13/07/20091 River restoration design and construction - Celine Gallay

Our experience in river restoration design and construction for the Environment Agency Céline Gallay

Senior Engineer

Halcrow Group Ltd

Gallayc@halcrow.com

2 River restoration design and construction - Celine Gallay13/07/2009

Introduction

I will discuss the following topics:

• Understanding the design and information on how to restore 

• Landowner engagement, constraints and buy-in into the design

• Our experience of framework contractors in river restoration

• The need for flexibility in the design and adequate supervision

• How to program the works for the low flow period

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Understanding the design and information on how to restore• Simple design with two categories: structures and in-river

restoration works

• Structures: balance design life, Eurocode standards / structures similar to historical structures

• Conflict between different protected species in different channels: the client must prioritise species at an early stage

• RRC manuals: good source of information on restoration techniques

• More information on ideal flow conditions to provide good habitats for different species would be useful

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Landowner engagement, constraints and buy-in into the design

• Consultation of landowner is required at the earliest opportunity ideally with outline design

• Good to have a showcase project. E.g. Barton Court on Kennet

• Convincing the landowner that fish will not be lost due to removal of weed rack

• Strategic River Avon Restoration : removal of weirs/hydroelectric schemes

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Our experience of framework contractors in river restoration

• Works have been delivered through the NCF or the Minor Works Framework

• Competent framework Contractors to build structures but some lack experience in river restoration techniques

• Wylye: river restoration works were carried out by a fencing sub-contractor

• Avington: stone riffle rolled to a flat finish

• Lessons learnt: during tender process, a client should request CVs of key construction staff for the works, which demonstrate past experience in river restoration

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The need for flexibility in the design and adequate supervision

• Flexible design to accommodate protected species. E.g. water voles at Avington

• Not an exact science – design needs to be adapted on site

• Importance of Environmental Clerk of Works on site and a site supervisor (part-time basis)

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How to program the works for the low flow period

• Best period from mid-July to mid-October during the low flow season

• Budget allocated for the whole project in the same financial year (April to March) resulting in a great challenge to have works on site before September.

• Programme of works was developed with the Environment Agency SW Blandford office:

• Reaches of the River Avon and its tributaries in need of River Restoration were identified and prioritised, with a costed action plan taking into account the likely landowner collaboration,

• A PAR was prepared for a 5 year programme of works allowing design during a financial year and construction during the summer of next financial year,

• This approach also allows the packaging of projects and hence cost savings.

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Example of strategic River Restoration Project (River Avon)

5-year programme

2011-12 2012-13 2013-14 2014-15 2015-16

Package yr 1 yr 2 yr 3 yr 4 yr 5

1(a) - iStructural work - simple (designs ongoing) Construct

1(a) - ii Structural work - simple Appraise & design Construct

1(b) Structural work - complex Negotiate & appraise Design Construct

2(a) - i In-channel & riparian work - simple Construct

2(b) - iIn-channel & riparian work - complex Negotiate & appraise Design Construct

3 (a) - iiCollaborative - simple 'quick win' partnerships Construct

3 (b) - iiComplex collaborative - complex partnerships

Negotiate/build partnerships & appraise Design Construct

Logical sequence of programme

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Conclusion

• Additional information on ideal flow conditions for protected species would be useful

• Early landowner engagement is essential

• Selected EA framework contractor for tenders should demonstrate past experience in river restoration

• Flexible design and adequate site supervision are required

• A more strategic catchment base approach to river restoration should be considered to provide better value for money