13 - Modelling of hydrological processes in a floodplain wetland

Summary

ABSTRACT This paper considers the importance of interactions between hydrology and ecology for a floodplain peat bog in Central England. Narborough Bog is covered by wet woodland and a reed-bed dominated by Phragmites. There has recently been a reduction in the relative abundance of wetland species due to changing hydrological conditions. The maintenance of near-surface water table elevations is essential to the preservation of the present ecology of this regionally important site, and this is largely dependent upon external factors such as precipitation, evapotranspiration and river levels.

The results of a detailed programme of hydrological monitoring, including the monitoring of water tables, are described and a model of the site hydrology is formulated. This conceptual model is tested using a numerical model (MODFLOW) employing field measured hydraulic parameters. The ability of the model to predict water table responses to varying hydrological inputs is discussed.

The model results are placed within a longer term context which includes the frequency and coverage of overbank events, and the implications of the varying contribution of different components of the water budget for site ecology are described.

INTRODUCTION

Wetlands form ecotones between terrestrial and aquatic ecosystems; they typically possess high levels of species diversity and represent a valuable refugia for rare fauna and flora (Everett, 1989; Wheeler, 1988). There is increasing evidence of their hydrological role in regulating surface and groundwater resources (Carter, 1986), which has strengthened the case for wetland preservation. However, their successful conservation requires quantification of the balance between wetland water inflows and outflows and examination of their relationship to fluvial processes (Mitsch & Gosselink, 1986).