Regional Pilot Schemes Multi-Layer Safety Eemsdelta; Developing Area-Specific Risk Strategies
Coastal safety is vitally important to a climate-proof development of the Ems delta. In an earlier report, Integrale Klimaatadaptatie Eemsdelta [Ems Delta Integrated Climate Adaptation, IKE], particular choices had been made with regard to Ems harbour. The specific situation in Delfzijl calls for further study. Two main alternatives have been elaborated for the major part of the coast:
- traditional coastal defence (raising and widening the existing sea wall)
- widening the coastal defence system (more robust and more flexible, featuring more opportunities for other functions)
It has been concluded that more insight is needed into alternative impact-reducing measures in accordance with the multi-layer flood risk management concept. This study provides insight into the consequences of measures, including in the second and third layers of the multi-layer flood risk management concept.
Results
The area of focus is the Ems harbour – Groningen – Delfzijl triangle. In this area, located inside the dykes, measures have been defined during pilot projects. Areas outside the dykes near Delfzijl and Ems harbour have also been examined. The measures have been assessed on the basis of an assessment framework commissioned by the STOWA Foundation for Applied Water Research and the Delta Programme. The framework has been coordinated with the province of Groningen in relation to the “other values”.
The assessment framework also comprises financial criteria: economic risk, casualty risk, investment costs, total costs, and efficiency. In addition to the quantitative assessment, it offers room for a qualitative assessment. The pilot projects have enabled experts to indicate their assessment of the impact that a measure might have on “other values”, such as support, spatial quality, Nature, cultural history, feasibility, tourism, accessibility, and evacuation. These criteria enable a more broad-based consideration of the effects of measures, rather than an assessment solely based on economic criteria.
During the pilot project, protective measures have been defined for the project area. The measures are, in part, based on maps with the calculation results of the reference situations inside and outside the dykes. For the second pilot project, a selection of the most promising measures from the first pilot project has been analysed and presented. For each measure, the total costs have been calculated as well as the extent to which it reduces the overall risk. The participants have indicated how each individual measure scores with respect to other values.
The conclusion as regards the methodology is that, in view of the national importance of natural gas extraction, a major damage and risk component is missing from the calculations, by not factoring in flood damage to gas plants. As a result, the risk in the reference is underestimated, as is, consequently, the effect of measures in the first and second layers of multi-layer flood risk management. Adding vital objects to damage calculations is, therefore, of paramount importance.
With respect to the area studied, the following strategies appear most favourable in terms of investment costs versus reduction of the overall risk:
- improving the current primary dyke near Holwierde, thus reducing the flood risk;
- constructing a secondary dyke in mid-Groningen (the cost of any engineering works required is, however, not yet taken into account in this option);
- constructing a secondary dyke around the North-Eastern districts of the city of Groningen;
- constructing ring dykes around gas plants.
Significant linkage goals have been identified with respect to some measures:
- Relocating the primary dyke in accordance with two different variants. Implementation of the measure will generate a new tidal area. The flood defence system may additionally be combined with a new pipeline from Ems harbour.
- Improving the Northern Eemskanaal dyke in combination with a traffic route. This measure will reduce the risk of gas plants in the South being flooded as a result of a dyke collapse, and improve the accessibility and evacuation options for the Delfzijl/Appingedam region.
The project that was carried out, and the pilot projects, mainly focused on the quality of linkage opportunities. A follow-up will require the conversion of the qualitative assessment into a quantitative assessment of the linkage opportunities.
Contact person
Matthijs Buurman
Province of Groningen
+31(0)6-15068217
m.buurman@provinciegroningen.nl