The concept of indeterminacy is built into any study of hydrology, whether contemporary or historical.  Rivers, creeks, streams are in constant, dynamic flux with varying levels of human influence from relatively pristine to the buried, channeled and culverted forms that are often our focus on this site.  The term, obviously means ‘not determinate’, but elaborating somewhat in simple terms via Webster, is “not precisely fixed in extent; indefinite; uncertain” or via the OEDNot exactly known, established, or defined“. 

The idea of looking at historical maps to unlock the stories embedded is further complicated by this variation of time, as maps represent a fixed point in time but are not a specific known entity.  This happens in many cycles, including daily, tidal, and also seasonal variations, but over time, this accumulated energy creates meanders that snake across the floodplains driven only by hydraulic rules and adjacent land characteristics.  Less dynamic rivers or streams may maintain fidelity over time, while highly dynamic streams can move.

There have been some interesting aerial versions of stream change via the recently launched Google Timelapse, however, my go-to for visualizing indeterminate river are the Harold N. Fisk’s 1944 study of Geological Investigation of the Alluvial Valley of the Lower Mississippi River.  Fisk was a Professor of Geology at Louisiana State University. Known as the Fisk Maps, these made the rounds of landscape and mapping blogs over the past decade, blowing people away with both their complexity and artistry.

The ability to use two-dimensional graphic techniques to represent temporal change is the subject of much discussion in visualization and landscape urbanism circles, to name a few, and these maps are often held up as positive examples of showing dynamic processes.  A wealth of information is found on the US Army Corps of Engineers’ site for the Lower Mississippi Valley Engineering Geology Mapping Program including the full report, large format.  [Note: these files are large so I’m not directly linking to the zip files direct – so follow the link above]

The expanse of the Lower Mississippi alluvial valley drainage shows how much movement the river on it’s 600 mile journey through the Central Gulf Coastal Plan from southern Missouri to the Gulf of Mexico a massive delta landscape that has been massively altered by natural and human processes for decades, showing that even with our technological advances, the river often still doesn’t obey our wishes.  [Aside: For some great reading on this, check out McPhee’s ‘The Control of Nature’, one of the best on the topic]

The idea of dynamism is key and the study of this change over time offers an interesting dilemma.  The ever changing paths of meanders are able to be mapped in modern times, but previous paths require understanding geologic cues to trace that which had not been mapped.  The black and white maps show the overlay of dashed meanders with aerial photography, which in the mid 1940s, was not new, but was still a relatively nascent planning technology, albeit rapidly expanding due to advances in World War II.   It will be interested now with accessible tools like Google Earth and the constant documentation of detailed aerial and satellite imagery to see how a study like this would be done today.  This map below is one of the figures in Fisk’s report, showing dramatic changes of a section of the river at a historic ‘Diversion Point’

The main report has predominately black-and-white imagery, probably due to reproduction costs in the 40s, but they still hold up.  Any who has read a geotechnical report knows many of the techniques for representation of borings and soil strata know they can sometimes be a bit try and technical.  This report is somewhat dense (and to be honest I’ve only skimmed some parts) but the visuals are so compelling.

Large, multi-page pull outs of regional geologic sections remind me of the early figures of von Humboldt, which contrary to more modern interpretations had a certain life to them.

Even the meander diagrams (in this case showing uses of clay plugs to control river bend migrations) are pretty cool in black and white.

Similarly, detail diagrams of braided stream topography and floodplain deposition are works of art, while also attempting to communicate immense amounts of technical information.

My hidden gem here is this graphic table of Geologic Time which traces Eras base a billion years and overlays the idea of big time with the relative amount of our recent human history.  I’m pretty sure I’ve seen this reproduced in modern geotech reports, or somewhere, but there’s something about serious report containing imagery of cave-people and dinosaurs to put the breadth of time in perspective.

Anyone who’s attempted to communicate using black and white figures knows they are tough to pull off graphically.  The above examples show that there’s a lot of information that can be conveyed in simple linework and that it doesn’t need to feel static.  That said, the beauty of the Fisk maps are the dynamic color plates, easily highlighting change and dynamic processes. A representive full map below shows the interplay of linework, hatching and color to bring the technical information to life.

A close up of a different map, showing the immense amount of information in meanders, oxbows, eddies, and the extensive floodplain of this massive river system.

The legend shows the color coding scheme based on when the rivers were mapped (solid) and those dervied from clues via aerial photograph analysis (hatches).

The entirety of the set of meander maps (that were rectified) has been stitched together – and is sort of incredible, via a Nerdist post from 2014.  I’d love to print out these full size and display somewhere.

These meander maps are a next iteration of earlier mapping, derived from a series of Stream Channel maps from 1939 (also available via the LMV Mapping page) that show the most recent survey work (when I say recent I mean 1700s to early 1900s.  It’s  still impressive (and a bit simplified) to see the amount of channel change.  Not sure if Fisk was involved in these maps, as they predated his involvement in the final report, but there’s similarities in graphic style and content.

While the maps of the meanders get much of press, I’m also a big fan of the Stream Courses (these are also part of the Fisk report, downloadable as plates via LMV Mapping page) which are larger maps showing multiple, color-coded maps of stream change over the past 2-3000 years.  One of the maps below shows a section of the main step and remainder of the valley.

The key gives some idea of the way time is juxtaposed spatially on the map.

You can pinpoint the specific stream courses and alluvium in an enlargement, telling another complex story of river movement.

The reports and links abound with interesting information, such as the Entrenched Valley System, which delineates a dendritic network which contains the main channels and tributaries of the Lower Mississippi basin.  This visual technique is somewhat more topographic, hinting at the tracery of valley to upland and basin shape that would be visible, and perhaps offered some resistance to channel migration over time.

This entrenched valley structure is shown in larger context, as the main stem outfall potentially being directed towards a real hidden river – a “submarine canyon” in the Gulf of Mexico.  I’d be curious if that is the actual hydrology based on our current knowledge, but I’d not thought of subsurface hydrological flow influencing river systems (although in retrospect it makes perfect sense).

Some other interesting maps that tie in basin and river specific info are accessed via main LMV Mapping page.  These show geological investigations and Alluvial Deposits throughout all of the basins.  Clicking on a basin will get you to specific 15 minute quadrangle maps, selectable within the study area.

The maps show distribution of alluvial deposits, which is less about channelization than the overall reach of the floodplain hydrology.  The difference between low-lying Baton Rouge, for instance with a wide flat deposits.

… contrasted with a more northern location, Caruthersville, Missouri which shows a long series of bends and oxbows left over time.

I also love the annotated sections showing strata via geological investigation, in this figure for Caruthersville highlighting predominate soil types.


As mentioned, the idea of indeterminacy is writ large in the study of hidden hydrology as it connects historical ecology to the modern metropolis.  History is a series of touchstones over time, and the information we have is always incomplete, requiring us to interpret the data points we have and make inferences to that which exists in the gaps of knowledge.  If we are to use the historical maps and sources we must understand this process (and perils and pitfalls) and be respectful of what we know and that which we can never know. Indeterminacy, as with life, is the heart of these explorations.

The work of Fisk on these maps is also a great example of looking back in time at a dynamic system and unlocking the story in visual terms.  The visualization challenges can be addressed in a number of ways, and technologies of visualization exist today that our predecessors didn’t have, but also show that we don’t need to rely on too much technology to tell a vibrant story – a pen and paper, perhaps some color, as proven above, can tell many tales.






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