P1: Freshwater: Drainage Basins Flashcards
1
Q
6 features of a drainage basin
A
- Watershed
- Source
- Tributary
- Confluence
- Floodplain
- Mouth
2
Q
Input to drainage basin
A
Precipitation (rainfall, snow, frost, hail, dew)
3
Q
Flows in drainage basin
A
- Throughflow
- Surface run-off (overland flow)
- Groundwater(base) flow
- infiltration
- Percolation
4
Q
Stores in drainage basin
A
- Cryosphere
- channel stores
- vegetation
- Soil
- Aquifers
- Atmosphere as water vapour
5
Q
Outputs from drainage basin
A
- Transpiration
- Evaporation
- Sublimation
6
Q
5 characteristics of precipitation that impact local hydrology (movement of water)
A
- Total amount of precipitation
- Intensity
- Type (e.g. snow or rain)
- Geographic distribution
- Variability
7
Q
In which 2 rocks does percolation happen fast
A
- carboniferous limestone
- chalk
(both quite permeable)
8
Q
3 favourable conditions for evaporation
A
- over oceans and seas
- warm
- dry
9
Q
6 factors that affect evaporation
A
- temperature
- humidity
- wind speed
- availability of water
- vegetation
- surface colour
10
Q
what do regional and local water budgets tell us
A
- regional level tells us amount of water available for human use
- local level tells use how amount of water available in the soil
11
Q
Water budget equation
A
P + Qin = ET + ∆S + Qout
P = precipitation (rain, snow, etc.)
Qin = water flow into the watershed
ET = quantity of evapotranspiration from soils, surface water, plants, etc.
∆S = Change in water storage
Qout = sum of water flowing out of the watershed
12
Q
6 factors affecting water budget and how
A
Permeable rocks and porous soils
- Encourage infiltration and percolation, meaning flow is slowed down and there’s an increased storage in the water basin
Dense forests
-Intercept rainfall, absorbing water through the canopy
Shape, relief and size of drainage basin
- Influence amount of water flowing overland
Vegetation density
- Affects patterns of water flow and stores in the basin
Seasonality
- There will be more water in wet seasons, which will create a water surplus
Climate
- Determines the amount and type of precipitation that transfers through a river basin
13
Q
river discharge equation
A
discharge= cross sectional area x velocity
14
Q
how to calculate cross sectional area
A
- calculate mean depth by taking 10 depth measurements of depth across the river from bank to bank at one site
- add all values together and divide by number of measurements for mean depth
cross sectional area= width x mean depth
15
Q
how to calculate velocity
A
- take 3 measurements 3 times
- place float in left of stream, then centre of stream, then right of stream
- repeat 3 times
- take average time for left of stream, centre of stream and right of stream
- take average of these three averages
16
Q
what 2 things determine water flow
A
- gravity
- frictional resistance with river bed/banks
17
Q
2 factors affecting stream energy
A
- channel volume
- channel shape
18
Q
features of river when there is turbulent flow
A
- complex channel shapes
- high velocities
- cavitation (air bubbles trapped in water)
19
Q
features when there is laminar flow
A
- shallow, smooth, straight channel with low velocities
- in groundwater and glaciers but not rivers
20
Q
how to measure stream efficiency
A
cross sectional area/wetted perimeter
- higher ratio means greater efficiency
21
Q
What do silt and clay create
A
steep, deep, narrow valleys
22
Q
what do sand and gravel promote
A
- wide, shallow channels
23
Q
4 erosion methods
A
- hydraulic action
- attrition
- abrasion/corrasion
- solution/corrosion
24
Q
6 factors affecting erosion
A
- load (heavy and angular loads increase erosion)
- velocity
- ph levels (more acidic more solution)
- geology
- humans (deforestation, bridges, dams)
- gradient
25
5 transportation methods
- Suspension
- Saltation
- Traction
- Solution
- Floatation
26
Stream capacity
maximum amount of debris a stream can carry
27
competence
diameter of the largest particle carried
28
Critical erosion velocity
the minimum velocity to move grains of a specific size
29
What does hjulstrom curve show
- the relationship between velocity and discharge (efficiency)
- It shows the velocities at which sediment will normally be eroded, transported or deposited
30
3 reasons why deposition would take place
