Bathymetry

 

Various techniques are used to measure the bathymetry, i.e. the under water topography.

 

Tachymeter

With the aid of a light / laser beam a tachymeter can measure at the same time both the direction (horizontal and vertical angle) and the distance to a reflector.

The tachymeter is installed at a point with known coordinates, the reflector is positioned at the point to be measured.

The measurement data is stored in the device for later analysis, e.g. to produce a digital terrain model.

Tachymetrical measurements have a very high accuracy of +- 1cm even for distances of several kilometers.

 

 

GPS

Today, with the aid of the satellite based Global Positioning System GPS using the "Differential GPS" method the location of a measurement point can be determined with a precision of +- 2 cm.

This method is especially used when the access to the research area is difficult and no fixed points with exact coordinates are known.

 

 

GPS and Sonar

With the aid of a sonar (echolot) the depth of water at a given point can be determined.

Together with the GPS data the bathymetry of a research site can be determined and in this way e.g. a digital terrain model can be produced.

 

Boat equipped with measurement instruments
(Sonar, GPS, Laptop). Photo: NOK, CH-Baden

Echogramme of the change from the shallow water zone (with vegetation) to the slope edge with descending terrain.

 

Besides important characteristical data such as the extend of the shallow water zone or the location of the slope edge, bathymetrical data from repeating mesurements can be used to determine in which areas of the research sites sediments have been eroded or deposited / accumulated.

 

Bathymetry of the research site La Neuveville, Levées des Larrus

 

Erosion and deposition / accumulation of sediments between the summer of 2002 and 2004 at the research site Ipsach Erlenwäldli.