Tag Archives: habitat

Working on the Eden

In August 2016 we were contracted by Kent Wildlife Trust to install a backwater on the River Eden near Penshurst in Kent.

The river Eden is in the upper reaches of the Medway catchment and joins with the Upper Medway approximately 1 km downstream from Penshurst.

What is a backwater and why is it needed?

A backwater is an aquatic habitat connected to the main channel, sometimes only during higher water levels. Backwaters can be formed naturally as a river migrates across its floodplain, cutting off meanders.

Backwater habitats can be used on rivers that have been straightened or resectioned to increase the diversity of flow, habitat and ecology.

In this case we were asked to install a backwater that would provide two important functions for the river depending on the flow. In high flows, the backwater would become a refuge of slack water for adult fish to rest in until the normal flows return. In normal flows, the shallower water left in the backwater will warm up quicker than the main channel and act as a nursery area promoting the growth of young fish fry.

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Photo provided by Kent Wildlife Trust of project area last Winter 2015

What we did

The project got off to a quick start with local tree surgeon Ivan Carson, from Penshurst Tree Surgery, making short work of the 3 cricket bat willows.

These willows were coppiced to near ground level to allow more sunlight to reach the backwater – helping to raise water temperature during normal flows. A bonus benefit of this tree removal is a reduction in the amount of leaf litter entering the backwater, reducing future maintenance.

With a tight schedule, work on the backwater commenced. First the old fence was removed and the topsoil was stripped back.

Our expert excavator, Jimmy, started shaping the backwater entrance. All the spoil we removed was tracked to the far end of the landowner’s orchard to improve their existing track.

Everything seemed to be going smoothly until Jimmy’s bucket hit something solid! This turned out to be a huge tree trunk of approx 1 m diameter running parallel to the river, across the backwater entrance.

digger-and-trunk

trunk

With no idea how long the trunk might be, we decided to remove the central section. Most of it was actually below water level, which meant our saw wasn’t quite up to the job. Fortunately, Ivan kindly lent us one of his and the obstacle was overcome by our very own Toby.

The silver lining of this small delay was that we didn’t need to install any large woody as cover for fish.  We even spotted a Perch of approx. 1.5 lbs sunning itself in the shallows until it was spooked, and darted underneath one of the remaining stumps – woody cover in action!

Whilst Jimmy was finishing off the backwater, Toby and Alex started to install the new fencing around the backwater. This fencing will exclude cattle from the backwater, preventing over-grazing and reducing bank erosion.

fencing

With the backwater construction complete, it was time to add the plants. Marginal plant plugs were added around the backwater, and wild flower seed was scattered on the ground to provide some ground cover before winter.

clearing-up

The landowner seemed really happy with the final result – especially once he saw all the marginal plants.

The project took 6 days to complete and we look forward to seeing how the backwater matures overtime.  Lots of fish fry were spotted on our most recent site visit which suggests we did a good job!

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Water quality improvements are on par at Richmond Park

Shortly I will post another blog updating you on how the river improvement works in Richmond Park are settling in one year after they were completed. Although the river habitat works have been completed (for now!) work has by no means ended. In addition to improving the habitat, our attention is also focused on addressing the poor water quality entering into the Brook.

Upstream of the Richmond Park golf course, rain water pours off the surrounding urban catchment and notably down the incredibly busy and often choked A3 at Roehampton Hill. It then flows down the gulley pots, into a surface water drain before this opens out into a ditch which flows across Richmond Park Golf Course before discharging into the Beverley Brook. Such road runoff is known to cause detrimental effects to the aquatic environment, not only from the significant quantities of sediment carried in it, but additionally from the contaminants bound to it. These include Poly Aromatic Hydrocarbons (PAHs), hydrocarbons and heavy metals. Our aim was to therefore capture the sediment and the contaminants before they reach the Brook. This was achieved with a two pronged attack.

