Hydraulics and Coastal Engineering Seminar Series

Overview of all meetings:

January 2014: ir. Rebeca Gonzalez and dr. ir. Tomas Van Oyen May 2013: prof. H.E. de Swart and A. Nnafie (UUtrecht) October 2013: dr. ir. Wael Hassan and ir. Dieter Meire May 2013: prof. H.E. de Swart and A. Nnafie (UUtrecht) February 2013: dr. ir. Bas Borsje (UTwente) and ir. Leen Baelus (UGent)

January 2014

Validation of LSPIV to acquire 2D free-surface flow fields for vegetated rivers - R. Gonzalez

In the field of ecohydraulics, modelling efforts are undertaken to describe the self-organisation of vegetation patterns in rivers streams. Two-dimensional data with high spatial and temporal resolution are necessary for the development of a (horizontal) 2D model. However, the use of single point measurements is labour intensive and highly expensive. In this presentation, the validation of large scale particle velocitmetry (LSPIV) to adquire 2D surface velocity fields for vegetated streams is presented.

Sorting out sorted bed forms - T. Van oyen

The occurrence of sorted bedforms on inner shelves of coastal seas is investigated. These features consist of alternating bands of coarse and fine grains, with small topographic undulations. It is illustrated that inherent feedbacks between alongshore currents, sea waves, bottom topography and roughness variations result in the emergence of morphological patterns, similar to the observed bed features. We find that two modes are amplified which display different characteristics, yielding a possible explanation to the diversity exhibited by sorted bedforms in the field. The results illustrate that both roughness variations and bottom topography influence the generation of sorted bedforms.

October 2013

Modeling of uniform and size graded sands under sheet-flow conditions - W. Hassan

The present study concentrates mainly on the influence of sediment gradation on the wave- induced sediment transport and can be considered as a logical next step in an ongoing line of cross-shore sand transport research. The study focuses at improving our basic understanding of size-graded and uniform sand transport mechanisms in cross-shore direction under oscillatory sheet-flow conditions. Sheet-flow is the dominant transport mode during storm conditions, when coastal and seabed erosion and deposition processes are generally very strong. Moreover, this study aims at improving the performance of model concepts for the description of both the rate and size-composition of the transported sand. Improved modeling tools will be developed through a strong interaction between experimental laboratory research, on the one hand, and different types of mathematical transport modeling on the other hand.

Interaction between neighbouring patches: impact on flow and deposition - D. Meire

In the field of ecohydraulics, much effort has been paid to describe the flow for uniform meadows of vegetation. However, in the field (lowland rivers or tidal flats), vegetation almost never appears uniformly, on the contrary, often a patchy formation can be observed. Although some studies describe the flow characteristics around one patch, almost no information on the influence of multiple patches on the flow field is available. In this presentation, the flow and sedimentation patterns in the wake behind neighboring patches will be illustrated and discussed.

May 2013

The nonlinear response of sand ridges on the shelf to extraction of sand; a model perspective - H.E. de Swart and A. Nnafie

The morphology of many storm-dominated inner shelves (depths of 10-20m) is characterized by patches of shoreface-connected sand ridges, which result from interactions between waves, currents and the sandy bottom. Examples include the inner shelves of Long Island and the North Sea. Typical spacings between successive ridges are in the range 4-10 km and their crests form an angle of 200-400 with the coastline. Shoreface-connected sand ridges have heights of several meters, they evolve on a timescale of centuries and they migrate several meters per year along the coast. Because of their large sand volumes, shoreface-connected sand ridges are considered as potential sources to extract sand for e.g. beach nourishments. However, sand extraction might destabilize the ridges and might remove the natural onshore sand supply to the nearshore zone, leading eventually to beach erosion. A process-based model is used to gain insight into the physics underlying the response of shoreface-connected sand ridges to sand extraction.

In this seminar, we present results on how extraction modifies 1) the ridges and 2) the sediment exchange between the inner shelf and nearshore zone.

February 2013

Biogeomorphology of coastal seas - B. Borsje

Benthic organisms live in the top centimeters of the seabed and change the structure of the seabed in ways not done by physical processes alone, either by reworking the sediment (e.g. bioturbators) or by providing structures (e.g. tube-building worms) and thereby create, modify and maintain habitats.
Due to the interaction between the tidal current and the sandy seabed tidal sand waves are formed, which change in form continuously and thereby controlling the spatial and temporal distribution of benthic organisms.
During this seminar we explore the mutual interactions between small-scale benthic organisms and the large-scale underwater landscape of coastal seas, by combining field observations, flume experiments and model studies.

Measurements of impact forces and water pressures on the crest of a breakwater - L. Baelus

For the structural design of flood retention measures or other constructions at the coastline, the impact forces on these structures need to be identified. Empirical formulas allow the determination of the overtopping volumes for a large variety of dikes or breakwaters. Only limited theories have been derived to assess the forces caused by these overtopping volumes on structures positioned at the crest of breakwater. Therefore, scale model tests are being executed in the wave flume to determine an optimal geometry of this type of construction. Measurements of impact forces and water pressure, used for the design of the construction, will be discussed in this presentation.