developing a new decision support framework for sustainable drainage design

Developing a New Decision Support Framework for Sustainable Drainage Design

Jo-fai Chow1,2,3, Dragan Savić1, David Fortune2, Netsanet Mebrate2 and Zoran Kapelan1

Introduction The vulnerability of drainage systems and the importance of flood risk management have drawn increasing public attention following major flood events around the globe.

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.

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.

Summary 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.

Key References 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.

Challenges

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.

1 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

Decision Support Framework

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.

Future Development 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.

Prototype SuDS Treatment Train Optimisation Framework

Optimisation Parameters, Range and True Values SuDS Key Performance Indicators Graphical Outputs

Min. Max. Description of KPI Value

SuDS Technique 1 to 16 10 1 16 Infiltration Basin Peak Flow at Outlet (m3/s) 2.73

Physical Dimension 1 1 to 10 10 10 29 11.9 Total Storage Required (m3) 6187

Physical Dimension 2 1 to 10 34 19 26 21.4 Time to Reach Peak Flow (min) 238

Physical Dimension 3 1 to 10 62 2 5 3.7 Total Nitrogen 6.75

Inflitration % (Side) 1 to 10 67 0 25 16.8% Total Phosphorus 8.52

Inflitration % (Base) 1 to 10 16 0 25 4.0% Total Suspended Solids 5.70

SuDS Technique 1 to 16 1 1 16 Pervious Pavements Hydrocarbons 10.78

Physical Dimension 1 1 to 10 59 10 33 23.6 Heavy Metals 5.45

Physical Dimension 2 1 to 10 25 6 43 15.3 Faecal Coliforms 18.56

Physical Dimension 3 1 to 10 20 1 3 1.0 SuDS 1 WLC (£ at 2012 value) £175,620

Inflitration % (Side) 1 to 10 14 0 25 3.5% SuDS 2 WLC (£ at 2012 value) £225,519

Inflitration % (Base) 1 to 10 25 0 25 6.3% SuDS 3 WLC (£ at 2012 value) £317,955

SuDS Technique 1 to 16 13 1 16 Stormwater Wetlands Total WLC (£ at 2012 value) £719,093

Physical Dimension 1 1 to 10 95 19 26 25.7

Physical Dimension 2 1 to 10 74 9 36 29.0 Other MeasurementsPhysical Dimension 3 1 to 10 48 1 3 1.7

Inflitration % (Side) 1 to 10 94 0 25 23.5% Description of KPI ValueInflitration % (Base) 1 to 10 91 0 25 22.8% SuDS 1 Total Surface Area (m2) 254

SuDS 2 Total Surface Area (m2) 359

Optimisation Objectives and Penalty Function SuDS 3 Total Surface Area (m2) 743

Total Surface Area (m2) 1,357

Type Objective Value SuDS 1 Land Value (£ at 2012 value) £31,803

Hydraulics Maximise -0.29% SuDS 2 Land Value (£ at 2012 value) £89,861

Costs Minimise 719,093 SuDS 3 Land Value (£ at 2012 value) £130,084

Penalty Cost Avoid 40,951,441,427.47 Total Land Value (£ at 2012 value) £251,747

Background Calculations - Optimisation Contraints and Penalty Costs Other Controls

Level Penalty Cost Description of KPI Settings

2.5 9,358,715,432.56 Hydraulics Flow Calculation Method (Choose) Muskingum

5000 23,744,725,994.91

180 0.00

10 0.00

10 0.00

10 0.00

10 7,848,000,000.00

10 0.00

No Constraint

50 0.00

50 0.00

50 0.00

100 0.00

100 0.00

100 0.00

40 0.00

40 0.00

40 0.00

allowed No Constraint



40,951,441,427.47

Hydraulics

Land Value

Pollutant

Concentration

at Outlet

(mg/L)

Whole Life

Cost

Location 1

True Value RangeDescription

Optimsation

Range

Optimisation

Value

ContraintsDescription of KPI

True Value

SuDS 1 - Dimension 2 (m)

Total Suspended Solids

Hydrocarbons


should be <=

should be <=

should be <=

should be <=

should be <=

should be <=

Faecal Coliforms

should be <=

HydraulicsPeak Flow at Outlet (m3/s)

Total Storage Required (m3)Time to Reach Peak Flow (min.)

