Transition structures in grass slopes of primary flood defences tested with the wave impact generator

Paul van Steeg, Astrid Labrujere, Roy Mom

Wednesday 1 july 2015

11:00 - 11:15h at Africa (level 0)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 9F. Engineering - River

The stability of grass slopes on primary flood defences under wave attack is an important aspect with respect to the strength of the entire dike. Therefore there is a need to understand the behaviour of grass slopes under hydraulic loads. Since grass cannot be scaled properly, research is usually conducted in full-scale wave flumes or, more recently, with use of several hydraulic simulators such as the wave impact generator. The wave impact generator is a special designed machine which simulates a sequence of wave impacts by releasing amounts of water on a grass slope. The hydraulic load is comparable with the load due to an irregular wave field with a significant wave height of Hs _ 0.6 m – 0.7 m and a wave steepness of sop _ 0.05 which represents riverine wave conditions. The development of the wave impact generator is described in Van Steeg et al (2014a). Within the project WTI 2017 (“Research and development of safety assessment tools of Dutch flood defences”) the wave impact generator was applied on several existing dikes. Variations on the dikes were different grass and clay quality (described in Van Steeg et al, 2014b), but also several transitions and objects. The present paper will describe and analyse tests that were performed on transition structures and objects in the grass slope. It was concluded that for several tests the stability of the grass slope was significantly lower when a transition or object was applied. This implies that transition structures are in some cases normative for the strength of grass slopes. References Van Steeg, P., Klein Breteler, M. and Labrujere, A., 2014a, Design of wave impact generator to test stability of grass slopes under wave attack, (in press), 5th Conf. on the Application of Physical Modelling to Port and Coastal Protection, Coastlab, 29 Sept. – 2 Oct. 2014, Varna, Bulgaria. Van Steeg, P., Klein Breteler, M. and Labrujere, A., 2014b, Use of wave impact generator and wave flume to determine strength of outer slopes of grass dikes under wave loads, (in press), 34th Int. Conf. on Coastal Engineering, 15-20 June 2014, Seoul, Korea