River landscapes (theme 2) Flashcards
Bedload
Material carried by a river
Discharge
Volume of water passing a specific point at a specfic time
Drainage basin
The area the river collects its water from
Watershed
Boundry or edge of a drainage basin
Tributary
A smaller river flows into a larger one
Confluence
Where 2 rivers meet
Mouth
Where the river meets the sea
Source
The start of the river
What is water discharge measured in?
Cumecs (cm3/second)
Surface run off
unconfined flow of water over the ground surface,
Infiltration
The rate at which water soaks/hits the round
Through flow
water flows from soil down hill to the river
Perlocation
water moving downwards through soil and rock to the groundwater
Transpiration
Plants return water to the atmosphere via leaves
Groundwater
Water stored underground
Groundwater flow
Water flows through porous rocks downhill to river
Interception
Plants and trees delay water from reaching the ground
Precipitation
Rain snow sleet hail
where in a river is the gradient the steepest
The upper course
What do we call the path a river takes as it flows downhill?
The rivers course
In the upper course, is erosion or deposition more prominent ?
Erosion
What does an upper course look like?
Steep sided V shaped valley
Channel is narrow and shallow
In the middle course, is erosion or deposition more prominent ?
Both are equal
Amount of discharge in the upper course is
Small
What does the middle course look like?
Gentle slope
Channel is wider and deeper than upper course
In the lower course, is erosion or deposition more prominent ?
Deposition
What does the lower course look like?
Valley is wide and flat
Channel is wide and deep
How does an increase in urbanisation increase flooding?
Increase in land use means more impermeable surfaces leading to an increase in surface run off.
Also leads to a reduction in evapotranspiration so there are fewer plants/trees
How does afforestation decrease flooding?
-More roots holding soil together
-Higher rates of interception by leaves so less water reaches the ground more slowly
How can an increase in agriculture increase flooding?
-Overgrazing compacts soil leading to higher surface run off and risk of flooding
-Inflitration is also lower
-
3 human activites that increase flooding
-Urbanisation
-Agriculture
-Industry
How are gorges formed?
When waterfalls retreat over time
How are waterfalls formed
The soft rock is eroded quicker than the hard rock and this creates a step.
As erosion continues, the hard rock is undercut forming an overhang.
Abrasion and hydraulic action erode to create a plunge pool.
Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
This process continues and the waterfall retreats upstream.
How are interlocking spurs formed?
In the upper course, valleys are steep and V-shaped because most erosion happens vertically downwards.
The rivers do not have a lot of energy as there is not a lot of fast-moving water. This lack of energy means that they do not erode sideways (lateral erosion). Instead, they follow the winding path through the valley.
These interlocking hillsides are the interlocking spurs.
Features of the upper course
Waterfalls
Gorges
Interlocking spurs
How are meanders formed?
Erosion and deposition in parts of rivers that have deep riverbeds and shallow riverbeds creates meanders.
When a river bends, the current is fastest (carrying the most energy) at the outside of the bend. This high energy water erodes the side of the river, creating a river cliff.
The current is weakest where the water is shallowest, opposite the river cliff. More sediment is deposited here because the current has less energy to carry it along the river. This creates slip-off slopes.
How are ox bow lakes formed
As erosion continues, the river’s bends get nearer to each other and create a swan’s neck meander (a small piece of land between bends).
During a flood, high energy water will breach the meander neck.
This makes the river flow in a straighter and faster course.
Over time, deposits will fill in the meander bends.
The meander becomes cut off from the river, forming an ox-bow lake.
Features of the middle course
Oxbow lake
Meanders
what are flood plains
Wide area of flat land that surrounds the lower courses at the borrom of the river
What are flood plains caused by
Meander migration
How are levees formed
When a flood happens, water overflows over the banks of a river.
The larger sediments that were being transported by the river will be deposited first.
After lots of floods, levees (which are natural piles of sediment) are created at the side of the river.
How are esturiees formed
At high tide, the river overflows its banks.
Because the water is moving slowly at this point, the sediment it is transporting gets deposited.
These sediments build up over time to form large mudflats.
Where are esturies found
tidal areas at river mouths
Factors effecting flooding
Land use
Precipitation
Geology
Relief of land
Hard enginerering to reduce flood risk
Embankments and levees
Flood walls
Dams ad resoivours
Flood Barriers
Soft enginerring ways to reduce flood risk
River restoration
Washlands
Floodplain rentention
Plant trees ( afforestation)
What rivers caused the flash flood in boscastle
Rivers valency and jordan
2 Human causes of boscastle flooding
-Bridges were small and blocked debris so water was trapped
-Houses were built on flood plain so when river breaks banks it flooded houses
3 natural causes of boscastle flooding
Confluence of two rivers caused more water to flood
Steep valley slopes so water flowed into village
Impermable sources
2 Human impacts of flooding in boscastle
58 properties flooded
0 deaths
84 cars wrecked
2 economic impacts of flooding in boscastle
2 million in damage
90 % of industry relies on touriusm
1 environmental impact of flooding in boscastle
Trees uprooted and carried downstream
Human causes of somerset flooding
-Human activity lowered drainage basin
-Farming removed plants so less interception
-Houses built on low lying land
Environmental causes of somerset flooding
-Lowest lying land in UK
-Jet stream over UK causing 3x more rainfall
Social impacts of somerset flooding
-165 homes effected for 3 weeks
-Disrupted personal lives (schooling,work)
-Loss of valued items
Ecomonic impacts of somerset flooding
-16 million in damages
-Insurance prices raised
-Housing prices decreased
Environmental impacts of somerset flooding
-Wildlife habitats destroyed in flooding
Short term responses to somerset flooding
-People evacuated
-Pumped water back into sea
Long term responses to somerset flooding
-Raised river bank
-Flood walls
-Dredged river
