Tag Archives: Hogsmill

Hogsmill Newsletter: May Edition

The latest edition of the Hogsmill Newsletter is now available to download. It summarises the results of River Monitoring Initiative (RMI) sampling together with other pollution monitoring and activities and events along the river.

Hogsmill Newsletter May 2017

If you have any comments or suggestions about the newsletter please contact:  Peter Short: rpetershort@hotmail.com

River Club Weir Removal

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No 12 on the Hogsmill obstruction hit list was the River Club weir.

With very shallow flows plunging over its crest, and a drop of 0.7 m between the upstream and downstream water levels, this weir on the Hogsmill near Tolworth was a complete barrier to fish passage under the majority of flow conditions. On each flank, the concrete and stone abutment walls were also structurally failing.

After lengthy discussions, in the course of which no justification for keeping or maintaining this weir could be established, we worked with the Environment Agency and Thames Rivers Trust to undertake a full weir removal.

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Once we had accessed and prepared the worksite, we began breaking up the main part of the weir using a long reach excavator with a hydraulic breaker attachment. It’s amazing how solid parts of these structures are, but our operator Roo’s patience eventually prevailed!

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Over 30 tonnes of concrete was removed from the channel and collected by a grab lorry.

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The stone walls were then broken up, and the new bank profiles were installed using a range of sustainable and biodegradable materials.  Native marginal plants and seed were then added to the new banks, which over time will provide erosion control and great habitat.

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It’s great to see the channel upstream already returning to a more natural state. Within a few days of removing the weir, a resident koi carp had moved from the upstream pool and was enjoying exploring some new habitat. This bodes well for all our native fish species we know are in other parts of the Hogsmill.

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We had fantastic weather throughout the duration of the project, although we could really do with some rain, as most of the rivers across the South East of the UK are experiencing extreme drought conditions.

A big thanks goes to to our local Environment Agency staff, Thames Rivers Trust, The River Club, two very supportive landowners and Roo Newby for his excavator operating skills.

We’ll now be focusing on the six remaining obstructions to fish passage with our aim of restoring this lovely (previously neglected) river to a more natural and improved ecological state.

Why remove weirs? Some excellent diagrams on how weirs affect river habitat and geomorphology have been produced by the Wild Trout Trust and you can also read our article on how weirs affect fish communities.

Before and After photos

BEFORE AND AFTER 1

The Timelapse Video

Keep up to date with the Hogsmill

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There is a new newsletter for anyone interested in or involved with the health of the Hogsmill. It summarises the results of River Monitoring Initiative (RMI) sampling together with other pollution monitoring and activities and events along the river.

Hogsmill Newsletter March 2017

If you have any comments or suggestions about the newsletter please contact:  Peter Short: rpetershort@hotmail.com

Volunteers Join Forces for the Hogsmill

The Hogsmill river doesn’t know how lucky it is!

Last week, 30 volunteers joined SERT and ZSL at London Zoo for the 2017 Hogsmill Forum.

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The Forum is an opportunity for us and ZSL to say thank you to all the volunteers who help us with our projects on the Hogsmill – Pollution Patrol and the Riverfly Monitoring Initiative.

It is also a chance to share wider plans for the river with the local community,  discussing ideas and actions for the coming year; all of which feed in to the Hogsmill Catchment Partnership which SERT host.

If you are interested in either project, get in touch – volunteering@southeastriverstrust.org

And why not have a read of these presentations which our speakers delivered through the course of the day?

Presentations:

Many thanks to ZSL for hosting us, and for letting us have a look around the zoo after the meeting!

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Hogsmill reconnected to the Thames with new fish pass in Kingston

The Hogsmill gauging station is an Environment Agency flow monitoring structure, essential for water resources planning and regulation.  It is the furthermost downstream weir in the catchment and poses a significant barrier to fish passage, preventing the recolonisation of fish to the river from the Thames below. Addressing passage at this key site has been discussed for several years but due to the sensitivity and importance in the recorded flow-gauging data, in combination with the unconventional structure it has resulted in a complicated and extensive process to identify and develop a suitable solution. JBA have helped inform the positioning of the upper baffle and through a programme of spot gaugings will update the rating of the gauging station.

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The impassable Hogsmill Kingston gauging station

The selected approach is a variation on the Low Cost Baffle (LCB) Solution as we have used elsewhere, whereby rigid baffles are put on the downstream weir face in a specific geometry and spacing to slow the water, deepen the flow and provide a distinct passage route on the weir face. However, due to the significantly steeper gradient at the site in comparison to that the design was developed for, the Trust and EA have modified the arrangement to help promote the correct hydraulics to enable fish to pass.  The maths aside, in essence this meant that each line of baffles is incrementally taller than the last, starting at 120mm and ending at 288mm at the downstream end.

