Sensitivity of 2D Hydrologic–Hydrodynamic Simulations to Wet–Dry Tolerance and Hydrological Drying Configurations in Iber

Two-dimensional hydrologic–hydrodynamic models based on shallow water equations require careful specification of wet–dry treatment parameters. However, wet–dry tolerance (depth thresholds) and drying algorithms are often set to defaults without systematic evaluation, particularly in intermittent-flow environments where these settings directly control surface activation and drainage connectivity. This study assesses the sensitivity of discharge estimation, inundation extent, and hydrograph stability to wet–dry tolerance (εwd) and hydrological drying configurations in the Iber modeling tool, applied to the lower reach of the Riera de la Bisbal (El Vendrell, Catalonia, Spain) under a triangular inflow hydrograph peaking at 586 m3/s, representing an approximate 500-year flood scenario. Four configurations were tested by combining two wet–dry tolerance values (εwd = 1 mm and εwd = 1 cm) with hydrological drying enabled or disabled on an unstructured mesh of 15,339 elements. Peak discharge at the outlet varied by only 0.5% across configurations, confirming low sensitivity under high flow conditions. However, local depth behavior differed substantially, with a peak depth difference of approximately 34% in a flood-prone diagnostic cell and flooded areas ranging from 65,687 m2 to 69,262 m2 depending on configuration. The results indicate that agreement in the outlet hydrograph is not a sufficient criterion for assessing local inundation quality, and that wet–dry configuration choices have operationally relevant consequences for flood-risk mapping and design in urban intermittent streams. Local peak-depth sensitivity was evaluated at five diagnostic cells (zones A–E), with peak-depth ranges across configurations varying from 2.5% to 116.4%; the 34.0% range at Zone A was intermediate within the selected locations.