River Environments: –
During the cycle, water is held in a number of stores and transfers between them, these stores are: The atmosphere: Water here exists either as vapour or as droplets in clouds
The land: Water is stored on the surface in rivers, lakes and reservoirs. Water is taken in by plants and stored in vegetation for a time. Also stored below the ground in the bedrock as the groundwater store. Can also exist as ice for example in ice sheets, glaciers, snowfields.
The Sea: Over 95% of the Earth’s water is stored in the sea, mostly as liquid but can also be stored in icebergs.
The hydrological cycle is a closed process as the amount of water on earth doesn’t change
The Water Transfers: –
Evaporation: The heat of the sun converts liquids into gas (water vapour). The water vapour rises from the sea store into the atmosphere
Transpiration: Plants take up liquid water from the soil and release it into the atmosphere as water vapour.
Condensation: The water vapour in the atmosphere cools down and turns into liquid, the liquid takes the form of water droplets that appear as clouds.
Precipitation: The transfer of water in any form (rain,hail, snow) from the atmosphere to the land
Overland flow: The water flows on the land until it makes its way to a stream, river or lake.
Infiltration: When the water soaks through into the ground into an aquifer or groundwater store
Percolation: The downwards movement of water through soil towards the rocks
Groundwater flow: When the water flows through the rocks underground and makes its way to a river/stream/lake.
- A drainage basin is an area of land where the precipitation collects and makes its way to a common body of water
The different types of erosion: –
Hydraulic Action: When the force of the water erodes the river banks, water gets into cracks and expands, fracturing the rock over time
Attrition: The collision between sediment particles, the rocks become smaller and smoother over time
Abrasion: Rocks are flung at the river bank, wearing it down
Solution: Water dissolves sediment
Flood Hydrographs:
Lag time is the time between the highest point of rain and the peak flow. Calculates how quickly the water enters the river. Higher Lag time=Water takes longer to enter river.
Rainfall is always shown by the bars, Discharge is shown by the curve, Time is on the x axis
A steep slope or impermeable rock increase surface runoff.
Permeable rock, and woodland decreases runoff (Trees intercept water) Urban areas also increase run off as the ground becomes impermeable
The amount of water a river is carrying at a time is called the discharge, it’s measured in cumecs.
Flooding occurs when the discharge exceeds the maximum river storage.
The factors that affect river regimes:
The intensity and amount of rain- If the rain is heavy it won’t sink as the ground will be saturated, instead it will become overland flow and reach the river quicker.
Temperature, If the temperature is below freezing, the precipitation will be in the form of snow and snow can take weeks to melt, if the ground remains frozen the melting snow will reach the river faster however.
Steep Slopes will cause faster surface runoff so water will reach the river quicker. A more gentle slope could result in the water sinking into the soil, delays the water reaching the river.
Impermeable rock means that water won’t sink in and therefore it reaches the river quicker
Trees and Plants intercept the water and delay it from reaching the river, run off is increased in urban areas as concrete is impermeable
Human Intervention, dams hold back river discharge and therefore reduce the risk of flooding downstream. Reservoirs can control the flow of water.
Different types of weathering:
Mechanical/Physical weathering: Water enters the cracks in a rock and freezes, the water expands and fractures the rock.
Temperature increases and decreases, causing the rock to expand and contract, as this happens a few times the rock structure weakens.
Plants can grow in the soil that has collected in cracks. As the plant grows, the cracks expand and the rocks split. (Also Biological weathering).
Earthquakes weaken the rock structure and the rocks wear down over time.
Biological weathering: Some animals might possibly dig holes into the rock, weathering it over time and other animals might trample the rock overground and wear it down.
Plants growing in cracks.
Chemical Weathering: Due to human pollution acid rain can sometimes occur, dissolving the rock and weathering it.
Types of River Transportation: The movement of material (known as the load) by the river. The load is material that has been washed or fallen into the river as well as material that has been eroded by the river.
Solution: The material is dissolved in the water and transported downstream.
Traction: Heavy rocks and boulders roll down the river bed
Saltation: Small boulders bounce along the bed
Suspension: Lighter materials are carried along by the river flow
Deposition: When the material transported by the water is laid down. Occurs when there’s a decrease in the river energy, speed and discharge.
Characteristics of the Lower/Middle/Upper course:
UPSTREAM:
- Steep sided v-shaped valleys as the bed is eroded vertically.
- Larger and more jagged rocks as they haven’t been eroded yet
- Shallow water and narrow streams
- Has interlocking spurs which form when the river swings from side to side.
Gorges which are steep sided narrow valleys with a stream or river running through along the bottom.
LOWER COURSES:
Meanders, a bend in the river, common in the middle and lower course as the vertical erosion turns into sideways erosion. The force of the water erodes outwards as the water if fastest on the outside of the bends and slower on the insides of the bends.
Oxbow lakes, as the sideways erosion continues in the river the bend of the meander becomes larger, in times of floods, load is deposited at the neck of the meander and the bend breaks off, creating an oxbow lake.
