This review paper investigates the determinants of modelling choices, for numerous applications of 1-D free-surface flow and erosion equations, across multiple spatiotemporal scales. We aim to characterize each case study by its signature composed 5 of model refinement (Navier-Stokes: NS, Reynolds-Averaged Navier-Stokes: RANS, Saint-Venant: SV or Approximations of Saint-Venant: ASV), spatiotemporal scales (domain length: L from 1cm to 1000 km; temporal scale: T from 1 second to 1 year; flow depth: H from 1mm to 10 m), flow typology (Overland: O, High gradient: Hg, Bedforms: B, Fluvial: F ) and dimensionless numbers (Dimensionless time period T*, Reynolds 10 number Re, Froude number Fr, Slope S, Inundation ratio Ëz, Shields number 0). The determinants of modelling choices are therefore sought in the interplay between flow characteristics, cross-scale and scale-independent views. The influence of spatiotemporal scales on modelling choices is first quantified through the expected correlation between increasing scales and decreasing model refinements, identifying then flow ty15 pology a secondary but mattering determinant in the choice of model refinement. This finding is confirmed by the discriminating values of several dimensionless numbers, that prove preferential associations between model refinements and flow typologies. This review is intended to help each modeller positioning his (her) choices with respect to the most frequent practices, within a generic, normative procedure possibly enriched 20 by the community for a larger, comprehensive and updated image of modelling strategies.