Bossington Test

Project background

In 2006 and 2010 Natural England (NE) confirmed that the river Test was failing its SSSI designation and was duly classified as being in ‘unfavourable condition’. An Environment Agency walkover survey followed in 2012, from ‘top to bottom’ of the river Test catchment, as part of its Test & Itchen river restoration strategy. Its purpose was to identify priority locations for restoration. All six of the Bossington estate reaches were subsequently prioritised due to a number of key criteria including historic weir structures providing a major impediment to natural flows, fish passage, heavy sedimentation and the failure of key plant and invertebrate species such as Watercrowsfoot (Ranunculus Spp) and Baetid invertebrates.

During May 2012 Bossington estate approached chalk stream restoration specialist Simon Cain of Cain Bio-engineering Ltd. (CBE) to discuss these concerns about habitat deterioration. The company was subsequently commissioned to survey and prepare restoration designs for all six beats on behalf of the Bossington Estate/Environment Agency partnership, with a view to implementing those designs in a series of phased projects.

To date and in collaboration with EA’s Test & Itchen project officer, Heb Leman and Estate Trustee/Farm Manager William Buckley, Cain Bio-engineering has now delivered two of the six projects with a further two, the House and Home beats, currently underway as a joint project. The ‘House & Home’ beat restorations are the focus of today’s site visit and the guided tour will provide T&I members with a unique public viewing of a major river restoration project in full swing.

We hope you enjoy reading about this ground-breaking project.

William Buckley, Trustee & Estate Manager had this to say:

“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”

Project Brief

Project description: This 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, an 800-metre 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. SO20 6LT

Historical impacts on the riverine environment: Understanding the historical context of these weirs and the associated environmental damage, was key to informing the solution. The legacy of sub-optimal flow impacts from weir impoundments dates to the mediaeval floated water meadow system, an ingenious irrigation system involving the passage of flowing river water over an intricate arrangement of ridges and furrows to enhance winter grass and hay production. The ‘drowning’ practice was finally abandoned during the early 20th Century. Whilst the original purpose and vintage of ‘Home weirs’ installation (and longevity of the now-defunct Bossington water meadow system) is surmised, the weirs and their impounded flows appear to have been adapted to power an early (Victorian?) hydropower-scheme and most recently – up until 2017- were used to divert elevated river flows into a ‘perched’ trout-rearing stew pond. Suffice to say, the profoundly detrimental impact of impounded, canal-like flows on the river habitat at this location, meant that both weirs and the stew pond had to go.

The following historical activities added further to the degradation at this location;

  • WWII Channel dredging for anti-tank defences and/or
  • Post-war bed dredging and lowering of the water table for arable farming and ‘improved’ lowland grazing.
  • ‘Bunding’ of the impounded (perched) watercourse to prevent inundation of its natural floodplain during high flows.
  • Habitat degradation associated with, sub-optimal flow velocities including deposition of a heavy sediment load and high Biochemical Oxygen Demand (BOD) resulting from algal blooms and Phosphate-related eutrophication.

Key work & services provided:

The Bossington Estate client requested a design/build service to include:

  • An initial consultancy site assessment, detailed Topographic survey and outline detailed design leading to;
  • Submission of Environmental Protection Regulation (EPR) consent documents and associated consultation with Environment Agency (EA)
  • Provision 0f consented detailed designs including Risk Assessments, Method Statement, Protected Species surveys and detailed cost analysis.
  • Project delivery – Including detailed site supervision, on-site technical direction and client reporting throughout the two-month project delivery period.
  • Post-project monitoring including assistance with planting operations – Bankside margins and instream Macrophyte ‘weeds’ – Water parsnip, Ranunculus, & Starwort.

Work/Solution

The key project objective was to return the linear, over-deep, impounded, slow-flowing and sediment-filled channel to a free-flowing state over a shallow, letterbox-shaped, gravel-bed profile. Following weir removal, this was achieved by in-filling the dredged ‘U’-shaped cavity with ca. 4,000 tonnes of ‘as dug’ gravel to reinstate the 1:400m gradient through a series of meanders.  The new channel, with flows streaming down the enhanced gradient, was then spot-treated with ca.1,500 tonnes of gravel using a variety of techniques to create a varied bed morphology and to equitably distribute ‘fluvial energy’ between, around and over a series of inside-meander deflectors, pools, riffles, glides and ‘pocket’ water. These techniques are illustrated throughout the report.

For ease of reference the following description of ‘how we built it’ conforms to the route shown in the Test & Itchen Association’s site visitors guide below. Points 1 to 11 highlight key features of interest throughout the restoration site and provide a detailed insight into all aspects of works undertaken with images showing the river status before, during and immediately after project completion.

Fig 1. T&I project site map with key points of interest

We will be providing further detail on the 11 key points of interest. To discover more about this extensive restoration project, click on the highlighted chapters below;

  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 ‘House Beat’ weir structures
  9. ‘Home beat’ D/S Weir pool & Riffle
  10. Nursery side stream
  11. ‘Home beat’ to Bailey bridge

 

Team Profiles

William Buckley is the managing trustee for Bossington Estate and has run the Estate and fishery since 2010. The Estate has 2.5 miles of double bank fishing on the main River Test, comprising 7 beats, and 2 miles of the Wallop Brook tributary.  William recognised that remedial work was urgently needed to reverse historic impacts on the rivers ecology, fish habitat, morphology and hydrology to ensure that Bossington Estate would continue to offer the very best chalk stream fishing for generations to come. In 2011 William engaged Simon Cain of Cain Bio-Engineering to work with the Estate to undertake an assessment and restoration of all the Bossington Test beats. Work has now been completed on two thirds of the fishery following the recent removal of Home Beat’s double weir system. This, the most ambitious project to date, enabled the combined restoration of the adjoining House and Home beats, together with the creation of a dedicated 200m spawning and nursery stream for wild trout and salmon.

Heb Leman is the Test & Itchen (T&I) Restoration Strategy Project Officer for the local Environment Agency (EA) Fisheries, Biodiversity and Geomorphology Team based in Romsey. Heb has worked in T&I for over 20yrs, first as a Fisheries Officer, then as the Fisheries Technical Specialist and since 2012, as the Project Officer for the T&I Restoration Strategy, a joint initiative between the EA and Natural England (NE) with the aim of working collaboratively with land owners to restore the rivers Test and Itchen. The T&I SSSI’s are currently classified as being in unfavourable condition. The aim of the Strategy is to enhance, were necessary, the habitat in both rivers to encourage chalk stream flora and fauna to flourish so that both rivers can be classified as being in favourable condition. To date the Strategy has worked with over twenty owners for the benefit of these two world-famous chalk rivers. The ‘Home Beat’ weir removal and 800m river restoration at Test Bossington is EA & EN’s largest and most ambitious collaborative project to date.

Simon Cain is an award-winning aquatic bio-engineer and river restoration specialist who pioneered catchment-scale chalk stream restoration on the Hampshire Avon during the early 1980’s. Over the past 35 years his Hampshire-based company, Cain Bio-engineering, has delivered habitat-focussed projects on all the key chalk stream catchments including a 7 km restoration of the river Nar in Norfolk. Recent projects include the restoration of a failing dam, lake restoration and stream diversion for the Defence & National Rehabilitation Centre (DNRC), two extensive Mill leat systems with river habitat restorations on the river Itchen and large-scale inter-tidal sea defences using innovative sediment traps. Current projects include re-alignment of the river Mersey to protect threatened infrastructure for a national utility, and a major design and consultancy assignment for an international environmental agency in America. The Bossington weir project is his most notable contribution to the river Test restoration strategy to date.