1. Developing a New Decision Support
Framework for Sustainable Drainage Design
Jo-fai
1,2,3,
Chow
1,
Savić
Dragan
2,
Fortune
David
Netsanet
2
Mebrate
and Zoran
1
Kapelan
Introduction
Challenges
Summary
The vulnerability of drainage systems and the
importance of flood risk management have
drawn increasing public attention following
major flood events around the globe.
Identifying the optimal combination of different
SuDS techniques with regard to performance,
social-environmental impact and cost:
• The number of possible SuDS combinations
can grow into hundreds and thousands
depending on site characteristics. The
traditional trial and error approach is not
suitable. More sophisticated search methods
based on computation intelligence such as
evolutionary optimisation is recommended.
• The proposed design will be checked and
evaluated by various parties throughout a
project cycle. It is important to provide a
framework for consistent evaluation.
The existing software tools are not sufficient for
sustainable drainage design as they lack the
emphasis on social impact and cost-benefit. We
are developing new software tools that will
allow drainage designers to determine optimal
combinations of SuDS efficiently and will enable
stakeholders to compare and evaluate best
trade-off between water quantity, quality,
amenity value and whole life costs.
Sustainable drainage systems (SuDS) have
been proposed as better alternatives to
conventional drainage systems. Compared to
traditional pipe and storage networks, SuDS
bring additional values such as treatment and
biodiversity to the development site.
Traditional Drainage Systems –
Conveyance & Storage
Sustainable Drainage Systems –
Source Control & Treatment
Figure 1 – examples of both conventional and sustainable
drainage systems.
SuDS in Drainage Models
Several drainage software packages have
already included SuDS modelling modules (e.g.
WinDes and XPSWMM). This allows users to
configure various SuDS components in their
drainage models and to run simulations in
order to determine the impact of different
SuDS techniques on flooding, water quality as
well as life cycle cost.
Porous car park
Swale
Decision Support Framework
A prototype decision support framework has
been developed to look at changes in hydraulic
performance (flow and storage), water quality
(pollutants concentration) and costs (capital
and operational expenditure) based on
different SuDS techniques and sizes. Indicators
for social impact will be implemented in the
next phase of the project. In order to search for
optimal solutions effectively, multi-objective
evolutionary optimisation functionality has
been implemented into this prototype using
GANetXL (Savić, 2011). Users can choose and
compare various drainage design options from
the Pareto front with different trade-off
between costs and system performance.
Prototype SuDS Treatment Train Optimisation Framework
Location 1
Location 2
Location 3
SuDS Technique
Physical Dimension 1
Physical Dimension 2
Physical Dimension 3
Inflitration % (Side)
Inflitration % (Base)
SuDS Technique
Physical Dimension 1
Physical Dimension 2
Physical Dimension 3
Inflitration % (Side)
Inflitration % (Base)
SuDS Technique
Physical Dimension 1
Physical Dimension 2
Physical Dimension 3
Inflitration % (Side)
Inflitration % (Base)
1 to 16
1 to 10
1 to 10
1 to 10
1 to 10
1 to 10
1 to 16
1 to 10
1 to 10
1 to 10
1 to 10
1 to 10
1 to 16
1 to 10
1 to 10
1 to 10
1 to 10
1 to 10
True Value Range
Min.
Max.
