Case study:River Tarrant Rehabilitation Project

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Location: 50° 53' 9", -2° 4' 58"
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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


Approximate locations for different rehabilitation measures
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Catchment and 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) 263
263 m
0.263 km
26,300 cm
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

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

Reach length directly affected (m) 429.7
429.7 m
0.43 km
42,970 cm
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

Mitigation of a pressure
Hydromorphology uniform channel
Biology limited habitat diversity
Physico-chemical
Other reasons for the project


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

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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