On the influence of river Basin morphology and climate on hydrogeomorphic floodplain delineations

Elevation-based hydrogeomorphic models are widely used to parsimoniously delineate floodplains with limited input data using topographic gradients to distinguish floodplain areas from hillslopes. Hydrogeomorphic models generally use scaling laws to assess flood flow depths as a function of contributing drainage areas. Floodplains are consequently mapped as those areas underlying maximum flood levels. Recent scientific literature has demonstrated that hydrogeomorphic models consistently perform from regional to global scale, validating geomorphic floodplain delineations in diverse morphological and hydroclimatic river settings. Nevertheless, the relationship between model fidelity, basin morphology, and basin hydroclimatic conditions is still unclear. Specifically, further investigations on the applicability of scaling laws in semi-arid and low-gradient basins is needed. In this work we investigated how climatic variability and basin slope can influence the parameterization of the abovementioned scaling laws in support of hydrogeomorphic floodplain modeling. Eleven basins in the west-central United States were selected as case studies. This research demonstrated that sub-basins slope and annual rainfall are the most influential morphometric and climatic parameters on scaling law regressions. Specifically, we found that scaling relationships are inconsistent in defining semi-arid basin floodplains (average annual rainfall lower than 570 mm) with low-gradient valley slopes (lower than 5%).