About

Ajay B. Limaye is an Associate Professor in the Department of Environmental Sciences. He earned his Ph.D. from the California Institute of Technology in 2015. His research focuses on the evolution of landscapes on Earth and other planets, with particular attention to the role of rivers. His current research topics include river forms, dynamics, and deposits; landscape and sedimentary records of climate on Mars and Titan; and the feedbacks between landslides and ecology in central Virginia. Limaye employs tools such as remote sensing, geospatial analysis, numerical modeling, and laboratory experiments to conduct his research. His work aims to understand the processes shaping planetary surfaces and landscapes, contributing to the fields of geomorphology and planetary geology.

Research topics

• Geology
• Geomorphology
• Computer science
• Geometry
• Environmental science

Selected publications

• Bridging Gaps in Satellite Observations of River and Delta Landscapes Using Image Warping

  Water Resources Research · 2025-05-01 · 1 citations

  articleOpen accessSenior author

  Abstract Satellite images are increasingly used to monitor changes in fluvial landscapes such as channel migration, bar development, and avulsion. Yet, spatial and temporal gaps in image data — due to intervals between observations, cloud cover, or sensor malfunctions — limit their applicability. This study tests whether image warping, a well‐established technique that generates smooth transitions between images, can bridge these gaps in observations of fluvial landscapes. The approach applies several steps to satellite images: (a) creating channel masks, (b) delineating channel topology, (c) correlating topologic components and defining control points, (d) calculating transformations between image pairs using control points, and (e) warping channel masks based on these transformations. This approach produces intermediate channel configurations from pairs of input images. We apply this technique to two case studies: the rapidly migrating Ucayali River in Peru and the actively prograding Wax Lake Delta in Louisiana. The reconstructions show channel migration and/or progradation that are consistent with actual observations, indicating reasonable estimates to fill gaps between satellite observations. Importantly, the accuracy of the reconstructions depends on the careful selection of the input images to avoid abrupt geomorphic changes that could compromise the warping process. By combining the surface reconstruction for the Ucayali River with a simple model for channel and floodplain aggradation, we construct a stratigraphic model directly informed by the satellite observations. These case studies suggest that applying image warping to Earth‐surface observations has the potential to overcome gaps in satellite data availability and translate observations directly to models for fluvio‐deltaic stratigraphy.

  PublisherOA PDFDOI

• A Geometric Algorithm to Identify River Meander Bends: 2. Test for Characteristic Shapes

  Journal of Geophysical Research Earth Surface · 2025-03-01 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract River meander bends are widely considered to have recurring shapes. Formal classifications of meander bends have provided an important framework for basic research and practical applications in river engineering and restoration. However, the central role of expert interpretation in both mapping and classifying meander bends leaves persistent uncertainty for whether their shapes do form patterns or instead represent a continuum of forms. This study analyzes meander bend shapes derived in a companion paper about the Beatton River, Canada, to test whether meander bends show repeating shapes without the prior assumption that such patterns exist. Meander bends are compared using Fréchet distance, a curve similarity measure, and evaluated for common shapes using agglomerative hierarchical clustering. The case study indicates that normalizing meander bend coordinates by wavelength and amplitude yields clusters of meander bends with internally consistent shapes. Characteristic meander bends for each cluster are derived by averaging the normalized coordinates and rescaling by the mean amplitude and wavelength for the source meander bends. Whereas automatically mapped meander bends vary in number and extent with a dimensionless amplitude threshold ( A st *), the characteristic meander bends are generally robust against variation in this parameter within its effective range (0.1 A st * 1). By establishing a test for characteristic shapes among populations of multifarious meander bends, the analysis enables new tests for environmental controls on channel form, a standard for assessing the fidelity of numerical models for planform evolution, and a method to design nature‐based templates for river restoration and engineering.

  PublisherOA PDFDOI

• A Geometric Algorithm to Identify River Meander Bends:1. Effect of Perspective

  Journal of Geophysical Research Earth Surface · 2025-03-01 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract Channels form meander bends, whether in rivers or on glaciers, volcanoes, coastlines, or the seafloor. Therefore, isolating meander bends is instrumental in characterizing channel shape and its relationship to the surrounding environment. The common approach of delimiting meander bends using inflection points yields isolated arcs that differ from traditional depictions. This study develops a geometric algorithm for mapping meander bends to bridge this gap. The approach accounts for two perceptual factors: observer viewpoint and the scale of significant deviations in the river path. The channel centerline is divided into three elements: arcs of positive/negative curvature, and effectively straight reaches with dimensionless amplitude ( A st *) below a threshold. Meander bends are formed by connecting reaches between arcs of similar curvature and trimming to where the openness, or viewshed, falls below the value for a straight line (180°). A case study for the Beatton River, Canada, shows the method captures the full extents of meander bends and reproduces a common classification (simple vs. compound) and scaling between wavelength and channel width ( 12 w c ) from visual interpretation. The number and extents of meander bends change with A st *; 0.1 < A st * < 1 prevents over‐segmentation without lumping adjacent meander bends. The approach further indicates two mapping solutions that correspond to viewpoints on opposite sides of the river. By harmonizing the geometric definition of a meander bend with its traditional depiction, this approach advances the quantitative analysis of channels across geologic environments. A companion study tests whether the mapped meander bends have characteristic shapes.

