An audit of the surface water outfalls in the River
Ravensbourne - ‘Outfall Safari’
December 2017
UK & Europe Conservation Programme
Zoological Society of London
Regent's Park
London, NW1 4RY
www.zsl.org/conservation/regions/uk-europe/london’s-rivers
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Acknowledgements
This project, funded by The Rivers Wetlands and Community Days Fund and City Bridge Trust,
has been delivered in partnership with Thames21 with the support of the Environment Agency
and Thames Water. It would not have been possible without the help of all the dedicated
volunteers who collected the data.
Introduction
Misconnected wastewater pipework, cross-connected sewers and combined sewer overflows
are a chronic source of pollution in urban rivers. An estimated 3% of properties in Greater
London are misconnected (Dunk et al., 2008) sending pollution, via outfalls, into the nearest
watercourse. There is currently no systematic surveying of outfalls in rivers to identify sources
of pollution and to notify the relevant authorities. The ‘Outfall Safari’ is a survey method
devised to address this evidence gathering and reporting gap. It was created by the Citizen
Crane project steering group which consists of staff of Thames Water, Environment Agency
(EA), Crane Valley Partnership, Friends of River Crane Environment, Frog Environmental and the
Zoological Society of London (ZSL). It was first used on the River Crane in May 2016.
Aims
The aims of the River Ravensbourne Outfall Safari were to:
Record and map the dry weather condition behaviour of surface water outfalls in the
Ravensbourne catchment rivers;
Assess and rank the impact of the outfalls and report those that are polluting to the
Environment Agency and Thames Water;
Build evidence on the scale of the problem of polluted surface water outfalls in Greater
London; and
Recruit more volunteers and further engage existing volunteers in the work of the
Ravensbourne Catchment Partnership.
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Method
The survey of outfalls was conducted between 11th October and 9th November 2017. In total, 23
trained volunteers took part in the Outfall Safari. Volunteers were trained at the Lewisham Arts
Café in Manor Park. Training, delivered by ZSL, Thames21 and Thames Water included:
An overview of water quality issues in the River Ravensbourne;
Information on outfalls and how they become polluted;
Information on Thames Water’s surface water outfall team;
Instruction on how to assess each outfall using the project App and how to upload
information to the database; and
A health and safety briefing and signing of the risk assessment.
During the training, volunteers were assigned lengths of the River Ravensbourne to survey.
Further coordination of survey dates and reaches was conducted by the volunteers on a closed
Facebook group set up specifically for the Outfall Safari. Groups of volunteers were free to
conduct the survey of their reach when convenient to them, within the survey period, provided
there had been no rain for 48 hours prior to survey. A period of 48 hours of no rain is required
before any survey work as rainfall and high surface water flows can obscure the negative
impacts of outfalls by washing away sewage fungus, discoloured sediments and rag.
Approximately 28.7km of the River Ravensbourne was surveyed by the Outfall Safari in total. Of
this, 25.25km was surveyed by Thames21 and volunteers and 3.45km was surveyed by the
Environment Agency (see Figure 1).
Typically, the majority of the survey work for an Outfall Safari would be conducted from the
riverside path, with only the occasional need to enter the river to properly assess and
photograph outfalls. This is because Outfall Safari surveys are generally led by volunteers only,
working in pairs (as a minimum) or groups. However, for the River Ravensbourne Outfall Safari
volunteers were accompanied by Thames21 staff on surveys, as well as ZSL staff on some
occasions. In these cases, and where river depths were low enough, surveys were conducted in-
channel.
The risk assessment for riverside outfall surveying highlighted the need to assess conditions in
the river before entering it and stressed that volunteers should only enter the river channel if
the level was lower than Wellington boot depth (c. 35cm). During the training volunteers were
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also shown images of Giant Hogweed (Heracleum mantegazzianum). It was essential that
volunteers could identify Hogweed before undertaking any survey work as it is a relatively
common plant along the banks of rivers in Greater London and can burn and blister skin if
touched. Waders and stabilising poles were used by in-channel survey teams.
In addition to personal protective equipment (PPE) volunteers took a printed handout,
designed to help with ranking the impacts of each outfall, and a smart phone or tablet loaded
with a specially created data entry app.
