Hydrodynamics of salt marsh creek systems: Implications for marsh morphological development and material exchange

TLDR

Tide‑dominated marshes feature integrated ebb‑aligned drainage systems that act as major conduits for material exchange, and in north Norfolk the highly unsteady creek flows produce velocity and stress transients driven by tidal‑prism discontinuity and vegetated surfaces; marsh morphological development follows a form‑process feedback where the marsh surface separates depositional and erosional regimes, and vertical growth increases the intermittency of creek sediment transport. The study aims to focus on direct measurement of marsh surface processes rather than relying solely on creek flux measurements. Marsh morphological development is governed by a form‑process feedback with the marsh surface as a topographic threshold, and velocity transients are associated with large discharges that must be accounted for in material flux computations. Creek flux measurements alone are insufficient to estimate total material budgets because a large proportion of tidal exchange occurs via the marsh edge, and these results are relevant to marshes of varying geometry across the tidal energy spectrum.

Abstract

Abstract Integrated ebb‐aligned drainage systems are a feature of tide‐dominated marshes, and are generally regarded as major conduits for material exchange. In north Norfolk, highly unsteady creek flows exhibit well‐developed velocity and stress transients which result from the discontinuous nature of the tidal prism and the interaction of shallow water tidal inputs with hydraulically rough vegetated surfaces. Marsh morphological development is governed by a form‐process feedback, in the sense that the marsh surface acts as a topographic threshold separating the depositional regime of below‐marsh tides from the erosional (ebb‐dominated) regime of over‐marsh tides. Vertical marsh growth results in increasing intermittency of creek sediment transport. Furthermore, velocity transients are associated with large discharges which must be allowed for in material flux computations. Creek flux measurements are not in themselves sufficient to estimate total material budgets, since a large proportion of tidal exchange may take place via the marsh edge. Such studies should focus instead on direct measurement of marsh surface processes. These findings have relevance beyond this back‐barrier setting to marshes of different geometry, occupying a broad range of the tidal energy spectrum.