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English summary - Natuurherstel Tiengemeten

Tiengemeten, restoration of freshwater tidal area in the Haringvliet estuary, the Netherlands (10GEMETEN)Tiengemeten is an island in the Haringvliet estuary in the Dutch Rhine-Maas Delta. As a result of the closure of the Haringvliet (NL) in 1970, the tidal rise and fall in the estuary is now severely limited, with serious consequences for the composition of vegetation and fauna in the Haringvliet. The surface area of the intertidal area with a daily ebb and flood has been greatly reduced, with a consequent sharp decline in the ecological features of the Haringvliet.

Since 1990, the restoration of the freshwater tidal area and the associated habitat types and target species has become an important goal of nature restoration and development in the estuary of the Rhine-Maas Delta.

With an area of 700 hectares, Tiengemeten is the most sizeable restoration project in the estuary. Tiengemeten has been designated as a Nature 2000 area and comes within the scope of both the Habitat Directive and the Bird Directive.
The island consisted of 700 hectares of agricultural land and some 300 hectares of reed and shrub vegetation. The present island nature reserve of Tiengemeten is subdivided into three spheres: Wistfulness (Weemoed), Wealth (Weelde) and Wilderness (Wildernis).

The project organisation Tiengemeten was a cooperation of Dienst Landelijk Gebied, Rijkswaterstaat, Provincie Zuid-Holland, Gemeente Korendijk and Natuurmonumenten.The project organisation was responsible for the development of the three spheres of Tiengemeten.The project was aimed at the development of the current agricultural polders into a tidal landscape with creeks, reedlands, brushwood, tidal forests (Wildernis) and backlands with an open swamp landscape (Weelde). In the eastern part of the island lies Weemoed, where the cultural history of the island is preserved, although this area falls outside the scope of the 10GEMETEN project. Weemoed was realised at the same time as the 10GEMETEN project.

Actions and means involved

The developments at Tiengemeten will establish an important link for the natural environment in the Rhine-Meuse Delta. In addition possibilities arebe developed for nature-based recreation; since 2007 there is the Tiengemeten Nature Information Centrea, in a former barn at the island.

The 10GEMETEN project focused on the development of the robust Delta environment in the Weelde and Wildernis areas. The most important measures in Wildernis were being taken in the Mariapolder, Grevesweg and Brienenswaard areas. In Weelde measures were being taken in Middenpolder and Benedenpolder.

In the Mariapolder the ground level was lowered so as to create shallow water and mudflats on a large scale. In addition the dike was cut through so that Mariapolder is directly connected up with the Haringvliet. The Grevesweg was being removed and excavated to link up with Greveskreek. The latter creek is connected up with the present drainage ditches, so that these act as side creeks. The quay between Brienenswaard and Blanke Slikken was lowered across its full length. 

In the Middenpolder and Benedenpolder the surface level was being partly reduced. This created a basin area part of which will be permanently filled with water. The basin was enclosed on the south side by a 100 m wide embankment, rising above the surrounding ground level by around 1 m. A spillway set into the embankment enables water to flow in and out of the basin at high-water levels. The more elevated elements are also under water. The sealed road was removed and excavated to form a deeper creek. On the northern side the basin is bordered by the present quayside, which acts as the future backbone of the island. The most important development of the area has taken place along this quay. Cycle paths and footpaths were created along the project area, for nature based recreation.

Expected results

The ‘10GEMETEN’ project was concerned with the restoration of a freshwater tidal area. By lowering the ground level, cutting through embankments and excavating creeks, 700 hectares of tidal area were restored, together with the habitats typical of such areas. The priority habitat type is alluvial forest with Alnus glutinosa and Fraxinus excelsior. The restored intertidal area forms an important link in the national ecological network of the Rhine-Maas Delta. Species such as the microtis oeconomus arenicola and acipenser sturio are typical target species for freshwater tidal areas. 10GEMETEN isalso an important foraging area for crex crex and botaurus stellaris. 

10GEMETEN has become a nature conservation island on which nature-based recreation - for which there is a great demand in the densely populated western urbanization of the Netherlands - also is possible. At the nature information centre visitors are able to obtain information on the nature restoration and further developments on Tiengemeten and the national and international importance of the project. The nature information centre is strategically located, near the ferry jetty.