With this novel approach the Trust and the Environment Agency are keen to establish how efficiently the pass/easement operates, as the principle could be adopted at other similar challenging sites. In order to get a comprehensive assessment, an exciting opportunity arose to work with Durham University who will use the project as part of a wider study looking at fish passage past human made barriers. That’s the good news. The bad news being that in order to be ready for the dace spawning season I was committed to delivering for three weeks through the bleak days of January and February. The summer would have been far too pleasant.

Due to the non-standard design the baffles were manufactured as a bespoke commission carried out by Northwood Forestry & Sawmills, made of oak as opposed to the standard recycled plastic. Once complete, myself and Norm spent the first week of the year huddled in his workshop drilling and bolting the stainless steel angle to each baffle which would enable them to be securely fixed to the concrete weir. All 36 pieces of the jigsaw were complete, coded and stacked in the lockup ready for installation.

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In the workshop with Norm fixing the stainless steel angle to the baffles

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Half of the baffles with angle attached and coded ready to go

The baffles would have to wait, as first we needed to help fish of the anguilliform variety, eels, to also be able to successfully navigate past the weir. With the eels having already made the 6000+km epic journey from the Sargasso Sea we were keen to ensure this weir would not be an abrupt dead-end. Although there was an eel pass on the weir, it has been largely ineffective for some time. A new and improved pass was called for, so out with the old and in with the new.

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Out with the old…

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and in with the new

With the eel pass installed, preparation to fix the baffles was underway. This primarily revolved around creating a dry working area, not necessarily an easy task when working in a river but with the temporary coffer dam supplied from RN Inspection Services this was achieved with unbelievable effectiveness.

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The coffer dam installed providing a manageable working area behind

For the next two weeks, Roo and I lugged baffles, drilled holes, spaced, chocked, clamped, injected resin, removed then re-erected the dam and battled the elements. As the jigsaw slotted together the theoretical schematic drawing I was now well familiar with became a reality.

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The baffles being clamped into position before the stud secured to the concrete with resin

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Getting into the flow of things

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Half way!

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Time to move the dam and install the second half of the baffles

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Finished! The notch bisecting the baffles to allow a deeper channel for fish to pass

Once complete, the time came to remove the dam and allow the water to flow over and through the baffles. With this action the Hogsmill became re-connected to the Thames once again.

The time lapse of the build conveniently summarises the full 3 weeks into 1 minute video can be seen here:

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About to ‘pull’ the dam

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Flow and fish passage returned to the channel

Over the coming year JBA (hydrology experts) will undertake a spot flow-gauging program, to ensure that the weir continues to gauge accurately with the modifications. Meanwhile Angus at Durham University and ourselves will monitor the LCB fish pass/easement aiming to understand its performance for coarse fishes such as chub, dace and roach.

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One aspect of the monitoring is a camera looking across the upper notch

A BIG thanks to: All those involved in the various teams at the Environment Agency, partners in the project especially those in Hydrometry and Telemetry and Fisheries.  Angus, Martyn and Jeroen at Durham University for bringing their wealth of monitoring experience and expertise to the project. JBA for carrying out the hydraulic assessments associated with the project. Bedelsford School who kindly agreed to us hooking up to their electricity supply to power the monitoring equipment. Rob Waite at the Royal Borough of Kingston for helping us to secure access and parking at the site. The Thames Anglers Conservancy, especially Will, for getting involved and helping to install the eel pass. Norm Fairey for your continued help with all things fishy and manufacturing. And my good mate Roo for the long hours, hard graft, permanently cold hands and near permanent good humour.

 

Get ready for London Rivers Week 2017

Get your diaries out and calendars open, the dates for London Rivers Week 2017 have been confirmed!

LRW logo finalLondon Rivers Week 2016 brought together many partners across London, delivering a total of 35 public events to get everyone involved with their local river. This year, we want to make it even bigger and better.

London Rivers Week 2017 will start on Monday 26th June and run through to Sunday 2nd July. During this week, organisations across London will put on a variety of river themed events including cleanups, guided walks, information talks, citizen science taster sessions and more.

To find out more about London River Week, check out the Thames 21 website page where all the events will be listed: http://www.thames21.org.uk/londonriversweek/

Until then, keep your eyes peeled for more details on what is to come!

