Flows, Transport, and Effective Drag in Intertidal Salt Marsh Creeks

Intertidal creeks (channel width <5 m) weave through salt marshes, delivering water, nutrients, and sediments into the marsh interior and affecting spatial heterogeneity in plant and animal distributions. Despite their global prevalence, creek connectivity, and the mechanisms controlling cross-marsh hydrodynamics, remain poorly resolved. In this study, we measured flow and total suspended solids transport in three intertidal creeks within a confined drainage basin in a Georgia, USA salt marsh. We discovered that the effective drag is 3-12 times greater than bed drag, reaching levels similar to those observed in coral reefs. Furthermore, the drag between tidal flood and ebb phases differs, indicating an asymmetric drag. Analyses of along-channel momentum reveal that pressure gradient O(10-3-10-2) m/s(2) and friction O(10-3-10-2) m/s(2) dominate creek momentum balance. Divergence in tidal and suspended solids transport between adjacent creeks revealed contrasting tidal transport asymmetries (i.e., flood or ebb dominated) within this confined basin. We discuss how these differences may alter the eco-geospatial evolution of salt marshes and their response to sea-level rise.

Automated summary

Intertidal creeks play a significant role in connecting salt marshes and influencing the spatial heterogeneity in plant and animal distributions. The study reveals that the effective drag in these creeks is significantly higher than bed drag, leading to asymmetrical drag between tidal flood and ebb phases. Pressure gradient and friction dominate creek momentum balance, highlighting potential impacts on eco-geospatial evolution of salt marshes.