Rain gardens are used to solve urban problems related to the negative impact of stormwater. (1) Scientific contributions from different countries provide general guidelines for the design and operation of rain gardens in different geographical areas. Given the small spatial scale of rain gardens, the use of existing infiltration models often leads to design errors. (2) The purpose of this paper is to develop a hydrological model by introducing a system of equations that extends the ability to calculate the rate, flow rate and time of saturation of layers with moisture and rainwater leakage from the rain garden system. (3) The results obtained allow us to describe the dynamic processes of passage and saturation of layers of the rain garden at a certain point in time, which extends the ability to calculate the flow rate. It was established that the smaller the area of the rain garden compared to the area of the catchment basin, the faster it reaches its full saturation. Increasing the thickness of the rain garden layers allows for an increase in the efficiency of water retention at a lower value of the area ratio. (4) The practical significance of the results obtained is especially important for the correct description of hydrodynamics in the system and determining the optimal conditions for the effective functioning and management of the rain garden structure for any climatic region.

Rainwater management is one of the important problems of cities. At very strong downpours, storm sewer systems may not capture the rainwater, which floods pavements and roadways. The water flushes fuel and oil traces after vehicles, fallen debris, and other pollutants, which will be moved to the ground, ponds, rivers, seas, etc. In past, the problems were solved using engineering approaches – a set of rainwater receivers, a duct network, and at best, wastewater treatment plants. Now, the sponge city concept is a better solution that uses a biotechnological way for throttling water flows, drainage, and purifying them. The work aims to improve the design of roads to fully absorb rainwater from them with maximum convenience for road users. We propose a design of roads using special “green structures” – rain-garden bands along the sides of roadways. We tested its ability of water capturing on the example of Kyiv city by matching the ability with the strongest precipitation observed. In addition, the proposed plants can extinguish the energy of bouncing cars during road accidents for the protection of pavements.

Implementing rain garden (RG) designs is widespread worldwide to reduce peak flow rates, promote stormwater infiltration, and treat pollutants. However, inadequate RG design degrades its hydrological behaviour, requiring the development and validation of an appropriate hydrological model for the design and analysis of structures. This study aimed to improve a hydrological infiltration model based on Darcy’s law by taking into account the height of the water column (HWC) at the surface of the RG and the filtration coefficients of soil materials. The model was tested by simulating the hydrological characteristics of a rain garden based on a single rain event of critical intensity (36 mm/h). Using the validated model, design curves were obtained that predict the performance of the RG as a function of the main design parameters of the structure: water column height, ratio of catchment area to structure area, layer thickness, and soil filtration coefficient. The hydrological efficiency of the RG was evaluated in terms of the time of complete saturation, filling of the structure with water, and determining the change in HWC caused by changes in the parameters. The filtration coefficient and thickness of the upper and intermediate infiltration layers of the RG are the main parameters that affect the depth of saturation of the layers of the structure and the HWC on the surface. The model is not very sensitive to the model parameters related to the lower gravel layer. If the top layer’s thickness increases by 10 cm, it takes longer to fill the structure with water, and the HWC on the surface reaches 0.341 m. The rain garden’s performance improves when the filtration coefficient of the top layer is 7.0 cm/h. Complete saturation and filling of the structure with rainwater do not occur within 7200 s, and the water column reaches a height of 0.342 m at this filtration coefficient. However, the rain garden’s effectiveness decreases if the filtration coefficient of the upper and intermediate layers exceeds 15 cm/h and 25 cm/h, respectively, or if the catchment area to RG area ratio decreases to values below 15. The modelling results confirm that considering the HWC in RG hydrological models is essential for designing structures to minimise the risk of overflow during intense rainfall events.

The proposed methodology for estimating the reduction of CO2 emissions by green constructions (green roof and facade greening) due to the “cooling effect” during the cooling period allows to calculate CO2 savings in warm periods of the year. For Kyiv, in July, the reduction of CO2 emissions per m2 at coal using is 133 g / m2, during the warm period of the year – 515 g / m2; using gas – 78 g / m2 and 303 g / m2. It is established that the energy savings of a green roof depends on the thickness of the thermal insulation of buildings: the thicker insulation causes the less green roof contribution to energy savings. However, the significance of their effectiveness remains. Green roofs can be especially effective in switching from gas to local solid fuels: peat waste, pellets, etc. As a practical recommendation, it is proposed to coordinate the placement of greened and ungreen parts of the green roof with rooms under the roof, which allows to reduce the refrigeration load on air conditioning. In addition, recommendations on grass care on the green roof have been developed. To maximize the cooling effect, it is necessary to maintain grass height no more than120 mm. Before the beginning of the transition period, it is necessary to stop mowing the grass, which reduces the cooling effect.