RCEM 2019
BOOK OF ABSTRACTS
AUCKLAND, NEW ZEALAND
16
TH–21
STNOVEMBER 2019
I
BOOK OF ABSTRACTS
AUCKLAND, NEW ZEALAND
16
TH–21
STNOVEMBER 2019
EDITED BY:
HEIDE FRIEDRICH AND KARIN BRYAN
2019
The impact of basin geometry on the long-term morphological evolution of
barrier coasts: an exploratory modelling study.
K.R.G. Reef1, P.C. Roos1, H.M. Schuttelaars2, S.J.M.H. Hulscher1
1 Water Engineering and Management, University of Twente, Enschede, the Netherlands. K.r.g.reef@utwente.nl 2 Applied mathematics, Delft University of Technology, Delft, the Netherlands.
1. Introduction
Barrier coasts cover 10% of the worlds coastline (Stutz and Pilkey 2011) and are important coastal systems that are often found near densely populated areas. Because of their importance, human interventions in barrier coast systems are common. A frequently applied intervention is the reclamation of land, resulting in a reduction of the tidal basin. Even though land reclamations in barrier coast systems are common, only little is known about their effect on the long-term (decades to centuries) morphological evolution of barrier coasts.
In this work we aim to investigate the effect of a basin reduction in one part of a tidal basin on the equilibrium configuration (i.e. size and spacing) of tidal inlets in the entire basin (i.e. both the affected and unaffected parts of the basin). Because a basin reduction is essentially a sudden change from one geometry to another, we study the equilibrium configuration of inlets for various basin geometries (reflecting different basin reductions). This reveals how the equilibrium configuration of the inlets would change if a new geometry is imposed through a basin reduction.
2. Methods
We use an idealized barrier coast model that is an extension to the model of Roos et al. (2013), but now allowing for arbitrary basin geometries instead of only a rectangular basins. The model simulates the morphological evolution of multiple tidal inlets (n=50) towards an equilibrium configuration. The morphological evolution is based on the stability concept of Escoffier (1940), while the hydrodynamic part of the model is based on the linearized shallow water equations that are solved analytically. An example model run is shown in Figure 1.
3. Results
By performing a sensitivity analysis of basin geometry (with a wide and narrow part in the basin as in Figure 1), we studied the effect that basin geometry has on the equilibrium configuration of tidal inlets.
Our results show that three processes affect the equilibrium configuration of tidal inlets. First, there are wider inlets in the wider part of the tidal basin for a larger basin width. Second, there is an equilibrium value for both the inlet width per km and number of inlets per km, due to bottom friction. Third, resonance affects the width and number of inlets in both the wide and narrow part of the basin.
4. Conclusions
We studied the effect of basin geometry on the long-term morphological evolution of barrier coasts using an idealized model, that allows arbitrary tidal basin geometries; and identified the most relevant processes. Acknowledgement
This research was carried out within the WADSnext! project, funded by the `Simon Stevin Meester' prize (awarded by NWO to S.J.M.H. Hulscher), Deltares, and the 4TU centre for fluids and solid mechanics.
Bibliography
Escoffier EF (1940) The stability of tidal inlets. Shore and Beach 8:114–115
Roos PC, Schuttelaars HM, Brouwer RL (2013)
Observations of barrier island length explained using an exploratory morphodynamic model. Geophys Res Lett 40:4338–4343.
Stutz ML, Pilkey OH (2011) Open-ocean barrier islands: Global influence of climatic, oceanographic, and depositional settings. J Coast Res 27:207–222.
Figure 1: Example run of our barrier coast model with non-rectangular geometry; showing: A: the initial over-saturated barrier coast (top view), B: the evolution of the tidal inlets (line stack), C: the equilibrium configuration (top view).
