Game and Parks makes topographic maps to provide fisheries managers with detailed information to be used in management and monitoring of Nebraska’s lakes. Detailed bathymetric lake maps are also produced and made available to the public on the our website.
First, an outline of the lake is created from an aerial photo or satellite image, and a series of survey transects are drawn perpendicular to the shoreline. This information is loaded onto a laptop computer and will serve as a guide to ensure a sufficient amount of data is collected during the survey.
Data is collected in the field using specially designed survey equipment including a GPS receiver and multi-beam depth sounder.
Using computer software, the GPS and depth sounder are linked together on a laptop that is able to display 3-dimensional points that contain latitude, longitude and depth. The position of the boat is displayed on a map containing the lake outline and transects allowing the driver to travel along each transect collecting points.
In addition to the boat survey, a GPS base station is set up at a known latitude, longitude and elevation in close proximity to the lake. This base station will communicate with roving receivers carried in backpacks which are used to get an elevation of the water allowing the points collected on the boat to be converted from depths to real elevations. The roving receivers can also be used to map habitat structures and exposed shorelines during low water conditions.
The next step is to import the points into a computer program, where they can be transformed into a detailed contour map of the lake. From this map, general information about the lake physical properties can be derived including the volume, area and depth. The final step is to add in special features showing amenities (boat ramp, restrooms etc.) and where fish attractor structures have been added after the lake was initially mapped.