Formation and evolution of a tidal channel network within a constructed tidal marsh
Faculty of Sciences. Biology
Geomorphology. - Amsterdam
, p. 114-125
University of Antwerp
The morphogenesis of tidal channel networks that dissect intertidal flats and marshes has been studied especially by morphodynamic modeling, while relatively few empirical data exist on high-resolution field observations. Here we measured the spontaneous formation and evolution of a tidal channel network in a newly constructed tidal marsh (Scheldt estuary, Belgium) over a period of 4 years, by high-accuracy topographic surveying with a temporal resolution of 1 year at high spatial resolution considering all channels deeper than 0.1 m. As a reference, topographic measurements with a similar high resolution were performed in a nearby, mature natural tidal marsh network. Based on the field surveying and additional GIS processing, we derived several geometric and hydraulic parameters (channel width, depth, eroded volumes, cross-sectional area, length profiles, drainage density, mainstream length, tidal discharge and watershed area), and compared the evolution of geometric relationships in the constructed marsh with the natural tidal marsh. In this way we have evaluated how fast an equilibrium state was attained. We found that after 2 to 3 years of tidal working the cross-sectional areas of former ditches in the constructed marsh were in equilibrium with the corresponding tidal discharge. Furthermore we observed that the mainstream lengths and the drainage densities for the smaller watershed areas were comparable with the natural tidal marsh, demonstrating the rapid headward growth of newly forming channels and tributary channel formation near the channel heads. Newly formed channels preferentially developed in the low elevation zones of the constructed marsh and channel extension was not significantly influenced by the presence or absence of vegetation. However, the overall channel drainage density and channel cross-sectional areas of the newly formed channels were still lower compared to the natural tidal marsh after 4 years. This indicates that further channel network extension and continued channel deepening can be expected in the coming years.