Freshwater - drainage basin hydrology and geomorphology Flashcards
(134 cards)
1
Q
Define drainage basin
A
The area drained by a river and its tributaries.
2
Q
Key features of the Mississippi drainage basin
A
- Located in the USA
- Covers an area of 1.24 million square miles
- Crosses 2 Canadian provinces and 31 US states before reaching the Gulf of Mexico
- 3 major rivers and 100s of smaller rivers flow into it
- 4th largest drainage basin in the world
3
Q
Define confluence
A
Where a smaller river flows into a larger river
4
Q
Define Floodplain
A
An area of flat land on either side of the river
5
Q
Define mouth
A
Where the main channel reaches the sea or lake
6
Q
Define source
A
The start of the river
7
Q
Define tributary
A
A smaller river channel that flows into a larger river
8
Q
Define Watershed
A
The divide between one drainage basin and another
9
Q
Inputs of a drainage basin
A
Precipitation of varying type and intensity
10
Q
Outputs of a drainage basin
A
- Evaporation
- Transpiration
11
Q
Flows in a drainage basin
A
- Infiltration
- Throughflow
- Overland flow
- Base flow
12
Q
Stores in a drainage basin
A
- The cryosphere
- Vegetation
- Soil
- Aquifers
- Lakes
13
Q
Describe surface run-off
A
Surface run-off refers to overland flow. It occurs when precipitation exceeds the infiltration rate and when the soil is saturated.
14
Q
In what 4 ways can water enter the river channel?
A
- Precipitation
- Throughflow
- Groundwater flow
- Surface run-off
15
Q
What is the fastest way water enters the river?
A
Surface run-off
16
Q
Define water table
A
The permanently saturated zone within solid rocks and sediments
17
Q
Groundwater accounts for ….% of all freshwater. Fill in the gap.
A
96.5
18
Q
What are aquifers made of?
A
Permeable rocks like sandstone
19
Q
Define cryosphere
A
The snow and ice environment
20
Q
Define discharge
A
The volume of water passing a given point over a given time measured in cumecs.
21
Q
Define cross sectional area
A
The mean depth multiplied by the channel width
22
Q
Define wetted perimeter
A
The length of channel bed and banks in contact with the running river
23
Q
Define hydraulic radius
A
The cross sectional area divided by the wetted perimeter
24
Q
What does hydraulic radius indicate?
A
The efficiency of a stream’s shape
25
Define velocity
The speed and direction of the flowing river, measured in meters per second
26
Define channel roughness
The degree of irregularity in the channel bed and bank, e.g. rocks, boulders and obstacles
27
Define abrasion
The wearing away of the bed and bank by the load carried by the river
28
Define attrition
The wearing away of the load carried by the river due to collisions over time
29
Define hydraulic action
The force of air and water on the banks of the river
30
Define solution (erosional process)
The chemical process caused by the removal of chemical ions, especially calcium
31
Define suspended load
The load carried in the flow of the river
32
Define solution (transportation process)
The chemically dissolved load in the river.
33
Define saltation
The load that bounces along the bed of the river
34
Define traction
The larger load that rolls along the bed of the river
35
Define bedload
The load that moves along the bed
36
Define infiltration
The process by which water soaks into or is absorbed by the soil
37
Define surface run-off
Water that flows over the land's surface
38
Define throughflow
The process of water flowing through the soil in natural pipes
39
Define percolation
The process of water flowing slowly downwards from the soil into the bedrock
40
Define recharge
The refilling of water into pores where the water has dried up or been extracted by human activity
41
Define springs
Where groundwater flow reaches the surface
42
Outline the different time frames in which water moves between stores and flows in a drainage basin
1. Short time frame - water enters as rain and stays in the system for minutes or hours before evaporating back into the atmosphere
2. Medium time frame - water infiltrates the soil and in cooler temperatures can stay for days in upland fens and bogs where the soil acts like a sponge, storing the water for weeks and months
3. Long time frame - deep percolation of water into groundwater storages such as aquifers can store the water for decades and even millennia
43
Outline the different speeds in which water flows through the drainage basin
1. High speed - surface run-off such as overland flow in streams and rivers is very fast flowing transporting water over large distances
2. Medium speed - water that flows through the soil in throughflow travels more slowly and overs less distance, however, throughflow can be efficient and rapid through worm channels in the soil
3. Low speed - the slowest flow is groundwater flow due to the time it takes water to percolate into the aquifer and then flow through the aquifer system
44
Describe the water budget
The water budget examines how changes in stores within the drainage basin are influenced by the balance of inputs and outputs in the basin
45
The water budget is an important tool for .... .... .... . Fill in the gaps.
Drainage basin management
46
What factors influence the water budget?