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Eel Passage on the Hogsmill

During the summer a collaborative project between Zoological Society of London (ZSL), Surrey Wildlife Trust Kingston Group and the South East Rivers Trust (SERT) was undertaken to improve elver and eel passage on one of the lower weirs of the Hogsmill, the Clattern Bridge weir.

The European eel is a critically endangered species and needs all the help we can give it.  Pollution, overfishing, global warming, disease and habitat loss have all contributed to the demise of this charismatic species. The eel has a fascinating and mysterious life cycle in which it starts life in the Sargasso sea as a larvae, migrates across the oceans via currents to European rivers, metamorphosing a couple of times on the way to become glass eels and then elvers.

Once in rivers, such as the Thames and the Hogsmill, they migrate upstream to find habitat in which to grow and develop into yellow eels. After 5-20 years of life in rivers like as the Hogsmill they metamorphose again into silver eels and travel back to the Sargasso Sea to complete their life cycle.  Weirs and habitat loss in our rivers are factors that cause issues for eels and stop their upstream migration to suitable habitat.

This project involved installing plastic tiles covered in regularly spaced plastic protrusions onto the weir face.  The weir at Clattern Bridge is smooth and has shallow fast water flowing over it.  The tiles allow eels to wriggle up the weir and into the river upstream enabling them to carry on their migration. Eels are not very good swimmers compared to other fish and prefer to ‘wriggle’ so increasing friction in this way is ideal for them!

Below is a great video of eels using a similar design on the Wandle:

Armed with a couple of battery drills, some long drill bits and various stainless steel fixings we attached a continuous line of tiles to the weir surface.

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It was a lovely sunny day and perfect for a day in the river!

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A big thanks to the Kingston local branch of SWT who provided funding for materials, drill bits and fixings and to ZSL for supplying manpower and eel tiles.

Elvers migrate upstream between April-September and so we are hoping they will appreciate our efforts when they arrive in 2017!

Author: Tim Longstaff

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The Hogsmill: A Work of Art

You may remember that earlier this year we were lucky enough to spend a week in the Hogsmill with the Lower Mole Partnership. It was a chilly week in March but all our volunteers were enthusiastic and we managed to restore 500m of river through the Hogsmill Local Nature Reserve. With wood from the local area we created 9 brash berms, narrowing the river to increase local flow diversity. We pulled out 48 railway sleepers to reconnect the river to a natural bank, and in more difficult places we naturalised the bank with pre-planted coir rolls. A busy week to say the least.

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What we weren’t aware of was that Peter, from the Lower Mole Partnership, turned our week in the river into a work of art. Check it out…

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It was such a great week and we hope to be back again – with another painting!

Outfall Safari on the Hogsmill

ZSL and the Hogsmill Partnership are looking for volunteers to help us map polluted outfalls on the Hogsmill this October.

While walking the Hogsmill you may have noticed all the different pipes that can be found along the river bank. These pipes are usually part of our surface water infrastructure, transporting clean water from our roads and roofs into the river. However in some cases, these pipes or outfalls can be polluting the Hogsmill as they have been misconnected.

Polluted Outfall

Misconnections are a BIG issue for urban rivers and the Hogsmill Catchment Partnership have been working hard to start addressing this on the Hogsmill River.

A misconnection is when a toilet or washing machine has been connected to the surface water drain heading straight to the river, instead of the sewer system. You can read more about misconnections at on the Connect Right website.

Connect Right

This October, ZSL are running an Outfall Safari to map all these pipes heading into the Hogsmill, and assessing their condition to check for misconnections.

Volunteers will receive training on how to recognise signs of pollution at these outfalls and record the pipes on a new smartphone app. This survey data will greatly improve our understanding of the river system and help to target sources of pollution.

Interested?

If you would like to join the team, you can sign up on EventBrite to register your interest. Once you’ve registered, more information will be sent to you about where and when the training sessions will take place.

Sign Me Up!

For more information contact by email: Joe.Pecorelli@ZSL.org, or phone: 07974 725 557
Outfall BannerPlease register your interest to help at: hogsmilloutfalls.eventbrite.co.uk

You’ll need to read this before your training session: 2016-Pre-training-information-for-Hogsmill-Outfall-Safari-Volunteers..pdf

New London Partnership Project to tackle Urban Pollution

We have teamed up with Thames 21 on a new project to tackle urban pollution across London’s rivers.

Many improvements in the quality of urban rivers have been made in recent years, but lots of serious water quality issues remain. One of the biggest issues is ‘urban runoff’, where a toxic mixture of contaminants derived from urban areas drain straight into rivers.

