The three‐dimensional configuration of sedimentary landforms in intertidal environments represents a major control on regional hydrodynamics. It modulates the location and magnitude of forces exerted by tidal currents and waves on the landform itself and on engineered infrastructure such as sea walls or coastal defences. Furthermore, the effect is reflexive, with the landforms representing an integrated, long‐term response to the forces exerted on them. There is a strong reciprocal linkage between form and process (morphodynamics) in the coastal zone which is significantly lagged and poorly understood in the case of cohesive, vegetated sediments in the intertidal zone. A method is presented that links the geometric properties of the tidal flat–salt marsh interface to the history and potential future evolution of that interface. A novel quantitative classification scheme that is capable of separating marsh margins based on their functional form is developed and is applied to demonstrate that relationships exist between landform configuration and morphological evolution across a regional extent. This provides evidence of a spatially variable balance between self‐organized and external controls on morphodynamic evolution and the first quantitative basis for a quick assessment procedure for likely future dynamism. © 2019 John Wiley & Sons, Ltd. A morphometric classification of salt marsh marginal landforms is developed, allowing a regional‐scale inventory to be established from LiDAR data. Comparison of margin type with historical morphological changes reveals clear associations between margin configuration and dynamism, providing a quantitative basis for the rapid evaluation of likely system dynamism that may be useful to conservation practitioners or site managers