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Oil from the A3 covering the surface of the pond in the golf course. Thick black sediment covers the bed

First of all, mid-fairway at the upstream end of the golf course we opened the ditch out to create an on-line pond, known to us as a silt trap but to golfers as a feature water hazard. With help from Rob McInnes, the pond’s size was calculated so that all coarse sediment down to 0.1mm would drop out as a consequence of lowering the velocity of the flow. A shallow marginal ledge was incorporated along the length of the pond, which has been planted with a mix of wetland plant species to promote deposition, whilst providing species and habitat diversity. By emptying the pond regularly, the silt is removed from the system and the effectiveness of the trap is maintained.

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Starting to open the ditch out

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A few months after completion, the pond is trapping plenty of silt (and plenty of golf balls)

The second measure took place a few hundred metres further down the ditch where an existing online pond, in the shape of a ring doughnut, provided an excellent opportunity to be modified to create a wetland. The plan was to re-jig it so that the doughnut became a U-shape. This prevents short-circuiting, therefore increasing retention times, reducing velocities and again promoting a depositional environment.

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The pond before works start

The pond was too deep to plant straight into, so we needed to find spoil to fill it in. What better way to produce the spoil than dig a second wetland immediately upstream of the first, which will increase the treatment capacity further.

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Re configuring and filling in of the pond

Six thousand plants consisting of over 20 species were planted in the wetlands. The dense structure created by the plants results in even finer sediments being captured than in the silt trap upstream.

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The wetlands newly planted with 6000 plugs and fenced off

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August and the plants have established

Furthermore, this has now created a fantastic wetland habitat full of dragonflies, damselflies and frogs to name a few. Both the silt trap and wetlands have been fenced off and have bird twine strung over them to prevent the large population of geese from nobbling the plants before they had the chance to establish. The total area of both is approximately 800 metres square.

A simple water level control structure was created at the outlet of each wetland. As sediment accumulates and reduces the depth of water over time, another drop board can be put in, allowing the water depth to be increased, therefore reducing maintenance requirements and prolonging the life of the wetland.

The effectiveness of the installed measures is currently being monitored, however a coincidental site visit during a pollution event helped to anecdotally demonstrate the effectiveness. Run-off from a presumed building site was bringing significant quantities of sand rich water into the ditch. After the silt trap, the turbidity of water flowing out was visually improved. Walking further down the ditch network, after flowing through both wetlands, we were incredibly impressed to see that the water flowing out and into the river was clear to the eye. Although this was always the theory behind why we created these features, to see it work first hand to such a great effect was brilliant and hugely satisfying. With contaminants generally being bound to sediment, this clearly demonstrates not only a reduction of sediment input to the river but indirectly of contaminants too.

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Thick sandy water flowing into the sediment trap

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Water in the ditch downstream of the sediment trap and both wetlands

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Significantly improved water clarity entering into the Beverley Brook

Job done!! (for now anyway). I am now working up the next phase of water quality improvements. Updates will follow shortly.

As always, the success of this project is down to the valuable contribution of many people and organisations.

Big thanks to the ongoing project partners; the Environment Agency, Defra, The Royal Parks and Friends of Richmond Park. Thanks to Jon Dummett and Gary Stewart at Glendale Golf Course for surprisingly being so willing in allowing us to dig up their course and for their continued support since. Thanks to Rob McInnes at RM Wetlands & Environment Ltd for guiding the designs, Ben and the guys at Aquamaintain for braving the cold February days delivering the work and again for planting it up. Thanks to Thames Water for providing the flow meter which was installed in the ditch network to inform the design and finally, to Layla at Queen Mary University for monitoring the work.

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!

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.

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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The Beverley Brook Needs Your Vote!

Bags of HelpThe Beverley Brook Catchment Partnership have been successful in securing a Tesco grant from the Bags of Help fund – but we need your vote!

If you are shopping in the Sutton/Cheam area between now and Sunday 9th March, why not shop in a local Tesco store and give your vote to our project?

