NRA THAMES 63 Fact File

THE TIDAL THAMES

GUARDIANS OF THE WATER ENVIRONMENT

NRA National Rivers Authority Thames Region FACT FILE-THE TIDAL THAMES

This is one of a number of Fact Files which cover all the main rivers in the Thames Region of the National Rivers Authority. Due to its size and importance the Thames itself is covered by four fact files, dealing with the Upper Thames, from source to its confluence with the Windrush, the Middle Thames from the Windrush down to the Kennel and the Lower Thames from the Kennet to . This fact file deals with the Tidal Thames through .

Figure 1 F A C T S IN BRIEF Map of tidal Thames to show main landmarks and major sewage treatment works • The Tidal Thames extends from Teddington in West London to Shoebury BECKT0N ESSEX CANVEY just East of Southend, a total length of SEWAGE WORKS about 100 Km. Victoria Docks

• The width of the increases from less than 100m in the upper reaches to more than 7Km at Southend. CROSSNESS Gravesend • The Thames catchment covers an area SEWAGE WORKS Greenhithe

of approximately 14,000 square kilometres with a population of over 11 Freshwater KENT million people. Thames TEDDINGTON WEIR • Teddington weir is the official tidal limit. - T o DISTANCE FROM LONDON BRIDGE IN KILOMETRES 15 • The freshwater flow at Teddington in winter may exceed 30,000 Ml/day.

• Teddington flows are strongly influenced On the outer estuary the area around by abstraction from the freshwater Thames Southend is a popular seaside resort with 3 for public drinking water supplies. The E.C. Designated bathing beaches. Teddington flow is normally maintained at a minimum of 800 Ml/day but this may be Despite the world decline in shipping reduced to 200 Ml/day in times of drought. Tilbury is still the busiest port in the UK.

• The Thames is one of the cleanest There are a number of passenger boats metropolitan estuaries in the world with operating on the river with the most over 50 resident species of fish. popular routes being from Westminster downstream to Greenwich and upstream • Since 1964 over 110 different species to and Hampton Court. of fish and 1 hybrid have been recorded in the tideway. In 1993 the total tonnage of cargo handled on the tidal Thames was • Angling is free and popular where there is 53 7 million tonnes. good access to the bank and foreshore, below London Bridge. The tidal Thames is a very important tourist attraction, being • The lower estuary is widely regarded as a the backdrop to many of London’s substantial nursery ground for important most popular sites. These include commercial species of fish such as sole and , The bass. There are commercial fisheries for Houses of Parliament. Tower eel, sprat and sole. There is a cockle Bridge, Tower of London and the fishery to the east of Southend. Cutty Sark. • The Thames estuary is important for Numerous events are traditionally recreation. In London large parks provide held on the Tidal Thames including riverside views and leisure activities in the Oxford and Cambridge boat race and The Tidal Thames areas like Richmond, Kew and Battersea. the Great River Race. Recreational boating takes place throughout the estuary with contact sports such as windsurfing in the areas close to the sea. THE NATIONAL RIVERS AUTHORITY (NRA)

Established on 1st September 1989 the NRA is an independent public body charged with safeguarding and improving the natural water environment. It is responsible for flood defence, regulating the quality of rivers and groundwaters, balancing the needs of various water users, protecting and improving fish stocks and promoting water-based recreation of all kinds. The NRA is committed to improving wildlife habitats and conserving the natural environment in all it undertakes.

FLOOD DEFENCE One of the most important responsibilities of the NRA is the control of flooding and in the lower part of the Tidal Thames the main threat is from the sea. Defences include raised river embankments, flood gates at strategic points such as the Barking Barrier and by far the largest structure, the Thames Barrier. The Thames Barrier, which was completed in October 1982, spans the 520 metre wide Woolwich reach and consists of 10 separate movable steel gates, each pivoting and supported between concrete piers and abutments which house the operating machinery. During the first ten years of operation, the Barrier was closed eleven times to protect London.

