1. Commercial sites and the delivery
of sustainable drainage
ACO Technologies plc: Martin Fairley – Research Director
HR Wallingford: Bridget Woods Ballard – Principal Engineer

2. Content
• Commercial Urban application of SuDS – challenges
• Importance of stakeholder group – supermarket sector example
• Use of ‘hypothetical model’, objectives, results
• Recent academic studies
• Future sustainable drainage strategies for the commercial sector?
• Research imperatives

3. Commercial urban sites:
challenges & opportunities
Challenges:
•Existing dense urban infrastructure
•Limited infiltration (soils, contamination)
•Single property – drainage approved but not adopted
•Stormwater ‘intensive’
Opportunities:
•9000+ UK sites (larger grocery retail)
•Top 3 combined turnover >£112bn
•53p in every £1 spent is on food and beverage
•Commercial objectives & CSR
•Part of the community – sustainability leadership?

4. Impact of parking?
• Tippecanoe County, Indiana: parking lots make
up more than 6.57% of the total urban footprint
• ≈ 75% commercial
• area of parking lots exceeded the area of parks
in the city limits by a factor of three
The environmental and economic costs of sprawling parking lots in the United States:
Amélie Y. Davis a,c, Bryan C. Pijanowski a,∗, Kimberly Robinsona, Bernard Engel b

5. Commercial car
park characteristics
• Increase runoff and contaminant loadings to freshwater systems
• Contribute to urban heat island effect
• Biologically inert
• Maintenance sealant (PAH) impacts

6. Development of a
‘hypothetical’ model

7. Model constraints & objectives
Design constraints:
• Zero infiltration
• 1:60 gradient across site
• Minimum 2 treatment stages
• 1:100 year event managed on-site
Objective:
•To test SuDS in ‘commercial’ context
•To review potential economic/affordability implications
•To look at delivery and modelling challenges
•To engage the supermarket ‘giants’ in the debate
•To promote the consideration of future design options

8. Future: explore potential
for retro-fit

9. The Draft National
Standards / BS 8582
Infiltration, where possible
Interception
No runoff for 5mm rainfall
Peak flow control
1:1 year to greenfield/pre-development rate
1:100 year to greenfield/pre-development rate
Volume control
1:100 year 6 hour to greenfield/pre-development volume
Water quality
Minimum 2 treatment components for commercial sites

10. Interception delivery
Infiltration
Rainwater harvesting
(Y/D < 0.9, BS8515)
Green roof >50%
Permeable pavement
Vegetated systems
Assumptions?
4 X rule – vegetated surfaces
2+ X rule – PP + infiltration
1 X rule – PP no infiltration, green roof

11. Volume control delivery
Further infiltration
Further rainwater harvesting
Tight control of runoff volume
exceeding greenfield/pre-
development (LTS)
(2 l/s/ha max)

12. Conveyance to minimalist
vegetated SuDS
Benefits
•No loss of parking spaces
•Conventional car park surface construction
Limitations
•Non-compliant Interception?
•Treatment sufficiency?

13. Satisfying ‘interception’ rule
Benefits
•Conventional car park surface construction
•Compliant solution
Limitations
•Loss of parking spaces - £2000 / space / week
•Additional landscape maintenance

14. Permeable sub-base
Benefits
Conventional car park surface construction
•No loss of car park spaces
•Compliant solution
Limitations
•Interception compliance?
•Cost?

15. Modelling challenges
• Interception
• Treatment
• Complexity of multiple level flow controls, storage minimisation and optimisation

16. Urban runoff contaminants:
what are of
concern ?
• A Minimum Data Set of Water Quality
Parameters to Assess and Compare
Treatment Efficiency of Stormwater
Facilities
Simon Toft Ingvertsen,* Marina Bergen Jensen, and Jakob Magid

17. How are they most effectively
controlled?
…Results showed that about 99% of road-associated particles
(number concentrations) are smaller than 20 μm.
Characteristics of road sediment fractionated particles captured from paved surfaces, surface run-off and detention basinsM. Kayhanian ⁎, E.R.
McKenzie 1, J.E. Leatherbarrow 2, T.M. Young (2012)
•Fine particles play major roles in controlling the fate of metals
•In the US, most quality criteria for metals are in the dissolved form
•Drying process important for XOC’s
•Combined aerobic / anaerobic zones for nutrients
•Treatment train – that integrates sedimentation and filtration, probably most effective
(with some redundancy for robust control)
•Is it more cost effective to treat small events, and discharge larger ones without?
•Need for design to minimise re-suspension of particulates

18. Conclusions
• Compliance with draft Standards not significantly more costly ‘provided that Interception
can be met in an affordable way’
• Where even very limited infiltration can be mobilised, subsurface storage could
potentially be used to facilitate disposal of 5mm
• Green roof crucial to Interception delivery
• Detailing and modelling skills key to minimising impact of drainage requirements where
space is valuable
• R&D into understanding and appropriately mitigating environmental risk associated with
runoff from commercial car parking would be of great value
• And this requires understanding of the efficiency of vegetated components and
proprietary products in treating likely pollution levels