With your votes, we could get an extra £4000 to the project! The money will be used to make improvements to the Beverley Brook through Richmond Park following our recent restoration works. There will even be community planting days which you could get involved in.

So what are you waiting for, go vote for Project Two: Richmond Park River Enhancements!

Our Project

 

Tree Planting in Richmond Park

I am sure you have all been following the progress in Richmond Park with our Beverley Brook Restoration Project. Well now that the main channels works have been completed, we were ready to move on to the next stage: tree planting.

Tree Planting

Adding the right number of trees along the channel is crucial to restoring the habitat. Trees provide excellent cover for fish from predation, the shade they create helps to keep the river cool in the summer months, they provide habitat for birds and insects and the seeds as a food source. However too much shade can prevent marginal, emergent and submerged plant growth, so a balance has to be struck.

On a sunny February morning we were joined by seven volunteers from Friends of Richmond Park to plant nearly 200 trees along the two restored sections on the Beverley Brook.

To ensure we got it right, Toby (Senior Projects Officer at SERT) had worked closely with Royal Parks’ Julia (Head of Ecology) to map out where each species should be planted and how many.

More Trees

Tree species planted included several types of willow (white, grey, osier and goat) as well as alder, black poplar, blackthorn, hawthorn, hazel, birch and elm. All trees were given a protection from grazing and from high flows to give them the best chance at establishing. Given the flashy nature of the Beverley Brook, those trees planted closer to the channel were given some extra protection from strong flows with a large stake providing cover.

More trees

Next on the agenda for this project is to add plants to the marginal habitats in April. Watch this space and come and get involved!

Big thank you to our volunteers from Friends of Richmond Park: Brian, Ian, Janet, Jed, Mike, Roger and Simon.

Lovely gravels

Restoration to the Beverley Brook in Richmond Park (Phase 1)

The write up of the introduction to the project can be viewed here.

I have now returned from being out at Richmond Park delivering the first phase of restoration to the Beverley Brook in Richmond Park. It has been a while and lots has happened which I am keen to share. I suggest you make a cuppa, take a seat and get comfy.

The Beverley Brook possesses incredibly flashy characteristics due to the urban nature of the river with a significant proportion of the catchment being coated in hard, impermeable paving. With the plan to be on-site for seven weeks through the British autumn undertaking a significant amount of in-channel works to 600 m of river, we were firmly in the hands of the weather once again.

The aim of the project is to enhance the heavily degraded, uniform and generally inhospitable channel so that it would be more inviting to the native fauna and flora that should be present and abundant.

A sorry state at the start of the project

A sorry state at the start of the project

Before the works started we undertook a range of monitoring to capture the baseline condition of the river. These will be vital and incredibly interesting to refer to in the years to come to demonstrate the effectiveness of the project. The monitoring included a two day fish survey undertaken by the Environment Agency, habitat mapping, aquatic invertebrate and plant surveys, sediment analysis and novelly for us, a drone recorded aerial video and photography of the site with some exciting low fly-over manoeuvres.

Drone in Action

Drone action

The work then commenced. With the help from the Aquamaintain guys once again and with Trevor behind the controls of the long reach excavator, we set about spicing up the bland channel. The key to this was variety. A variety of flow types, a variety of channel widths, depths and bank profiles. By adding diversity, a mosaic of habits would be created, providing for  a range of species throughout their life stages.

When discussions about the project first started with the Royal Parks a year or so ago, I could not believe my ears when they announced that there was no shortage of trees and rootwads we could source from the Park to use in the river. With this rare offer, I was like a kid in a sweet shop. With the help of Mick Baker, the Park’s go to forester, dozens and dozens of oak trees were felled (I must add this is as part of the Park’s management regime), the root balls dug up and all carried down to the river by the mighty forwarder (tractor).

