HSRR09: Adaptive strategies for the urban floodplain of Hotspot Rotterdam

The areas outside the levees in Rotterdam will face two important developments in the next few years. While climate change increases the risk of flooding of the areas outside the levees, land use in these areas is intensifying. This aggravates the risks of future disasters, while at the same time the increased economic value could cause the possible consequences of flooding to become more severe.

The present study describes a strategy aimed at reducing vulnerability by minimizing the consequences of a potential flood. One line of approach would be to make adjustments to the physical design of the built environment and to alert the users and residents to the risks involved. Research is required to gather data on such adaptive strategies in order to be able to formulate flood management policy for the areas outside the levees. The study consists of a definition phase and a project phase. This report discusses the results of the definition phase.

The objective of the overall survey is to develop a flood-proof strategy to design a sustainable, internationally distinctive and attractive residential and business environment in newly to be developed and existing areas outside the levees in the Rotterdam region. The purpose of the definition phase is to gain a clear understanding of the knowledge available and the knowledge that is still lacking, assess the demand for expertise in greater detail, and to prepare the further approach for the project phase of the study.

Approach

To accelerate the process of gaining a clear understanding of the existing knowledge concerning adaptive building and to assess the demand for expertise in greater detail, the members of the consortium actively participated in work meetings. In addition, two expert meetings were held that were attended by representatives from the corporate sector, the government and the parties responsible for development and construction. The following substudies were carried out:

• International exploratory survey of adaptation strategies applied by European delta cities (Delft University of Technology).
• survey into the level of vulnerability of areas outside the levees to high tides and storm surge flooding (INBO and dS+V).
• survey of adaptive strategies, measures and methods (Deltares).
• field analysis for the areas outside the levees (Arcadis), concerning the roles, responsibilities and interests of the public and private parties involved in spatial development in the areas outside the levees.

Results of the substudies

International exploratory survey of adaptation strategies applied by European delta cities
The exceptional position of the Dutch delta makes it difficult to compare and implement good international examples of adaptive strategies for the areas outside the levees. As a delta city, Rotterdam takes up a unique position and therefore requires a unique approach. This should be an approach in which the flood management strategies at various levels are linked together and coordinated, and that does justice to the scale and dimensions of the areas outside the levees.

Four scenarios for interventions in the river water discharge system demonstrate that the conditions for ‘adaptive building’ strongly depend on choices made at a regional level. These scenarios furthermore demonstrate that training our administrative focus on flood management strategies will cause changes in the conditions for natural processes and generate opportunities for economic and urbanization processes. In addition, we found that there is a need for a balancing tool that will shed light on the water level limits up to which adaptation on a local level is likely to succeed, and which water levels will require us to proceed to more drastic interventions on a regional scale.

Exploratory survey into the level of vulnerability of areas outside the levees to high tides and storm surge flooding
Floodings outside of levee protection can be predicted fairly accurately, and are accompanied by low water levels and flow velocities in the areas concerned. Furthermore, the highest water level in the River Maas will drop again soon as a result of tidal movements. Material damage as a consequence of inundation will reach significant proportions. The risk that inundation of the areas outside the levees will occur is reduced by raising the entire area and by applying a high allocation level (height above Amsterdam Ordnance Datum at which the site is officially required to be maintained) in new property development.

Rotterdam’s areas outside the levees are safe. The largest part of the land outside of levee protection has been raised to between 3.0 and 3.5 m above Amsterdam Ordnance Datum. Only a few areas containing historic buildings (Noordereiland and Heijplaat) run a high risk of sustaining flood damage. In future, sea level rise will increase the risk of inundation of the areas that are located outside of levee protection.

Extremely high water levels are controlled by the Maeslantkering. If this flood barrier fails to close (highly unlikely), the water levels in the areas outside the levees will follow the North See level. A storm surge at sea coinciding with peak river discharge could lead to high water levels that will impact the areas outside the levees. Modified and more intensive use of the areas outside the levees will significantly increase the potential damage and social consequences of inundation.

The areas outside the levees differ widely in nature. Apart from a difference in altitude, there are differences in terms of the character and the level of depreciation of the existing buildings, their use and the dynamics of their development. These parameters ensure that the so-called adaptive capacity takes on overriding importance in deciding on an adaptive strategy that is likely to be successful. Assessment of this adaptive capacity is an important step in the process of phrasing the adaptive strategy.

Exploratory survey of adaptive strategies, measures and research methods
No legal standards apply to the protection against flood of the areas outside the levees. The basic principle is that residents and users are personally responsible for taking mitigating measures and that they personally bear the risks of flood damage.

