Balancing aggradation and progradation on a vegetated delta: The importance of fluctuating discharge in depositional systems

Journal Article · Wed Oct 04 00:00:00 EDT 2017 · Journal of Geophysical Research. Earth Surface

DOI:https://doi.org/10.1002/2017JF004378· OSTI ID:1398923

Piliouras, Anastasia  ^[1]; Kim, Wonsuck  ^[2]; Carlson, Brandee  ^[3]

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1. Univ. of Texas at Austin, Austin, TX (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Univ. of Texas at Austin, Austin, TX (United States)
3. Univ. of Texas at Austin, Austin, TX (United States); Rice Univ., Houston, TX (United States)

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. Furthermore, 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.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1398923
• Report Number(s): LA-UR-17-24401
• Journal Information: Journal of Geophysical Research. Earth Surface, Vol. 122, Issue 10; ISSN 2169-9003
• Publisher: American Geophysical Union
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
Earth Sciences