A Transit Through Galloway Space: Process Dominance Naturally Changes as Deltas Grow

River deltas are coastal landforms that encompass valuable resources and diverse ecosystems. Conservation and resource extraction is complicated because deltas are dynamic and it is challenging to understand the relationships between boundary forcing and the resultant form. Galloway (1975) paved the way for better understanding the relationship between processes and form with his famous ternary diagram, which suggests delta morphology is a function of the relative strength of fluvial, wave and tidal energy. Using sediment flux ratios at the river mouth, we can now plot entire deltas in ternary space. However, these ratios change as deltas grow because distributary channels divide the sediment, relative angles of wave approach evolve with shorelines and the tidal prism enlarges as delta networks expand. Thus, a delta initially characterized as river-dominated may transition to wave or tidal-dominated. To test this idea, we reframed the Galloway diagram as sediment flux ratios at individual channel mouths to see if individual channels on the same delta evolve independently and affect delta-scale transition. Deltas were numerically produced in Delft3D using a suite of physical parameters to establish a range of relative river, wave and tidal strengths in ternary space. Analysis included extraction of river, wave and tidal flux values each individual river channel mouth, as the delta temporally evolved. Further, an a priori delta-scale sediment flux estimate was calculated to investigate the migration of individual channels in relation to delta-scale sediment flux values. Preliminary results suggest individual river mouths transit through ternary space, at times occupying space dominated by processes inconsistent with the delta-scale estimate. If wave or tide sediment fluxes are large enough, then deltas that are initially river-dominated will eventually transit into opposite regions of ternary space. Additionally, river dominated deltas were shown to evolve into tidally dominated space due to a flattened slope profile from continuous aggradation, leading to larger tidal intrusion lengths. The results suggest that deltas can be compounded with channels dominated by different processes and this implies that stratigraphic interpretations of deltas may be more complex than previously thought.