RiversMoving stuff around

Watershed

By Shannon - DEMIS Mapserver, GFDL, https://commons.wikimedia.org/w/index.php?curid=10326481

All of the land where water runoff ends up in the river

Tributaries feed the main stream (the river)

DividesBoundaries between watersheds

Typically, determined by the ocean or major bay the rivers flow into

The Great BasinFlows into? All water in this

watershed evaporates, sinks underground, or flows into lakes.

How Rivers FormChannel erosion:

Surface runoff creates a depression as it flows downhill

Runoff forms a gully, which can become a permanent stream

How Rivers FormChannel erosion:

Streams continue to erode their channels by transporting soil, loose rock fragments, and dissolved minerals downhill

Faster streams cause more erosion

How Rivers FormDischarge (how much water) Gradient (how steep it is)

How Rivers FormMeander - why rivers are rarely straight

1944 map, showing 1000 years of Mississippi River meanders

The Mississippi River has been changing its course since it formed

Detail of 1944 map, compared to satellite image of same area

Historical MeandersThe state borders of most Eastern US states were made official in the early 1800s. (purple line)

Arkansas is on this side

Mississippi is on this side

How does that happen?

But that’s not all...A meander can get cut off by its own deposition and form a lake...

...and the force of erosion can carve out the bends in a downstream direction

Resulting in something like this:

So where does all that eroded material go?Floods and floodplains:

Natural levees, which are higher river banks, build up during flood events

Some sediment is deposited on river banks, some on surrounding land

So where does all that eroded material go?The rest:

Is carried downstream to the end of the river

Sediment is deposited when the river slows down

Deposits into a larger body of water are called deltas

Have these processes shaped Florida’s rivers?

How have human activities changed the Apalachicola?Jim Woodruff Dam

Dredging

Drinking water

Flood control

Intracoastal Waterway