Mould, D.J.; (2008) Multi-scale assessment of wetland hydrological function at a wet grassland in southeast England. Doctoral thesis , University of London.

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Abstract

An examination of the hydrological functioning of a wet grassland in southeast England is undertaken within the context of scale issues. The importance of wetland hydrological functioning is demonstrated, alongside highlighting a gap in the literature of how scale issues affect contemporary wetland hydrological science. The subsequent assessment of hydrological functioning at a field site at Otmoor, Oxfordshire, is thus undertaken at both the field and catchment scales. At the field scale, an intensive field campaign over 18 months establishes the dominant hydrological processes as being precipitation and evaporation, the latter with losses of up to 5 mmday1 driving an unexpected diurnal fluctuation in soil water levels. The dominant hydrological function was surface water storage, showing potential conflict with current land management practice of raising water levels for wetland restoration purposes. The impact of scale issues on numerical models is assessed through utilisation of a multi-scale model. At the catchment scale, the wetland's impact was assessed through increasingly complex numerical models, ultimately an event-based hydrodynamic model, and is shown to be significant to flood management downstream at Oxford. Decreasing peak flood flows through flood storage was the dominant function, as dictated by surface topography, whereas other online floodplain areas within the catchment increase time to flood peaks by attenuating flow through surface roughness, confirming the importance of wetlands to river flow. Surface roughness was therefore shown to be critical for wetland behaviour at different scales for different wetland types, indicating the importance of scale to wetland hydrological processes. The significance of initial model conceptualisation was demonstrated, and several recommendations were made for modelling procedures in order that scale issues be incorporated and prevented from causing complications in future modelling work. These include taking an iterative approach to increasing understanding through modelling, and linking models of different scales.

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