WATER QUALITY

Pollution control staff obtain water quality information from nine automatic monitoring stations sited strategically between The Thames Barrier Kew and Purfleet, see figure 2.

Sediment samples are also taken at several sites throughout the estuary annually. During the bathing season, from May to September the NRA regularly samples the bathing water at the 3 bathing beaches in accordance with the European Community Bathing Water Directive. Bathing water quality sample results can be obtained from Southend- on-Sea Borough Council or the NRA. The NRA also monitors recreational waters on the coast which have been identified as bathing areas but are not formally identified under the Bathing Water Directive.

Data on dissolved oxygen, temperature and conductivity is collected continuously via a telemetry system by computers at the authority’s offices in Crossness and Reading. This information can be displayed on a screen. In addition, manual sampling is undertaken using a survey launch. About 20 sites along the tideway are sampled weekly in the Summer and fortnightly in the Winter for a broad range of determinands. In addition 6 key sites are sampled monthly for heavy metals, organic pollutants and other persistent chemicals.

Beach sampling FLORA AND FAUNA Fisheries and Biology staff conduct surveys of the fish in the tidal river in order to assess the health, diversity and number NRA Biology, Fisheries and Conservation staff work closely together on the tidal Thames, particularly in the area o f habitat of fish. These produce information on contaminants within the fish tissues, the prevalence of disease and o f the general protection and enhancement, where responsibilities both compliment and overlap with each other. community structure. This information contributes to the monitoring of water quality and habitat and provides vital Within London the changes from a freshwater information upon which decisions on the maintenance, river to an estuary o f international importance. The plants and development and improvement o f the fishery are based. A animals that inhabit the river reflect this change, resulting in a biannual survey is conducted at six key sites in May and wide variety of species and habitats to be found in this September along with fortnightly surveys of the cooling water continuous corridor, making the tidal Thames a unique habitat intakes at Tilbury . resource within the centre o f London. The principal species of fish in the upper river from Biology Teddington to Battersea are those found in the freshwater Biologists regularly sample the animal and plant communities Thames, with dace and roach dominant. Of the more marine of the river to assess the effect of pollutants on the species, sole, whiting and sprat are common in the river environment. The diversity and number of invertebrate below Dartford. Many estuarine species show marked animals (worms, snails, shrimps, etc) in the river reflects the seasonal patterns in their movements. In the early spring smelt overall water quality and habitat variety of the tidal Thames. travel up river to Wandsworth to spawn on gravels. These are Work is being done to help us understand more fully how the followed by large numbers of flounder fry which ascend right study o f these small animals can show the effects o f both up to Teddington. Then come elvers or young eels. Later in development and pollution on the river. the summer, waves of bass fry move up as far as Chelsea, along with juvenile and adult thin lipped grey mullet. The invertebrate distribution o f the Thames estuary closely reflects the changes in salinity and the habitat diversity of the The smelt is a fastidious species, generally in decline estuary. More than 350 freshwater, estuarine and marine throughout Western Europe. The contrasting strong recent macrofaunal species have been recorded over recent years. In recovery of the species in the Thames gives this population an the upper Thames estuary typical freshwater species such as important conservation status and a role in quality monitoring. insect larvae and molluscs occur with decreasing diversity Conservation downstream attributed to a reduction in habitat diversity and increasing saline penetration. In the mid Thames estuary The fauna within the channel has expanded with worms are dominant with a downstream sequence of species improvements in water quality, with species such as mute associated with salinity. Typical estuarine species such as the swans, great crested grebes, cormorants and kingfishers all crustacean Corophium volutator and the polychaete worm found on the river, with cormorants and Shelduck roosting on Nereis diversicolor are also present, particularly on the inter­ the numerous jetties downstream. The numerous islands also tidal mud banks. The outer estuary is an area o f brackish provide refuges fo r many o f these species, as well as water to full seawater salinity and supports the greatest variety containing areas of important wet woodland. of invertebrates with polychaete worms, crustaceans, Inter-tidal mudflats along the lower reaches provide valuable molluscs, sea anemones and sea urchins being the most feeding areas for a variety of bird species such as common. oystercatcher, dunlin and redshank, while the shingle beaches Fisheries upstream are utilised by species such as carrion crow, black­ headed gull, heron and coot. The estuary plays a crucial part in the life-cycle of many fish and acts as an important nursery area for many marine and Areas of natural bank contain a variety of habitats important estuarine species, such as plaice, bass, sole, mullet, flounder for birds, fish and invertebrates such as reedbeds and relic and smelt, by providing a rich food source and protection saltmarsh. Much of the river has been embanked and although from predators. not as valuable, can still contain some unusual plant species such as petillary-of-the-wall and hemlock water dropwort. Further downstream the grass flood embankments provide a valuable habitat for butterflies, crickets and more unusual plants.

