Urban dunes : Towards BwN design principles for dune formation along urbanized shores

Sandy shores worldwide suffer from coastal erosion due to a lack of sediment input and sea-level rise. In response, coastal sand nourishments are executed using ‘Building with Nature’ techniques (BwN), in which the sand balance is amplified and natural dynamics are instrumental in the redistribution of sand, cross- and alongshore. These nourishments contribute to the growth of beaches and dunes, serving various design objectives (such as flood safety, nature, and recreation). Nevertheless, human interference (such as buildings and traffic) along urbanized sandy shores may have significant, yet poorly understood, effects on beach and dune development. Better insight is required into the interplay of morphological, ecological and urban processes to support Aeolian BwN processes for dune formation and contribute to the sustainable design of urbanized coastal zones. This paper aims to bridge the gap between coastal engineering and urban design by formulating design principles for BwN along urbanized sandy shores, combining nourishments, natural dune formation and urban development on a local scale to strengthen the coastal buffer. The first part of the paper analyses sedimentation processes in the (built) sea-land interface and identifies spatial mechanisms that relate coastal occupation to dune formation. Hence a preliminary set of design principles is derived by manipulating wind-driven sediment transport for BwN dune formation after nourishment. In the second part of the paper, these principles are applied and contextualized in two case-studies to compare their capability for BwN in different coastal profiles: the vast, rural, geomorphologically high dynamic profile of a mega-nourishment (Sand Motor); versus the compact, highly urbanized, profile(s) of a coastal resort (Noordwijk). Conclusions reflect on the applicability of BwN design principles within different coastal settings (dynamics, urbanity) and spatial arrangements facilitating BwN dune formation

Experiment-supported modelling of salt marsh establishment

Recently, the use of salt marshes in front of hard structures is increasingly proposed as a more sustainable coastal protection measure. Yet, salt marsh restoration and creation is often hampered by the lack of a thorough understanding of initial vegetation establishment. Recent studies highlight the importance of bed level change for salt marsh development. In this study we continue the examination of the impact of bed level change on salt marsh development, focussing on the prediction of salt marsh establishment and the implications for coastal management. First, a test with Spartina anglica seedlings (Cordgrass) in a wave flume showed that long-term (seasonal) bed level change is more important for seedling survival than direct wave impact at the shoot. Therefore, we subsequently incorporated bed level change in the Windows of Opportunity (WoO) framework. Lastly, this revised WoO framework was applied to the design of the Marconi pioneer salt marsh (The Netherlands). Combining the WoO framework with a morphodynamic model (Delft3D) showed its potential for salt marsh design. The framework can be used to determine whether salt marsh establishment is possible, to find out which conditions are limiting establishment and to design engineering measures creating the conditions that facilitate salt marsh establishment