Association of tidal channel tributaries with mainstem meander bends: Landform patterns to inform tidal marsh restoration design

Species recovery and coastal resilience programs are spending hundreds of millions of dollars on coastal habitat restoration, particularly for tidal marshes. Tidal channels are central to tidal marsh function, and fortunately quantitative design guidance is available for how many and what size tidal channels are appropriate for a marsh restoration footprint. But guidance on where those channels should be located within the restoration footprint and how the channel networks should be structured is more limited. Inappropriately locating new tidal channels could result in restoration failure, if the channels are not sustainable (i.e., fill with sediment) in their chosen locations. Using natural tidal landforms as a template for restoration design can help minimize the risk of channel design failure. Excavating 2nd- or higher-order channels will require making decisions on where channel tributaries should be located. To address this design issue, I examined three distinct tidal marsh systems (the Skagit Delta in Washington State, USA; Ochlockonee Bay in Florida; and Tubul-Raqui in Chile) for patterns in tidal tributary channel locations. The results indicate that tributary channels are randomly encountered along the mainstem channel for large channels, but for small channels they are disproportionately located on the concave banks of meander bends, and they are generally larger in these locations. Design of tidal channel networks that mimics natural landforms should accelerate restoration site maturation and development of maximal hydraulic and ecological function. • Tidal tributaries typically join concave rather than convex mainstem meander banks • For small channels, tributaries are more common on meanders than straight reaches • For small channels, tributaries to meanders were larger than to straight reaches • Results provide guidance for restoration design—where tributaries should be located