On the application of OBS measurements on mixed sediments and the coupling to fixed turbidity limits

7-8 November 2019. Ahoy, Rotterdam, the Netherlands

Lumborg U - DHI, Denmark; Bundgaard K - NIRAS, Denmark

Summary: Calibration between NTU and SSC can vary by a factor of ten between fine grains and sand. This paper will demonstrate that OBS devices can be highly sensitive with regards to grain size, and it will look at the link to general light dampening and the use of SSC in turbidity limits.

OBS applied in Rødsand, Denmark

• Measuring nephelometric turbidity units (NTU) is a popular and relatively simple method as a proxy for illustrating the suspended sediment concentration (SSC)
• Converting NTU to SSC is not a simple task. Transfer function is sensitive to grainsize
• Conversion factors may vary up to a factor 15 with varying grainsizes
• A specific NTU corresponds to an infinite number of SSCs, depending on the local grainsize
• Applying a certain NTU as an environmental limit does not necessarily provide the required environmental protection

Last update: 12 September 2019