General
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.
NUTS Code
Ticino
RBD code
CH50
Transboundary
0
Data provider
Anais Hanus, ACTeon
Source(s)
NWRM(s) implemented in the case study
Longitude
6.15
Latitude
46.2
Site information
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
Light or indepth?
Light
Average slope range
0.0
Monitoring maintenance
Monitoring impacts effects
0
Performance
Performance impact estimation method
Unknown
Design & implementations
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 | |
|---|---|---|---|---|---|
Lessons, risks, implications...
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
|
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, general governance and design targets
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 |
|---|
Socio-economic
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
Biophysical impacts
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
