Case study:Castle Irwell Urban Wetland

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Location: 53° 30' 29", -2° 16' 11"
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Project overview

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Status Complete
Project web site
Themes Flood risk management, Habitat and biodiversity, Social benefits, Urban
Country England
Main contact forename Gary
Main contact surname Morris
Main contact user ID User:Gjmorris
Contact organisation Environment Agency
Contact organisation web site http://https://www.gov.uk/government/organisations/environment-agency
Partner organisations
Parent multi-site project

Case_study:River Irwell Restoration Project

This is a parent project
encompassing the following
projects
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Project summary

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There is a well recorded history of flooding in Salford from the River Irwell, with the most severe events occurring in 1866 and 1946 and more recently in 2008 & 2015. Therefore there was a need to improve the standard of flood protection from a 1 in 75 to a 1 in 100 year standard. The only remaining area of greenspace to accommodate such a scheme was on the Castle Irwell site. To undertake this innovative project the Environment Agency worked in partnership with Salford Council and University of Salford, to design and construct a new flood storage basin to better protect 1,900 homes and businesses, but also create a multifunctional recreational space including new urban wetland in heart of Salford. The site is set on a large meander loop of the River Irwell in an urban area of Lower Kersal just 2.8km from Manchester city centre. As a former recreation site, it was an oasis of green in a largely urban environment, but had limited wildlife value. Appraisal and design work started in January 2013 with construction beginning in 2015. The flood basin and wetland will be fully operational by June 2017 at a cost of approximately £9 million. Working with local community, the University of Salford, Salford City Council, the Environment Agency identified an opportunity to work together to use land owned by University and Council to create a new flood basin to help reduce flood risk to people and property just downstream, but also create a new urban wildlife asset in the heart of city, interlinking with neighbouring River Irwell local wildlife site and Kersal Dale Local Nature Reserve on opposite bank. Once the overall joint agreement for construction of new flood basin and wetland was agreed with all parties, and initial meetings with local community groups to seek their views, the Agency brought in the expertise of the Wildfowl and Wetlands Trust to help develop detailed designs and maintenance plan for new 5.5Ha urban wetland

Community involvement - Community consultation, Community Events, River open days; River Walks; Bioblitz event; Education events, School Tours.

Monitoring surveys and results

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The overall scheme has an integrated maintenance and management plan, while wetland has separate maintenance and management plan written by Wildfowl & Wetlands Trust and with prime focus of this being simplicity of management. With both plans integrated as part of site’s long term maintenance, this will ensure as the site develops and establishes, appropriate management will be conducted by agreed respective parties, to ensure in the long term the flood basin remains a functioning flood risk asset, but also an important new local wildlife and amenity resource for future. Fixed point photography overlooking the new wetland has been installed on neighbouring flats which will monitor the establishment of newly constructed scheme. The new wetland is also attracting interest from local monitoring groups, including Greater Manchester birders through Winter Wetland Bird Blitz organized by Greater Manchester Ecology Unit and results will be updated to the Greater Manchester Records Centre. The University of Salford are also keen to monitor the wetland as part of their future courses for environmental studies.

Lessons learnt

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Some of the issues faced as part of project was to show it was feasible to construct a new wetland within an Agency flood basin without undermining it’s integrity and primary function, and ensuring the wetland had sufficient water to support the varied priority wetland habitats sought. This was achieved by undertaking groundwater monitoring and ground investigations, with results fed back into design. Another essential element of the wetland design was to ensure that it would be relatively simple to manage, i.e., by ensuring good vehicular access, and ensuring new wetland habitats were easily maintainable by local conservation groups and council, and reduced risk of competition between wetland habitat types. The urban wetland is located in the lower Irwell; a catchment that has significant infestations of invasive non-native species. Therefore an invasive control programme was essential, and integrated as part of construction works. Also a long term monitoring and control programme will be adopted as part of overall capital scheme maintenance.


Image gallery


Aerial photo of wetland
Salford basin completed wetland.jpg

File:Castle Irwell FSB.pdf

File:Salford Scheme Wetland GA.pdf

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Catchment and subcatchment

Catchment

River basin district North West
River basin Upper Mersey

Subcatchment

River name Irwell / Man. Ship Canal (Kearsley to Irlam Locks)
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 134
134 m
0.134 km
13,400 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Suburban
Waterbody ID GB112069061450



Site

Name Castle Irwell, Salford
WFD water body codes GB112069061451
WFD (national) typology HMWB
WFD water body name Irwell (Croal to Irk)
Pre-project morphology
Reference morphology
Desired post project morphology no deterioration
Heavily modified water body Yes
National/international site designation
Local/regional site designations local wildlife site
Protected species present Yes
Invasive species present Yes
Species of interest Wintering wildfowl - golden eye, tufted duck, pochard
Dominant hydrology Groundwater
Dominant substrate Cobble
River corridor land use Urban
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) 2.3km
2,300 m
230,000 cm
Project started 2014/08/13
Works started 2015/03/11
Works completed
Project completed 2017/07/10
Total cost category 5000 - 10000 k€
Total cost (k€)
Benefit to cost ratio
Funding sources Environment Agency Grant in Aid, Government Growth funding, Salford Council

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

Supplementary funding information

Working with local community, the University of Salford, Salford City Council, the Environment Agency identified an opportunity to work together to use land owned by University and Council to create a new flood basin to help reduce flood risk to people and property just downstream, but also create a new urban wildlife asset in the heart of city.



Reasons for river restoration

Mitigation of a pressure
Hydromorphology
Biology
Physico-chemical
Other reasons for the project The main reason to construct scheme was to build new flood storage basin to improve standard of protection of downstream Salford and Manchester.


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor Introducing large woody debris, Floodplain reconnection, Floodplain creation, Buffer strips, Habitat creation
Planform / Channel pattern
Other
Non-structural measures
Management interventions Habitat management
Social measures (incl. engagement) Community consultation, Community Events, River open days, School Tours
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

Link Description

Supplementary Information

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