With surface water drains often running straight into rivers, these contaminants are washed directly and unfiltered into urban rivers when it rains. During these ‘first flush’ events, river water often changes from being clear and colourless to being an opaque grey-black colour, and water analysis shows that a complex mixture of hydrocarbons, fine particles, nutrients, microorganisms and heavy metals are the cause.

First Flush samples from the River Wandle

First Flush samples from the River Wandle

In urban areas the contaminants causing rivers to run grey-black in colour may have a greater impact, but the locations at which they enter a river are often unknown, and they are relatively costly to survey, with samples needing to be processed by a lab.

Our project with Thames 21 is testing a low-cost sampling method that can be used by volunteers to identify complex urban contamination. In particular, it aims to investigate Surface Water Outfalls (SWOs) which discharge contaminated urban runoff into London’s tributaries of the River Thames.

The method being developed is based on evidence from data collected on the River Wandle, and urban sites in Wigan in NW England, which show that Total Suspended Solids (TSS) are strongly correlated with several important heavy metals and E. coli (a bacterium which can indicate faecal matter) and can therefore be used as a low-cost proxy to identify problematic concentrations of these contaminants.

The next step in this project is for us and Thames 21 to create Pollutant Profiles for our rivers to see if they match this correlation. You can follow progress on the project on our Twitter feed @SE_Rivers_Trust with #TSS!

Restoring the Hogsmill with Volunteers

A lot of our projects recently have been large scale – removing weirs, installing fish easement solutions and reprofiling large sections of river. But now it was time for the real professionals to step in…

Volunteers

For one week in March, Toby and I were in chest waders in the Hogsmill in Ewell. Over 5 days, we were joined by volunteers from the Lower Mole Project and other local volunteers from the Hogsmill Pollution Patrol and the Wandle – all trying river restoration first hand.

The River Hogsmill is a chalk stream in south London where we’ve been working to increase habitat connectivity over the last few years. Toby has been busy removing weirs where possible, or installing rock ramps to make them passable to fish.

In Ewell, Toby removed 3 small weirs to open up fish passage throughout this 1.6 km stretch. What was missing was fish habitat.

So what did we do?

The Hogsmill through the Open Space is artificially straightened and canalised with wooden toeboarding. There is little habitat variation in channel with slow moving water and a silty bed.

Straight Channel

On the first day, a team of volunteers got stuck in pulling out the large railway sleepers serving as toe boarding. Over the next four days, a total of 48 sleepers were removed – the first step in naturalising the bank for 1km through the park.

Sleepers

Meanwhile, carefully-selected trees were felled to increase light reaching the river. With this material, we started to create brash berms to narrow the channel and increase flow.

A holding log was placed at the downstream end of the berm and secured in place with posts and wires. Then brash from the surrounding areas was added to build up a berm.

Holding Log

This was all secured in place with chestnut posts and wire across the brash after some technical “squishing”…

Squishing

Over the next four days, the volunteers created a further 8 berms. You can see from the photos that the river began to respond instantly. Flows were increased where the channel was narrowed and scoured pools started to form.

On the last day we moved our attention further downstream to the site of a weir removal in 2014. Here a small weir and concrete abutment walls were reduced, but due to the close proximity of the path had to leave a semi-engineered bank.

To enhance this, pre-planted coir rolls were fixed along the bank to soften this edge and create a more natural marginal habitat.

Coir Rolls

To install these though was no simple task. They were secured in place with chestnut stakes and wire thread round the posts and through the mesh of the bank line. Believe me, that was a skill in itself…

Wiring Coir Rolls

Here are some photos of what we all achieved..

Finished!

Big thanks to everyone who came along!! We’d also like to thank Epsom & Ewell Borough Council and the Lower Mole Project.

The 2016 Hogsmill Forum

The Hogsmill River may have its problems, but it is one of the lucky urban rivers to have huge community support and many enthusiastic volunteers.

We run our Pollution Patrol on the Hogsmill, tracking down polluted outfalls and misconnections. While ZSL run the Riverfly Monitoring Initiative which uses the kick sampling of invertebrates to check for organic pollution.

So to thank everyone for their hard work, both projects combined for a joint Hogsmill Forum – kindly hosted by ZSL at London Zoo.

Hogs Forum

The event was a huge success with some really interesting discussions on the priorities for the Hogsmill going forward. Below you can download PDFs of the presentations.

Presentations:

 

Calling Hogsmill Volunteers!

Thursday 17th, Friday 18th & Saturday 19th March
10am – 4pm
Hogsmill Open Nature Reserve

This March, the South East Rivers Trust are delivering some restoration works on the Hogsmill through the Hogsmill Open Nature Reserve, and we are looking for volunteers to join us.

