Figure 9. Channel changes. Channelization and dams have resulted in the 

encroachment of vegetation into the channel. These photographs collected by 

Norm Stuckey were taken before and after pile dikes were constructed on the 

Missouri River and clearly show the increase in flood plain adjacent to the 

channel, the decrease in width of the channel, and the change in the natural 

character of the channel. 

For further information please contact: 

John A. Moody – jamoody@usgs.gov, (303) 541-3011 

USGS Branch of Regional Research, Central Region 

P. O. Box 25046, MS418 

Denver Federal Center 

Lakewood, CO 80225–0046 

(303) 236–5021 

Figure 7. Hydraulic Geometry. The 191 measurements of river width represent a 

subset of all the channel widths recorded by Lewis and Clark. For these 

measurements, the drainage areas were determined by the authors of this fact 

sheet. The relation between river width, and the drainage area, is shown for 

plains rivers (downstream from the Yellowstone River) and for mountainous 

rivers (upstream from the Yellowstone River and some tributaries to the Columbia 

River). The relations are basically the same as those relations published about 

150 years later by other scientists. 

Figure 8. Suspendedsediment changes. The 

sediment discharge was 

estimated to have been about 

300 million metric tons per 

year during the time of the 

Lewis and Clark expedition. 

This sediment built and 

replenished the coastal area 

of Louisiana surrounding the 

Mississippi River. Today, 200 

years after the expedition, as 

a consequence of dams, 

bank stabilization, and 

channelization projects, the 

lower part of the Missouri 

River carries only 80 million 

metric tons per year. 

rappid and roling motion extends itself in a circular manner in

every direction arround interrrupting the smooth, tho’ rappid

surface of the water for many yards... ” Fort Mandan

Miscellany .

Changes in 200 Years 

Dams for navigation, flood control, agriculture, and water supply 

coupled with navigation improvements have changed the rivers 

traveled by Lewis and Clark. Nineteen major dams now control 

the Ohio River, six dams control the main-stem Missouri River, 

and eight dams control the Columbia and Snake Rivers traveled 

by the Lewis and Clark expedition. Many smaller dams have 

been built as stock ponds and water-supply reservoirs. Reservoirs 

now cover many of the meanders, riffles, rapids, and falls 

encountered by the Corps of Discovery. Dams regulate the 

hydrologic regime and biological communities downstream, and 

they trap sediment (fig. 8). Sediment that was once “thrown out”

by tributaries has been reduced, and a “river full of Sand bars and

riffles” has largely disappeared in many places. Many navigation 

improvements take the form of channelization and bank stabilization. These improvements have shortened the rivers, decreased 

the water-surface area, and decreased the number of sandbars and 

islands (fig. 9). These changes have altered the landscape and 

ecology of the rivers and lands explored, measured, and observed 

by Lewis and Clark. 

References cited: 

Moulton, G.E., ed., 1983–93, The journals of the Lewis & Clark 

 expedition, 8 volumes: Lincoln, University of Nebraska Press. 

Moody, J.A., and Meade, R.H., in press, Lewis and Clark’s observations 

and measurements of geomorphology and hydrology and changes 

with time: U.S. Geological Survey Circular 1246. 
Channel-Scale Geomorphic Features 

Riffles, rapids, falls, sandbars, point bars, and braided streams 

generally are mentioned as obstacles to the expedition. For 

example, while descending the Ohio River in the fall of 1803 

when the Ohio River was especially low: 

“...[s]truck on a riffle which we got over with some difficulty

and in the distance of two miles and a half passed 4 others three

of which we were obliged to drag over with horses; the man

charge me the exorbitant price of two dollars for his

troubles...” 6 September 1803.

At the Great Falls of the Missouri River Clark, took time to 

measure the falls (fig. 3). Sandbars were numerous on the 

Missouri and were mentioned often as the party labored upriver. 

