In the June issue of Maritime Engineering we presented a set of papers from the 7th International Association for Hydro-environment Engineering and Research (IAHR) symposium on river, coastal and estuarine morphodynamics (RCEM), which was held in Beijing in September 2011. The focus of the June issue (Townend et al., 2013) was on estuaries and inlets. In this issue we present two more papers that relate to the open coast.
The RCEM 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 two papers from RCEM in this issue focus on the behaviours and modelling of embayed beaches. The first reports the results of a detailed monitoring programme of Cempedak Bay beach on the east coast of Malaysia (Ab Razak et al., 2013). This covered a period of 3 years during which a beach-nourishment scheme was implemented. The authors analyse the monitoring data, along with associated wind and wave data, to develop an understanding of the dominant controls on the beach. Using this information they develop a reasoned assessment of how the recharge scheme has performed. In so doing, they also provide some useful insights into the capability of an empirical model for planform prediction.
The second paper from RCEM explores that ability to link models of beach plan shape and cross-shore development to establish a more detailed representation of the key processes. Zhou et al. (2013) explain the additional steps needed to make such a link and they test the resulting model on a case study of Bournemouth beach in the UK. The paper provides a useful exploration of what is entailed in building a model composition from a number of existing models and how the OpenMI standard can help support this type of development. The case study highlights the needs of engineering applications using this type of model and assesses how well the model composition performs.
The difficulty in predicting the planform is highlighted in both cases. For the Bournemouth beach this is attributed to the influence of nearshore tidal currents that are not represented in the model. Application of the parabolic bay model to assess planform stability in Cempedak Bay also proved difficult and the authors contend that this was due to the difficulty in selecting the diffraction point. Interestingly, they also discuss the role of the Cempedak river, which outflows to the north of the recharged area. However, because the sediment load is low, the influence of the river is not considered to influence beach morphology. Experience elsewhere in trying to fit the parabolic model to natural coastlines suggests that river and estuary outfalls often have to be treated as a ‘virtual headland’. For large rivers, such as the Humber, the potential for a significant influence on the hydrodynamics and hence the morphology is clear. The question is then how small can such outflows be and still have an influence? Osborne Reynolds' pioneering modelling work on inlets and estuaries (Reynolds, 1887) showed that only very small river flows were needed to maintain an estuarine channel (less than 1 m/s at prototype scale). Therefore, it may be that relatively small cross-shore flows can have a significant influence.
Whilst extending the theme of the influence of river discharges at the coast, the third paper explores a somewhat different aspect: the impact of significant river flows on sea levels. Subrath–Ali et al. (2013) analyse the effects of peak flows from the Orinoco River on seasonal sea level variation in the Gulf of Paria. The authors reference other sites from around the world where similar effects have been observed and measured. They describe the processes contributing to this effect, which needs to be accounted for in the design of maritime infrastructure and in particular when considering the potential impacts of climate change. In such situations those impacts may require consideration of the cumulative impact of ocean water level increase plus higher river discharges that can further increase those sea levels in semi-enclosed water bodies.
The final paper in this issue deals with another challenge at the coast: dealing with public perceptions of flood risk. We are reminded that providing the level of protection provided in the past may not continue to be funded in the future and that, in England, the government's Department for Environment, Food and Rural Affairs (Defra) led a Coastal Change Pathfinder programme to explore new ways of adapting to coastal change. Under this programme, a number of projects were delivered by English local authorities working in partnership with their communities, to trial innovative approaches to planning for and managing coastal change.
Hickman and Flikweert (2013) describe one of these projects looking at engagement approaches to raise the level of awareness of risks and preparedness required in the event of potential flooding. This paper highlights some of the challenges faced in dealing with a diverse community, with findings ranging from a complete lack of awareness of the risks through to some resistance to the messaging from local business interests. Observations here on the effectiveness of various tools and techniques should prove valuable for other authorities faced with similar issues to address.
