Transgression and Tidal Creek Development : The Role of Ecological Processes

Tidal channels are one of the most common and prominent geomorphic features on salt marshes. Because of their much smaller resistance to water flow compared with that of the densely vegetated marsh area, well developed tidal channels often function as arteries and carry significant amount of water as well as sediments during both the flood and ebb period of salt marshes hydraulic cycle. Therefore features of tidal channels, such as their drainage densities, overall network structures and spatial distributions, as well as the geometries of individual channels, determine to a very large degree, the overall hydrology of the salt marshes, and consequently, the ecology of the salt marshes. Recently, a simple model has been developed focusing on the initiation as well as the evolution and development of tidal channels. Despite the simplicity of the model, many important features of the tidal channels development, such as the well known fact of the rapid growth and extension of the channel networks in the young and fresh marshes, and the subsequent retreat and reduction of channel networks in the mature and old marshes, have all been faithfully reproduced. The effort has also been made to delineate the relative effect of different hydraulic parameters, such the local marsh elevation, tidal range, and the flow resistance coefficient of the salt marsh vegetation, in terms of their importance to the equilibrium value of the tidal channel drainage density. The model is entirely built from the physical perspective of the salt marsh environment, namely the biological components has been compressed and simplified to two parameters, which are the vegetation encroachment rate and the flow resistant coefficient. The model can however be extended to include many key ingredient of the bio-geo-chemical interactions. The current model does provide a framework for future development of much more sophisticateds models that can capture the essencial bio-geo-complex processes of salt marshes.