However, during the return trip in 1806, they traveled down the 

Missouri River after the summer peak runoff, and Clark commented on how the river had changed: 

“...in places where there was Sand bars in the fall 1804 at this

time the main Current passes, and where the current then

passed is now a Sand bar-Sand bars which were then naked are

now covered with willow Several feet high...” 20 August 1806.

Figure 3. The Great Falls of the Missouri River. It took the expedition about a 

month (June 16 to July 14, 1805) to portage around these falls. Clark made the 

original horizontal measurements in poles (16.5 feet) and the vertical measurements in feet. These have been plotted to show the profile of the Great Falls in 

1805. The total horizontal distance was 14.83 miles with a total drop of 360 feet, or 

an average slope of 0.005. Superimposed upon Clark’s profile of the Great Falls 

are the approximate locations of four dams. The largest fall, 93.75 feet high 

according to Clark, is now part of the Ryan Dam. Crooked and Rainbow Falls 

were measured by Clark to be 34 and 47.67 feet high. They can still be seen today 

(photograph from National Park Service). 

The braided character of the Missouri was first noted on October 

6,1804, 

“...we made Severl. Attempts to find the main Channel between

the Sand bars...we have been obgd to hunt a Chanl. For Some

time past the river being devided in many places in a great

number of Chanels...”

and along a braided reach in the Rocky Mountains, the beaver’s 

role as a geomorphic agent was mentioned: 

“...the river in many places among the clusters of islands is

constantly changing the direction of such sluices as the beaver

are capable of stoping or of 20 yds. in width. this anamal in

that way I beleive to be very instrumental in adding to the

number of islands with which we find the river crouded ...”

24 July 1805.

Figure 4. Bank erosion and 

point bar deposition. Lewis and 

Clark observed and described 

this geomorphic process, 

which is recognized today as a 

mechanism that nat-urally 

maintains the character of 

meandering river: 

“...In every bend the

banks are falling in from the

Current being thrown

against those bends by the

Sand points which inlarges

...Sand and Clay easily

melts and Slips into the

River, and the mud mixes

with the water & the Sand

is washed down and

lodges on the points...” 5

August 1804.

In this aerial view of the 

Powder River in southeastern 

Montana, the river is flowing 

down the page, and the 

channel is about 50 yards wide. 

River Processes 

Lewis and Clark described many examples of the geomorphic 

processes that change rivers and landscapes. Bank erosion was 

reported primarily during periods when the river was rising 

(fig. 4). Eolian transport was first mentioned near the Big Sioux 

River: 

“...The Wind blew hard...and raised the Sands off the bar in

Such Clouds that we Could Scercely See this Sand being fine

and verry light Stuck to every thing it touched, and in the Plain

for a half a mile the distance I was out every Spire of Grass was

covered with the Sand or Dust...” 23 August 1804.

Lewis wrote this description of suspended-sediment transport: 

“...The river Platte does not furnish the Missouri with it’s

colouring matter, as has been asserted by some...The water of

the Platte is turbid at all seasons of the year, but it is by no

means as much so, as that of the Missouri; the sediment it

deposits consists of small particals of white sand, while that of

the Missouri is composed principally of a dark rich loam in

much greater quantity...” Fort Mandan Miscellany.

Clark made this quantitative measurement of the suspendedsediment concentration downstream from the Kansas River: 

 “...The water we Drink, or the Common water of the

 missourie at this time, contains half a Comn Wine Glass of

 ooze or mud to every pint...” 21 June 1804.

Bedload transport was described by Lewis at the mouth of the 

Platte: 

“...The bed of the river Platte is composes almost entirely of

white sand, the particles of which, are remarkably small and

light; these collecting, form large masses, which being partially

buoyed up, are hurryed along the bottom by this impetuous

torrent, with irresistible force; sometimes obstructed by each

other, suddonly stop; and form large sandbars in the course of a

few hours, which are again as suddenly dissipated to form

others, and to give place perhaps to the deepest channel of the

river...” Fort Mandan Miscellany.
Channel-Scale Geomorphic Features 

Riffles, rapids, falls, sandbars, point bars, and braided streams 

generally are mentioned as obstacles to the expedition. For 

example, while descending the Ohio River in the fall of 1803 

when the Ohio River was especially low: 

“...[s]truck on a riffle which we got over with some difficulty

and in the distance of two miles and a half passed 4 others three

of which we were obliged to drag over with horses; the man

charge me the exorbitant price of two dollars for his

troubles...” 6 September 1803.

