Both the temporary works needed during construction and the permanent final structures will be located on the Thames’ foreshore, potentially changing the way water and sediment moves in the river. We’ve looked at these changes as input to understanding the impact they might have on nearby structures, on river navigability, ecology, as well as being able to inform the design of the structures themselves to minimise these effects.
Future proofing the design
The design life of Thames Tideway Tunnel is 120 years. With the predicted effects of climate change, average sea level and river flows are expected to change over this time, so we‘ve used the validated whole estuary numerical model to simulate the potential extreme currents which might occur over the design life of the tunnel, redefining the extreme or ‘most onerous’ hydrodynamic conditions which the designs will need to be ready for.
Monitoring the effects
The construction of the Thames Tideway Tunnel is split in to three work packages; West, Central and East. Each package includes a number of CSO interception and shaft construction sites.
For the Central area, we are supporting the contractor team – a Ferrovial Agroman and Laing O’Rourke joint venture - to develop and implement a Scour and Accretion Monitoring and Mitigation Plan (SAMMP) for each site of temporary river works. The SAMMP collates the predicted effects of the works on scour and accretion in the river, the understanding of bed level variability and outlines how the river bed level will be monitored during and following the construction of the temporary works. The SAMMP then describes the action that will be taken to mitigate the effects where necessary. The SAMMP is an important document for the construction process and needs to be approved by the relevant regulatory bodies.
The SAMMPs for the Thames Tideway Tunnel are based on an exceptional baseline dataset covering quarterly bathymetric surveys since the end of 2013. The baseline data is key in understanding the natural variability in bed levels which would be expected in a dynamic area such as the tidal Thames and defining appropriate thresholds for any mitigation actions to be triggered.