Why do we need MELODY?

To achieve a climate-proof coast, we must better understand the lower shoreface, which forms the essential link between the offshore seabed and the nearshore zone. In many cases, it is an important natural sediment source controlling coastal response to sea level rise. The lower shoreface also plays an important role in how human activities (e.g. offshore wind farms, sand extraction) affect the beaches and dunes that we all love.

Lower shoreface sand transport and morphodynamics are complex and poorly understood. We know little of the processes of moving sand in the on- and offshore direction that add up to a subtle, yet essential net sand transport. The same goes for the intriguing interactions between bedforms, tidal sand waves in particular.

This project will improve understanding of the lower shoreface bed dynamics, by combining field data and different new numerical models. These models will help coastal management to deal with climate change effects (such as sea level rise), and to find suitable locations for offshore sand extraction and wind farms, facilitating energy transition, in harmony with other seabed activities.

Key aspects of lower shoreface: sand transport, tidal sandwaves and marine & coastal management

THREE INTERRELATED KEY ASPECTS OF LOWER SHOREFACE BED DYNAMICS ADDRESSED IN MELODY:

For adequate and sustainable marine & coastal management, we must understand both sand transport processes and the dynamics of tidal sand waves

Scientific challenges

Our understanding of the lower shoreface seabed dynamics is limited by several complicating factors, which form the inspiration for the subprojects in MELODY:

  • Net cross-shore sand transport is a subtle effect of much larger gross rates in opposite directions, with a strong episodic forcing. Sand transport across the lower shoreface is controlled by various competing processes due to waves, currents and wave-current interactions. Net sand transport is the resultant of small rates during normal day conditions, and much higher rates during storms. The episodic nature, relatively low net values and non-negligible bedload contribution make it difficult to accurately measure and predict lower shoreface sand transport. → PhD1 (Philippe)

  • The variety of morphodynamic patterns that are an integral part of the lower shoreface. Among these patterns, tidal sand waves can be viewed as the most relevant from an engineering perspective. These patterns result from lower shoreface sand transport and, at the same time, affect it. However, the scale interactions between tidal sand waves and background topography (e.g., ridges and lower shoreface) are not yet understood. How do sand waves affect the larger-scale flow patterns? And how do they interact with background morphodynamics? → PhD2 (Laura)

  • The short-term lower shoreface sand transport processes and longer-term sand wave dynamics have been studied in isolation. How form roughness, near-bed turbulence, current deflection and circulation patterns induced by tidal sand waves affect lower shoreface sand transport is unknown. Conversely, it is unknown how detailed sand transport processes, especially during storms, influence the dynamics of tidal sand waves. → PhD1 & PhD2 (Philippe & Laura)

  • The lower shoreface sand transport processes are not fully understood, and no generally-valid sand transport models are available. This greatly hampers the prediction of lower shoreface morphodynamics, and the ability to assess the impact of climate change (SLR and possibly changed wind conditions, wave climate and river discharges) and increasing offshore seabed activities related to climate change (e.g. offshore wind farms and sand extraction pits). → Postdoc

Scientific challenges

Our understanding of the lower shoreface seabed dynamics is limited by several complicating factors, which form the inspiration for the subprojects in MELODY:

  • Net cross-shore sand transport is a subtle effect of much larger gross rates in opposite directions, with a strong episodic forcing. Sand transport across the lower shoreface is controlled by various competing processes due to waves, currents and wave-current interactions. Net sand transport is the resultant of small rates during normal day conditions, and much higher rates during storms. The episodic nature, relatively low net values and non-negligible bedload contribution make it difficult to accurately measure and predict lower shoreface sand transport. → PhD1 (Philippe)

  • The variety of morphodynamic patterns that are an integral part of the lower shoreface. Among these patterns, tidal sand waves can be viewed as the most relevant from an engineering perspective. These patterns result from lower shoreface sand transport and, at the same time, affect it. However, the scale interactions between tidal sand waves and background topography (e.g., ridges and lower shoreface) are not yet understood. How do sand waves affect the larger-scale flow patterns? And how do they interact with background morphodynamics? → PhD2 (Laura)

  • The short-term lower shoreface sand transport processes and longer-term sand wave dynamics have been studied in isolation. How form roughness, near-bed turbulence, current deflection and circulation patterns induced by tidal sand waves affect lower shoreface sand transport is unknown. Conversely, it is unknown how detailed sand transport processes, especially during storms, influence the dynamics of tidal sand waves. → PhD1 & PhD2 (Philippe & Laura)

  • The lower shoreface sand transport processes are not fully understood, and no generally-valid sand transport models are available. This greatly hampers the prediction of lower shoreface morphodynamics, and the ability to assess the impact of climate change (SLR and possibly changed wind conditions, wave climate and river discharges) and increasing offshore seabed activities related to climate change (e.g. offshore wind farms and sand extraction pits). → Postdoc

BATHYMETRIC CHART OF PART OF THE NETHERLANDS COASTAL ZONE, SHOWING THE LOWER SHOREFACE AND A VARIETY OF RHYTHMIC BEDFORMS INCLUDING TIDAL WAVES

Data from Rijkswaterstaat & Netherlands Hydrographic Service

Aim & objectives

The overall aim of MELODY is:

To improve understanding and modeling of the lower shoreface sand transport and morphodynamics, in order to determine how offshore seabed activities and climate change impact coastal morphology.

