Kenneth Pye Associates Ltd.
 Scientific Research, Consultancy and Investigations

              
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Soft cliff erosion study, Mersey Estuary, UK
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Project funded by Liverpool City Council for the Speke Garston Coastal Reserve Steering Group

As part of the redevelopment of the former RAF Speke Airport on the north side of the Inner Mersey Estuary, it is proposed to create a coastal reserve for recreational enjoyment and environmental protection.  The site (10 km south-east of Liverpool city centre) includes a 5 km stretch of boulder clay cliffs which are unprotected and subject to erosion.  This study investigated the rate of cliff recession, and its likely impact on the Mersey Way long distance footpath (which runs along the top of the cliffs), the runway at the present Liverpool John Lennon Airport, and the Liverpool Sailing Club site.  The specific questions addressed were:

• The rates and causes of historical soft cliff erosion along the north shore of the Mersey between Garston and Dungeon Lane

• Likely future rates of cliff erosion along this frontage

• How far back the Mersey Way would need to be re-located in order to ensure that it will not be affected by future erosion in the medium term (20-50 years).

• The effect of current and likely future erosion on the perimeter of Liverpool John Lennon Airport and the Liverpool Sailing Club.

Historical changes were assessed using historical maps, charts, ground surveys and aerial photographs. Field sampling and laboratory analysis of cliff sediments gave an estimate of the erodibility of the cliffs.  An evaluation of all existing data relating to the process regime, including wind, wave and tide data, sea level rise, site drainage and the position and morphology of the river channel, allowed a prediction of the future likely recession rate of the cliffs over a 50 year timescale.

Phase 2 of the project involved a feasibility study into nourishment of the mudflat and/or sandy beach area fronting the cliffs. Potential sources of sand and mud were researched, including the use of sediment currently dredged from the navigation channels within the Mersey Estuary. Bathymetric survey data were used to generate a digital elevation model of the foreshore, and calculate the volume of sediment required to increase the level of the mudflat and beach to different design standards.

Cliff slump with exposed boulder clay, near                            Recession of the cliff top to the boundary fence
Dungeon Lane                                                                       and disappearance of the Mersey Way footpath

Aerial photograph of the Speke Cliffs and Liverpool John Lennon Airport in summer 2000.

Map showing the changing position of the cliff and mean high and low waters along the Speke frontage of the
Mersey Estuary (same area as the aerial photograph above).

Wind rose showing the average wind conditions        Historical sea levels at Liverpool, measured since 1858
at Liverpool Airport for the period 1994-2004.        (Source: Proudman Oceanographic Laboratory).

Publications and Reports

Pye, K. and Blott, S.J. (2006). Speke-Garston Coastal Reserve. Cliff Protection by Foreshore Nourishment: A Feasibility Study. Kenneth Pye Associates Ltd., External Investigation Report ER603.

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. and Blott, S.J. (2004). Speke Garston Coastal Reserve: Soft Cliff Erosion Study. Kenneth Pye Associates Ltd., External Investigation Report ER505, 76 pp.

Kenneth Pye Associates Ltd. - Environmental Consultants
Page last modified: July 11, 2007