River Rhine - IJsseluiterwaarden Olst
River Rhine - IJsseluiterwaarden Olst
The IJssel is one of the large branches of the Rhine. The river starts at Westervoort, near the city of Arnhem and ends in Lake IJssel. The length of the IJssel is 125 km and the average discharge is 340m3/s.
Pressures and Drivers
In the 18th century, the Pannerdensch canal was dug to facilitate year-round shipping. By law, the river minimally receives 1/9th of the total Rhine water. River bends were cut off to channelize the river and the newly acquired flood plains were cut off from the rivers influence by dikes. To keep a sustainable shipping depth, groins were constructed. In the remaining flood plains, gravel and sand abstraction created deep, isolated gravel pits with little ecological value. These measures have lead to a deterioration of typical river habitats and species.
Project IJsseluiterwaarden-Olst is part of the national plan ‘Room for the River’ and has been in development since 2005. The project first started as ecological restoration project to improve the EHS (Ecologische Hoofd Structuur), but later the project was included in the Room for the River plan giving it the main goal of lowering the expected high water level in 2015.
With expected climate change, the current flood defense structure cannot guarantee the legal norms. Therefore, measures to give the river more room (Kernbesluit Ruimte voor de Rivier) are planned for the flood plains in the IJssel. IJsseluiterwaarden Olst is one of these projects. The measures also incorporate more room for riverine habitats in the flood plains.
One of the main goals of the IJsseluiterwaarden Olst project is lowering the normative high water level with 7.8 cm in 2015.
The specific ecological goals are mainly focused on preserving and creating possibilities for typical river habitat types. These types are according to the Dutch habitat list.
- Preserve and improve conditions for target fish species of the Habitat Directive
- H1134 European bitterling (Rhodeus sericeus amarus)
- H1145 European Weather Loach (Misgurnus fossilis)
- H1149 Spined Loach (Cobitis taenia)
- H1163 European Bullhead (Cottus gobio)
- Preserve and improve conditions for target species of the Habitat and Birds Directive
- H1166 Northern crested newt (Triturus cristatus)
- Migrating birds
- Breeding birds
- Preserve and improve habitat types from the Habitat Directive, namely
- H3270 Slikkige Rivieroevers
- H3150 Meren met Krabbenscheer
- H6120 Stroomdalgrasland
- H6430_A Ruigten en zomen
- H6510_A Glanshaver- en vossenstaarthooilanden
- H91F0 Zachthoutooibos
- H6430C Hardhoutooibos
For flood protection, the criterion that has to be reached is a decrease in normative high water level with 7.8 cm by 2015.
For the ecological status, no clear criteria are mentioned.
The measures in the floodplain are carried out in three project areas, namely Welsumerwaard, De Roetwaarden and De Enk/De Zaaij.
In this area, a side channel is made that consists of an isolated channel and a channel that is connected to the IJssel with a threshold of NAP +3.8 m, separated by the road to the local ferry. The area will be maintained by mowing 4x a year and extensive grazing.
In the Roetwaarden, current inlet in the upstream sand pit is rearranged to accommodate better discharge capacity during high water and the current threshold of NAP +3.6 m is kept. A levee with trees is removed to improve the discharge. The sand pits downstream are connected to the IJssel using a regulated weir which to protect the hinterlands from water damage during high water and drought during normal water. The area is maintained by mowing.
De Enk/De Zaaij
In De Zaaij, no excavation works are planned and the current land use is mostly maintained. Closer to the Duursche Waarden, floodplain forest is allowed to develop. In the Enk, one side channel is planned, in extension of the side channel in the Roetwaarden. The side channel is 100 meters wide and has a maximum depth of NAP – 2.5 m. The surrounding land is lowered to NAP + 3.0 m and slowly increases to NAP + 5 m at the river dune of Fortmond. This creates a gradual variation in elevation gradient which is characteristic for the landscape.
For the Environmental Impact Assessment, the current state of the ecological, hydro-morphological and social-economic factors had to be determined. The exact method of acquiring the monitoring data is unknown.
Monitoring will mostly be targeted at hydro-morphological processes in the side channel, vegetation development and effects of recreation on nature. A monitoring plan for these three aspects is proposed. For vegetation development, the monitoring should first be yearly to assess how the pioneer vegetation responds and how much this affects the roughness of the floodplain. Afterwards, monitoring every six years is proposed.
In the Environmental Impact Assessment, the impact of the measures on flood protection, hydro-morphology, ecology and social-economic factors is assessed. A summery is given here, for further details please check the document.
The ecological response is difficult to determine. The planned measures create 16.3 ha of side channels which increase the opportunities for habitats in and near open water. However, in large part of the current agricultural activities remain and areas are maintained by mowing. This reduces the opportunities for dynamic processes and succession. In total, 83 ha of new nature are created, but the effects the different habitattypes currently present in the area is limited. Only a positive increase of riverine forest (zachthoutooibos H91E0A) is expected. For species in the Habitat and Birds directive, neutral or positive effects are expected. Significant positive impacts are expected for Kingfisher, other fish eating birds and duck species of subfamily Aythyinae and Anatini. A slight positive impact is expected for European Bitterling (R. sericeus amarus), River Clubtail (Gomphus flavipes) and Spined Loach (C. taenia). A slight negative effect is expected for grass eating water birds, because of loss of pastures to nature development.
Because of the extra side channels, the main channel suffers from sedimentation between kmr 958 and 960. The total dredging volume is 6100 m3.
Flood protection response
The planned measures in combination with the desired vegetation roughness lead to a lowering of the normative high water level with 8.24 cm at river km 956.5. This leaves a 0.4 cm maintenance zone where extra vegetation development can be allowed. Downstream of the planning area, the water level increases with a maximum of 0.5 cm at river km 962.6, near the Duursche Waarden.
During high or low water, transverse flows can occur when water flows between the main channel and side channels. These flows have a sudden negative effect on ships and can lead to more accidents and decrease in speed. The guideline for the flow speed is 0.15 m/s, but in some places this guideline is passed. The river authority (Rijkswaterstaat) has to assess these effects and determine further action.
To make new nature areas possible, 85 ha of agricultural land is lost, but in most of the project area the current agricultural land use can be continued.
The new nature areas will be accessible for recreation. New cycling and walking paths as well as a bridge over the new side channel in De Enk will be made to further improve the recreational infrastructure. This will lead to a slight positive effect on recreation in the area.
Landscape and Cultural values
The measures should not have a negative effect on the typical IJssel landscape morphology. Side channels are a normal part of this landscape type, but it replaces the historical-cultural landscape structure for agriculture. Digging in the floodplains can have devastating effects on the archeological value of the area, but the exact loss of value still has to be determined by further research.
In this project, governmental organizations of all levels work together.
Dienst Landelijk Gebied Oost (national authority)
Gemeente Olst-Wijhe (municipality)
Provincie Overijssel (regional authority)
Rijkswaterstaat Oost-Nederland (national water authority)
Staatsbosbeheer (Rechtspersoon met Wettelijke Taak, private organization with legal tasks)
The project is funded by the national government as part of the Room for the River plan
Marcel Tonkes (Provincie Overijssel)
Tel.: 0031 38 4997852
(Dutch) IJsseluiterwaarden Olst Milieueffectrapport definitief 20-2-2012
(Dutch) IJsseluiterwaarden Olst folder