Experiments by Invited Researchers


Barrier Dynamics Experiments (BARDEX)

Project acronym: HyIII-Delft-11
Name of Group Leader: Prof. Jon Williams, University of Plymouth
User-Project Title: Barrier Dynamics Experiments (BARDEX)
Facility: Delta Flume
Proceedings TA Project: Bardex (barrier dynamics experiment): a laboratory study of gravel barrier response to waves and tides
Data Management Report: There is no Data Management Report available for this project

User-Project Objectives

The BARDEX experiments were designed to investigate gravel barrier behavior at prototype scale. Specifically, they aimed to investigate the morphological response of a gravel barrier to simulated random wave fields and to varying water levels. Studies were also undertaken to examine fundamental processes associated with beach face sediment transport and barrier overwash and breaching. All BARDEX workpackages (WPs) aimed to produce highquality data sets for process studies and for model calibration and testing. WP1 (Barrier Stability and Over-wash) aimed to improve understanding of overwash sediment transport and the threshold conditions for overwash occurrence. WP2 (Barrier Groundwater) aimed to investigate the role of back-barrier lagoon levels on the dynamic groundwater profile through the barrier and to assess whether varying groundwater levels may induce differing morphological response at the beach face. WP3 (Swash Sediment Transport) aimed to improve understanding of sediment transport processes on the beach face under accretionary and erosive conditions. WP4 (Nearshore Hydrodynamics and Sediment Processes) aimed to examine hydrodynamics and sediment transport at locations from the swash region to locations offshore from the barrier. WP5 (Integration and Modelling) aimed to develop new practical modelling tools to: (a) predict barrier morphology from the offshore limit of sediment transport to the lee side of the barrier; and (b) predict the response of barrier morphology to beach recharge.

Short description of the work carried out

The BARDEX project met all the objectives set out above. A high quality data set was produced and is currently being analysed by the BARDEX Partners. Preliminary results from BARDEX were disseminated at the International Coastal Symposium in Lisbon at the end of April 2009. A workshop to be held in Delft on June 2009 will finalized papers for submission to a Journal Special Issue and allow wide dissemination. The challenging requirement to simulate a tide and to maintain high of low water levels on either side of the barrier was addressed successfully by Deltares. There were no difficulties encountered during the experiments.

Highlights of important research results

Work in WP1 has quantified overwash sediment transport and threshold condition for overwash and breaching using for the first time a combination of tidal modulations and varying wave conditions. Changing the beach groundwater table in WP2 have shown that lowering the water table enhances net onshore sediment transport in the swash zone and berm development. This was most pronounced with a steady sea level and longperiod
waves. Elevating the groundwater table results in net offshore sediment transport and erosion in the swash zone, and was most pronounced during tidal simulations. Elevating the groundwater table for the steady sea level
tests and lowering the groundwater table during the tidal tests had a limited effect on the beach profile development. In WP3 data have improved process understanding and modelling of swash sediment transport on the beach face under accretionary and erosive conditions. The data enhance field data obtained in the UK
at Slapton Sands in May 2008. Instruments deployed offshore in WP4 have provided new information on turbulence production over very rough boundaries and on coarse particle bedforms and beach step processes. The calibration and validation of the Xbeach model using BARDEX data will allow improved prediction of gravel barrier morphodynamics. This in turn will have a range of practical applications concerned with the use of coarse material for coastal protection works.