-Rivers Flashcards
What is the river’s profile and how does it change?
The river’s profile is a diagram of a river that shows the change in altitude and relief of a river through different courses. From the upper course the river’s profile is at a high altitude and the relief is very steep, as we go into the middle and lower course, the river decreases in altitude and the land becomes flatter.
What is the river’s cross profile and how/why does it change?
A river’s cross profile is a diagram that shows a river’s river channel shape, its valley, its valley floor, river bed by cutting across the river. It can show us evidence of erosion and deposition.
In the upper course, the river’s cross profile can show that the river channel is narrow and shallow (as less erosion has occurred due to the small amount of discharge in the channel so less abrasion and hydraulic action has occurred), and it shows that the river valley is steep and deep as mostly vertical erosion occurs due to the high gravitational potential energy. we also see there’s a small valley floor as the river doesn’t meander side to side.
In the middle course, the river becomes wider and deeper as more discharge is collected into the channel, acting as more erosional potential through abrasion and hydraulic action happens both vertically and laterally as meanders form here. This means that the valley floor is wider. The valley becomes more gradual due to both types of erosion.
In the lower course the river is the deepest and widest due to the most erosion occurring here as most discharge is in the channel. It’s valleys are very flat, making them prone to flooding, creating flat flood plains either side.
What are the types of erosion? (4)
Hydraulic action- the sheer force of water bashing against the earth, trapping air and water in the cracks that expand and eventually chip off bits of earth.
Abrasion- when the sediment grinds along the sides of the river in a sand paper motion that wears down the river channel.
Attrition- when multiple pieces of load bash into one another creating smaller, finer and rounder pieces of load.
Solution- as the river is slightly acidic, it can wear and dissolve sediments into its flow.
What are different transportation processes? (4)
Traction- huge pieces of load (boulders) that are too heavy to be carried in the river’s flow, instead they roll at the bottom of the river bed.
Saltation- when medium sized sediment are light enough to be semi suspended in the river’s flow but not entirely , they bounce along the river bed.
Suspension- when sediment is light enough to be carried in the river’s flow.
Solution- when they sediment becomes the flow.
Why does a river deposit sediment?
When the river’s velocity decreases, its kinetic energy decreases, meaning the river loses the energy used to transport sediment, this may be due to more friction acting on the water resulting in the river dropping its sediment onto the floor.
-the volume of the discharge in the river decreases
-the river becomes more concentrated with sediment
-the river experiences more friction
-the river bed becomes shallower
What are interlocking spurs?
Interlocking spurs are areas of more resistant rock that hasn’t been eroded by water.
Located where there are areas of more and less resistant rock, the less resistant (softer rock) gets eroded down due to gravity, hydraulic action and abrasion erodes away leaving the areas of more resistant rock exposed as interlocking hills as the water moves around it.
What is discharge?
Discharge is the volume of water in a river in a certain point measured in cumecs. Discharge varies in relation to the amount of rainfall received.
What is peak rainfall?
the maximum volume of precipitation received by an area in a high rainfall event.
What is storm runoff?
The extra discharge in a river before reaching bankfull capacity.
What is the discharge line?
the line that shows the volume of water flowing past a certain point at a certain time during the rainfall event.
What is peak discharge?
the maximum discharge received during an event
What is baseflow?
the normal volume of discharge in a river.
What is lag time?
the amount of time between peak rainfall and peak discharge.
What is bankfull discharge?
The maximum volume of discharge a river can contain before breaking its banks
What is the rising limb?
The increasing amount of discharge in a river before reaching peak discharge
What is the falling limb?
the decreasing volume of discharge in a river after the peak discharge.
What are the elements in a storm hydrograph? (9)
-discharge line
-rising limb
-falling limb
-peak rainfall
-peak discharge
-baseflow
-storm runoff
-lag time
-bankfull discharge
Give examples of soft engineering strategies for floods:
-flood warnings/ flood meters.
-river restoration
-flood plain zoning
-afforestation
