C.O. van IJzendoorn1,2*, M.E. Wengrove2 , K. Ostrow2, M.A. Winters3, B.G. Ruessink1
1 Utrecht University, the Netherlands; 2 Oregon State University, USA, 2 Greater Farallones Associations/NOAA, USA
* Corresponding author: c.o.vanijzendoorn@uu.nl
Introduction
Coastal dunes provide coastal protection and ecosystem services like recreation, habitat, and drinking water. Coastal dunes are under increased pressure due to urbanization and sea level rise. The value of coastal dunes as a Nature-Based Solution (NBS) is becoming increasingly recognized, so measures are being taken to maintain, restore or create coastal dune areas (Lodder, et al. 2021).
Coastal engineers and managers traditionally assess the performance of coastal dunes based on their capacity to provide coastal protection (Figlus, 2022). For example, the strength of coastal dunes can be calculated based on a set volume of sand that needs to remain after a design storm. This provides valuable information about the short-term, protective capacity of coastal dunes. However, it does not provide information on future coastal dune development or the state of the ecosystem.
For future adaptation, it would be valuable for management and engineering projects to include quantitative assessment of objectives such as coastal resilience and ecological restoration. By including quantitative assessments ecosystem services can become an integral part of design. We present a framework (Figure 1) that can be used by researchers, engineers and planners to work towards quantitatively incorporating dune growth and ecological processes in the coastal dune NBS design.
Objective and Methods
The implementation of coastal dunes as an NBS can be prompted by social, engineering and ecological problems, such as coastal erosion, habitat loss, and sand nuisance. Measures to ‘enhance’ coastal dunes include dune preservation, artificial blowout construction, vegetation planting, sand fencing, and artificial and hybrid dune construction. The applicability of these measures depends on the project objectives and environmental setting.
A range of models is available to simulate coastal dune development processes such as dune erosion (DUROS, X-Beach), dune building (AeoLiS, CDM), ecological development (GenVeg), and shoreline change (ShorelineS, CoSMoS COAST). Geometric models (CS-model, DRT) offer a simplified way to simulate both dune erosion and growth. All these models are continuously being developed, and they are increasingly combined and applied.
The suitability of different models to assess coastal dune NBS depends on project objectives. When assessing coastal protection objectives, a dune erosion model may suffice. However, assessing sand nuisance reduction may require an aeolian transport model, while the success of ecosystem restoration may only be replicated with an ecological model. More generically, it is expected that exploratory modeling using simplified models is suitable for (long-term) policy decisions, whereas detailed modeling using process-based models is more suitable for engineering design decisions.
Results
The proposed framework emphasizes that different models are required to assess different project objectives during the iterative design of coastal dune NBS. The future assessment of objectives will depend on determining which quantitative criteria are best used to measure success for each objective. Additionally, knowledge about the physical system will be needed that is currently relatively unknown compared to knowledge applied in designing/managing dunes for coastal protection. For example, dune growth and ecological processes will require knowledge about accommodation space, sediment supply, and characteristics of plant species needed for coastal dunes to develop. In future work, we aim to improve knowledge of unknown factors within the framework (bolded, Figure 1) and improve the applicability of various models for assessing the objectives of projects that use coastal dunes as an NBS.
Figure 1. Framework for the implementation of coastal dunes as a nature-based solution (adapted from Ostrow et al. 2022). Parameters in bold are relatively unknown.
References
Figlus, J., (2022). Designing and implementing coastal dunes for flood risk reduction. In Coastal flood risk reduction, 287-301, Elsevier.
Lodder, Q., et al., (2021). Chapter 9: Beaches and Dunes. International Guidelines on Natural and Nature-Based Features for Flood Risk Management. U.S. Army ERDC.
Ostrow, K., Guannel, G., Biondi, E. L., Cox, D. T., & Tomiczek, T., (2022). State of the practice and engineering framework for using emergent vegetation in coastal infrastructure. Frontiers in Built Environment, 8, 923965.
