An in-depth analysis of Natural Water Retention measures in the Rhine basin

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Case study

The International Commission for the Protection of the Rhine states that the Rhine has lost 85% of its floodplains. Through time, people have drained sloping hills and valleys for agriculture and urbanization. As a consequence, water travels faster downhill, causing higher flood peaks and longer droughts. Water managers widely agree that by restoring natural drainage conditions in stream valleys, water discharge into rivers slows down, mitigating the build-up of flood peaks. In a previous study, Wetlands International analysed the potential of restoring the sponge function in wetland soils in the Rhine basin as a nature-based solution (NBS) with potential impacts from local to basin scale. A follow-up study demonstrated the scale of impact of ‘sponge restoration’ and the size of the restored area needed to have a meaningful impact at the Rhine river basin level. This new project aims to improve the technical and governance analysis of the aforementioned studies, for a specific site: the Upper Kyll catchment, upstream of the Steinebrück discharge station, northwest of Frauenkron.

Technical analysis

The technical analysis will include/ improve upon the:

  • Calibration SWAT + model. The SWAT+ model accuracy can be improved through calibration to improve the model accuracy, and thereby improve the assessment of the hydrological effects of the NBS;
  • Water quality. Converting pasture near the stream to natural wetland vegetation results in lower nutrient input and concentrations in surrounding surface water. In addition, the restored wetland areas will likely retain nutrients from upstream farming areas as well. These impacts will become clear with SWAT + modelling;
  • Estimations will be made regarding the investment, (avoided) operation and maintenance costs on the level of the Upper Kyll catchment, and the costs of large scale implementation of wetland restoration in the Rhine catchment;
  • Through the use of the ‘TEEB-checklist’ of goods and services, relevant ecosystem services and their potential benefits will be identified. This includes a qualitative expert judgement of the value and magnitude of each service in the study area;

These ecosystem services are studied by a Master thesis student, Olaf de Haan. His thesis qualitatively studies the effects of wetland restoration on ecosystem services. For both before and after introducing the restored wetland to the system, the ecosystem services are identified, understood and linked to other services and factors within the system. Additionally, the wetland contribution to the identified ecosystem services is studied. Four different ecosystem services which can be obtained by implementing natural sponges are explored; water retention, water purification, biodiversity and wet-farming.

  • The return on investment based on the identified benefits of the NBS will be identified, including financing possibilities to recover the costs through available market instruments and public programmes.

Management and governance

The management and governance analysis will include:

  • Descriptions of the stakeholders, their roles and positions;
  • An exploration of the commitment of the agricultural/forestry sectors and authorities and any prehistory of cooperation;
  • Descriptions of ways to involve the public in the development and/or deployment of the NBS;
  • The technical, institutional and financial capacity of actors to implement the NBS and define needs to improve capacity;
  • A developed and tested business and governance model.

This new project aims to improve the technical and governance analysis of the aforementioned studies.

Header image: Rhine River, Germany © Phillip Glickman