Chapter 18: Stream(River Transport), From Mountains to Oceans

Mississippi River and Continental Divide

mississippi river drainage basin is the largest in the US, drainage basin of the colorado river covers much of the arizona(eg hoover dam); mississippi river is a border river(transboundary)between a few states

red river branch

red river forms the Texas-Oklahoma border - transboundary river

dunajec river

border river between southern poland and northern slovakia. it changes course over time shich that it is not a border river in some areas

river drainage systems: the drainage divide

indiivudal drainage basins are seperated by divides(typically local elevation highs; continetal divides)

drainage basins are reasonably stable features, but can change as erosion or clime distrupt or divide teh flow

logitudinal profiles

water flows from high to low elevations; it is the plot of elevation vs distance along the stream channel.

the profile typically becomes flatter as elevation decreases as water current is slower downstream

river valley, channel, and floodplain

valley: the entire area from ridge to ridge. the cross-section is often V-shaped, but can be flat bottomed or U shape(glaciers)

channel: actually occupied by the stream

floodplain: the area on either side of the channel where water overflows during floods

sediment transport in river channels

1) suspended load - current flowing over a bed of gravel, sand, silt, and clay carried a suspended load of finer particles and transported in suspension

2) as current velocity increases, the suspended load grows and the increased force of the floow generates an increase in bedload, typically sand and gravel is trandported to the bottom of the stream bed by rolling and sliding

3) saltation is when particles jump around, smaller particles jump higher than larger particles, typically sand

sediment transport in rivers

currents with a higher velocity can carry larger grains.

capacity: the total sediment load carried bt a river flow; capacity increases with increasing flow volume and higher flow velocity

competence: the river’s ability to carry material of a given size; increases with higher flow velocity

braided streams

braided streams with multiple channels are most common in - high energy systems liek mountain valleys with steep slopes, large flow variations,a nd high sediment load(poorly sorted sediements)

stream channel patterns

rainfall and snowmelt gather to create streams and rivers, meandering channels form course grained sediments are deposited, as teh slope decreases rivers form braided channels, natural levees maintain the flow of water

the current slows and deposits its fine sediments as a delta

an oxbow lake in montana

oxbow lake was abandoned cause of flooding which cut off the other part of the meandering river

meandering streams

low velocity, low sediment streams form meanders - thye are curvy and bending along the valley floor

they shift from side to side in a snaking motion

the current is faster at outside banks, which are eroded and sediments get depositied inside banks forming point bars, the bends grow closr and point bars get bigger

during a major flood, a river could cut across the loop adn it beocmes an oxbow lake, erosion could also cut it off

point bar

water current is so low sediments are depositied here in meandering streams

stream floodplains

in between floods, sediments are deposited only within the channel, during a flood water spreads over the floodplain, rapidly loses velocity, and drops its sediments along the immediate borders of the channel, forming levees