We will particularly address the important interactions between sand transport processes, tidal sand waves and the lower shoreface seabed as a whole. The research has the following specific objectives:

  1. To develop an efficient sand transport model for the complete Dutch Lower shoreface, including effects of wind, waves, tide, river discharge, temperature and salinity and with real-time forcing. This will include parameterizations of form roughness generated by sand waves, provided by PhD2. (PhD1)
  2. To identify the controlling lower shoreface sand transport mechanisms. In particular the balance between low transport rates during normal day conditions, and much higher transport rates during storm events. This will lead to insights on how to schematize the forcing and sand transport processes to be used by PhD2. (PhD1)
  3. To understand the hydrodynamic feedback between tidal sand waves and larger-scale topography (sandbanks, shoreface-connected ridges, lower shoreface), leading to parameterizations of form roughness generated by sand waves to be included in larger-scale models (to be used by PhD1), as well as knowledge on how the background topography affects flow patterns and by this sediment transport near sand waves. (PhD2)
  4. To understand sand wave morphodynamics superimposed on background topography, in (i) an idealized geometric setting for a detailed process analysis, and (ii) a more complex setting (realistic forcing/bathymetry, sophisticated transport model provided by PhD1) which enables assessment of the impacts of human interventions. (PhD2)
  5. To use these models to assess the morphodynamic impact of climate change & offshore seabed activities. (Postdoc)
Three bedforms depending on temporal and spatial scale

LOWER SHOREFACE BEDFORMS, OCCURRING OVER A WIDE RANGE OF SPATIOTEMPORAL SCALES, HIGHLIGHTING TIDAL SAND WAVES:

Arrows indicate scale interactions; MELODY addresses the two-way coupling with larger-scale topography (solid arrows)

Methodology

The research objectives shall be achieved in two parallel PhD projects (objectives 1 to 4), supplemented with a utilization-oriented Postdoc project (objective 5).

The project will run for 5.5 years. The PhDs will be employed for 4 years, from the start of the project. The Postdoc, employed for 3 years, will start after 2.5 years, when the new findings and models by the PhDs become available.

The research will be monitored through a series of half-yearly User Committee meetings and a closing dissemination workshop.

Project structure with sub projects of two PhDs and one Postdoc

MELODY STRUCTURE WITH 3 INTERACTING SUBPROJECTS

Cooperation

PhD1 (Philippe) and PhD2 (Laura) are employed at the Water Engineering and Management (WEM) department at the University of Twente (UT), with frequent visits to Deltares and short stays at the University of Copenhagen, Ghent University and the University of Nottingham. The Postdoc will be employed by UT and work part-time at Deltares. He/she will also visit University of Queensland, Australia where prof. dr. R.W.M.R.J. Ranasinghe holds a visiting professor appointment.

We do not need to gather new data; all required data are both available and accessible. This includes long-term high-resolution echo soundings on the Netherlands Continental Shelf (NCS) and hydrodynamic and sand transport process data from field campaigns such as KG2.0. These are readily available through our partners’ advanced databases such as Deltares’ repository (Open Earth), also containing tools for analysis, and allowing for version control of all data.

The research team guarantees international collaboration with shoreface experts. Prof. dr. Troels Aagaard (University of Copenhagen) is an expert in the field of shoreface morphodynamics and will contribute to the project by sharing knowledge and data of shorefaces in Denmark and elsewhere. Similarly, Prof. Dr. Vera Van Lancker (Royal Belgian Institute of Natural Sciences/Ghent University) and Prof. Dr. Dodd (University of Nottingham) will contribute with their expertise on seabed data and observations (Van Lancker) and numerical modeling (Dodd), respectively.

Uniqueness of the project

  • The development and application of an efficient 3D wave-current sand transport model of the complete Dutch lower shoreface to identify the controlling sand transport mechanisms. (PhD1, Philippe)

  • The development and application of a morphodynamic model to unravel the scale interactions between tidal sand waves, shoreface-connected ridges, and the lower shoreface as a whole. (PhD2, Laura)

  • Bridging the gap between the scientific knowledge of the lower shoreface bed dynamics by the PhDs and the practical questions by the Users related to effects of climate change and human interferences. (Postdoc)

  • A research team featuring academic researchers as well as coastal engineers that will collaborate closely, for instance by hosting academic researchers at Deltares. The User Committee is diverse with practitioners from engineering consultancy firms and government agencies. This will lead to scientifically and societally relevant research questions, and ensures the immediate dissemination of the scientific results and models.