See The Mississippi River's Hidden History, Uncovered By Lasers

Using hyperprecise LiDAR data, a cartographer maps the river’s bends and channels over time with mesmerising results.

FOR CARTOGRAPHERS AND cartophiles, Harold Fisk’s 1944 maps of the lower Mississippi River are a seminal work. In the mid-20th century the geologist charted the river in stunning detail and accuracy, using aerial photos and local maps. The centerpiece of his report was 15 maps showing the meandering Mississippi and its historical floodplains stretching from Missouri to southern Louisiana.

Left: A 1944 map by geologist Harold Fisk charts a 64-kilometre stretch of the Mississippi River from Friars Point to Gunnison, Mississippi. Fisk used aerial photos and maps to estimate the past and then-present channels.
Right: By comparison, a map created using lidar shows shifts over the past 75 years. Erosion and changes in flow caused the channel to widen in the middle of the image and migrate toward the south.

More than seven decades later, Daniel Coe, a cartographer for the Washington Geological Survey, wanted to re-create Fisk’s maps with greater accuracy and a new aesthetic. Coe had the advantage of hyperprecise U.S. Geological Survey (USGS) data collected using lidar, a system of laser pulses sent from aircraft to measure topography. The lasers detect the river’s shape along with everything around it—every house, tree, and road. Strip away these layers of vegetation and human add-ons, and Coe’s maps show the river’s bare-ground geomorphology: once lazy bends replaced by direct flow, old floodplains cut off by levees and dikes.

Mississippi’s Tunica Lake, in this image’s central oxbow bend, was once part of the Mississippi River. In the 1940s the Army Corps of Engineers cut the bend to straighten the river and shorten the shipping route.
Rivers meander by eroding one bank and depositing sediment on the other.The colors show the shipping route.
IMAGE BY DANIEL COE

USGS scientists collect lidar data (almost all of it open-source) to visualise how land evolves, and enterprising mapmakers can interpret the data in new ways. Slight changes in elevation can be the difference between a peaceful river and a devastating flood. Excessive soil runoff from agriculture can cause river migration and create longer shipping routes.

Farms near Moorhead, Mississippi, are often flooded in the winter for rice production and to help promote bird habitats. The colours in this lidar-derived image represent different elevation levels.
IMAGE BY DANIEL COE

All of the above makes a river’s past behaviour the best indicator of how it might react to future landslides, floods, or erosion. “The most surprising thing is how much of an imprint is still left on the landscape,” says Coe. “It’s like seeing fingerprints the river left behind.”

 

Lead Image: Vibrant maps from aerial laser data—known as lidar—show the position and elevations of the Mississippi Delta. This stretch shows historical movement and shape-shifting across three counties in Mississippi.
IMAGE BY DANIEL COE

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