1. Climate
2. The type of underlying bedrock and soil
3. The shape, size and relief of a drainage basin
4. Vegetation density
47
Outline the role of climate in influencing the water budget
The climate determines the amount of precipitation, type of precipitation and how water transfers through the drainage basin
48
Outline the role of the underlying bedrock and soil in influencing the water budget
Permeable rock and more porous soils encourage infiltration and percolation and slow down flows and increase stores within the basin
49
Outline the role of the shape, size and relief of a drainage basin in influencing the water budget
The shape, size and relief of a drainage basin are also going to shape the amount of water infiltrating or flowing overland.
50
Outline the role of vegetation in influencing the water budget
Vegetation density will influence the patterns of water flow and storage in a drainage basin. Dense forests intercept rainfall, absorbing it through the canopy and root systems, increasing infiltration and slowing down overland flow.
51
Give place context for the River Teviot
The River Teviot is located in Scotland and drains an area of 326 km^2 above Hawick.
52
Suggest factors influencing the water budget of drainage basin of the River Teviot
1. Relief - steep gradient; the river cuts down from around 500m to 256m over a distance of approximately 30km.
2. Underlying bedrock - shale (mostly) and sandstone
3. Climate (main factor) - warm temperatures in the Spring and Summer
53
How does relief influence the water budget of the drainage basin of the River Teviot?
The steep gradient makes it difficult for water to infiltrate the soil leading to high amounts of surface run-off.
54
How does the underlying bedrock influence the water budget of the drainage basin of the River Teviot?
Shale, being the most common bedrock of the basin, has a low permeability which encourages run-off. Sandstone, which is less common in the basin, is more permeable allowing for more percolation.
55
How does climate influence the water budget of the drainage basin of the River Teviot?
The warmer temperatures in the Spring and Summer lead to increased outputs from evapotranspiration so less precipitation enters the river as streamflow.
56
Define erosion
The breaking down of rock by a moving agent e.g. the river
57
Define transportation
The carrying of load by the river
58
Define deposition
The drop in energy of the river and the resulting release of transported load
59
Define vertical erosion
The cutting down of the river into the bed, deepening the channel
60
Define lateral erosion
The cutting in of the river into the bed, widening the channel
61
Define capacity (river)
The total amount of load being transported in the river
62
Define competence
The maximum size of load the river can transport
63
Outline the role of erosion in shaping upper course landforms
The upper course of the river is at a high altitude, therefore it has high potential energy. This potential energy can be converted into kinetic energy to vertically erode the channel. Hence why waterfalls, potholes and rapids from in the upper course.
64
Outline the role of erosion in shaping middle course landforms
The middle course of the river has less potential energy because it's at a lower altitude compared to the upper course, therefore the rate of vertical erosion falls. Thus, the water flows more efficiently in the channel so it's able to erode laterally making the channel wider. Hence why meanders form and migrate across the floodplain over time.
65
Outline the role of deposition in shaping lower course landforms
The river is transporting high amounts of load in the lower course. As the river floods, it deposits some of this load across the floodplain. The river also experiences a fall in energy as it approaches the sea at estuaries and deltas, leading to deposition.
66
Outline the spatial variation of erosion transportation and deposition along the course of the river.
The upper course is dominated by erosion, the middle course - transportation - and the lower course - deposition.
67
What are the 4 types of erosion?
1. Hydraulic action
2. Abrasion
3. Solution
4. Attrition
68
What factor increases hydraulic action?
Floods - the running water has a lot more energy to erode the channel
69
What is the main factor that increase abrasion?
The supply and size of rocks being transported by the river. During a flood the river can transport larger rocks because it has more energy. Abrasion is also more common in the upper course because there is a greater supply of rocks from the bedrock.
70
What is the main factor that impacts the rate of solution in a river?
The type of minerals in the bedrock. Dissolvable minerals in bedrock such as gypsum will dissolve in contact with water.
71
Which factors affect flow dynamics at meanders?
1. Gradient
2. Channel shape
3. Underlying bedrock
72
Explain how the factors affecting flow dynamics mean that rates of velocity and erosion vary across the channel.
Steep sections of the river have more potential energy to erode. Other sections of the channel have bedrock with varying resistance, creating steps, rapids and waterfalls because softer sections of bedrock erode faster. At meanders where rivers change direction and curve, the fastest flow is pushed to the outside of the bend eroding the bank, whereas deposition occurs in the inside bend because it's shallower, so water uses more energy to overcome friction and so deposits load.
73
What are the 4 main ways rivers transport load?
1. Traction
2. Saltation
3. Suspension
4. Solution
74
Define sheet flow
The movement of gravel as one mass along the bed
75
What type of transportation is mainly occurs in the upper course of a river?
