D.W. Dunsbergen's research while affiliated with Delft University of Technology and other places

The problem of the stability of tidal inlets has been approached on a rational basis. The hypothesis of equilibrium concentration, as proposed by Di Silvio (1989), has been used in combination with an appropriate sediment transport formulation. Analysis showed that an Engelund-Hansen's type of approach provided a reasonable basis for our purpose. This makes it possible to develop a stability equation that includes most of the morphological parameters and it allows the evaluation of wave action on morphologically stable channels. An interesting application is the evaluation of stability conditions of channels in ebb tidal deltas, subject to wave exposure. Our analysis is applied to two major inlets on the Dutch coast: Texel Inlet and Haringvliet Estuary, after closure. Detailed hydrographic and morphologic information, including wave data, are available for both inlets. When we apply our analysis to the Texel Inlet we find that wave action is only important when the assumption is made that the grain size of bottom sediment in the gorge and in the delta channel have the same values. It is hypothesized that this condition may occur in the winter months, when wave activity is significant. When the grain size of the bottom sediment in the delta channel is smaller than in the gorge (a condition that corresponds with available field data), no influence of wave action on the size of the cross-section can be detected. This situation may represent summer conditions. For the mouth of the Haringvliet Estuary after closure, we find that wave action has a significant influence on the depth of the entrance channel. These results show that the proposed method of evaluation is applicable for determining the stability profiles of tidal channels, in wave-protected areas as well as in ebb tidal deltas under the influence of wave action. It is found that the results are sensitive to the value of some essential environmental parameters, such as median grain size and Chezy coefficient, which reduces the practical applicability of the findings in cases where this information is not available. Further studies are recommended on this issue.

Through historical analysis of the interaction between societal issues, end-user needs and research advances this paper intends to reveal the differences in perception about the usefulness and effectiveness of coastal research that appear to develop during subsequent research programme stages between different stakeholders. These perception differences are the probable reason for the limited scales of lifetime of research programmes. Our historical analysis indicates that both the assessment of the initial contents and the process of research programmes nearly by default lead to a growing divergence between drivers and users of knowledge and developers of knowledge. Making use of these findings a methodology is suggested to avoid or at least postpone this divergence. This might lead to more useful and more effective research programmes with a longer lifetime to the benefit of society, end-users and researchers.