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RESEARCH ARTICLE
Contents Vol 60(7)

A new radiometric instrument for in situ measurements of physical sediment properties

W. Jacobs A E , M. Eelkema A , H. Limburg B and J. C. Winterwerp C D
+ Author Affiliations
- Author Affiliations

A Delft University of Technology, Faculty of Civil Engineering and Geosciences, Hydraulic Engineering Section, PO Box 5048, 2600 GA Delft, The Netherlands.

B Medusa Explorations B.V., PO Box 623, 9700 AP Groningen, The Netherlands.

C Delft University of Technology, Faculty of Civil Engineering and Geosciences, Environmental Fluid Mechanics Section, PO Box 5048, 2628 CN Delft, The Netherlands.

D Deltares, PO Box 177, 2600 MH Delft, The Netherlands.

E Corresponding author. Email: walterjacobs@hotmail.com

Marine and Freshwater Research 60(7) 727-736 https://doi.org/10.1071/MF08056
Submitted: 27 February 2008  Accepted: 18 February 2009   Published: 28 July 2009

Abstract

Information on the sedimentological composition of sediment beds in marine wetlands is important for the study of the complicated interactions between physical, biological and chemical processes. In situ soil sample collection and subsequent laboratory analyses using traditional methods is rather time consuming. The present paper presents the Medusa (Multi Detector system for Underwater Sediment Activity) RhoC system. ‘Rho’ refers to density and ‘C’ to the activity concentration of the decaying isotopes adhered to the sediments. The new instrument directly translates (the attenuation of) natural radioactivity to sedimentological data concerning the depth-averaged sediment composition and vertical density profiles of the upper 15 cm of the sediment bed. The accuracy and applicability of the instrument were assessed to illustrate its potential and limitations. Results from a field campaign on several intertidal flats and from similar measurements in the laboratory for controlled circumstances were compared with data obtained by traditional analyses. The instrument generates accurate results for the depth-averaged sediment composition. Vertical density profiles are also well represented by the RhoC after smoothing and correcting the data for partly saturated soils. Thus, Medusa RhoC is a useful and practical tool to provide accurate sedimentological data in a fast and cost-effective way. The combination of sedimentological relations with the data obtained by RhoC further increases the applicability of the new instrument.

Additional keywords: clay, cohesive sediment, intertidal, mud, natural radioactivity, sand, Western Scheldt Estuary.


Acknowledgements

This research was supported by the Dutch Technology Foundation STW, the Applied Science Division of NWO and the technology program of the Ministry of Economic Affairs. The authors would like to thank The Netherlands Institute of Ecology for their assistance during the field campaign and the laboratory analyses. In particular we would like to thank Daphne van der Wal and Francesc Montserrat. We are also thankful for the assistance of Marco Tijs, Medusa Explorations B.V., and for the use of facilities at the Laboratory of Fluidmechanics, Faculty of Civil Engineering, Delft University of Technology. The comments of Maarten van der Vegt and the anonymous reviewers of the manuscript are highly appreciated.


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