Channel Migration in Experimental River Networks Mapped by Particle Image Velocimetry. Issue 1 (30th December 2021)

• Record Type: Journal Article
• Authors: Chadwick, A. J.; Steel, E.; Williams‐Schaetzel, R. A.; Passalacqua, P.; Paola, C.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-30
• Subjects: channel migration -- river networks -- river deltas -- particle image velocimetry; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2021JF006300
• Languages: English
• ISSNs: 2169-9003

Abstract

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. Plain Language Summary: River deltas change over time as channels move to distribute water, sediment, and nutrients across the coastal plain. Channel movements are documented worldwide in decades of satellite imagery, but are difficult to measure efficiently and precisely with existing approaches. Here, we present a new automated method to extract channel motion data from overhead images using particle image velocimetry (PIV). Originally designed to track particles moving in a fluid, the PIV algorithm can be adapted to track channels migrating on a delta surface. Using data from a laboratory experiment, we show that PIV‐derived channel motions are accurate and comparable to manually drawn maps and an independent image‐registration technique. Unlike existing approaches, PIV specifically measures gradual channel migration, excluding other types of change such as river floods and diversions. Application of PIV to river networks can provide new insight into how rivers migrate; for example, results from the experiment indicate that rivers migrated more slowly during sea‐level rise and that ∼40% of channel migration was directed upstream and downstream rather than sideways. Key Points: Particle image velocimetry (PIV) can be adapted to accurately capture channel‐bank motions in experimental river networks PIV specifically targets the process of channel migration, excluding changes associated with overbank flows and channel avulsions Experimental channels migrated ∼10 channel widths between avulsions, with ∼60% of migration directed normal to the mean flow