Proto-type Experiment of Sediment Transport in Shallow water

Lead Research Organisation: Plymouth University
Department Name: Sch of Marine Science & Engineering


The ability to predict how much sand moves under ocean waves and currents, at what rate, and where it goes, is critical for managing our coastal industries, ports, harbours, shipping routes, offshore energy infrastructures, beaches, estuaries, cliffs and the low-lying coastal environments they protect. This is particularly true in a setting of expected sea level rise and enhanced utilization of the coastal ocean.

The effects of coastal erosion and flooding to settlements and natural resources is widely publicised, yet unfortunately our ability to predict the location and extent of damage remains poor, particularly over the timescale of years. This information is also required to design and predict the life of coastal engineering projects to mitigate the socially, ecologically and economically important impacts of erosion and flooding.

Considering the state of current knowledge, the biggest leaps in improving such predictions, will come from improved understanding of what controls the direction and rate of transport of the sediment which makes up the seabed. Just like predicting the weather, the goal of researchers in the field of coastal engineering is to produce accurate operational models of sediment transport and the resulting changes caused to the shape of the seabed.

This project is motivated by the observation that sediment transport predictions get progressively worse as water depths decrease to just a few metres (i.e. near land: arguably the most important area) because of the increasing importance of very small-scale processes of which we have inadequate understanding. Until recently, sensing technologies to measure accurately and rapidly at this small scale did not exist. Fortunately, commercially-available sensors now exist which are able to measure flow speeds at the required resolution. In addition, in conjunction with our project partners we have recently developed and tested new sensors which can provide us information on how much sediment is in the water, and how the seabed evolves over individual waves. By conducting detailed laboratory experiments with these new sensing technologies in a 'life-size' wave flume, we aim to further our understanding of all these very small scale processes which appear to be more important in shallow water.

We aim to use the knowledge gained about these small scale sediment transport processes and implement them in models to predict the resulting changes to the seabed. By using measurements of this bed evolution taking in the wave flume, we'll be able to identify which of these various processes are most important, and what is the best way to incorporate them into models which predict the evolution of our coastline.

Finally, we aim to make the entire data set publicly-available and accountable using a database linked web application which permits the user to easily specify their data requirements and data format. The coastal engineering and planning community will be able to browse, explore and download the data freely. Software developers and environmental consultants will be able to use the data set as a benchmark with which to test future models of sediment transport and coastal evolution. Finally, other scientists will be able to easily scrutinise our findings and use the data for their own analyses, which will serve as the basis for future progress in this important field of research.

Planned Impact

The aim of the project is to collect an extensive laboratory data set and use it to parametrise the phase-dependency (at intra-wave time scales) of a collection of second-order processes thought to be important in transporting sediment in shallow water, in order to improve time-averaged predictions of sediment transport under waves. We believe the project can be only one step removed from the end user by packaging the our findings in ways which can have immediate application in existing process-based models for predicting the transport of sediment by waves and currents, and the associated changes to the configuration of the seabed. Given the anticipated completeness of the data set, it could prove a major step to providing a much-needed 'benchmarking' standard for testing developments in process-based coupled hydrodynamic-sediment-transport models. As such, it could prove extremely useful for academic and consultant researchers and software developers alike.

Being associated with the EU Framework 7 Hydralab IV project BARDEX II, representing 2 months of large-scale facility time already awarded to the research team to carry out an extensive set of wave flume experiments, along with a budget for travel to meetings between an international team of project partners, this project represents enormous value-for-money. Funds are requested only to maximise the impact of this exciting set of experiments, on both the academic and end-user communities. This includes three elements: 1) staff time required to carry out the experiments effectively, to collate and analyse the data, and to develop improved modelling approaches; 2) staff time to create and implement a publicly available web-accessible data application and algorithm repository; and 3) a modest budget for dissemination activities, including software and data storage for the data server and travel to national and international conferences attended by academic and consultant coastal engineers.

The extensive data set promises to impact significantly beyond the above specific objectives of this project. Research areas of most immediate relevance are: a) sediment transport and bathymetric change seaward of the inner surf zone; b) turbulence in oscillatory flows; c) general hydrodynamic model validation; d) general sediment transport model validation in any shear-dominated flow (oceanic, fluvial, aeolian); e) validation and development of sensors for turbulence, accurate boundary distance measurements, and high concentration of granular materials; and f) fundamental studies of any flows where exchanges between granular and fluid phases are important.

The data might have widespread importance to continuing advancements in modelling sediment transport in shallow water oceanic environments, as well as wider application in the fields outlined above. It is therefore important that the interfaced data server is designed to be: a) easy to use (and not just by experts in the field of nearshore sediment transport); b) flexible (such as options to view and download specific portions of the data and meta-data); and c) interactive (such as options to visualise the data in various ways). The form of this data product may form a blueprint for future data dissemination from important sets of experiments, and even foster a new type of online collaboration. It will be important to ensure the applied coastal engineering community is adequately informed of these developments. This will be carried out through conference presentations, articles in technical literature, and posts to various well-subscribed mailing lists. Important research findings will be published in coastal/hydraulic engineering journals.
Description We have been able to identify that shear stress in the swash under beaches displays the same dependency to Reynolds number that most other flows behave. Previous researcher had not identified this because of an incorrect formulation of the appropriate Reynolds number. This finding makes accurate modelling of swash processes more straight forward.
Exploitation Route Proper implementation of the Reynolds number and the resulting friction factors will improve morphological models of swash zones.
Sectors Environment,Leisure Activities, including Sports, Recreation and Tourism

Description Hydralab+
Amount € 5,000 (EUR)
Funding ID 654110 
Organisation European Commission 
Department Horizon 2020
Sector Public
Country European Union (EU)
Start 05/2017 
End 10/2017
Title Public database of proto-type scale laboratory tests on swash, wave breaking and barrier dynamics 
Description Five key objectives were central to the Bardex 2 hydralab experiments. WP1 - barrier hydrology: to observe, quantify and model the dynamic groundwater conditions within the barrier, subject to varying wave, water-level and back-barrier lagoon conditions. WP2 - swash and berm dynamics: to examine the relative roles of advected bore-generated turbulence versus local boundary layer processes in the full column sediment transport processes in the swash zone; to resolve the role of barrier hydrology in controlling equilibrium morphological response at the beach face. WP3 - swash-surf zone exchange and bar dynamics: to determine and quantify the dominant hydrodynamic and sediment transport mechanisms responsible for swash-surf zone sediment exchange; to identify key processes responsible for onshore and offshore bar migration. WP4 - barrier overwash: to quantify overwash threshold for different wave and water-level conditions; to investigate the effect of groundwater gradients on overwash processes; to compare overwash processes on sand and gravel barriers. WP5 - Sediment resuspension and bed morphology: to observe and measure vortex resuspension process and bedform dynamics under shoaling and breaking waves; to quantify changes in the magnitude and direction of sediment transport (bedload and suspended load) in the region just outside the surf zone. WP6 - numerical modeling: to further develop and rigorously test advanced process-based cross-shore hydro-morphodynamic models that address bar and barrier dynamics, and barrier destruction through overwash. 
Type Of Material Database/Collection of data 
Year Produced 2014 
Provided To Others? Yes  
Impact An entire volume of Coastal Engineering (Elsevier) is dedicated to the results of this work.