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Water monitoring Credit: Graham Meller


How do you monitor a tidal river?


millions of tonnes of raw sewage passes, untreated, into the River Thames each year. Infrastructure development in London includes new commercial and residential properties, as well as car parks, roads and paths. These hard, non-porous areas increase the speed with which rainfall enters the drainage system; thereby exacerbating the problem. However, sustainable urban drainage systems (SUDS) now feature in many new developments and these initiatives help to slow the flow. In addition, local authorities are increasingly looking to utilise natural flood management tools to help cope with high precipitation events rather than building infrastructure which transfers the problem elsewhere (downstream). Much of the bankside in London is concrete or metal, which drastically reduces the habitat for many riverine species, so developers are now being encouraged to create green wetland areas which enhance biodiversity and create a more attractive view for valuable bankside properties. In addition to the challenges posed by urban


development, climate change is increasing the urgency with which urban drainage and wastewater treatment issues must be addressed. Climate predictions indicate that London is likely to experience more extreme weather events, so drainage and wastewater infrastructure must be


Instrumentation Monthly April 2021


designed to meet these growing challenges. The River Thames and its major tributaries are


the primary water resources in a total catchment serving a population of over 12 million people. There are over 3,000 licensed abstractions of water, accounting for approximately 55 per cent of effective precipitation. In addition there are over 10,000 consents to discharge sewage or trade effluent into the catchment. This means that, in terms of rainfall versus abstraction, the Thames is the most heavily used river in Britain.


Thames Tideway scheme


The three key components are collectively known as the London Tideway Improvements. They are:


1


The construction of a deep storage and conveyance (4.3 miles) tunnel from the Abbey


Mills Pumping Station near Stratford to Beckton Sewage Treatment Works. The Lee Tunnel was opened in January 2016 and captures 16 million tonnes annually from the single largest CSO in London. This is allowing the tidal River Lee (a tributary of the Thames) to regenerate.


2


The second component of the scheme has upgraded and extended London’s five major sewage


treatment works. This is enabling them to treat greater volumes of sewage, which reduces the need for CSO discharges.


3


The 25 km Thames Tideway Tunnel is being constructed between Acton in west London,


travelling through London at depths of 30 to 60 metres, using gravity to transfer waste eastwards. The tunnel closely follows the route of the river, intercepting targeted CSOs that currently discharge an average of 39Mm3


of untreated sewage per year.


Once complete, it will connect to the Lee Tunnel and sewage will be pumped to the Beckton Sewage Treatment Works by the Tideway Pumping Station. The TTT is so large that it is the width of three double-decker buses side by side; consequently, in addition to providing interception to CSOs, it will also offer substantially increased storage capacity during peak flows.


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