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Define a System
An assemblage of interrelated parts, mostly sharing the same common characteristics
What four common characteristics do systems share?
1) A structure within a boundary
2) Both inputs and outputs and processes
3) Involving the flow of material
4) Either in isolation, closed or open systems
Define a Transfer and give an example
Links or relationships between components. Such as inputs, outputs and stores. ENERGY and MATTER can flow between components.
Example: infiltration
What is Steady State?
Where energy and matter entering a system is equal to energy or matter leaving the system
Define a Boundary
The edge of a system, differs in terms of what will and won't pass through it. Most important feature of a system
Define a Closed System
A system where matter cannot enter or leave, but energy can.
Give an example of positive feedback cycles?
- Climate Change
- Deforestation
What are negative feedback cycles
Changes in a system are nullified and returns the system to dynamic equilibrium.
Give an example of a negative feedback cycle
- Changing sea surface temperatures (More clouds and lower temperatures)
What is a cascading system?
Where an output for one system becomes the input for another.
(Precipitation is an output for the atmosphere and an input into the Hydrosphere)
What are the five major systems on Earth?
Atmosphere
Biosphere
Cryosphere
Hydrosphere
Lithosphere
Approximately how much of Earth's water is freshwater? (Not salty)
2.5%
Approximately how much of Earth's freshwater is not stored in Ice Caps or groundwater?
1-2%
How much of Earth's surface do Ocean's cover and what is the average depth of the ocean?
Cover 72% of Earth's surface
Average depth is 2.3 miles
Why is evaporation and condensation important for water stores
Evaporation allows hot air to rise, condensation allows it to fall and be transferred back into the lithosphere and biosphere.
What are the changes of state from solid to liquid and vice versa?
Melting
Freezing
What are the changes of state from liquid to gas and vice versa?
Evaporation
Condensation
What are the changes of state from solid to gas and vice versa?
Sublimation
Deposition
Why does evaporation occur?
Energy from solar radiation heats water. Rate depends on amount of solar energy, density of water and humidity.
Why does condensation occur?
Air cools and cannot hold as much water vapour. Excess water is converted back to a liquid.
What is adiabatic cooling?
When the volume of air increases but the temperature stays constant.
When did the most recent interglacial period begin?
12,500 years ago
What are two main ways water stores are changed?
Any two from
- Climate Change
- Cryospheric processes
- Clouds
What are the three Milankovitch Cycles?
Eccentricity
Obliquity
Precession
Give two key facts about Eccentricity
Any two from
- Affects the shape of Earth's orbit
- Orbit becomes circular to oval
- Takes around 100,000 years
- Earth is further away from the sun at times
Give two key facts about Obliquity
Any two from:
- Affects the Earth's axis
- Angle from the vertical changes from 22.5-24.5'
- Takes around 41,000 years
- Current at 23.5'
Give two key facts about Precession
Any two from
- Affects the Earth's axis
- The axis itself wobbles (Similarly to a spinning top)
- Takes around 19,000 - 24000 years for one cycle.
What are aerosols?
Tiny particles of salt and dust in the air.
What happens when aerosols and water vapour collide with each other?
If the air is cooled, water sticks to aerosols, forming large droplets
How are clouds form from water droplets?
Water droplets start to stick together, which can only happen when the air is saturated and cannot hold more water vapour
What are three different types of rainfall?
Frontal
Orographic
Convective
What causes Frontal Rainfall?
When a warm air mass meets a cold one, the warm mass is forced above the dew point where precipitation falls
What causes Orographic Rainfall?
On high ground, warm air is forced upwards by the terrain. Air cools at higher altitudes which leads to precipitation
What is a rain shadow?
Created on the opposite side of a mountain, where all the precipitation has fallen on the other side of the mountain
What is Convective Rainfall?
Ground heated by solar radiation, rapid evaporation leads to "Sunshine and Showers".
Volume of rising air increases without heat (Adiabatic cooling) and condenses.
What type of rainfall does convective rainfall lead to?
Short, heavy showers.
Define the Water Balance
The relationship between inputs in the drainage basin system and the outputs.
What is the Water Balance Equation?
P = Q + E +/- S
P = Precipitation
Q = River Runoff
E = Evapotranspiration
S = Storage
Define Soil Moisture Surplus
Precipitation exceeds evapotranspiration. Excess water for plants, recharge and runoff
Define Soil Moisture Utilisation
Evapotranspiration exceeds transpiration. Water stores used by plants or lost to evaporation
Define Soil Moisture Deficit
All moisture has been used, plants wilt or adapt to survive
Define Soil Moisture Recharge
Precipitation exceeds evapotranspiration. Soil fills up from infiltration
What is a River Discharge?
The volume of water passing a measuring point in a given time. Measured in cumecs (Cubic metres per second)
How do you calculate River Discharge?
Multiply cross sectional area by the river velocity
What is the difference between a river regime and a storm hydrograph?
A river regime is usually taken over a greater temporal scale (Annually), compared to a storm hydrograph
Give three factors that affect river discharge
Any three from
- Rock Type
- Soil Type
- Land Use
- Rainfall
- Relief
- Weather Conditions
What is the difference between a flashy and subdued hydrograph?