Legend River Surveyed
Figure 1 – Map of Area of River Ravensbourne Surveyed
A
B
Key –
Section A: Deptford Creek mouth to Deptford Bridge (TQ 37804 77753 to TQ 37426 77022) Section B: Deptford Bridge to Lewisham town centre (TQ 37416 76890 to TQ 38156 75895) Section C: Lewisham town centre to Catford, South Circular (TQ 38142 75774 to TQ 37327 73569) Section D: River Pool, South Circular to Southend Lane (TQ 37257 73384 to TQ 36965 71652) Section E: Southend Park to Cator Park (TQ 37051 71446 to TQ 36385 69987 and to TQ 36620 70047) Section F: River Quaggy, Lee High Road to Cator Park (TQ 38403 75574 to TQ 40891 75026) Section G: Tudway Road to Dowding Drive (TQ 40968 74972 to TQ 41254 74703) Section H: South Circular to Chinbrook Meadows (TQ 41302 74597 to TQ 41026 71834) Section I: River Ravensbourne, Linear Park to Ravensbourne Avenue (TQ 37276 73045 to TQ 39282 69556) Section J: Recreation Road to Glassmill Lane (TQ 396151 69268 to TQ 39844 69121) Section K: Westmoreland Road to Hayes Road (TQ 40321 68500 to TQ 40424 68091) Section L: B265 to London South East Colleges, Bromley (TQ 40614 67928 to TQ 41448 67176) Section M: Bromley Common to Turpington Lane (TQ 41884 67258 to TQ 42117 67032) Section N: Crofton Road to Sparrow Drive (TQ 44105 65854 to TQ 44383 66386) Section O: Clock House to Elmers End (TQ 36434 69457 to TQ 35917 68455 and TQ 35618 68724) Section P: Stone Park Avenue to Langley Sports Ground (TQ 37669 68424 to TQ 37692 67331) Section Q: Chaffinch Brook, railway to Fairford Avenue (TQ 35806 67936 to TQ 36039 67603)
C
D
E
F
G
H I
J
K
L
M
N
O
P Q
A
B
The App
For ease of data collection from the river, the volunteers used an app created in Epicollect 5
(five.epicollect.net). Created by researchers at Imperial College, Epicollect is free and openly
available. Once a project is set up in Epicollect it provides an app for remote data collection and
upload, usable on GPS enabled smart phones, and a web portal to access and download the
data. The outfall assessment form created in the app consisted of ten questions for volunteers
to fill in at each outfall. The questions are taken directly from the form that Thames Water use
for assessing the impact of outfalls and are shown in Table 1.
Table 1 – Questions used in the Epicollect app to assess each outfall and their corresponding Impact Score
Question Options EA score
1. Volunteer name
2. Date of survey
3. GPS location
4. Photo of the outfall
5. Description of the nearest landmark
6. Which bank is the outfall on (when looking downstream)
7. Ranking of the flow coming out of the outfall
a. No Flow
b. Trickle
c. Low Flow
d. Moderate Flow
e. High Flow
8. Ranking of the visual impact of the outfall
a. No visible effect 0
b. Within 2m of outfall 2
c. Impact 2 to 10m 4
d. Impact 10 to 30m 6
e. Impact greater than 30m 10
9. Ranking of the aesthetics of the outfall
a. No odour or visible aesthetics 0
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Conversion of Outfall Assessment to Impact Scores
To assist with prioritisation of the outfalls, the Environment Agency provided a method of
converting the assessment data to a numeric impact score for each outfall. These scores are
shown in the right hand column in Table 1.
Reporting
Volunteers are advised at the time of training that any outfall with an impact score ≥ 10, from
the options in questions 8 and 9, should be reported directly from the river to the Environment
Agency’s Incident Hotline and Thames Water. Both Thames Water and Environment Agency
also receive a copy of this report.
Data Processing
Outfall data were checked to remove double entries and longitude and latitude coordinates
were converted to National Grid References using www.gridreferencefinder.com.
Results
The volunteers photographed, located and assessed a total of 198 outfalls. Of this total 73
showed some signs of pollution and scored ˃ 0 and of these 38 had a score ≥ 4. The details of
31 outfalls with an impact score of ≥ 4 are given in Table 2.
