Tackling floods and droughts with NBS

The river system of Dove and Gose Elbe (Hamburg, Germany) has to cope with floods and, more recently, with droughts. The distribution of the storage volume during flood events is now managed by the monitoring and control system, improved and finalised by RECONECT. Thanks to the project, hybrid solutions will also be implemented combining existing grey infrastructure and Nature-based Solutions

Brookwetterung (drainage system). Source: D. Ackermann, LSBG
Figure 1: Geographical location of the Demonstrator

Water-related hazards affecting the area

The area is mainly exposed to floods (affecting mainly settlement areas and agriculture) due to the combination of:

  • High water levels in the Elbe River over a long period (several days) due to wind from western directions.
  • High discharges within the river system Dove/Gose Elbe and its tributaries (Bille) due to continuous rainfall over a long period (several days).
  • Low water levels in the Elbe River over a long period (several weeks) due to low inland runoff and wind from eastern directions.
  • Low discharges within the river system Dove/Gose Elbe and its tributaries (Bille) due to long droughts (several weeks).

NBS implementations in the area and benefits expected

Nature-based Solutions in the area focus on the reactivation and the distribution of the storage capacity of the rivers Bille, Dove and Gose Elbe, their tributaries and trenches and their flood plains in the area of 175 km², to create more retention volume for water during flood events. At the same time, necessary stable water levels in the rivers can be provided during droughts.

Figure 2: the envisaged NBS in the German demonstrator
  • Reducing flood hazard and lowering of water level
  • Economical savings from operating the pumping stations
  • Reduction of the total amount of water
  • Creating storage for the dry periods (to be addressed in the next project phase)
  • Improved ecological condition of the area due to optimised use of the retentions and floodplains
  • Increase in the biodiversity of flora and fauna
  • Improved liveability and social value of the area also contributing to the tourism, that is gaining relevance in the area
  • Reduced number of assets affected by floods
  • The grey infrastructure is being converted into hybrid solutions by combining the existing grey assets (such as sluice gates and pumping stations) and NBS. The project is thus contributing to the mindset change and as such sets a cornerstone in the future management of large scale NBS in Hamburg and beyond.
  • We are expanding the existing linear and disciplinary approach (a piecemeal approach to floods and drought management) into a holistic, which will be taken up by the governance structures in Hamburg, after the project lifetime.

Status of work

The project is currently in the implementation phase. All necessary preparatory actions have been accomplished, including the pre-processing of data and models for the RECONECT NBS operation and controlling system, the purchase of equipment and the preliminary screening of the potential retention areas.

Figure 3: Implementation of the NBS for the Dove and Gose Elbe river system- the current status (1)-(3) and some further steps (4) and (5)

What has been the main lesson in working on RECONECT?

NBS as an idea is appealing and usually well received by the administration and decision-makers. However, the mechanisms for its implementation are still underdeveloped and their development and consideration will require time. Moreover, although it appears reasonable to consider both benefits and co-benefits for the implementation of measures, in practice it turns to be far more challenging than presumed. It lies to a large extent on the different responsibilities and expertise required to address different benefits e.g. flood peak reduction and improvement of the liability of the area.

Have you identified other areas where to use the same approach?

The presented approach has a replication potential in those areas where drainage capacity is limited due to the tidal regime and influence. This can be found at tributaries along the Elbe Estuary (Stör, Krückau, Este, Oste). Apart from similar challenges, those areas share similar geographical features, but also governance, social and cultural settings. Other rivers in Northern Germany discharging into the North Sea such as Weser represent areas with further replication potential and should be further explored.

What is a relevant achievement you are most proud of?

The RECONECT activities in the German demonstrator brought change and new developments in two main aspects: technical and social/institutional. The first one is related to the deployment of the innovative technology for smart management of hydro-meteorological events, mainly floods, demonstrating the potential to upgrade the grey infrastructure with the NBS approach i.e. optimising the operation of the existing sluice gates and creating necessary retentions, rather than implementing another mere technical solution (for example by constructing another sluice gate).

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Reconect

The RECONECT project demonstrates the effectiveness of Nature-Based Solutions for hydro-meteorological risk reduction in rural and natural areas www.reconect.eu