Flashy hydrographs have a shorter lag time and steeper increase in river discharge compared to subdued hydrographs.
Flashy hydrographs also typically have a higher peak discharge.
Define a drainage basin
An area of land drained by a river and its tributaries
Define an Input and give an example
An addition into a system from outside the boundary INTO the system
Example: Precipitation
Define an Output and give an example
A removal from the system through the boundary to OUTSIDE that system
Example: Runoff
Define a Store and give an example
Stores hold matter or energy for some time.
Example: Trees
What is the Residence Time?
How long a store of energy or matter remains in that store for.
Does a glacier have a shorter or longer residence time than a river?
Longer
Define an Open System
A system where matter and energy can enter and leave.
Define an Isolated System
A system where neither energy nor matter can enter or leave.
What is dynamic equilibrium?
Where the inputs and outputs into a system are not static but are balanced over time.
What are positive feedback cycles?
The responses of a system by moving further away from dynamic equilibrium (Vicious Cycle)
What is the Drainage Density?
Total length of all streams in the drainage basin / total area in the drainage basin
Define Source
The point where a river begins
Define Confluence
The point at which two rivers join
Define Tributary
Where a river joins a larger river
Define Watershed
An imaginary line that separates a drainage basin from another
Define Estuary
Last section of a river influenced by tidal flows and salt water
Define a river mouth
Where the river meets an ocean, sea or lake
Define Antecedent Conditions
The conditions in the air before an extreme weather event
What are the key factors that affect evaporation?
Humidity
Temperature
Area of surface storage
Cloud Cover
Hours of Sunlight
Wind Speed
What are the key factors that affect transpiration?
Temperature
Hours of Sunlight
Type of vegetation
Vegetation Density
Seasonal Vegetation
Antecedent conditions
What are the key factors that affect Interception?
Vegetation Type and Density
Volume of precipitation
Wind
Amount of surface water
Precipitation Intensity
What are the key factors that affect Infiltration?
Type of Soil
Volume of precipitation
Relief Angle
Height of water table
Type of Rainfall
Antecedent Conditions
What are the factors that affect Percolation?
Geology
Depth of Rocks
Antecedent conditions
Height of water table
Volume/Intensity of Precipitation
Has does a drainage basin size affect its drainage
If the drainage basin is smaller, it takes less time for the water to reach the river, so the lag time is shorter.
Why does irrigation have an effect on rivers?
Channel levels are lowered, as well as groundwater levels if they are the irrigation source
Does a circular or elliptical drainage basin drain faster?
Circular
What do urban landscapes typically have more of that reduces infiltration?
Impermeable surfaces
What is an indented landscape and how does it affect runoff?
Indented landscapes collect water and reduce runoff rates, more infiltration.
Why does deforestation affect the water cycle?
Microclimates change, leading to more arid conditions because transpiration ceases, so river channels dry up.
What does saturated ground and melting snow lead to more of?
Surface runoff and increased river discharge
Do permeable rocks encourage more or less surface runoff than impermeable rocks?
Less
Why does the change in season affect river discharge (Think deciduous trees)
Deciduous trees lose their leaves during the winter, so this decreases interception
What is a key driver of deforestation in South America?
Cattle Ranching and Sugar Cane farming
What percentage range of deforestation will have small scale damage?
What percentage range will have extensive damage?
Small Scale: < 20%
Extensive: > 50%
Give two advantages of soil draining
Any two from
- Improves soil structure
- More favourable conditions for microorganisms
- Earlier sowing
- Improved crop yields
- Less soil compaction risk
Give two disadvantages of soil draining
Any two from
- Increase throughflow speed
- Dry topsoil subject to wind erosion
- Nitrate losses lead to eutrophication
How far did the water table fall during Peak Abstraction in London (1960's)
88m below sea level
Why was the London Underground at risk during the 1970's?
3m/year rise in the water table following deindustrialisation.
What is the main risk to aquifers in London?
Saline intrusion - If groundwater levels are lower near the Thames.
Where is the River Exe?
Devon. In between Dartmoor and Exmoor.
Source is North of Exeter
Give features of the River Exe's drainage basin
Long shaped, steep sided valleys in middle courses. High drainage density and lots of tributaries
Does the River Exe have a flashy or subdued river regime?
Flashy
What is the maximum altitude of the drainage basin?
516m
What % of rocks on the River Exe are considered high permeable?
2.5%
What % of the drainage basin is
- Woodland
- Grassland
Woodland: 13%
Grassland: 57%
What % of total land use is farmland
80.5%
How many properties are at risk of flooding on the River Exe?
11,000
Which areas of the River Exe are at most risk of flooding and why?
Exeter and Tiverton
- Main urban areas with lots of impermeable surfaces
Why are there lots of drainage ditches in the River Exe's drainage basin?
Farmers encouraged to dig them to increase food production after WW2.
What is the name of the key Reservoir on the River Exe?
Wimbleball Reservoir
How much water is held in the Wimbleball reservoir and why is this important
120 million litres. Reduces flood risk to Exeter and Tiverton
What is the main type of farming in the River Exe drainage basin?
Pastoral Farming (Cattle, sheep)
Who is involved in the Exmoor Mires project?
South West Water
Environment Agency
Exeter University
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