Observations of cross-shore sediment transport and formulation of the undertow

A new set of data from a large-scale sand bar migration experiment is presented. During this experiment, two sandbars were generated. One of the bar was generated by the action of undertow, and sediment moved offshore. The other bar was generated by the shoreward movement of sediment coming from the first bar. The principal mechanism responsible for shoreward movement is associated with effects of velocity asymmetry. Analysis of bathymetric surveys and suspended sediment concentration data reveals that suspended load contributed to a large extent to the formation of the first bar. Bed load was also important, and was moving in the same direction as suspended load. For the second bar, shoreward sediment movement occurred as bedload. Suspended load was moving in the opposite direction as bed load. This difference in sediment movement is explained by the predominance of the undertow in the suspended sediment flux. Two models were tested to reproduce the observed sediment transport, a wave-averaged (energetics) model and a wave-resolved model. After proper calibration, both models yielded satisfactory results. Calibration efforts highlighted the need for robust models of sediment pickup functions and sediment eddy diffusivity. They also showed the need for a deterministic undertow models. Formulations of the undertow are presented. These formulations are valid for all relative water depths, and include mean current advective terms. These formulations show that the forcing of the undertow is depth-uniform, assuming linear water wave theory. The model is tested against four datasets to evaluate the possibility of a deterministic model. Although a constant eddy viscosity would yield such a model, no universal parametrization could be determined

The Power of Three: Coral Reefs, Seagrasses and Mangroves Protect Coastal Regions and Increase Their Resilience

Natural habitats have the ability to protect coastal communities against the impacts of waves and storms, yet it is unclear how different habitats complement each other to reduce those impacts. Here, we investigate the individual and combined coastal protection services supplied by live corals on reefs, seagrass meadows, and mangrove forests during both non-storm and storm conditions, and under present and future sea-level conditions. Using idealized profiles of fringing and barrier reefs, we quantify the services supplied by these habitats using various metrics of inundation and erosion. We find that, together, live corals, seagrasses, and mangroves supply more protection services than any individual habitat or any combination of two habitats. Specifically, we find that, while mangroves are the most effective at protecting the coast under non-storm and storm conditions, live corals and seagrasses also moderate the impact of waves and storms, thereby further reducing the vulnerability of coastal regions. Also, in addition to structural differences, the amount of service supplied by habitats in our analysis is highly dependent on the geomorphic setting, habitat location and forcing conditions: live corals in the fringing reef profile supply more protection services than seagrasses; seagrasses in the barrier reef profile supply more protection services than live corals; and seagrasses, in our simulations, can even compensate for the long-term degradation of the barrier reef. Results of this study demonstrate the importance of taking integrated and place-based approaches when quantifying and managing for the coastal protection services supplied by ecosystems

Catching the Right Wave: Evaluating Wave Energy Resources and Potential Compatibility with Existing Marine and Coastal Uses

Many hope that ocean waves will be a source for clean, safe, reliable and affordable energy, yet wave energy conversion facilities may affect marine ecosystems through a variety of mechanisms, including competition with other human uses. We developed a decision-support tool to assist siting wave energy facilities, which allows the user to balance the need for profitability of the facilities with the need to minimize conflicts with other ocean uses. Our wave energy model quantifies harvestable wave energy and evaluates the net present value (NPV) of a wave energy facility based on a capital investment analysis. The model has a flexible framework and can be easily applied to wave energy projects at local, regional, and global scales. We applied the model and compatibility analysis on the west coast of Vancouver Island, British Columbia, Canada to provide information for ongoing marine spatial planning, including potential wave energy projects. In particular, we conducted a spatial overlap analysis with a variety of existing uses and ecological characteristics, and a quantitative compatibility analysis with commercial fisheries data. We found that wave power and harvestable wave energy gradually increase offshore as wave conditions intensify. However, areas with high economic potential for wave energy facilities were closer to cable landing points because of the cost of bringing energy ashore and thus in nearshore areas that support a number of different human uses. We show that the maximum combined economic benefit from wave energy and other uses is likely to be realized if wave energy facilities are sited in areas that maximize wave energy NPV and minimize conflict with existing ocean uses. Our tools will help decision-makers explore alternative locations for wave energy facilities by mapping expected wave energy NPV and helping to identify sites that provide maximal returns yet avoid spatial competition with existing ocean uses

