Geological structures beneath the River Thames in London: findings from the Thames Tideway Tunnel investigations

The Thames Tideway Tunnel is 25 km long and extends west – east through central London, beneath the River Thames for most of its route. A detailed preconstruction ground model has been assembled, using data from borehole and river-borne seismic reflection survey investigations. The two data sets have together delineated several significant geological structures along the route.The investigations have led to an improved understanding of the morphology of some structures, such as the Greenwich Fault, London Bridge Fault Zone, Millwall Anticline and Greenwich-Plaistow Syncline, which were only generally indicated during preliminary desk studies. Other structures, such as the Putney-Hammersmith Fault Zone, Chelsea Embankment Fault Zone and Lambeth Anticline, are entirely new discoveries.Most of the structures described here have characteristics compatible with strike-slip displacement and, although this has been previously widely suspected, this paper presents new evidence towards this. When intersected by the tunnel during its construction phase, they have imposed significant changes in geological strata, leading to changes in the performance of tunnelling plant or creating adverse ground conditions. Their early identification by the ground model has assisted engineering design and planning, for the benefit of construction cost efficiency and, importantly, Health and Safety of underground personnel.Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

Modelling Microplastics in the River Thames: Sources, Sinks and Policy Implications

With widespread, long-term historical use of plastics and the presence of microplastics in a range of new and existing products, there is rising concern about their potential impacts on freshwater ecosystems. Understanding how microplastics are transported and distributed along river systems is key to assessing impacts. Modelling the main flow dynamics, mixing, sedimentation and resuspension processes is essential for an understanding of the transport processes. We use the new, processed based, dynamic, integrated catchments (INCA) microplastics model and apply this to the whole of the freshwater catchment of the River Thames, UK, to evaluate inputs, loads and concentrations along the river system. Recent data from UK water industry studies on microplastics in effluent discharges and sewage sludge disposal has been utilised to drive the INCA microplastics model. Predicted concentrations and microplastic loads moving along the river system are shown to be significant, with a build-up of concentrations along the river, with increasing deposition on the riverbed. The potential impacts on aquatic ecosystems are evaluated and a review of policy implications is explored.

The Great Stinks

This chapter discusses one of the first dead zones, the River Thames near London in the 19th century. London used the river as a sewer to dispose of untreated human waste and garbage, causing oxygen to disappear and gut-wrenching odors to well up, shutting down the city in the summer of 1858, aka the Great Stink. The sewage also carried pathogens that contaminated drinking water. The chapter also points out that dead zones were common in other rivers near large cities, including the Delaware River south of Philadelphia. Wastewater treatment solved the problem, and oxygen has returned to the River Thames, the Delaware River, and many other urban rivers in rich countries. Also discussed is the fact that fish and other aquatic life have also returned, but not completely. Adequate dissolved oxygen is essential, but more is needed to make a habitat livable and to ensure the complete recovery of aquatic life.