ICSE6 Paris - August 27-31, 2012 Grass cover failure following in situ wave overtopping experiments - Peeters et al., ICSE6-081 Application of different failure models for the grass cover following in situ wave overtopping experiments at the land-side slope of a river dike in Belgium Patrik PEETERS 1 , Leen DE VOS 2 , Bart VANDEVOORDE 3 & Jentsje VAN DER MEER 4 1 Flanders Hydraulics Research, Antwerpen, Belgium e-mail: patrik.peeters@mow.vlaanderen.be 2 Flanders Geotechnical Division, Gent, Belgium 3 Research Institute for Nature and Forest, Brussel, Belgium 4 Van der Meer Consulting, Heerenveen, The Netherlands Key words Wave overtopping simulator, erosion, grass cover failure Abstract In situ wave overtopping tests were performed on typical dike structures along the Schelde in Flanders (Belgium) with the Dutch Wave Overtopping Simulator. For a storm duration of 2 hours, wave overtopping characteristics were derived for significant wave heights ranging from 0,75 to 1 m and peak periods between 3 and 4 s. Prior to the in situ experiments, soil investigations were executed together with a detailed study of the quality of the grass cover. During the tests, video recordings were made and detailed pictures of the damage were taken. Water content and evolution of the grass cover were monitored. At one location, no failure was experienced up to 50 l/s per m, even after applying initial damage to the surface protection. Other locations failed after facing 30 l/s per m. Different erosion resistance as well as (superficial) slip models are reviewed and compared to the outcomes of the in situ wave overtopping experiments. I INTRODUCTION Failure of the grass cover following wave overtopping can be the first step towards breaching of the embankment. The Sigmaplan, the safety plan for the river Schelde, foresees in an arbitrary chosen freeboard of 0,5 m to limit possible wave overtopping. In order to increase knowledge of the driving forces, factors and mechanisms, necessary to understand grass cover failure, full scale tests were performed on typical dike structures along the Schelde in Flanders (Belgium) with the Dutch Wave Overtopping Simulator with focus on (estuarine) river conditions. Different types of erosion can be distinguished (Figure 1). Failure of the grass cover is commonly predicted from hydraulic indicators like flow velocity u, shear stress  (~u 2 ) and stream power or work W (~u 3 ). Available failure (prediction) models for erosion are applied to the results of the in situ wave overtopping tests in Flanders (Belgium). Surface erosion Superficial slip erosion (turf sliding) Headcut erosion Figure 1: Different types of erosion of the grass cover [Valk, 2009]. 1247