Author(s): M. A. Van Heereveld; R. O. T. Zijlstra
Linked Author(s):
Keywords: River groynes; Flood risk; Navigation; Bed degradation; Ecology; Landscape; Fairway improvement; Morphodynamics; EU Water Framework Directive; EU Habitats Directive
Abstract: The reason to build river groynes in The Netherlands since 1830 was to fix the fairway in the river bed and improve the (safe) discharge of ice. These conventional groynes have proven to be reasonably effective until today. However, the current context of the river groynes has changed significantly and their performance must now be considered in a modern and far more complex context. The new context comprises contradictory demands such as reduction of peak water levels and improvement of the fairway in terms of navigability. Additionally, it is considered necessary to restore and improve ecological values, spatial quality and to halt the ongoing bed degradation of the river. These modern demands give rise to reconsideration of the current river groynes and harmonisation of river hydraulics and morphology. In an attempt to meet these demands, two innovative groyne designs, the Island Groyne and the Louvre Groyne, have been developed. In the innovative groynes contain significant improvements in terms of quality of the fairway (mainly through minimising depth limitations and improving the flow conveyance), ecological connectivity and potential (in line with the EU Habitats Directive and Water Framework Directive), quality of landscape and the perception of groynes in it, sustainability and morphological stability of the river. The morphological improvements result in a significant reduction of the amount of maintenance dredging required, as well as structural maintenance (outflanking), which makes both innovative groynes also economically attractive options. The aforementioned benefits incorporated in the design of a single groyne are an important achievement since establishing lower peak water levels typically implies increasing the flow cross-section, which inherently compromises the quality of the fairway, particularly during periods of lower discharges. This effectively limits the extent to which peak water levels can be reduced or the discharge capacity can be increased. Nevertheless, a reduction of some 7 cm seems feasible with both innovative groyne designs, which is an important contribution to flood safety. Whilst the Louvre Groyne has received a recommendation for further research from the committee of experts, the Island Groyne is one of the four prize-winning conceptual designs in the Rijkswaterstaat / CUR Design Competition: “Groynes for the Future”, held in December 2006. The conceptual designs are conceived by a consortium consisting of Royal Haskoning (lead), Radboud University of Nijmegen, Bureau Stroming and Struiksma River Engineering. Although detailed designs have not been part of the conceptual designs, the paper introduces the principles of both innovative concepts and addresses the high potential that both designs bear in them in terms of harmonising 21st century demands. Their high potential is not only relevant for the Dutch main rivers but for many other rivers in the rest of the world with similar problems.
Year: 2007