Topic 4: Rivers Flashcards
(96 cards)
1
Q
What is soil creep?
A
Individual particles of soil moves slowly down a slope under the force of gravity. They collect at the bottom of the valley sides. The river may then erode this material.
2
Q
What is slumping?
A
This happens when the bottom of a valley side is eroded by the river. The slope becomes wet and material above slumps downwards, rotating as it does so. This often happens when the material is heavy.
3
Q
What is traction?
A
Large particles being pushed along the sea bed
4
Q
What is saltation?
A
Pebble sized particles which are pushed along the sea bed
5
Q
What is suspension?
A
Slit and clay carried by water, small particles
6
Q
What is solution?
A
Soluble materials dissolved in water
7
Q
What is vertical erosion?
A
This DEEPENS the river valley (and channel) making it V-SHAPED. It’s dominant in the UPPER COURSE of the river. High TURBULENCE cause the ROUGH, ANGULAR PARTICLES to be scraped along the river bed, causing intense DOWNWARDS erosion.
8
Q
What is lateral erosion?
A
This WIDENS the river valley (and channel) during the formation of MEANDERS. Its dominant in the MIDDLE and LOWER COURSES.
9
Q
What is the river course?
A
Path of the river as it flows downhill
10
Q
What is the upper course of a river?
A
Closest area to the SOURCE of the river
11
Q
What is the middle course of a river?
A
The middle area of the river
12
Q
What is the lower course of a river?
A
Closest to the MOUTH of the river
13
Q
What is the river valley?
A
Rivers form valleys as it flows downhill
14
Q
What is the long profile of a river?
A
Gradient (steepness) of the river
15
Q
What is the cross section of a river?
A
Shows you what the cross section of a river looks like
16
Q
What is river discharge?
A
The volume of water flowing in a river.
17
Q
What is river discharge measured in?
A
m^3 /sec
18
Q
What are the characteristics of the upper course of a river?
A
Gradient = steep
V -shaped valley, steep sides narrow, shallow channel
19
Q
What are the characteristics of the middle course of a river?
A
Gradient = medium
Gently sloping valley sides wider, deeper channel
20
Q
What are the characteristics of the lower course of a river?
A
Gradient = gentle
Very wide, almost flat valley very deep, deep channel
21
Q
Where is the river Eden?
A
North-west England, between the mountains of the Lake district and the Pennines.
22
Q
A
23
Q
How long is the river Eden?
A
145km from source to mouth
24
Q
Where is the river Edens source and mouth?
A
Source = Pennine hills in south Cumbria
Mouth = Solway Firth at the Scottish border
25
What does weathering do in rivers?
Weathering BREAKS DOWN ROCKS on the valley sides.
26
What type of weathering is freeze-thaw in rivers?
Mechanical weathering
27
What is freeze-thaw weathering in rivers?
1) Happens when the temperature alternates above and below 0°c
2) Water GETS INTO rocks that has CRACKS, e.g granite. When the water FREEZES it EXPANDS, which puts PRESSURE on the rock. When the water THAWS it CONTRACTS, which RELEASED the pressure on the rock.
28
What are the 4 processes of erosion?
1) Hydraulic action
2) Abrasion
3) Attrition
4) Solution
29
What is hydraulic action in rivers?
The FORCE of the water BREAKS ROCK PARTICLES AWAY from the RIVER CHANNEL
30
What is abrasion in rivers?
Eroded ROCKS picked up by the river SCRAPE and RUB against the CHANNEL, wearing it away. MOST EROSION happens by ABRASION.
31
What is attrition in rivers?
Eroded ROCKS picked up by the river SMASH INTO EACH OTHER and break into SMALLER FRAGMENTS. Their EDGES also get ROUNDED as they rub together.
32
What does attrition cause to the particle size in a river?
The FURTHER the material travels, the more ERODED it gets - attrition causes PARTICLE SIZE to DECREASE between a river's SOURCE and its MOUTH.
33
What is solution in rivers?
River water DISSOLVES some types of rock.
34
What are two examples of solution in rivers?
