Repeated continental glaciation of the US Central Lowlands disrupted pre-Pleistocene fluvial drainage networks by filling valleys, rerouting major rivers, and incising oversize meltwater channels. Post-glacial landscapes are characterized by large fractions of non contributing area (NCA) which does not contribute flow to external drainage networks by steepest decent algorithms. Analysis of land surfaces most recently glaciated between 130,000 and 10,000 years ago suggests that NCA is lost over time as fluvial networks are reestablished. Low surface slopes combined with significant fractions of NCA make such fluvial network growth difficult to reconcile with standard treatments of flow routing. We develop modules in Land Lab that allow for connection of NCA via filling and spilling from closed depressions on the surface and through groundwater flow across subtle surface water divides to explore the impacts of these mechanisms of flow accumulation on the pace of evolution and morphology of resulting river networks. This work highlights the more general need to consider the relationship, or lack of relationship, between topography and river discharge.