Modeling the impact of spatially-variable vegetation on hydrological connectivity and residence time distributions in river deltas
Abstract
Field work and modeling results have shown a significant amount of flow exchange between the distributary channels and inundated islands in deltaic systems. Vegetation is known to significantly alter flow in wetland systems, but the effect of the spatial distribution of vegetation patches on connectivity and residence times in coastal deltas remains an important question. This research aims to determine to what extent vegetation patch size, percent cover, and hydraulic roughness within deltaic islands influences hydrological connectivity and the residence time distribution of an idealized deltaic system. A two-dimensional hydrodynamic model was used to numerically solve the shallow water equations in an idealized channel-wetland complex, modeled after Wax Lake Delta in coastal Louisiana. Several types of spatially-variable scenarios were modeled, including maps with patches of vegetation distributed randomly throughout the islands according to some percent cover and patch size. Vegetation was modeled as a modified bed roughness, which was varied by several orders of magnitude above the bed roughness to account for variations in vegetation density. Each patched model run was then compared to an equivalent run with an averaged uniform roughness in the islands. In general, we find that patched runs tend to demonstrate much more connectivity than their equivalent uniform runs, particularly in scenarios with denser vegetation and larger patch sizes. When percent cover is above the percolation limit of 41% vegetation, patched scenarios do not vary considerably from their uniform equivalent - however, below the percolation limit, much more connectivity is observed in the patched runs, particularly those with a percent cover value of approximately 20%. In all patched cases, island residence times were observed to be higher than those in the uniform runs, in some cases by a considerable amount. These effects could be significant for modeling ambient nutrient removal in deltaic systems. In addition, the formation of high-velocity secondary channels in the islands was observed, which could potentially offer insights into sediment transport and the geomorphological development of coastal deltas.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H53E1754W
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 1803 Anthropogenic effects;
- HYDROLOGYDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1824 Geomorphology: general;
- HYDROLOGY