DITCH: a model to simulate field conditions in response to ditch levels managed for environmental aims

Wetland areas are frequently managed by manipulating the water levels in the surrounding ditches, with the aim of restoring or enhancing the wetness of the site, especially for the ecological requirements of some bird populations. The extent to which water tables in the centre of fields can be controlled by this action can be simulated through the use of a model, Drain Interaction with Channel Hydrology (DITCH), based on drainage theory. DITCH successfully predicted the pattern of water table behaviour on two wetlands sites, in the Norfolk Broads and Somerset Levels areas in the UK. The model can also be used to predict the strength of the soil surface and the extent of surface flooding. When used to examine the effects of alternative ditch management regimes within the two test areas, the model shows that the effects of ditch management options are not easily converted into impacts in the centre of the fields. If the effects are nor sufficient, then hydrological manipulation of sites to achieve or improve wetland status may require more active intervention (C) 2000 Elsevier Science B.V. All rights reserved.