The 7th International Association for Hydro-environment Engineering and Research (IAHR) symposium on river, coastal and estuarine morphodynamics (RCEM) was held in Beijing in September 2011. A number of those presenting at the symposium were invited to submit papers to form a themed issue of Maritime Engineering. In total, eight papers were accepted for publication and will be presented in two RCEM themed issues. This themed issue focusses predominantly on estuaries and inlets and a second issue, to follow, will focus on the open coast.
This symposium was jointly hosted by Tsinghua University and the UNESCO International Research and Training Centre on Erosion and Sedimentation. In total, 318 abstracts were submitted to the symposium. The abstracts were reviewed by the international scientific committee and 261 were accepted. The symposium was attended by 258 researchers and scientists from 29 countries and regions. Four keynote lectures were delivered in plenary sessions and 12 invited lectures were presented in parallel sessions. More than 200 contributed lectures were presented by delegates at 36 parallel sessions. A selection committee attended all the sessions and recommended five papers for the best presentation award. The paper by Trang-Thu Vu, which is included in this issue (Vu and Tan, 2013), was one of the winners of the best presentation award.
Our knowledge of sediment dynamics and the associated morphodynamics of estuarine systems needs urgent improvement to support sustainable management, if we are to protect against flooding and ensure a healthy balance between preservation of nature and economic use of the estuaries. The four papers in this themed issue contribute to the required improvement by addressing a number of fundamental issues: graded sediment, especially sand–mud mixture (the first two papers); channel–shoal interaction (the second and third papers); and turbulence and mixing (the fourth paper). Besides contributing to our fundamental knowledge, the papers also have their value for engineering and management practice. As an example, local mitigating measures, as studied in the second paper (Dam and Bilek, 2013), are being considered more and more to preserve the ecologically valuable intertidal flats in the Western Scheldt in the Netherlands against the cumulative effects of century-long land reclamation and deepening of the estuary. Protecting structures and sediment nourishment are also necessary for the tidal flats in the neighbouring Eastern Scheldt because fully restoring the morphological equilibrium in the estuary after the construction of the storm surge barrier is not feasible. Such examples demand an in-depth knowledge of estuarine behaviour, while also providing a valuable archive of historic records that help to illuminate how such dynamic systems respond to anthropogenic interventions. More research, as described in the four papers, is needed to provide those charged with managing our estuaries with better knowledge and predictive tools.
The first two papers in this issue provide two case studies looking at morphological change in two estuaries with mixed sand–mud environments. The paper on the Gironde estuary in France focuses on the large scale (Huybrechts and Villaret, 2013), whereas the other paper examines a more local scale, considering the changes caused by the construction of two cross-shore groynes near Waarde in the Western Scheldt (Dam and Bilek, 2013). To model the Gironde estuary the Telemac finite-element system has been applied to predict the medium-term bed evolution. The results highlight the relative influence of including a graded sediment description in the model, compared with a uniform sand bed. The suspended sediment concentrations are better reproduced when a graded sediment is used and the morphodynamic model results show qualitative agreement with observations of the bed evolution in the central part of the estuary. The model of the Waarde examines the ability to predict the mud flat that has developed between the groynes and scour that has occurred at the tip of the groynes. Both the sand and mud fraction have contributed to this change and the modelling approach adopted is able to represent the observed changes and clearly distinguish between sand- or mud-dominated areas.
The third paper continues the theme of morphological development but now at the scale of intertidal creeks and creek networks. Iwasaki et al. (2013) use physical and numerical modelling to examine the initiation and development process of tidal creek networks. As well as using the numerical model to emulate the results of the physical model, the authors experiment with a range of model grids to demonstrate the influence of gird resolution on the initiation process. Interpreting the results, the authors are also able to relate the model morphology to observed channel and network geometric characteristics.
In the final paper we move away from morphological prediction and consider one aspect of a human activity – dredging – that can have a major impact on morphology. The paper by Vu and Tan (2013) examines the performance of silt screens used to control the movement of sediment, especially close to the operation of a dredger or in the vicinity of particularly sensitive habitats. The study reported looked at the changes in flow and turbulence induced by the silt screen using a series of laboratory experiments. The results highlight the importance of silt screen depth in the design and deployment of this type of device.