Observations of remote and local forcing in Galveston Bay, Texas

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references (leaves 84-87).Issued also on microfiche from Lange Micrographics.A high quality set of 321 days of sea level and wind records and of 126 days of current records, from winter to spring, has been used to examine the relative importance of remote and local forcing on the subtidal response in Galveston Bay, Texas. The observations show that the subtidal water surface energy increases with decreasing frequency, and that amount of energy increases with distance towards the end of the estuary. The surface setup and the water elevation at the entrance of the bay are asymmetric. The surface setup is more skewed than the sea level. The analyses show that the sea level and current subtidal fluctuations, at the entrance of the bay, are driven primarily by the remote forcing. For the sea level fluctuations, the remote forcing is four times more important than the wind stress at the entrance of the bay, and only two times more important at the end of the bay. The surface setup is primarily responsive to the shore normal wind stress. For the setup, the local forcing is two times more important than the remote forcing

The Power of Three: Coral Reefs, Seagrasses and Mangroves Protect Coastal Regions and Increase Their Resilience

<div><p>Natural habitats have the ability to protect coastal communities against the impacts of waves and storms, yet it is unclear how different habitats complement each other to reduce those impacts. Here, we investigate the individual and combined coastal protection services supplied by live corals on reefs, seagrass meadows, and mangrove forests during both non-storm and storm conditions, and under present and future sea-level conditions. Using idealized profiles of fringing and barrier reefs, we quantify the services supplied by these habitats using various metrics of inundation and erosion. We find that, together, live corals, seagrasses, and mangroves supply more protection services than any individual habitat or any combination of two habitats. Specifically, we find that, while mangroves are the most effective at protecting the coast under non-storm and storm conditions, live corals and seagrasses also moderate the impact of waves and storms, thereby further reducing the vulnerability of coastal regions. Also, in addition to structural differences, the amount of service supplied by habitats in our analysis is highly dependent on the geomorphic setting, habitat location and forcing conditions: live corals in the fringing reef profile supply more protection services than seagrasses; seagrasses in the barrier reef profile supply more protection services than live corals; and seagrasses, in our simulations, can even compensate for the long-term degradation of the barrier reef. Results of this study demonstrate the importance of taking integrated and place-based approaches when quantifying and managing for the coastal protection services supplied by ecosystems.</p></div

Moderating effects of natural habitats on storm surge and waves.

<p>Profiles of surge (top subplots), wave height (middle subplots) and bathymetry, with habitats (bottom subplot) in the fringing and barrier reef profiles during the synthetic hurricane. Profiles of wave height in the absence of wind are shown to illustrate the extent of wave re-generation that occurs in the lagoons.</p

Protective role of corals, seagrasses and mangroves during non-storm conditions under present sea-level conditions.

<p>Bar plot of average wave height at the shoreward edge of the submerged mangrove forest (top subplots) and bed scour volume over the submerged mangrove forest (bottom subplots) computed for different combinations of live reef, seagrass meadows and mangroves presence, under present sea-level conditions. Vertical tick marks indicate 1 standard deviation value around the mean. Circles represent minimum and maximum values. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158094#pone.0158094.s005" target="_blank">S5 Fig</a> for box plot version of this figure for a future sea-level rise scenario.</p

Summary of non-storm wave climate statistics in the lagoon for different reef conditions.

<p>Summary of non-storm wave climate statistics in the lagoon for different reef conditions.</p

Protective role of corals, seagrasses and mangroves during storm conditions.

<p>Coastal protection services provided by coral reefs, seagrass beds and mangroves, under present day sea-level conditions, for various combinations of live and dead habitats during a hurricane. Patterns are the same for the future sea-level rise scenario (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158094#pone.0158094.s006" target="_blank">S6 Fig</a>).</p

Non-Storm Wave Statistics Offshore of Belize.

<p>Non-Storm Wave Statistics Offshore of Belize.</p