Chalk & Limestone
35
What are the 4 processes of transporting eroded material in rivers?
1) Traction
2) Saltation
3) Suspension
4) Solution
36
What is traction in rivers?
LARGE particles like boulders are PUSHED along the RIVER BED by the FORCE OF WATER.
37
What is saltation in rivers?
PEBBLE-SIZED particles are BOUNCED ALONG the RIVER BED by the FORCE OF WATER.
38
What is suspension in rivers?
SMALL particles like SLIT and CLAY are carried along by the water.
39
What are two examples of small particles carried by suspension in rivers?
Slit & Clay
40
What is solution in rivers?
SOLUBLE MATERIALS DISSOLVE in the water and are CARRIED ALONG.
41
What is deposition in rivers?
Deposition is when a river DROPS the ERODED MATERIAL it's transporting.
42
When does deposition happen in rivers?
It happens when a river slows down (loses velocity).
43
What are the 4 main reasons why deposition occurs?
1) The VOLUME of WATER in the river FALLS
2) The AMOUNT of ERODED MATERIAL in the water INCREASES
3) The water is SHALLOWER e.g. on the INSIDE OF A BEND.
4) The river REACHES its MOUTH
44
Where are waterfalls and gorges found in rivers?
In the UPPER COURSE
45
Where do waterfalls form in rivers?
Where a river flows over an area of HARD ROCK, followed by an area of SOFT ROCK.
46
How does a waterfalls and gorges form in rivers?
1) The SOFTER ROCK is ERODED, by hydraulic action and abrasion, more than the HRADER ROCK, creating a 'STEP' in the river.
2) As water goes over the step it ERODES MORE AND MORE of the softer rock.
3) A STEEP DROP is eventually created, which is called a WATERFALL.
4) The HARD ROCK is eventually UNDERCUT by erosion. It becomes UNSUPPORTED and COLLAPSES.
5) The collapsed rock are SWIRLED AROUND at the foot of the waterfall, where they ERODE the soft rock by ABRASION, forming a deep PLUNGE POOL.
6) Over time, MORE UNDERCUTTING causes MORE COLLAPSES. The waterfall will RETREAT, moving back up the channel, leaving behind a steep-sided GORGE.
47
Where do interlocking spurs form in a river?
In the UPPER COURSE
48
How do interlocking spurs form in rivers?
1) In the UPPER COURSE of a river most of the EROSION is VERTICALLY DOWNWARDS. This creates STEEP-SIDED, V-shaped valleys.
2) The rivers AREN'T POWERFUL ENOUGH to ERODE LATERALLY (sideways) - so they have to WIND AROUND the HIGH HILLSIDES that stick out into their paths on either side.
3) The HILLSIDES THAT INTERLOCK with each other as the river winds around are called interlocking spurs.
49
Where (how) are meanders formed?
Meanders are formed by erosion and deposition in the middle and lower courses of a river, in areas where there are both SHALLOW and DEEP sections in the channel.
50
How are meanders formed?
1) The CURRENT (the flow of water) is FASTER on the OUTSIDE of the bend because the river channel is DEEPER - there's LESS FRICTION to SLOW the water down.
2) So more EROSION - abrasion and hydraulic action - takes place on the OUTSIDE of the bend, forming RIVER CLIFFS.
3) The CURRENT is SLOWER on the INSIDE of the bend because the river channel is SHALLOWER, there's more friction to SLOW the water down.
4) So eroded material is DEPOSITED on the INSIDE of the bend, forming SLIP-OFF SLOPES.
51
What is current in rivers?
The flow of water
52
What are ox-bow lakes formed by in rivers?
Meanders
53
How do ox-bow lakes form in rivers from meanders?
Meanders get LARGER over time - they can eventually turn into an OX-BOW LAKE:
1) EROSION causes the OUTSIDE BENDS to get CLOSER
2) Until there's only a SMAL
BIT OF LAND LEFT between the bends - this is called the NECK
3) THE diver BREAKS THROUGH this land, usually during a FLOOD
4) And the river flows along the SHORTEST COURSE
5) DEPOSITION eventually CUTS OFF the meander
6) Forming an OX-BOW LAKE
54
What are floodplains in rivers?
