A Pilot-Scale Evaluation of Greenroof Runoff Retention, Detention, and Quality
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Vegetated roofs are becoming more commonly deployed as a means of mitigating stormflow in urban areas. A greenroof performance comparison of stormwater runoff has yet to be conducted with controlled rain events and quantifiable antecedent soil moisture. This study aimed to investigate the rainwater management provided by various greenroof design schemes. Runoff retention, peak flow lagtime, conductivity, and pH of ten different small-scale greenroof schemes were observed and analyzed under repeatable rain simulations in a pilot-scale study. Sedum rupestre Angelina, Sedum hispanicum, Trifolium repens (white clover), Trifolium pratense (red clover), Vinca major (Big-Leaf Periwinkle), and Lolium multiflorum (ryegrass) were grown in the same type of soil media but separate 2′ × 2′ trays at depths of 5 cm and 14 cm to observe how soil depth and root zone development affects stormwater flow through for each plant type. Results showed that increased green roof soil depth improved water retention and runoff lagtime; the effect of plant type was mixed and inconclusive. Runoff conductivity test results depended primarily on soil depth and the existence or absence of vegetation. Testing results show that pH normalization provided by a greenroof does not depend significantly with the substrate depth.