Combined Modelling of Groundwater Table and Open Water Level in Raised Mires

Wetlands are mostly characterized by a large proportion of open water and frequent inundation. In most soil water flow models little attention is payed to phenomena related to open water. In this study, limitations of one dimensional soil water flow models in wetlands are identified. A simple model approach for incorporating the relation between open water and groundwater in soil water flow models is introduced. This model concept is implemented in an extended version of the SWATRE model and tested with data from three lowland raised mires (Engbertdijksvenen, Fochteloërveen (The Netherlands) and Leegmoor (Germany)). The model runs are evaluated by comparing measured and calculated groundwater levels. Results show that the runs with the extended SWATRE model (Standard Error of estimate 4.32-10.9 cm) are considerably better than runs with the standard SWATRE model (Standard Error of estimate 17.6-33.2 cm). It is concluded that a modified quasi two-dimensional approach improves the simulation of water table fluctuations in wetlands.