Flashcards in UK river landscapes Deck (37):
what happens in the upper course of a river?
In the upper course, the river has lots of energy.it is trying to reach its base level, far below.It mostly erodes downwards. This is called vertical erosion. vertical erosion in the upper coast produces a v-shaped valley
what happens in the middle course of river?
in the middle course, the river is closer to its base level. vertical erosion is less. The river uses a lot of energy to transport its load of eroded material.in the middle course, the river uses surplus energy to erode sideways. This is called lateral erosion. The valley is wider and flatter and the slopes are more gentle
what happens in the lower course of the river?
in the lower course, the river is close to is base and carries a heavy load of eroded material. If the river slows down it deposits material.
what are the river processes?
erosion,transportation and deposition
name the four processes of erosion
hydraulic action, solution. attrition and abrasion
what are the four types of transportation?
traction,saltation, suspension and solution
what is traction?
large boulders roll along the river bed
what is saltation?
smaller pebbles are bounced along the river bed,picked up and then dropped as the flow of the river changes
what is suspension?
finer sand and silt particles are carried along in the flow, giving the river a brown appearance
what is solution?
minerals from rocks such as limestone and chalk are dissolved in the water and carried along in the flow, although they can not be seen
what is deposition?
when the river loses energy (slows down) it drops some of its load
how are waterfalls formed?
1)band of more resistant rock lies over less resident rocks
2)less resident rock is eroded more quickly leaving a 'step'-the waterfall
3)more resistant rock is undercut, forming an overhang
4)overhang can no longer be supported, blocks of rock fall down.
5)powerful fall of water erodes plunge pool using fallen rocks
6)waterfall retreats-up stream
how is a gorge formed?
over a very long time, the process of undercutting and collapse is repeated and repeated, and the waterfall retreats up stream. A steep sided gorge is formed
how is an oxbow lake formed
2)the neck narrows
3)an ox bow lake is formed
what is a flood plain?
a wide, flat area of land either side of a river and experiences floods hen the river tops its banks
What are levees?
the deposition process, which takes place during flooding, continues until eventually embankments are created beside the rive
when does river flooding occur?
when the volume of water discharge is so great that all the water can not be contained in the river channel
what do hydrographs shows?
the relationship between precipitation and discharge
what are the factors affecting the risk of river flooding?
-previous weather conditions
what does a flood hydrograph show?
how a river responds to a rainstorm
what is the lag time?
the difference between the peak of the rainstorm and the peak of the river discharge
how do dams and reservoirs reduce the risk of flooding? (hard engineering)
they store water when rainfall is high and then release it gradually through the year
name a positive and negative of dams and reservoirs
+can also provide other benefits such as hep generation, tourist attraction, provision of shrinking water
-they are very expensive to build; need large areas of land to be flooded, so many people may have to move house
how does river straightening reduce the risk of flooding? (hard engineering)
reduces channel friction so water moves out of the area faster
name a positive a negative for river straightening
+most done in the uk when river transport was economically important; straighter courses are quicker for boats to use
-moving water quickly out of one area increases the risk of serious flooding downstream; straightened banks often collapse
what are embankments? (hard engineering)
artificially raise river banks
how do embankments reduce the risk of flooding?
the river can hold more water
state a positive and negative of embankments
+cheaper to build then other hand engineering strategies. they can be simple earth banks piled up by a bulldozer
-less reliable than other strategies ,because unless the embankments are repaired regularly ,erosion weakens them
what does flood relief channels do? (hard engineering)
when a river is flooding, water can be diverted into these channels to protect nearby housing.
name a positive and a negative of flood relief channels
+they are very effective: a flood relief channel around a town gives thousands of houses a high level of protection from floods
-increased risk of flooding downstream, where the relief channel re-joins the river; channels are also expensive
name an advantage and disadvantage of flood warnings and preparation (soft engineering)
+cheap and effective
-does not prevent flooding
name an advantage of flood plain zoning (soft engineering)
+makes sure floods cause minimum disruption to people and property
-no good for at-risk areas that have already been built
how does the planting of trees reduce flooding? (soft engineering)
increases the infiltration and reduces surface runoff
name and advantage and disadvantage of planting trees to reduce flooding?
+also reduces soil erosion
-trees take time to grow and to take effect
what does river restoration include? (soft engineering)
returning straightened rivers to their natural courses ,removing concreate channels, reintroducing marshland and lowering flood plains
what are the effects of river restoration methods
slow river flow, reducing flood risk downstream