SUDS Retrofits in Scotland

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SUDS Retrofits in Scotland
Barbara Barbarito Environmental Quality
Advisor Scottish Water
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Summary

• SUDS retrofits in Dunfermline
• SUDS retrofits for Bathing Waters improvements
• Caw Burn wetland

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Retrofitting Sustainable Urban Drainage Systems-
Dunfermline Case Study

• Scottish Executive
• Scottish Water
• SEPA
• Hyder Consulting

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Desk based study investigating Dunfermline and
Iron Mill Bay
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Objectives

• Identify and rank in order of importance areas
  contributing to the flow in the sewer system
• Establish runoff generated by the subcatchment
  targeted for investigation
• Identify areas where SUDS could be retrofitted
• Assess costs and benefits of SUDS vs conventional
  approaches
• Quantify water quality improvements that can be
  provided by introducing SUDS

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Results

• Road and roof area contributes the highest
  percentage of runoff to the combined system.
• Suds retrofits in isolation will not solve
  problems with the sewerage system-need strategic
  approach.

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SUDS Retrofit Research Project Ayrshire study

• Scottish Executive
• Scottish water
• SEPA
• WS Atkins

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Aim
To pilot SUDS techniques to minimise CSO spills
impacting onto identified bathing waters by
limiting the entry of surface water into the
combined sewer system.
Study area Ayrshire
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Objectives

• Identify sites suitable for retrofitting SUDS
  facilities
• Design and construct SUD schemes
• Undertake pre and post construction monitoring
• Compare the cost and benefit of the constructed
  scheme to conventional alternatives
• Develop methodologies for the adoption of SUDS
  retrofitting, to assist the incorporation of
  retrofitting into Water Industry capital
  investment programmes

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Method
Phase 1 Site identification, feasibility and
selection of sites for SUDS implementation
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Method
Phase 2 Detailed design, construction,
monitoring, cost comparison, reporting

• Irvine industrial estate - combination of
  conventional drainage network and feature pond
• Girvan residential area - filter drains to
  intercept land and roads drainage, with
  underground infiltration device.

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Results

• Retrofitting in isolated areas across a given
  catchment is unlikely to significantly reduce the
  frequency and volume of sewage discharges to
  receiving waters
• SUDS may be retrofitted for similar costs to
  those estimated for conventional solutions.
• Retrofit SUDS can offer longer term benefits in
  comparison to conventional practice, through
  reduced maintenance and operational expenditure.

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Caw Burn Wetland Catchment Improvements (Stage
1)

• SEPA
• Scottish Water
• University of Edinburgh (Dr Kate Heal Dr Miklas
  Scholtz)
• Stirling University (Dr Nigel Willby)

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Caw Burn Wetland
Constructed in 1996 to treat diffuse pollution
entering the Caw Burn (West Lothian) from the
Houston Industrial Estate, Livingston
Overflow to SUDS
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SUD system
The system includes a main settlement pond and a
vegetated overland flow zone (wetland)
The flow enters the pond through a culvert (A
891 m2 d60 mm)
Is then directed to the wetland (A 4060 m2
d800 mm)
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Benefits

• Effective in removing sediments, oil, detergents
  and other pollutants
• Increase in diversity of aquatic life in 2Km of
  Caw Burn downstream
• Caw Burn class improved from River Quality Class
  D (seriously polluted) to C (poor)

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Problems
System is considerably undersized
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Problems ..cont

• 25 of pond volume has been in filled by
  sediments since construction reduction in water
  retention time
• Preferential flow and short circuiting
• Evidence of increased erosion over time
• Algae also appear to increase

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Proposed options
Likely to raise water quality to class B

• Flooding of entire valley floor
• Construction of additional offline SUDS

• Repair gaps in hearth bank where short circuits
  occur
• Block preferential flow pathways
• Remove sediments from settlement pond

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For More Info please contact Barbara.Barbarito_at_sc
ottishwater.co.uk Bess.Homer_at_scottishwater.co.uk