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. 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 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 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 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 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 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, 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 Full Context Pathway(aka Context) Default view Area(aka Level or Site) ALL