What will we be doing? 

We are going to be implementing some restoration through a 1 km stretch of the Hogsmill, such as installing Large Woody Material, bank softening and channel narrowing. These techniques will help increase flow diversity in the river, creating habitats for invertebrates, fish and other wildlife.

Make sure you sign up!
For each day, we are looking for a maximum of 15 volunteers to join us. So if you are interested in joining one or all days, please email Polly as soon as you can to book your place at volunteering@southeastriverstrust.org.

Once your place is confirmed, we will send round more details nearer the time on where to meet us, timings and what you need to bring.

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Happy Anniversary to the Hogsmill Pollution Patrol

Pollution on the HogsmillWith the start of 2016 comes the One Year Anniversary of our Hogsmill Pollution Patrol scheme – and what an amazing job it has done so far!

Throughout 2015, our trained volunteers have been monitoring 15 outfalls on the Hogsmill for signs of pollution such as misconnected appliances and sewage discharge.

Together they have submitted 470 reports of pollution to us. Working with the Environment Agency and Thames Water, we have been able to start investigating these issues and begin work towards rectifying them to improve water quality on the Hogsmill River.

To read the latest update of our work, please download our Newsletter below.

Pollution Newsletter December 2015

If you see pollution on your river, call the Environment Agency hotline on:

0800 80 70 60

Pollution

Polluted Outfalls and Riverfly Monitoring

Last week I was lucky enough to visit the Hogsmill River twice with some of our dedicated Pollution Patrol volunteers.

The Team!

From left to right: Geoff, Me (Polly), Steph, Peter, Bill and Jan

Our Pollution Assessment Volunteers (PAVs) work hard to track down and monitor polluted outfalls on the river, sending reports to the Environment Agency for action.

On Wednesday we were joined at a particularly bad outfall by our local Environment Agency Officer Steph to take some samples.

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Sewage fungus at the outfall

Steph sampled for ammonia, which is used as an indicator of raw sewage entering the river, and for oxygen available to river invertebrates and fish. Oxygen is a good indicator of how polluted an outfall is, as bacteria use up oxygen to break down organic pollutants, which reduces oxygen available to other species which can sometimes result in fish kills.

Sampling for Oxygen

For this week, both readings were fine.

This is one of many outfalls we’ve been looking at. You can find Steph’s updated report here.

Hogsmill Report July 2015

On Friday I was invited along to the monthly Riverfly Monitoring session at the same outfall with the same dedicated team. Every month they get together at this location and take a kick sample of invertebrates as an indicator of how healthy the area is.

Riverfly Monitoring

Some invertebrates such as caddis flies are very sensitive to pollution and are therefore an excellent indicator of water quality. If this is something you might be interested in, check out the website here!

Thank you to all our volunteers working on the Pollution Patrol scheme – we are making progress!

What have we been up to?

We have had a busy start to 2015 – maybe it is time for you to catch up with what we have been up to?

River Restoration ~ Luke has been busy transforming the Ravensbury Park Back Channel on the River Wandle for both the local community and wildlife. Read all about his progress here.

Pollution Control ~ Olly has been working hard trialling new methods to mitigate against urban diffuse pollution. We have trialled Siltex in Carshalton Ponds and installed Mycofilters at problematic outfalls.

Looking Forward ~ We’ve got restoration projects this year on the Hogsmill and Beverley Brook so keep your eyes peeled for more updates!

First Class Degree in Fish Passage at Kingston Uni

When working in channel you really are dependent on dry weather conditions. This is especially so on the Hogsmill which acts like a spate river, with large flashy flows shortly after rain events.  I have been incredibly fortunate with the weather for a long run of things. Unfortunately, things had to change and change they did. I return from site after a wet and challenging month.

The Hogsmill splits just upstream of the Knights Park Campus at Kingston. There is a large head weir on the main channel and on the side channel, two lower head weirs at either end of a sloping 24m concrete spillway. Both channels were completely impassable to fish, with the exception of eels on the main weir thanks to the eel pass installed by the Zoological Society London (ZSL) and monitored by the University.

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The upstream weir flowing onto the sloping concrete spillway

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The downstream weir with shallow plunging flows

Addressing passage on the main weir would be both feasibly and financially unviable. Instead attention was focused on the side channel. The water flowed over both the side channel weirs in shallow, plunging flows and over the spillway it was fast and shallow. Kingston University kindly agreed to the Trust carrying out the work as continued partnership working following on from the habitat works carried out earlier on the year at the Campus.

