Geological constraints on mesoscale coastal barrier behaviour

Abstract

Barrier/lagoon systems occupy a significant part of the world's coast. They are diverse in size, morphology, geological and oceanographic setting, and morphodynamic behaviour. Understanding the behaviour of barriers at 10 1 to 10 2 year and 10 1 to 10 2 kilometre scales (mesoscale) is an important scientific and societal goal, not least because of the preponderance of intensive coastal development in a time of global climate change. Such understanding presents significant challenges. Challenges in describing mesoscale system behaviour relate largely to the incomplete evidence base of (i) morphological change in system components, (ii) dynamic and internal forcing factors (drivers) and (iii) geological constraints. These shortcomings curtail the development of baseline datasets against which to test models. Understanding observed changes and thereby predicting future behavioural patterns demands assumptions and simplifications regarding the linkages between initial state, dynamic drivers, system feedbacks and a multiplicity of geological constraints that are often location-specific. The record of mesoscale change is improving with the acquisition of long-term morphological datasets. Advances in technology and chronological control mean that geological investigations can now provide decadal to century-scale temporal resolution of morphological change. In addition, exploratory modelling is improving understanding of the influence of various dynamic and geological factors. most cases unquantified and are usually disregarded when conceptualizing and modelling barrier evolution. Consideration of the geological influences is, however, essential in efforts to predict future behaviour at mesoscale (management) timescales.

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems

“…Coastal dunes exist in a variety of forms, and when left to evolve naturally, their changes are controlled primarily by wind, waves, ecomorphodynamic factors and framework geology (Hesp, ; Lentz and Hapke, ; Cooper et al ., ; Wernette et al ., ). Generally, winds exceeding the sediment entrainment velocity threshold mobilize sand from the sub‐aerial portion of the beach and deposit it when wind speeds are reduced around vegetation and topographic features, typically within the upper backshore and incipient dune (Hesp, ).…”

Overwash‐dominated stratigraphy of barriers with intermittent inlets

“…The profile response of barriers to sea‐level rise is often viewed in terms of three competing models (Cooper et al, ). These include erosion, where the barrier sediment is redistributed into the shoreface (e.g.…”

“…In many such models, the barriers on coastal plains are dominated by distinctive sedimentary signatures associated with migrating tidal inlets driven by longshore sediment transport (FitzGerald et al, ; Maio et al, ; FitzGerald et al, ; Hein et al, ). These are coupled with complex back‐barrier stratigraphic signatures including salt marsh and lagoonal deposits that reflect, amongst other controls, a strong inheritance of the local bedrock framework on both inlet and barrier evolution (Cooper et al, ). The morphological changes and resulting barrier stratigraphy are related to episodic events such as channel deflections, breaching, and sediment bypassing (Tye and Moslow, ; FitzGerald et al, ).…”

Directional dependency and coastal framework geology: implications for barrier island resilience

“…In this paper, the term "framework geology" is defined as any subsurface variation in geologic structure, where variability in geologic structure can result from variations in sediment type (i.e., sand vs. silt), differences in compaction, or significant changes in the subsurface organic content or mineralogy. This term encompasses the subsurface and bathymetric geologic structure (onshore and offshore), which may include rhythmic bar and swale structures (Houser and Mathew, 2011;Houser, 2012), shoreface attached sand ridges (SASRs) overlying offshore glacial outwash headlands (Hapke et al, 2010;Schwab et al, 2013), or buried infilled paleo-channels (Anderson et al, 2016;Browder and McNinch, 2006;Fisk, 1959;McNinch, 2004;Schupp et al, 2006;Simms et al, 2010). Since the framework geology can provide insight into historical patterns of island transgression (Hapke et al, 2016;Houser, 2012;Houser et al, 2015;Lentz et al, 2013), it is vital to better understand how the framework geology influences variability in modern beach and dune morphology (Cooper et al, 2018).…”

“…Padre Island National Seashore (PAIS) on North Padre Island, Texas, represents an ideal location to test this hypothesis because previous studies have documented significant variability in the subsurface framework geology ( Fig. 1; Anderson et al, 2016;Fisk, 1959;Wernette et al, 2018;Weymer et al, 2018;Weymer, 2012, and there is substantial alongshore variation in beach and dune morphology. Given that the dominant current along the central Texas coast flowed from north to south during the Holocene (Sionneau et al, 2008), it follows that the dominant alongshore sediment transport gradient during that time also flowed from north to south.…”