Hans Wilson & Associates, Inc. (HWA) uses a computer linked system to conduct bathymetric surveys. The basic equipment setup consists of an echo-sounder which is connected to transducer, GPS system, and laptop computer. HWA uses an Odom Single Beam Hydrotrac model echosounder. The Hydrotrac employs highly integrated digital and analog circuitry, proven display technology and power efficient thermal printing techniques. Two 16-bit processors share the real-time tasks of digitizing, printing, and interfacing, making the lightweight system an extremely capable tool. The Hydrotrac has a depth range from 0.8 feet to 2,000 feet while most of our surveys are seldom deeper than 25’. The echo-sounder stores data on the computer while conducting the survey. The echo-sounder also physically graphs the bathymetric data on chart paper.

The computer uses the 2008 Hypack software to collect, store, and reduce all data from the Hydrotrac echo-sounder. HYPACK, Inc develops Windows-based software for the hydrographic and dredging industry. HYPACK® is one of the most widely used hydrographic surveying packages in the world, with over 4,000 users. It provides the surveyor with all of the tools needed to design their survey, collect data, process it, and generate final products. Whether you are collecting hydrographic survey data, environmental data, or just positioning your vessel in an engineering project, HYPACK® provides the tools needed to complete your job.

The GPS system consists of a Trimble AgGPS 132 receiver with sub-meter accuracy. The GPS antenna is place directly above the transducer during data collection, resulting in zero offset between the depth location and the latitude and longitude. The transducer is a 200 kHz, 4°, single “Q” narrow beam transducer designed for work in shallow water.

In addition to collecting depth information electronically, we also use the more traditional tape and rod survey. This is done in locations where vessel access might be restricted for instance a narrow tidal creek requiring dredging. We also field verify the electronic depths using the survey rod. In many cases the electronic survey will pick up the top of the silt layer while the survey rod can penetrate the silt and establish the depth of the hard bottom.

All depths are referenced to a known datum, typically North American Vertical Datum from 1988 (NAVD 88). For certain surveys that are submitted to the regulatory agencies the depths are referenced to Mean Low Water (MLW) datum. Many surveys are referenced to mean lower low water, typically the datum for nautical charts, to assure the available depth exists during the lowest tides of the year. In addition, periodic checks of the tide elevation occur during a bathymetric survey. The fluctuation in the tide is noted and imported into the data as a correction factor so the depths are referenced consistently throughout the survey to a common datum.

The final product from a bathymetric survey is a full color contour map that is overlain on a project aerial. The location of the depths are referenced to the Florida state plane coordinate system. The map information is then used to plan a site. Planning might include determining where to moor vessels, to calculate volumes that need to be dredged to restore or create depth in channels or basins, or simply to manage vessel traffic around a construction site like the example below.

Bathymetric Survey