- A decrease in the volume of water
- A shallow gradient that decreases velocity
- An increase in friction between water and the channel
31
4 step formation of waterfall
1. Occur on horizontally bedded rocks
2. Soft rock is undercut by hydraulic action and abrasion
3. Due to the weight of the water and no support, the waterfall collapses and retreats upstream
4. Over thousands of years, waterfalls may create a gorge
32
1. The river erodes the outer bank of a bend, creating a cutbank
2. Deposition occurs along the inner bank, forming a point bar
3. As the water flows faster along the outer bend (cutbank) it erodes the bank more, deepening the channel
4. Sediment is deposited along the inner bend (point bar), causing the bank to build up
5. Over time, erosional and depositional processes cause the river to develop a sinuous, meandering course
33
2 step how floodplain forms and develops
1. river floods
2. alluvium is a mix of sand and gravel that is eroded on outside of the meander and this material is deposited when river floods to build up floodplain
34
4 step formation of levee
1. formed when river repeatedly floods
2. each time river deposits material on banks/floodplain
3. heavy sediment is deposited first closest to bank
4. this creates levee which is a raised bank
35
When and how do deltas form
- form when river flows into standing body of water
- causes rapid drop in stream velocity
- causes deposition of material to form delta
36
Cuspate delta description and example
- triangle of deposition
- eg: Nile delta
37
Arcuate delta description and example
- river branches out like a tree amongst deposition, and includes some lagoons
- eg: Ganges delta
38
Bird's foot delta description and example
- very complicated, interweaving, intricate flow of water through deposition
- eg: Mississippi delta
39
two variables that hydrograph compares
- Rainfall received during an event in mm
- River discharge in m3/sec (cumecs)
40
3 times when rising limb is steep
- flash flood
- in small drainage basins
- in urbanised areas
41
2 times when peak discharge high
- large basins
- steep catchment areas
42
3 factors affecting lag time
- stream order
- basin shape
- steepness
43
what is recessional limb influenced by
- local aquifers
- local geology
- catchment area (a smaller area will have steep recessional limb)
44
what 2 things does hydrograph size depend on
- rainfall amount (higher rainfall, bigger hydrograph)
- basin size (bigger basin, bigger hydrograph)
45
River regime (annual hydrograph)
- shows pattern of seasonal variation in river discharge over a year)
46
Recurrence interval
Frequency of flood events
47
8 physical factors affecting flood risk
- precipitation type and intensity
- temperature and evapotranspiration
- antecedent moisture (moisture levels in soil)
- drainage basin size and shape
- drainage density
- slopes
- vegetation type
- porosity of rocks and soils
48
how does precipitation type/intensity influence flood risk
- intense rainfall causes overland flow
- Low intensity rainfall will percolate the soil, reducing the peak of the flood
- Intense rain compacts the ground, reducing infiltration
- Rapid melting of snow can cause high rates of overland flow
49
how does temp/evapotranspiration influence flood risk
- Warm air can hold more water
- Higher temperatures lead to more evaporation meaning less water in the rivers
50
how does antecedent moisture influence flood risk
- If the ground is saturated, overland flow will quickly be produced
51
how does drainage basin size/shape influence flood risk
- Smaller drainage basins respond more quickly to rainfall conditions
- Circular basins respond more quickly to floods than linear basins
52
how does drainage density influence flood risk
- High drainage density increases overland flow
53
how do slopes influence flood risk
- Steeper slopes create more flooding
54
how does vegetation type influence flood risk
- Deciduous trees lose their leaves and therefore there is less interception
55
how does porosity of rock/soil influence flood risk
- Chalk and gravel are permeable and allow for percolation
56
Human factors affecting flood risk
- urbanisation
- deforestation
- channel modification
57
6 ways urbanisation influences flood risk
- increases magnitude/ frequency of floods because more impermeable surfaces like roads
