Rivers Flashcards
how does a fully developed meander form from a gently weaving stream?
a low velocity stream will have a low sediment load (small alluvium), as the sediment builds up, the river is able to cut deeper into the river banks causing a meander (loop)
how does an ox-bow lake form?
as sediment deposits along the banks, the river takes a short cut (the quickest route) and joins differently
why do we often stabilise meanders?
we often try to stabilise meanders because we want to use the fertile flood-plain for agriculture - this can be done, but there will probably still be a risk of flooding
if the river is fast flowing (high velocity) what does this mean about sediment transport?
if velocity is high then the river will transport a lot of sediment, and braided channels
develop
what are natural levees?
a naturally forming embankment alongside a river that prevents it from flooding adjacent land when the water level is high (by raising the river bank)
what happens when a river floods?
when the river does spill over its banks, water that was flowing very quickly in the main channel slows down as it spills over, depositing material which it can no longer carry at the reduced speed, when the river level subsides, water is trapped on the flood plain behind the levees, and silt and clay settles out to make fertile agricultural land
what is a delta?
When a river reaches a lake or the sea the water slows down and loses the power to carry sediment . The sediment is dropped at the mouth of the river. Some rivers drop so much sediment that waves and tides can’t carry it all away. It builds up in layers forming a delta.
what is a distributary?
A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel - they are a common feature of river deltas.
what is an antecedent stream?
it is a where a previously existing rivers appears to cut through a ridge but it was actually there before the folding of the land takes place - the river maintains its course
does a fast-flowing river always erode rock quickly?
even a very powerful river can erode rock quite slowly - weathering rate is dependent on rock type and hydrology dynamics
what is the equation for river flow (general flow equation)?
Q = VA where v = velocity of river and A = shape of the river channel
if a river has a steeper gradient what does that mean for the flow?
faster the flow
what are stream orders?
a measure of the relative size of streams and rivers, the smallest tributaries are referred to as 1st order streams, while the largest river in the world is a 12th order stream
what order are most of the rivers and streams in the world?
approx. 80% of the rivers and streams in the world are of first and second order
what type of drainage pattern do you get on uniform ground?
river networks form dendritic (tree-like) patterns cutting valleys into uniform geological materials
