining water depth and identifying bottom surface features.

No matter what method is used, environmental factors must be considered as they can adversely affect the accuracy of hydrographic surveys. These factors include but are not limited to water levels (e.g. ocean tides), current, wind, wave action and water temperature. Keeping a close eye on weather patterns for survey scheduling purposes is a major factor in acquiring accurate, usable data.

Advanced investigations of underwater features found during the initial survey can be performed by underwater video cameras or commercial divers.  Depending on the application, the appropriate equipment and method should be carefully chosen by a qualified professional to obtain the necessary information for the unique project goal.

If you have upcoming projects that you think may benefit from a hydrographic survey or have any questions concerning hydrographic surveys, please call us at Merrill Corporation and ask for Mike Count.  He would be happy to speak with you.

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