There are a variety of important adjacent habitats which are dependent on the Thames. These include grazing marshland at Rainham, relic watermeadows at Richmond and areas of open water at Thamesmead. NRA staff are also carrying out a programme of habitat enhancements, including the establishment of marginal reed beds.

Sorting sample fish from the Tidal Thames Development Pressures

Effective water quality management will help to protea and The following are the main consented discharges into the further encourage the major ecological resource which has Tidal Thames:- developed in the Thames in recent decades. However, development pressures can threaten the resource by habitat DISCHARGE AVERAGE FLOW TYPE OF EFFLUENT degradation. Many riverside developments seek to involve (CUBIC METERS DAY) some encroachment onto the foreshore, which provides rich

and diverse habitats for fish, birds, invertebrates and plants. As River Thames

statutory consultees in planning control, the NRA will seek to Mogden STW 420,000 SewageEffuent protect and enhance the ecological resource. Major Kew STW 46,000 Sewage Effluent encroachments will tend to be resisted on flood defence and Shell Centre 9,000 Cooling Water environmental grounds. With minor issues, there may be British Telecom 23,000 Cooling Water some scope for mitigation to offset any loss of foreshore. Tate and Lyle 41,000 Trade Tidal creeks which exist at the mouths of the tributary streams Beckton STW 1,000,000 Sewage Effluent provide unique habitats for flora and fauna and act as Crossness STW 550,000 Sewage Effluent important refuge areas for fish life. Today, many of these Purfleet Board Mills 6,000 Trade creeks exist against a background of industrial decay. Often Long Reach STW 190,000 Sewage Effluent the public perception is that these creeks contain nothing of value to protect. Many developers view the economic Van Den Berghs 30,000 Cooling Water regeneration of these areas as necessarily involving the Cory Hall Aggregates 7,200 Trade installation of a barrage at the creek mouth. Experience has Scott Ltd 12,600 Trade shown that this can have undesirable environmental Tilbury STW 10,700 Sewage Effluent

consequences and may not achieve the goal o f assisting Gravesend STW 4,200 Sewage Effluent

regeneration. A more sensitive approach can realise Canvey Island STW 5,300 Sewage Effluent regeneration hand in hand with protection and enhancement Southend STW 36,500 Sewage Effluent of these increasingly rare features. I n gre bourne Riverside STW 110,000 Sewage Effluent DISCHARGES Dartford Creek All discharges are regularly monitored. These include some of AR-JO Wiggins 10,000 Trade the largest sewage treatment works in Europe at Mogden, Carbonless Papers Ltd Beckton and Crossness, which serve the population o f London. We also monitor two paper mills at Northfleet and Mucking Creek Dartford, a board mill at Purfleet and a sugar refinery at Standford Le Hope STW 4,400 Sewage Effluent Silvertown. Pitsea Creek Basildon STW 9,500 Sewage Effluent Monitoring of the two oil refineries at Stanford Le Hope and water used for cooling purposes at Thameside power stations Benfleet Creek comes under Her Majesty’s Inspectorate of Pollution (HM1P). Benfleet STW 6,1 00 Sewage Effluent HMIP CONTROLLED DISCHARGES TO THE THAMES

Shell UK Ltd

4 discharges 310,500 Trade, Cooling +

Surface Water

Mobil Oil Co.

