City of Gothenburg

Gothenburg is located on the west coast of Sweden at a very challenging location regarding flood risks. The city faces challenges regarding rising sea levels, the river Göta älv which passes through the central city and several minor streams within the city. 

Since the early 2000´s, the city has conducted several feasibility studies regarding flood risk analysis and measure strategies. Gothenburg has decided a long-term strategy for flood risk management in the comprehensive planning. The medium-term solution involves riverside protection along the river, and the long-term measure concerns large-scale barriers.

The increased risk of heavy rainfall due to climate change further increases the risk of pluvial flooding.

The city is also working with long-term cloudburst planning using catchment based cloudburst plans, in a similar manner to the ones that have been planned for Copenhagen.

The purpose of the case is to further investigate the existing monitoring/regulation system of Mölndalsån by:

1. Establish a description of an event-driven action-/decision chain from a forecast of a high-water weather event at the Mölndalsån outlets in Göta älv and upstream to the outlet of Stensjö dam.
2. Expand the above analysis to include the retention subsystem just above Stensjö dam i.e. Stensjön, Rådasjön/Massetjärn and Landvettersjön and the Landvetter dam.
3. Validate the system performance/characteristics for chosen boundary conditions and constraints and for chosen weather events.

The objective is to clarify under what requirements and boundary conditions that central Gothenburg and Mölndal can be kept storm safe by controlling the Mölndalsån stream and it´s outlets through high-water gates to Göta älv. The aim is to investigate the use of formal methods in order to propose alternative control strategy for Stensjö dam or improvements/simplifications to the work-in progress control strategy for controlling Mölndalsån to manage high water events in Göta älv.

The case analysis is expected to use formal methods (or other methodology that can be used for subsequent system validation of requirements and boundary conditions) that clarifies/distributes requirements and boundary conditions for critical water levels/flows.

In particular, the requirements for high-water forecasting should be analysed. Specifically, the minimum requirements for forecast horizon (h) and forecast deviation (cm, h) must be determined to ensure that the weather event can be effectively managed through the regulation of the high-water gates and the Mölndalsån stream for the selected weather scenarios.

The aim of the case study is to answer the following research questions:

• How can formal methods be used to clarify and validate under what requirements and boundary conditions that central Gothenburg and Mölndal can be kept safe from a storm flood in the sea (and Göta älv)?
• How can formal methods and forecast driven analysis contribute to an improved performance of the current regulation of Mölndalsån to adapt it to future challenges of closing the gates to Göta älv at storm flood events?
• To what level of detail can such a water system feasibly be modeled using Modest as formal specification language? What limitations are there currently for verifying safety properties and other properties of interest?

Gårda dämme, one of several dams along Mölndalsån.

Gothenburg is participating in StormSafe through the High Water Protection Program Högvattenskyddsprogrammet - Göteborgs Stad  who is the project owner.

Several departments within the city of Gothenburg are involved, as well as external expertise who have formerly been involved in the planning and feasibility studies regarding climate adaption of Gothenburg (rising sea levels, high flows in watercourses and cloudburst).

Involved universities are Lund, Twente, Aalborg and Eindhoven University of Technology. They are all contributing to the case study with their expertise from different disciplines. 

A number of external stakeholders have been identified and prioritized for invitation in the project discussions. Among them are universities such as University of Gothenburg, Chalmers University and Linköping University. Additional priority stakeholders are national authorities as well as stakeholders within the energy sector.

Gothenburg´s complex situation requires co-ordination and co-operation between several stakeholder, both within the administration of the City of Gothenburg and other property owners and companies. 

To monitor and regulate the system is a great challenge. A monitoring/regulation system exists today for one of the main streams that flows through the city, Mölndalsån. There has also been a hydraulic modelling made for Mölndalsån.

The main reason for Gothenburg to participate in the StormSafe project is generally to gain further knowledge and investigate how a future, city-wide monitoring/control system could be developed, which should include the long-term measures that are needed on a city-wide level. Within the Gothenburg case study, investigations will be made regarding the value of using formal methods to validate the current monitoring system in use. The methodology of formal methods will also be of great value to consider when developing the software for the future flood regulating system with large-scale barriers.

Through participation in StormSafe, the city of Gothenburg will gain valuable knowledge and inspiration from other European cities that have been, or are, in the same situation.

The outcome from the Gothenburg case study can contribute to a deepened understanding of how a complex system which include rising sea levels and higher flows in watercourses can be dealt with. Many cities in Sweden and in the other participating countries faces similar problem and could benefit from expected results from the case study.

• Högvattenskyddsprogrammet - Göteborgs Stad
• mölndalsån.se
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