  PublisherDOI

• Forecasting Channel Response to Extreme Floods Using River Morphology: Lessons from Hurricane Helene

  Abstracts with programs - Geological Society of America · 2025-01-01

  article
  PublisherDOI

• Coherent Motion of Channel Threads in the Braided Brahmaputra‐Jamuna River

  Journal of Geophysical Research Earth Surface · 2025-06-01 · 3 citations

  articleOpen accessSenior author

  Abstract Braided river channels are formed by multiple channel threads that often shift laterally through either abrupt avulsion or more coherent migration over time. Several approaches have been developed to quantify the planform change of braided rivers, but predicting this change remains challenging due to the intricate structure of the channel network and the strong sensitivity of planform morphology to water stage. To address these challenges, we developed an approach to test whether individual channel threads move laterally across annual timescales. We then test whether a curvature‐driven model for the migration of meandering rivers can similarly explain the motion of braided channel threads. As a case study, we analyze the migration pattern of the Brahmaputra‐Jamuna River, whose discharge is strongly seasonal due to the monsoonal hydroclimate. We characterize planform morphology by selecting low‐stage water masks derived from Landsat images. We find that from 2001 to 2021, ∼43% of the total length of channel threads migrated coherently, at an average rate equivalent to ∼30% of the local width of the channel thread per year. Migration rate is weakly related to channel‐thread width. In three examples, the migration rate is closely related to the channel‐thread curvature, and the curvature‐driven model successfully describes their migration. By connecting the motion of channel threads with their planform geometry, the analysis suggests that the seemingly chaotic motion of braided rivers is somewhat organized over decadal timescales, indicating the potential for better hazard and flood predictions for communities living within and along these river channels.

  PublisherOA PDFDOI

• Response of submarine braided channels to varying inflow hydrographs: Geomorphic experiments and stratigraphic implications

  Sedimentology · 2024-09-30 · 1 citations

  articleOpen accessSenior author

  Abstract Submarine channels on the seafloor experience a range of turbidity current‐flood hydrographs. The characteristics of the flood hydrograph influence channel dimensions, the number of channel threads (i.e. braiding intensity) and the depositional properties of sandbars within the channels. However, the morphodynamic response of submarine braided channels to different hydrograph patterns is poorly understood. In this study, six geomorphic experiments are used to test how varied flood hydrographs affect the braiding intensity and sandbar geometry within submarine channels. Three experiments represent the control group with constant density‐current inflow, and three experiments use different time‐varying hydrograph patterns. The experiments show that, as the inflow‐to‐sediment discharge ratio increases, multiple small channels coalesce into a few main channels, causing a decrease in active braiding intensity defined by the channel threads with flow. When the flow returns to the initial low flow rate, active braiding intensity increases again. These observations show that the inflow‐to‐sediment discharge ratio determines the value of active braiding intensity. Additionally, active braiding intensity is directly proportional to dimensionless sediment‐stream power and dimensionless stream power, in agreement with previously established trends for both submarine and fluvial braided channels. In contrast to active braiding intensity changes, the measured sandbar aspect ratio and compactness ratio (i.e. ratio of planform area to perimeter) of submarine braided channels is insensitive to changes in the hydrograph. However, when inflows reach peak discharge, the higher transport capacity erodes pre‐existing deposits, forming noticeable erosional surfaces, and subsequently depositing thicker sandbars during that stage. These observations imply that sandbar planform morphology is largely insensitive to hydrograph, but hydrograph variability induces a greater variability in the resultant stratigraphic packages. The experimental results predict that field‐scale stratigraphy should be dominated by strata deposited during intervals of high flow, but that these strata will also exhibit reduced lateral continuity compared to formation scenarios with constant discharge.

  PublisherOA PDFDOI

• Topography‐Based Particle Image Velocimetry of Braided Channel Initiation

  Water Resources Research · 2024-04-01 · 2 citations

  articleOpen access

  Abstract River channels shape landscapes through gradual migration and abrupt avulsion. Measuring the motion of braided rivers, which have multiple channel threads, is particularly challenging, limiting predictions for landscape evolution and fluvial architecture. To address this challenge, we extended the capabilities of image‐based particle image velocimetry (PIV)—a technique for tracking channel threads in images of the surface—by adapting it to analyze topographic change. We applied this method in a laboratory experiment where a straight channel set in non‐cohesive sediment evolved into a braided channel under constant water and sediment fluxes. Topography‐based PIV successfully tracked the motion of channel threads if displacements between observations were less than the channel‐thread width, consistent with earlier results from image‐based PIV. We filtered spurious migration vectors with magnitudes less than the elevation grid spacing, or with high uncertainties in magnitude and/or direction. During braided channel initiation, migration rates varied with the channel planform development, showing an increase as incipient meanders developed, a decrease during the transitional braiding phase, and consistently low values during the established braiding phase. In this experimental setup, migration rates varied quasi‐periodically along stream at the half scale of initial meander bends. Lateral migration with respect to the mean flow direction was much more pronounced than streamwise migration, accounting for approximately 80% of all detected motion. Results demonstrate that topography‐based PIV has the potential to advance predictions for bank erosion and landscape evolution in natural braided rivers as well as bar preservation and stratigraphic architecture in geological records.

