Unique Delta Flume waves to test nature-friendly riverbank defences
The Dutch river area is vulnerable. The river nature is deteriorating, weather conditions are becoming ever more extreme, and rivers are important transport links. To improve natural resilience, hard riverbanks will be made natural again where possible. The first nature-friendly riverbank defences will be tested in the Delta Flume at Deltares in November.
As part of the River Widening 2.0 (Room for the River 2.0), Water Framework Directive (WFD) and Programmatic Approach for the Main Water System (PAGW) programmes, work is taking place on improving flood risk management and the ecological water quality of the Dutch rivers. Hard banks will, where possible, be made natural again. Where possible because waves from shipping can result in severe erosion and instability in natural banks. That has consequences for flood risk management.
Exact level of wave reduction afforded by natural protection still unknown
Natural banks are desirable to achieve WFD objectives, for example, but safety must not be compromised. The current technical solutions are often less nature-friendly. Wooden screens, brushwood dams, or rows of poles with fascines (bunches of willow branches) can be used to create sheltered areas that reduce wave energy. This is a Nature-based Solution (NbS) that already being used in regional waters with recreational shipping. However, research into the exact level of wave reduction has been very limited on rivers with mainly commercial shipping.
Trial of unique long primary ship wave
The study of the wave-reduction properties of different wooden screens in the Delta Flume is unique. Never before has such a highly robust 1.8 m thick wooden screen been built and tested. Although the Delta Flume is well known as the place for generating the largest (in other words, the highest) waves in the world, this study will actually test, for the first time, typical long primary ship waves with periods of up to 50 seconds.
The aim is to determine the level of wave reduction with different screen thicknesses. In addition, the study will also look at failure mechanisms during construction (low fill level of the screen due to the buoyancy of the wood) or due to crumbling (degradation) and the impact on wave-reduction capacity.
Basis for design and maintenance guideline
The study is a part of the Vaarwegen perceel 2 maintenance contract with Rijkswaterstaat East Netherlands. Under that contract, Strukton and Van Den Herik (private sector), Rijkswaterstaat (government) and Deltares (knowledge institute) are working together to test innovations for application. The results will ultimately constitute the basis for design and maintenance guidelines for wooden screens as foreshore defences and/or emergency measures.
