Quantifying Bed Level Change at the Transition of Tidal Flat and Salt Marsh

Quantifying Bed Level Change at the Transition of Tidal Flat and Salt Marsh: Can We Understand the Lateral Location of the Marsh Edge?

Willemsen, P. W.J.M. (University of Twente; Universiteit Utrecht; Deltares)
Borsje, B. W. (University of Twente)
Hulscher, S. J.M.H. (University of Twente)
Van der Wal, D. (Universiteit Utrecht; International Institute for Geo-Information Science and Earth Observation (ITC))
Zhu, Z. (Universiteit Utrecht)
Oteman, B. (Universiteit Utrecht)
Evans, B. (Cambridge Coastal Research Unit; University of Cambridge)
Möller, I. (University of Cambridge)
Bouma, T.J. (TU Delft Environmental Fluid Mechanics)

2018-10

Bed level dynamics at the interface of the salt marsh and tidal flat have been highlighted as a key factor connecting the long-term biogeomorphological development of the marsh to large-scale physical forcing. Hence, we aim to obtain insight into the factors confining the location of the marsh edge (i.e., boundary between tidal flat and salt marsh). A unique data set was collected, containing measurements of daily bed level changes (i.e., integrative result of physical forcing and sediment properties) at six intertidal transects in the North Sea area. Moreover, various biophysical parameters were measured, such as sediment characteristics, waves, inundation time, and chlorophyll-a levels. The data show that both bed level change and waves decreased from the lower intertidal flat toward the marsh edge and further diminished inside the marsh. However, no direct general relation was found between waves and bed level change. Bed level change inside the marsh was always small, regardless of wave energy. By combining the data sets, we demonstrate that the location of the lower marsh edge is restricted by two interacting factors: inundation time and bed level change. For vegetation establishment to withstand longer inundation stress, which slows down plant growth, more stable bed levels are required so that plants are not heavily disturbed. Conversely, to withstand more dynamic bed levels that disturbs plant growth, lower inundation stress is needed, so that plants grow fast enough to recover from the stress. The results suggest that bed level change is important in determining the position of the marsh edge.

bed level dynamics
field observations
marsh edge location
nature-based flood defense
salt marsh dynamics
tidal flat

http://resolver.tudelft.nl/uuid:389cac64-ee7e-44ce-ae0e-ccb6d2173edf

https://doi.org/10.1029/2018JF004742

2169-9003

Journal of Geophysical Research: Earth Surface, 123 (10), 2509-2524

Institutional Repository

journal article

© 2018 P. W.J.M. Willemsen, B. W. Borsje, S. J.M.H. Hulscher, D. Van der Wal, Z. Zhu, B. Oteman, B. Evans, I. Möller, T.J. Bouma