Quantitative assessment of hydrological efficiency of rain garden design in the context of managing the volume and quality of storm effluent

Rain gardens are a popular element of green infrastructure, often integrated into the sponge city concept to address stormwater management issues. Such structures perform three main functions: reducing the volume of water runoff from the catchment area, reducing peak flows in the drainage system, which is critical for preventing overloading of the sewer network, and improving water quality, which contributes to the preservation of groundwater. The design of rain gardens is based on specific requirements and characteristics that determine their construction and calculation methods to achieve optimal parameters, such as area and depth. Scientometric analysis shows that significant research contributions are made by different countries, but most existing rain garden systems are based on general recommendations, which can lead to problems in their operation. The purpose of the work is to develop a model for calculating the main parameters of rain gardens and methods for assessing their hydrological efficiency in order to improve their implementation in the urban environment. A numerical model for calculating the effective area of a rain garden is presented, which considers one rain event and excludes overflow. Methods are proposed for evaluating three key functions of rain gardens in the context of stormwater management: a method for determining runoff reduction, a method for estimating annual runoff reduction, a method for peak runoff reduction, and a method for estimating total pollutant reduction.