6 Discharges 216,000 Trade, Cooling +

Surface Water

Littlebrook Power Station 5.042,710 Cooling Water

(Max Volume)

Tilbury Power Station 2,727,561 Cooling Water

Greenwich Power Station 2.273 Cooling Water

Lots Road Power Station 285,747 Cooling Water

Sewage Treatment Work STW flows are dry weather flows.

Beckton sewage treatment works outfall WATER QUALITY OBJECTIVES and overflowing cesspools. Gas works were a particular problem due to the toxic nature of their by-products. Two key Water quality objectives have been set for the tideway and are factors spelt the final destruction of the Thames, the outlined below. The tideway is split into three reaches to take introduction of the water closet which dramatically increased into account the transition from the freshwater to the marine the volume of water-borne waste and the abolition of environment. Each reach has a different salinity range and cesspools by an Act of Parliament in 1843- This meant that all supports different biological communities. All three reaches the waste from London’s population was discharged untreated must be o f suitable quality to allow the passage of migratory into the Thames. Water was still being abstracted from the fish, including salmon. Thames through London for public consumption and The upstream reach, from Teddington to Battersea must waterborne diseases like cholera were rife. In 1849, 14,000 maintain a freshwater coarse fishery; the middle reach from people died of cholera. By then the fish had disappeared and Battersea to Mucking, must support an estuarine fish the London reaches of the river were in a dreadful state. population and a commercial eel fishery and the third reach The story of the clean up begias in the mid 19th Century. In from Mucking to the sea must maintain a marine fishery and the summer of 1856 a heat wave occurred and the appalling EEC Designated Bathing Beaches. smell from the river caused so much discomfort to Members of The tidal creeks are equally important and their objectives are the Houses of Parliament that in an effort to counteract the compatible with the adjoining tideway. smell sheets soaked in disinfectant were hung over the From these objectives a series of chemical and biological windows. This prompted Parliament into action. In 1857 the standards are derived (see figure 3) and compliance with Thames Conservancy Act founded the Thames Conservancy these standards should ensure that the objectives are with pollution prevention powers from Staines to the North achieved. Compliance for the upper and most of the middle Sea. Its powers did not extend to the control of sewage estuary is assessed using data from the Automatic Quality disposal. This was dealt with by a system o f intercepting Monitoring Stations, while the seaward section of the river is sewers, designed by Sir , completed in 1874. assessed using samples obtained using a boat. Running either side of the river they carried most of London’s sewage eastward to two large disposal works, where the POLLUTION AND CLEAN UP OF THE TIDEWAY sewage was discharged to the Thames on the ebb tide from The Thames suffered from severe pollution for many years. It large storage tanks. was a thriving salmon river once with records showing up to In central London the state of the river greatly improved. 3000 fish per year being sold in London fish markets as late as However, down river in the vicinity of the outfalls the river 1800. Until recently the last salmon recorded upstream of was in an unsatisfactory state and big mud banks were London Bridge was caught in 1833. building up. In 1878 the Thames pleasure steamer Princess London’s population increased dramatically during the 19th Alice sank after a collision in the vicinity of the Beckton outfall Century from 1.25 million in 1820 to 4.75 million in 1880. and an enquiry into the great loss of life concluded that the Britain’s industrial output also expanded rapidly dealing with deaths had been accelerated by the putrid state of the water. A about a third o f total world trade at its peak. London dealt Royal Commission set up in 1882 resulted in new treatment with a large proportion o f this. In the early part of the 19th Century most of the waste from London’s population was discharged into cesspools, the contents of which were periodically removed and used as fertiliser on agricultural land. The industrial revolution was well under way and an increasing number of factories, slaughter houses, tanneries and other industries appeared on the banks o f the Thames and its tributaries. CHEMICAL STANDARDS BIOLOGICAL STANDARDS IN ANY QUARTER - 0 .0 . 