The opportunities of sea-level rise for drowning deltas

'Drowned Deltas', a seed money project of the Water, Climate & Future Deltas hub, aims at identifying new opportunities for future sustainable drowned deltas.

Drowned Delta

Deltas worldwide are under pressure due to sea-level rise. Solutions for dealing with sea level rise have mainly focused on preventing deltas from drowning. But what if sea-level rise will further increase beyond the point that sustaining a ‘dry’ delta is no longer feasible?

The Drowned Deltas project aims to explore what opportunities lie beyond the horizon when deltaic areas are forced to transition to a ‘wet’ or ‘drowned’ stage. What new opportunities may arise from extreme sea-level rise? What can we learn from other deltas worldwide about possible ‘drowned’ ecosystems, ecosystem services and land uses? Do we need to include future ‘drowned’ Dutch delta scenarios in our current delta planning to anticipate for this inevitable future to ensure that when it happens, it happens in the most optimal way?

To answer these questions a literature study was performed and an interactive workshop on the opportunities of a drowned Dutch delta was organised. For the literature study, the necessary abiotic conditions for five coastal ecosystems, their ecosystem services and the expected abiotic conditions for a future drowned Dutch delta under a two meter sea-level rise scenario were reviewed.

The workshop consisted of presentations and exercises about a future drowning Dutch delta. The participants designed a future drowned Dutch delta on a map, pitched their ideas and formulated research questions that came to mind while creating a future drowned Dutch delta. At the end of the day the research questions were valued by dividing funding (chocolate coins) over the questions. The goal of the workshop was to obtain new insides and to define research questions about the opportunities of drowning deltas.

Project period: June-November 2019.

Result of the project

Literature review results

The review of the five coastal ecosystems (mangroves, oyster reefs, seagrass meadows, coastal peat and mangroves) showed that these ecosystems could play an important role for future drowned deltas. For each ecosystem it was studied at which location (climate) around the world they occur, which (abiotic) conditions are required and which services the ecosystem provides. To get an overview of the required (abiotic) conditions per ecosystem, a table with these data was created. The most important services they could provide are: coastal protection, food supply, carbon sequestration, sediment trapping, water purification, recreation, fresh water supply and biodiversity.

Besides a table about the necessary (abiotic) conditions for ecosystems, a second table was created containing information on the expected future (abiotic) conditions for a drowned Dutch delta under a two meter sea-level rise scenario.

Workshop results

New insights derived from the workshop were that drowned deltas could provide opportunities for energy generation and transport. Other new insights on the topic discussed during the workshop were the danger for environmental pollution caused by drowning, the importance of governance in the process to a sustainable delta and the knowledge gaps that need to be filled concerning the future physical conditions of the Dutch delta.

Key research questions on Drowned Deltas

Physical conditions:

  • What will be the natural responses of the Dutch delta (physical, ecology) to the interaction of (different rates of) sea-level rise and river discharge? And how will this natural response differ from our ‘locked in’ urbanised and diked delta?
  • How will the Dutch rivers respond to the combined effect of sea-level rise and climate change?
  • What is the balance between sedimentation and erosion rates, the feedbacks, and how to use this for adaptation?

Governance:

  • How do we plan for this uncertain future (stakeholder participation, transition management)? How to make present decisions future-proof?
  • Which steering mechanisms concerning governance are useful in order to create the necessary movement and adaptation?

Environmental pollution:

  • What is a decision structure to tackle abandonment dismantling and re-use of structural elements in the Netherlands?
  • How do we deal with future pollution due to drowning?

Conclusions

The most important knowledge gained during the project are the necessary conditions for five important ecosystems, the expected abiotic conditions for a future drowned Dutch delta and the opportunities that ecosystems in a future drowned Dutch delta could provide. One of the new insights derived during the workshop are the opportunities for energy generation and transport. Furthermore, the workshop gave insight in the danger of environmental pollution that will arise during drowning, the importance of governance in the process towards a drowning delta and the most important unknowns for the physical conditions of a future drowned Dutch delta. Finally, the formulated research questions during the workshop are an important output of the project. They provide valuable input to direct follow-up research towards the Dutch Drowned delta. And this is crucial because it will happen sooner or later, quoting Peter Kuipers Munneke: “The questions is not if the Netherlands disappears below water, but when.”

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