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Our work focuses on fluvial geomorphic processes, often viewed through the lens of bed surface grain size, sediment supply, and sediment transport. The size, spatial distribution, and mobility of coarse sediment on the bed of a river controls channel slope, shapes channel plan form morphology, and provides the architecture for aquatic habitat.
Lithologic Controls on Sediment Pulse Persistence Downstream
Rivers downstream from volcanoes are subject to large sediment pulses that reshape channels and impact flood hazards. Our work on channels in the Pacific Northwest shows how the abrasion of weak volcanic clasts rapidly produces fine sediment during transport, while stronger grains persist downstream. Field data from 4 stratovolcanoes in the region suggest that these mountains produce sediment that varies dramatically in texture and degree of hydrothermal alteration, resulting in a wide range of coarse sediment persistence as sediment pulses pass downstream. Our field data are informing morphodynamic modeling via the Landlab Network Sediment Transporter (see below) to advance our understanding of how lithology and channel geometry govern sediment pulse evolution and cascading hazards.
Fordham et al. 2023 | Pfeiffer et al. 2022 | Yanites et al. 2025
This work evolved from my work as a postdoc working on NSF PREEVENTS 'MoGEOH', a 5-year collaborative research project focused on a mountains-to-coastline approach to flood hazard prediction lead by Erkan Istanbulluoglu (UW CEE). Recent work has been supported by NSF GLD #2138504, in collaboration with Jon Czuba and PhD student Fatemeh Shacheri (Virginia Tech).
Fluvial Response to Post-Fire Debris Flows
Wildfires alter hillslopes and channels, amplifying sediment delivery via debris flows. In burned basins, these events can deposit large pulses of coarse and fine sediment, changing channel morphology and sediment transport. Recent work combines Structure from Motion field surveys, lidar differencing, and sediment transport modeling to quantify how post-fire debris flows drive channel response and recovery in burned mountainous watersheds across the West Coast of the US.
The Landlab NetworkSedimentTransporter: 1D Morphodynamic Modeling
The NetworkSedimentTransporter (NST) is an open-source Landlab component for simulating sediment transport and channel evolution in 1D river networks. NST tracks individual grains and bed elevation changes, enabling researchers to explore the interplay of sediment pulses, abrasion, and geomorphic thresholds. This tool is widely used to model river response to disturbances such as volcanic sediment inputs and debris flows.
Pfeiffer et al. 2020 | NST CSDMS Clinic Tutorial Notebooks
This work is a collaboration with Jon Czuba, Katy Barnhart, Eric Hutton, and is currently supported by NSF CSSI #2104055.
The effects of sediment supply on channel morphology and bed mobility
Classic geomorphic relationships do not account for the effect of river bed sediment supply on channel hydraulic geometry and grain size. Similarly, a simplistic view of bed mobility based on the threshold channel concept would suggest that gravel beds mobilize during bankfull flow, every ~1-2 years. Compiling published field measurements and leveraging publicly accessible USGS streamgage data, I have worked to better understand the role sediment supply plays in controlling channel geometry, bed mobility, and patterns of channel aggradation and incision. High sediment supply rivers tend to have finer grained beds, mobilize more frequently, and fluctuate more dramatically in bed elevation.
Papers: PNAS, 2017, GRL, 2018, WRR 2019
Predicting habitat via grain size
We have developed a physically-based, empirically calibrated approach to predicting grain size distributions from high resolution LiDAR (Light Detection and Ranging)-derived topographic data for a 77 km2 watershed along the central California Coast. This approach builds on previous efforts in that it predicts the full grain size distribution and incorporates an empirically calibrated shear stress partitioning factor. Predicted grain size distributions are used to calculate the fraction of the bed area movable by spawning fish. We then compare the ‘movable fraction’ to 7 years of spawning survey data. We find that movable fraction explains the paucity of spawning in the upper reaches of the drainage, but does not explain variation within the mainstem.
Paper: ESPL, 2016
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