Modeling Sediment Bypassing around Idealized Rocky Headlands

Abstract

Alongshore sediment bypassing rocky headlands remains understudied despite the importance of characterizing littoral processes for erosion abatement, beach management, and climate change adaptation. To address this gap, a numerical model sediment transport study was developed to identify controlling factors and mechanisms for sediment headland bypassing potential. Four idealized headlands were designed to investigate sediment flux around the headlands using the process-based hydrodynamic model Delft-3D and spectral wave model SWAN. The 120 simulations explored morphologies, substrate compositions, sediment grain sizes, and physical forcings (i.e., tides, currents, and waves) commonly observed in natural settings. A generalized analytical framework based on flow disruption and sediment volume was used to refine which factors and conditions were more useful to address sediment bypassing. A bypassing parameter was developed for alongshore sediment flux between upstream and downstream cross-shore transects to determine the degree of blockage by a headland. The shape of the headland heavily influenced the fate of the sediment by changing the local angle between the shore and the incident waves, with oblique large waves generating the most flux. All headlands may allow sediment flux, although larger ones blocked sediment more effectively, promoting their ability to be littoral cell boundaries. The controlling factors on sediment bypassing were determined to be wave angle, size, and shape of the headland, and sediment grain size.

Wave and Tidal Controls on Embayment Circulation and Headland Bypassing for an Exposed, Macrotidal Site

“…Other efforts have attempted to use numerical models of idealised headlands to determine the major controls on bypassing [38] and found, as expected, that sediment bypassing increases under larger, more oblique waves. However, such efforts have limited predictive capacity if they become too abstracted from naturally observed headlands.…”

“…The impact on circulation and bypassing of commonly observed coastal features, such as islands, ridges, and canyons, as well as headlands of varying size, shape, and alignment should be investigated. The latter was undertaken by [31,38] but is not yet at a stage where informative predictions can be made for an unseen headland. Our site-specific method of predicting headland bypass offers a convenient means of estimating bypassing rates for a single, site-specific headland.…”

High‐efficiency gravel longshore sediment transport and headland bypassing over an extreme wave event

“…While it is relatively straightforward to predict bypassing rates around groynes and other near‐idealized structures (e.g. Pelnard‐Considere, ; Larson et al ., ), it has proven far more difficult to predict bypassing around the complex morphology of natural headlands (George et al ., , ; Vieira da Silva et al ., , ; McCarroll et al ., ), and no generalized formula exists for predicting headland bypass rates. Given the underdeveloped state of research in this area and the near absence of robust observations of headland bypassing rates, the measurements described here are of significant value.…”

Wave, Tide and Topographical Controls on Headland Sand Bypassing

“…Predictions of bypassing magnitude were initially proposed by McCarroll et al (2018), where a headland-specific parameter was conceived based upon modeled daily sand bypassing of a macrotidal headland. George et al (2019) found that bypassing is controlled by wave angle, headland size and grain size. Valiente et al (2020) show that headland bypassing of multiple headlands is predictable as a function of offshore wave power, although this requires a computationally expensive numerical model to first calibrate a polynomial to each headland.…”

“…The influences of bathymetric expression and sediment spatial variability in sand bypassing rates are yet to be quantified. Additionally, while waves are the primary driver of headland sand bypassing based on observation and modeling studies (George et al, 2019;Goodwin et al, 2013;McCarroll et al, 2018;Vieira da Silva et al, 2018), tidal elevations and tidal currents play a secondary role (McCarroll et al, 2018(McCarroll et al, , 2021. Costa et al (2019) indicate nonlinear interaction between waves and tides can increase bypassing by an order of magnitude relative to tides-alone.…”