The chosen solution was two-fold. A rock ramp would be built at the downstream weir to step the river down in the form of a passable channel. On the concrete spillway four lines of rock would be fixed to the bed. Varying sized gaps (notches) are left in each line so that water is retained in the channel even under low flow conditions and a variety of pass conditions are provided. These rock lines serve to back the water up, increasing depth and slowing velocities. This backing up then effectively ‘drowns out’ the top weir which would also be ‘notched’ to reduce the height.

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Notching the upper weir

Roo Newby from Aquamaintain was brought in to give a hand, whilst gracing me with his northern charm and banter. The first job was to create a dry working area. A cofferdam was set up at the top of the channel to direct all of the flow down the main channel.

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The cofferdam in place, in theory providing a dry working area

The next job, which took the best part of three weeks, was to place all of the 20t of stone into position in order to create the desired flow conditions. With incredibly limited machinery access to the channel, the chore of moving it all fell to Roo and I. We grunted and moaned our way through it, placing, moving and repositioning each stone several times before finally fixing them. By the end of the job we have grown muscles on our ears.

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The boulders placed into position on the spillway

Key stones on the spillway were fixed into position by drilling through them and into the bed. The hole in the bed was then cleaned and a section of steel rebar fixed with resin. The stone was then lifted and fitted snugly back onto the bar.

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Using resin to fix the rebar into the holes

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The line of rebar to secure the upper line of boulders of the rock ramp

The key stones and all other non-load bearing stones, were concreted into position. The key stones in the rock ramp were secured using multiple techniques. At the downstream end of the ramp, chestnut stakes were driven into the bed to stabilise the lower line. The second line relies on mass and by being keyed in by the rip rap rock on either side. The third line was concreted onto the existing weir apron. The upper line of stone sits on the weir sill and was secured by the resin and rebar technique.

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Roo ‘mucking in’ the third line of boulders in the rock ramp

The job was hampered by mizzly conditions to start followed by heavy rain. Roo and I then both succumbed to river lurgy, no doubt caused by the sewage in the river as a consequence of combined sewage outfalls flowing after the rain, in combination with the massive misconnected drains issue present throughout the catchment. The heavens continued to open with annoyingly frequent regularity resulting in several days having to be abandoned due to a flooded working area. The rain built up to a crescendo with apocalyptic volumes falling last Sunday, giving the work a true baptism of fire with the cement barely having time to dry. But it stood up to the battering.

With the exception of the upstream weir, the rest of the work would now be passable for elvers (young eel) and eels. To assist them past the upper weir, a ramp of concreted in stones was installed to provide climbing media for them to get up and over. They can now continue onto the next stretch of river. During the work, four elvers were found in the channel. This pleasingly and clearly demonstrates that the past work of installing eel passes on the weirs downstream is working.

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Eel passage through the rock ramp…

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and over the upper weir

Both weirs have been drowned out with average depths of 300mm through the rock ramp and up the length of the spillway. A diversity of flows throughout the work provides passable notches and importantly vital resting pools. Perturbation boulders break up the most intense flows, adding complexity as well as potential habitat.

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The lower weir before the work

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The rock ramp in place

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The rock ramp working under moderate flows

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Looking up the spillway at the upper weir

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and after where the upper weir has been drowned out (note the complexity of flows and slack resting pools

Before the work was even completed, we saw two fish using the rock ramp, giving real confidence that the design was working and demonstrating their real desire to push their boundaries. With the University stretch being the most prolific for fish in the whole river, the door has just been opened for them to begin to repopulate upstream.

Thanks to Kingston University, specifically Sivi Sivanesan for allowing and assisting us with this project. A BIG thanks for all the hard, back breaking work from Roo from Aquamaintain and to Jack for his days on site.

Of rock-ramps and fish

And the fish easement work on the Hogsmill continues. This time our work is focused on the river around the Thames Water Sewage Treatment works situated in Berrylands, Surbiton, specifically the stretch from the railway bridge down towards Kingston Cemetery.

The over-widened channel here reduces water depth which, along with three small weirs and a lot of concrete-lined channel in between, effectively prevents fish from moving upstream.

So these weirs will have to go. Or will they? Toby’s work connecting reaches of the Hogsmill to free fish movement has shown an alternative – slow the flow and over they go! Building rock ramps and pool passes drown out these structures enabling fish to navigate their way over them.

