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Abstract Deltaic river networks naturally reorganize as interconnected channels move to redistribute water, sediment, and nutrients across the delta plain. Network change is documented in decades of satellite imagery and laboratory experiments, but our ability to measure and understand channel movements is limited: existing methods are difficult to employ efficiently and struggle to distinguish between gradual movements (channel migration) and abrupt shifts in river course (channel avulsions). Here, we present a method to extract channel migration from plan‐view imagery using particle image velocimetry (PIV). Although originally designed to track particles moving in a fluid, PIV can be adapted to track channels moving on the delta surface, based on input estimates of channel width, migration timescale, and maps of the wet‐dry interface. Results for a delta experiment show that PIV‐derived vector fields accurately capture channel‐bank movements, as compared to manually drawn maps and an independent image‐registration technique. Unlike other methods, PIV targets the process of channel migration, excluding changes associated with channel avulsions and overbank flow. PIV‐derived migration rates from the experiment span an order of magnitude and are reduced under lower sediment supply and during sea‐level rise, supporting recent models. Together, results indicate that PIV offers a fast and reliable way to measure channel migration in river networks, that channel migration rates under non‐cohesive conditions can displace channels a distance comparable to their width in the time needed to aggrade ∼10% of the channel depth, and that migration direction is ∼60% orthogonal to mean flow direction and ∼40% flow‐parallel overall.
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Sediment Load and Grain Size Controls on Channel Migration Patterns in Experimental Deltas
Abstract Understanding channel migration is essential in interpreting long‐term evolution of fluvial systems and their deposits. Using data from an experimental delta, we analyzed the kinematics of the upstream channel and assessed the relative dominance of continuous lateral channel migration versus abrupt changes (i.e., avulsions). Detailed investigation of channel centerline location at minute intervals reveals a short‐term correlation between the magnitude of migration rates measured at the same location and a spatial correlation that diminishes with distance between points. The main finding is that the channel migrates across the entire deltaic domain without large and abrupt lateral shifts but through continuous lateral migration at variable rates. Long periods of back and forth small moves are separated by short bursts of rapid lateral migration. This finding contradicts the default expectation that that aggrading systems are characterized by avulsions and suggests that highly mobile rivers tend to avulse less. We contrast this with another experiment conducted under similar conditions but with finer sediment supplied at a lower rate which shows drastically less lateral migration; the kinematics is instead dominated by periodic flow reconfiguration episodes akin to avulsions, an indication that channel migration‐style depends on the sediment load. The characteristics of these two experiments parallel two regions of the Mississippi River, the meandering and highly mobile alluvial plain and the less dynamic deltaic region, suggesting that bedload sediment deposition at the transition into backwater zone plays an important role in re‐shaping the river planform and migration style.
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- Award ID(s):
- 1854452
- PAR ID:
- 10369114
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 127
- Issue:
- 5
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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