Modeling & Simulating Storm Surge in Cedar Key

I first visited Cedar Key in 2005, during early research on Rosewood. A lot has changed since then. Some of this is the normal ebb and flow of a coastal town, some of it from increasing tourism, and some from the growing threat of sea level rise and storm surge. Much of my earlier research uses digital technologies to interpret archaeological materials. These same technologies support different forms of analysis. This post explores (very) preliminary work on the formal modeling and simulation of geophysical processes associated with storm surge, and specifically how this threatens Cedar Key’s archaeological and historical resources.

[Updated November 9, 2019 to include DualSPHysics work – see below]

This begins with predicting storm surge as accurately as possible. Many researchers use bathtub models, which assume areas with lower elevations than the floodlevel (represented as a flat surface across an area) will be flooded, like a bathtub. Although these models produce pleasing graphics, they are of limited use in planning for events like hurricanes and storm surge, which interact in complex ways with local landforms (e.g., bathymetry).

The National Oceanic and Atmospheric Association (NOAA) has a better model. This Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model estimates storm surge heights resulting from historical, hypothetical, or predicted hurricanes by taking into account the atmospheric pressure, size, forward speed, and track data of hurricanes as well as local landforms. NOAA even provides a useful program to project the effects of different hurricanes. We can use the SLOSH Display program to estimate surge for different hurricanes in the Cedar Key area. NOAA estimates the model is accurate to within 20%.

SLOSH Display results for a category 2 hurricane traveling NNE at 15mph in the Cedar Key area.

The results of the SLOSH model can be exported to a GIS file. A few tweaks produces an accurate and useful visualization. The following graphic is the result of (1) projecting the exported polygon data into a coordinate system matching a digital elevation model (DEM) of Cedar Key (derived from LiDAR data), (2) converting the polygon to a raster, and (3) using raster math to compare/subtract the elevation data from the predicted storm surge. The resulting image indicates which areas will be inundated, and by how much.

Results of comparing SLOSH Display results with LiDAR-derived DEM of Cedar Key, Florida.

The above analysis refines simulations of surge waters through Cedar Key, and not just today but historically as well. I use historical aerials and maps to virtually reconstruct Cedar Key as it existed in the past. The following images have approximate building footprints from 1920.

I use open source (free) programs to reconstruct Cedar Key and simulate surge. Blender, with the Flip Fluids add-on, allows me to reconstruct the town in 1920 and simulate how surge waters might move through the area. Preliminary results are choppy to cut down on computing time (hours instead of days or weeks!). One consequence of my attempt to cut down on processing time is that the water is modeled as large particles. This results in the water looking like large drops, and gives the impression of a miniature model being flooded.

A (very) preliminary simulation of storm surge in Cedar Key using Blender.

The GIS analysis tests the Blender-based simulation, which is not a scientific simulation. For this I’m using DualSPHysics, another open source program that models hydrodynamic forces with smoothed physics. This uses some of the same information as the Blender-based simulation, specifically the LiDAR-derived DEM, but there is more control over the simulation. The initial parameters for DualSPHysics are set up using FreeCAD. I’m able to fine tune things like wave height and period.

Setting up the initial model and simulation parameters for DualSPHysics.

The simulation is exported to Paraview, an open source data visualization application. This visualizes the particles used to simulate moving water.

Image of fluid particles moving through a digital version of Cedar Key.

Although DualSPHysics and Paraview can produce compelling visualizations. Exporting the results to Blender produces more realistic animations.

This work will support many projects. This includes a collaborative project with the Cedar Key Historical Society to create a public experience exploring storm surge inside a VR reconstruction of Cedar Key. Imagine ‘stepping’ into a virtual Cedar Key – capable of representing the town at different times – to select and view different storm surges moving through the town (and around the user!). This will provide a way for keeping the threat of hurricanes present in a way that living memory often fails to do. The ideas animating this work are partly drawn from my growing interest in disaster anthropology, and the role that social processes play in framing and forgetting past disasters, social vulnerability, and risk.

I’ll continue to update this page with new visualizations as the simulations are refined. So, check back!

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