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ABSTRACT Natural river diversion, or avulsion, controls the distribution of channels on a floodplain and channel sandstone bodies within fluvial stratigraphic architecture. Avulsions establish new flow paths and create channels through several recognized processes, or styles. These include reoccupying existing channels, or annexation, downcutting into the floodplain, or incision, and constructing new channels from crevasse‐splay distributary networks, or progradation. Recent remote sensing observations show that avulsion style changes systematically moving downstream along modern fluvial fans but, to date, no studies have assessed the significance of these trends on fluvial fan stratigraphy. Here, spatiotemporal changes in avulsion stratigraphy are investigated within the Salt Wash Member of the Morrison Formation, deposited in the Cordilleran foreland basin during the Late Jurassic epoch. Measured sections and photographic panels were analysed from 23 locations across the Salt Wash extent. Avulsion style was identified in the stratigraphic record by the basal contact of a channel storey with underlying strata: channel–channel contacts indicate annexation, channel–floodplain contacts indicate incision and channel–heterolithic contacts indicate progradation. Contact types change downstream, such that channel–channel and channel–floodplain contacts dominate proximal locations, while channel–heterolithic contacts become increasingly prevalent downstream. Outcrop results were compared to a numerical model of fluvial fan formation and remote‐sensing analysis of avulsions on modern fans. In both additional datasets, channels in proximal fan positions tend to avulse via annexation, reoccupying abandoned channels, while channels in more distal positions tend to avulse via increasingly significant progradation. These findings suggest a relationship between newly recognized downstream changes in avulsion style and well‐established downstream changes in fluvial fan architecture. Furthermore, this suggests that fan architecture can inform interpretations of ancient fluvial dynamics, including avulsion behaviour, and that avulsions can cause stratigraphically significant and measurable changes to fan architecture.
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EMPTY CONTAINERS, OVERFLOWING RIVERS: STATE FUNDED FENCING AND IMPACTS IN EAGLE PASS, TEXAS
Abstract This study uses hydraulic modeling to examine the impacts of two new fence sections at Eagle Pass, Texas: a container fence and a state-funded fence section south, and downstream, of the already modeled federal border fence. We used the model Nays2DFlood to compare fence and non-fence conditions at various recurrence intervals to determine how the fence is affecting flood extents, water depth, and water velocity. Water depth is deeper in the channel and the floodplain and shallower directly at the fence line when compared to non-fence conditions. Water velocity is faster within the channel and the floodplain and slower at the fence line during fence conditions. These impacts have the potential to adjust sediment regimes at this location and downstream of this area, altering water quality and channel morphology. Demographic analysis also show that particularly susceptible populations, including a majority Latino, low income individuals, those under 5, and those 65–74, are present in large numbers at these fence sections and are therefore vulnerable to flooding. Supplemental material is available for this article online.
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- Award ID(s):
- 1911512
- PAR ID:
- 10427454
- Date Published:
- Journal Name:
- The Texas Journal of Science
- Volume:
- 75
- Issue:
- 1
- ISSN:
- 0040-4403
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.32011/txjsci_75_1_Article2
