Geo-hydrologic design procedure for peat dykes under drying conditions

In the summer of 2003 a peat dyke failed at Wilnis in the Netherlands during a very dry period. To assess the consequences of droughts for peat dykes, this paper presents a geo-hydrologic design procedure. The procedure couples an agro-meteorological model based on the Penmann-Monteith expression and a groundwater flow model based on the Richards equation. The first model calculates potentuial fluxes at the surface of the flow domain that account for precipitation and evaporation, and fluxes in the root zone of the flow domain that account for transportation by grass covering the peat dike. The second model computes actual fluxes as both types of processes give rise to non-linear conditions. The model is validated for a peat dyke and extreme water table positions that are likely to occur once in a period of 400 years are calculated.