Coping with Global Change – Flexible Design for Sustainable Urban Water Systems

Jochen Eckart, Seneshaw Tsegaye, Kala Vairavamoorthy

Global Change Pressures are Associated with Huge Uncertainties

Uncertainty in quantity & qualityUncertainty in

demand

Uncertainty in urbanization

Uncertainty in carrying capacity/breakage rate

Uncertainty population

Uncertainties are Increasing during Life Span of Urban Water Systems

2000 2010 2020 2030 2040 2050

2000 2010 2020 2030 2040 2050

Flexibility as Approach to Cope with Uncertainties

Flexible Urban Water Systems

Definition of Flexibility as Basis for Theory of Flexible Design

Flexibility is the ability of urban water systems to use their active capacity to act to respond on relevant alterations during operation in a performance efficient, timely and cost effective way.

• Deal with future uncertainties• Characteristics of the change process

• Change the system during operation

Range of change: Range of future states which could be managed

Performance: Homogeneity system performance for life span

Effort of change: Cost of change and duration of change

Metrics of Flexibility

3 Metrics for the Measurement of Flexibility

Flexible Water Distribution Systems

T0 T1T2 Time

Clustered Design

Clustered & Flexible WDS

ARUA

Clustered & Flexible WDSCase Study Arua

• Small emerging town in Eastern Uganda• Current Population:107,000• Population 2032: 160,000 - 220,000

Identify Optimal Clusters for WDS

Existing Central System

New Development plan (Forest Area)

Emerging Area

1

3 4

5

6 7

9

8

10

1112

13

14

15

16

 

 

 

 

River Enyau

2

(a)

 

 

 

 

 

 

 

S1

S2

S3

S4

S5

S7

S8

S6

(b)

Current source (S9)

 

 

Minimization of Source-demand Distance - Demand Assignment

Minimization of Source-demand Distance - Demand Assignment

Legend

Closer Far

1 2 3 4 5 6 7

M1 M2 M3 M4 M5 M6 M7 Closer to source center Far from source center

Membership M9

M8

 

Parcel assignment (Minimized Euclidean norm)

Membership M of parcels based on source-demand distance

Maximizing Inter-Cluster Homogeneity

Cluster using K-means Algorithm Final cluster boundaries

C1

C2

C4

C4C5

C6

C7

C8

C9

7694 7694 7694

8860 8860

12809 12809

14909

7694

8860

17217

14909

12809

8860

7694

Future Demand(m3/d)

A1

A2

A3

T0

(2012)

 

T1

(2017)T3

(2027)Time(year)

A4

T2

(2022)

A5

T4

(2032)

Clustered WDS Offers Higher Flexibility Than Centralized WDS

Scenario no.

Regret(m3/US$)

Central Cluster1 17.7 0.02 17.5 0.03 17.6 0.04 17.7 0.05 17.7 0.06 14.5 0.07 14.2 0.08 13.6 0.09 12.4 0.0

10 12.0 0.011 8.0 0.0

Maximum regret 17.7 0.0

Minimax regret Cluster

Flexible Drainage Systems

Flexible Urban Drainage Systems - Case Study ‘Hamburg-

Wilhelmsburg’

Key Facts• residential area with

400 living units• total area 17 ha• 60% impervious area• High uncertainties -

consequences climate change

Comparison Flexibility Provided by SUDS and Separate Sewer

SystemAlt 1 SewerAlt 2 SUDS

Adaptation of Sewer System During Operational Life Span

Alt 1 SEWERS

Time

Perf

orm

ance

UV

Runo

ff

-30

0

+30

+60

+90

EAC: EUR 246.011

Performance: 51

Adaptation of SUDS During Operational Life Span

Alt 2 SUDS

Time

Perf

orm

ance

UV

Runo

ff

-30

0

+30

+60

+90

EAC: EUR 32.694

Performance: 64

Range of change (R in m3) Scenario 1 Scenario 2 Scenario 3 Max Regret (Rr)

Alt 1 SUDS 123 -25 31 0

Alt 2 Sewer 123 0 31 25

Performance (U95) Scenario 1 Scenario 2 Scenario 3 Max Regret (Ur95)

Alt 2 SUDS 64 80 74 4

Alt 1 Sewer 51 83 78 13

Effort of change (EAC in EUR)

Max Regret (EACr)

Alt 2 SUDS 32,694 16,983 20,463 0

Alt 1 Sewer 246,011 20,109 20,900 213,317

SUDS provides a higher flexibility than sewers

SUDS Provide Lowest Minimax Regret

It’s already happening – Emscher Region, Germany

Planning to decouple areas from sewer system using SUDS – extend of decoupling is uncertain

Building a new main sewer system – if decoupling is successful dimensions of the sewer can be reduced

Both projects are implemented at the same time – how to consider the uncertainties for the design of

the sewer system

Flexibility Options Used to Save Investment Costs

Solution: • Need for flexibility option which can be implemented if

decoupling is not achieving planned goal• Flexibility option – land reserved to build central retention basins

required if decoupling goals are not achieved• The new sewer can be dimensioned smaller even if the

decoupling is not implemented now

Move away from a deterministic, path-dependent approach to a more flexible & adaptive approach

Take home message

Thank You