Author(s): Ligaya Wopereis; Paul Van Steeg; Myron Van Damme

Linked Author(s): Ligaya Wopereis, Paul Van Steeg, Myron Van Damme

Keywords: Erosion; Grass; Dike; Field measurement

Abstract: Dikes are used around the world to protect the hinterland from flooding and are becoming increasingly important due to sea-level rise, subsidence of the hinterland, the increase in urban population, and more severe droughts and rainfalls. A significant part of the Netherlands is below sea level and is therefore particularly vulnerable requiring a risk-based approach resulting in tolerable failure probabilities for each dike section. To determine the failure probabilities each relevant failure pathway, consisting of multiple failure nodes, should be addressed. An important failure node is the failure of grass revetments due to hydraulic loading such as wave impact, wave run-up and wave overtopping. After failure of the grass revetment, subsequent nodes can lead to failure of the dike. The strength of a dike, therefore, depends on the erosive properties of its top layer consisting of grass and clay. These properties need to be accurately quantified to calculate the failure probability of a dike, which is challenging due to the complex character and heterogeneity of grass and clay. These properties are typically estimated using experimental methodologies, but these methodologies are not a suitable approach to collect the large amounts of data required to obtain better estimations. Large-scale facilities, such as large-scale flumes (e.g. Delta Flume), run-up simulator, overtopping simulator, and wave impact generator, are accurate but are, due to its scale and operability, considerably more expensive. Smaller devices such as the JET and HET are too small to account for the structure of clay and are influenced by local heterogeneity. It is critical to develop a novel and innovative experimental method with a suitable scale. This paper proposes the fire hose method, which is an easy-to-operate, medium-scale physical experimental device that applies a load in situ to test the erosive properties of grass and clay. This method only requires two people to operate and has been tested three times in the Netherlands with promising results. The experimental setup consists of a pump, a pressure hose, and a frame on which the nozzle is mounted. During the experiment, the grass revetment is loaded by a continuous jet of water. The erosion characteristics are measured throughout the experiment. The acquired data can be combined with large-scale methods, to strengthen the results and acquire, fast and efficiently, the necessary amount of data.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221654

Year: 2022