Case study:River Tarrant Rehabilitation Project

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Location: 50° 53' 8.71" N, 2° 4' 58.11" W

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Project overview

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Status	Complete
Project web site
Themes	Environmental flows and water resources, Habitat and biodiversity, Water quality
Country	England
Main contact forename	Sarah
Main contact surname	Guest
Main contact user ID	User:RachelM
Contact organisation	Environment Agency
Contact organisation web site	http://www.gov.uk/government/organisations/environment-agency
Partner organisations
Parent multi-site project	Tarrant Monkton
This is a parent project encompassing the following projects	No

Photo and map showing location of works

Project summary

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A very uniform 500m section of the Tarrant, with extremely limited existing habitat diversity, was modified using a number of different techniques. The main work involved re-profiling the bed to create some variation in long and cross-section. No re-profiling of banks was undertaken, nor did the work involve any land-take. In the upstream sub-sections A-B live willow logs/stakes were also installed into the river or up the bank slopes in specific locations.

The physical modifications of re-distributing bed material around, installing log deflectors and occasional short stake to form pollards, was completed in just over two days. Work was completed within four days by wiring down firmly each of the installed willow logs and cutting pinning stakes back to log height.

Monitoring surveys and results

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Monitoring was completed before works to detirmine where works should be focused. Monitoring was also completed after the works to establish how successful the project had been.

At the very least periodic visits to the site should be made to help ensure grazing management is ideal for the conditions that develop. Repear photographs are recommended for the archive. Biological monitoring may be of limited value if pre-conditions have not been recorded.

Lessons learnt

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Providing cattle and sheep do not have access to the channel on a permanent basis, the created features of pools, runs and low-flow self-cleansing sections will not only be sustained, but improve over time. The hoped for growth of willow to form both habitat and landscape improvements has less chance of guaranteed success - the logs and stakes have been left far too long (over seven months at least) for ideal use. They have also been installed much later in the season than is the norm to encourage sprouting and rooting. When installed in the dormant period, or spring / early summer, sprouting is accompanied by rapid root growth - both will be limited now, and roots may not have sufficient dampness to succeed.

Keeping the banks fenced for two years will be ideal if any growth of willows is to reachits maximum potential; thereafter periodic grazing will help keep lower branches in check and be good for all other aspects of the marginal vegetation (as well as restore full grazing potential)

Image gallery

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Approximate locations for different rehabilitation measures

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district South West River basin Dorset Subcatchment River name TARRANT Area category 10 - 100 km² Area (km2) Maximum altitude category 200 - 500 m Maximum altitude (m) 263263 m <br />0.263 km <br />26,300 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Arable and Horticulture Waterbody ID GB108043016070 Other case studies in this subcatchment: Tarrant Monkton Rehabilitation Project Site Edit site Name WFD water body codes GB108043016070 WFD (national) typology WFD water body name TARRANT Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present No Invasive species present No Species of interest 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 Edit project background Reach length directly affected (m) 429.7429.7 m <br />0.43 km <br />42,970 cm <br /> Project started Works started 2013/07/22 Works completed 2013/07/25 Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources 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 Edit reasons for restoration Mitigation of a pressure Hydromorphology uniform channel Biology limited habitat diversity Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Bed reprofiling, Bank stabilisation Floodplain / River corridor Planform / Channel pattern Flow deflectors Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit 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 Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information