Blue Green Solutions

32

33

Blue Green Solutions Guide

Case study 2: London Decoy Brook

Monetisation of the wider benefits of retrofitting BG solutions for 

management of environmental risks to urban infrastructure.

Background

BG Systems Approach 

BG solutions, in the form of integrated, vegetated, 

Sustainable Urban Drainage Systems (SUDS), 

improve flood alleviation capacity. However, they 

also provide wider, ecosystem service derived 

benefits. The wider benefits are usually not 

included in cost-benefit analyses, thereby greatly 

undervaluing BG solutions’ use as strategic 

assets. 

Imperial College London worked with the 

London Environment Agency (EA), London 

Borough of Barnet and AECOM to provide 

compelling and robust evidence for BG Solutions’ 

cost effectiveness within the UK Flood Risk 

Management Planning Framework

33

. 

To develop and deliver a framework for quantifying 

the wider benefits of BG solutions, the Decoy Brook 

catchment in London (UK) was used as a case study. 

The brief for Decoy Brook was to protect the critical 

infrastructure assets Golders Green and Finchley 

Road junctions, Golders Green tube station, Finchley 

Road police station and electrical substations. A 

set of BG solutions were co-designed with the 

stakeholders via a workshop, with the aid of the 

Adaptation Support Tool software developed during 

the Blue Green Dream project. 

The financial appraisal of the wider benefits of 

the BG solutions, such as amenity, air quality, 

biodiversity and surface water charges reduction, 

was done using CIRIA’s Benefits for SUDS Tool 

34

. 

This encompasses the standard approach to 

appraising flood risk in the UK (as defined in the 

Multi-Coloured Manual Handbook

35

). 

16

Selection and grouping of BG solutions for the cost-benefit analysis

Finally, the project explored potential funding 

mechanisms to promote the wider uptake of BG 

solutions in London. 

Main Outcomes

The economic viability of BG solutions increases 

considerably when wider benefits are considered: 

for the case study area, compared to flood-risk 

benefit estimations only, they increased the value 

of the benefits provided by the selected options 

by 60 per cent to 184 per cent. 

The pathway towards wider scale BG solutions 

retrofit in London is to “cost-share” i.e. split the 

investment costs among multiple stakeholders 

(including critical infrastructure owners) by 

highlighting the additional services provided to 

each stakeholder (info box).

17

t2

Benefits breakdown per stakeholder group

Cost effectiveness of BG solutions – flood only vs. wider benefits comparison

Catchment - scale solution

BGS 1

BGS 4

BGS 5

BGS 2

BGS 3

·  Infiltration Strips

·  Urban Wetland

·  Ranwater tank at

   golders Green Station

·  Infiltration Strips

·  Bio-swale

·  Roof disconnection

·  East pond

·  West pond

Police

station

detailed

solution

OPTIONS

FLOOD-ONLY 

BENEFITS COST RATIO

WIDER BENEFITS

COST RATIO

INCREASE OF BCR WHEN 

INCLUDING WIDER BENEFITS

BG-S 1

BG-S 2

BG-S 3

BG-S 4

BG-S 5

0.32

0.66

0.64

0.47

0.65

0.91

1.06

1.82

0.97

1.46

184%

60%

184%

106%

125%

100%

35%

84%

184%

 

increase in economic value of SUDS 

benefits can be achieved if wider benefits are 

included in analysis.

35%

 of total BG solution benefits can be 

related to commercial sector and 

infrastructure owners

---

34

35

Blue Green Solutions Guide

Case study 3: Budapest City Park 

(Varos Liget)

Use of the BG systems approach to create a closed loop, zero waste, urban 

metabolism for a mixed use district and park.

Background

The Budapest City Park area covers approximately 

100 hectares. Within its perimeter it hosts 

restaurants and a number of institutions: a 

thermal bath, city-zoo, hospital, and several 

museums. The area is being redeveloped, with 

key aims being to significantly reduce water & 

energy consumption and waste generation, and 

to increase annual visitor numbers (approximately 

2 million at the time of the study) to 4 million by 

2019. 

BG Systems Approach 

Main Outcomes 

Key figures

For this project, the local BG Team (Biopolus) 

developed and applied a Metabolic Mapping 

Methodology. This involves the systematic 

analysis of water, energy and waste flows (inputs 

and outputs) for the park, taking into account 

daily and seasonal variations. The “metabolic”, 

i.e. material/energy transformation processes, 

covered bioenergy, waste heat, material, and 

water recovery.

The integrated waste and energy recycling 

solution developed delivers potential water 

savings of 95 per cent, organic waste reductions 

of 65 per cent, and a thermal energy recovery of up 

to 12 megawatts (MW) or 35 per cent.  The overall 

payback period is potentially less than 6 years 

with respect to the cost of the infrastructure.

Aerial view and location map of the Budapest City Park

18

19

Schematic of the Urban Metabolic flow.

Energy

Organic

Water

Heat recovery

Bioenergy recovery

Primary energy

Primary energy

Waste

Wastewater

Water products

Products

Losses

Drinking water

Fresh materials

Fresh water

Rain water

Materials recovery

Water recycling

---