Towards a future-proof ‘Hand aan de Kraan’ methodology
At the request of the Ministry of Climate and Green Growth, TNO investigated the feasibility of a probabilistic approach* for assessing subsidence caused by gas and salt extraction in the Wadden Sea. In the report ‘Hand aan de Kraan (HadK) methodiek in perspectief’ (in Dutch), TNO demonstrates that such an approach is useful and delevops alternatives to the current assessment methodology.
Download the report (in Dutch) here in the NLOG Knowledge base.
Background
In 2021, the Adviescollege Hand aan de kraan Waddenzee evaluated the HadK methodology and concluded that the methodology is effective but should better account for the greater uncertainties in the future. This applies in particular to the sediment supply capacity, i.e. the natural capacity of the Wadden Sea area to adapt to sea level rise or subsidence through sediment supply via the sea channels.
Incorporating all uncertainties
In the new approach, subsidence, sea level rise and sediment supply capacity are each represented by an uncertainty distribution. Exceeding the sediment supply capacity does not immediately lead to the drowning of the Wadden Sea. Research by Deltares shows that such exceedance will, over the long term, result in a persistent decline in the intertidal area. This probabilistic approach also enables calculation of the likelihood that adaptive capacity will be exceeded, both with and without resource extraction.
New approach proves useful
The approach proved to be useful when TNO applied it to two areas in the Wadden Sea** that differ most from each other in terms of sediment balance. TNO then developed two alternatives for the current subsidence assessment. One of these explicitly accounts for rising sea levels due to climate change and the potential for earlier exceedance of the adaptive capacity, and is therefore preferred by TNO.
TNO advice
TNO advises the Ministry of Climate and Green Growth to introduce this new approach phased approach. In the report, TNO provides alternatives in case implementation proves challenging.
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* An approach that explicitly accounts for all uncertainties
** Pinkegat and Vlie tidal basins