Simple Rainfall-Runoff Transformation for the Evaluation of Green Roof Stormwater Runoff Volumes

One of the key elements in the development of analytical models is the rainfall-runoff transformation, through which the probability distributions of the rainfall characteristics can be mathematically transformed into the probability distributions of the runoff. As a result, the degree of the complexity of analytical models essentially depends on how the rainfall-runoff transformation is formulated, in other words, how many parameters are associated with the transformation. In the past, the simple two-parameter rainfall-runoff transformation formulated with runoff coefficient and depression storage has been widely employed in the development of analytical models for urban stormwater quantity and quality controls, among which include the derivation of long-term stormwater control measures such as the average annual runoff volume, volumes of runoff controlled and spilled from the storage facility. From the perspective of runoff quality, the simple rainfall-runoff transformation has also been widely used for developing stormwater quality control measures such as the average event mean concentrations, the average annual pollutant loads and the fraction of pollutant removal in the storage facility, etc. One of the purposes of these studies is to verify the applicability of analytical models for urban catchment stormwater control from either a quantity or quality perspective. However, despite a long history and extensive experience in the development of analytical models, case studies are few and experiences are extremely limited regarding the applicability of analytical models for green roof runoff. While the simple rainfallrunoff transformation has been employed extensively in runoff control analysis for a general urban catchment, what if analytical models are applied exclusively to estimate the volume of green roof runoff? Are analytical models based on the simple rainfall-runoff transformation sufficient for the evaluation of both the control and garden runoff along with the total runoff? The major purpose of this study is aimed to address these concerns while evaluating the applicability of the simple analytical models through on-site monitored green roof runoff data.