Rootwads and LWM ready to be used

Rootwads and LWM ready to be used

Some of the LWM stockpile seen from the air

Some of the LWM stockpile seen from the air

Mick bringing down another load of oak tree tops

Mick bringing down another load of oak tree tops

The wood was introduced to the river in a variety of methods to perform a number of tasks. In places, masses of the tree tops and smaller limbs were stacked up against the bank extending between a third to half way across the channel. These were compacted with the huge force of the excavator and then secured with posts and fencing wire. This technique reduces the channel width to give the river more energy whilst providing complex habitat both above and below the water line. Furthermore, the dense network of branches creates slack water, encouraging silt to drop out whilst also capturing leaves and seeds. Overtime, these structures will consolidate and vegetate to form a new bank. By alternating the bank these are constructed on, a meandering sequence is created in conjunction with the next method, backfilled faggots.

Tree tops and brash in the foreground before being compressed and secured

Tree tops and brash in the foreground before being compressed and secured

Faggots (brash bundles) are fixed to the bed with posts and wire to create the new bank line, again reducing the channel width in places from 7 metres down to 2.5. The steep banks are then regraded and the spoil placed behind the faggots to produce low lying berms which in time will become wetlands when marginal plants establish.

Faggots with incorporated LWM being used to narrow the over-wide channel

Faggots with incorporated LWM being used to narrow the over-wide channel before being backfilled with the regraded banks

Protruding out of the tree tops and faggot berms, larger tree trunks, rootwads and multi-limbs (Large Woody Material, LWM) where fixed into place, extending out across the channel.

Rootwads providing complex cover

Rootwads providing complex cover with a backfilled faggot berm behind

Doing so is a great way to not only provide complex cover but is also a way to reinstate energy back to the river. As water rushes over, under and past the structures, the bed is scoured, creating deeper holes and throwing up the cleaned gravels into shoals and bars. This is a truly rewarding aspect of the work, identifying where and how to place the wood. Even under low flows, the impact can be felt immediately with the gravels being kicked up around your feet. A day later, the bed downstream is glowing with gravels as opposed to the previous uniform blanket covering of sand. And again, after higher flows, features are carved out and created.

LWM immediatley forming holes, shoals and riffles

LWM immediatley forming holes, shoals and riffles

The banks were also naturalised as we progressed downstream. The steep gradient was reduced where possible to provide transitional areas between the terrestrial and aquatic habitats. Intermittently, hugely over-engineered concrete headwalls with tiny two inch blocked land drains poking out scared the bank. Being redundant, these were removed with a total of 20 tonnes of concrete being mucked-away from site.

Another concrete headwall being removed

Another concrete headwall being removed

Significant regrading of the perched banks to form a wide wetland area on an inside meander, soon to be planted

Significant regrading of the perched banks to form a wide wetland area on an inside meander, soon to be planted

A key aspect of the project is to restrict deer access to the channel. To do this the entire 600m length which is divided into two sections was fenced off. However, to prevent them accessing the stretches by simply walking up the channel, we had to construct river gates at the ends of the sections. In a river as deeply incised and flashy as the Beverley Brook is here, this took some doing. We ordered in several chunky telegraph poles. Some were cut and notched to form half jointed A-frames. These were positioned in deep holes high up on the banks. Mounted onto these, the excavator lifted 12 metre telegraph poles to span the channel. From these using stainless steel eye bolts and chains, oak gates from wood sourced and milled in the Park and manufactured by our good friend, Norm Fairey were hung. The principle being that the river gates prevent deer passing but importantly not causing a debris build up.

A section of the 600m of fencing which has been erected

A section of the 600m of fencing which has been erected

The moment of truth, the telegraph pole spans the 12m gap before the braces are removed from the A-frames and the holes are filled with concrete

The moment of truth, the telegraph pole spans the 12m gap before the braces are removed from the A-frames and the holes are filled with concrete

Jack standing back and admiring one of the three telegraph pole river gates completed

Jack standing back and admiring one of the three telegraph pole river gates completed

A conveniently placed bridge provides the structure for the fourth set of gates

A conveniently placed bridge provides the structure for the fourth set of gates

The last task was to create a deer and dog access point. These access points prevent the banks being eroded (poached) with the subsequent input of sediment to the channel. The banks were regraded to a shallower angle and first armoured with 20 tonnes of gabion stone and then covered with compacted scalpings.