At the Great Falls of the Missouri River Clark, took time to 

measure the falls (fig. 3). Sandbars were numerous on the 

Missouri and were mentioned often as the party labored upriver. 

However, during the return trip in 1806, they traveled down the 

Missouri River after the summer peak runoff, and Clark commented on how the river had changed: 

“...in places where there was Sand bars in the fall 1804 at this

time the main Current passes, and where the current then

passed is now a Sand bar-Sand bars which were then naked are

now covered with willow Several feet high...” 20 August 1806.

Figure 3. The Great Falls of the Missouri River. It took the expedition about a 

month (June 16 to July 14, 1805) to portage around these falls. Clark made the 

original horizontal measurements in poles (16.5 feet) and the vertical measurements in feet. These have been plotted to show the profile of the Great Falls in 

1805. The total horizontal distance was 14.83 miles with a total drop of 360 feet, or 

an average slope of 0.005. Superimposed upon Clark’s profile of the Great Falls 

are the approximate locations of four dams. The largest fall, 93.75 feet high 

according to Clark, is now part of the Ryan Dam. Crooked and Rainbow Falls 

were measured by Clark to be 34 and 47.67 feet high. They can still be seen today 

(photograph from National Park Service). 

The braided character of the Missouri was first noted on October 

6,1804, 

“...we made Severl. Attempts to find the main Channel between

the Sand bars...we have been obgd to hunt a Chanl. For Some

time past the river being devided in many places in a great

number of Chanels...”

and along a braided reach in the Rocky Mountains, the beaver’s 

role as a geomorphic agent was mentioned: 

“...the river in many places among the clusters of islands is

constantly changing the direction of such sluices as the beaver

are capable of stoping or of 20 yds. in width. this anamal in

that way I beleive to be very instrumental in adding to the

number of islands with which we find the river crouded ...”

24 July 1805.

Figure 4. Bank erosion and 

point bar deposition. Lewis and 

Clark observed and described 

this geomorphic process, 

which is recognized today as a 

mechanism that nat-urally 

maintains the character of 

meandering river: 

“...In every bend the

banks are falling in from the

Current being thrown

against those bends by the

Sand points which inlarges

...Sand and Clay easily

melts and Slips into the

River, and the mud mixes

with the water & the Sand

is washed down and

lodges on the points...” 5

August 1804.

In this aerial view of the 

Powder River in southeastern 

Montana, the river is flowing 

down the page, and the 

channel is about 50 yards wide. 

River Processes 

Lewis and Clark described many examples of the geomorphic 

processes that change rivers and landscapes. Bank erosion was 

reported primarily during periods when the river was rising 

(fig. 4). Eolian transport was first mentioned near the Big Sioux 

River: 

“...The Wind blew hard...and raised the Sands off the bar in

Such Clouds that we Could Scercely See this Sand being fine

and verry light Stuck to every thing it touched, and in the Plain

for a half a mile the distance I was out every Spire of Grass was

covered with the Sand or Dust...” 23 August 1804.

Lewis wrote this description of suspended-sediment transport: 

“...The river Platte does not furnish the Missouri with it’s

colouring matter, as has been asserted by some...The water of

the Platte is turbid at all seasons of the year, but it is by no

means as much so, as that of the Missouri; the sediment it

deposits consists of small particals of white sand, while that of

the Missouri is composed principally of a dark rich loam in

much greater quantity...” Fort Mandan Miscellany.

