| Summary: | Evaluation of the effect of green roofs to reduce the risk of flooded networks A short study has been performed in order to assess the potential effect of green roofs concerning reduced demands for pipe dimension. The study has been performed using hydraulic models of the stormwater network. The stormwater model is fictitious even though it is a model of a real network the amount of impermeable surfaces connected to the network are augmented to make them critical to changes i.e. that increased loads causes flood. Two different types of roofs have been tested at two different climate conditions from Sweden. The study was performed with mike urban (Dhigroup.com) a market leading modeling software in Sweden. The modeling software has tools for supporting calculations of different SUDS (sustainable urban drainage systemes) such as green roofs, bio retention cells and infiltration trenches. The tools are quite similar to the tools included in another software SWMM (EPA) The build-up of the roofs in the model are modelled after a real roof in Kiruna. One roof consists of a thicker sedum-herbs-grassroof with a thickness of approximately 110-140 mm and the other 40 mm thick. None of the roofs had any technical constructions under in order to delay the runoff. Only water absorbing mats for the vegetation. Two different climates were simulated using precipitation, and temperature calculated evaporation using open data from the Swedish Meterological and Hydrologic Institute, SMHI. The locations chosen was from Kiruna in the north of Sweden and from Malmö. Only summer periods were studied. The main mechanisms for stormwater reduction and detention are 1. Reduction of the total runoff due to wetting of the materiel. When the water content in the soil is under the field capacity there will be an additional loss for saturating the material to make it drip through. 2. Slowing the runoff for more intense rains by detention. Green roof substrates are quite permeable but for heavier rains it can be limiting and thus leading to ...
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