10
10
34
62
67
16
1
59
25
20
14
25
13
95
74
48
94
91
1
10
19
2
0
0
1
10
6
1
0
0
1
19
9
1
0
0
True Value
16
29
26
5
25
25
16
33
43
3
25
25
16
26
36
3
25
25
Description of KPI
Infiltration Basin
11.9
21.4
3.7
16.8%
4.0%
Pervious Pavements
23.6
15.3
1.0
3.5%
6.3%
Stormwater Wetlands
25.7
29.0
1.7
23.5%
22.8%
Optimisation Objectives and Penalty Function
Description of Optimisation Objective
Positive if the performance is better than defined targets
WLC (CAPEX, OPEX and Land Value)
Penalty as a results of contraints
Hydraulics
Costs
Penalty Cost
Type
Maximise
Minimise
Avoid
Graphical Outputs
Objective Value
-0.29%
719,093
40,951,441,427.47
Flow Rate at Various Stages of SuDS Treatment Train
Value
Peak Flow at Outlet (m3/s)
Total Storage Required (m3)
Time to Reach Peak Flow (min)
Total Nitrogen
Pollutant Total Phosphorus
Concentration Total Suspended Solids
at Outlet Hydrocarbons
(mg/L)
Heavy Metals
Faecal Coliforms
SuDS 1 WLC (£ at 2012 value)
Whole Life SuDS 2 WLC (£ at 2012 value)
SuDS 3 WLC (£ at 2012 value)
Cost
Total WLC (£ at 2012 value)
20
Inflow (Connection1)
18
2.73
6187
238
6.75
8.52
5.70
10.78
5.45
18.56
£175,620
£225,519
£317,955
£719,093
Hydraulics
Outflow (Connection 1) -> Inflow
(SuDS 1)
Outflow (SuDS1) -> Inflow
(Connection 2)
Outflow (Connection 2) -> Inflow
(SuDS 2)
Outflow (SuDS 2) -> Inflow
(Connection 3)
Outflow (Connection 3) -> Inflow
(SuDS 3)
Final Outflow at Outlet
16
14
Flow (m3/s)
Description
Pond
SuDS Key Performance Indicators
Optimsation Optimisation
Range
Value
12
10
8
6
4
2
Peak Flow Constraint
0
0
50
100
Other Measurements
Description of KPI
Value
SuDS 1 Total Surface Area (m2)
2
Surface Area SuDS 2 Total Surface Area (m2)
SuDS 3 Total Surface Area (m )
Total Surface Area (m2)
SuDS 1 Land Value (£ at 2012 value)
200
250
300
SuDS 2 Land Value (£ at 2012 value)
SuDS 3 Land Value (£ at 2012 value)
Total Land Value (£ at 2012 value)
Storage Required at Various Stages of SuDS Treatment Train
254
359
743
1,357
£31,803
£89,861
£130,084
£251,747
Land Value
150
Duration (Minutes)
35
Storage (Connection 1)
30
Storage (SuDS 1)
25
Volume (m3)
Optimisation Parameters, Range and True Values
Storage (Connection 2)
20
Storage (SuDS 2)
15
Storage (Connection 3)
10
Background Calculations - Optimisation Contraints and Penalty Costs
should be <=
should be <=
should be <=
should be <=
should be <=
should be <=
should be <=
should be <=
should be <=
is
is
is
Quality
1
Storage (TOTAL)
0
50
100
Muskingum
150
200
250
300
Duration (Minutes)
Pollutant Concentration (mg/L)
Cost Summary
£600,000
Total
Nitrogen
35
30
25
20
15
10
5
0
Heavy
Metals
Concentration
(Inlet)
Total
Phosphorus
Concentration
(Regulation
Targets)
Concentration
(Outlet)
£500,000
£400,000
£300,000
£200,000
£100,000
£0
Total
Suspended
Solids
Hydrocarbo
ns
SuDS1
CAPEX
Flow Rate at Various Stages of SuDS Treatment Train
SuDS2
OPEX (over 50 years)
Land Value
SuDS3
Whole Life Cost (over 50 years)
Inflow (Connection1)
20
18
Outflow (Connection 1) -> Inflow
(SuDS 1)
Outflow (SuDS1) -> Inflow
(Connection 2)
Outflow (Connection 2) -> Inflow
(SuDS 2)
Outflow (SuDS 2) -> Inflow
(Connection 3)
Outflow (Connection 3) -> Inflow
(SuDS 3)
Final Outflow at Outlet
18
12
10
8
6
4
Final Outflow
14
12
10
8
6
4
2
0
50
100
150
200
250
