Understanding Flow Slides in Flood Defences
Research Summary
During a flow slide, large amounts of soil move down an underwater slope. A flow slide is able to remove an entire dike or dune section which poses a severe threat to the water safety of low-lying countries.
The ability to predict flow slides is an important asset for the design of flood defence measures, their construction, maintenance and safety assessment; even more so in view of intensifying land use and the impact of climate change on low-lying coastal areas worldwide.
Flow slides are not yet well understood. Their study requires an integrated approach of fluid and soil mechanics; soil movement induces turbulent water motion which in turn interacts with the eroding soil surface. Currently, such an integrated approach is lacking. Studies so far mostly rely on empirical approaches that apply to specific circumstances only and use considerable simplifications. Physical experiments involve high costs as scale effects necessitate large test facilities and such tests often only allow predictions for specific projects. This makes the safety assessment of flood defences and the development of measures to prevent flow slides difficult and costly.
In the proposed interdisciplinary project, an integrated numerical solution for the simulation of underwater flow slides from initiation up to deposition of sediments will be developed through enhancement of a numerical method, the so-called material point method (MPM). Laboratory experiments will be performed to gain deeper insight into soil and fluid mechanical processes that occur at the onset of and during flow slides. They further serve for the validation of the developed numerical solution method. New physics-based models for soil-water interaction, soil heterogeneity and turbulent flow as relevant to flow slides will be formulated and existing models will be extended. They will be translated into purpose-built, efficient algorithms to be integrated into available Anura3D MPM software.
Utilisation
Measures taken in the Netherlands in recent years to counteract flow slides involved costs amounting to M€ 100.
Results of this project will allow an accurate and site-specific evaluation of the vulnerability of flood defences to flow slides. This enables integrated probabilistic safety assessments of flood defences - and also an estimation of the post-failure ability of a flood defence to prevent flooding. Results of this project will thereby allow for much more refined and thus economical maintenance works.
The devised enhanced Anura3D MPM software is a 3D generic numerical method for integrated geotechnical and hydraulic analyses that can also be applied to other erosion processes than flow slides. It will for example also be of benefit to the Dutch offshore industry. Numerical analyses will help to raise the level of confidence in innovative technologies, e.g. for scour protection, protection of offshore pipelines, dredging and the exploration of hydrocarbon reservoirs. Furthermore, advanced mathematical solutions developed in the frame of this project are expected to find their way into other commercial software, e.g. the Plaxis FEM software for geotechnical applications.
With regard to academia, this project prepares the ground for future high-level national and international collaborations between applicants and academia as well as the high-tech industry.
