No abstract

This study investigates how roof substrate and vegetation affect rainwater retention. The investigated parameters are lightweight substrate ratio, substrate depth, precipitation and vegetation type. A planting box was placed on the roof of a building to simulate a green roof. Scheduled artificial rainfall was used to test the rainwater retention capacity of various substrates, substrate depths and plant types. The experimental results indicate that precipitation, substrate depth, substrate ratio and vegetation type affect the rainwater retention capacity of green roofs. The rainwater retention rate is inversely proportional to precipitation intensity; that is, about 87-100% of rainwater is retained for light rain, 62-84% for moderate rain and only 26-33% for heavy rain. Different plants have different abilities to retain rainwater. In this study, Dianella ensifolia cv. 'Silvery Stripe' and Schefflera arboricola have the best water retention rates of 37-100%. Of the total amount of rainwater retained, the substrate accounts for 77-98% and vegetation accounts for 2-23%. In the sub-tropical region, the green roof water retention rate is roughly 30% of the total storm precipitation (100 mm). Thus, using a green roof is an effective strategy for managing urban stormwater.

Roll waves commonly occur in overland flow and have an important influence on the progress of soil erosion on slopes. This study aimed to explore the evolution and mechanism of roll waves on steep slopes. The potential effects of flow rate, rainfall intensity and bed roughness on the laws controlling roll wave parameters were investigated. The flow rates, rainfall intensities and bed roughness varied from 5 to 30 L/min, 0 to 150 mm/h, and 0.061 to 1.700 mm, respectively. The results indicate that roll waves polymerize significantly along the propagation path, and bed roughness and rainfall affect the generation and evolution of roll waves. The wave velocity, length and height decreased with bed roughness, whereas the wave frequency increased with increasing bed roughness under fixed flow rate and rainfall intensity conditions. Rainfall increased the wave velocity and wavelength and decreased the wave frequency. The wave velocity, height and wavelength tended to increase with an increasing flow rate. Rainfall promoted the generation of roll waves, whereas bed roughness had the opposite effect. The generation of roll waves is closely related to the Froude number (Fr) and flow resistance. In this experiment, the range of the Reynolds number for the roll waves generated in the laminar region was 142–416, and the range of the flow resistance coefficient was 0.64–4.85. The critical value of the Fr for flow instability in the laminar region was approximately 0.57. Exploring the generation and evolution law of roll waves is necessary for understanding the processes and dynamic mechanisms of slope soil erosion.

No abstract