Saturated and unsaturated flow dynamics in a floodplain wetland

This paper describes initial work modelling unsaturated processes within floodplain wetlands. The limitations of solely considering the dynamics of the wetland water table and hence saturated processes are examined. Water table, precipitation and evapotranspiration data from Narborough Bog, a degraded floodplain wetland of 10 ha in Leicestershire, were used in the development of a one-dimensional saturated-unsaturated flow model using UNSAT1. Hydraulic parameters were derived from a combination of field and laboratory analysis of wetland deposits previously undertaken to develop a saturated flow model of the wetland. Additional parameters describing unsaturated flow were derived by a mathematical approximation based upon the soil moisture characteristic of representative wetland sediments. The resulting model is used to explore the interaction between water table position, vertical soil moisture fluxes and evapotranspiration. Model simulations are completed over a 25-day period, and used to indicate the relationship of moisture content to key hydraulic properties of soil profiles typical of the wetland and illustrate the way in which this varies laterally along a transect. The results highlight the need to consider the importance of correct description of the wetland substrate and, notwithstanding difficulties in describing unsaturated flow parameters, there is a considerable need to improve the description of near-surface wetland water fluxes and their expansion to two dimensions. Copyright (C) 2000 John Wiley & Sons, Ltd.