Theme 2b Rivers Flashcards
(17 cards)
1
Q
How river transports materials ?
A
- Traction - rolling stones along the bed
- Saltation - sand-sized particles bounce along the bed in a leapfrog motion
- Suspension - silt and clay-sized are carried within the water flow
- Solution - Minerals dissolve in the water
2
Q
Brief description of a drainage basin
A
- Drainage basins act as a system with inputs, (precipitation)
- Transfers (stemflow, inflitration, percolation, surface run-off, throughflow, groundwater flows)
- Stores (interception, surface storage, soil moisture storage, groundwater storage)
- Outputs (evaporation, transpiration, evapotranspiration)
3
Q
What are the 4 types of erosion by river
A
- Attrition - large particles such as boulders collide and break into smaller pieces (upper course)
- Hydraulic action - the sheer force of the river dislodges particles from its banks and bed
- Corrasion/abrasion - smaller particles rub against the river banks and bed like sand-paper (lower course)
- Corrosion - acids in the river dissolve rocks (occur at any part of the river)
4
Q
What are the river landforms ?
A
- V-shaped valleys
- Interlocking spurs
- Waterfalls
- Rapids
- Potholes
- Meanders
- Ox-bow lakes
- Delta
- Flood plain
- Levées
5
Q
Describe the formation of V-shaped valleys
A
- Near to its source, a river is high above sea level => most of the erosion is vertical
- In theory, this produces vertical valley sides
- Once exposed the valley sides sides are weathered => loose material falls down the slope & carried away by river
=> Resulting in a steep sided V-shape valley
6
Q
Describe the formation of interlocking spurs
A
- In the upper valley, a river is in the mountains
- Water takes the easiest path downhill => twists and turns around the high land (spurs)
=> forming interlocking spurs
7
Q
Describe the formation of waterfalls
A
- Occur because the river flows over hard rock which erodes slowly
- Beneath is softer rock which is eroded faster to form a “step”
- The force of the water erodes the bottom of the waterfall to form a plunge pool
- The rock gets undercut as the soft rock erodes so that it eventually collapses
8
Q
Describe the formation of rapids
A
- Also form where the river passes over hard rock
- Either the band of rock is very deep or there are a series of shallow rock bands.
9
Q
Describe the formation of potholes
A
- Can be found in the middle and upper valley where a river flows over solid rock
- Swirling water forms eddies
- Cause stones to move in circular motions
=> Eroding circular holes in the rock
10
Q
Describe the formation of meanders
A
- Wide sweeping bends found in the lower course of the river
- Formed by a combination of lateral erosion & deposition
- Help form the flood plain
11
Q
Describe the formation of ox-bow lakes
A
- Form when the neck of the meander becomes very narrow
- During high flow or floods, the river cuts through the neck & straightens its course
- Deposition occurs on the bank of the river
- The cut-off meander is an ox-bow lake
12
Q
Describe the formation of delta
A
- Form when a large river is carrying a high sediment load
- The river loses energy as it enter a lake or sea (at the mouth of river)
- The sea is sheltered and has few currents to carry away the sediment
=> It is deposited in the mouth - Sediment is deposited and chokes up the channel forming islands
- The river breaks up around these deposits forming several channels called distributaries
13
Q
Describe the formation of flood plain
A
- The river widens its valley by lateral erosion
- At times of high discharge, the river has plenty of energy => carries a lot of material in suspension
- When the river floods, the water spreads across the flat land
- The sudden increase in friction reduce the water’s velocity & fine silt is deposited
- Each time the river floods, it deposits a layer of fine silt; this is a flood plain
14
Q
Describe the formation of levées
A
- When a river floods, the coarsest material is deposited (on the edges of the river)
- Forming a natural embankment called a levée
15
Q
Causes of flooding
A
- Steep-sided channel - river channel surrounded by steep slopes => fast surface run-off
- Lack of vegetation/woodland - trees & plants intercept precipitation
=> little vegetation in drainage basin results in high surface run-off - Drainage basin in urban area - Consist impervious surfaces => encourages overland flow => water is take quickly to channel, especially if the rooftop is sloping
- Deforestation - causes soil erosion => sediments going to the river, decreases the cross-sectional area
16
Q
Soft engineering flood management methods
A
- Afforestation - trees are planted in the catchment area => intercept the rainfall & slows down flow of water to river
- Floodplain zoning - local government create policies to control urban development on or closed to flood plain
- Washlands - river is allowed to flood naturally in wasteland areas
=> prevent flooding in other areas - River restoration - removing hard engineering, restoring the channel back to is natural state => reduces flooding downstream
- Warning systems - network of warning sirens => give people early warning to possible fllods
17
Q
Hard engineering flood management methods
A
- Dams - built to control the rate of discharge, holding back water and released in a controlled way
- Embankments - man made raised river banks => increasing discharge river can hold
- Channelisation - widening/deepening the river channel => carry more water or straighten to let water move away quicker
- Flood relief channels - divert some of the flood away from the main channel
- Flood walls - vertical barriers, made from concrete => reduces erosion
- Storage areas/washlands - area close to the river => fill water in river during periods of overflowing
