Survey Operations have been associated with the new Mersey Crossing, now the Mersey Gateway Bridge, since 2004. Initial work was undertaken over an estuarial area of some 750 acres (300 hectares), undertaking the hydrodynamic monitoring surveys in the intertidal zone to record the movement of sediments and erosion of the surrounding salt marsh areas.
Work involved the use of boats, hovercrafts, wet-bikes and quad atv’s. Measurements were made using GNSS, Laser Scanning and Sonar to record river estuary bed levels. Survey visits were made at regular intervals throughout the bridge feasibility, design and construction processes.
As the Manchester Ship Canal abuts the estuary, possible scour of the river bed sediments along the canal retaining wall were cause for concern. In addition, the original ‘Silver Jubilee’ Road Bridge and the ‘Britannia’ rail bridge, spanning the narrow ‘Runcorn Gap’ were also monitored for bridge pier foundation scour.
These areas were surveyed and monitored using our hydrographic survey vessel ‘White Osprey’. Our work involved the modelling of the river bed, were taken on a regular basis to allow the Consulting Engineers to compare results and measuring the possible development of scour.
Images of the Case Study are provided to show the overall size and complexity of the new bridge development. Survey Operations are currently monitoring the estuary ‘post construction’ to provide the Environmental Consultants with results of sediment movement and salt marsh erosion, now the new bridge has been constructed across the estuary.
