Tidal networks 2. Watershed delineation and comparative network morphology

Through the new method for automatic extraction of a tidal network from top ographic or bathymetric fields described in a companion paper [Fagherazzi e t al., this issue], we analyze the morphology of aggregated patterns that w e observe in nature in different tidal environments. Specifically, we defin e, on the basis of a hydrodynamic analysis, a procedure for watershed delin eation and for the identification of the "divides" for every subnetwork and look at the resulting drainage density and its related scaling properties. From the systematic, large-scale plots of drainage density and channel wid th versus watershed area we address the issue of a possible geomorphic crit erion that corresponds to the parts of the tidal landscape that are charact erized by river-like features. We also analyze the relationship of total co ntributing tidal basin area to channel widths and to mainstream lengths (Ha ck's law). We study comparatively probability distributions of total draina ge areas and of "botanical" mass (the area of the channelized landscape ups tream of a given section) for tidal and fluvial patterns and find altered s caling features of tidal landforms that reflect the complex interactions of different mechanisms that shape their geometry. Simple geomorphic relation ships of the types observed in the fluvial basin (e.g,, power laws in the w atershed area versus drainage density, mainstream length, or channel width relationships) do not hold throughout the range of scales investigated and are site-specific. We conclude that tidal networks unlike rivers exhibit gr eat diversity in their geometrical and topological forms. This diversity is suggested to stem from the pronounced spatial gradients of landscape-formi ng flow rates and from the imprinting of several crossovers from competing dynamic processes.