Water monitoring

If water samples are taken from a river at 9am on consecutive days, it is reasonable to

be able to directly compare analytical results, unless the water at the sampling location is tidal. This is because water quality is heavily affected by the state of the tide, which presents a significant monitoring challenge in the lower reaches of many rivers. The River Thames, for example, is tidal all the way up to the Teddington weir in west London, and with a tidal range of up to seven metres, this river is particularly challenging to monitor. To overcome this, scientists at the company Meteor Communications have developed a continuous monitoring and data management system that is able to remove the effects of tide and unveil the true underlying water quality. In the following article, Meteor’s managing director Matt Dibbs explains how water quality monitoring has developed, and how this can be used to monitor recent improvements in tidal rivers such as the Thames.

years. Consequently, samples have been taken for testing throughout the river’s recent history, helping to track water quality trends and identify trace pollutants. However, continuous monitoring is required where it is necessary to detect pollution incidents and effectively measure the impacts of mitigation measures. Apart from natural factors and variations, the main issues with potential to significantly affect water quality in the Thames are treated effluent discharges and sewage overflows during heavy rainfall.


BaCkgRounD Rising in Gloucestershire and flowing through the Cotswolds, passing Oxford and Windsor, the River Thames meets the North Sea after passing through London. Stretching for 215 miles, the Thames is the longest river entirely in England and provides amenity value for large numbers of citizens. However, it has long been used as a source of drinking water, whilst also being the repository for sewage and wastewater. Today, wastewater is largely treated before discharged into the Thames, but during heavy rainfall wastewater overflows into the Thames,


he quality of water in the River Thames has been a major concern for the inhabitants of London for over 150

significantly affecting water quality. To address this, the Thames Tideway Tunnel (TTT) is being built to gather overflows and direct them to the Beckton Wastewater Treatment Works. Once complete, the TTT will need to be able to demonstrate improvements in water quality - monitoring systems that take account of the tide will therefore be essential. In the past, prior to the implementation of

London’s sewerage system, the effects of domestic and industrial discharges were more serious. In the 19th century, news reports described the Thames as a vast, foul-smelling drain. In the summer of 1858, water quality was so bad that the smell of the river, known as the ‘Great Stink’, caused Parliament to leave London. Subsequently, Sir Joseph Bazalgette was contracted to design and build a sewer system. At the time of the Great Stink, London was home to just two million people, but fortunately Bazalgette had the foresight to build a sewer system for a population twice that size, and much of the system remains in good working order. However, whilst these Victorian initiatives helped to lower pollution levels, water quality remained poor into the 1960s; the combined effects of inadequately treated sewage, industrial discharges, thermal pollution from power stations and the extensive use of non-biological

detergents meant that parts of the estuary were incapable of supporting common river species such as insect larvae, crustaceans and fish.

ToDay’s ChaLLenge Almost nine million people now live in the capital, so significant investment has been made in the city’s wastewater infrastructure in recent decades. However, during periods of high rainfall, the system is still unable to cope with the volume of flow, and excess wastewater overflows via combined sewer overflows (CSOs) directly into the Thames. As a result,

April 2021 Instrumentation Monthly

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