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Water quality in the River Thames
has been linked to the activities of mankind for centuries. In 1858
Parliament had to be suspended because of the stench arising from
pollution in the river, but today MP's noses are no longer necessary
for the detection of water pollution; a network of sixty highly
sophisticated monitoring stations relay live water quality data
from YSI 'sondes' to the Environment Agency (EA) and other stakeholders.
Rising in Gloucestershire and flowing through the
Cotswolds, passing Oxford and Windsor, the River Thames meets the
North Sea after passing through London. With a length of 215 miles,
the Thames is the longest river entirely in England. However, the
water quality of the river is constantly under threat and for this
reason, the EA's Matt Loewenthal believes that the River Thames
and its major tributaries are more closely monitored than any other
rivers on the world.
Thames History
In 1849 14,000 Londoners died of cholera and fish could no longer
survive in the polluted Thames estuary.
The 'Great Stink' of 1858 was precipitated by the effects of the
industrial revolution and by sewage from London's growing population.
This was recognised at the time and resulted in the construction
of massive sewers to the north and south of the river. Similar huge
undertakings took place to ensure water supply, with the building
of reservoirs and pumping stations on the river to the west of London.
However, whilst these initiatives helped to limit 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 considered 'biologically dead'.
Water quality improvements
During the 1960s and 70s, improvements were made at the two main
sewage treatment plants at Crossness in southeast London and Beckton
in east London, resulting in a dramatic improvement in water quality.
As a result, many different animals, birds and fish have returned
to live and breed in the estuary. Today there are 121 different
species of fish and over 170,000 birds in the estuary.
A colony of seahorses was recently discovered in the Thames and
this has been hailed as definitive proof that water quality is improving.
However,
Neil Dunlop of the Environment Agency (EA) says, "I'm not sure
that a recent improvement in water quality is the main issue with
the seahorses. We're not quite sure why they're here, but the river
water has been clean enough for seahorses for some time. It could
simply be down to improved monitoring."
Matt Loewenthal manages the Environment Agency's
automated water quality monitoring network in the Thames region.
Commenting on water quality trends in recent years he says, "The
decline of manufacturing industry in the region, coupled with investments
and improvements in wastewater treatment systems have undoubtedly
contributed to an overall improvement in Thames river water quality.
However, we regularly record pollution incidents that arise from
CSOs (Combined Sewer Overflows). These are detected by a sudden
sags in Dissolved Oxygen often in conjunction with a rise in Ammonium."
(see Graph)
Combined sewer overflows
CSO is the discharge, during rain storms, of untreated wastewater
from a sewer system that carries both sewage and storm water (a
combined sewerage system). The increased flow caused by the storm
water runoff exceeds the sewerage system’s capacity and the
sewage is forced to overflow into streams and rivers in the area
through CSO outfalls.
Changing rainfall patterns caused by climate change
and urban development have meant that London's 140-year-old sewage
system is often unable to cope with the combined flow from the city's
sewage and storm water system. Of the 57 CSOs in London, 36 are
considered ‘unsatisfactory’ in terms of frequency of
discharge and/or environmental impact. Even during periods of moderate
rainfall, the overflows discharge storm water and sewage into the
River Thames on average once a week. Around 20 million cubic metres
of untreated sewage is discharged into the Thames every year.
Urban development including new housing, roads and
even the creation of hard, non-porous parking areas in residential
areas, have made a significant contribution to increasing levels
of precipitation rapidly entering the drainage system and thereby
exacerbating the problem. However, sustainable urban drainage systems
(SUDS) now feature in many new developments and these initiatives
will help to prevent the sudden surges of influent at wastewater
treatment plants.
Nevertheless, Matt Loewenthal believes that water quality in the
Thames has reached a 'tipping point'. He explains, "The River
Thames and its major tributaries are the primary water resources
in a catchment with a population in excess of 12 million people.
There are over 3000 licensed abstractions of water, accounting for
approximately 55% 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."
"At the same time, climate change is creating
more erratic weather conditions and London is located in one of
the driest parts of Britain with annual rainfall of 750mm, which
is even lower than Dallas, Texas. This heightens the significance
of CSOs and the decision to construct a £2billion plus underground
tunnel to deal with the discharge from 36 London CSOs has not come
a moment too soon."
'Tideway Tunnel'
The UK Government gave permission for the Tideway Tunnel in March
2007. The storage-and-transfer tunnel will run beneath the Thames
from Hammersmith in West London and convey the discharges for collection
and treatment in east London.
The new tunnel is not due for final completion until
2020, and Matt Loewenthal believes that water quality monitoring
will play a vital role in the intervening period. "Even after
the tunnel is finished" he says, "there will still be
an important role for monitoring to play in the protection of the
Thames from illegal discharges and failures to comply with discharge
consents."
Monitoring network
As a consequence of the increasing environmental pressures on water
resources the Thames Region of the EA has developed a network of
fixed, transportable and fully mobile Automatic Water Quality Monitoring
Stations (AWQMS) each of which has two common features.
Firstly, each station collects water quality data from a YSI water
quality 'sonde'. These sondes cleverly incorporate a number of sensors
into an instrument no larger than two feet of an average drainpipe.