Illustration of a typical rock-ramp (Source: Thorncraft and Harris, 2000)

Illustration of a typical rock-ramp (Source: Thorncraft and Harris, 2000)

After a few essentials from the Environment Agency, Thames Water and Network Rail we ought to have this project going in the next couple of months. More to follow shortly…

Reference

Thorncraft G. and Harris, J.H. 2000. Fish passage and fishways in New South Wales: A status report, Technical Report 1/2000 prepared by NSW fisheries for Cooperative Research Centre for Freshwater Ecology.

Obstruction at the A3 (but in the river, not on the road)

With barely enough time to draw breath, attention jumped from the headwaters in Ewell to the middle reaches near Tolworth, where the Hogsmill flows under the A3. The water through the culvert under the road is shallow. At the downstream end there is a 36 cm fall over a 30 metre long spillway, 34 cm of which is within the first 14 m. To top it off the concrete then comes to an abrupt end in the form of a 25 cm high weir. The cumulative effect of all of these factors result in, not only a completely impassable structure but also a concrete eye-sore.

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Looking downstream along the spillway.

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The weir at the downstream end.

With the budget unsurprisingly insufficient to stretch to the grand civil engineering feet of closing the A3, tearing up the road, breaking out all of the concrete, putting in a new bridge and then reinstating the road, we had to look for an alternative solution. A more cost effective and less disruptive easement was required. The chosen solution is two-fold. Firstly, the weir would be ‘drowned out’ by raising the water level downstream to back up over the spillway. Secondly, where the water depth tapers off up the spillway, a series of baffles will be secured to the concrete river bed to slow the flow and increase depth.

In order to drown out the weir, a ‘close-to-nature’ pool pass was designed in-house. In essence, the water level would be raised and then incrementally lowered by a series boulder bars. In each line a notch or gap is left in order to focus the flow and allow a place for fish to pass. Although this may sound a simple idea, plenty of calculations were required and carried out with the much appreciated help of colleague Tim Longstaff.

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Site set-up.

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Material being delivered.

This was not only a technical job but also one undertaken on a big scale.  In total 63 boulders of Purbeck stone supplied by Lovell Purbeck, each weighing between half and one tonne would need to be positioned into upstream facing, self supporting curved lines with their heights set to very fine tolerances. A 22 tonne excavator with a 15.5m reach complete with a grab were hired in complete with the very skilled hands of Barry Richards from Land & Water at the controls.

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The goliath.

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Barry at the helm.

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The first of 3 loads of Purbeck stone being unloaded.

In addition to the 45t of boulders that went into the construction of the boulder bars, a further 4t was used as 12 perturbation boulders and 25t of smaller Purbeck boulders were used as armouring.  A further 160t of Horsham stone was used to sit the upper boulder bar on, act as foundations and to help ‘waterproof’ the bars. The inclusion of all of this material encourages self-cleansing pools by increasing the flow thus reducing siltation and contaminant accumulation.

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The upper boulder bar complete.

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Steady progress.

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The boulders being placed into position with the long reach machine.

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The long reach living up to its name. The notch clearly visible in the upstream bar.

After the initial two days setting up the site and doing the required tree works, the build was completed in six days in which time we created a large scale water feature which now provides much needed fish passage.

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Before the work…

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and after from the same position.

The stretch has been completely transformed. Five large boulder bars now transect the channel; between each, deep pools provide vital resting areas for passing fish, connected by passable streaming flows. Each pool has a several large perturbation boulders to dissipate the energy of the water by breaking up the flow. These also serve as cover, habitat and to prevent the pools from being easily fished with nets. The weir has now disappeared, with 30cm of water now over the bottom 14m of the spillway and increased depth extending a total of 20m. Shortly the baffles will be fixed to the upper section of spillway to complete the solution.

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Complete, looking downstream…

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and upstream.

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Resting pools with boulders for refuge.

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Looking upstream at the alternating notches …

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with passable flows between each.

Formerly this stretch of river, although possessing a deep pool popular with fish, was dark and the bed littered with building debris, litter and rusting metal. There are now three good sized pools and two smaller ones. Light can now reach the river so vegetation will soon establish. The kingfisher, although initially a little disgruntled by our presence, is now successfully fishing for dace and roach that have already taken up residence in the pools and wagtails are now regularly seen running along each of the boulder bars.

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The weir, now you see it…

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and now you don’t (taken from the same position).

This project and the recent work at Green Lanes have both been the largest carried out in-house by the Trust and we are pleased to say both have gone very much to plan with great outcomes.

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We had a bit of time left over so we chiseled a Michelangelo’s David’esque sculpture out of one of the boulders. Oh no, its Tim.

