Tidal Dynamics and Estuarine Management in the Humber Estuary, Englandby J. S. Pethick, Univ of Hull, Hull, United Kingdom,
Abstract: The rate at which tidal energy is dissipated, that is the power expenditure, at any point along an estuary is dependent on the morphology of the estuary. The most important of the morphological controls of tidal power expenditure is estuarine width, although depth and velocity do play a part in the energy balance. In an 'ideal estuary', power expenditure per unit bed area will be constant throughout the length of the estuary and, in order to attain such an ideal, the estuary width will adopt a configuration usually described as a trumpet shaped or flared. This paper examines the power expenditure in the Humber estuary, England, a macro-tidal estuary with a 7.2m tidal range, a width at the mouth of 14km and a length of 100km. The paper compares the present variation in power expenditure along the length of this estuary with the theoretical 'ideal' expenditure. It demonstrates that anomalies in the power expenditure, that is deparatures from the theoretical constant, can be explained by reference to variations in the present estuarine morphology, variations which, in turn, are explained by reference to the history of the estuary. In this case, estuarine history includes natural events, such as post-glacial sea level changes, occurring throughout the Quaternary, as well as more recent, anthropomorphic, interference with the estuary morphology. Thus 19th century agricultural reclamation of inter-tidal areas is shown to have a profound effect on the power expenditure in the present day estuary, deflecting this from the theoretical distribution and therefore setting up counter-balancing morphological adjustments in the estuary including serious bank erosion. The recognition that such recent, small scale, modifications to the estuary as inter-tidal reclamation can have a noticeable effect on the estuarine dynamics, allows the principles outlined above to be used as a predictive tool for estuarine management as well as a record of historical changes. The paper suggests that any engineering works which will alter the estuarine morphology, however slightly, will alter the balance of power expenditure in the estuary as a whole. Prediction of the degree of such changes and of the likely morphological response to it may therefore be an important first stage in the modelling of proposed estuarine works.
Subject Headings: Estuaries | Tides | Hydro power | Case studies | Fluid velocity | Sea level | History | Energy dissipation | United Kingdom | England | Europe
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