Global warming and climate change affect the number and magnitude of floods dramatically which necessitates effective flood management plans and innovative solutions. Flood management in basin scale involves preliminary flood risk assessment followed by hydrological models to obtain rainfall-runoff relations of watersheds and hydraulic models of critical stream tributaries and main river to obtain flood extent, depth, and velocity to generate flood hazard maps. Then, flood risk maps are developed which are used to take mitigation and remediation actions. Green Infrastructures (GI), which are also known as Low Impact Developments (LID) and are part of the Nature Based Solutions, have gained importance recently in decreasing the negative impacts of floods on urban areas. Therefore, they play an important role in flood control. GIs such as vegetated swales, bioretentions, infiltration trenches and rain gardens emerge as an alternative to traditional infrastructure storm water drainage systems. Thus, large scale outdoor experiments are conducted with Rainfall-Watershed-Green Infrastructure (RWGI) experimental setup located in Avcilar Campus of Istanbul University-Cerrahpaşa to be able to understand the hydrological behaviour of GIs and model them accurately. The RWGI is a large-scale experimental system comprising a sprinkler system for simulation of rainfall, a steel plate representing the watershed area, and GI modules of bioretention, trench and swale. Overflow and Drainage Flow are measured to obtain hydrographs out of the GI modules under different rainfall scenarios. The Environmental Protection Agency Storm Water Management Model (EPA SWMM) is one of the few software, which can model many types of GIs and can be used for prediction of their effect under different scenarios before implementation. Yet, EPA SWMM still needs improvement for accurate simulation of GIs. Thus, experimental results are made use of both testing the GI modelling performance of EPA SWMM in and improving it where necessary