by Daniel B. Botkin, originally published by Perigee Books, a division of Penguin/Putnam, 1999.

This book, originally published as “Passage of Discovery“, is an ecologist’s guide to the first half of the Lewis and Clark trail, their travels up the Missouri River from St. Louis to Three Forks, MT.  I have decided to share this book with the readers of my website, and I am going to present the entire book here, one chapter at a time, with a new chapter appearing each week.  There are more than 40 chapters.  If you follow along and read all of them, you will learn about the entire Missouri River as seen by Lewis and Clark at the beginning of the 19th century, and as I visited it during the 1990s to see what they had seen, and to learn how the countryside had changed.  Comparing what Lewis and Clark saw with what we see today is one of the best insights we can get of how nature and environment in American has changed since European settlement.   I hope you enjoy it and find it rewarding.

- Daniel B. Botkin

All of the chapters published thus far can be found in the Passage of Discovery category. Please note that they are listed in reverse order of date posted.

More books by Daniel Botkin are available for purchase from the Center For the Study Of the Environment bookstore.

12.  Shilling Wildlife Area: How the Platte Changes the Missouri

Shilling Wildlife Area is on the Platte River within view of the confluence with the Missouri.  To reach this wildlife area from Omaha take Route 75 south to Route 34. Follow the business loop of 34 through the town and then follow signs to the Shilling Wildlife.  From there you can go to the Plattsmouth Boat Ramp for another perspective.  Exiting the Shilling Wildlife Area, follow the road left (east) to that ramp.

From Iowa take the exit on Interstate 29 to Route 34.  Cross the Missouri River and follow Route 34 business loop north through Plattsmouth.  On the main street you will pass the County Courthouse and a sign that says “Historic Plattsmouth Welcomes You”.  Follow signs to the Shilling Wildlife Area.

On  July 21, 1804, Lewis and Clark had reached the mouth of the Platte River, at the time a well-known tributary of the Missouri.  It was a big river, one of the largest of the Missouri’s tributaries, and it was fast and full of large sandy sediment.  The sand was “remarkably small and light” and “easily boiled up and is hurried by this impetuous torrent in large masses from place to place with irristable forse.”  If Lewis needed any more evidence that rivers, as with all of nature, is in constant flux, he found it in the Platte, even more turbulent than the Missouri.  The sands were collecting and forming sandbars in the course of a few hours which “as suddingly disapated to form others and give place perhaps to the deepest channel of the river.”

The Platte flowed, Lewis wrote, with “a boiling motion” which he speculated was the result of “the roling and irregular motion of the sand of which its bed is entirely composed” — a good insight.  The bottom of the Platte, like the Missouri, is formed of its own sediment rather than bedrock or large boulders.  These bottom sediments are moved along by the water much the same way that wind drives sand.  Sediment dunes form just as sand dunes form from the wind.  These little hillocks force the water up and over, creating turbulence.  The resulting motion flows downstream and upwards, reaching the surface as large bubbling bursts that look just like boiling water in a kettle.  You can see this motion in the Missouri River when you stand along the shore.

Lewis and Clark measured the speed of the rivers, and found the Platte the fastest, running “at least” eight miles an hour.  The Missouri above the Platte was running about 3 ½ miles an hour in its widely dispersed, complex floodplain of many channels.  Below the Platte and influenced by that river, the Missouri was running five and a half miles an hour.  The faster a river flows, the heavier and coarser material it can carry, so the Platte could carry a sandy load, while the Missouri could lift only smaller silts.  Also the two rivers drained different kinds of countryside.  The Platte watershed is mostly sandy soils eroded from the Rocky Mountains and then deposited in western Nebraska long before, only to be picked up again and transported by the Platte.  The Missouri drains a landscape where the ice-age glaciers created soils of  many sizes of particles including small silts and clays.

At the mouth of the Platte the two kinds of sediment loads came together but did not yet mix.  The Platte was so swift and powerful that its current, having entered the Missouri River channel, forced the Missouri’s waters against the far bank “where it is compressed within a channel less than one third of the width it had just before occupyed,” Lewis wrote.  The currents could be distinguished by their colors.  The Platte did “not furnish the missouri with it’s colouring matter as has been asserted by some, but it throws into it immence quantities of sand.”  Lewis claimed that the separation of the currents “abates but little until it’s junction with the Mississippy.”

Both rivers were so full of sediment that neither was clear, but there was a difference.  The Platte deposited “very fine particles of white sand while that of the Missoury is composed principally of a dark rich loam – in much greater quantity.”   The Platte’s waters were “turbid at all seasons of the year but is by no means as much so as that of the Missourie.” These two painters of landscape had different palates and different styles of painting.

The Platte has a great effect on the Missouri in other ways than shoving its current to one side of the channel.  Above the Platte and below Gavins Point Dam — the farthest downstream of the dams on the Missouri — the channel is eroding and deepening — but this erosion is only in the main river channel, not in the surrounding floodplain. The river is incising itself into the engineered floodplain.

Below the mouth of the Platte, the river is depositing material on the bottomlands.  The floodplain is accumulating material, while the main channel, functioning as designed by the Army Corps of Engineers is not changing its depth; it is neither eroding or sedimenting.

The accumulating material on the Missouri River floodplain below the Platte has an important effect on floods.  This accretion is raising the level of the floodplain relative to the artificial levees, shrinking the height of the levees relative to the floodplain. The total volume of water that can be held back by the levees is therefore less.  It is like a stream carrying sand and silt into a swimming pool and depositing those sediments in the quiet waters.  Over time the sediments build up on the bottom and the pool can hold less water.  This was a factor that made the large floods of the 1990s so catastrophic.  In 1998, the Army Corps of Engineers reduced the flow from Gavins Point Dam, claiming bottom aggradation below Omaha was causing lowland flooding.

The aggrading land below the Platte has other biological effects.  As the floodplain builds up, its soils become drier; there are fewer wetlands but the soil becomes better for farming, at least where the deposits are not heavy sands.  Overall the floodplain habitats become fewer and simpler.

The Missouri is a complex system; fingers of tributaries feed waters of different colors, qualities, speeds and amounts into the main channel.  In this sense, the Missouri is many rivers, not one.  What happens on the tributaries affects the Missouri, and many of these have been channelized and controlled to prevent flooding.  Water from channelized tributaries flows faster and adds more quickly to the flood waters of a rising and dangerous Missouri.  The quality of the water from tributaries affects the Missouri, as does the chemical runoff from farms, industries and houses.  Just as the Missouri drains one-sixth of the continental United States, so does that land affect the quality of the Missouri’s waters.

Mark Brohman, and I drove to Shilling Wildlife Area at the mouth of the Platte.  Mark is the environmental scientist and lawyer with the State of Nebraska Department of Game and Parks who had taken me to Hamburg Bend as well.  Here, we watched people fish and tow their boats out of the Missouri as dusk fell.  The tumbling, mixing currents of the Platte and the Missouri still rushed together, still boiled, and still were able to evoke in us the feel of prairie and river countryside and remind us of the importance of the intimate linkages between rivers and their landscape and the constancy of change in nature.