3. Why London?
• Overburdened Sewer
System
• Thames Tunnel
Controversy
• Variety of Urban
Environments
Source: Google maps
Source: Google maps
Source: Google maps
4. Key Questions
1- Can literature on stormwater
runoff reduction be made
consistent?
2- How significant would the
runoff reduction be if SuDS
where widespread in London?
3- Is further study needed? If so,
in which areas/fields?
1-To critically appraise the
published literature on SuDS
runoff reduction.
2-To assess whether identifying
separate urban environments
aids literature appraisal.
3- To obtain a general overview
of the effect widespread SuDS
would have on different urban
environments.
Objectives
6. Urban Environments
• High population density
• Low % of open spaceTier A
• Low population density
• Low % of open spaceTier B
• High population density
• High % of open spaceTier C
• Low population density
• High % of open spaceTier D
• Low population density
• Very high % of open spaceTier E Source: Google maps
Source: Google maps
Source: Google maps
Source: Google maps
Source: Google maps
7. Urban Environments
• 85 Wards
• 22% of inner London areaTier A
• 46 Wards
• 22% of inner London areaTier B
• 21 Wards
• 6% of inner London areaTier C
• 49 Wards
• 31% of inner London areaTier D
• 21 Wards
• 19% of inner London areaTier E Source: Google maps
Source: Google maps
Source: Google maps
Source: Google maps
Source: Google maps
11. Specific SuDS - Green Roofs
Key Studies:
Stovin 2009: UK based
extensive roof study
34% Average based of 11
events with 80mm substrate.
Mentens et al. : Compilation of
German-based studies.
Extensive roofs data based of
121 annual performances.
Intensive roofs data based of
11 annual performances.
0
10
20
30
40
50
60
70
80
Minimum Maximum Median Average 80 mm
substrate
RunoffReduction(%)
Substrate scenarios
Green roof data selection
Mentens et
al._
Intensive
Mentens et
al._Extensive
Stovin
2009_Extens
ive
12. Specific SuDS - Permeable
Pavements
Key studies – Paved Surface runoff reduction
James and Thompson (1997): 39-62%
Pratt et al. (1995): 53-63%
Gilbert and Clausen (2006): 72%
Difficulties in Applying Permeable Pavements:
• Limited infiltration rate –useful in low intensity events but
can fail to perform in intense storms.
• Already partially implemented – adequate modeling will
require a street-by-street analysis.
• Intrusive and expensive to retrofit. – additionally will need
regular maintenance
• Limited load – different load capacities result in different
runoffs.
http://southcoastenergychallenge.org/blog/permeable-paving
http://www.google.es/imgres?um=1&hl=es&biw=1366&bih=589&tbm =isch&tbnid=Z2 foqn80YSyQ1M:&imgrefurl=http://greenvalues.cnt.org/national/&docid=N0Cf9l598Q4GxM&im gurl=http://greenvalues.cnt.org/nati onal/im ages/permeable_pavement.j pg&w=300&h=225&ei =6gWZUcmiL8Sk0AWCxoCoCA&zoom=1&ved=1t:3588,r:22 ,s:0,i:154&iact=rc
&dur=511&page=2&tbnh=166&tbnw=228&start=17&ndsp=16&tx=103&ty=73
13. Specific SuDS –Ground Infiltration
Wide variety of options: rain
gardens, soakaways, swales, ponds,
etc.
Area intensive – Will be applicable
in a significant manner for Tier C but
not for Tier A.
Deemed unsuitable for London
ground conditions. (Thames Water)
Roldin et al. (2012), Copenhagen-based
study:
“The selected case study combines many of the
worst possible conditions for infiltration”
Estimated a 10-30% annual runoff reduction
through widespread soakaways and swales.
(This being the ‘Realistic Scenario’)
http://www.buffalorising.com/2009/02/pushing-green-at-canal-side.html
http://greatecology.com/10-ways-low-impact-
development-reduce-swurp-footprint-2/
14. Tier A
Tools with greatest potential:
• Green roofs
• Permeable pavements (but suffer
severe retrofit limitations)
Estimated global runoff effect:
Green Roofs – 23% annual runoff
reduction respect to Tier’s total
rainfall.
