Performance of lateral velocity distribution models for compound channel sections

Hydraulic engineering studies related to floods usually require the lateral distribution of flow velocity across the compound channel section, constituted by the main channel and the floodplain. 2D-Horizontal numerical models (such as the public domain software RMA2 of USACE) are now broadly accepted as an appropriate theoretical model to solve this problem. However, as in the majority of applications the longitudinal scale of flow variation is much larger than the lateral scale of variation (given by the flow width), the longitudinal and lateral flow variations can be accounted for separately (Menéndez 2003); the first one, through well-established 1DLongitudinal models based on de Saint Venant equations (Cunge et al. 1980), while the second one, using 1D-Lateral models. 1D-Lateral models, which solve the lateral distribution of the longitudinal depth-averaged flow velocity, have become the subject of analysis and application in recent years. They run between simple and relatively old empirical and heuristic formulations such as the methods of Lotter (1933), or Divided Channel Method (DCM, used in software HEC-RAS, 2001), Horton (1933), and Pavlovski (1931) to physically-based equations, like the Lateral Distribution Method (LDM) proposed by Wark et al. (1990).