10
8
4
2
0
50
100
Duration (Minutes)
150
200
250
Peak Flow Constraint
0
300
0
50
100
Duration (Minutes)
Storage Required at Various Stages of SuDS Treatment Train
30
12
6
Peak Flow Constraint
0
300
Total Storage
30
150
200
250
300
Duration (Minutes)
Storage Required at Various Stages of SuDS Treatment Train
Storage (Connection 1)
Outflow (Connection 1) -> Inflow
(SuDS 1)
Outflow (SuDS1) -> Inflow
(Connection 2)
Outflow (Connection 2) -> Inflow
(SuDS 2)
Outflow (SuDS 2) -> Inflow
(Connection 3)
Outflow (Connection 3) -> Inflow
(SuDS 3)
Final Outflow at Outlet
Final Outflow
14
2
Peak Flow Constraint
0
Inflow (Connection1)
16
Flow (m3/s)
Final Outflow
14
16
Total Storage
Storage Required at Various Stages of SuDS Treatment Train
Storage (Connection 1)
30
Total Storage
Storage (Connection 1)
25
Storage (SuDS 1)
25
Storage (Connection 2)
20
Storage (Connection 2)
20
Storage (Connection 2)
15
Storage (SuDS 2)
15
Storage (SuDS 2)
15
Storage (SuDS 2)
10
Storage (Connection 3)
10
Storage (Connection 3)
10
Storage (Connection 3)
Storage (SuDS 3)
Storage (TOTAL)
0
0
50
100
150
200
250
5
0
300
Storage (SuDS 3)
50
100
Cost Summary
Total
Nitrogen
Heavy
Metals
£600,000
35
30
25
20
15
10
5
0
£500,000
Total
Phosphorus
Concentration
(Regulation
Targets)
Concentration
(Outlet)
Total
Suspended
Solids
200
250
0
300
Costs
Final Pollutant Conc.
Storage (TOTAL)
50
100
Heavy
Metals
£300,000
£200,000
£600,000
35
30
25
20
15
10
5
0
£500,000
Total
Phosphorus
£100,000
SuDS1
CAPEX
Concentration
(Regulation
Targets)
Concentration
(Outlet)
£0
OPEX (over 50 years)
SuDS2
Land Value
SuDS3
Whole Life Cost (over 50 years)
Cost Summary
Total
Nitrogen
Concentration
(Inlet)
Hydrocarbo
ns
Total
Suspended
Solids
150
200
250
300
Duration (Minutes)
Pollutant Concentration (mg/L)
£400,000
Storage (SuDS 1)
Storage (SuDS 3)
0
Duration (Minutes)
Pollutant Concentration (mg/L)
Concentration
(Inlet)
150
5
Storage (TOTAL)
0
Duration (Minutes)
Final Pollutant Conc.
Volume (m3)
Storage (SuDS 1)
20
5
Costs
Final Pollutant Conc.
Pollutant Concentration (mg/L)
Heavy
Metals
£300,000
£200,000
£600,000
35
30
25
20
15
10
5
0
£500,000
Concentration
(Inlet)
Total
Phosphorus
£100,000
SuDS1
CAPEX
Concentration
(Regulation
Targets)
Concentration
(Outlet)
£0
OPEX (over 50 years)
SuDS2
Land Value
SuDS3
Whole Life Cost (over 50 years)
Somewhere in between:
stakeholders to decide
what is the best trade-off
between two objectives.
Cost Summary
Total
Nitrogen
£400,000
Hydrocarbo
ns
The following tasks have been scheduled for
the second phase of the project:
• Quantifying and including more optimisation
objectives for social impact.
• Mutli-objective optimisation engine written in
MATLAB codes with main focus on fast and
parallel execution utilising both CPU and GPU.
• Full integration with new drainage design
software suites (e.g. XPDrainage) developed
by Micro Drainage and XP Solutions.
Key References
Flow Rate at Various Stages of SuDS Treatment Train
20
Outflow (Connection 1) -> Inflow
(SuDS 1)
Outflow (SuDS1) -> Inflow
(Connection 2)
Outflow (Connection 2) -> Inflow
(SuDS 2)
Outflow (SuDS 2) -> Inflow
(Connection 3)
Outflow (Connection 3) -> Inflow
(SuDS 3)
Final Outflow at Outlet
16
Future Development
Savić, D.A., Bicik J. and Morley M.S. (2011).