  PublisherOA PDFDOI

• Scour-depth variability controls channel-scale stratigraphy in experimental braided rivers

  Journal of Sedimentary Research · 2024-04-10 · 1 citations

  articleSenior author

  ABSTRACT Braided rivers distribute sediment across landscapes, often forming wide channel belts that are preserved in stratigraphy as coarse-grained deposits. Theoretical work has established quantitative links between the depth distribution of formative channels in a braided river and the geometry of their preserved strata. However, testing these predictive relationships between geomorphic process and stratigraphic product requires examining how braided rivers and their deposits coevolve, with high resolution in both space and time. Here, using a series of four runs of a physical experiment, we examine the controls of water discharge and slope on the resulting geometry of preserved deposits. Specifically, we focus on how a twofold variation in water discharge and initial riverbed slope affects the spatiotemporal distribution of channel depths and the geometry of preserved deposits of a braided river. We find that the channel depths in the laboratory experiment are described by a two-parameter gamma distribution and the deepest scours correspond to zones of erosion at channel-belt margins and channel-thread confluences in the channel belt. We use a reduced-complexity flow model to reconstruct flow depths, which were shallower compared to channel thalweg depths. Synthetic stratigraphy built from timeseries of topographic surfaces shows that the distribution of cut-and-fill-unit thickness is invariant across the experiments and is determined by the variability in scour depths. We show that the distribution of cut-and-fill-unit thickness can be used to reconstruct formative-channel-depth distributions and that the mean thickness of these units is 0.31 to 0.62 times the mean formative flow depth across all experiments. Our results suggest that variations in discharge and slope do not translate to measurable differences in preserved cut-and-fill-unit thickness, suggesting that changes in external forcings are likely to be preserved in braided river deposits only when they exceed a certain threshold of change.

  PublisherDOI

• Timescale of the Morphodynamic Feedback Between Planform Geometry and Lateral Migration of Meandering Rivers

  Journal of Geophysical Research Earth Surface · 2024-02-01 · 2 citations

  articleOpen accessSenior author

  Abstract Across varied environments, meandering channels evolve through a common morphodynamic feedback: the sinuous channel shape causes spatial variations in boundary shear stress, which cause lateral migration rates to vary along a meander bend and change the shape of the channel. This feedback is embedded in all conceptual models of meandering channel migration, and in numerical models, it occurs over an explicit timescale (i.e., the model time step). However, the sensitivity of modeled channel trajectory to the time step is unknown. In numerical experiments using a curvature‐driven model of channel migration, we find that channel trajectories are consistent over time if the channel migrates ≤10% of the channel width over the feedback timescale. In contrast, channel trajectories diverge if the time step causes migration to exceed this threshold, due to the instability in the co‐evolution of channel curvature and migration rate. The divergence of channel trajectories accumulates with the total run time. Application to hindcasting of channel migration for 10 natural rivers from the continental US and the Amazon River basin shows that the sensitivity of modeled channel trajectories to the time step is greatest at low (near‐unity) channel sinuosity. A time step exceeding the criterion causes over‐prediction of the width of the channel belt developed over millennial timescales. These findings establish a geometric constraint for predicting channel migration in landscape evolution models for lowland alluvial rivers, upland channels coupled to hillslopes and submarine channels shaped by turbidity currents, over timescales from years to millennia.

  PublisherOA PDFDOI

• Confinement effects of experimental submarine braided channels

  Zenodo (CERN European Organization for Nuclear Research) · 2023-02-03 · 1 citations

  datasetOpen access

  Videos and dataset for submarine braided channels with effects of confinement widths.

  PublisherDOI

Frequent coauthors

• Jean‐Louis Grimaud

  Centre de Géosciences

  23 shared

• Michael P. Lamb

  California Institute of Technology

  19 shared

• Chris Paola

  University of Minnesota

  14 shared

• Brady Z. Foreman

  Western Washington University

  11 shared

• Steven Y. J. Lai

  11 shared

• Yuan Li

  University of Virginia

  7 shared

• Alejandro Tejedor

  Universidad de Zaragoza

  7 shared

• Zexia Zhang

  6 shared

Education

• Ph. D., Division of Geological and Planetary Sciences

  California Institute of Technology

  2014

• B. A., Department of Earth and Planetary Sciences

  University of California Berkeley

  2007