Variation of uncertainty of drainage density in flood hazard mapping assessment with coupled 1D–2D hydrodynamics model

Abstract Coupled 1D–2D hydrodynamic models are widely utilized in flood hazard mapping. Previous studies adopted conceptual hydrological or 1D to evaluate the impact of drainage density on river flow. However, affects not only flow, but also flooded area and location. Therefore, this work adopts model SOBEK investigate The uncertainty mapping is assessed by a designed case real case, Yanshuixi Drainage Tainan, Taiwan. Analytical results indicate that under same return period rainfall, reduction tributary drainages (indicating lower density) an underestimate drainages. This causes higher peak discharges total volume drainages, leading flooding certain downstream reaches, thereby overestimating area. decreases with increased rainfall. We suggest modeling low rainfalls requires For extreme rainfall events, could be selected, local key areas should raised.