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The Hogsmill in February 2018
Another cold and dreary period up to the middle of the month, but with plenty of water in the river it was
jolly boating weather on the Hogsmill and not too bad for ducks either!
“HMS Kingfisher” on the Hogsmill “Oh what an ugly duckling. Get out of my river!”
This newsletter summarises the results of River Monitoring Initiative (RMI) sampling on the Hogsmill in
February, together with other pollution monitoring and River-related activities and events.
The RMI is a national scheme for monitoring the health of rivers. Volunteers undertake regular surveys using
a standard net sampling technique to count the number of certain “water quality sensitive” invertebrates.
An overall “score” is then calculated. A sharp fall or a drop below a “trigger” level could indicate pollution.
This can then be reported to the Environment Agency (EA) to enable further investigation.
Misconnected wastewater pipes and cross-connected sewers are a major source of pollution in the Hogsmill.
Under a Pollution Patrol scheme organised by the South East Rivers Trust (SERT), volunteers undertake
regular assessments of the outfalls thought most susceptible to pollution, the results being reported to EA
and Thames Water (TW) to help steer remedial work.
If you see pollution along the river or indications of possible pollution, such as dying fish, please call the EA
Hotline: 0800 80 70 60; and if possible take a photo.
The Hogsmill in February
Another month with above average rainfall: over 75mm in the 4 weeks between scheduled RMI sampling
dates. But apart from a large surge in river level following heavy downpours in late January, the rain was
more spread out so both level and flow were relatively stable. We have now had nearly 4 months when the
levels have been much improved from the lows of last summer.
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All of our sites had a steady flow and a good depth of water when we took RMI samples. At Berrylands and
Bonesgate the levels were the highest for at least a year; and even at Ewell and upstream at Green Lanes,
where levels are typically relatively low, there was a reasonable flow of water.
Bonesgate Berrylands
Middle Mill Green Lanes Downstream
Green Lanes Upstream Ewell Storm Tanks
0.8
0.9
1.0
1.1
1.2
1.3
May
-16
Jun
Jul
Au
g
Sep
Oct
No
v
Dec
Jan
-17
Feb
Mar
Ap
r
May Jun
Jul
Au
g
Sep
Oct
No
v
Dec
Jan
-18
Feb
Met
res
*Average for 4-5 weeks before RMI "weekend"
Average River Level at Worcester Park*
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We are not aware of any new pollution incidents. But this has been “rag, scum and litter” month along the
Hogsmill. As well as near the “usual suspects” – the 2 Storms Tanks and the Sewage Treatment Works –
large quantities of rag were in the bank vegetation in other areas, such as by Green Lane Recreation Ground.
Brown water and scum were again flowing from the Bonesgate; and with vegetation now at its winter low,
the large amounts of litter along the banks, especially by the road and foot bridges, were particularly obvious.
With regular rainfall, visible signs of pollution around outfalls were relatively few, but the outfall near the
mouth of the Green Lanes Stream that was a “hotspot” when we did the Outfall Safari was again covered
with rag down the face, and is this month’s “horrid outfall”.
Rag near Ewell Storm Tanks Rag by Green Lane Recreation Ground
Scum on the Bonesgate A morning’s litter pick by the Hogsmill in Old Malden
Litter along Hogsmill Lane Kingston Green Lanes Stream outfall
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Hogsmill RMI in February
6 sites were surveyed between the 14th and 17th of February, mostly in sunshine for a change. The counts
and scores were generally better than last month so perhaps the critters came out “to play” in the sun!!
Key features were:
A score of “4” at Middle Mill and another breach. This may have partly been a legacy of January’s
pollution from the Sewage Treatment Works, though the counts and score were not significantly out
of line with previous Februarys so there was probably also a seasonal element;
A “5” at Ewell Storm Tanks. Only a small rise in score, but numbers were well up – the olive count
was the highest for 2 years – and close to those needed for a “6” or “7”. There was still rag around
the site, but perhaps the improved flow of water had diluted the impact of last month’s overflows;
A “9” at the downstream Green Lanes site, mainly from a “seething mass” of gammarus, and only the
third time such a score has been recorded here. This is particularly surprising following the major
pollution incident at The Epsom Storm Tanks last month. Perhaps the major clean-up operation
mounted by TW mitigated the impact;
A score of “8” at the upstream Green lanes site, with counts very close to last month’s; and an
improvement in counts and score at Berrylands;
The only site with a lower score than January’s was Bonesgate, which was down to “6”. This was
sampled soon after heavy rain and was the site most affected by the brown scummy water from the
Bonesgate, both of which could have had an effect.