Clark made this quantitative measurement of the suspendedsediment concentration downstream from the Kansas River: 

 “...The water we Drink, or the Common water of the

 missourie at this time, contains half a Comn Wine Glass of

 ooze or mud to every pint...” 21 June 1804.

Bedload transport was described by Lewis at the mouth of the 

Platte: 

“...The bed of the river Platte is composes almost entirely of

white sand, the particles of which, are remarkably small and

light; these collecting, form large masses, which being partially

buoyed up, are hurryed along the bottom by this impetuous

torrent, with irresistible force; sometimes obstructed by each

other, suddonly stop; and form large sandbars in the course of a

few hours, which are again as suddenly dissipated to form

others, and to give place perhaps to the deepest channel of the

river...” Fort Mandan Miscellany.
Figure 9. Channel changes. Channelization and dams have resulted in the 

encroachment of vegetation into the channel. These photographs collected by 

Norm Stuckey were taken before and after pile dikes were constructed on the 

Missouri River and clearly show the increase in flood plain adjacent to the 

channel, the decrease in width of the channel, and the change in the natural 

character of the channel. 

For further information please contact: 

John A. Moody – jamoody@usgs.gov, (303) 541-3011 

USGS Branch of Regional Research, Central Region 

P. O. Box 25046, MS418 

Denver Federal Center 

Lakewood, CO 80225–0046 

(303) 236–5021 

Figure 7. Hydraulic Geometry. The 191 measurements of river width represent a 

subset of all the channel widths recorded by Lewis and Clark. For these 

measurements, the drainage areas were determined by the authors of this fact 

sheet. The relation between river width, and the drainage area, is shown for 

plains rivers (downstream from the Yellowstone River) and for mountainous 

rivers (upstream from the Yellowstone River and some tributaries to the Columbia 

River). The relations are basically the same as those relations published about 

150 years later by other scientists. 

Figure 8. Suspendedsediment changes. The 

sediment discharge was 

estimated to have been about 

300 million metric tons per 

year during the time of the 

Lewis and Clark expedition. 

This sediment built and 

replenished the coastal area 

of Louisiana surrounding the 

Mississippi River. Today, 200 

years after the expedition, as 

a consequence of dams, 

bank stabilization, and 

channelization projects, the 

lower part of the Missouri 

River carries only 80 million 

metric tons per year. 

rappid and roling motion extends itself in a circular manner in

every direction arround interrrupting the smooth, tho’ rappid

surface of the water for many yards... ” Fort Mandan

Miscellany .

Changes in 200 Years 

Dams for navigation, flood control, agriculture, and water supply 

coupled with navigation improvements have changed the rivers 

traveled by Lewis and Clark. Nineteen major dams now control 

the Ohio River, six dams control the main-stem Missouri River, 

and eight dams control the Columbia and Snake Rivers traveled 

by the Lewis and Clark expedition. Many smaller dams have 

been built as stock ponds and water-supply reservoirs. Reservoirs 

now cover many of the meanders, riffles, rapids, and falls 

encountered by the Corps of Discovery. Dams regulate the 

hydrologic regime and biological communities downstream, and 

they trap sediment (fig. 8). Sediment that was once “thrown out”

by tributaries has been reduced, and a “river full of Sand bars and

riffles” has largely disappeared in many places. Many navigation 

improvements take the form of channelization and bank stabilization. These improvements have shortened the rivers, decreased 

the water-surface area, and decreased the number of sandbars and 

islands (fig. 9). These changes have altered the landscape and 

ecology of the rivers and lands explored, measured, and observed 

by Lewis and Clark. 

References cited: 

Moulton, G.E., ed., 1983–93, The journals of the Lewis & Clark 

 expedition, 8 volumes: Lincoln, University of Nebraska Press. 

Moody, J.A., and Meade, R.H., in press, Lewis and Clark’s observations 

and measurements of geomorphology and hydrology and changes 

with time: U.S. Geological Survey Circular 1246.