Exploring the sensitivities of crenulate bay shorelines to wave climates using a new vector-based one-line model

Abstract

We use a new exploratory model that simulates the evolution of sandy coastlines over decadal to centennial timescales to examine the behavior of crenulate-shaped bays forced by differing directional wave climates. The model represents the coastline as a vector in a Cartesian reference frame, and the shoreface evolves relative to its local orientation, allowing simulation of coasts with high planform-curvature. Shoreline change is driven by gradients in alongshore transport following newly developed algorithms that facilitate dealing with high planform-curvature coastlines. We simulated the evolution of bays from a straight coast between two fixed headlands with no external sediment inputs to an equilibrium condition (zero net alongshore sediment flux) under an ensemble of directional wave climate conditions. We find that planform bay relief increases with obliquity of the mean wave direction, and decreases with the spread of wave directions. Varying bay size over 2 orders of magnitude (0.1-16 km), the model predicts bay shape to be independent of bay size. The time taken for modeled bays to attain equilibrium was found to scale with the square of the distance between headlands, so that, all else being equal, small bays are likely to respond to and recover from perturbations more rapidly (over just a few years) compared to large bays (hundreds of years). Empirical expressions predicting bay shape may be misleading if used to predict their behavior over planning timescales.

Coastal Modelling Environment version 1.0: a framework for integrating landform-specific component models in order to simulate decadal to centennial morphological changes on complex coasts

“…The Coastal One-line Vector Evolution (COVE) model is a special case of a one-line model designed to handle complex coastline geometries, with high-planform-curvature shorelines (Hurst et al, 2015). COVE was inspired by the coastal evolution model of Ashton et al (2001) but also includes wave refraction around headlands.…”

“…The current version of the CoastalME framework assumes alongshore uniformity to calculate wave refraction (i.e. application of Snell's law), simple rules to estimate diffraction as described by Hurst et al (2015) and two different approaches to calculate wave transformation due to shoaling and energy dissipation. The first approach is based on linear wave theory and assumes no energy losses due to wave breaking or bottom friction, in a manner equivalent to the method used by Hurst et al (2015) in COVE.…”

“…application of Snell's law), simple rules to estimate diffraction as described by Hurst et al (2015) and two different approaches to calculate wave transformation due to shoaling and energy dissipation. The first approach is based on linear wave theory and assumes no energy losses due to wave breaking or bottom friction, in a manner equivalent to the method used by Hurst et al (2015) in COVE. The second approach uses the CSHORE wave propagation module which includes energy dissipation due to wave breaking and bottom friction (Kobayashi, 2016).…”

“…We use the simple rules approach described by Hurst et al (2015) to modify the wave height and direction due to diffraction of waves in the shadow zone. CoastalME traverses all coastline cells searching for shadow zones.…”

“…Significant effort has been oriented in this direction during the last decade, in particular by the Open Modelling Interface (OpenMI) and Community Surface Dynamics Modelling System (CSDMS). OpenMI emerged from the water sector as a way to link existing stand-alone models that were not originally designed to work together (Gregersen et al, 2005), while CSDMS draws on a large pool of well-understood open-access models (Hutton et al, 2014). The promise of OpenMI and CSDMS is to provide a unified system to link various models in order to explore broader system behaviour.…”