40% FOR 80% TIME 0.0. 10% FOR 95% TIME MINIMUM 0.0 5% SAT TEDDINGTON SELF SUPPORTING DACE FISHERY This and the steadily growing MAXIMUM TEMPERATURE 2TC. COMPLIANCE WTTH EC TO AS NOICATED BY PRESENCE OF FISH OF THE YEAR. DANGEROUS SUBSTANCES DIRECTIVE. DAUGHTER BATTERSEA BMWP SCORE GREATER THAN 25. population led to an increase in DIRECTIVES * RED LIST STANOARDS M AMY QUARTER - 0.0. 30% FOR 80% TIME W M U M OF 9 SPEOES OF RSH TO BE D e m R E D DUAWG D.O. 10% FOR 95% TIME MINIMUM D O S% SAT NTAKE SURVEYS pollution from industrial wastes MAXIMUM TEMPERATURE 2 * C COMPLIANCE WTTH EC TO DANGEROUS SUBSTANCES DIRECTIVE. DAUGHTER MUCKING DATA FROM COMMERCIAL EEL RETURNS TO BE EXAMMED DIRECTIVES 8 RED LIST STANOAROS AS A POTENTIAL FUTURE STANDARD IN ANY QUARTER - 0.0 00% FOR 80% TIME 0.0. 10% FOR 85% TIME MINIMUM D O 5% SAT MUCKING MAXIMUM TEMPERATURE 2 9 C COMPLIANCE WITH EC SUITABLE STANOARDS TO INCLUOE MEASURE OF TO COMMERCIAL FISH CATCHES AND PROTECTION OF DANGEROUS SUBSTANCES DIRECTIVE, DAUGHTER MARINE NURSERY GROUNDS TO BE EVOLVED DIRECTIVES. BATHING BEACH AMO BATHM G WATERS SEAWARD LIMIT DIRECTIVES 8 RED LOT STANOARDS Pollution Load Discharged to River (Tonnes/Day) I eaeEfun Q IndustrialEffluent Q Sewage IEffluent I The improvement was only only was improvement The Tilbury. _ _ rsns, n smlr ok t eko ws opee in completed was Beckton at work similar and Crossness, 10% 1966.inconcentration achieved was which of migratoryfishenable to to improved theshouldThames be of as decline to the began f o quality Tideway the 1918) - (1914 War First World the After temporary. effluentitsand disposal at sea. sewage the from matter solid of out n 94 gety nagd e wrs a oee at opened was works new enlarged greatly a 1964 In oxygen dissolved minimum a recommended Itpass through. that studyquality Pippardconcluded water thetheand works estuary.a polluted the As studyof commissioned government 1951 theinThames. Then of Professor A J SPippardchaired a pollution siltation and into investigation an began Authority, detergents, non-biodegradable and works gas and stations power from pollution industrial thermal discharges,effluent, sewage of effect non-biodegradable combined f the 1950’s, o the use By detergents. widespread the to due worse further to led London throughout works treatment sewage and sewers to damage bomb 1945) - (1939 War settling the Crossness, involving and Beckton at employed being methods or rm 90 16 ta fs wr asn fo to absentfrom 1964 1920 that were - fish from poor and to continued population industrialisation London’s more fully understood. The Thames Survey Committee sewage Committee main the Survey of improvement an Thames for need The the identified understood. fully was more Tideway the of pollution investigations these of result Pollution Research Board at the request of the of Portthe Research Pollution requestat Board theof Water the by up set Committee, Survey 1949 Thames theIn that riverso virtuallyaquality was wasproduced Water dead. made were which problems pollution World Second the During increase. —■ Year ■— »— i 90 90 90 90 1990 1980 1970 1960 1950 120 D i s s o l v e d O x y g e n % s a l . oe n Point and Zone Oxygen Dissolved ay Tidew 4 Figure reach of the river where the storm sewage was discharged.was stormthe riverthewhere reach sewage of ThisLslittle dilution, the removed. provide andoxygen rapidly tributaries.materialorganic isoxidised The dischargesthesein polluting additional an also is There Beckton. and Chiswick high f o times at Therefore, rainfall. heavy by generated is system sewerage London’s summer. the during overflows now is quality water managing in significantfactor most The UtilitiesThames Water negotiated. was theand NRA previously the in abundant populations fish of presence The TODAY MANAGEMENT TIDEWAY the and river the from away discharges industrial some eut i te eeomn o n ct oye “a” n the in “sag” oxygen acute an of development the results in low are flows freshwater the When river. the in bacteria water by fresh and works sewage the een from betw discharged load situated outfalls sewage storm 20 than more from load polluting large a receives tidal Thamesrainfall, the 19th its mid and Century the in designed network a on based