Flat areas of land that flood, the FLOOD PLAIN is the WIDE VALLEY FLOOR on either side of a river which occasionally GETS FLOODED.
55
What are levees in rivers?
Levees are NATURAL EMBANKMENTS (raised bits) along the EDGES of a RIVER CHANNEL.
56
How a levees formed?
1) During a flood, ERODED MATERIAL is DEPOSITED over the whole flood plain.
2) The HEAVIEST MATERIAL is DEPOSITED CLOSEST to the river channel, because it gets DROPPED FIRST when the river SLOWS DOWN.
3) OVER TIME, the DEPOSITED MATERIAL BUILDS UP, creating LEVEES along the edges of the channel.
57
Where are floodplains, levees and deltas all found in rivers?
In the LOWER COURSE
58
How are floodplains formed?
1) When a river FLOODS onto the flood plain, the water SLOWS DOWN and DEPOSITS the ERODED MATERIAL that it's TRANSPORTING. This BUILDS UP the flood plain, which makes it HIGHER.
2) MEANDERS MIGRATE (move) ACROSS the flood plain, making it WIDER.
3) Meanders also migrate DOWNSTREAM, FLATTENING out the valley floor.
4) The DEPOSITION that happens on the SLIPP-OFF SLOPES of meanders also BUILDS UP the flood plain.
59
What are deltas in rivers?
Deltas are LOW-LYING AREA where a river meets the SEA or a LAKE
60
How are deltas formed in rivers?
1) Rivers are forces to SLOW DOWN when they MEET THE SEA or a LAKE. This causes them to DEPOSIT the MATERIAL that they're carrying.
2) Id the SEA DOESN'T WASH AWAY the material BUILDS UP and the CHANNEL GETS BLOCKED, This forces the channel to SPLIT into lots of SMALLER RIVERS called distributaries.
3) Eventually the material BUILDS UP SO MUCH that the LOW-LYING AREAS OF LAND called DELTAS are FORMED.
61
What are smaller rivers called that come of a main river called?
Distributaries
62
What are storm hydrographs in rivers?
These show the changes in river discharge around the time of a storm.
63
What is peak discharge in rivers?
The HIGHEST DISCHARGE in a period of time
64
What is Lag time in rivers?
The DELAY between PEAK RAINFALL and PEAK DISCHARGE
65
What is rising limb in rivers?
The INCREASE in river discharge as RAINWATER flows into the river.
66
What is FALLING LIMB in rivers?
The DECREASE in river discharge as the river returns to its normal level.
67
What is the proper word for absorption by the ground?
Infiltration
68
Why does lag time happen?
This is because most rainwater DOESN'T LAND DIRECTLY in the river channel, there's a delay as rainwater GETS TO THE CHANNEL.
69
What does Antecedent mean?
Previous
70
What are the different factors that affect storm hydrographs in rivers?
If MORE WATER flows as RUNOFF the LAG TIME will be REDUCED. This means DISCHARGE will INCREASE and the HYDROGRAPH will be STEEPER because MORE WATER gets o the river in a SHORTER SPACE OF TIME.
71
What are the 5 physical factors that affect lay time, discharge and the shape of the hydrograph?
1) Geology
2) Soil type
3) Slope
4) Drainage basin type
5) Antecedent conditions
72
What are the 2 human factors that affect lay time, discharge and the shape of the hydrograph?
1) Urbanisation
2) Deforestation
73
How does geology affect storm hydrgraphs?
Water CAN'T INFILTRATE into IMPERMEABLE rocks, so there's more RUNOFF.
74
How does soil type affect storm hydrgraphs?
More IMPERMEABLE soils e.g. clays, CAN'T INFILTRATE as much water as SANDY SOILS, which INCREASES SURFACE RUNOFF. SHALLOWER SOILS also become saturated MORE QUICKLY than DEEPER SOILS.
75
How does slope affect storm hydrgraphs?
