Evaluating direct and strategic placement of dredged material for marsh restoration through model simulations

Dredged material can be used for marsh restoration by depositing it on the marsh surface (thin-layer placement), by releasing it at the mouth of channels and allowing tidal currents to transport it onto the marsh platform (channel seeding), or by creating new marshes over shallow areas of open water. We investigate the efficacy of these different methods using a comprehensive 2D marsh evolution model that simulates tidal dynamics, vegetation processes, bank and wave erosion, and ponding. Total marsh area is assessed over 50 years in an idealized microtidal marsh under different relative sea level rise (RSLR) scenarios. For a given volume of total sediment added, the frequency of deposition is relatively unimportant in maximizing total marsh area, but the spatial allocation of the dredged material is crucial. For a given volume of sediment, thin-layer deposition is most effective at preserving total marsh area, especially at high rates of RSLR. Channel seeding is less efficient, but it could still provide benefits if larger amounts of sediment are deposited every 1-2 years. Marsh creation is also beneficial, because it not only increases the marsh area, but additionally slows the erosion of the existing marsh. The 2D model is highly computationally efficient and thus suited to explore many scenarios when evaluating a restoration project. Coupling the model with a cost assessment of the different restoration techniques would provide a tool to optimize marsh restoration.

Modeling Marsh Dynamics Using a 3-D Coupled Wave-Flow-Sediment Model

Salt marshes are dynamic biogeomorphic systems that respond to external physical factors, including tides, sediment transport, and waves, as well as internal processes such as autochthonous soil formation. Predicting the fate of marshes requires a modeling framework that accounts for these processes in a coupled fashion. In this study, we implement two new marsh dynamic processes in the 3-D COAWST (coupled-ocean-atmosphere-wave sediment transport) model. The processes added are the erosion of the marsh edge scarp caused by lateral wave thrust from surface waves and vertical accretion driven by biomass production on the marsh platform. The sediment released from the marsh during edge erosion causes a change in bathymetry, thereby modifying the wave-energy reaching the marsh edge. Marsh vertical accretion due to biomass production is considered for a single vegetation species and is determined by the hydroperiod parameters (tidal datums) and the elevation of the marsh cells. Tidal datums are stored at user-defined intervals as a hindcast (on the order of days) and used to update the vertical growth formulation. Idealized domains are utilized to verify the lateral wave thrust formulation and show the dynamics of lateral wave erosion leading to horizontal retreat of marsh edge. The simulations of Reedy and Dinner Creeks within the Barnegat Bay estuary system demonstrate the model capability to account for both lateral wave erosion and vertical accretion due to biomass production in a realistic marsh complex. The simulations show that vertical accretion is dominated by organic deposition in the marsh interior, whereas deposition of mineral estuarine sediments occurs predominantly along the channel edges. The ability of the model to capture the fate of the sediment can be extended to model to simulate the impacts of future storms and relative sea-level rise (RSLR) scenarios on salt-marsh ecomorphodynamics.

Managing the Hazards of Aeolian, Fluvial and Coastal Erosion in Gudhi Area-Northern Kuwait Bay

Kuwait Institute for Scientific Research plans to set up some research facilities within the Gudhi area, which lies north of the coastal spill of Kuwait Bay. The area is about 653,000 m2, the region highly sensitive from an environmental perspective and ecological. It is a coastal strip dominated by rich fauna and flora mainly Nitraria retusa forming large nabkhas that attract many wildlife scientists. The presence of nabkhas is a good indicator of fluvial and aeolian activities in the area. The establishment of infrastructures within this area is anticipated to cause significant damage to wildlife. Additionally, any future infrastructures in the area is under the following threats: 1-S and encroachment as it is located within an active wind corridor. 2-Fluvial action during flood seasons as it is located at downstream of Jal Al-Zur watershed. 3-The wave erosion along 1200m coastal margin. As an important role of KISR is the attention and care regarding the environmental aspects associated with project actions, therefore, it is proposed that a proper scientific research project should be implemented prior to the establishment of any infrastructure development. The main objective of this study is to assess and control hazards in the Gudhi area by implementation of native plants and mangroves landscape design. Assessment and monitoring of fauna and flora have provided initial information on existing vegetation, soil properties that are considered important to quantify ecological conditions prior to actual vegetation plantation establishment or restoration effort. Nitraria and Lycium populations were found the most proper in controlling hazards of mobile sand and flush floods for the study area.

The influence of rock uplift rate on the formation and preservation of individual marine terraces during multiple sea-level stands

Marine terraces are a cornerstone for the study of paleo sea level and crustal deformation. Commonly, individual erosive marine terraces are attributed to unique sea-level high stands based on the reasoning that marine platforms could only be significantly widened at the beginning of an interglacial. However, this logic implies that wave erosion is insignificant at other times. We postulate that the erosion potential at a given bedrock elevation datum is proportional to the total duration of sea-level occupation at that datum. The total duration of sea-level occupation depends strongly on rock uplift rate. Certain rock uplift rates may promote the generation and preservation of particular terraces while others prevent them. For example, at rock uplift of ~1.2 mm/yr, the Marine Isotope Stage (MIS) 5e (ca. 120 ka) high stand reoccupies the elevation of the MIS 6d–e mid-stand, favoring creation of a wider terrace than at higher or lower rock uplift rates. Thus, misidentification of terraces can occur if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their relative elevations. Developing a graphical proxy for the entire erosion potential of sea-level history allows us to address creation and preservation biases at different rock uplift rates.