Access point in the foreground with the most downstream river gates behind marking the end of the restored section or river

Access point in the foreground with the most downstream river gates behind marking the end of the restored section or river

As I mentioned at the beginning, we were needing the autumn weather to be kind to us. Who could believe it? Throughout the first three and a half weeks we barely had a drop, allowing great progress with the in-channel works and with ground conditions holding up well. After that, we did lose a couple of days due to rain and the spatey flows but I considered we had been lucky and gratefully accepted it.

The New Year has provided the first heavy flows. I managed to get down to the river yesterday and waded the length inspecting how things are bedding in.  I am pleased to say that the restoration has certainly been successful in the aim of providing variety. With more energy, the river at last has active functioning processes.

Before, blandness!

Before, blandness!

And after, variety is the spice of life!

And after, variety is the spice of life!

The Large Woody Material is scouring holes with loose gravel riffles forming downstream. The bed on outside of the meanders is deepening with large deposits of sediment forming shallow berms on the inside. The tree tops are accumulating sediment and consolidating quickly. The water’s surface is rippled and broken making the river audible once again. Even whilst doing the work, each morning a walk up the river demonstrated the immediate effectiveness with dace and chub taking up residence in new lies and pools where before there were none. I am thoroughly looking forward to seeing how the river adjusts and naturalises over the coming weeks, months and years.

So moving on, next month we start addressing diffuse urban pollution entering into the Brook from the A3 by digging a sediment trap and creating two wetlands. We are also having our first of several planting days. This one introducing trees to the river banks to provide shade and Large Woody Material in the future. We will keep you posted.

There are so many people to thank. The funders; The Friends of Richmond Park, The Royal Parks, the Environment Agency and the Beverley Brook Catchment Partnership. And those that helped out;  Simon, Julia and Adam at The Royal Parks, the guys at Aquamaintain; Ben, Dave, Jack, Zac, Lloyd and Roo. Trevor from Land & Water  in the machine, Norm Fairey, Curling Fencing Contractors, Mick Baker, Andy Birnie, Colin Hampton, Luke and his drone, the list goes on. Thank you all.

 

Action on the River Teise!

We’ve started our project on the River Teise to make a weir passable for fish migration.

Weirs were introduced years ago to help control the flow of water, allowing our ancestors to operate mills. Nowadays many remain in rivers despite no longer being required.

Weirs are a barrier to fish passage and leave the habitat fragmented with fish populations isolated. In the event of pollution or other presures like climate change, these isolated populations are at greater risk with nowhere to escape to.

Although being a barrier to fish migration is a significant problem, weirs also interrupt the natural flow of rivers, resulting in a degradation of habitat. Upstream of weirs, water is slowed down which causes silt to drop out and accumulate in the channel.

This image from the Wild Trout Trust explains the effects of weirs on fish habitat:

WTT Weir

Funded through Defra’s Catchment Partnership Action Fund, we’ve started works on a weir on the River Teise – where Olly and Rosie carefully removed a number of boards from the top of the weir.

Weir Board Removal

After removing the boards, the impounded water levels upstream dropped noticeably, revealing many natural features of the river which had been drowned out when the weir was put in place.

Before

Before

AfterAfter

New Habitats

Some of the diverse new habitat revealed by lower water levels above the weir

The next phase of the project is to remove the impoundment and enable full fish passage and habitat restoration, so watch this space!

River Restoration in Richmond Park

Richmond ParkWe’ve started our latest restoration project in Richmond Park, working to enhance the Beverley Brook in partnership with The Royal Parks, The Environment Agency, the Friends of Richmond Park and the Beverley Brook Catchment Partnership.

