Groundwater table lowering due to surface water lowering : knowledge-base for damage-risk assessment (KEM-16b)

In this report, comprehensive groundwater modelling is presented to clarify the relationship between (i) lowering of the surface water level (SWL) of ditches and water courses in a polder setting, and (ii) the lowering of the groundwater table (GWT) caused by the SWL lowering. Focus is on the lowering of the annually lowest GWT during drought, relevant for damage risk. A graphical table is presented that allows estimation of how much GWT lowering has occurred, or will occur, for a given SWL lowering. The table distinguishes four characteristic soil profiles and allows assessment of the influence of several local and regional hydrogeological conditions. The new table improves older (1987) guidelines.