Bossington Revisited

14 September 2021

Bossington Revisited

“Yet another skilfully executed project from Simon Cain and his team at Cain Bio-Engineering.  Cain Bio-Engineering not only delivered everything we had hoped for but exceeded many of our expectations on the project. The partnership between Cain Bio-Engineering, the Environment Agency and Bossington Estate has now delivered three restoration projects in under five years. Two-thirds of the River Test beats at Bossington have been returned to a favourable condition.  Special thanks to Simon Cain and Heb Leman from the EA for this amazing legacy to the Estate.”
William Buckley Bossington Estate Managing Trustee & Estate Manager

This was, and still is, a ground-breaking, catchment-scale river restoration project on the middle Test centred around the removal of a sizeable and historic double weir installation. Following its removal, a 900-metre double bank length of degraded and sediment-filled chalk stream habitat was restored on the ‘House’ & ‘Home’ beats, up and downstream of the old weir location. The project included the restoration of a derelict 200m side channel to create a salmon & wild trout nursery on the world-renowned Bossington Estate Trout Fishery in the village of Houghton near Stockbridge, Hampshire.

Understanding the historical context of these weirs and the associated environmental damage was key to informing the solution. Please use the following links below to discover more about the scale and complexity of the Bossington Test reborn project.

  1. ‘House beat’ – R/H branch (Bossington mill race d/s to Wallop brook confluence)
  2. ‘House beat’ L/H branch – (Upper reach to top boundary)
  3. Gravel extraction site
  4. ‘House beat’ L/H branch (bottom reach to confluence)
  5. Pipe bridge crossing – Upper ‘House Beat’
  6. ‘House beat’ Central
  7. ‘Home beat’ U/S Weir pool & Fishing hut
  8. Double ‘Home Beat’ weir structures
  9. ‘Home beat’ D/S Weir pool & Riffle
  10. Nursery side stream
  11. ‘Home beat’ to Bailey bridge
  12. Ecological monitoring
  13. Native planting of margins and in-stream macrophytes

The Results

The prospect of salmon spawning within weeks of major river surgery was a tall order given that previous spawning attempts in the sedimented channel would have been remote, if not physically impossible in the pre-restoration reach. This was due to decades of vast silt deposits and almost total lack of clean spawning gravel right the way up to the top project boundary. Project completion was therefore accompanied by a liberal dose of ‘hope’ based on the principle that ‘If you mend it, they will come’.

The following post-restoration update is primarily a visual one, based on images taken during several return site visits dating from January 2018 through to September 2019. The last image was taken towards the end of a successful client fishing day on the restored beat.

April 2019 – Upper house beat showing project top boundary 16 months after restoration. Numerous wild trout redds were observed here.

April 2019 – Ranunculus crowns already growing profusely in the new river gravels. Flow velocity is key to stimulating healthy weeds.

April 2019 – Detail of the developing inside meander wetland habitat, essential to swim-up fry, brook lamprey and numerous invertebrate species.

April 2019 – Overhead aerial view detailing the use of live willow boughs to create a sedimented inside meander. The outside bend was excavated to compliment this installation in what was previously a linear channel.

May 2019 – View of the restored reach.

April 2019 – Spot the redd! In January 2018, just three weeks following project completion, a hen salmon was observed spawning in the newly dressed gravel bed, centre image.

April 2019 – Detail of salmon redd seen in the photo above. The same site was re-visited the following year with a new redd cut immediately adjacent to the one above.

April 2019 – General view of the confluence showing the restored LH salmon-spawning branch (right of shot) with its double meander sequence and use of fallen tree deflectors to create inside bend sediment traps.

NB: The RH Wallop Brook branch (left of shot) was originally scheduled for similar restoration treatment. This was abandoned at the EPR consenting stage due to EA/NE concerns that creation of a trackway through the woodland to deliver gravel to water’s edge, would damage SSSI interests. The Wallop Brook reach therefore provides a useful ‘Control’ by way of comparison with the adjacent restored channel.

House Beat – Main Channel

April 2019 – Confluence pool d/s to Pipe Bridge Riffle – Significant flow velocities were generated here following the upstream works. These were baffled (attenuated) by the creation of the substantial Pipe Bridge gravel Riffle seen the bottom centre of the image. Concerns were nevertheless raised by the estate keeper regarding the forces generated by these surcharged flows and specifically regarding the hostile environment for stockfish. It is interesting to note the profusion of Ranunculus seen at this location. This was also the location where significant numbers of salmon parr were recorded by EA’s electrofishing team during late summer 2019.