The detailed results are below:
0.0
2.0
4.0
6.0
8.0
10.0
RM
I Sco
re
GL Upstm GL Downstm Ewell Storm Tanks Bonesgate Berrylands Middle Mill
Total Score Hogsmill February 2018
Olives Caseless caddis Cased caddis Gammarus
5
As for individual species:
The highlight was the 1300 plus gammarus found at the downstream Green Lanes site. Only on 4
previous occasions, all in 2014, have more than 1000 gammarus been recorded on the Hogsmill;
Apart from this, overall gammarus and olive numbers were broadly similar to January, maintaining
the recent improvement in numbers;
Caddis numbers were fairly low, but what they lacked in quantity was again made up by “quality”
with another wide variety of shapes and sizes, particularly at the Green Lanes sites;
“Catches” of fish and other species were relatively low this month, but we did find a number of
stickleback at Berrylands and a very large bullhead at Bonesgate, which looked as if it would soon see
the “patter of tiny fins”.
“Less than half a sixpence!” “Long stick” cased caddis
“Stone” cased caddis “Mum to be?”
Sprucing up and transforming the Hogsmill
February was a busy month for tidying up the Hogsmill greenspace and taking forward projects with the
potential to transform the environment along the river.
The terrific team and volunteers from the Lower Mole Project spent 3 days cutting back scrub and trimming
trees by the Hogsmill in Berrylands: paths across Elmbridge Meadows were cleared and will hopefully now
dry out; and the bank was opened up so more light should reach the river.
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Elmbridge Meadows path Opening up the bank by Green Lane Bridge
About 35 hardy souls braved a cold Sunday morning to join the Malden Manor Community Group for a clear-
up by the Hogsmill in Old Malden. With great support from SUSTRANS, the Kingston Environment Trust and
the Ahmadiyya Association, over 30 bags of litter were collected; some “large rubbish” was removed from
the river bed; a riverside path was restored; and bulbs were planted.
“Cor, this isn’t half heavy!” The final touches to the restored path
A day of scrub clearance beside the Tolworth Brook completed preparations for the “capital works” stage of
the project to revitalise the Raeburn Open Space in Berrylands. As well as cutting back brambles, volunteers
took time out to try to ensure one local resident would remain safe! Contractors are scheduled to start
work soon taking out concrete banks, removing a weir and installing a new bridge.
Hard at work clearing brambles “Please make the Open Space a better place for me!”
Another exciting development is that, with EA funding and support from the local council, SERT is
undertaking a feasibility study of ways to mitigate the impact on the upper Hogsmill chalk stream of the poor
water quality in the Green Lanes Stream. It is currently investigating an option that would divert the Stream
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through a meandering channel across Chambermead meadow re-joining the main river about 200 metres
downstream of the current confluence. Wetlands and ponds and scrapes would be constructed in the
meadow that would reduce the impact of pollution and sediment and also lower flood risk by attenuating
peak flows down the Stream. If you’d like to know more about the project, please contact Toby Hull at SERT:
Chambermead meadow “That’s 25k cubic metres of spoil to move!”
The Hogsmill Forum
35 of us enjoyed the excellent hospitality of London Zoo for the annual Hogsmill Forum with the aim of
improving communications between volunteers and the main agencies and groups working on the river; and
supporting further development of volunteer work in the catchment.
The Hogsmill Forum (photo thanks to Sivi) “Can I join the RM!? I’m good at counting bullheads!”
Copies of the presentations from EA, TW, Thames21 and SERT are available on SERT’s website.
https://www.southeastriverstrust.org/hogsmill-forum-2018/
There were some follow-up actions from the discussion:
fine-tuning RMI sampling. We agreed that on an experimental basis we would add counts of a few
extra species plus photos of the river to our monthly sampling so as hopefully to improve our
understanding of the impact of factors like low flow. SERT will be producing guidance on the changes;
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strengthening communications with the volunteer network. TW and EA agreed to consider whether
more information from their sensors and from TW’s Environment Protection and Network Resolution
Team reports could be shared on a regular basis so as to inform and to improve analysis of our
invertebrate and outfall pollution monitoring. SERT will be taking this forward through the
Catchment Partnership.
Particularly exciting is that Thames 21’s “lab boat” – “HMS Kingfisher” – has arrived and has been tested on
the Hogsmill. This remote controlled boat has sensors that measure several indicators of water quality, such
as dissolved oxygen, conductivity and temperature. Hopefully it will soon be able to measure nitrogen,
phosphates and more. It also has software enabling the data to be geo-referenced and viewed in real time.
River trials near Green Lane New Malden
The plan is to survey as much of the Hogsmill as possible over the next few months to create a map of water
quality on the river and then to repeat this as often as possible over the rest of the year. The boat will also
be available to measure water quality soon after any new pollution incidents or a sharp change in RMI score.
So it should provide a step change in our ability to assess water quality on the Hogsmill.
Thames21 would love local volunteers to assist in carrying out these surveys. If you’d like to help please
contact Caitlin Curry at Thames 21: [email protected]
Comments on this newsletter and suggestions and contributions for future editions would be welcome.
Please also send these to Peter Short: [email protected]