- more gutters which increase drainage density and
- riverside facilities reduce carrying capacity
- the removal of trees can decrease evapotranspiration and interception
- the construction of houses and other commercial businesses increase peak discharge
- construction of storm drains will provide local relief but this may aggravate flood problems lower down the river
58
2 ways deforestation influences flood risk
- increases flood run-off
- decreases channel capacity due to an increase in deposition in the channel
59
2 ways channel modification influences flood risk
- speeds up water movement, reducing lag time
- Enlarging channels through levees allows more water to be carried
60
What is used to predict river flooding
- weather satellites
- radars
61
3 ways to improve flood prediction
- Mapping of channels
- More detailed collection of meteorological information
- More sharing of information about the risk of flooding between countries who share international drainage basins
62
3 advantages of dams
- hold back water during time of flood and release again when flood risk is reduced
- tourism
- stores water in reservoir
63
4 disadvantages of dams
- Increase in loss of water due to evaporation
- Channel erosion
- Possible spread of diseases such as malaria
- clear people land and habitats to build
64
2 advantages of afforestation
- Could increase interception and reduce overland flow
- Could possibly soak up excess rainwater
65
2 disadvantages of afforestation
- Young trees cannot absorb or intercept as much as more mature trees
- Most trees lose their leaves in the winter and so interception reduction is decreased
66
3 advantages of channel modification
- can be achieved in different ways: straightening or enlarging
- Enlarging the cross-sectional area increases the bankfull discharge and hydraulic radius
- Velocity can increase if meanders are removed
67
3 disadvantages of channel modification
- Expensive
- May have to remove buildings to complete channel modification
- may only reduce risk at one part of the river
68
3 advantages of levee strengthening
- Can protect buildings in the surrounding areas from flooding
- Barriers are less expensive than channel modification
- Can be used to divert water to less valuable land
69
4 ways to plan for flood
- place sand bags by doors and along walls
- seal doors and windows
- build house on stilts
- place electrical generators higher up in buildings
70
4 factors that influence physical water scarcity
- Level of precipitation
- Population growth
- Water availability
- Water demand
71
2 factors that influence economic water scarcity
- Poor management of water resources
- Lack of water infrastructure
72
What is drought caused by and why
- Changes in atmospheric circulation, such as a shift in the position of the Inter-tropical Convergence Zone (ITCZ) or El Niño
This leads to:
- A lack of precipitation as a result of short-term changes or longer-term trends
- The lack of rainfall is often combined with high temperatures, which increases evaporation
73
7 impacts of drought
- livestock and animals die
- more forest firs as vegetation is dry
- conflicts over water supply
- children miss school in LICS because have to travel further to collect water
- lack of food if crops can't be irrigated
- damage to ecosystems/loss of habitats
- reduced economic development as water is not available for industry
74
4 factors that water quantity depends on
- Rates of rainfall
- Groundwater and river flows
- Transpiration
- Evaporation
75
3 factors affecting water quality
- use of fertilisers and pesticides from agriculture
- sewage water
- industrial processes
76
3 factors that could be limiting water access
- abundance of water
- infrastructure
- cost
77
3 ways agriculture impacts water quality
- waste water from farming
- fertilisers, herbicides, pesticides
- soil erosion
78
6 step process of eutrophication
1. excessive nutrients from fertilisers run-of from land into water
2. aquatic plants flourish and grow rapidly
3. algae also grows rapidly
4. algal bloom prevents sunlight from reaching aquatic plants so water oxygen levels fall
5. decomposition rate increases which increases aerobic respiration which means even less oxygen
6. organisms like fish die
79
positive feedback loop of algae blooms
