LIFE Project Cover Photo

Restoration of the dynamics of Rhine alluvial habitats on Rohrschollen island

Reference: LIFE08 NAT/F/000471 | Acronym: Rohrschollen island

PROJECT DESCRIPTION

BACKGROUND

Of the many ecosystems found in the great alluvial plains of Europe, the richest and most complex are the dense, temperate and deciduous ‘gallery’ forests that form on regularly-flooded corridors along the banks of rivers flowing from the Alps. They are notable for their wealth of tree, shrub and large creeper species. However, these forests are regressing as a result of the ‘domestication’ of these rivers. Consequently, the four major European rivers flowing down from the Alps - the Rhine, Rhone, Danube and Po - have lost most of their riparian forests. Rohrschollen Island, on the Rhine 10 km upstream from Strasbourg, contains the priority habitats ‘Alluvial forests with Alnus glutinosa and Fraxinus excelsior’ and ‘Riparian mixed forests along the great rivers (Quercus robur, Ulmus laevis, Ulmus minor)’, and another seven habitats listed in Annex I of the Habitats Directive. These habitats are being lost due to the absence of dynamic flooding and the resulting plant succession.


OBJECTIVES

The objective of the Rohrschollen island project was to restore the alluvial dynamics based on the natural hydrological regime of the river Rhine. The project aimed to demonstrate that dynamic flooding is a means of preserving the character of the alluvial and riparian forest habitats, and restoring the necessary conditions for plant succession. The project also aimed to re-establish functional exchanges between the river and the aquifer, and restore the ecological connections between the island and the Rhine.


RESULTS

The Rohrschollen island project restored dynamic flooding on this island in the Rhine, and restored alluvial forest habitats and favourable conditions for the many species associated with those habitats included in annexes I and II of the Habitats and Birds Directives. These species include the common kingfisher (Alcedo atthis), great egret (Egretta alba), great crested newt (Triturus cristatus) and, most notably, the spined loach (Cobitis taenia), which is scarce in the Rhine-Ried-Bruch alluvial sector of the Lower Rhine. The project also restored connections between the island and the Rhine.

The project firstly carried out studies (e.g. topography, sedimentology, water connectivity, and concerning the spined loach population) to determine the most appropriate works to be implemented. Many authorisations had to be obtained, given the fact that the island is located in international waters and that it is adjacent to a power station that depends on water flow to produce energy. Following these preliminary studies, the proposed conservation actions were designed to meet safety, legal and technical requirements.

The main project action was the creation of a water intake structure on the southern part of the island, so that the island’s hydrographic network (the Bauerngrundwasser) could be supplied directly from the Rhine with between 5 and 80 m3 per second of water, depending on the river's natural hydrological conditions. Additional work on the secondary branches of the main stream on the island established effective exchanges with the river.

To restore dynamic flooding, substantial earthworks and civil engineering works were carried out on the island. In addition to setting up the water intake and regulation structure, a channel more than 1 km long was dug to bring water from the Rhine to the island’s existing water network. The channel was deliberately undersized to enhance forest flooding and for it to evolve into a near-natural watercourse. Downstream, a submersible 22 metre-wide water connecting construction was created and fitted with passages at different levels, permitting the passage of upper and bottom feeding fish. An integrated nozzle removed sediment accumulated during floods and a device enabled a permanent water flow onto the island. This represents an added value to the restoration of the alluvial forest, notably for spined loach habitats. By 2014, a significant number of young spined loach were observed on the island.

In 2015 the island was successfully flooded twice, with a maximum water flow of 80 m3/s. It is too early to produce data showing the favourable impact this will have on the targeted habitats and species. Nonetheless, a number of interesting observations were made after the flooding. For example, the banks of the watercourses on the island have changed (creating new habitats), and mud accumulated in the riverbed has been evacuated (favouring the colonisation by other species). Up to 6 to 8 induced annual floods are planned with an average of 50 submersion days each year. Scientific monitoring is being carried out in the framework of a partnership between the City of Strasbourg and the University of Strasbourg. It will be continued over the coming years in a reduced form by the City of StrasbourgThe project has therefore contributed to the wider aim of restoring Europe’s gallery forest habitats along the rivers flowing from the Alps. It also contributes to the presence of willow and alder wood habitats at the Rohrschollen site; these are essential for the regeneration of alluvial forest dynamics, but are increasingly rare elsewhere in the Rhine valley.

The ambitious nature of the project, in artificially recreating a hydrosystem to improve the ecological state of the Rohrschollen island nature reserve, has provided an interesting and valuable demonstration of this approach. A number of individual techniques used within the project were also innovative, such as 3D visualisation using lasers, photographs and airborne infrared thermal imagery, and the use of a hydrophone. The project generated employment to carry out the works, for example, for consultants, engineers, and building companies, thereby contributing to the local economy. A number of awareness-raising activities were carried out aimed at the general public, explaining the value of restoring and maintaining the threatened habitats, and advising when planned flooding events will occur.

Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).

ADMINISTRATIVE DATA


Reference: LIFE08 NAT/F/000471
Acronym: Rohrschollen island
Start Date: 01/01/2010
End Date: 30/06/2015
Total Eligible Budget: 2,080,000 €
EU Contribution: 1,040,000 €
Project Location:

CONTACT DETAILS


Coordinating Beneficiary: Ville de Strasbourg
Legal Status: PUBLIC
Address: 1 Parc de l'Etoile, 67076, Strasbourg Cedex, France
Contact Person: Catherine LE QUANG
Email: Send Email
Website:


LIFE Project Map

ENVIRONMENTAL ISSUES ADDRESSED

THEMES

  • Ecological coherence
  • Freshwater

KEYWORDS

  • forest ecosystem
  • river
  • island
  • restoration measure
  • population dynamics
  • endangered species

TARGET EU LEGISLATION

  • Directive 92/43 - Conservation of natural habitats and of wild fauna and flora- Habitats Directive (21.05.1992)
  • Directive 79/409 - Conservation of wild birds (02.04.1979)
  • COM(2013) 249 final “Communication from the Commission on Green Infrastructure (GI) - Enhancing Europe’s Natural Capital” (06.05.2013)
  • COM(2011) 244 final “Our life insurance, our natural capital: an EU biodiversity strategy to 2020” (03.05.2011)
  • Directive 2006/44 - Quality of fresh waters needing protection or improvement in order to support fish life – Fish Directive (consolidated) (15.10.2006)

TARGET HABITAT TYPES

  • 91E0 - "Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae)"
  • 91F0 - "Riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia, along the great rivers (Ulmenion minoris)"

SPECIES

  • Egretta alba
  • Alcedo atthis
  • Cobitis taenia
  • Triturus cristatus

NATURA 2000 SITES

Type Code Name
SCI FR4201797 Secteur Alluvial Rhin-Ried-Bruch, Bas-Rhin
SPA FR4211810 Vallée du Rhin de Strasbourg à Marckolsheim

BENEFICIARIES

Name Type
Ville de Strasbourg Coordinator
None Participant

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