A critical review of closure depth theories and uncertainties: implications for shoreline modelling and coastal management

Abstract

The sustainability of coastal systems is being increasingly compromised as a result of climate-related coastal hazards and increasing human occupation of coastal zones. Shoreline models play an important role in predicting and understanding coastal systems behaviour, informing coastal resilience and adaptation strategies. A critical parameter in these models is the depth of closure ($DoC$), which defines the seaward extent of significant cross-shore sediment transport and shoreline morphodynamics. There are considerable uncertainties associated with estimating and identifying the $DoC$, which has implications for the accuracy of shoreline predictions and ensuing coastal management decisions. We, therefore, provide a critical literature review of existing theories and methods for defining and estimating the $DoC$, highlighting the complexities, uncertainties, and challenges. We also explore the role of the $DoC$ in shoreline models, paying particular attention to their applicability across variations in timescale and coastal environments while considering the associated implications for coastal management decisions. Our findings highlight the need for standardised estimation methods and a better understanding of the $DoC$ to improve the reliability and applicability of shoreline models across coastal morphologies and tidal environments. Our findings also emphasise the need for a paradigm shift in practice – from continuing to develop and apply flawed shoreline models to addressing the uncertainties underpinning the formulation and specification of key model parameters, of which the $DoC$ is arguably the most critical. This shift is needed to enhance the predictive power and reliability of shoreline models, to better inform decision-making for coastal management and governance.