2018 EA Electro-fishing report detailing salmon parr results on ‘House Beat’

The graph compares the catches of salmon parr at all of the Catch Per Unit Effort (CPUE) surveys that we conducted on the Test & Itchen in the summer of 2018: the sites are set out from upstream to downstream, (left to right on the graph). One site on the Itchen did trump Bossington, but only just!
Our CPUE survey method is as follows:

  • One anode
  • One dip net
  • “E-Fish” battery-powered backpack electric fishing unit (typically 120v, 40hz, 10% pulse width for chalk streams)
  • 5-minutes of fishing in upstream direction over suitable salmon parr habitat (built-in timer on a backpack)
  • 75m distance fished
  • Anode swept left & right across a two-metre wide transect
  • Pros: well-suited to wide, fast, weedy chalk stream habitats where quantitative sampling impossible; a large number of samples can be completed in short time, giving dense geographical coverage; consistent methodology allows comparison between sites & years
  • Cons: only semi-quantitative, population estimate cannot be made

“I certainly didn’t expect it to yield more parr than anywhere else on the Test or Itchen this year. Really brings home the message; “Build it and they will come!”  Clearly, an inspired bit of river mending.”
Dom Longley – Senior Environmental Monitoring Officer (Analysis & Reporting)

April 2019 – The image shows fast flows discharge over pipe bridge riffle into the central House Beat. Now that Ranunculus has bulked out the flows, the oxygenated riffle pool is a prime holding area for both stocked and wild fish. They are challenging for the visiting angler to see due to the choppy surface conditions, but the fish are there and in significant numbers. This is also a prime location for Blue Winged Olive hatches. On-going monitoring of invertebrates is underway.

October 2017 (left) and the same reach April 2019 (right).

Home Beat Pool & Fishing Hut

April 2019 – Downstream view of Home beat pool showing the new bank configuration following the double weir removal. Whilst several hundred tonnes of toxic sediment were/was? removed, the over-deep bed was then re-claimed with a similar volume of gravel such that the attractive, albeit shallower, pool feature has been maintained. The embankments were designed to ensure an equitable flow split between the main river whilst providing an ideal open amenity area for guest anglers and an ideal spot for fly fishing tuition.

April 2019 – Upstream view of Home Beat pool following weir removal. A substantial gravel riffle was placed at its downstream end to optimise the pool feature. Ranunculus growth has been prolific.

May 2019 – Restored weir pool with the famous thatched fishing hut.

Nursery stream

Prior to the secondary and smaller weir removal, nursery stream was a forgotten, over shaded and neglected backwater flood relief channel with minimal fishing or conservation interest to the main commercial activities of the estate. The prospect of weir removal and the re-introduction of perennial flows provided a unique opportunity to create nature-like wildlife habitat.

December 2015 – Downstream view of Nursery stream before weir removal and channel restoration

November 2017 – Following weir removal with re-instated flows in the over-wide channel. An extensive tree-thinning exercise was also undertaken to allow light back into the channel.

April 2019 – The restored channel seen here 6 months after restoration. Bankside trees were simply felled across the channel and left in situ to mimic natural tree fall in a couple of locations. Because the intention was to create an unconstrained natural habitat, it allowed a free hand to do just that and without the constraint of having to provide open water for ease of angling. Ca 100 tonnes of gravel was transported in across the main river on 10-tonne dumpers and distributed throughout the over-wide channel to create a series of meanders, pools and spawning riffles.

The following images provide a snapshot of the restored ‘Nature-like’ Nursery Stream six months following restoration works.

May 2019 – Downstream view from the off-take hatch pool.

May 2019 – Downstream view from gravel riffle to the first treefall, seven months after restoration, with encroaching marginal vegetation pinching flows to enhance the new meander sequence.

May 2019 – Upstream view to treefall feature seen in photo 16 showing channel development. Pinched flows are under-cutting live willow boughs, placed at low level on the true RH bank to create a deep mid-channel scour hole beneath the overhanging tree cover. Note the way in which impeded central channel flows beneath the fallen trees is causing a deflected LH bank flow path hard up under the embankment beneath the base of the tree trunks. This is a good example of ‘Natural process’ when rivers are left to do their own thing.

May 2019 – Upstream view of the downstream end of Nursery Stream, shortly before its main-river confluence. Gravels were added throughout to ensure a ‘push’ of water to attract salmonids into this inviting backwater habitat.

May 2019 –Recovering classic dry fly beat

“The Environment Agency through the ‘Test and Itchen River Restoration Strategy’ was delighted with the finished collaborative restoration at Bossington Estate in 2017. Thanks to the forward-thinking attitude of Bossington Estate, Cain Bioengineering has been able to transform and return an impounded, canal-like section of the River Test into a free-flowing Chalk river as it deserves to be. Over time the increased velocities and light will encourage and provide perfect habitat for a variety of Chalk stream flora and fauna for the benefit of the SSSI and the estate”
Heb Leman – Test and Itchen Restoration Strategy Project Officer, Solent Area Fisheries, Biodiversity and Geomorphology team.

‘If you mend it they will come’.

If you would like to read further about the project please click here for the Bossington Reborn project report.