The STEEPER the slope, the LESS INFILTRATION and the HIGHER the RUNOFF
76
How does drainage basin type affect storm hydrgraphs?
CIRCULAR drainage basins have a SHORTER LAG TIME and HIGHER DISCHARGE that NARROW BASINS because water reaches the MAIN RIVER CHANNEL AT THE SAME TIME. In a narrower basin, water from the FAR END of the basin TAKES A LONG TIME to reach the main channel.
77
How does antecedent conditions affect storm hydrgraphs?
Perviously WET or VERY COLD WEATHER can INCREASE SURFACE RUNODD because water can't infiltrate SATURATEDor FROZEN SOIL.
78
How does urbanisation affect storm hydrgraphs?
Water CAN'T INFILTRATE into IMPERMEABLE surfaces e.g. tarmac or concrete, so there's MORE RUNOFF. GUTTERS and DRAINS quickly take runoff to rivers, which RAPIDLY INCREASES DISCHARGE.
79
How does deforestation affect storm hydrgraphs?
Trees TAKE UP WATER from the ground and STORE IT, which REDUCES RUNOFF. CUTTING DOWN trees INCREASE RUNOFF and causes MORE WATER to enter the river channel, which INCREASES DISCHARGE.
80
What is an example of impermeable soil?
Clays
81
What are 2 examples of impermeable surfaces?
Tarmac & Concrete
82
How did antecedent conditions affect Eden?
November 2015 was the SECOND WETTEST month ever recorded in north Cumbria - this meant the SOILS were already SATURATED and river DISCHARGE was HIGH.
83
How did heavy rainfall affect Eden?
During Storm Desmond more than 300mm fell across the Cumbrian hills in 24 HOURS, which was the highest rainfall ever recorded in the UK.
84
How did short lag time affect Eden?
The rainwater across the drainage basin QUICKLY reached the MAIN CHANNEL at Carlisle.
85
How did blockages affect Eden?
DEBRIS carried by floodwater BLOCKED BRIDGES and smaller channels, FORCING WATER out of the river channel.
86
How did insufficient drainage affect Eden?
Runoff from IMPERMABLE SURFACES in Carlisle ran quickly into DRAINAGE SYSTEMS. These COULDN'T COPE with the volume of water and OVERFLOWED, making the flooding WORSE.
87
What is hard engineering in rivers?
MAN-MADE STRUCTURES built to CONTROL THE FLOW of rivers and REDUCE FLOODING.
88
What is soft engineering in rivers?
Schemes set up using KNOWLEDGE of a RIVER and its PROCESSES to REDUCE THE EFFECTS OF FLOODING.
89
What are the 4 main hard engineering methods used to manage rivers?
1) Flood Walls
2) Embankments
3) Flood Barriers (Floodgates)
4) DEMOUNTABLE FLOOD BARRIERS
90
What are the 2 main soft engineering methods used to manage rivers?
1) Flood retention
2) River restoration
91
What are flood walls in river management?
Artificial berries built along the river banks to increase the height of them, to hold more water. However these can be very expensive and can be unsightly.
92
What are embankments (levees) in river management?
These are raised parts of land, raised either naturally or artificially, they stop water from entering valuable area. But are expensive and may burst ender pressure or the water may get over the embankment causing more damage.
93
What are flood barriers (floodgates/storm surge barriers)?
Floodgates are built near the mouth (end) of a river to prevent flooding. This can be opened and closed protecting large areas, but have high costs and need regular maintenance.
94
What are demountable flood barriers in river management?
These provide temporary protection against flooding. The barriers are only put up when there's a flood forecast, so there is a risk that they are not put up in time. They are quite expensive, but they don't spoil the look of attractive locations.
95
What are flood plain restoration in river management?
These are strategies to maintain the river's original floodplain, as this allows the river to flood causing less money to be spent on defences, but restricts development and can't be used in urban areas.
96
What are river restoration in river management?
These are strategies to restore the river's natural course, making the river more natural by taking away embankments, etc. but flood banks are often still needed as changes in land use may cause side effects.
