Decision-making on adaptation measures in (re)development project in unembanked areas

Decision-making on adaptation measures in (re)development project in unembanked areas

The recent high water levels in December (2023) and January (2024) have reignited the debate on building in unembanked areas. The unique event of the Maeslantkering closure due to high water in 21 December 2023, for the first time since its construction, highlights the urgency of preparatory measures against flood risks. Unembanked areas, due to their direct proximity to the sea or river, are particularly vulnerable to floods. Without appropriate measures, the risk of flooding increases due to rising sea levels, increased peak river discharges, and land subsidence. The allure of waterfront locations, combined with the ongoing housing crisis and urbanization trend, has led to numerous plans for urban unembanked area developments across the Netherlands, such as the Merwe-Vierhaven (M4H) area in Rotterdam, where 17,500 new homes are planned to be built by 2040.

To effectively address the impacts of climate change and avoid passing on the consequences of current construction to future generations, adaptation measures are crucial for (re)developments in unembanked areas. This article will delve into the complexity of building in unembanked areas, explore suitable evaluation methods for flood risk measures, and address stakeholders’ needs. 

Complexity of unembanked areas

To provide a brief introduction: unembanked areas lack protection from dikes and dunes. While they face a higher risk of flooding compared to embanked areas, their elevated terrain often results in lower flood levels. Floods in these areas typically cause water-related inconveniences rather than life-threatening situations, making buildings in unembanked areas not inherently unsafe, but rather posing different risks. 

In contrast to embanked areas, where the Dutch government is legally obligated to provide flood protection, residents and users in unembanked areas must take responsibility for preventive measures and bear the risk of water damage themselves. Apart from a few exceptions for large companies, damage caused by water coming from the sea, a river or an inland waterway due to a primary flood defence has overflowed or failed is not insurable in the Netherlands and all houses in unembanked areas are excluded from insurance anyways. Moreover, these areas lack standardized safety levels and there are different legal responsibilities and duties, which stakeholders find challenging.

Despite the different kind of risks involved, unembanked areas remain attractive for area (re)development, provided that flood risk considerations are incorporated into design and construction. Research indicates that investing in climate-proof cities is more cost-effective than recurrent damage repairs. Urban development offers an opportunity for flood risk management, emphasizing the need for collaborative efforts to reduce flood risks by either preventing floods or minimizing their impact.

How to arrive at the most suitable set of measures?

Adaptation measures can be taken at different levels (e.g., regional, local, or building), and the location characteristics call for a tailor-made approach. The fact that many parties are involved or affected in flood risk management and spatial planning, the dependency on decisions taken at different (governmental) levels, and uncertainties in the rate and magnitude of climate change complicate the question of how to deal with flood risks on a local level in unembanked area development.

However originally designed for the embanked areas, the Dutch multi-level safety (MLS) approach consisting of layers (1) prevention (2) spatial interventions (3) crisis management, is well applicable for the unembanked areas too. The proposal to expand the MLS approach with additional layers for (4) recovery and (5) water awareness aligns with the challenges faced in unembanked area development. Next, methods such as adaptive pathways (AP) and adaptive tipping points (ATP) have been used for adaptation strategies in unembanked areas. These resilience-based planning methods offer valuable guidance in the decision-making process and serve as an effective means to facilitate ongoing decision processes by assisting decision-makers in choosing future adaptation options that align with changing environmental and societal conditions.

