Description: A reduced-complexity model for river delta formation – Part 2: Validation of the flow routing scheme Earth Surface Dynamics Discussions, 2, 871-910, 2014 Author(s): M. Liang, N. Geleynse, D. A. Edmonds, and P. Passalacqua In a companion paper (Liang et al., 2014) we introduced a Reduced-Complexity Model (RCM) for river delta formation, developed using a parcel-based "weighted random walk" method for routing water and sediment flux. This model (referred to as "DeltaRCM") consists of a flow routing scheme as the hydrodynamic component (referred to as "FlowRCM") and a set of sediment transport rules as the morphodynamic component. In this work, we validate the flow routing scheme (FlowRCM) via a series of hydrodynamic tests by comparing the model outputs to Delft3D and theoretical predictions. These tests are designed to reveal the capability of FlowRCM to resolve flow field features that are critical to delta dynamics at the level of channel processes. In particular, we focus on (1) backwater profile, (2) flow around a mouth bar, (3) flow through a single bifurcation, and (4) flow through a distributary channel network. We show that while the simple rules are not able to reproduce all fine-scale flow structures, FlowRCM does capture flow field features that are essential to deltaic processes such as bifurcations and avulsions. Finally, we discuss advantages and limitations of FlowRCM and identify environments most suitable for it.