Rivers Flashcards
(93 cards)
1
Q
Define long profile
A
The change in the gradient of the river course from the upper course to the lower course.
2
Q
Define cross profile
A
A cross section of the river - this shows a ‘slice’ of the river valley and channel
3
Q
What is a v-shaped valley?
A
A valley with steep sides and a narrow bottom that has been formed by erosion
4
Q
What is a tributary
A
A smaller river or stream flowing into a larger river
5
Q
What is a confluence
A
The point where two rivers meet
6
Q
Define load
A
The amount carried by a river
7
Q
What are the characteristics of the upper course of a river
A
- steep gradient
- narrow v-shaped valley
- narrow & shallow river
- large angular sediment load
- mostly erosion taking place
8
Q
What are the characteristics of the middle course of a river
A
- shallower gradient
- asymmetrical valley cross section
- deeper and wider river channel
- smaller / rounder load
- balance between erosion and transportation taking place
9
Q
what are the characteristics of the lower course of the river
A
- very low gradient
- very wide, very deep river channel
- small suspended load
- mostly deposition taking place
10
Q
define erosion
A
the wearing away of rock by the natural processes e.g. river / sea
11
Q
name 4 processes of erosion
A
hydraulic action
abrasion
attrition
solution
12
Q
define hydraulic action
A
fast flowing water pushes air into cracks and the force of this causes the channel to break up over time
13
Q
define abrasion
A
sand and pebbles are dragged along the river bed, wearing it away
14
Q
define attrition
A
rocks and stones wear each other away as they knock against each other
15
Q
define solution (erosion)
A
rocks e.g. limestone are dissolved in acid rainwater
16
Q
define transportation
A
the movement of eroded material by natural processes e.g. river / sea
17
Q
name the 4 processes of transportation
A
- traction
- saltation
- suspension
- solution
18
Q
define traction
A
largest material rolled and dragged along the river bed, often only moving in times of flood
19
Q
define saltation
A
smaller stones and pebbles are bounced along the river bed
20
Q
define suspension
A
smaller particles (e.g. sand and silt) are carried within the river channel
21
Q
define solution (transportation)
A
some material is dissolved into the river water and transported this way
22
Q
define deposition
A
when a river drops the sediment it is carrying
23
Q
when does a river deposit its load?
A
- drier weather (less water, so less energy)
- velocity decreases (less speed, so less energy e.g. inside a bend)
- river floods (water flows onto the flood plain, increase in friction, so energy decreases depositing fine silt and clay)
24
Q
name the landforms formed by erosion
A
waterfall
gorge
interlocking spurs
25
name the landforms formed by erosion and transportation
meanders
| ox-bow lakes
26
name the landforms formed by deposition
floodplains
| levees
27
name the landforms found in the upper course of a river
waterfalls
gorges
interlocking spurs
rapids
28
what is a waterfall
vertical fall of water over a steep drop
29
how does a waterfall form?
1. water flows over harder rock with softer rock beneath
2. the softer rock is eroded by hydraulic action and abrasion, much faster (differential erosion) creating a step in the river
3. the hard rock is undercut by erosion creating an overhang
4. the hard rock is also eroded, but much slower. eventually it collapses into the plunge pool
5. this process repeats over time causing the waterfall to retreat and a gorge to form downstream
30
what is a gorge
a steep-sided cut through landscape formed by a waterfall retreating
31
what is a plunge pool
the area of deep water at the bottom of the waterfall formed by hydraulic action and abrasion
32
what are interlocking spurs
hillsides that look like a zip formation - the river winds around the sections of land that stick out (spurs)
33
how are interlocking spurs formed?
in the upper course, rivers aren't powerful enough to erode laterally so they wind around the hillsides creating a zig-zag shaped flow
34
Name the landforms found in the middle course
meanders
| ox-bow lakes
35
what is the thalweg
line of fastest flow
36
what is a meander
bend in the river
37
what is an ox-bow lake
horse-shoe shaped lake that is formed when a meander is cut off and becomes isolated
38
explain how an ox-bow lake forms
1. the fastest flow is on the outside of the meander resulting in erosion (hydraulic action and abrasion) on the outside bend
2. the neck of the meander is eroded and it becomes narrower
3. when there is high discharge (often in flood) the river cuts through the meander and takes a straight course
4. as the flood waters go down, deposition occurs at the edge of the straight channel cutting off the ox-bow lake
39
name the landforms found in the lower course
floodplains
| levees
40
what is a floodplain
the flat area where a river floods
41
what are mudflats
large flat areas of mud which is fine silt and clay deposited by a river, often when in flood
42
what is a levee
a raised river bank
43
how is a levee formed?
