An official website of the United States government
This study aims to identify the natural processes and the subsequent responses to coastal engineering and development on the alongshore evolution of the IB-BI-LBI inlet-barrier system. The primary focus will be the quantification of barrier island and inlet sediment partitioning at decadal to centennial timescales, from 1839-1941. We analyze historical alongshore evolution and track coastal engineering efforts at the Island Beach–Barnegat Inlet–Long Beach Island, NJ barrier-inlet system, which has transitioned from natural to highly developed over the past 180 years. We build a quantitative mass-balance framework that tracks sediment reservoir volumes and transport fluxes within the barrier-inlet system to describe both the natural and developed alongshore evolution of this system. We find that minor coastal engineering efforts, including the construction of small-scale wood and stone jetties, not only shift sediment transport locally, but also shift system-wide sediment transport based on inlet-barrier island interactions and sediment partitioning. Better understanding these different modes of past evolution can help to guide coastal management strategies as beach nourishment increases in cost, sea level-rise accelerates, and extreme storm patterns change.
more »
« less
The Future of Developed Barrier Systems: 2. Alongshore Complexities and Emergent Climate Change Dynamics
Abstract Developed barrier systems (barrier islands and spits) are lowering and narrowing with sea‐level rise (SLR) such that habitation will eventually become infeasible or prohibitively expensive for most communities in its current form. Before reaching this state, choices will be made to modify the natural and built environment to reduce relatively short‐term risk. These choices will likely vary substantially even along the same developed barrier system as these landscapes are rarely uniformly managed alongshore. Building on the results from a companion paper, here we use a new modeling framework to investigate the complexities in barrier system dynamics that emerge as a function of alongshore variability in management strategies, accelerations in SLR, and changes in storm intensity and frequency. Model results suggest that when connected through alongshore sediment transport, barriers with alongshore variable management strategies—here, the construction of dunes and wide beaches to protect either roadways or communities—evolve differently than they would in the absence of alongshore connections. Shoreline stabilization by communities in one location influences neighboring areas managed solely for roadways, inducing long‐term system‐wide lags in shoreline retreat. Conversely, when barrier segments managed for roadways are allowed to overwash, this induces shoreline curvature system‐wide, thus enhancing erosion on nearby stabilized segments. Feedbacks between dunes, storms, overwash flux, and alongshore sediment transport also affect outcomes of climate adaptation measures. In the case of partial, early abandonment of roadway management, we find that system‐wide transitions to less vulnerable landscape states are possible, even under accelerated SLR and increased storminess.
more »
« less
- Award ID(s):
- 1832221
- PAR ID:
- 10499619
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Earth's Future
- Volume:
- 12
- Issue:
- 4
- ISSN:
- 2328-4277
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract. Barrier islands are low-lying coastal landforms vulnerable toinundation and erosion by sea level rise. Despite their socioeconomic andecological importance, their future morphodynamic response to sea level riseor other hazards is poorly understood. To tackle this knowledge gap, weoutline and describe the BarrieR Inlet Environment (BRIE) model that cansimulate long-term barrier morphodynamics. In addition to existing overwashand shoreface formulations, BRIE accounts for alongshore sediment transport,inlet dynamics, and flood–tidal delta deposition along barrier islands.Inlets within BRIE can open, close, migrate, merge with other inlets, andbuild flood–tidal delta deposits. Long-term simulations reveal complexemergent behavior of tidal inlets resulting from interactions with sea levelrise and overwash. BRIE also includes a stratigraphic module, whichdemonstrates that barrier dynamics under constant sea level rise rates canresult in stratigraphic profiles composed of inlet fill, flood–tidal delta,and overwash deposits. In general, the BRIE model represents a process-basedexploratory view of barrier island morphodynamics that can be used toinvestigate long-term risks of flooding and erosion in barrier environments.For example, BRIE can simulate barrier island drowning in cases in which theimposed sea level rise rate is faster than the morphodynamic response of thebarrier island.more » « less
-
Overwash is the cross‐shore transport of water and sediment from a waterbody over the crest of a sand or gravel barrier beach, and washover is the resulting sedimentary deposit. Washover volume, and alongshore patterns of washover distribution, are fundamental components of sediment budgets for low‐lying coastal barrier systems. Accurate sediment budgets are essential to forecasting barrier system sustainability under future climate‐driven forcing. However, comprehensive surveys of three‐dimensional washover morphology are challenging to deliver. Here, we use the results of a physical experiment, analysis of lidar data, and examples of washover characteristics reported in the literature to develop scaling relationships for washover morphometry that demonstrate volume can be reasonably inferred from planform measurements, for washover in natural (non‐built) and built barrier settings. Gaining three‐dimensional insight into washover deposits from two‐dimensional information unlocks the ability to analyze past aerial imagery and estimate contributions from washover flux to sediment budgets for past storms.more » « less
-
Abstract It is widely recognized that waves inhibit river mouth progradation and reduce the avulsion timescale of deltaic channels. Nevertheless, those effects may not apply to downdrift‐deflected channels. In this study, we developed a coupled model to explore the effects of wave climate asymmetry and alongshore sediment bypassing on shoreline‐channel morphodynamics. The shoreline position and channel trajectory are simulated using a “shoreline” module which drives the evolution of the river profile in a “channel” module by updating the position of river mouth boundary, whereas the channel module provides the sediment load to river mouth for the “shoreline” module. The numerical results show that regional alongshore sediment transport driven by an asymmetric wave climate can enhance the progradation of deltaic channels if sediment bypassing of the river mouth is limited, which is different from the common assumption that waves inhibit delta progradation. As such, waves can have a trade‐off effect on river mouth progradation that can further influence riverbed aggradation and channel avulsion. This trade‐off effect of waves is dictated by the net alongshore sediment transport, sediment bypassing at the river mouth, and wave diffusivity. Based on the numerical results, we further propose a dimensionless parameter that includes fluvial and alongshore sediment supply relative to wave diffusivity to predict the progradation and aggradation rates and avulsion timescale of deltaic channels. The improved understanding of progradation, aggradation, and avulsion timescale of deltaic channels has important implications for engineering and predicting deltaic wetland creation, particularly under changing water and sediment input to deltaic systems.more » « less
-
Wind flow over coastal foredunes adapts to vegetation, resulting in spatial gradients in bed shear stresses that contribute to the formation of localized bedforms. Under- standing, and having the capability to numerically predict, the distribution of sedi- ment deposited within sparsely vegetated dune complexes is critical for quantifying the ecological, protective, and economic benefits of dune management activities. Data from wind tunnel experiments have indicated that there is a spatial lag from the canopy leading edge to a downwind location where sediment deposition first occurs. The length scale of this deposition lag is further quantified here using new field mea- surements of aeolian sediment transport across sparsely vegetated managed dune systems in Oregon, USA. We develop a deposition lag length scale parameter using both lab and this new field data and then incorporate this parameter into the process-based aeolian sediment transport model, Aeolis, which also includes a new far-field shear stress coupler. Results from numerical simulations suggest that the spatial deposition lag effect is significant for model skill in sparsely vegetated dunes. We observe with field and laboratory observations that, as canopy density increases, the length of the deposition lag decreases. As such, within the model framework the implementation of the deposition lag length does not affect the results of models of coastal dune geomorphological evolution within higher density canopies. Dune can- opy density can vary due to natural (e.g., storm overwash, burial, die-off) or anthro- pogenic (e.g., managed plantings, dune grading) processes.more » « less
