Lek bij Everdingen - Groyne shields
Lek bij Everdingen - Groyne shields
Key features of the case study
Site description
The Lek river is one of the major Rhine tributaries in the Netherlands. The river is channelised and groynes are present to keep the river suitable for navigation purposes. Also, banks are fixated to avoid sediment input into the main channel. The specific site of this project is situated near the town of Everdingen. The area is characterized by continual passing of ships and barges. This causes disturbance of the water flow which in turn is thought to disturb the biota in the groyne areas.
Measures selection
To avert the disturbance in the water flow caused by passing ships a number of groynes were shielded off by artificial structures placed in front of the groynes. These structures were made of two rows of wooden poles with branches in between them. The reasoning behind this measure was that the coils in the water would be stopped by these poles and a more suitable habitat, primarily for macrophytes, would be established in the groyne fields. The presence of macrophytes would in turn increase habitat availability for fish and benthic invertebrates. Benthic invertebrates were thought to also be able to benefit from the newly available substratum of the wooden poles. In some of the groyne fields the bank fixation was (partially) removed so that more knowledge of the effect of the shielding could be retrieved from monitoring efforts.
Success criteria
The goal of the project was to stimulate the development of shore and waterplant vegetation. This may also positively affect the other WFD BQEs, namely benthic invertebrates and fish. No definitive values were determined for the success or failure of the project or the respective BQEs at the start of the project. The BQEs were all monitored and evaluated by experts in their respective fields.
Ecological response
Benthic Invertebrates
Benthic invertebrates were monitored in 2006 and 2008. The conclusions from the monitoring is that there are no significant differences between the groyne fields that are shielded by the rows of poles and those that are not. This leads to the conclusion that the measure does not have the desired effect on benthic invertebrates.
Macrophytes and phytobenthos
Macrophytes were monitored in both shielded and unshielded fields. Another hypothesis was tested by making enclosures of wire frames. This was done to eliminate possible grazing by water-birds. Results show strong signs of grazing in non-enclosed parts of the groyne fields. Macrophyte development has been limited, even in the enclosures. No clear difference in macrophyte occurence was found between shielded and unshielded areas. The conclusion is that the artificial structures do not promote the occurrence of macrophytes so far. It should be noted that more time may be needed for the desired effect to present itself.
Fish
The difference in fish composition and occurrence between the groyne fields (both shielded and unshielded) is quite large. This has led to difficulties in determining statistically significant effects. The general image is that some specific fish species are benefiting from the shields and are showing increase in presence of brood. The expectation is that with time the vegetation will develop further and with that the fish population will benefit as well.
Hydromorphological response
Not monitored.
Monitoring before and after implementation of the project
The project makes use of a selective placement method. It is assumed that groyne fields are identical, as such selective placement of shields makes it possible to test the effectiveness of the method. Shielded and unshielded groynes are monitored for the different BQEs. Monitoring and related studies were carried out by the Rijkswaterstaat Waterdienst Oost and by AquaTerra-KuiperBurger. All monitoring data is property of Rijkswaterstaat Netherlands.
Socio-economic aspects
Ecosystem goods and services
There are no clear goods or services associated with this project.
Conflicts and synergies
Potential synergies could be seen in the form of maintaining the channel for navigation and flood protection. However, both of these points were not negatively affected by the project; the project never aimed or succeeded to improve them.
Project costs
Monitoring
- Benthic invertebrates: 66 500.- Euro
- Nematodes: 23 300.- Euro
- Fish: 88 700.- Euro
- Vegetation: 49 300.- Euro
- Chemical: 9 500.- Euro
Total costs
237,300.- Euro
Contact person within the organization
Extra background information
References