Six outfalls that volunteers scored ≥ 4 have not been included in Table 2 for further
investigation (photo ID numbers 36, 60, 61, 122, 191 and 193). Those outfalls showed
accumulations of a red-brown ‘slime’ (see Figure 2) that is likely to be a bacteria that
proliferates by oxidising iron in the water (‘iron mould’) and is not related to misconnections.
b. Faint smell, slight discolouration 2
c. Mild smell, mild discolouration, small
coverage of sewage fungus 4
d. Strong smell, strong discolouration, large
coverage of sewage fungus and/ or litter 6
e. Gross smell, gross sewage 10
10. Other signs of pollution
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Figure 2 - Examples of ‘Iron Mould’ Around Outfalls on the River Ravensbourne
One outfall (photo ID number 150), located on the left bank near to 32 Mottingham Lane, SE12
9AN (TQ 41216 73656), is not included in Table 2 either as the pollution assessment indicated
the presence of oil, rather than pollution as a result of a misconnection (impact score 4) (see
Figure 3).
Figure 3 – Oil Pollution near to Mottingham Lane
Two outfalls that scored ≥ 10 were reported to the Environment Agency from the river and the
reference numbers of those reports are included below (see points one and two). Those two
outfalls were also reported to Thames Water on 30th November 2017. Details of an additional
two outfalls that scored ≥ 10 but had not been reported at the time of survey were passed on
to both the Environment Agency and Thames Water on 28th November 2017 and 30th
November 2017, respectively (see points three and four). One further outfall that scored ≥ 10
but had also not been reported from the river was reported to Thames Water and the
Environment Agency on 13th December 2017 (see point 5). The location and impact score of all
five outfalls is included in Table 2 below.
1. South Norwood Country Park, photo ID number 55, Environment Agency reference
1564670, Thames Water reference 71130789777
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2. Croydon Road (A232), photo ID number 40, Environment Agency reference 1563571,
Thames Water reference 71130787904
3. Lennard Road Bridge, photo ID number 189, Environment Agency reference 1570730,
Thames Water reference 71130790012
4. Sydenham Cottages, photo ID number 164, Environment Agency reference 1570728,
Thames Water reference 71130790532
5. Farnaby Road, photo ID number 200, Environment Agency reference 1573123, Thames
Water reference 71213787204
The full 2017 River Ravensbourne Outfall Safari dataset is available from ZSL. Table 2 – Details and photos of River Ravensbourne outfalls with an impact score of ≥ 4
Photo ID
Number Location Details NGR
Bank Side
Outfall Score
Photo
17
End of the River Pool, at confluence with the River
Ravensbourne, near to Pool Court, SE6 3JQ
TQ 37279 73042
Right 8
34 Near to University Hospital
Lewisham, Albacore Crescent, SE13 7HR
TQ 37748 74604
Right 4
15
38
Near to 2 Ormonde Avenue, 5m downstream from Crofton
Road (A232) bridge, Orpington, BR6 8JP
TQ 44096 65857
Left 4
39
Near tennis court next to Chinbrook Meadows, near
Amblecote Road and Meadow Lane, SE12 9TE
TQ 41045 71973
Right 4
40 Crofton Road culvert, 207-213
Crofton Road (A232), Orpington, BR6 8PT
TQ 44104 65849
Left 10
55
South Norwood Country Park, top of West Chaffinch Brook, 100m upstream of tram stop, near to Harrington Road, SE25
4NE
TQ 35072 68390
Right 12
16
64 Southend Park, near 105-115 Meadowview Road, SE6 3NH
TQ 37045 71447
Right 6
73
Royal Bank of Scotland Sports Ground, between Copers Cope Road and Worsley
Bridge Road, Beckenham, BR3 1RL
TQ 36959 71099
Right 6
96 42 Dermody Road, SE13 5HB TQ
38823 74981
Left 4
17
103 86 Manor Lane, SE13 5QP TQ
39349 74715
Right 4
104 Near Manor Lane bridge, 88
Manor Lane, SE12 8LR
TQ 39342 74699
Left 4
105 South-west part of Manor House Gardens, near to 63 Manor Lane, Lee, SE12 8LN
TQ 39367 74733
Left 6
18
111 Osborne House, near 78
Meadowcourt Road, Blackheath, SE3 9DP
TQ 39889 75157
Left 6
No photo available
120 Near to 19 Bamford Road,
Bromley, BR1 5QP
TQ 38659 71438
Right 4
19
124 Downham Stream, near 1 Cress Mews, Bromley, BR1
4LU
TQ 38713 71378
Right 4
132
Between Westhorne Avenue and Eltham Palace Road, near 442 Westhorne Avenue, SE9
5LT
TQ 41402 74396
Right 4
135 South Circular, near 465
Westhorne Avenue, Lee, SE9 5LR
TQ 41357 74463
Left 4
139 Near to 182 Eltham Road, SE9
5LN
TQ 41310 74601
Right 4
20
141 Under bridge near to 128
Eltham Road, SE9 5LW
TQ 41032 74695
Right 4
146 44 Mottingham Lane, SE12
