Tidal Networks: Form and Function

We review some geomorphological properties of tidal networks and their embedded landforms, aiming at inferring their leading eco-morphodynamic interrelations. Indeed the interplay of vegetation patterns (hence the ecological edge) and surface morphology (including the nested networks cutting through salt marshes and their embedding tidal flats, overall portraying an inevitably complex coevolution) is key to the dynamics of the tidal landscape. Through the extraction of network patterns from topographic or bathymetric fields and aerial imaging, we consider analyses of the resulting morphologies what-ever their age and stability, in particular by looking at the structures that control the landscape-forming hydrodynamics. We also provide a brief but hopefully significant comparative analysis with river networks, to look at similarities and departures in the light of invariance properties over a range of scale, which, of course, bear dynamic implications. Watershed delineation through the identification of suitable ‘divides’, elongations of nested tidal basins, regime (or empirical regime-like) theories, statistics of network lengths, drainage densities facing the patterns of halophytic vegetation (in itself a key morphodynamic factor) and meandering features are considered. Great diversity is observed, rather than common patterns, in the tidal landscape. This diversity is suggested to stem from the pronounced spatial gradients of landscape-forming flow rates and to the imprinting of several crossovers from competing dynamic processes that confuse any tendency towards scale-invariant forms and functions. We claim that this basically differs from the river basin morphology owing to the dominance of invariant fluvial erosion processes over many scales therein.