There are two strategies that may help to increase safety in terms of flood management in the areas outside the levees and to reduce flood damage:

1. reduction of the risk of inundation due to high water levels (prevention);
2. adjustment to changing circumstances (increasing adaptive capacity or flexibility).

The current flood management strategy predominantly aims to reduce the risk of inundation due to high water levels, by means of local measures such as overall raising of the areas and determining a safe allocation level, and on a regional level by means of the Maeslantkering, for instance. However, this strategy is vulnerable. The second strategy focuses on increasing the adaptive capacity of the area:

1. mitigating the consequences of high water levels (reducing the damage);
2. increasing the capacity for recovery and repair (increasing the resilience).

Force field analysis
Utilization of the potential in the areas outside the levees faces challenges of a physical and technical, as well as an organizational, institutional and financial nature. Co-creation, co-operation, co-production and co-financing are preconditions for seizing the opportunities together and realizing high-quality combined residential and business areas outside the levees. Rather than obligations, the main focus should be on what people want and need. It is important to focus on collaboration in conducting research, creating and taking advantage of interlinked forces, interests and phenomenons (trends and global developments). This requires a framework that facilitates connection, sharing a vision on key principles, room to experiment, collaboration arrangements, and investment strategies.

Conclusions and themes of research

Use of space: from adaptive building to a comprehensive adaptive strategy – Finding the right balance and clarifying the interaction between physical spatial measures and legal planning measures is an important focus in the follow-up survey.

Future resilience: a successful adaptive strategy responds to a changing reality – In defining an adaptive strategy, we should also consider the timing of various implementations, as well as any interdependencies and relationships between the various measures and the extent to which they allow adjustment to the selected strategy. The ‘Adaptation Tipping Point Approach’ may prove useful in identifying and analysing dependencies, robustness and flexibility of the measures.

Flood management: local and regional aspects and the relationship with flood management strategies in the Rijnmond region – The success of any adaptation strategy will depend on the strategy’s ability to contribute to flood management and safety on a local and regional level as well as at the level of the Rijnmond delta. The study into the interaction between measures at various levels is an important element of the project phase.

Politico-administrative considerations: establishing flood management standards – Responsibility for flood management in the areas outside the levees is vested in the regional and local authorities. The task definition and opportunities for a storm surge resilient layout are directly related to the basic principles applied in the areas outside the levees with respect to flood management and flooding.

Planned economy: storm surge resilience as part of the land utilization – Innovations are required in order to establish a connection between the investments for short- and long-term climate adaptation tasks. For this purpose, we should investigate ways in which the value of storm surge resilience can be included in the land utilization.

Perception: raising awareness on flood management and feasible adaptive measures – Unfortunately, there is a downside to a relatively high level of safety provided by flood management. Overall awareness of the vulnerable position of the areas outside the levees is relatively low1 for residents and users. The survey questions should centre on this area of tension between opportunities to raise awareness and the feasibility of adaptive strategies.

Legal planning considerations: embedding and incorporating adaptive strategies and measures – In practice, laws and regulations often prove to be an impediment to the implementation of adaptive measures. The feasibility of any adaptation strategy will largely depend on innovations in laws and regulations and current policy.

Positioning of the project phase of the study into adaptive strategies

The objective of the survey is to contribute expertise on the subject of applicable adaptive strategies and measures for flood protection in the areas outside the levees. The survey consists of three parts:

1. Part 1 focuses on the vulnerability of the areas outside the levees to changing water level conditions. This part involves conducting a system analysis of the three case study locations. This system analysis consists of a flood analysis, a vulnerability analysis and an analysis of the adaptive capacity of the three case study locations.
2. Part 2 is a design-driven, research-based study at four case study locations in Rotterdam and the surrounding region. Adaptive strategies and measures are explored and the interdependencies between the measures are illustrated. The proposed measures are assessed by expert judgement for compliance with criteria concerning flood management, spatial quality, increase in property value, administrative support, planned economy and process-related criteria, etc. In addition, based on one or several elaborated case studies, we will zoom in on the planned economy aspects of the adaptive proposals.
3. The final part describes generic and specific conclusions and provides the building blocks for an adaptation strategy for the areas outside the levees.

During all of the study phases, knowledge will be tested and generated in a number of concrete case study locations. In close collaboration with stakeholders in the areas outside the levees, the feasibility of promising adaptive strategy will be assessed.

The report Adaptive strategies and the Rotterdam Floodplain H. Meyer & W. Hermans, (2009). Adaptive strategies and the Rotterdam Floodplain.