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Thames Tideway Tunnel

Specialist Consultants in the Aquatic Environment


Developing new water quality standards for the Tideway

Nationally significant infrastructure project (NSIP)

Construction of 22km ‘super sewer’ to capture combined sewer outfall (CSO) discharges entering the Thames estuary, currently causing mass fish mortality.

11 sets of structures within construction programme, including Pumping Stations, Jetties and Cofferdams within the intertidal.

Thames Water appoints THA Aquatic director Dr Andy Turnpenny to expert panel, examining options for improving waste water treatment in the Thames Tideway to achieve EU water quality standards compliance.


Dr Turnpenny developed an innovative model used as the basis for developing new water quality standards for the Thames Tideway.
The Tideway Fish Risk Model (TFRM) was used to predict the effects of low dissolved oxygen caused by sewage discharge on fish populations in the Tideway. It also enabled testing of various engineering options, including the Thames Tideway Tunnel and sister project, the Lee Tunnel.


Preparations of the planning application for the Thames Tideway Tunnel project began in 2010 with the scheme deemed to be a Nationally Significant Infrastructure Project (NSIP), consented by the Planning Inspectorate through a Development Consent Order.
There was a strong requirement from regulators to minimise the impact of the scheme within the intertidal and subtidal zones of the river due to its importance as a habitat for migratory fish and other wildlife.

Our involvement:

THA Aquatic were responsible for preparing the fisheries component of the  Environmental Impact Assessment (EIA) for the scheme. Working closely with the project engineers, we helped identify and resolve potential objections from the regulators, optimising the schemes design from an ecological perspective.
As part of the baseline characterisation for the project we undertook monthly juvenile fish surveys and analysed Environment Agency fish survey datasets dating back to 1992. Our specialists presented at stakeholder engagement workshops throughout the project and contributed to submissions during the DCO Examination process.
On receipt of the development consent order THA Aquatic were retained by Tideway to continue to provide expert advice and implement the mitigation and compensation strategy for aquatic ecology.

“THA Aquatic have provided expert fisheries inputs on the Thames Tideway Tunnel project since 2010. Their pragmatic approach to finding solutions to issues raised by stakeholders during the design development and EIA stages of the project helped to ensure that there were no sustained objections to the scheme on aquatic ecology grounds at public examination. Over the years their specialists have represented Tideway at a number of public fora and helped to promote the long term environmental legacy of the project through their Tideway funded work on fish habitat refuges.”

Alan Lewis: Thames Tideway Tunnel

For more information on the Thames Tideway Tunnel.


The Thames Tideway Tunnel scheme had the potential to significantly impede the migratory pathway of juvenile fish moving up the Thames to reach optimal habitat.
As part of the aquatic mitigation and compensation strategy for the project, THA Aquatic undertook a study comprised of field and flume trials to assess the effectiveness of habitat micromeasures placed on the river bed to offer refuge from strong tidal currents.

THA Aquatic investigated methods to improve fish migration through the estuary which resulted in the development of small baffle type structures placed on the river bed.
These habitat micromeasure structures were developed through laboratory flume research and preliminary field trials conducted in 2013 and 2014.
Our 2016 study aimed to determine whether small and juvenile fish would hold their position among the habitat micromeasure structures when compared to similar natural habitat where no structures were present.
60 of the refuge structures were set on the river bed at an experimental site on the Chiswick Eyot in West London.
To assess fish usage the site was monitored over a ten day period using sonar imaging device ARIS.
Seine netting was conducted at the end of the ebb tide each day.

Seine netting at Chiswick Eyot

Sonar imaging footage revealed fish were more likely to maintain their position or ‘hold station’ in the vicinity of the habitat refuge structures.
These fish were found to range in size from 53mm to 566mm, demonstrating the benefits of the structures to a number of fish species and life stages.

If you want to find out more about our aquatic services, please get in touch now