A big thanks has to go to Tim, our hired in help from Aquamaintain for putting in some long hours, hard graft and welcome suggestions. Thanks to Barry, the digger driver, for making the large machine operate as if it were one of his own limbs, great skills! Thanks also to Rob Waite at the Royal Borough of Kingston for allowing us access to the site and for making the process so swift and effortless, Darryl-Clifton Day and the Environment Agency Fisheries Team who kindly contributed the recycled plastic baffles that will shortly be installed and Malcom Newson who gave advice and assistance with some calculations. Thanks to the EA for carrying out the utility search and thanks to all the others not mentioned who supplied us with materials or their time to enable to project to go to plan.

Fish passage and habitat works in the headwaters of the Hogsmill River

I am now back in the office and it’s time to update on the past six weeks which has been a busy time on the Hogsmill delivering a couple of projects in-house.  I will go back to the 11th of August when we started work at the confluence of the Hogsmill River and Green Lanes Stream. This is right up in the headwaters in Ewell within a kilometre of where the water flows out of the chalk to form the river.

In 1960, during the period when  concrete was considered the must-have look for most rivers, the entire confluence was dredged excessively deep, widened and entombed in a concrete cast. The best habitat within the Hogsmill River has since been cut off to fish by a sloping 35 metre length of uniformly wide concrete channel in conjunction with a small weir. Not wanting to do things by half, the banks were also cloaked in one metre high concrete and stone walls. The habitat was consequently considerably lacking, although nature has attempted to take a foothold with some sedge hanging precariously to cracks and crevices in the failing walls or with watercress clinging to silt deposits.

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The channel before work.

The aim of this project would address both these issues. Fish passage would be returned to the upper Hogsmill with the removal of the concrete bed whilst a 150 m cumulative length of river bank would be naturalised. With the scale of the work beyond that of our normal trusted volunteers, we brought in the great assistance of Aquamaintain Ltd. The work took three and a half weeks on site in which time 200 tonnes of concrete were removed from site in addition to a further 40 tonnes of soil.

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Concrete…

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concrete…

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followed by more concrete, 200 tonnes in total.

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You have to break a few eggs to make an omelette!

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The new channel being formed. Note the previously high banks on the left that have now been regraded as seen on the right.

Most of the large pieces of sandstone contained within the walls were recycled on site in various guises. Some were used to fill the gabion baskets forming the headwall for a surface water drain perched high on the bank. Other bits were used to make rock rolls that would stabilise the toe of exposed banks most susceptible to erosion. First though, the stone had to be broken up ‘convict style’ with a sledge hammer, a painstaking chore as Jack will vouch for. Finally, other pieces were placed in the completed channel to provide habitat diversity and create a variety of flow types.

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Jack at work breaking the stone up to fill the rock rolls

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The gabion headwall going in before the banks get regraded to match the front slope.

The banks have been naturalised with a combination of hazel faggots, site won brash, rock rolls and coir geotextile for temporary soil protection. A sinuous meandering channel form has now replaced the former straight and wide channel. Variations in depth, width and the inclusion of gravel, small boulders and multiple pieces of Large Woody Debris and root wads have all provided a diversity of habitat and complex flows within the channel. The low lying wetlands have been seeded with a mix of native species in addition to several hundred plants being introduced as a bit of kick start. Give it a year or two for the vegetation to establish and this stretch will be looking like the chalk stream that it should be.

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On completion. A new meandering and naturalised channel.

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The impounded stretch is returned to fast flowing water.

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Clean imported gravels, deeper holes, large wooded debris, root wads and planted marginal area.

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Looking upstream.

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The river already naturalising within a couple of weeks as watercress takes up a new residence.

The South East Rivers Trust has worked up this project with the continued support of Epsom and Ewell Borough Council who kindly contributed both financially and with their time, in particular that of Stewart Cocker and Christopher Stone.

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Finally, the before shot…

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and after.

This work is a continuation of the Catchment Restoration Fund Project funded by Defra, addressing fish passage along the length of the river. In combination with our two weir works last summer, also located in the Hogsmill Local Nature Reserve, this means that there is now a 1.5 km unobstructed stretch of river.

Without delay, work finished at the Green Lane on Wednesday and kicked off at Elmbridge Meadows on Thursday. Read on for what we are doing there.

A big thanks goes to the project partners, Epsom and Ewell Borough Council, especially to Stewart Cocker and Christopher Stone. Thanks to the EA for part funding the habitat element of the work and for undertaking the utility search. Thanks to Surrey County Council for permission to alter their asset. Finally, a BIG thanks to Ben, Jack and Tim from Aquamaintain for all the help, hard graft and good company.