How Strong Are Our Levees? Hydraulic Analysis Based on Polder2C’s Project in Situ Testing

Abstract

In the prospect of climate change, and especially sea level rise, the Polder2C’s project has been set up to improve, among others, knowledge of external erosion processes on seashore earth dikes. Within the project, overflow, overtopping and breaching in-situ tests are carried out in the Hedwige and Prosper polder, while numerical models are set up to improve technical analysis of testing results. This paper describes blind predictions of water depth and flow velocity on the slope of a levee during an overflow event, before the test is conducted, using a range of different state-of-the-art numerical models. This model predictions were performed by several Polder2C’s project partners. All models considered the same levee geometry, roughness of the grass cover layer and upstream boundary conditions and the models were not calibrated afterwards. The aim of the comparison is to identify best numerical tools to predict flow patterns for different hydraulic loading conditions, since it determines the erosion process, which is to be analyzed as a second step. Homogeneous results have been found with the different deployed models, with some spread partially linked to numerical uncertainties, and calculation methods. The next steps are calibrating of the numerical models (e.g. the roughness of the grass cover layer) and modelling of the erosion process under the calculated hydraulic loading conditions. This will lead to a better understanding of erosion processes under overflow conditions. The test data will be made publicly available, to make it accessible for people outside the project as well.