Continental Shelf Research 24 (2004) 1–11 A conceptual framework for the erosion behaviour of sand–mud mixtures M. van Ledden a, * ,1 , W.G.M. van Kesteren a,b , J.C. Winterwerp a,b a Faculty of Civil Engineering, Department of Hydraulic Engineering, Delft University of Technology, Stevinweg 1, P.O. Box 5048, 2600 GA Delft, The Netherlands b WL|Delft Hydraulics, Rotterdamseweg 185, P.O. Box 177, Delft, The Netherlands Received 8 November 2002; received in revised form 11 August 2003; accepted 16 September 2003 Abstract The erosion behaviour of sand–mud mixtures is not well understood. As a first step, a conceptual framework for the erosion behaviour of sand–mud mixtures is proposed and validated with data from field and laboratory experiments based on appropriate parameters for cohesion and network structure. Six bed types with different characteristics are distinguished in relational diagrams. Validation with experimental data shows that observed transitions in erosion behaviour are clearly delimited in these diagrams. Mud content (%o0.063 mm) as a descriptor for the transition between non-cohesive and cohesive erosion behaviour turns out to be less generic than the clay content (%o0.004mm). Furthermore, an estimation of the relevance of these compositional bed types in natural systems shows that the frequently observed constant ratio between clay and silt in the bed sediments of some depositional system strongly limits the number of relevant bed types in that system. r 2003 Elsevier Ltd. All rights reserved. Keywords: Erosion; sand–mud mixtures; Sediment behaviour; Cohesion; Network structure 1. Introduction Along rivers, estuaries and coasts, deposits of (non-cohesive) sand and (cohesive) mud are often observed. An understanding of the depositional processes and the ability to predict the dynamic behaviour of these sediments is necessary for sustainable management, maintenance and devel- opment of such systems. For example, large-scale erosion of sand along coasts can destabilise dunes and dikes, whereas the distribution of mud determines which areas collect pollutants, as these tend to adhere predominantly to cohesive sedi- ments (cf. De Groot et al., 1982; Zwolsman et al., 1996). Historically, many investigations have been carried out for (non-cohesive) sand beds and (cohesive) mud beds separately to improve our understanding of their erosion behaviour (Mitchener and Torfs, 1996). Based on these results, various conceptual models and mathe- matical formulations have been developed for the ARTICLE IN PRESS *Corresponding author. Tel.: +31-0-24-3284227; fax: +31- 0-24-3605486. E-mail address: m.vanledden@royalhaskoning.com (M. van Ledden). 1 Present address: Royal Haskoning, Barbarossastraat 35, P.O. Box 151, 6500 AD Nijmegen, The Netherlands. 0278-4343/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2003.09.002