YSI sondes have been specifically designed to meet the requirements
of users that require highly accurate, reliable data from instruments
that can be unattended for considerable periods of time.
Secondly, collected water quality data is transmitted to EA offices
via telemetry. YSI normally provides this facility with the use
of radio, mobile phone or satellite telemetry, however, the EA in
the Thames Region already operates a true ‘real time’
system based on ‘Meteorburst’.
Environmental monitoring often takes place in remote
locations where coverage from mobile phone networks is incomplete
and the topography or distances involved preclude conventional radio.
This is why, for example, the Agency is working with YSI on projects
that use satellite telemetry. However, in the Thames region the
infrastructure is in place for a Meteorburst data collection system,
which means that the cost of adding further stations is minimal.
Data is transmitted via Meteorburst by bouncing
signals off of ionised particles high in the atmosphere that result
from meteorite activity. Using this method it is possible to transmit
data over distances of up to 600 km.Water quality data is collated
centrally and can be accessed via the regional telemetry system
or the internet ( for selected stakeholders) via Desktop pc or PDA/BlackBerry.
There are four basic types of AWQMS, all of which
employ the same YSI multiparameter water quality sonde:
1. Traditional brick buildings providing intake, surface and wastewater
protection data to the EA, Thames Water and Vivendi.
2. The Green Box is a transportable, drop-down system featuring
state of the art instrumentation that requires significantly reduced
maintenance in the field.
3. The Trailer system is a fully mobile AWQMS, providing
the same data outputs as the above. It was developed in order to
provide a flexible and cost effective platform for short to medium
term deployments on problem discharges investigations and pollution
incidents.
4. The Suitcase System is a portable solution for
short-term deployments on pollution incidents and investigations.
Data from the AWQMS is described as real-time because sampling takes
place every 15 minutes. The procedure is as follows:
Firstly, a pump from within the WQMS draws river water into the
sample chamber that contains the YSI sonde, over a period of 4 minutes.
This ensures that the sample is representative before a reading
is taken from each of the sensors.
Once a reading has been taken, the pump stops and backflushes to
prevent any build-up of solids.
The telemetry unit then transmits the data via Meteorburst technology.
The master station at Newbury or Crystal Palace automatically sends
a return message once it has received and checked the data. The
data is then wiped from the telemetry unit until the next 15-minute
data set.
The YSI sonde does not therefore require internal
memory in this application. However, the Environment Agency have
purchased large numbers of these sondes with internal batteries
and dataloggers so that water quality data can be saved for subsequent
manual download when used as stand-alone loggers.
Advantages of continuous monitoring
Each YSI sonde is loaded with sensors such as dissolved oxygen,
temperature, pH, conductivity, turbidity, ammonium, Blue Green Algae
and chlorophyll and as such it is able to detect pollution from
almost any source. Real time and historical data is also used by
regulation, consenting and ecological appraisal teams as an additional
risk management tool.
In contrast to spot sampling, continuous monitoring is able to detect
pollution at any time, 24 hours per day, 365 days per year.
Pollution incidents may result in a loss of dissolved
oxygen (which causes fish kills) however; they will often also give
rise to alterations in other parameters such as Ammonium, Turbidity
and pH.
In addition to pollution from what are known as
‘point sources’ AWQMS are being developed to monitor
‘diffuse pollution’. This is pollution that has many
smaller sources occurring throughout a catchment. Not easily detectable
in the short-term but made more obvious following an analysis of
long-term trends.
A further advantage to long-term monitoring lies
in its ability to provide a picture of the background water quality,
so that any subsequent patterns in water quality can be judged according
to whether they are normal with respect to diurnal, seasonal or
climate change.
Perhaps one of the most important benefits of an
integrated system that monitors an entire catchment is the ability
to track events such as algae blooms using YSI chlorophyll sensors
and new blue green algae sensors. This coupled with data from the
turbidity and ammonium probes is very useful information for intake
protection at water treatment plants – operators may shut
down intakes if, for example, algae or ammonia levels are too high
and a network such as that on the Thames is able to provide advance
warning of pollution.
Such comprehensive information is also highly valuable from an environmental
perspective because pollution events such as fish kills or poor
water quality can be traced to a specific source.
Traditionally, one of the problems associated with
long-term monitoring of natural water is bio-fouling. The EA has
resolved this issue by employing YSI sondes, by pumping samples
into a test chamber and by the inclusion of back-flushing in the
monitoring routine.
In many other applications, particularly in those for which mains
power for pumps is not available, it is necessary to deploy sondes
that are capable of withstanding biofouling for extended periods.
Under these circumstances YSI has developed an ingenious adaptation
which incorporates small wipers that regularly clear the sensors
of any fouling before readings are taken.
Trials have found that unattended YSI sondes are able to operate
for up to three months in even high-fouling conditions when deployed
with YSI’s extended deployment facility.
Summary
Whilst Thames river water quality has certainly improved, the river
is still under pressure as a result of CSOs and high numbers of
both abstractions for drinking water and consented discharges. However,
Matt Lowenthal believes that through the EA's partnership with YSI
they have been able to develop a highly effective monitoring network
with the capability to monitor long-term trends and short-term pollution
incidents.
As Matt says, "If you don't monitor it, you can't manage it!"
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