river landscapes Flashcards
what are the changing cross profiles of a river?
Upper course - steep gradient + v-shaped valley + river load(rocks) is high as rocks have not eroded yet + rocks are angular + narrow and shallow river channel + vertical erosion cutting down + interlocking spurs because of water following the path of least resistance
Middle course - water flows faster than in upper course + U-shaped valley + lateral erosion is most imminent here + gentle gradient + small meanders + small pebbles and clays + channel is deeper and wider
lower course - mainly alluvium(flat) + the load has turned to fine sediments + water flows the fastest
what is a river long profile and how does it change?
long profile is a line representing a river from its source to its mouth(where it meets the sea)
patterns of changing cross profiles?
from source to mouth: gradient decreases channel width and depth increases velocity of water flow increases discharge increases
types of erosion?
abrasion: load scraping against the bed and bank
solution: weak chemical reaction between water and rock
attrition: load breaks up due to collisions with other load
hydraulic action: the force of the moving water against the bed and bank
explain why rivers deposit sediments?
When the river loses energy and capacity, it drops off any of the material it has been carrying including sediments, pebbles, etc. The dropping off of load by the river is called deposition. It is most dominant in the lower course.
different landforms resulting from erosional processes?
waterfalls
meanders
oxbow lakes
explain the formation of oxbow lakes?
A river in its final course to a sea or lake meanders widely. This causes the erosion of the soil on the outside of its bends because of the friction between the sides of the river and the fast-flowing water. When erosion occurs at a meander, a meander neck is formed, and it is gradually narrowed as the river erodes into it until the meander is cut entirely from the main flow of the river. As water chooses the easiest path, it stops flowing into the broken meander and deposition seals off the meander entirely, forming an oxbow lake.
explain the formation of river beaches?
River beaches form on the inside of a bend due to slip-off slope. A slip-off slope forms when the water on the inside of a bend flows slower and deposits sediments which are usually pebbles, gravel and sand. The build-up of sediments leads to a slope. As lateral erosion becomes more imminent, the slope becomes more apparent.
explain the formation of meanders?
In the middle course, the river has more energy and a high volume of water. The gradient here is gentle and lateral (sideways) erosion has widened the river channel. The river channel has also deepened. A larger river channel means there is less friction, so the water flows faster.
As the river erodes laterally, to the right side then the left side, it forms large bends called meanders.
The force of the water erodes and undercuts the river bank on the outside of the bend which causes the formation of a river cliff.
Explain how deposition landforms are
formed (levees, flood plains, estuaries)
Floodplains and levées are depositional features found in the middle and lower course. They form when the river floods and oversteps its banks. As a result, the river lose energy due to friction and deposits its load. larger material is deposited next to the channel while smaller material is carried away. The large material deposited next to the channel form levees and the layers of material deposited from repeated floods create a floodplain.
Using an example of a river valley in the
UK identify the major landforms of erosion
and deposition
The river Tees has a waterfall called high force. it has formed due to soft rock below a layer of hard rock being eroded through hydraulic action and abrasion. This undercuts the hard rock, leaving an overhang. As the soft rock continues to retreat, the overhang cannot stay suspended anymore and the ledge collapses, causing rocks to fall into the plunge pool.
examples of soft engineering strategies?
washlands - areas on the flood plain that are allowed to flood.
afforestation - trees planted in the drainage basin intercept rainfall and take water out of the soil. The water then evaporates through the transpiration of the trees and surface run-off is thus reduced. This prevents rivers from flooding during periods of high precipitation.
land use zoning - Different areas are allocated for different uses. For instance, major building projects are placed in low-risk areas while open spaces for leisure are placed in high-risk areas since flooding would be less costly for them.
Using an example of a flood management
strategy in the UK, evaluate the
economic, social and environmental issues
The river jubilee is a flood relief channel in the UK which cost 330 million pounds to build. However, it has brought along many social economic and environmental issues.
One social issue that has arisen from the
natural and human factors that affect flood risk?
natural factors - type and amount of rainfall can influence flood risk. Intensive rainfall produces
human factors - Land use which creates impermeable surfaces or reduce vegetation reduce interception and shorten lag time.
what is lag time?
it is the time interval between peak rainfall and peak discharge.
