Identification of river channel bankfull geometry from topographic indicators extracted from high-resolution digital elevation datasets

River channel bankfull geometry and discharge are important features providing valuable insights into fluvial monitoring and flood recurrency. The bankfull stage represents the riverbank position that approximates the level at which water overflows onto the floodplain. Bankfull discharge is considered the channel-forming discharge, with a recurrence interval of approximately 1.5 years. Bankfull floods are significant, as they are highly effective in changing channel shape and characteristics. Their recurrence intervals can be used for stream assessment and have implications for infrastructure design and flood mapping. Additionally, gaining insights into the factors influencing floodplain inundation across various time periods is crucial, as the frequency of flood events is predicted to rise with the increase in global temperatures.

In this contribution, we present a novel approach to identify the bankfull geometry through a set of dedicated MATLAB functions. A Digital Elevation Model (DEM) with ground resolution of 1 m/pixel is used as input elevation dataset, obtained with airborne LiDAR (Light Detection and Ranging) survey. The selected river channels are divided in regularly spaced sampling sections, where the bankfull geometry is extracted. Then, the hydraulic depth function that plots the elevation above the river thalweg vs. the ratio between the area and the width is computed for every section. Then, the elevation above river associated to the lowest and the most prominent peaks of the function, corresponding respectively to the bankfull stage or bankfull/floodplain inflection point and to the floodplain, are automatically extracted for each section. Manning’s equation is then applied to the hydraulic geometry corresponding to the lowest peaks elevation to compute the bankfull discharge at every river channel section. The validation process includes the comparison between the results obtained through the automatic bankfull geometry and discharge estimation and discharge data available from river hydrological gauges. Results demonstrate that the developed approach is effective to delineate the bankfull geometry from high-resolution DEMs and complements traditional qualitative field observations. Thus, our approach represents a cost-effective alternative for mapping detailed spatial variations over large spatial extents that are difficult to cover with traditional fieldwork.