Traction because the river has enough energy
76
Why does the river no longer flow over bedrock in the middle and lower course of the river?
Because the bedrock has been submerged by deposits over hundreds of years
77
What is the most common type of transportation in the middle and lower course of the river?
Suspension - dissolved load from minerals is also transported in solution.
78
The ability of a river to transport or deposit load depends on the .... of the load and the .... .... of the river. Fill in the blanks.
1. load
2. flow velocity
79
What are basic rules that can be observed about the ability of a river to transport or deposit load?
1. More velocity is needed to pick up material than to carry it in suspension
2. The division between transportation and deposition is smaller - only a small decrease in velocity will lead to deposition
80
What are dynamic braided environments and why are they significant?
Dynamic braided environments are braided channels that are commonly found in glacial rivers or arid environments where rivers experience large fluctuations in discharge over different time frames. Flash floods from tropical downpours or melting glaciers result in high rates of erosion of deposits and transportation increases. At the end of the flood, discharge returns to base flow and the river will deposit the load. The result is a dynamic river environment with frequent fluctuations in flow with varying degrees of erosion, transportation and deposition. The channel is said to be braided because the channels will merge and swell in size during peak flow, then will break up into many breads during times of slower flow to find the path of least resistance.
81
Outline how river processes occur over varying time scales.
Depositional events take place over a number of hours or days, with rivers typically flooding their banks every two to three years. Meander development and migration takes place over decades and centuries, whilst full floodplain development occurs over millennia.
82
Define cap rock
A layer of hard rock underlaid by a layer of softer rock
83
Define gorge
A steep-sided valley downstream of a waterfall
84
Define differentiated erosion
Differences in the rate of erosion due to differences in rock resistance
85
Define plunge pool
A deep basin shape where water pools below a waterfall
86
Define overhang
A ledge of cap rock caused by the plunge pool undercutting it
87
Define undercut (feature)
The cave-like feature eroded behind the waterfall
88
What is unique to the upper course of a river allowing it to produce landforms such as v-shaped valleys and interlocking spurs?
The river has enormous gravitational potential energy which it converts to kinetic energy. The river wants to reach the sea as efficiently as possible and so vertically erodes the channel and in doing so shapes the landscape over over thousands of years to produce the unique landforms.
89
How are interlocking spurs formed?
The river bends around sections of the valley called spurs. These spurs form as a result of the river moving around more resistant rock to take the past of least resistance as it saves energy by doing so. In the process, interlocking spurts are formed as one looks upstream.
90
How are steps, rapids and potholes formed?
Through differentiated erosion of the bedrock
91
Most waterfalls form as a result of .... .... of the bedrock in the .... .... of the river. Fill in the gaps.
1. differentiated erosion
2. upper course
92
Explain and describe the formation of waterfalls (4)
Waterfalls form in the upper course of the river due to differentiated erosion. Softer layers of rock underlying a harder layer are vertically eroded. Processes such as hydraulic action, abrasion and solution combine over hundreds of years to form a deep plunge pool. Over time the force of the water deepens the plunge pool further and it undercuts the hard cap rock above. This creates an overhang that eventually is left unstable and collapses. Hard angular rock further deepens the plunge pool through abrasion and the waterfall increases in height and retreats upstream. Over thousands of years, this leaves a steep-sided gorge downstream.
93
What is a textbook example of a waterfall?
The River Tees in the UK. It has a layer of hard rock called Whin Sill that forms the cap rock. A layer of softer rock called sandstone and shale underly the Whin Sill.
94
Floodplains and river landforms form over different .... .... from just days to thousands of years. Fill in the gaps.
time scales
95
Define bluffs
Raised hills that mark the furthest point of the floodplain
96
Define floodplain
An area of flat land at the sides of the river caused by erosion and deposition
97
Define levées
Raised embankments, formed by deposition found on the banks of the river
98
Define friction
A contact force acting against the river that takes energy from the river
99
Define meander
A snake-like bend in the river channel found in the middle or lower course
100
Explain how a drainage basin functions as an open system
It allows the movement of energy and matter across its boundary; therefore, it's an open system.
101
As the river moves downstream the river channel ...., moves away from the confines of the .... .... and floodplains form. Fill in the gaps.
1. flattens
2. v-shaped valley
102
Describe the role of erosion in floodplain development
In the middle course, there is far less gravitational potential energy and so the river begins to erode laterally rather than vertically. Lateral erosion of the channel causes it to not only get wider over time but also causes the river position to migrate and change location. This process, over thousands of years, helps to erode a floodplain.