sewage storm from loads organic additional massive the water the f o privatisation following inputs. So and temperature sewage storm water quality, effluent works sewage Teddington weir, at water flows freshwater are influencing time this during factors quality main The months. summer the over particularly quality, water river of management careful returnrecordtherea was 338of salmon. to salmon returning allow to Thames lower the weirs atthroughout passes of construction the and river freshwater the into fish young of introductionthe involved This commenced. Thames the to salmon return the and of river cleaner aabout hydraulic capacity is inadequate to cope with the flows flows the with cope to inadequate is capacity hydraulic between agreement operating formal a 1989 in industry for need the highlighted has river the of reaches polluted 1993 upstream. In proceeding before Weir at and Moisey recorded trapped are adults Returning grounds. spawning reach Scheme Rehabilitation Salmon Thames the 1979 In 1974.in Figures See 4and5. brought gradually detergents biodegradable of introduction 1974. Improvements to the sewage works, the diversion o f f o diversion the works, sewage the to 1974. Improvements Dissolved oxygen (% ASV) (See figure 6). In the most severe circumstances, generally generally circumstances, severe most the In 6). figure (See The cost o f improving London’s sewage system to eliminate eliminate to system sewage London’s improving f o cost The The direct injection o f oxygen was the only practicable practicable only the was oxygen f o injection direct The to fall may concentration oxygen the storms, summer after the storm sewage problem would be hundreds of millions of of millions of hundreds be would problem sewage storm the deaths. fishresults in which zero, near equ ipm ent and tech nology supplied by British O xygen xygen O British by supplied nology tech and Thames a ent of ipm hull equ the using 1980, in launched injection was oxygen vessel mobile prototype A location. right the at and pounds. This, and the considerable engineering problems problems engineering considerable the and This, pounds. method o f ensuring that oxygen was supplied at the righttimethe at supplied was thatoxygen ensuring f o method water. This prototype had an output o f 10 tonnes o f oxygen oxygen f o tonnes 10 f o output an had prototype This river intoit inject and water. air the from oxygen extract to Company involved, meant that alternative measures had to be sought. be to had measures thatalternative meant involved, eainl xeine on salse te ed o a for need the established soon experience perational O Barge. This vessel, known as “Thames Bubbler”, utilised utilised Bubbler”, “Thames as known vessel, This Barge. per day and had to be tow ed into position by tugs. tugs. by position into ed tow be to had and day per cam e into operation in 1989. O w n ed by Water Thames by ed n w O 1989. in operation into e and cam output (on 1050.5 metres by Bubbler of xygen o dimensions Thames overall with new file), fact greater f the o result front ith a w As vessel manoeuvrability. built ose rp u p day and average operating costs o f million/year.£0.25 f o costs operating average and day metres, a gross tonnage of 592 tonnes and costing £3 million5 costing and 592tonnes of tonnage gross a metres, sewage treatment works between 1st May and 31st October to 31st and 1stOctober May between works treatment sewage tlte, hs esl a a otu of3 tne o xgn per oxygen of tonnes 30 f o output an has vessel this Utilities, allows for the suspension o f abstraction by Thames Water Water Thames by abstraction f o suspension the for allows agreement operating the Bubbler, the of use the to addition In weir to counter the effect o f storm sewage. storm f o effect the counter to weir reduce the effective oxygen load on the Tideway. It also also It Tideway. the on load oxygen effective the major the reduce for standards quality effluent improved imposes Utilities in order to increase freshwater flows over Teddington Teddington over flows freshwater increase to order in Utilities Normal Oxygen Sag Curve Effect of Storm Sewage Storm Effectof Discharge Dissolved on Oxgen SagCurve Oxygen Normal T T T T T REFERENCES he he he he he T T R T L vi g in iv orati n io t a r to s e hames hames hames T Distance above/below London(km) Bridge above/below Distance R -G W G - T mes e am h c rd eco a f med rm sfo ran

