The Standards of Practice for Surveying in the State of Alabama defines a hydrographic survey as the determination of data relating to bodies of water, including depth of water and configuration of the bottom, directions and force of current, and location of fixed objects for survey and navigation purposes.
Most hydrographic work is used to generate a Digital Terrain Model (DTM) for monitoring and GIS mapping purposes. While not a new type of surveying, technology like GPS and sonar systems has increased the accuracy and comfort level of the data produced by hydrographic surveys. In years past, hydrographic surveys of smaller bodies of water were conducted by rudimentary, time-consuming, and often inaccurate methods.
Our current process for conducting a hydrographic survey starts with accessing the body of water to determine the best-suited boat and equipment for the job. The sonar we use is like a transducer on any depth finder, but it’s linked to a survey-grade GPS or robotic system. During the data collection, the surveying equipment solves for an X, Y, and Z location on the submerged sonar. At the same time, the sonar is sounding a depth to the bottom of the water body. When the data is processed, the sounding depth is added to the Z location, providing an elevation of the floor of the water body.
This technology can be utilized in various areas of engineering and surveying. The generated DTM can be used to plot cross-sections, monitor dredging, monitor silt volumes, or perform other functions.
Sain Associates provided a hydrographic survey of Lake George, an approximately 40-acre lake in Irondale, Alabama. The hydrographic survey was very beneficial to Lake George’s members as it allowed them to see the bottom contours of the lake, which extended down to 23 feet. The survey also revealed an underwater creek channel, humps, and other lake features.