Permeable pavements: impossible to
estimate due to limited information.
While Green roofs would provide
important benefits, in terms of runoff
reduction even ‘optimal’ retrofitting
wont have a significant enough
impact.
Source: Google maps
15. Tier C
Tools with greatest potential:
• Green roofs
• Permeable pavements (but suffer
severe retrofit limitations)
• Soakaways and Swales.
Estimated global runoff effect:
Green Roofs – 20% annual runoff
reduction respect to Tier’s total
rainfall.
Soakways/Swales – 1m3 of storage per
13m2 of impermeable surface, results
in 13,4% reduction of the annual
runoff.
SuDS runoff storage/attenuation would
bring relief to traditional CSO systems,
which would still be needed.
Minor disconnection scenarios might
be possible.
Source: Google maps
16. Tier B
0
10
20
30
40
50
60
70
80
90
25 to Per. -25 50 to P. -50
RunoffReduction(%)
Scenarios
Case Study in Putney Bridge, London
(Stovin et al. 2012)
Stovin et
al._December
Typical
Stovin et al._
October Typical
Stovin et al._
Annual typical
• 63% annual runoff reduction
• ~50% of impermeable surface
disconnection.
• Ideal scenario, very difficult to
implement in this Tier.
• Very vulnerable to intensive
storms.
CSO drainage will be needed.
However there is a large
potential for SuDS-based
attenuation which should be
explored during CSO design.
Source: Google maps
17. Tier D
0
20
40
60
80
100
120
25 to Per. -25 50 to P. -50
RunoffReduction(%)
Scenario
Case Study in Frogmore
(Stovin et al. 2012)
Stovin et
al._December
Typical
Stovin et al._
October Typical
Stovin et al._
Annual typical
Markurssen at al. & Villareal et
al. data coincides with Ashley
et al.
• 58% to 54% annual runoff
reduction
• Easier to implement in this
Tier
• Less vulnerable to intense
storms.
Suggests ample opportunity
for integrating SuDS into CSO
designs, reducing their
designed intake.
Source: Google maps
18. Tier E
0
10
20
30
40
50
25 to Per. -25 50 to P. -50
RunoffReduction(%)
Scenario
Case Study in West Putney
(Stovin et al. 2012) Stovin
et
al._Dec
ember
Typical
Stovin
et al._
Octob
er
Typical
Stovin
et al._
Annual
typical
• 34% annual runoff reduction
• However, Flow is remarkably
smaller to any other Tier
• Follows that vast open green area is
already having a huge impact.
• Design might accommodate rainfall
storage through ponds.
0
0.5
1
1.5
2
2.5
3
3.5
Existing -50
RunoffFlow(m3/s)
Scenarios
Flow Comparison
Tier E_October 2000
Tier E_Annual
Tier D_October 2000
Tier D_Annual
Tier B_October 2000
Tier B_Annual
SuDS should definitely be integrated
into CSO Design, the large open areas
should be explored as a way to
integrate large disconnection
scenarios.
19. Conclusion
Runoff reduction:
o Tier A: >23%
o Tier C: >33
o Tier B: 63%
o Tier D: 54-58%
o Tier E: 34%
Ideal Global scenario:
44.7% total annual reduction
More detailed studies are
needed in global SuDS
scenarios as a whole, with
emphasis on large population
density areas (Tiers A and C) http://www.google.com/imgres?um=1&sa=N&biw=1366&bih=665&hl=es&authuser=0&tbm=isch&tbnid=tyhcZg1klcVy7M:&imgrefurl=http://www.touri
st-destinations.net/2013/01/london-travel-guide.html&docid=J6v3nxqsyMYDXM&imgurl=http://3.bp.blogspot.com/-i83l-
2yiFRM/UOn56uDlQZI/AAAAAAAACBA/p4qK_ees5j8/s1600/london-.jpg&w=784&h=516&ei=RwGVUc-
FBMaR7AburIGYBQ&zoom=1&ved=1t:3588,r:61,s:0,i:352&iact=rc&dur=955&page=4&tbnh=178&tbnw=260&start=54&ndsp=20&tx=100&ty=94