9AW
TQ 41192 73550
Left 6
164 Sydenham Cottages, near to 72 Edward Tyler Road, SE12
9QF
TQ 41139 72662
Left 20
169 156 Marvels Lane, SE12 9PG TQ
41066 72475
Left 4
21
172 Bromley Lawn Tennis and
Squash Rackets Club, near to 65 Hayes Road, BR2 9AE
TQ 40424 68090
Right 6
183 Kangley Bridge Road, SE26
5BW
TQ 36686 70936
Left 4
22
184 Near to industrial building complex, Kangley Bridge
Road, SE26 5BW
TQ 36719 70976
Left 4
189 Bridge near to 173 Lennard Road, Beckenham, BR3 1QN
TQ 36461 70419
Right 16
192 Cator Park, near to Capital Ring, Beckenham, BR3 1LL
TQ 36454 70193
Right 4
200 Near 188 Farnaby Road,
Bromley, BR2 0BB
TQ 38944 70050
Right 10
23
201 Shortlands Golf Course, near 146 Ravensbourne Avenue,
Bromley, BR2 0AY
TQ 38969 69925
Left 4
204 Shortlands Golf Course
(upstream), near 47 Meadow Road, Bromley, BR2 0DX
TQ 39294 69555
Right 4
205
Shortlands Golf Course (upstream), near 100
Ravensbourne Avenue, Bromley, BR2 0AX
TQ 39080 69711
Right 4
Discussion
This Outfall Safari surveyed approximately 28.7km of the River Ravensbourne and found 31
polluting outfalls (score of ≥4) (excluding outfalls with ‘iron mould’ and pollution unrelated to
misconnections). This is approximately 16% of all outfalls assessed, which is comparable to the
proportion of polluting outfalls on other London catchments including the River Pinn and River
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Ingrebourne. The consistently high number of polluting surface water outfalls that have been
reported through the Outfall Safaris to date demonstrates the likely scale of the problem across
London. The findings of this report further support the need to increase efforts to properly
address this pollution source which compromises the ecological value of rivers in London.
Some outfalls pollute intermittently and may not have been detected as a problem during the
survey but this report represents an audit of how outfalls, within the surveyed area, were
behaving during the survey. Outfalls could intermittently cause more serious problems than
impact scores may suggest depending on what was observed at the time of the Outfall Safari
survey.
A small number of outfalls that were observed during the Outfall Safari with no flow were not
recorded on the app, including some outfalls that showed signs of pollution. The correct
methodology for the Outfall Safari was clarified by ZSL staff once this became apparent.
However, as a result the number of outfalls requiring further investigation is likely to be slightly
underrepresented.
In addition, a small number of outfalls were recorded on the app as a single entry but with a
note referring to multiple outfalls (two, four or six outfalls) i.e. there were a number of similar
pipes in close proximity that were uploaded as a single entry (or outfall) to the app.
Photographs of only one of the outfalls in each of these cases were uploaded to the app. It was
therefore not possible, at the data analysis stage, to determine if those multiple pipes were
part of a single outfall structure or entirely separate outfalls altogether. These outfalls were
analysed as single structures, it is therefore possible that the number of outfalls assessed is
underrepresented.
A number of polluting outfalls that were in need of urgent attention (score of ≥ 10) and should
have been reported directly to Thames Water and the Environment Agency from the river at
the time of the survey were only reported later, at the time of writing this report. Reluctance to
report from the river has also been a problem on other Outfall Safaris. As the highest scoring
polluting outfalls these have the greatest potential to cause damage to the ecology of the river
and any delays to remediate these increase the risk of damage. For any future outfall surveys
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ZSL will make the reporting protocols during volunteer training clearer and add a clearer
prompt in the app that reminds the user to report an outfall that scores ≥ 10.
The draft results of this Outfall Safari and the preceding five Outfall Safaris are presented
collectively in one London-wide report, published November 2017, which includes
recommendations to reduce existing and prevent future misconnections.
References Dunk, M.J., McMath, S.M., Arikans, J., 2008. A new management approach for the remediation
of polluted surface water outfalls to improve river water quality. Water Environ. J. 22, 32–41.
Contact details Joe Pecorelli: Project Manager – Conservation Programmes