River Estuaries and Deltas, An estuary is any area where a freshwater river or stream meets the ocean, a river delta is a landform that forms from the deposition of sediment carried by a river. When the river reaches the lake or the sea, the water doesn’t have any energy to continue transporting the load and instead just drops it. An estuary is a body of water, a delta is a body of land.
Floodplains, land around rivers which experiences flooding during periods of high discharge
Levees, a ridge on the side of rivers formed by deposition of sediment by overflowing water
Formation of a waterfall:
Waterfalls are usually found in the upper level of a river, they occur when there’s hard rock overlying soft rock, the water and the rocks erode the soft rock below, creating a plunge pool.
The soft rock is undercut by erosion and the soft rock is eroded further, creating a hard rock overhang
The hard rock overhang above the plunge pool collapses as its weight is no longer supported
Erosion continues and the waterfall retreats upstream leaving behind a gorge
Mass Movement: The movement of a large quantity of material downslope due to gravity.
Loose rock or soil lies on top of impermeable rock
When it rains it leads to erosion and undercutting of the river bank and the soil becomes saturated
The river bank becomes unstable and the soil is lubricated by more rain
Slumping occurs due to gravity as layers of loose soil slide into the river
Soil creep is when the load slowly creeps down the slope because of gravity and it collects at the bottom of the valley side and is eroded by the river.
Water uses, demand and supply:
Fresh water is used for:
Domestic use, bathing and showering, flushing toilets, drinking and cooking, washing clothes and dishes, watering the garden etc.
Industrial use, producing a wide range of goods and generating electricity
Agricultural use, used for irrigating crops and providing drinking water for livestock
Leisure use, sport fishing on rivers, sailing on lakes and ponds, watering golf courses/other sports pitches
Water demand and consumption have greatly increased during the last 100 years, mostly due to the rising population. Other factors are:
Rising standard of living, as the world develops people use much more water in domestic use (Baths, piped water, washing machines, swimming pools).
The rise in agricultural productivity needed to feed the rising population means that more water is used in farming (mostly for irrigation)
Industrialization, water is used for cooling down machinery and generating electricity
In undeveloped countries most of the water is used for agriculture and little for industry or domestic use, in developed countries most of the water is used for industry, followed closely by agriculture and then domestic use.
Sources of water:
- Rivers and Lakes
- Reservoirs which are artificial lakes created by building a dam across a valley and allowing it to flood, the water is collected and stored behind the dam
- Aquifers and wells, most of the world’s water supply lies underground, this groundwater can be extracted by drilling wells and the water can then be raised to the surface by buckets or pumps
Water Supply:
The global distribution of water is uneven, areas such as Africa, the Middle East and Australia have a water deficit due to the lack of precipitation and some countries have a water deficit due to a large population and rapid development, such as India.
Water Quality:
Clean water is important as drinking unclean water could result in a number of diseases such as cholera. Water quality is poorer in drier climates as during dry periods any water that remains on the surface Becomes stagnant, Pollution also affects water quality.
Sources of Pollution:
Agriculture:
- Liquid from silage and animal manure enters rivers (Silage is a high moisture grass mix fed to animals).
- Fertilisers and pesticides seep into the groundwater.
- Deforestation means that there aren’t any trees to intercept the runoff and the runoff carries soil and silt into the rivers, can have serious effects on fish and humans drinking water.
Industry:
- Taking water to cool machinery and then returning it to the river at a higher temperature can upset eco-systems.
- Spillages from industrial plants such as oil refineries can enter rivers and pollute the water.
- Working of metallic minerals and the heavy use of water when processing the ore means that toxic Substances from this will eventually make it to the river.
Domestic:
- Sewage from houses makes its way to water sources and pollutes them.
- Use of river for washing clothes and bathing contaminates the water.
- Emptying chlorinated water from swimming pools into water sources contaminates the water.
Managing the supply of clean water:
Collection:
- Water is first collected from either rivers, reservoirs, lakes or wells
Treatment:
- After collecting the water, it must be treated, water collected often contains silt, soil, bacteria, algae, viruses, fungi, minerals and chemicals such as fertilisers
Different ways of treating water:
Chlorination– To control growth of algae or any other small animals.
Aeration- Removes small pieces of metal.
Sedimentation- To remove large solid sediments
Filtration- Removes smaller pieces of rock/sand
Disinfection- To kill bacteria
Water management isn’t only about providing clean water. Dams and reservoirs can also be used for generating electricity, flood control, improving navigation and increasing the availability of water in areas of high water demand.
Rivers Case Studies
Spain: Tagus-Segura project River Management in a Developed Country
Spain has a Mediterranean climate which means that are as in the south of Spain receive little rainfall, summer droughts are common.
