Item does not contain fulltextNCR-days, 15 november 200

Heereveld, M.A. van

Leuven, R.S.E.W.

Os, A.G. Van

Struiksma, N.

Winden, A. van der

English

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Water Management 
Proceedings NCR-days 2007 - 62 - 
River groynes for the future 
 
M.A. van Heereveld1, R.S.E.W. Leuven2 , A. van Winden3, N. Struiksma4 
1Royal Haskoning, P.O. Box 151, 6500 AD, Nijmegen, the Netherlands, m.vanheereveld@royalhaskoning.com; 
2Institute for Wetland and Water Research, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, the Netherlands; 
3Stroming, P.O. Box 31070, 6503 CB Nijmegen, the Netherlands; 
4Struiksma River Engineering, N. Bierkade 7, 8356 DH Blokzijl, the Netherlands 
 
Abstract 
The Island Groyne contains 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. It is 
also possible to effectively reverse on-going 
bed degradation. The morphological 
improvements result in a significant reduction 
in the amount of maintenance dredging 
required, as well as structural maintenance 
(outflanking), which makes innovative groynes 
economically attractive. 
 
Background 
In the Netherlands, since 1830, river groynes 
have been needed to fix the fairway in the river 
bed and to improve the (safe) discharge of ice. 
These conventional groynes have proven to be 
reasonably effective up until today. However, 
the current context of the river groyne has 
changed significantly and their performance 
must now be considered in a modern and far 
more complex context. This contemporary 
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 reverse the 
ongoing bed degradation of the river caused 
primarily through river normalisation and 
training. 
These modern demands have given rise to 
reconsideration of the current river groynes 
and harmonisation of river hydraulics and 
morphology. As the responsible authority for 
navigation and flood safety on the main rivers 
in the Netherlands, Rijkswaterstaat, in 
association with CUR, organised the design 
competition “Groynes for the Future”:  the 21th 
century demands were to be united in an 
innovative groyne design (CUR,  2006). This 
paper briefly reviews a prize-winning design of 
this competition: the Island Groyne. For a 
detailed description of an environmental 
assessment and a cost-benefit analysis 
reference is made to Van Heereveld et al. 
(2006).     
 
 
 
 
Figure 1. Artist impression of the Island Groyne. 
 
The Island Groyne  
The Island Groyne (Fig. 1) consists of an 
opening made in the existing groyne and a 
lengthened groyne head in the direction of flow 
(the Island). The opening is about 60 m2 and is 
constructed near the groyne head where flow 
intensity is greatest. The opening is 
submerged for about 300 days per year and 
allows for a reduction in peak water level of 
about 7 cm. A larger opening would be more 
difficult to compensate in terms of negative 
effects on the fairway quality and compromise 
the optimum balance between reduction of 
peak water levels, fairway improvement, 
ecology, quality of landscape and reversing the 
on-going bed degradation. This practical 
limitation also implies that a significant part of 
the existing groynes can remain intact which is 
not only favourable for ecology and quality of 
landscape but also for sustainability and cost. 
Moreover, since the opening is made near the 
groyne head, current attack is diverted from 
the river bank improving bank stability, fairway 
morphology and the need for maintenance on 
the groynes themselves (mainly outflanking 
and removal of vegetation). 
In case of the conventional groynes, sediment 
is deposited in the groyne fields during periods 
that groynes are submerged, while ship-
induced water motion is the primary driver for 
sediments eroding from the groyne fields 
during low water season (emerged state). The 
opening in the Island Groyne results in a more 
gradual flow distribution from the main channel 
to the river bank. The resulting sheltering effect 
will decrease the amount of sediment 
Water Management 
 - 63 -       Proceedings NCR-days 2007 
exchange between groyne field and fairway so 
that more sediment can be held in the groyne 
fields. Hence, sediment load on the fairway is 
limited during low water season as well as the 
local shortage of water depth due to temporal 
bed changes in the fairway. 
The Island further enhances the sheltering 
effect of the opening on the conditions in the 
groyne fields and also lowers (ship-)wave 
intensity. The visibility and navigability 
improves because the river is better defined 
when seen from the bridge of a vessel. Also, 
the Island can be fitted with two rather than 
one radar beacon as a further improvement of 
the fairway. 
The primary reason for lengthening the groyne 
head is to limit the amount of constriction scour 
and the downstream deposit of eroded 
material, which is important for depth limitation 
in the fairway. Altogether, the current amount 
of maintenance dredging required to keep the 
fairway navigable (usually during emerged 
state) is significant, but will be minimised 
through the Island, and effectively compensate 
the increasing flow area on the quality of the 
fairway. Over-compensation is also possible so 
that bed degradation may be stopped. 
 
Exciting ecological improvements 
The opening in the groyne and the shelter 
created in the groyne fields offers opportunities 
for improving ecological development. An 
increase in number and diversity of species is 
expected. Migration of species is also 
improved as the lower flow velocities in the 
opening are easily negotiated as opposed to 
the higher flow velocities around the groyne 
head and in the main channel in the existing 
situation. The sheltering also offers a more 
gradual transition from main channel to land, 
which is important for the quality of landscape 
and the way the landscape is perceived. By 
keeping the existing groynes intact and using 
familiar materials to construct the new parts, 
the cultural heritage that the groynes represent 
in the Dutch river landscape is justified. Yet, 
the Island Groyne bears a clear 21st century 
signature. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Meeting cost-effective high 
standards 
In terms of cost, the Island Groyne is 
competitive because use is made of the 
existing river training structures, doing justice 
to the capital it represents. Taking into account 
the lower cost of maintenance of the fairway 
and the groyne itself, the Island Groyne is 
even more competitive and sustainable than 
other types of groynes which do not comprise 
the optimum benefits of the Island Groyne. 
 
Conclusions 
With the Island Groyne, it is possible to 
establish peak water level reduction without 
consequences for the quality of the fairway. 
Moreover, improvement is possible, including 
the reversal of the on-going bed degradation. 
The design of the Island Groyne is robust and 
flexible: its performance under current and 
future conditions is easy to maintain, adding to 
the designs sustainability. 
  
References 
CUR / Rijkswaterstaat (2006), “Prijsvraag Kribben van de 
Toekomst” (in Dutch), ISBN 90-369-0008-5 
Van Heereveld, M.A., G.J. Akkerman, W. de Jong, 
R.S.E.W. Leuven, N. Struiksma, A. van der Winden 
(2006) “Eilandkrib: hoofdrapport en 
achtergronddocument”. Royal Haskoning, Radboud 
University, Bureau Stroming & Struiksma River 
Engineering, Nijmegen (in Dutch). 
 


River groynes for the future

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