Biophysical controls of marsh soil shear strength along an estuarine salinity gradient

Sea-level rise, saltwater intrusion, and wave erosion threaten coastal marshes, but the influence of salinity on marsh erodibility remains poorly understood. We measured the shear strength of marsh soils along a salinity and biodiversity gradient in the York River estuary in Virginia to assess the direct and indirect impacts of salinity on potential marsh erodibility. We found that soil shear strength was higher in monospecific salt marshes (5–36 kPa) than in biodiverse freshwater marshes (4–8 kPa), likely driven by differences in belowground biomass. However, we also found that shear strength at the marsh edge was controlled by sediment characteristics, rather than vegetation or salinity, suggesting that inherent relationships may be obscured in more dynamic environments. Our results indicate that York River freshwater marsh soils are weaker than salt marsh soils, and suggest that salinization of these freshwater marshes may lead to simultaneous losses in biodiversity and erodibility.

Rapid Landscape Changes in Plastic Bays Along the Norwegian Coastline

The Norwegian Coastal Current transports natural debris and plastic waste along the Norwegian coastline. Deposition occurs in so-called wreck-bays and includes floating debris, such as seaweed, driftwood and volcanic pumice, and increasing amounts of plastics during the last decades. Deposition in these bays is controlled by ocean currents, tidal movements, prevailing winds and coastal morphology. We have compared soil profiles, analyzed the vegetation and inspected aerial photos back to 1950 in wreck-bays and defined three zones in the wreck-bays, where accumulation follows distinct physical processes. Zone 1 includes the foreshore deposition and consists of recent deposits that are frequently reworked by high tides and wave erosion. Thus, there is no accumulation in Zone 1. Zone 2 is situated above the high tide mark and includes storm embankments. Here, there is an archive of accumulated debris potentially deposited decades ago. Zone 3 starts above the storm embankments. The debris of Zone 3 is transported by wind from Zone 1 and Zone 2, and the zone continues onshore until the debris meets natural obstacles. Plastic accumulation seems to escalate soil formation as plastic is entangled within the organic debris Mapping and characterizing the soil layers indicates that deep soils have been formed by 50 or more years’ accumulation, while the pre-plastic soil layers are thin. The plastic soil forms dams in rivers and wetlands, changing the shape and properties of the coastal landscape, also altering the microhabitat for plants. This case-study describes an ongoing landscape and vegetation change, evidently co-occurring with the onset of plastic accumulation. Such processes are not limited to the Norwegian coastline but are likely to occur wherever there is accumulation of plastic and organic materials. If this is allowed to continue, we may witness a continued and escalating change in the shape and function of coastal landscapes and ecosystems globally.

Formation and preservation of marine terraces during multiple sea level stands

<p>Marine terraces are a cornerstone for the study of paleo sea level and crustal deformation. Commonly, individual erosive marine terraces are attributed to unique sea level high-stands. This stems from early reasoning that marine platforms could only be significantly widened under moderate rates of sea level rise as at the beginning of an interglacial and preserved onshore by subsequent sea level fall. However, if marine terraces are only created during brief windows at the start of interglacials, this implies that terraces are unchanged over the vast majority of their evolution, despite an often complex submergence history during which waves are constantly acting on the coastline, regardless of the sea level stand.<span> </span></p><p>Here, we question the basic assumption that individual marine terraces are uniquely linked to distinct sea level high stands and highlight how a single marine terrace can be created By reoccupation of the same uplifting platform by successive sea level stands. We then identify the biases that such polygenetic terraces can introduce into relative sea level reconstructions and inferences of rock uplift rates from marine terrace chronostratigraphy.</p><p>Over time, a terrace’s cumulative exposure to wave erosion depends on the local rock uplift rate. Faster rock uplift rates lead to less frequent (fewer reoccupations) or even single episodes of wave erosion of an uplifting terrace and the generation and preservation of numerous terraces. Whereas slower rock uplift rates lead to repeated erosion of a smaller number of polygenetic terraces. The frequency and duration of terrace exposure to wave erosion at sea level depend strongly on rock uplift rate.</p><p>Certain rock uplift rates may therefore promote the generation and preservation of particular terraces (e.g. those eroded during recent interglacials). For example, under a rock uplift rate of ca. 1.2 mm/yr, Marine Isotope Stage (MIS) 5e (ca. 120 ka) would resubmerge a terrace eroded ca. 50 kyr earlier for tens of kyr during MIS 6d–e stages (ca. 190–170 ka) and expose it to further wave erosion at sea level. This reoccupation could accordingly promote the formation of a particularly wide or well planed terrace associated with MIS 5e with a greater chance of being preserved and identified. This effect is potentially illustrated by a global compilation of rock uplift rates derived from MIS 5e terraces. It shows an unusual abundance of marine terraces documenting uplift rates between 0.8 and 1.2 mm/yr, supporting the hypothesis that these uplift rates promote exposure of the same terrace to wave erosion during multiple sea level stands.</p><p>Hence, the elevations and widths of terraces eroded during specific sea level stands vary widely from site-to-site and depend on local rock uplift rate. Terraces do not necessarily correspond to an elevation close to that of the latest sea level high-stand but may reflect the elevation of an older, longer-lived, occupation. This leads to potential misidentification of terraces if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their elevations.</p>

