An official website of the United States government
Abstract Rivers are the primary conduits of water and sediment across Earth's surface. In recent decades, rivers have been increasingly impacted by climate change and human activities. The availability of global‐coverage satellite imagery provides a powerful avenue to study river mobility and quantify the impacts of these perturbations on global river behavior. However, we lack remote sensing methods for quantifying river mobility that can be generally applied across the diversity of river planforms (e.g., meandering, braided) and fluvial processes (e.g., channel migration, avulsion). Here, we upscale area‐based methods from laboratory flume experiments to build a generalized remote sensing framework for quantifying river mobility. The framework utilizes binary channel‐mask time series to determine time‐ and area‐integrated rates and scales of river floodplain reworking and channel‐thread reorganization. We apply the framework to numerical models to demonstrate that these rates and scales are sensitive to specific river processes (channel migration, channel‐bend cut‐off, and avulsion). We then apply the framework to natural migrating and avulsing rivers with meandering and braided planforms. Results show that our area‐based framework provides an objective and accurate means to quantify river mobility at reach‐ to floodplain‐scales, which is largely insensitive to spatial and temporal biases that can arise in traditional mobility metrics. Our work provides a framework for investigating global controls on river mobility, testing hypotheses about river response to environmental gradients, and quantifying the timescales of terrestrial organic carbon cycling.
more »
« less
Remote Sensing of Riverbank Migration Using Particle Image Velocimetry
Abstract Mobile river channels endanger human life and property and over centuries shape ecosystems, landscapes, and stratigraphy. Quantifying channel movements from remote sensing is difficult, in part due to the diversity of river mobility processes (e.g., channel migration, cutoffs, avulsion) and planform morphologies (e.g., meandering, braided). Here, we present a framework for quantifying riverbank migration from remote sensing that upscales recent methodological advances from laboratory flume studies utilizing particle image velocimetry (PIV). We apply PIV to image time series of 21 rivers worldwide, showing PIV ignores cutoff and avulsion processes by design and is well suited for tracking riverbank migration regardless of planform morphology. We show that PIV‐derived results for riverbank migration are consistent with published results from centerline‐ and bank‐based Lagrangian methods. Unlike existing methods, PIV offers a grid‐based Eulerian framework where defining channel centerlines is unnecessary and quantified uncertainty in riverbank positions is propagated into uncertainty in migration rates. PIV offers means to efficiently extract global patterns in riverbank migration from decades of satellite data, as well as investigate river response to climate change and human activities in our rapidly changing world.
more »
« less
- PAR ID:
- 10433300
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 128
- Issue:
- 7
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Source‐to‐sink transfer of sediment and organic carbon (OC) is regulated by river mobility. Quantifying trends in river mobility is, however, challenging due to diverse planform morphologies (e.g., meandering, braided) and measurement methods. Here, we utilize a remote‐sensing method applicable to all planform morphologies to quantify the mobility timescales of 80 rivers worldwide. Results show that, across the continuum from meandering to braided rivers, there is a systematic reduction in the timescales of channel mobility and—to a lesser extent—floodplain reworking. This leads to a decrease in the efficiency with which braided rivers rework old floodplain material compared to their meandering counterparts. Reduced floodplain reworking efficiency of braided rivers leads to smaller channel‐belt areas relative to their size. Results suggest that river‐mobility timescales derived from remote sensing can aid in the characterization of sediment and OC storage and transit times at a global scale.more » « less
-
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.more » « less
-
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.more » « less
-
Abstract The lateral migration of river channels is an important control on the evolution of alluvial fans, deltas, and floodplains. Lateral migration consists of both gradual riverbank migration and abrupt shifts in location due to avulsions or cutoffs. Methods exist to measure bank migration, but abrupt shifts in position are rarely considered or are not emphasized. Here we describe a new method using Landsat‐derived water occurrence images that primarily focuses on detecting when a channel has abruptly shifted position, either from avulsion or cutoff. The method does not assume any a priori model of channel geometry or evolution. Within a given area of interest, binary channel images created from the fluvial water occurrence record are stacked through time. Then a channel shift intensity, , is created by estimating the number of possible ending times for fluvial water voxels (a point in three‐dimensional space) in the stacked occurrence record. The number of possible end‐times for fluvial water voxels within a given region of the occurrence record reveals the likelihood that a reach of a river underwent an abrupt channel shift during the observation period. We present the results of this analysis for a 194 481 km2region of the Amazonian basin. Follow‐up validation found three avulsions and 270 cutoffs within regions identified by this method. We show that areas above a threshold contain an avulsion or cutoff with high probability. This highlights the method's potential to detect and quantify abrupt channel shifts at the basin scale. The method also successfully distinguishes between abrupt channel movement and complex braiding behaviour. As this method is applicable to any binary water‐masked time series images, future applications of this method have the potential to provide insight into the controls and spatial variance of avulsions and cutoffs across a variety of scales.more » « less
