Case study:Tichborne River Restoration Project

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Location: 51° 4' 7", -1° 10' 57"
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Project overview

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Status Complete
Project web site
Themes Environmental flows and water resources, Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology, Monitoring, Social benefits, Water quality
Country England
Main contact forename Hannah
Main contact surname Barclay
Main contact user ID User:Hbarclay
Contact organisation Environment Agency SSD
Contact organisation web site http://www.gov.uk/government/organisations/environment-agency
Partner organisations Aquascience Ltd, Natural England, The Trustees of the Tichborne Estate
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Tichborne post restoration

Project summary

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The Environment Agency are part of the Defra Group who aim to protect and improve the environment. Locally, our commitment to improving our rivers led to the development of the Test & Itchen River Restoration Strategy which identified measures to improve the physical condition of the rivers. In this, the Tichborne Stream was identified as requiring significant improvement measures to restore the SSSI/SAC and bring it into favourable condition. At the same time, the Trustees of the Tichborne Estate expressed a desire to remove silt from an on-line lake within the grounds of Tichborne Park. The lake falls within the River Itchen Site of Special Scientific Interest (SSSI). Subsequently, Aquascience Ltd, a company specialised in river restoration, produced an appraisal of the proposal to remove silt to investigate whether there were opportunities to benefit the SSSI features of the site. Aquascience’s investigations quickly recognised that the lake was a dominant component in the SSSIs unfavourable status. Their recommendations were to investigate the removal of impoundments and restoration of the chalk stream channel thus providing an opportunity to create a sustainable landscape with improved ecology which would rectify the issues identified as causing the unfavourable status of the SSSI.

This river restoration project is located on the Cheriton Stream (SU5733930218), a tributary of the River Itchen. The primary objectives of the restoration project were to create a sustainable environment to move the SSSI unit towards favourable condition and enhance the condition of the Special Area of Conservation (SAC) status by:

• Restoring natural chalk stream characteristics, e.g. gradient, sinuosity, profile, substrate • Removing obstacles to fish passage • Reducing/eliminating the need for human intervention of water level/flow management • Maximising physical and ecological diversity and • Reconnecting the river with the floodplain and wider landscape.

With this in mind Aquascience were employed to design a scheme which reinstated the river channel to a natural course in the flood plain, utilising relict channels wherever possible. The designs ‘off-lined’ the lake converting it to fen meadow and reed-swamp, two habitats which are features of the SSSI. The designs excluded any form of water level management structures and sought an outcome which would function as naturally as possible within this environment. One fixed impoundment and two adjustable sluices were removed. Overall, within the site 825m of channel were either reinstated, created or were enhanced with restored gradient and/or increased flows. In addition, a further 640m of channel were preserved as backwater features with connection to the main channel. The project was delivered in Spring 2017. This involved significant movements of excavated materials on site, many of which were used to partially fill the lake to create fen meadow. Material movements were undertaken using a mono-rail system and tracked dumpers working on bog mats. These measures ensured minimal impact on the terrestrial SSSI features. Trial holes had identified that a deposit of angular gravel was present throughout the project area at the desired elevation, thus relict features were simply excavated within their perceived planform down to the existing gravel. Sediment mobilisation was carefully managed throughout the delivery using a combination of managing flows within site channels, sediment barriers and the pumping of turbid waters onto flood meadows. Plant rich sward was stockpiled and used in the final stages of the project to instate characteristic plant material to the new channel banks and the fen meadow constructed within the lake. Channel profile and dimensions were designed after locating suitable reference sites up and downstream. However, the excavator operators were encouraged to be somewhat creative in the execution in order to create physical diversity in channel size and bank gradients.

Aquascience is a small company specialising in river, lake and wetland creation, restoration and management. Previous notable projects have included the Heritage Lottery funded (HLF) Itchen Navigation Heritage Trail Project and the urban river restoration project, Market Harborough on behalf of the River Welland Rivers Trust. Their role was to carry out an options appraisal, feasibility assessment and creation of subsequent detailed designs for the preferred option. They were also the principal contractor for the project. They have been involved at every stage of the project. Natural England were integral in the development of the project through the development of the Test & Itchen River restoration Strategy. They were a key partner in fulfilling the obligations to improve the condition of the SSSIs which is a fundamental objective of the England Biodiversity Strategy. Trustees of the Tichborne Estate and the landowners, Anthony and Catherine Louden oversaw the entire construction phase of the project. They contributed extensively to the options appraisal and development of the designs. Their vision for the site was evident and their commitment to the project was cemented with their substantial financial contribution to the works.

