Urban waterlogging stems from coverage with impervious surfaces and increasing rainfall intensity from climate change and variability, meaning that storm water cannot readily infiltrate the ground and excessive surface runoff leads to urban flooding. To reduce related environmental and safety risks, rainfall and groundwater level research was carried out in Kyoto Prefecture with two rain gardens (RG1 and RG2) to investigate flood mitigation functions using a tank model. During the 134 days of monitoring from July 14, 2017, to November 25, 2017, RG1 had seven overflow events with an average runoff control ratio of 63.94%, and RG2 had one event with a ratio of 95.97%. The RG1 tank model (two stages) showed that initial storage for the first and second depths was 6.912 × 10⁻¹¹ and 0 mm, respectively. The heights of the discharge holes were 20.857 and 0.784 mm for the first stage and 0.659 mm for the second stage, and the discharge hole coefficients were 0.529 and 0.002 for the first stage and 0.004 for the second stage. The results showed that RG1 had penetration hole coefficients of 0.138 (first stage) and 0.254 (second stage), with a water balance error of 0.017 (< 0.02) and a Nash–Sutcliffe efficiency coefficient of 0.922, indicating better reliability and quality than RG2 with the one-stage tank model. Peak flow simulation for mitigation showed that RG1 had a high overflow control ratio (mitigation time 2 h for instant rainfall of 100 mm/h), and can therefore be considered appropriate for other urban areas of Japan.

中文翻译：

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日本雨水花园的防洪功能

城市的涝灾源于不透水的地表覆盖，以及气候变化和多变性造成的降雨强度增加，这意味着雨水无法轻易渗透到地面，过多的地表径流导致城市洪水泛滥。为了降低相关的环境和安全风险，在京都府进行了降雨和地下水位研究，并建立了两个雨花园（RG1和RG2），以利用水箱模型研究防洪功能。在2017年7月14日至2017年11月25日的134天监测中，RG1发生了7次溢流事件，平均径流控制率为63.94％，RG2发生了1次事件，溢流率为95.97％。RG1坦克模型（两个阶段）显示，第一和第二深度的初始存储为6.912×10 ^-11和0毫米分别。第一阶段的排放孔的高度为20.857和0.784mm，第二阶段的排放孔的高度为0.659mm，第一阶段的排放孔系数为0.529和0.002，第二阶段为0.004。结果表明，RG1的穿透孔系数为0.138（第一阶段）和0.254（第二阶段），水平衡误差为0.017（<0.02），Nash-Sutcliffe效率系数为0.922，显示出比RG2更好的可靠性和质量。一阶段的坦克模型 峰值流量模拟的缓解措施显示，RG1具有较高的溢流控制率（对于100 mm / h的瞬时降雨，缓解时间为2 h），因此可以认为它适合日本其他城市地区。