Richmond Park is well known for its deer and its nationally important terrestrial habitats, e.g. acid grassland. Given this high status you would be forgiven for thinking that the river was also in good shape.  However, it’s actually not and its wildlife is relatively impoverished.

About 14% of the length of the Beverley Brook runs through the Richmond Park and so restoring the river through the park, presents an excellent opportunity to make a real difference to the whole river ecosystem.

Why is restoration needed?

The Beverley Brook, like many of London’s rivers, has been heavily modified in the past leaving a highly uniform river channel lacking in habitat diversity. The river channel has been over-widened and in places deepened along most of its length with all natural woody material and instream features being routinely removed from the channel for decades. Due to these reasons there is little variation in flow and depth and subsequently there is little habitat diversity for fish and aquatic invertebrates.

RP Before 2In addition to this the banks are very steep and the river is incised (if you stand on the top of the bank the river is quite a long way down!) and the banks have been subject to increased erosion due to the intense grazing of deer. The deer enjoy eating the succulent river bank plants. This means there is little vegetation left and there are no root structures to hold the soil on the river bank in place and so it washes into the river.  You may have seen a sandy bottom on the river bed: this isn’t actually what it’s meant to look like and is a result of the soil washing in and smothering the natural gravels on the river bed. This is a problem for the river ecosystem as many of the plants and animals that would naturally live in the Beverley Brook need the gravelly river bed habitats to survive.

SiltyBed           SteepBank

A natural river system has the ability to self-regulate but when it becomes modified, the processes can get out of kilter and we may need to intervene to kick start them again.  All of the modifications to the Beverley Brook have left the river with little power, taking away the opportunity for the channel to naturally fix itself with geomorphological processes.

RP Before 1What we are doing

A large river restoration project in the Park has been developed and funded in partnership with the South East Rivers Trust, the Royal Parks, the Friends of Richmond Park, the Environment Agency and the Beverley Brook Catchment Partnership. The aim of this project is to naturalise 600 m of the Beverley Brook through the park using a number of simple restoration techniques. These include:

  • Adding Large Woody Material to increase flow variation and provide a greater complexity of habitats for aquatic wildlife.
  • Re-profiling the incised and steep banks to enhance marginal habitats.
  • Narrowing and remeandering the channel to create a diversity of different flow patterns and produce marginal wetland berms.
  • Erecting fencing and river gates to temporarily exclude the deer to allow the banks to stabilise and for vegetation to recover.
  • Creating slower flowing areas as refuge for animals during the high flows which are typical of urban rivers such as the Beverley Brook. This is particularly important to help fish establish and not be washed downstream (and possibly right out of the river) in heavy rains.
  • Address the contaminated road run-off input into the river from the A3 by creating a siltation pond and wetland to trap and clean the silt from the road.

So it is going to be a busy couple of months on site and we are all excited about the results this project will bring!

You can read more about the project and how Richmond Park access will be affected during works on the Royal Parks website here.

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Wombles of Wimbledon: Beverley Brook

Last week, Luke and I were lucky enough to spend three days on the Beverley Brook in Wimbledon Common.

Like many rivers, the Beverley Brook has been modified over time to fit into our more developed urban landscape. Within Wimbledon Common, the river has been over straightened and reinforced with wooden toe boarding. As a result the flow of the river has become very uniform and lack the diversity needed for water biodiversity.

To address this we started a project to install Large Woody Material (LWM) into the river channel. LWM replicates a natural occurrence of trees and branches falling into rivers which then provides habitat for fish and invertebrates. The use of LWM in the right places can transform a still, slow-moving river into a highly diverse river channel with a variety of habitats for all life stages of fish and invertebrates.

Part of the Womble Team

Over the three days we had a number of volunteer helpers to help us move the timber logs, position them within the channel and fix them in place with hazel stakes and wire.