Water demand exceeds water supply in Spain
TheTagus Segura project is a 286km long series of aqueduct sand canals completed in 1978 to carry water from the 2 reservoirs in the upper Tagus valley to a large reservoir in the Segura valley
Once the water reaches the Segura valley it’s distributed to consumers in the provinces of Alicante, Murcia and Almeria
Most of the irrigation water has going to agri businesses rather than local farmers
Much of the water is now consumed by tourist sand urban developments rather than agriculture
The availability of water encouraged a wasteful use of it
China: The Three Gorges Dam – River Management in an Emerging Country
- The 3 Gorges Dam is a dam located in the Yangtze River in China.
- It took 10 years to build.
- It cost $28 billion, making it a very expensive river management project.
- It was mainly built to control flooding and generate electricity.
- The dam has greatly improved water transport along this section of the Yangtze Valley.
- It produces approximately 10% of China’s electricity (22,500 Megawatts).
- It provides power to 16 million people.
- An advantage is that hydroelectric power is renewable, a green source of energy that reduces carbon emissions and helps prevent global warming.
- The dam provides thousands of jobs, boosting the economy and lowering unemployment rates.
- The project will aid navigation and increase shipping on the river by 10 times. This will increase trade and boost the economy for towns and cities further up the river.
- A disadvantage is that 1.24 million residents had to be relocated to build the dam, and most of these people didn’t receive compensation to buy a new home.
- Because the river is slower now due to the dam, more silt/load is deposited upstream, so less load is deposited downstream. This increases flooding downstream.
- The reservoir built up behind the dam flooded around 1,300 archaeological sites.
- The water quality decreases as huge amounts of human/industrial waste are trapped behind the dam.
- The land downstream becomes less fertile as all the silt is trapped upstream.
The Chinese River Dolphin is now endangered as the dam prevents it from swimming to mate
The endangered Siberian Crane had its wetlands destroyed
People are at risk of land slides as the water in the reservoir erodes the valley sides and creates landslides.
Flooding – Causes and Control:
- Flooding occurs when the amount of water moving down a river exceeds the maximum capacity of the river’s channel.
- The excess water overflows the banks and spills out across the floodplain.
- Rivers can flood either due to Human factors or Natural factors.
- Most of the time, flooding happens due to heavy rainfall.
- The shorter the lag-time, the more chance of flooding.
Flooding can affect both humans and the environment:
Effects on environment:
- Landslides
- Soil Erosion
- Loss of wildlife habitats
- Destruction of settlements
- Vegetation destroyed
- Soil contamination by sewage
Effects on people:
- Death and injury
- Loss of belongings
- Damage to property
- Disruption to transport
- Death and injury
- Crops and animals lost
- Contamination of water supplies and loss of services
Controlling floods:
Construction: – Floods can be prevented by building hard-engineering structures such as dams. Artificial banks can also be raised to stop water from spilling over the sides; however, most hard-engineering methods are generally expensive to build.
Adjustment/Mitigation: – Flood control plans that try to minimise or avoid flood damage involve working with nature. This approach is called soft engineering; examples include preserving marshes and wetlands so that they act as sponges when it floods. Better flood warning systems and publicizing what to do in case of a flood also help.
Prediction: – Predicting river floods (their extent and depth) is important to control floods. It’s important as people can decide how high to build river embankments, and it also stops the building of houses, factories, and buildings where there’s a high risk of flooding.
Hazardous environments:
A natural hazard is a non-human event that threatens or causes damage and destruction to people, their property, and settlements. Examples: Earthquakes, Tsunamis, Floods, Tropical storms, etc.
Formation of a tropical storm:
- Tropical storms are usually found along the equator as the water there is warmer (27 degrees or above).
- The sun’s heat warms up the ocean surface, causing evaporation.
- Convection occurs as the warmer, less dense air rises and the cooler, more dense air sinks.
- A circulatory motion of air rotates the air anti-clockwise / clockwise depending on the hemisphere, encouraged by the Coriolis force.
Coriolis force – The force created by the Earth’s rotation.
- The swirling air picks up momentum and starts traveling in the direction of the prevailing wind or ocean currents.
- As the tropical storm travels over the ocean, it increases in strength as it’s in contact with warm ocean water.
Features of a Tropical Cyclone:
- Very strong winds, these can destroy trees, crops, buildings, transport links, power supplies, and communications.
- The torrential rain, this can lead to serious inland flooding and can trigger landslides.
- The storm surges, these are sudden rises in sea level associated with the very low pressure which allows the sea level to rise; storm surges can cause immense damage in coastal areas.
Earthquakes and Volcanoes:
- Volcanic eruptions and Earthquakes both result from plate movements.
Constructive plate boundaries: When 2 plates are moving apart, leaving a space, volcanoes are formed as the magma wells up to fill the gap.
Collisional plate boundaries: When 2 continental plates collide, neither plate is forced under and both are forced up.
Destructive plate boundaries: When an oceanic plate and a continental plate collide, the oceanic plate submerges as it’s more dense and the friction causes earthquakes and the melting of the oceanic plate; magma rises through the gaps.
Conservative plate boundaries: When plates slide past each other in opposite directions, the friction causes an earthquake.
Volcanic eruptions and earthquakes happen at tectonic plate boundaries, for example, the Pacific Ring of Fire.