SuDS 3 - Dimension 1 (m) should be <=

Use of infiltration at location 1 is

Location 2

Location 3




should be <=

should be <=

should be <=

Heavy Metals

Description of Optimisation Objective

Positive if the performance is better than defined targets

Surface Area

Total Nitrogen

WLC (CAPEX, OPEX and Land Value)

Penalty as a results of contraints

should be <=

should be <=

should be >=

Total PhosphorusPollutant

Concentration

at Outlet

(mg/L)

Physical

Restrictions

InfiltrationUse of infiltration at location 3 is

TOTAL Penalty Cost:

isUse of infiltration at location 2

should be <=

should be <=

should be <=




0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300

Flo

w (m

3/s

)

Duration (Minutes)

Flow Rate at Various Stages of SuDS Treatment Train Inflow (Connection1)

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

Peak Flow Constraint

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300

Volu

me

(m3)

Duration (Minutes)

Storage Required at Various Stages of SuDS Treatment Train

Storage (Connection 1)

Storage (SuDS 1)


Storage (SuDS 2)


Storage (SuDS 3)

Storage (TOTAL)

0

5

10

15

20

25

30

35

Total

Nitrogen

Total

Phosphorus

Total

SuspendedSolids

Hydrocarbons

Heavy

Metals

Pollutant Concentration (mg/L)

Concentration

(Inlet)

Concentration

(RegulationTargets)

Concentration

(Outlet)

£0

£100,000

£200,000

£300,000

£400,000

£500,000

£600,000

SuDS1 SuDS2 SuDS3

Cost Summary

CAPEX OPEX (over 50 years) Land Value Whole Life Cost (over 50 years)

Contact the Author The work presented here is part of author’s 4-year industrial PhD research project. For more information, please contact the author:

• Jo-fai Chow, STREAM Research Engineer

• E-mail: [email protected]

• Software by XP Solutions: http://www.xpsolutions.com/software/

Traditional Drainage Systems – Conveyance & Storage

Sustainable Drainage Systems – Source Control & Treatment

Towards Sustainability 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.

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.

Porous car park

Swale

Pond

Figure 2 – using Micro Drainage’s WinDes to model SuDS for a typical site development drainage design.

Figure 1 – examples of both conventional and sustainable drainage systems.

Figure 4 – prototyping a new decision support framework for SuDS using Microsoft Excel spreadsheet.

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300

Flo

w (m

3/s

)

Duration (Minutes)




0

5

10

15

20

25

30

0 50 100 150 200 250 300

Vo

lum

e (m

3)

Duration (Minutes)



Storage (SuDS 1)


Storage (SuDS 2)


Storage (SuDS 3)

Storage (TOTAL)

0

5

10

15

20

25

30

35

Total

Nitrogen

TotalPhosphorus

Total

SuspendedSolids

Hydrocarbons

HeavyMetals


Concentration(Inlet)

Concentration(RegulationTargets)

Concentration(Outlet)

£0

£100,000

£200,000

£300,000

£400,000

£500,000

£600,000

SuDS1 SuDS2 SuDS3

Cost Summary


Final Outflow

Total Storage

Final Pollutant Conc. Costs

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300

Flo

w (m

3/s

)

Duration (Minutes)




0

5

10

15

20

25

30

0 50 100 150 200 250 300

Vo

lum

e (m

3)

Duration (Minutes)



Storage (SuDS 1)


Storage (SuDS 2)


Storage (SuDS 3)

Storage (TOTAL)

0

5

10

15

20

25

30

35

Total

Nitrogen

TotalPhosphorus

Total

SuspendedSolids

Hydrocarbons

HeavyMetals





£0

£100,000

£200,000

£300,000

£400,000

£500,000

£600,000

SuDS1 SuDS2 SuDS3

Cost Summary


Final Outflow

Total Storage


0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300

Flo

w (m

3/s

)

Duration (Minutes)




0

5

10

15

20

25

30

0 50 100 150 200 250 300

Vo

lum

e (m

3)

Duration (Minutes)



Storage (SuDS 1)


Storage (SuDS 2)


Storage (SuDS 3)

Storage (TOTAL)

0

5

10

15

20

25

30

35

Total

Nitrogen

TotalPhosphorus

Total

SuspendedSolids

Hydrocarbons

HeavyMetals





£0

£100,000

£200,000

£300,000

£400,000

£500,000

£600,000

SuDS1 SuDS2 SuDS3

Cost Summary


Final Outflow

Total Storage


Figure 5 – exploring and comparing different design options from optimisation Pareto front .

Least-cost option: runoff satisfies minimum design requirement.

Most expensive option: runoff is further reduced at higher costs.

Somewhere in between: stakeholders to decide what is the best trade-off between two objectives.

Traditional Approach – Main Emphasis on Water Quantity

New, Integrated Approach – Balanced Emphasis

Figure 3 – Comparison of traditional and new approach.

Quantity Quality

Amenity

Quantity Quality

Amenity

Figure 6 – our vision: balanced emphasis on water quantity, quality and amenity for sustainable drainage

design with whole life costing analysis.

Cost

Performance

http://www.exeter.ac.uk/cws

http://www.microdrainage.co.uk/

http://www.stream-idc.net/



developing a new decision support framework for sustainable drainage design

Technology

value suds

inflow suds

life suds

surface area suds

various suds components

optimal combinations

total surface area m2

drainage models