GroMoPo Metadata for Thurne catchment ditch-aquifer model

Open drainage ditches located in low permeability material can interact with an underlying aquifer, especially if the drains almost or totally penetrate through to the aquifer. This interaction can be represented by drain coefficients incorporated in regional groundwater models. The drain coefficients depend on both the vertical distance from the base of the drain to the aquifer and the hydraulic conductivities of the low permeability deposits and the underlying aquifer. In a case study of drained marshes in the Thurne catchment in Norfolk, UK, drains with a water level below ordnance datum (OD) draw in saline water from the coast and freshwater from recharge areas. Pathlines, derived from a regional groundwater model analysis, explain the salinities measured in drains. In addition a series of vertical section numerical model solutions are used to develop general guidance on the selection of drain coefficients.