Engineering design guidelines for salt marsh development
Focused on the effect of grazing strategies on the coastal protection property
Z. Hábetler (TU Delft - Civil Engineering & Geosciences)
JJ de Vries – Mentor
Stefan G. J. Aarninkhof – Graduation committee member
Bram Christiaan Van Prooijen – Graduation committee member
V. Vuik – Graduation committee member
Mark van Koningsveld – Graduation committee member
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Abstract
The main objective and secondary objective, which corresponds to the in-depth research are as follows:
(1) To develop guidelines for engineers to include salt marshes in hydraulic infrastructure projects, subject to the Building with Nature philosophy.
(2) To investigate the effect of grazing at salt marshes on the coastal protection property.
This research concerns the development of guidelines for engineers to include salt marshes in coastal protection projects, subject to the Building with Nature philosophy. The results include important design aspects for engineers and an analysis of trade-offs between biodiversity and the coastal protection property of salt marshes.
This research is based on a literature study about the natural and artificial development of salt marsh. Thereafter, the effect of grazing on wave attenuation is modelled by the numerical model SWAN (Simulating WAves Nearshore). The effect of vegetation and the bathymetry is analysed. The vegetation data results from a grazing experiment at the salt marsh at Noord Friesland Buitendijks, in the north of the Netherlands. The results from the literature study and the in-depth research are translated to important design aspects within the engineering design guidelines for salt marsh development.
The main conclusion of the in-depth research is that the effect of vegetation on wave attenuation is small compared to the effect of wave breaking and bottom friction. Moreover, the variations in wave attenuation between the different grazing strategies is also small. However, grazing could be used as an ecosystem management strategy, as from literature it follows that grazing positively affects biodiversity. Although the effect of biotic factors on wave energy dissipation is small, the presence of a salt marsh indirectly affects wave attenuation. The salt marsh vegetation enhances sediment accumulation, which leads to a higher bottom profile elevation compared to the bare foreshore. This should be substantiated by future research.