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R a ( C ) 9 8 9 (1 T W sorton ratio esto L , dal a id ng in k r o s n o d n o T hames y r t n u o W R

f o y a w r e t a iver - L B W B L -

a L G

ife d n a reat B

d o o GG D - rrs oks oo T W idal (98 A ) 82 (19 tro l aterfow W R ilson iver dam - D - J (1987) (1987) The first indication o f a storm sewage problem is the the is problem sewage storm a f o indication first The hms ube i oeaig is elyet s otold by controlled is its deployment Bubbler operating, is Thames closely be can The sag this stations. f o movement monitoring and quality development water automatic by produced plot oxygen dissolved the on saga of development xgn ocnrtos il al o rtcl ees Oc the Once levels. critical to fall will concentrations that likely seems itoxygen if notice hours few a at deployed be can xgn s netd t h lws pit f h sg n it’s and sag the of point lowest sensors. the at oxygen injected is dissolved Oxygen on-board and room operation pollution the from information using scientific officer NRA a Bubbler Thames The software. using computer the monitored addition to storm events, due to the failure of of failure the to due events, storm to addition elyd ny ne prl de o h fc that fact the to due partly once, only was deployed 1993 it In summer. the during sufficiently itisisinjectedmostwhere required. ensureoxygen to followed isclosely tides thewith movement major STW’s to decrease their organic loads loads organic their decrease to STW’s major 34 indays, on 1989deployed theInwas Bubbler scale fish mortalities have occurred on the the on occurred have Tideway. mortalities fish scale - H J The rain radar system also gives access to to access gives also system radar rain The quality river supplement ill w officer duty if measure pre-emptive a as deployed be may large no 1989 in operation into came Bubbler ev rifl i atcptd I ti cnet a context, this In anticipated. is rainfall heavy Bubbler Thames the vulnerable, particularly is riverthe Summer the in drywhen Duringperiods London Weather Centre and rain radar radar rain and Centre the Weather from warnings London rainfall with information the Since summer. cooler and drier a had1993 nomto fo a ie ewr o ri gauges rain of network wide a from information Authority. Rivers National the from information H xat o ilger arrison B T B T B (97 H (1977) L d t atsford + P G P +

hc eals anal n sensitive in rainfall enables which Region Thames the throughout parts o f the catchment to be be to catchment the f o parts h fod oto ru prts aoperates group control flood the rainfall gauged When monitored. incatchmentany totals 20mmif or | National 0|vers Auttv | National 24hournotificationsystem. utchinson 10mm rain 1isinof hourrecorded 1 rant 'nfcrmaticn Centre 'nfcrmaticn L Head OfiHead td rdcdb heDsg urm Baosil 19 770 o o 7247. No. Job 670700 01494 Beaconsfield Quorum, Design e Th by Produced

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y c n e g a EEHN:074 535000 TELEPHONE: 01734

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