103
Describe the role of deposition in floodplain development
Unregulated rivers should flood every two to three years. Over thousands of years this amounts to many floods. Each time it does so, it deposits alluvium over its floodplain as the water comes in contact with vegetation on the floodplain, causing it to lose energy due to friction and so competence falls. Fine sediments held in suspension are transported right across the floodplain making a large flat area. These sediments build up over time covering any bedrock below.
104
How are levées formed?
They form as a result of repeated floods depositing larger sediments immediately at the banks. When the river floods, there is an immediate fall in energy. As a result, the competence of the river to transport larger gravels falls and so these are deposited at the banks. Repeated floods mean that these gravels create raised embankments called levées.
105
Define river cliff
A steep sided river bank on the outside bend of the meander
106
Define pool (meander)
A deep section of the channel on the outside bend of the meander
107
Define riffle
A shallow area of channel found in the straight section of the river between meanders, dominated by deposition
108
Define slip-off slope
A gentle slope found on the inside bend of the meander
109
Define river beach
An area of deposition found above the inside bend of the meander
110
Define thalweg
The shoot of fast-flowing water in the meander
111
Define helicoidal flow
The corkscrew motion that describes the flow dynamics of the thalweg
112
Define secondary cell
The pattern of flow that describes how some water moves from the outside bend to the inside bend
113
Define meander neck
The narrow section of floodplain separating two meander loops
114
Define ox-bow lake
A section of meander cut off from the main channel
115
Define meander scar
A dried up ox-bow lake
116
Outline how meanders form
Meanders form as a result of the river attempting to find a balance between its energy and the water and load it's transporting. They form through a combination of erosion and deposition.
117
What is unique about the flow dynamic of a meander?
It has a shoot of faster-flowing water called the thalweg on the outside bend and slower-flowing water with low energy around the inside bend. This variation in velocity leads to erosion of the outer bend and deposition on the inside bend, creating an asymmetrical cross-profile.
118
How does a meander get its asymmetrical cross-profile?
The thalweg erodes the outside bend creating a steep river cliff and a deep pool. Water on the inside bend has low energy and competence causing the river to deposit sediment. This creates a gentle slope that is characteristic of a slip-off slope.
119
How does a riffle section form?
It forms due to the deposition of sediment and gravel as the flow slows down as it leaves the meander loop.
120
What is a riffle section?
It's a straighter section of the river between two meanders. It's symmetrical and shallow.
121
The thalweg is able to erode the river cliff because of 2 key factors. What are they?
1. The thalweg has more energy due to greater velocity
2. It has a helicoidal flow that increases turbulence on the bank
122
Deposition on the inside bend is cause by 2 factors. What are they?
1. Slower-moving water has lower energy and competence and so naturally deposits sediments
2. The secondary cell moves sediment eroded from the river cliff across the channel to the slip-off slope
123
How are ox-bow lakes formed?
The thalweg erodes the outer bend of two meander loops. Through hydraulic action, abrasion and solution working together, the banks moves closer together, narrowing the meander neck. During a flood when the river energy and velocity are at their peak, the meander neck is cut through and the river flows straight. Fast flow is now focused in the middle of the channel and lower energy to the sides, which leads to deposition, which eventually cuts-off the former meander to create an ox-bow lake.
124
Describe an arcuate delta
A delta that is tide dominated and tends to be fan-shaped with many distributaries
125
Describe a Bird Foot delta
A delta that is river-dominated. The fast-flowing water relative to the lake or marine currents leads to the river extending outwards into the lake or sea.
126
Describe a cuspate delta
A delta that is wave dominated. The waves and currents of the lake or sea transport sediment away from the coast creating a flattened triangle shaped delta with few distributaries.
127
What are the three main types of delta?
1. Cuspate
2. Arcuate
3. Bird Foot
128
Define distributaries
The separate channels that form across the delta
129
Describe flocculation
Flocculation occurs due to a weak static charge that is created as freshwater and sediments meet salt water. This charge makes sediments sticky and allows them to flock together. They gain weight and are deposited.
130
Define bars
Areas of deposition
131
Define lagoons
Closed or open bodies of water within the delta containing brackish water
132
Define brackish water
Water created by the mix of freshwater and seawater
133
Conditions for Delta formation
1. A large amount of transported load in the river
2. Limited opportunity to deposit load along the course, e.g. no lake
3. Slow river velocity at the mouth
3. Relatively weak tidal and marine currents that cannot transport sediments away
4. Shallow coastal water, e.g. continental shelf
134
Key features of a generic delta structure
A delta is made of three levels. Larger more coarse sediments are deposited first to form topset beds. These beds are typically made of sand bars, lagoons and creeks. Smaller sediments are transported further out and are deposited to create lower foreset beds. The smallest and lightest sediments are transported the furthest and form bottomset beds. These are typically fine clays.
