Design, Stormwater Budgets and Water Quality of Christchurch Green Roof Systems

Engineered green roofs are becoming prevalent as low impact designs (LIDs) since they offer multiple benefits including stormwater control. Christchurch’s rebuilding plans strongly encourage LIDs including green roof systems but no performance data for these under local conditions are reported. In order to understand the hydrological response, and hence sustainability, of green roofs in Christchurch, different experimental systems were established and monitored for a year at the University of Canterbury. Six (each 2.4 m x 1.2 m) systems comprising unvegetated, sedum blends and native grasses blends of two substrate depths (105 mm and 152 mm) were installed on a 2% slope roof. Each modular system contained nine pre-grown Liveroof™ vegetated units enclosed in a watertight frame. Precipitation, effluent volume, water quality and soil moisture were measured following each rainfall event along with various continuously logged meteorological parameters to calculate evapotranspiration rates and hydrological budgets. Detailed design, hydrological and water quality results from monitoring these systems for their first year are presented to demonstrate how green roof systems respond under Christchurch’s climate.