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amending the Design criteria of URban defences in LECZs through Composite-modelling of WAVE overtopping under climate change scenarios

Periodic Reporting for period 1 - DURCWAVE (amending the Design criteria of URban defences in LECZs through Composite-modelling of WAVE overtopping under climate change scenarios)

Reporting period: 2019-03-01 to 2021-02-28

The IPCC Special Report on Ocean, Cryosphere in a Changing Climate states that global mean sea level will rise up to 1.1 m by the end of the century, exacerbated by the climate change. Hazards in coastal regions will increase depending on climate scenarios and significant changes in the coastal wave driven processes are expected. Major economic damages and loss of life are caused by waves that overtop and breach the coastal defences, as dramatically experienced during the last decades by the growing number of extra-tropical cyclones that led to more frequent and disastrous flooding events. Besides, while climate change increases the chances of disastrous events, population in coastal areas is expected to grow to nearly a billion people by 2060.
Under the complexity of the coastal environment and the changing wave forcing, holistic approaches are required to characterise the impact of extreme wave conditions and the risk associated to flooding events in order to guide the upgrade of existing coastal defences toward low-impact but cost-effective solutions.
The present project aims for a long term solution to cope with climate change and sea level rise in terms of requirements regarding coastal safety for low elevation coastal zones (LECZs). The project is focusing on coastal infrastructures in urban assets. Main goal is to contribute to the definition of new design criteria for wave action by modelling wave overtopping, which is the major cause of urban flooding in coastal areas. The main research findings are going to provide new insight to decision-makers for estimating the vulnerability of LECZs to climate change (societal aim).

A set of specific scientific goals is defined within the project.
1. To study post-overtopping processes by characterising overtopping flows on urban defences and coastal infrastructures.
2. To explore the influence of structural geometries on post-overtopping processes.
3. To relate overtopping flow characteristics to maximum exerted wave actions.
4. To determine the most appropriate overtopping flow characteristics in terms of design purposes.
5. To develop and release (for public use) a unique numerical model technique to simulate phenomena of interaction between coastal structures and sea waves.

To reach the scientific objectives, the project has employed both experimental and numerical modelling (i.e. composite modelling). On top, the Evolutionary Polynomial Regression data-driven technique was also used to find new correlations between wave impacts and overtopping flows.
The work consisted in experimental and numerical modelling on wave structure interaction phenomena. Experimental modelling has been carried out in both small- and large-scale wave facilities. Numerical modelling has employed a meshless Lagrangian particle-based and open-source solver, named DualSPHysics and the Non-linear Shallow Waters equation-based model SWASH.

First, physical model tests have been carried out in the small-scale wave flume facility, named CIEMito, at the Maritime Engineering Laboratory of the Universitat Politècnica de Catalunya - BarcelonaTech (LIM/UPC), in Barcelona (Spain). The adopted model scale was 1:50. The experimental campaign aimed at analysing the validity of the safety limits and design criteria for overtopping discharge. An urbanized stretch of the Catalan coast, exposed to significant overtopping events every stormy season, was selected as case of study, considered as representative of the sea promenade existing in the whole metropolitan area. The results proved pedestrian hazard is linked to the combination of overtopping flow velocity and flow depth rather than to single maximum values of one of these parameters.

Numerical modelling was initially employed to extend the results from the small-scale physical model tests beyond the range of tested conditions. This was done by employing both SWASH and DualSPHysics models. Numerical modelling was also employed to simulate real cases from coastal engineering thanks to the parallel power computing of GPUs. For it, a particular coastal infrastructure in urban asset with a high historical and social value, the Pont del Petroli pier in the area of Badalona, Spain, was selected as case of study. DualSPHysics was employed as an aid for the experimental campaign that has been carried out afterwards at LIM/UPC and demonstrated that the main failure mechanism that led to severe structural damage of the pier during the storm is related to the exceeded lateral soil resistance.

Finally, a second experimental campaign was carried out in the large-scale wave flume facility, named CIEM, at LIM/UPC. Wave loading and overtopping flows over the pier were assessed for extreme wave conditions, taking into account possible climate change scenarios. The experimental model results will be exploited to be directly employed for the pier reconstruction by the Badalona City Council.

All the aforementioned activity, together with other parallel or minor ones, in collaboration with Universities and Research Centres from all over the world (Flanders Hydraulics Research, University of Salerno, University of Western Australia, etc) led to 14 publications in international scientific peer-reviewed journals. Seven of them were focused on wave overtopping analysis and characterization, seven of them on numerical model implementation and validation, keeping a perfect balance between experimental and numerical modelling.

The outcomes of the conducted research have been accepted for presentation in 6 international conferences. Finally, dissemination activities comprise 1 publication in the Hydrolink IAHR Magazine, 3 invited keynote lectures, 1 organized international workshop and 2 organized training events on DualSPHysics.
Overtopping flow characteristics have been analysed for proper assessment of coastal safety and design of coastal structure, in order to update the current knowledge on wave overtopping and post-overtopping processes and design criteria of coastal defences. Further insight into the link between flooding caused by sea storms and overtopping waves and hazards for pedestrian, vehicles and infrastructures has been achieved.
Besides, the project has significantly contributed to engage a larger community of researchers and practitioners of SPH-based models via training, workshops, invited lectures.
Results of the project are going to be exploited for a real coastal infrastructure in urban asset with a high historical and social value.
During the projects activities to engage coastal communities on coastal safety problems and how research centres tackle them have been organized (invited workshop and keynotes in Belgium; visit from Badalona Major and major local media at UPC for the large-flume tests).
Finally, the project has been seeking dialogue and international collaborations, materialised in invited talks, workshops, training and joint publications with colleagues and partners from more than 10 institutions worldwide.
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Bike tour and in-situ lesson on coastal safety with Master students along the Catalan Coast
Large-scale experiments in CIEM flume