Estimation of rainfall threshold for flood warning for small urban watersheds based on the 1D–2D drainage model simulation

Flood warning systems can provide an effective and low-cost solution to protect urban residents especially in developing countries suffering from severe flood damages caused by weak capacity of defense structures. Rainfall Threshold for Warning (RTFW) is essential key accurate system. This study proposed easy-to-use mathematical equation RTFW small watersheds based on computer simulations. First, a coupled 1D–2D dual-drainage model was used simulate the flooded area nine Seoul, Korea corresponding 540 scenarios various synthetic rainfall events watershed imperviousness. Then, results 101 simulations that critical depth (0.25 m–0.35 m) were develop relates value event temporal variability (represented as coefficient variation or CV) imperviousness NRCS Curve Number CN). The suggest (1) exponentially decreases CV increases; (2) linearly CN (3) dominated when has low (e.g., < 0.2) while high > 0.4). For validation, applied system with two storm occurred 2010 2011 over 239 Seoul. showed hit, false missed alarm rates at 69% (48%), 31% (52%) 6.7% (4.5%), respectively (2011) event.