A Dutch study of the development of river deltas
Much of the Netherlands sits firmly on top of the Rhine delta, so it is quite understandable that the Dutch should take a particular interest in their development.
Researchers at the Delft University of Technology (TU Deft) have been adding information about the subsoil to an existing sedimentation and erosion model to obtain a clearer picture of how rivers and deltas develop over time.
A better understanding of the interaction between the subsoil and the flow process in a river-delta system not only plays a key role in the civil engineering aspects of delta management but improvements in geological knowledge are an important factor in the work of reservoir geologists.
Leading the study was Dr Nathanael Geleynse and the research findings were recently published in the journals Geophysical Research Letters and Earth and Planetary Science Letters.
The researchers studied the many factors involved in how a river behaves and how a river delta is created. Looking first at the river itself it is important to consider the kind of material that is transported to the delta. This might consist of small particles such as clay or larger particles like sand. Other important factors include the extent of tidal differences at the coast and the height of waves whipped up by the wind.
In this study the researchers from TU Delft worked closely with the independent Dutch-based research institute Deltares and made extensive use of the institute's computer models, Deft3D software. These models already take a large number of variables into account, but Dr Geleynse and his colleagues have now supplemented them with information on the subsoil.
It transpires that this variable also exerts a significant influence on how the river behaves and is closely related to the process of delta formation.
The Dutch Delta Commission was created in 1953 shortly after the disastrous inundation of the delta area that resulted in over 2000 deaths.
Management of the enormous quantities of water that flow to the North Sea through the south of the country is vital and the extra dimension that has been added to the model is important for delta management.
One of the Delta Commission's recommendations is the ''Room for the River'' project. Room must be created along the major rivers in the Netherlands to allow for the increase in their discharge. It is important to know what a river will do in that space.
Dr Geleynse explains that existing data is not sufficient to give us ready-made answers to specific management questions, because nature is not so easily tamed. However, it is possible to offer plausible explanations for the patterns and shapes that are seen on the surface.
''The flow system carries the signature of the subsoil, something we were relatively unaware of until now. Our model provides ample scope for further development and for studying various scenarios in the current structure.''
River management is all about short-term and possible future scenarios. Hundreds of millions of people in the world live in deltas and these urban deltas are expected to grow in the decades to come.