Hydrodynamic process, sediment movement and coastal inlet morphodynamics at the mouth of the River Ythan, Aberdeenshire
The research documented herein has been conducted at the mouth of the River Ythan situated at the northern end of Aberdeen Bay, Scotland - a sandy, depositional coastline. This thesis provides a detailed description of inlet development, contemporary morphodynamics, and analyses of principal net current flows and related sediment transport patterns. This is based on morphometric analysis of archival cartographic and photographic sources; sediment tracing using fluorescent dyed sand; deepwater and nearshore wave climate analysis; ground and bathymetric surveys and the deployment of Seabed Drifters and vaned floats. The Ythan mouth is classified as of the 'downdrift offset' type, in relation to a predominant, but low-magnitude, north-to-south wave energy/sediment flux residual. The nearshore zone of the adjacent coastline is characterised by a sequence of sub-aqueous bar forms which merge onshore with the ridge-runnel topography of the intertidal beach and laterally with the inlet entrance shoals. The hydrodynamics of the inlet and its approaches are dominated by tidal and marine (wave) processes. River discharge plays a generally subordinate role in the process environment, except during Law frequency/very high magnitude events. For a tidal inlet on a sandy coastline the Ythan mouth has proved unusually stable, both in gross position and detailed intertidal configuration, over the long 1834 - 1878 and short 1979) time scales. This is a reflection of a) the nature of the wave climate of Aberdeen Bay with medium energy levels and a near balance in drift and counter-drift alongshore (but with a predominant, slight southwards directed residual at the north end of the bay reflected in the predominant intertidal inlet configuration) b) a degree of lithological control exerted on inlet development and response by the underlying substrate of boulder basement and gravel ridges. This factor may explain the long term stability of the gross inlet form and position.