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I study rivers and the ways they transport sediment to understand flood hazard in the Pacific Northwest. I use data analysis, remote sensing and models to investigate how rivers are changing in shape and hydrologic regime.

PROJECTS

River Bed Morphodynamics During & Between Floods

"Can spatial changes in river planform geometry predict regions prone to erosion and deposition during floods?"

2021-Present

Understanding how river beds change during peak flows and recover between events is challenging because measurements of bathymetry and sediment-transport are often sparse or unavailable. Here, we use high resolution bathymetry data from the Waal River in the Netherlands to analyze whether spatial changes in floodplain geometry  can explain bed elevation changes during and between high flow events. The image below depicts a conceptual understanding of how the bed responds to spatial changes in flood extent in a river with uniform channel width but varying floodplain geometry.

Ahrendt_Figure1_B007.tif

Ahrendt, S., Blom A., Van Denderen, R. P., Schielen, R. M. J., Horner-Devine, A. R., (2022) Geometric floodplain controls on riverbed elevation change within and between flood events, River Flow 2022, The Eleventh International Conference on Fluvial Hydraulics [doi coming soon!]

Modeling HydroGemorphic Hazards (MoHGeoH)

"How do the ways rivers transport sediment affect flooding?"

2018-Present

Flood hazards in most basins are typically assumed to be driven by the frequency and intensity of high discharge events, but changes in a river’s conveyance capacity can also contribute substantially to flood hazards. Take the channel shown in the figure on the right where Q-bankfull is the bankfull flow capacity of the channel. This river section can flood by two mechanisms. 1: it can experience a discharge event ‘Q’ that exceeds Q-bankfull, or 2: sediment can deposit in the channel changing the channel’s conveyance capacity and causing water to flow overbank for what was previously a Q-bankfull event. It’s these changes in channel conveyance capacity that we are trying to understand in order to improve flood risk predictions.

Flood Mechanisms

Investigate the results here!

Ahrendt, S., Horner-Devine, A. R., Collins, B., Morgan, J., Istanbulluoglu, E., (2022) Channel Conveyance variability can influence flood risk as much as streamflow variaibility in western Washington State, Water Resources Research. https://doi.org/10.1029/2021WR031890

This collaborative project is funded as part of the NSF PREEVENTS program.

Rapid Groundwater Modeling: Method Development

"How can we improve rapid-aquifer level predictions by incorporating real-time data into physical models?"

2017-2018

Three-dimensional groundwater models can be time-intensive to calibrate and computationally-costly to run. Here, we propose a method for rapid groundwater modeling by calibrating recharge to a MODFLOW groundwater model to reported groundwater level or 'head' measurements. The figure below shows how these measurements (evident as little high-elevation contour points) are iteratively smoothed in a MODFLOW model of an unconfined region of the Mahomet Aquifer in Mason County, Illinois. This "Head-Specified" method provides a continuous aquifer surface at reduced computational times and calibration efforts.

Read more in abstracts here & here.

IPython Instructional Notebooks

Teaching model development with visual support

2017-2019

I am passionate about developing graphical support for teaching and research. Here, I developed instructional material for the Illinois State Water Survey to teach groundwater modeling using Python and Flopy.

Click the figures below for tutorials on:

1) Steady-state confined aquifer model

2) Steady-state model with a pumping well

3) Transient model with a river

Hercules Dome, Digital Elevation Model

Summer 2016

The goal of this project was to identify the optimal location for deep antarctic ice core drilling. In contribution, I created a Digital Elevation Model from CryoSat-2 radar altimetry data to be used in focusing ground-based surveying. The project was conducted at the St. Olaf Center for Geophysical Studies of Ice and Climate under the advice of Dr. Robert Jacobel as part of the St. Olaf College CURI undergraduate research program.

Read more in our AGU Fall 2017 abstract.

PUBLICATIONS

  • Ahrendt, S., Blom A., Van Denderen, R. P., Schielen, R. M. J., Horner-Devine, A. R., (in review) Geometric floodplain controls on riverbed elevation change within and between flood events, River Flow 2022, The Eleventh International Conference on Fluvial Hydraulics
     

  • Ahrendt, S., Horner-Devine, A. R., Collins, B., Morgan, J., Istanbulluoglu, E., (2022) Channel Conveyance variability can influence flood risk as much as streamflow variaibility in western Washington State, Water Resources Research. https://doi.org/10.1029/2021WR031890
     

  • Morgan, J. A., Kumar, N., Horner-Devine, A. R., Ahrendt, S., Istanbullouglu,
    E., Bandargoda, C., (2020), Simulating large-scale and long-term fluvial morphodynamics: The efficacy of using a morphological acceleration factor. Geomorphology, 356, p. 107088, https://doi.org/10.1016/j.geomorph.2020.107088

SELECTED PRESENTATIONS

AGU 2020 Virtual Presentation

CSDMS Summer Series 2020, Virtual Presentation

POSTERS

FIELD NOTES

Observing Sediment Transport Processes in Northern Minnesota:

Field Exercise for Hillslope Geomorphology with Dr. Alison Duvall

Map of Study Sites: Magnetic Rock Trail, MN

Digital Field Notes:

© Shelby Ahrendt 2022

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