Low sediment retention efficiency limits delta formation in tectonically confined high‐energy coastal systems

Abstract Although deltaic growth is commonly linked to high sediment supply, numerous river systems challenge this assumption by exhibiting limited or absent delta plains despite substantial sediment loads. We investigate this paradox in the west‐flowing Narmada and Tapi rivers of Peninsular India, which deliver sediment fluxes comparable with delta‐forming systems yet lack classic subaerial delta development at their mouths in the Gulf of Khambhat. Using an integrative analysis of geomorphic indices, sediment flux, stream power, bathymetry, tidal regime and available stratigraphic evidence, we evaluate sediment retention rather than sediment supply as the critical control on delta formation. Our results show that (i) steep, tectonically confined river gradients suppress floodplain development and accommodation creation; (ii) high monsoonal unit stream power maintains sediment in suspension during peak delivery; and (iii) strong tidal currents combined with a broad, topographically complex continental shelf promote efficient sediment dispersal and offshore export. Stratigraphic records suggest a brief late Holocene phase of progradation followed by incision, reflecting a highly dynamic accommodation regime influenced by tectonic uplift. We conclude that the absence of subaerial deltas at the Narmada and Tapi mouths does not reflect sediment limitation but instead represents a stable end‐member of tide‐dominated, morphodynamically constrained estuarine systems characterised by low sediment retention efficiency. This conceptual framework provides a basis for reinterpreting delta–estuary transition in other high‐energy, tectonically influenced coastal settings worldwide and highlights the need to move beyond sediment supply alone when assessing delta sustainability under future environmental change.