GANetXL: A DSS generator for multiobjective
optimisation of spreadsheet-based models,
Environmental Modelling & Software, Vol. 26,
551-561.
Flow Rate at Various Stages of SuDS Treatment Train
Inflow (Connection1)
18
Least-cost option: runoff
satisfies minimum design
requirement.
Figure 3 – Comparison of traditional and new approach.
Settings
Flow Calculation Method (Choose)
20
Hydrocarbo
ns
Amenity
Description of KPI
Hydraulics
Performance
Volume (m3)
New, Integrated Approach –
Balanced Emphasis
Quality
Amenity
9,358,715,432.56
23,744,725,994.91
0.00
0.00
0.00
0.00
7,848,000,000.00
0.00
No Constraint
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
No Constraint
No Constraint
No Constraint
40,951,441,427.47
0
Cost
25
Quantity
50
50
50
100
100
100
40
40
40
allowed
allowed
allowed
Penalty Cost
Storage (SuDS 3)
5
Figure 4 – prototyping a new decision support framework
for SuDS using Microsoft Excel spreadsheet.
Flow (m3/s)
In order to fill this gap, we decided to develop
additional software features that will put more
emphasis on social impact and will enable
stakeholders to maximise multiple benefits.
Quantity
2.5
5000
180
10
10
10
10
10
TOTAL Penalty Cost:
Yet the existing software modules are not
sufficient for sustainable drainage design as
they mostly focus on water quantity and
quality aspect. There is not enough emphasis
on the amenity value and cost-benefit analysis.
Traditional Approach – Main
Emphasis on Water Quantity
Level
Flow (m3/s)
Towards Sustainability
Contraints
should be <=
should be <=
should be >=
should be <=
should be <=
should be <=
should be <=
should be <=
Peak Flow at Outlet (m3/s)
Total Storage Required (m3)
Time to Reach Peak Flow (min.)
Total Nitrogen
Pollutant Total Phosphorus
Concentration Total Suspended Solids
at Outlet Hydrocarbons
Heavy Metals
(mg/L)
Faecal Coliforms
SuDS 1 - Dimension 1 (m)
SuDS 1 - Dimension 2 (m)
SuDS 1 - Dimension 3 (m)
SuDS 2 - Dimension 1 (m)
Physical
SuDS 2 - Dimension 1 (m)
Restrictions
SuDS 2 - Dimension 1 (m)
SuDS 3 - Dimension 1 (m)
SuDS 3 - Dimension 1 (m)
SuDS 3 - Dimension 1 (m)
Use of infiltration at location 1
Infiltration Use of infiltration at location 2
Use of infiltration at location 3
Hydraulics
Volume (m3)
Figure 2 – using Micro Drainage’s WinDes to model SuDS
for a typical site development drainage design.
Description of KPI
Other Controls
Figure 6 – our vision: balanced emphasis on water
quantity, quality and amenity for sustainable drainage
design with whole life costing analysis.
Total
Suspended
Solids
Costs
£400,000
£300,000
£200,000
£100,000
£0
SuDS1
CAPEX
OPEX (over 50 years)
SuDS2
Land Value
SuDS3
Whole Life Cost (over 50 years)
Most expensive option:
runoff is further reduced
at higher costs.
Figure 5 – exploring and comparing different design
options from optimisation Pareto front .
Contact the Author
The work presented here is part of author’s 4year industrial PhD research project. For more
information, please contact the author:
• Jo-fai Chow, STREAM Research Engineer
• E-mail: jo-fai.chow@microdrainage.co.uk
• Software by XP Solutions:
http://www.xpsolutions.com/software/
Centre for Water Systems, University of Exeter, United Kingdom (www.exeter.ac.uk/cws)
2 Micro Drainage (an XP Solutions company), United Kingdom (www.microdrainage.co.uk)
3 STREAM Industrial Doctorate Centre for the Water Sector, United Kingdom (www.stream-idc.net)
* Note: image courtesy of Micro Drainage and XP Solutions