Towards a dynamic approach of sequences of coral reef terraces

<p>Sequences of coral reef terraces result from the interplay between biogenic and clastic sedimentary production, relative sea level (RSL) variations, wave erosion and tectonic forcing. Reefal sequences are gold standard proxies for paleo-sea level and tectonic reconstructions, but their contribution is usually restricted to a bijective approach, correlating the single elevation and age of their inner edge to single sea level stands or coseismic offsets, and reciprocally. The increase of available data, such as coral datings and high resolution topography revealed major deviations from this bijective approach (corals from a single MIS on several terraces, and conversely, or MIS highstands not represented in a sequence).</p><p>The Cape Laundi sequence, Sumba island, Indonesia, demonstrates such deviations, with outcrops of corals from MIS 5e on as many as three terraces instead of a single terrace as commonly expected. A preliminar numerical model of coral reef terrace profile has been developed, integrating reef growth, wave erosion, RSL variations and tectonic deformation. The interplay between reef growth rate, tectonic displacements and RSL variations provides a plausible explanation for these numerous occurrences. The low growth rate of this reef appears to prevent coral from  saturating the accommodation space generated during sea level transgression, leading to the preservation of drowned platforms and reefal construction of similar age during regressions.</p><p>Preliminary results from numerical modeling reveal complex feedbacks between the processes shaping these morphologies. Tectonic deformation has a major influence on reef development, by favoring reef preservation at high uplift rates and controlling the available accommodation space for reef growth.. By taking into account the numerous feedbacks controlling reef morphology, we can investigate the significance of RSL variations, continuous and punctual rock uplift, biogenic activity, and clastic inputs on coral terrace morphology and chronostratigraphy. Our approach can bring crucial constraints to the rates and frequency of RSL variations. To do so, we further develop our numerical model in order to provide more robust insights on the controls of reefal sequences morphologies. </p>

Analysis of deformation features using integrated field methods and aerial drone imaging on the Bach Long Vy island, Gulf of Tonkin, Vietnam

<p>Situated in the junction between the Song Hong Basin and the Beibuwan Basin, the Bach Long Vy island exposes Paleogene syn-rift rocks not seen elsewhere in the Gulf of Tonkin. The island underwent a complex geological history related to the Cenozoic SE-ward tectonic escape of Indochina, recorded as deformation features along the outstanding, continuous coastal exposure. To analyze these deformation features in detail and relate them to the regional events, we acquired a high-resolution Unmanned Aerial Vehicle (UAV) dataset covering about 635,000m<sup>2</sup> of the 3.5 km long coastal outcrop. In addition, 656 strike and dip measurements were made and 390 photos were taken using smart phone apps, thus on-the-ground data were rapidly acquired and georeferenced. Strike and dip measurements from smart phone apps were periodically checked against traditional Brunton compasses for their reliability. The ground photos were correlated with the UAV image during interpretation. QGIS allows both datasets to be overlain on one another for detailed analysis and interpretation.</p><p>We interpreted 2236 deformation features from the dataset, which can be divided into three major types: sand injectites, NW-SE faults, and NE-SW faults. Sand injectites can be divided into three main types: linear dikes, irregular dikes, and massive remobilized sands. Linear dikes trend dominantly N80-100E.</p><p>NW-SE faults are closely spaced and have high dip with N110-130E trend. They consistently left-laterally offset sand dikes while most of the time left-laterally offset the gently dipping beds. Apparent right-lateral separation of beddings probably resulted from variation of the slip vector from horizontal pure strike-slip. Occasionally, sand dikes fill in these NW-SE faults. The offsets are small, mostly less than 1 m.</p><p>NE-SW faults are larger scale than the NW-SE faults, and are associated with drag folding of the strata. No fault surface kinematic indicators were found, probably due to wave erosion. The drag folds are consistently right-lateral, while the bedding separation can be either left-lateral or right lateral. Left-lateral separation is inferred to indicate a second phase of movement along the same fault. Sand dikes cross-cut the drag folds, thus sand dikes formed after the drag folds and the right-lateral motion on NE-SW faults.</p><p>The orientations of these deformation features are consistent with the regional stress field associated with the End-Oligocene inversion, which affected the northern Song Hong Basin and the western Beibuwan Basin due to transpression along the junction between the two basins. The inversion caused regional tilting and NE-SW right-lateral faulting, followed by the main phase of sand injection, and finally the left-lateral NW-SE faults that offset sand dikes. Previously the inversion event was characterized at large scale using industrial seismic and well data. This study provides further evidence of the inversion at the outcrop scale, well below the resolution of the seismic data.</p>