Social values and intangible criteria such as spatial quality, nature, cultural heritage, stress from floods, flexibility, and feasibility are crucial to include for robust decision-making on local flood risk measures. Yet, there is a lack of key figures and adequate valuation methods for these social values. So, although social cost-benefit analyses (CBAs) is a widely used tool in flood risk management, to support decision-making for local flood risk measures in unembanked areas, it runs into limitations. For these reasons, multi-criteria analysis (MCA) appears to be an appropriate tool to support decision-making on local flood risk measures in unembanked area development, as it is possible to include all relevant effects without having to measure or monetize them. Moreover, MCA can be combined with cost-effectiveness analysis (CEA) or a form of CBA to quantify the effects that are measurable or monetizable. Thus, to support decision-making on local flood risk measures in unembanked area development, the combination of MCA with CEA or some type of CBA is well suited. This is supported by literature such as De Moel et al. (2014) and Van Veelen (2016), as well as real-world examples such as the redevelopment of the Koningin Wilhelminahaven in Vlaardingen, where technical elements, management and maintenance, and spatial quality were important criteria in addition to costs and (water)safety, and HafenCity Hamburg, where the area was redeveloped using various starting principles (potential MCA criteria). The direct access of the land to the water was critical throughout the decision-making process due to spatial features and the preservation of the old harbor’s atmosphere. These methodologies allow for the balanced assessment of both critical quantitative and qualitative criteria. Moreover, using MCA facilitates the integration of diverse stakeholder perspectives, promoting a more inclusive decision-making process, which ultimately ensures broad consensus on the decisions made.

Stakeholders needs

Research on risk governance in unembanked areas has revealed the extensive involvement and impact of various stakeholders in the implementation of flood risk measures in unembanked areas. These stakeholders encompass a wide range, including public entities such as municipalities, provinces, water boards, and Rijkswaterstaat, as well as private entities like real estate developers, housing corporations, banks, insurers, and citizens. The primary barriers identified by stakeholders are currently associated with legal aspects, risk awareness and communication, and flood risk assessment of areas/properties.

There is a significant demand for well-defined guidelines, frameworks, and legal regulations governing climate-adaptive construction. Stakeholders emphasize the need for these requirements to be legally established, as stipulating and enforcing the criteria for climate-adaptive construction would create an equal playing field for all. The government is seen to play a leading role in this, both at the national level, where safety standards can be set for unembanked areas and laws can be introduced for climate-adaptive construction. At the municipal level, however, it is proven to be challenging, it is possible to put some sort of safety levels (e.g., issue level policy in Rotterdam) in zoning plans. Moreover, the government’s crucial role in communicating climate risks is also underscored by several stakeholders. Stakeholders stress the importance of specifying how risks should be assessed, ensuring a consistent risk indication for each area and its asset. Introducing a uniform approach makes it also more appealing for financial institutions, as they are more interested in the risk profile of assets rather than whether they are officially labeled as ’embanked’ or ‘unembanked’. Furthermore, there is an increasing demand for collaboration between private and public entities to facilitate effective knowledge sharing on unembanked areas and climate-adaptive construction. There remains a demand for a more detailed and transparent evaluation method to support decision-making for local flood risk measures in unembanked area development.

There are ongoing discussions on where and how to build, and stakeholders are figuring out how to navigate this. The main recommendation is to establish principles crucial for unembanked area development and then translate them into criteria for a MCA. Part of the MCA should include the (cost-)effectiveness of various measures and should take into account both social values and local characteristics of an area. Further research should look into how to legally assure climate-adaptive construction in unembanked areas, how to create more awareness on both flood risk and the unembanked areas themselves, on flood risk assessment methods and communication, and how to strengthen collaboration between private and public stakeholders working in flood risk management and spatial planning.


  • De Moel, H., Van Vliet, M., & Aerts, J. C. J. H. (2014). Evaluating the effect of flood damage reducing measures: a case study of the unembanked area of Rotterdam, the Netherlands. Regional Environmental Change.
  • Van Veelen, P. C. (2016). Adaptive planning for resilient coastal waterfronts: Linking Flood Risk Reduction with Urban Development in Rotterdam and New York City. A+BE| Architecture and the Built Environment.


The author would like to thank his first supervisor, Audrey Esteban, for the encouragement to write this article, and the other members of the committee, Ellen van Bueren and Matthijs Kok, and Vera Konings (Gemeente Rotterdam) for the guidance throughout the thesis research period.

Authors: Louis Nelen, Delft University of Technology

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