Evaluating Rain-Garden Bands: Filtration Properties and Implications for Urban Water Management

Efficient rainwater drainage is a challenge, especially for older areas of urbanized cities with drainage systems that have exceeded their planned service life. Overhauling these infrastructure systems requires high costs for materials and ongoing maintenance. In addition, old drainage systems often lack effective filtration mechanisms that could retain pollutants and ensure the treatment of rainwater, leading to pollution of groundwater and river water in the basins of the cities concerned. Rainwater management, combined with green infrastructure, can effectively minimize the risk of urban flooding and promote environmental filtration. The “sponge city” concept proposes a new type of green structure, the so-called rain garden bands, as a sustainable alternative that facilitates the rapid, uniform absorption and retention of rainwater and its treatment while reducing costs. Rain garden bands can remove heavy metals, inorganic substances, pathogens, fuels, and lubricants such as diesel fuel and used motor oil from rainwater. The study examines the resistance of Physocarpus opulifolia ‘Diabolo’ to fuels and lubricants, the ability of different layers to retain fuels and lubricants-contaminated water, and the filtration rate in filtration columns. This was achieved by introducing a predetermined volume of diesel fuel and used engine oil, recording the time required for the oils to pass through a sample of a given height, and then measuring the volumes of water and oil after flowing out at the base of the column. The results indicate that a decrease in the growth rate was observed for all plant species irrigated with fuels and oils and was most pronounced for the experimental objects watered with diesel fuel. It was found that it took about 10 days for the fuels and oils to pass through an 800-mm layer of soil, sand, and gravel to get the first samples at the outlet of the filtration column.