- Increased algae blooms lead to increased decomposition as light cannot reach aquatic plants
- Which decreases oxygen levels
- This reduces consumers and further increases algae growth
80
3 reasons why eutrophication is a problem
- nitrogen causes excessive growth of algae
- this can affect human health
- a loss of fertiliser is an economic loss for agricultural production
81
3 ways to resolve eutrophication
- Use different types of fertilisers and detergents, which may alter human effects of pollution
- Pump mud from eutrophic water
- Remove nitrates and phosphates from water
82
4 ways to avoid nitrate loss from northern hemisphere
- When soils are wet, avoid using nitrogen fertilisers
- Avoid applying nitrogen fertilisers to fields next to streams or lakes
- Avoid ploughing grass as it releases nitrogen
- Avoid applying fertiliser if rain is forecast
83
3 different types of irrigation
- total flooding (like on rice fields)
- sprinklers
- drip systems
84
when does salinisation occur
- to an increase of salt in the soil left as the water evaporates
85
5 impacts of irrigation
- loss of aquifer capacity
- reduction of water table
- reduction of albedo
- evapotranspiration rates increase
- tornado frequency increases
86
6 water management strategies
- water saving
- customer pricing
- water purification
- zoning
- rainwater harvesting
- new technologies
87
How does customer pricing (managing water) work?
- use meters to charge for domestic water use
- have a regulating authority to allow competition between water providers so water monopolies don't exist
88
How does water purification (managing water) work?
- Disinfected to remove harmful chemicals, suspended solids and gases
- Processes like light filtration and sand filters can distil the infected water
- most common type of disinfectant is chlorine, which has been used since 1854 in London
89
How does zoning (managing water) work?
- protecting areas from development to allow the safeguarding of water quality
- implement legislation to control water pollution levels
90
How does rainwater harvesting (managing water) work?
- capture water through pipes on roof
- through dams across stream waters
- through gravel-filled reservoirs to store water
91
3 examples of new technologies to manage water
- seawater desalinisation
- smart monitoring
- precision irrigation system
92
What is integrated river basin management?
- the process of coordinating conservation, management and development of water, land and related resources across sectors within a given river basin
- to maximise the economic and social benefits derived from water resources in an equitable manner
- while preserving and, where necessary, restoring freshwater ecosystems
93
4 components of IDBM
- water quality
- water supply
- flood control
- river channels
94
7 key elements to successful IDBM
- Integration
- timing
- participation
- scale
- knowledge
- capacity
95
4 costs of IDBM
- Difficulties in involving all the stakeholders who have differing priorities and views
- Projects are costly
- Accurate data is difficult to obtain
- Transboundary issues can be difficult to resolve
96
4 benefits of IDBM
- Helps to preserve biodiversity and maintain the ecosystem
- Ensures sustainable water use
- Minimises the risks and impacts of flooding
- Provides a reliable water supply
97
What is a wetland
- area of land which is permanently flooded
98
What is a Riverine wetland
- wetland located on floodplain
99
What is a Lacustrine wetland
- wetland located close to lakes
100
What is a Palustrine wetland
- fens and peatlands
101
What is a tidal wetland
- wetland on the coast
- caused by fluctuating tidal waves
102
What is a marine wetland
- coastal wetland
- formed near lagoons, estuaries and spits
103
3 threats to wetlands
- clearance to make way for housing and industry
- global warming because warmer temp leads to water loss
- changing sea and water levels because wetlands are highly dependent on them
104
5 benefits of wetlands
- livelihoods/income
- groundwater recharge
- shoreline stabilisation
- storm protection
- flood mitigation
105
3 uses of wetlands
- tourism
- peat
- wildlife resources
106
What is the Ramsar convention
- a convention aimed at conserving and sustainably managing wetlands
- signed by 60 countries
