National Id
Switzerland_02
Site name
Geneva
Summary
This case study is located in the city of Geneva, Switzerland. It describes how green roofs have been implemented on the roof of a hospital (0.55 ha) in order to decrease flood risks in urban areas. Indeed, this green roof is designed to retain about 30.25 m3/day water in the soil and plants and prevents it from running off. Compared to a traditionnal roof, the green roof retains about 60% of the water quantity that would run off otherwise. Moreover, green roofs are seen as a good way to recreate habitat in urban areas.
Light or indepth?
Light
NUTS Code
Ticino
RBD code
CH50
Transboundary
0
Data provider
Anais Hanus, ACTeon
Source(s)
Hopital cantonnal, zone sud; toiture végétalisée
Stormwater management at the local scale: a green roof study, review and lessons learned
NWRM(s) implemented in the case study
Green Roofs
Longitude
6.15
Latitude
46.2
Climate zone
cool temperate moist
Mean rainfall
915
Mean rainfall unit
mm/year
Average temperature
10,7
Mean evaportranspiration
1,5
Mean evaportranspiration unit
mm/day
Mean runoff
302
Mean runoff unit
450 - 600 mm
Average runoff coefficient
0,33
Type
Case Study Info
Average slope range
0.0
Monitoring impacts effects
0
Performance impact estimation method
Unknown
Application scale
Building
Installation date
1993-06
Age
20
Performance timescale
Immediate
Area (ha)
0.55
Area subject to Land use change or Management/Practice change (ha)
0.55
Size
0.6
Size unit
m
Design capacity description
The measure was designed to retain about 30.25 m3/day.
Max water retention capacity
30.25
Max water retention capacity unit
m3/day
Runoff treatment capacity
165
Runoff treatment capacity unit
mm/month
Constraints
The wind force can render it difficult to use some trees.
Favourable preconditions
The existence of unexploited wide areas like roofs enable the implementation of the measure.
Public consultation
0
Contractural arrangements
0
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Design consultation activity
Activity stage Key issues Name Comments
Design land use change
Land use change type
Design authority
Authority type Role Responsibility Name Comments
Other
Initiation of the measure
République et canton de Genève
Determination of design details of the measure
Nierle, Grand, Praplan et associés architectes SA
Architects
Determination of design details of the measure
Tremblet et Cie SA
Engineers
Determination of design details of the measure
Zanini-Baechli et associés
Engineers
Determination of design details of the measure
Walter Brugger
Architects
Implementation
Induni et Cie SA
Contractor
Implementation
Trogger SA
Contractor
Key lessons
The case study provides one example of how to implement and design green roofs.
Financing mechanism
0
Success factor(s)
Success factor type Success factor role Comments
Attitude of relevant stakeholders
main factor

The hospital, a private stakeholder, asked for implementing the measure.

Financing possibilities
main factor
Financing
Financing type Comments
Local funds
Barrier
Barrier type Barrier role Comments
Attitude of relevant stakeholders
main barrier
Green roofs implementation on public or private buildings depends on owners' will.
Lacking financing sources
secondary barrier
The cost of the measure can be a barrier if subsidies or other funds are not available.
Driver
Driver type Driver role Comments
Legal obligations
main driver
The federal law on water protection requests rain water infiltration in urban areas through retention measures.
Organisation committed to it
secondary driver
The Geneva Canton elaborated recommendations regarding water retention in urban areas
Financing share
Financing share type Share Comments
Policy description
The targeted problem is the runoff in urban areas, which increases flood risks.
Part of wider plan
1
Policy target
Target purpose
Improved Biodiversity
Increase Water Storage
Oher Societal Benefits
Policy pressure
Pressure directive Relevant pressure
Policy area
Policy area type Policy area focus Name Comments
Policy impact
Impact directive Relevant impact
Policy wider plan
Wider plan type Wider plan focus Name Comments
National
Water
Federal law on water protection, 24 january 1991
Local
Water
Cantonal law on water (L 2 05)
Policy requirement directive
Requirement directive Specification
Direct benefits information
Green roofs improve the microclimate.
Ancillary benefits information
Green roofs provide vegetation in a urban area, from which - in this case - hospital patients can benefit from.
Costs investment
4000000
Costs total
4000000
Ecosystem improved biodiversity
1
Information on Ecosystem improved biodiversity
Recreating habitat in urban areas.
Ecosystem provisioning services
0
Ecosystem impact climate regulation
No information available
Retained water
30
Retained water unit
m3/day
Information on retained water
This number is theoretical; no performance evaluation has been done.
Increased water storage
60
Runoff reduction
60
Increased water storage unit
% Percent
Runoff reduction unit
% Percent
Water quality overall improvements
Not relevant for this application
Soil quality overall soil improvements
Not relevant for this application