Rivers & Hydrology Flashcards
What is a drainage basin/ basin
The area that the river and tributaries drain into
Where does a river start and end
Starts - at source
Ends - at mouth
What is a confluence?
Where two rivers meet
What is a tributary?
Where small rivers join main rivers
What is it called when two rivers meet
a confluence
What is it called when a small river joins a main river?
Tributaries
what is watershed?
The area of land that drains to a particular point on a stream
What is a delta?
A low-lying plain of landform occurring at the mouth of the river
What shape of the valley is at the upper river?
V shaped = steep gradient
What does a V shaped valley mean
it has a steep gradient
where are rapids and waterfalls normally found
at the upper river
What are the 3 parts of a river course?
Upper
Middle
Lower
Which part of the river is normally used for sheep farming/ grazing, tourism and dams?
Upper
What is erosion like at upper rivers?
lots of vertical erosion
minimal lateral erosion
What is erosion like in middle rivers?
Equal amounts of vertical and lateral erosion
What is erosion like in lower rivers?
minimal vertical erosion
Lots of lateral erosion
What valley shape is in lower rivers?
U-shaped, wide and flat
Which part of the river meanders
Middle
What is the valley like in the middle of a river course?
Flat valley floor, sloping valley sides
What can the middle river course be used for?
fields and crops and animals
Villages and communication lines
What can lower river courses be used for?
Intensive farming, industry, towns, cities, ports, built on floodplains
Where would you find ox-bow lakes, Levées and Deltas?
At the lower course of a river
What are the 3 types of channel?
Straight channels
Braided channels
Meander channels
What are the features of a straight channel?
often man made
goes straight
some variation in flow
What are some features of a braided channel?
Have multiple channels and islands of sediment between channels
river deltas
Semi-arid environments
What are meander channels?
The bender bits of rivers that occur in the middle/ lower regions of the course
What is the River Rhone in south france an example of?
A braided channel
- has large delta at mouth
- sand and silt deposits caused river to split into 2 distributaries (Grande and Petite Rhone)
How do meanders form?
rivers create sediment in alternating bars (riffles) - when low flows in river and low hydraulic radius is enough to encourage deposits
Riffles lower hydraulic radius
Areas of high friction flow around deposit - creates flow variation - causes side-to-side motion
Pools are eroded in deeper riffle
What are riffles
Areas of shallow water caused by deposition of coarse sediment
What are river pools?
Areas areas of deeper water between riffles. Caused by Coarse pebbles create steeper gradient than eroded pools.
Which factors create a channel gradient
Riffles and pools
Where do ox-bow lakes form?
In the lower course of a river
How do ox bow lakes form
outside bend of river is continuously eroded
Neck of meander narrows
neck eventually breaks
Forms straight channel
Deposition continues, causing old meander to seal off
What is the riparian area?
the interface between land and a river/ stream
What are the 3 river processes?
Erosion
Transportation
Deposition
What is erosion
wearing away/ breaking down of material by an agent (in rivers, this is water)
What is transportation?
= movement of eroded material
What is deposition?
material drops out of solution – alluvium = the names of the load that is dropped
What 4 factors cause erosion?
Hydraulic action
Abrasion
Corrasion/ Attrition
Corrosion
What 4 factors cause transportation?
Traction
Saltation
Suspension
Solution
How does hydraulic action cause erosion?
force of water removing material from bed and banks
how does attrition cause erosion?
Rivers load collides with itself reducing rocks to particles – makes angular rocks more rounded
what is saltation?
when small pebbles bounce along the bed with the river flow - a type of transportation
what is suspension?
When fine particles (om, silt, clay) are carried in the river flow
How does solution cause transportation?
minerals dissolve in the water and are carried in flow (limestone, chalk = examples)
Which of the 3 river processes is most likely to change the shape of a river?
deposition
which part of the river has most deposition?
Lower course
Which part of the river does transportation mainly occur
Middle course
Which part of the river does erosion mainly occur?
upper course
Name 3 reasons why rivers lose energy
Gradient lessens low precipitation/ high evaporation Human abstraction (usage) Beaver dams Overflow into banks
What does a Hjulstrøm curve show?
it determines whether a river will erode, transport or deposit sediment
Which 2 curves make up the Hjulstrøm curve ?
A critical erosion velocity curve
A mean settling velocity curve
