Summary of research work about erodibility of grass revetments on dikes

Hoffmans, G. and van Hoven, A. and Steendam, G. and van der Meer, J. (2018) Summary of research work about erodibility of grass revetments on dikes. In: Protections 2018 (3rd International Conference on Protection against Overtopping), 6-8 June 2018, Grange-over-Sands, UK.

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Abstract

Grass prevents erosion of the subsoil and is an effective control measure for overflowing water as well as overtopping waves. This form of protection has long been used for agriculture drainage channels and on the slopes of dikes. Dutch river dikes usually have clay layers covered with grass on the crest and on both the landward and seaward slopes. Lake and sea dikes with hard revetment in the wave impact zone of the seaward slope also have a grass cover on the crest and the landward slope on a clay type of soil. For grass covers, relatively large forces are required to break up clay aggregates within the soil, while smaller forces may suffice to transport pure sand and small clayey aggregates. Therefore, at the onset of dislocation, a grass cover will experience considerable forces, which may be described by turbulence, especially on steep slopes. From 2007-2014 about 50 experiments at several locations on Dutch and Belgian dikes were conducted with the wave overtopping and also run-up simulator for assessing the erodibility of grass revetments. Based on these prototype tests the cumulative overload method has been developed, a model that predicts the damage of grass mats and failure of dikes provided the load of the wave run-up and/or wave overtopping and the erodibility of the soil are known. This paper discusses engineering methods for predicting the erodibility of grass revetments as well as the erosion of grass at transitions, e.g. at the edges of roads, transitions from hard to grass revetments and objects on dikes, for example trees.

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