Vegetation is an important component of constructional landscapes, as plants enhance deposition and provide organic sediment that can increase aggradation rates to combat land loss. We conducted two sets of laboratory experiments using alfalfa (Medicago sativa) to determine the effects of plants on channel organization and large-scale delta dynamics. In the first set, we found that rapid vegetation colonization enhanced deposition but inhibited channelization via increased form drag that reduced the shear stress available for sediment entrainment and transport. A second set of experiments used discharge fluctuations between flood and base flow (or interflood). Interfloods were critical for reworking the topset via channel incision and lateral migration to create channel relief and prevent rapid plant colonization. These low-flow periods also greatly reduced the topset slope in the absence of vegetation by removing topset sediment and delivering it to the shoreline. Floods decreased relief by filling channels with sediment, resulting in periods of rapid progradation and enhanced aggradation over the topset surface, which was amplified by vegetation. The combination of discharge fluctuations and vegetation thus provided a balance of vertical aggradation and lateral progradation. We conclude that plants can inhibit channelization in depositional systems and that discharge fluctuations encourage channel network organization to naturally balance against aggradation. Thus, variations in discharge are an important aspect of understanding the ecomorphodynamics of aggrading surfaces and modeling vegetated deltaic systems, and the combined influences of plants and discharge variations can act to balance vertical and lateral delta growth.
Bibliographical noteFunding Information:
Data for this paper are available through the Sediment Experimentalists Network (sedexp.net) Knowledge Base and the SEAD data repository (https://sead2. ncsa.illinois.edu/). This work was supported by NSF grant EAR 1324335 to W. Kim. We thank David Mohrig, John Shaw, and Doug Jerolmack for early reviews of this manuscript. We appreciate comments from Giovanni Coco, Karin Bryan, Jaap Nienhuis, Maarten Kleinhans, and two anonymous reviewers, which greatly improved the manuscript.
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All Science Journal Classification (ASJC) codes
- Earth-Surface Processes