Smart Rain Gardens as a Flood Risk Reduction Measure in Saitama City: A PySWMM-based Study

抄録

Frequent urban pluvial flooding due to heavy rainfall has occurred in densely populated residential areas in Japan in recent years. In the 21st century, low-impact development (LID) as a stormwater management (SWM) strategy has been advocated by many countries in response to such events. The use of rain gardens (RGs), a typical LID design approach, can effectively reduce urban pluvial flooding. However, in our previous analytical study of RGs in Saitama City, a suburb of Tokyo, we found that ordinary RGs were only effective during initial peak rainfall, which we assumed was related to limited soil permeability and the absence of active water management. To improve the role of RGs in reducing flooding, this study proposes the concept of smart RGs (SRGs). SRGs are controlled by soil sensors that detect zones of optimal soil permeability and moisture levels and use intelligent valves to direct rainwater to those zones via an infiltration piping system. The intelligent valves adjust the water flow rate and distribution to maintain a balanced infiltration rate across the different zones. By linking the sensors and intelligent valves to local weather forecasts, the smart valves can increase the infiltration rates of SRGs before the onset of a rainstorm. This ensures that the SRGs can hold more rainwater when the rainstorm arrives. This study aimed to verify the effectiveness of SRGs in reducing urban pluvial flooding during continuous rainfall in Saitama City using pySWMM simulations. The effectiveness of the SRGs was measured using two dimensions: overflow volume and infiltration volume. SRGs reduced the total runoff volume from 6% to 17% compared to RGs and demonstrated a 17.36% increase in the total infiltration volume compared to regular RGs.