Kenneth Pye
Associates
Ltd.
Scientific Research,
Consultancy and Investigations
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Morphological and bathymetric changes and their causes in the Mersey Estuary
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Project funded by the Department for Environment, Food and Rural Affairs as part of the Estuaries Research Programme (ERP) Uptake Project Changes in the morphology of the Mersey estuary, and their possible causes, have been investigated over a number of years using a combination of Historical Trend Analysis and Expert Geomorphological Assessment. Historical series of bathymetric charts were digitised and analysed within a GIS to provide quantitative estimates to changes in areas and sediment volumes above and below selected elevation planes.
Historical bathymetric maps of the Outer Mersey Estuary and Liverpool Bay, digitised from Admiralty charts
Results showed that the Mersey Estuary experienced major changes over the last 150 years, notably between the late 19th century and c. 1950. Since that time there have been relatively small-scale changes in overall morphology and sediment volume, although changes in individual banks and channels have occurred, with local effects on adjacent inter-tidal flats and saltmarshes. An analysis of data relating to possible natural and human factors which could have influenced these changes has indicated that training wall construction and dredging in the Outer Estuary and Liverpool Bay was the most significant factor contributing to change. These activities modified the hydrodynamic and sediment transport regime in such a way as to enhance an existing natural tendency for movement of sediment from Liverpool Bay and the Outer Estuary into the Inner Estuary.
Changes in other factors, including sea level, tidal range, wind / wave climate, freshwater flow and embanking / land reclamation, appear to have had very little effect. In recent decades the estuary has apparently approached a new condition of dynamic equilibrium, but is clearly susceptible to any future changes in natural or anthropogenic forcing factors.
Publications and Reports Blott, S.J., Pye, K., van der Wal, D. and Neal, A. (2006). Long-term morphological change and its causes in the Mersey Estuary, NW England. Geomorphology 81, 185-206. Pye,
K.,
Blott, S.J. and van der
Wal, D. (2002). Morphological
change as a result of training banks in the Mersey Estuary, northwest England.
SPME, Royal Holloway, University of London, Research
Report CS14, 30 pp. Brew, D. and Pye, K. (2002). Guidance Notes for Assessing Morphological Change in Estuaries. DEFRA / Environment Agency Research and Development Technical Report FD2110, 46 pp. van der Wal, D. and Pye,
K. (2000). Long-term morphological change in the Mersey Estuary,
northwest England. SPME, Royal Holloway, University of London, Research Report
CS4, 37 pp. |
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