- Levées form in lower course - raised river bed found alongside the river
- When flooding occurs water flows over the sides of the channel
- The velocity of the river decreases rapidly as the proportion of friction has increased significantly so the river starts to deposit material
- It would have been carrying larger sediments in the bank full stage as the river had more velocity, and these are deposited first at the edges of the river channel
- Finer sediments e.g. silt and mud are carried much further across the floodplain (as they are lighter) and deposited later as flood waters recede
- Over time, and after many floods, the height of the banks can be raised by as much as 2m
44
define river discharge
the amount of water flowing through the channel at a given point and time
measured in cumecs (cubic metres per second)
45
list the factors affecting river discharge
precipitation
relief
geology
landuse
46
when does flooding happen
when the level of a river gets so high it spills over the banks
47
how does prolonged precipitation affect discharge
- after a long period of rain, the soil becomes saturated which means that no other rainfall can infiltrate, so this increases surface runoff, which increases discharge quickly
48
how does heavy rainfall affect discharge?
water arrives too quickly for infiltration
so there's more surface runoff
discharge increases, increasing the risk of flooding
49
how does geology affect discharge?
clay soils are impermeable so there is less infiltration and more surface runoff
sandy soils allow infiltration, reducing surface runoff
50
how does relief affect discharge
steep-sided valleys cause water to flow faster to the river, so it flows too quickly for infiltration, increasing surface runoff, increasing discharge
51
how does urbanisation affect discharge
buildings made from impermeable materials e.g. concrete and tarmac
impermeable surfaces increases surface runoff and drain quickly into rivers, so discharge quickly increases
52
how does deforestation affect discharge
cutting down trees means there are less trees to intercept and store water, also less trees to take water up from the soil moisture storage, so there is more water as surface runoff and it gets to the river quicker, increasing discharge
53
what is a hydrograph
graph that shows the relationship between precipitation and discharge
54
what is a flashy hydrograph
more likely to flood
lower lag time
steep rising and falling limb
high peak discharge
55
what is a gentle hydrograph
less likely to flood
longer lag time
more gentle rising and falling limbs
lower peak discharge
56
what is lag time
the time between the peak rainfall and peak discharge
57
what is antecedent rainfall
previous or prior rainfall
58
define interception
when trees catch rainwater and store it, using it to grow / photosynthesise
59
define infiltration
when water soaks from the ground into the soil
60
what is impermeable rock
rock that is impossible for water to soak into e.g. granite
61
what is permeable rock
rock that allows water to pass through e.g. limestone
62
define surface runoff
water flowing over the land
63
what is hard engineering
man-made structures built to control flow of rivers and reduce flooding
64
what is soft engineering
schemes set up using knowledge of a river and its processes to reduce the effects of flooding
65
name 4 hard engineering strategies
dams and reservoirs
channel straightening
embankments
flood relief channels
66
name 5 soft engineering strategies
```
flood warnings
preparation
flood plain zoning
planting trees
river restoration
```
67
how do dams regulate flow
create a reservoir to store water and the flow of water is regulated through the flood gates being released
68
what are the benefits of building a dam
- reservoirs store water which reduces risk of flooding
| - water in reservoir can be used for drinking, or for HEP
69
what are the costs of building a dam
- very expensive
- reservoirs can flood existing settlements
- eroded material caught in the reservoir, and not deposited downstream reducing soil fertility, affecting crop yields
70
how does channel straightening reduce flooding
meanders cut out, channel straightened moving water away from settlements faster
71
what are the benefits of channel straightening
-water moves away quickly reducing flooding
72
what are the costs of channel straightening
- flooding moved downstream
| - more erosion downstream as water is flowing faster
73
how do embankments reduce flooding
raised river banks increase capacity so the river can hold more water
74
what are the benefits of embankments
-river can hold more water so less flooding
75
what are the costs of embankments
- fairly expensive
| - risk of severe flooding when they are breached
76
how do flood relief channels reduce flooding
channels divert water away from settlements
77
what are the benefits of flood relief channels
- river discharge is reduced so less flooding
| - gates on flood relief channels enables water flow to be controlled
78
what are the costs of flood relief channels
- increased discharge at confluence of relief and main channel
- if water level gets too high relief channels can flood
79
how do flood warnings reduce flooding
-environment agency communicates warnings to give people time to prepare
80
what are the benefits of flood warnings
- impact of flooding is reduced
| - farm land still receives fertile alluvial deposits
81
what are the costs of flood warnings
- don't stop the flood
| - some may not access warnings
82
how does preparation reduce flooding
buildings modified to reduce damage
| people make plans e.g. emergency kit with torch and blankets
83
what are the benefits of preparation
- impact of flooding is reduced
| - people less anxious
84
what are the costs of preparation
- doesn't guarentee safety in flooding
- doesn't stop the flood
- expensive
85
how does floodplain zoning reduce flooding
- it doesn't!
| - restrictions on building can reduce impermeable surfaces and expensive landuse near the river
86
what are the benefits of floodplain zoning
- risk of flooding is reduced - less impermeable surfaces
| - impact of flooding is reduced
87
what are the costs of floodplain zoning
- expansion of urban area is limited
| - not useful if areas already built on
88
how does afforestation (planting trees) reduce flooding
increases interception, and increases lag time as infiltration rates are higher
89
what are the benefits of afforestation
- discharge and flood risk are reduced
| - vegetation reduces soil erosion and provides habitats for wildlife
90
what are the costs of afforestation
-local flood risk can increase if no other action is taken
91
how does river restoration reduce flooding
this makes the river more natural e.g. removing man-made levees, so the floodplain can flood naturally
92
what are the benefits of river restoration
- flooding reduced downstream as discharge is reduced
- little maintenance is needed
- better habitats for wildlife
93
what are the costs of river restoration
-local flood risk increases
