FLUXOS-OVERLAND solved the 2D shallow water PDEs that accounts for inertial (local and convective), pressure, gravity and friction forces (momentum balance). The model can capture backwater effects (unlike the kinematic or diffusion waves). This is critical to simulate low-relief terrains. The model was originally developed for river reach flood simulations, and therefore it was repurposed here to allow for field and catchment-scale simulations and snowmelt forcing.  The topography (DEM) is used to capture snowmelt runoff pathways (there is no need to specify the location of the streams). This is important in regions with variable contributing areas such as the Canadian Prairies A module for drop inlet spillways and culverts was added. It is based on Bernoulli’s Equation (assumes pressure dominated at this stage) and head losses computed from the implicit Colebrook-White equation for both laminar and turbulent pipe flows, which is solved interactively using the Raphson-Newton interaction method.  Vegetation and other obstacles to the flow are included through distributed absolute roughness heights.