The first visit to Tichborne occurred in January 2014 shortly after Aquascience had been asked to look at the lake with a view to removing silt. The Tichborne Lake and River Restoration Feasibility Study was finalised in March 2014. The Tichborne River Restoration Design Rationale was finalised in April 2014 The process of compiling detailed designs was undertaken in the Spring of 2016 after which the applications for the Environmental Permit and Planning Permission were submitted. The project was delivered between the end February and June 2017.

Monitoring surveys and results

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One of the main objectives of the project was to deliver on the actions identified in the Test & Itchen Strategy. One action was to restore the stretch through weir removal to restore natural function. This has been achieved. Our objectives to restore natural chalk stream characteristics, remove obstacles, reduce/eliminate the need for human intervention and reconnecting the river within the floodplain are clearly demonstrable. The impounding structure and associated sluices have been removed and a characteristic gradient and sediment transport has been restored. The lake sediments have been off-lined from the channel system removing the potential phosphate enrichment of the downstream watercourse.

The final objective was to maximise the physical and ecological diversity. Fish surveys, invertebrate and crayfish monitoring have been carried out along with HABSCORE surveys which were conducted in order to monitor the physical habitat and track the changes that will occur as the channel becomes more established over time.

Jonathan Cox has provided information for the appropriate assessment and an assessment of the SSSI and the protected species. We also had an extended phase 1 Ecological Appraisal carried out by the Hampshire & Isle of Wight Wildlife Trust (HIWWT). Prior to this project this section of the Cheriton Stream had been heavily modified leaving a legacy of impoverished channels, a silt filled lake and a river that was disconnected from its flood plain. Please see the current site plan and proposed site plan drawings attached with this application. A significant achievement was met when the owners of Tichborne Park agreed to a significant landscape change to the park surrounding their grade II listed home. The lake had become a burdensome feature that would require significant resources to maintain. Once the agreement of the owners had been secured the designers and stakeholders of this scheme commenced with designs that aimed to restore a naturally functioning river channel. Some constraints existed, perhaps the most significant being the owners request that the river flowed close to the house to compensate for the loss of the lake. This entailed a diversion away from the natural path of the river for a small section of the project area. In all other areas channels were either created, reinstated or restored so that a natural path was achieved. Surveys have revealed a site now dominated by wild brown trout with eel, lamprey, bullhead and stickleback also present. Invertebrate monitoring has shown an abundance of gammarus, mayfly, stonefly and caddisfly to name a few.

Unfortunately, with the untimely death of Anthony Louden, it was deemed to be inappropriate to cover the project widely in the press as the family were already under great pressure. The extent of the project’s achievements in restoring the natural state and functioning of the river system is illustrated in the following table: Revived Relic Channel (m) Restored Channel with increased flow volume (m) Channel with Restored Gradient (m) Channels preserved as backwaters / seasonal flow channels (m) Upstream meadow 180 190 185 280 Lower meadow 195 75 260

Total 375 265 185 540

Cloudbase Aerial Art, a specialist aerial media company, have successfully taken extensive before and after photographs through the use of drones.

Lessons learnt

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An early challenge for this project was to influence the owners to agree to a major landscape change within the Grade 2 listed site. This was achieved by presenting to them the advantages of creating a natural and sustainable river system and the abandonment of an unsustainable and ecologically impoverished ornamental lake. Lesson learnt - engage early with the landowner.

The next challenge was to deal with the constraints of the site including: • Funding • Heritage • Ecology / SSSI features • Planning / permitting process • The moat

The planning process added approximately 6 months to the project. We did not foresee the challenges made during this process nor the length of time it would take to bring the process to a close. Conditions imposed added time and costs to the project.

Funding presented a challenge as is always the case with restoration projects. Funding was sourced from the EA, NE and the Trustees of the Tichborne Estate.

The ornamental moat previously relied on an outflow from the lake. This project incorporated a major restoration of the moat to isolate it from the Cheriton Stream. The heritage and ecological requirements were dealt with by engaging suitably qualified consultants so that the designs were suitable to achieve the necessary permits and permissions.


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Catchment and subcatchment

Catchment

River basin district South East
River basin Test and Itchen

Subcatchment

River name River Itchen (Cheriton Stream)
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 169
169 m
0.169 km
16,900 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB107042016670



Site

Name Tichborne
WFD water body codes
WFD (national) typology
WFD water body name Bourne Rivulet & Cheriton Stream
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation
Local/regional site designations SSSI (Site of Special Scientific Interest), Area of Special Conservation Interest
Protected species present No
Invasive species present No
Species of interest Brown Trout, bullhead (Cottus gobio), white clawed crayfish (Austropotamobius pallipes)
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m) 375
375 m
0.375 km
37,500 cm
Project started January 2014
Works started
Works completed
Project completed
Total cost category 100 - 500 k€
Total cost (k€)
Benefit to cost ratio
Funding sources Environment Agency, Natural England, Trustees of the Tichborne Estate

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

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Supplementary Information

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