Luke and Lawrence led the event, explaining how the positioning of the logs effected the flow of the river and could influence bank erosion. For example, if we placed a log facing downstream, this forced the flow of water into the bank creating a natural meander bend. Natural gravel deposits held in the bank will scour out and become available in-stream for fish and invertebrates.

The timber logs were heavy!

So working as a team, over three days we worked out where the logs would be of most benefit and got to work securing them in place.

It was hard work. Moving the large logs took four people and was still a struggle. However once they were in the river, they became a lot lighter. Once positioned, each log had to be secured with four hazel posts which were forced into the ground using a post knocker – another exhausting piece of equipment.

Securing

Once surrounded by hazel stakes, the logs were secured further with wire to be sure they were going nowhere in a flood.

In total we installed 17 LWM structures along a stretch of 200 m, approximately. Here are some photos to show you how the still slow-moving channel has now been transformed!

One finished deflector

Many thanks to all the volunteers for coming: Charles, Dave, Denisa, John, Keith, Kristina, Lawrence, Mark, Mike, Paul, Phil, Rob, Sue and Wally.

More deflectors

More!

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.

A little light goes a long way..

Our work on the River Wandle continues with a habitat and fish passage project on the Ravensbury Park by-pass channel. This work will address habitat deficiencies, stream form and fish passage around the tilting weir which is a significant barrier to upstream fish movement. To read more about this project click here.

Toe-boarded and impounded nature of the back channel

Toe-boarded and impounded nature of the back channel

Concrete lined banks as well as over shaded character that limits aquatic vegetation  growth

Concrete lined banks as well as the over shaded character that limits aquatic vegetation growth

Hogsmill: Assisting nature and being assisted by nature

Hogsmill Planting and Wooded Debris Fixing

Last Wednesday saw the Trust accompanied by the great volunteer help of Epsom and Ewell’s  Countryside Team return to the site of the weir removals that took place last August in the headwaters of the river in the Hogsmill Local Nature Reserve. The primary task was to kick start the establishment of the bank side vegetation which is required to encourage a complex root structure to help to stabilise the bioengineered banks. Planting took place towards the end of last years growing season and subsequently did not have long to settle in before winter took hold. This time we would give them the whole growing season to take hold. 

Semi-mature iris, hemp agrimony, purple loosestrife, meadow sweet, brook lime and a few bur reed, all purchased from a reputable supplier, were planted into the banks and marginal areas. In addition to these, translocated sedge taken from elsewhere nearby on the river were also introduced.  We undertook the planting at both the former weir sites. We now need a bit of sun and a bit of rain to encourage good growth, fingers crossed.

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Kitted up and ready to plant.

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The banks receiving a second coat of plants.

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A well deserved rest.

Now that we had helped nature, we now took advantage of an offering that nature gave in return. During the winds and rain in the winter a large branch had been washed down the river and become wedged in a normally straight channel against a stone wall on the right bank. With more high flows more wooded debris collected on the branch, consolidating and stabilising the raft further. As the high flows continued the river carved out a meander into the natural left bank. This has produced a deep sinuous run with adjacent complex cover.  In the slack water created behind the structure siltation has started to accumulate which has quickly become populated by various marginal plants. This type of habitat is severely lacking in the upper reaches of the Hogsmill. Keen to take advantage of this, the Environment Agency where approached by the Trust seeking permission to formalise and fix the structure into place. With flood consideration given, consent to go ahead was granted.

With help from Nigel, the branches that would potentially catch further debris where removed both above and below the water line. Untreated chestnut posts were driven into the river bed either side of the structure and fencing wire passed repeatedly over the structure from post to post and secured with staples. The wire was then tensioned and structure fixed by driving the posts down further.

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Before work..

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and after, clear of debris snagging branches.

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and after.

This is a great example to show that simple, quick and cheap techniques can sometimes be used to great effect.

Once again a big thanks goes to the kind help of the Epsom and Ewell’s Countryside Team volunteers as well as Stewart Cocker and Lindsay Coomber at Epsom and Ewell Borough Council for offering and arranging their time and energy.