The hydrology of a restored coastal dune slack, St. Fergus, north-east Scotland : an integrated field and modelling approach
This thesis examines the hydrological processes of a restored coastal dune slack at St. Fergus, north-east Scotland. The fundamental hydrological processes of the saturated and unsaturated zones of these habitats is relatively poorly understood yet these ecosystems are under increasing pressure from industrial and recreational development and the possible impact of climate change. Within a 1.2km2 catchment, a detailed field investigation was initiated at differing spatial scales to examine; (i) the spatial and temporal variability in soil moisture retention and movement through the unsaturated zone; (ii) the behaviour of the water table and; (iii) the main hydrogeochemical processes over the year October 1996 to September 1997. The field research was augmented with the development of a groundwater flow model of the site which was used in a predictive role to examine the possible implications of future climate change on the groundwater regime of the dune slack and the impact of this on the ecology and geomorphology of the dune system. The field and modelling results were integrated to provide a relatively holistic interpretation of the hydrological processes of the dune slack system. The soils of all study sites were relatively similar in their retention and temporal variability of soil moisture over the year. Soil moisture contents were generally very low, which was predominantly related to the low organic matter content and highly porous sediment. These soil properties resulted in great temporal variability in soil moisture content over the year with no pattern of higher retention in the winter and lower in the summer. Groundwater behaviour was also relatively homogeneous in the catchment, though local scale, transient processes and phenomena appeared to be important. The main influences on groundwater levels and direction of flow included; (i) the groundwater recharge processes (influenced by variable specific yield phenomena, preferential flow paths and the height of the capillary fringe); (ii) the hydrogeology of the site, particularly the complex plateau region; (iii) site topography; (iv) the shallow water table and; (v) terminal encroachment on to the dune slack. The modelling procedure highlighted the need for an integrated field and modelling approach as problems encountered were resolved through interpretation of the field data. Issues raised focused on scale and scaling in groundwater modelling, the validation of such models and the importance of good spatially distributed field data.