Deriving synthetic rating curves from a digital elevation model to delineate the inundated areas of small watersheds

Abstract

Study region: Two southern Quebec (Canada) watersheds were used to validate the proposed method for delineating inundated areas of small watersheds: the 554-km2 St.Charles and the 133 km2 À la Raquette watersheds. Observed data from six-gauge stations were used to validate the Synthetic Rating Curves (SRC) developed in the study. Study focus: This research focuses on the application of the Height Above the Nearest Drainage (HAND) method to derive SRCs and support floodplain mapping in small watersheds.Accurate floodplain delineation is crucial of flood management, particularly in datascarce regions. This study presents a novel approach using (HAND) approach to precisely identify flood-prone areas. It involves generating (SRCs) connecting discharge and terrain derived hydraulic characteristics, integrated into PHYSITEL; a Geographic Information System (GIS) for distributed hydrological modeling. The Froude number established a consistent relationship between mean discharge and water depth across various discharge levels, defining unique hydraulic regimes. A Global Sensitivity Analysis quantified the uncertainty associated with SRC parameters, guiding calibration efforts to achieve biases below 20%. For both watersheds, postcalibration results showed SRCs with NRMSE values between 0.03 and 0.62. HANDSRC-based inundated areas corroborated the Quebec City flood risk zones well, with over 70% recall and 90% precision, validating its efficacy. These results contribute significantly to the region by providing SRCs for ungauged river sections and delineating first-hand floodplain maps.

Keywords

• Floodplain mapping
• Height above the nearest drainage
• Global sensitivity analysis
• Manning equation