UK Physical/Rivers

What are the three different types of rocks?

Sedimentary, igneous, metamorphic and these three different rock types can be found in distinct areas of the UK.

Sedimentary rock info?

Made up of particles of sand and rock, which have been transported by wind, rivers and ice. Over millions of years the sediments accumulate which are compressed by the weight of the deposits above, into sedimentary rocks formed in layers, known as bedding planes.

What is the order of sedimentary rock compression e.g sand...?

Compressed sand forms sandstone and compressed mud becomes clay. Limestone and chalk come from the remains of dead plant, animal and marine species and are rich in calcium carbonate and contain fossils.

Igneous rock info?

Result of volcanic activity from past, when Britain was close to a plate boundary. Some igneous rocks are due to lava reaching the surface, (cooled and solidified to form basalt rock).

Give an example of igneous rock?

The Giant's Causeway in Northern Ireland.

Metamorphic rock info?

Existing rocks that are changed by intense heat and pressure at a plate boundary. These rocks start as either igneous or sedimentary rocks and are crystallised to form rocks such as slate and marble.

How have tectonic processes shaped the land (Sedimentary)?

Sedimentary rocks e.g. limestone and chalk contain fossils of marine animals and plants that lived in tropical seas. These were laid down over 30 million years ago when Britain was at a different latitude.

How have tectonic processes shaped the land (Igneous+Metamorphic)?

The presence of large areas of igneous and metamorphic rocks shows the UK must have once been at a plate boundary and had active volcanoes e.g Arthur’s Seat, Edinburgh.

How have glacial processes shaped the land (Top half of UK)?

During the last ice age these covered the top half of the UK. They were hundreds of metres thick and eroded the land in distinctive ways.

How have glacial processes shaped the land (Bottom half of UK)?

The bottom half of the UK was heavily influenced by glacial deposition. Clays and silts eroded by the glaciers were dumped and washed over southern areas.

In areas where there is Sedimentary rock, the relief of the land is much lower. Why? What are these areas known as?

This is because sedimentary rock is much easier to erode. These areas are known as the lowlands.

In areas where there is a greater concentration of igneous rocks the relief of the land is higher? Why? What are these areas known as?

This is because igneous rock is harder to erode. These areas are known as the uplands.

How has human activity helped create distinctive UK Landscapes? South Downs case study e.g No1 (Farming)?

Farming 85% of the national park is farmed with approx 1100 farms. Chalk grassland is good for grazing sheep because the grass is short whereas the clay grassland is more suitable for dairy cows because the grass is long. The south facing slopes are suitable for arable farming e.g. Wheat.

What are the advantages of farming in the S. Downs?

- Income supports the economy and provides 6% of employment in the NP

- Arable farming has supported rare bird species e.g skylark, partridge

-Hedgerows provides wildlife corridors for bats

What are the disadvantages of farming in the S. Downs?

- Arable farming decline and changes in practices have damaged wildlife habits

- Extensive sheep grazing has led to scrub encroachment

- Decline in chalk grassland due to the use of chemicals

How has human activity helped create distinctive UK Landscapes? South Downs case study e.g No2 (Forestry)?

Forestry Deciduous and coniferous woodland unevenly covers a total of 23.8% of the NP with the west having significantly more than the east.

What are the advantages of forestry in the S. Downs?

• Provide habitats for diverse range of wildlife

• Timber is a valuable sustainable product for construction and fuel

What are the disadvantages of forestry in the S. Downs?

- Removal of woodland for new development threatening ancient large-leaved lime woodland

- Lack of management is resulting in a decline in the quality of the chalk grassland

What are the impacts of settlements in the South Downs?

Settlements were built on the naturally formed slopes, which afforded them shelter. The South Downs = most populated National Park UK, around 120,000 people live there. A lot of of these people live in urban areas that surround the NP including the UK’s largest market towns, Lewes, Petersfield and Midhurst. Some of the original features have been replaced and a decline in local community places such as post offices, shops, pubs and schools.

Upper course means...?

More erosion

Source (upper course)?

Lots of tributries (branch looking things), lots of waterfalls and a narrow channel.

Middle course?

More bends (meanders and oxbow lakes) and slightly wider channel.

Lower course?

Wide channel (towards mouth = more water) and river meets sea.

Weathering definition?

Break down and decay of rock by natural processes acting on the valley sides.

Mass movement definition?

The downslope movement of material due to gravity.

Erosion definition?

The wearing away of rock and soil on the valley sides and bottom.

Transportation definition?

The process by which rivers move sediment and dissolved materials downstream.

Deposition definition?

The river drops the load it has been carrying as energy reduces.

What are the types of weathering?

- Biological = When plants/animals wear away any rocks

- Chemical = Slightly acidic rain water that wears away rock

- Mechanical = Physical changes causes rock to break down

- Physical = Water enters cracks in rocks, freezes, when water expands it pushes pressure on rock causing it to break into smaller pieces

What are the types of transportation?

- Traction = Large, heavy pebbles rolled along the river bed (near source)

- Saltation = Pebbles bounced along river bed near the source

- Suspension = Lighter sediment carried within water near mouth

- Solution = Transport of dissolved chemicals (depends on soluble rock presence)

What are the types of erosion?

- Hydrolic action = Water smashes against river bank, air gets trapped in crack, river bed/rock breaks

- Abrasion = Pebbles grind along river bank/bed in a sand paper effect

- Solution = Water dissolves certain types of rocks

What are the types of mass movement?

- Soil creep = When soil slowly moves down gentle slopes

- Slumping = Large block soil/rock slide down slope in one piece

What makes some rivers more likely to flood than others?

- Impermeable surfaces

- Previous heavy rainfall (ground can't absorb anymore water)

- Steep slopes (water runs straight to river)

- Low river banks (limited space for extra water and rainfall)

Hard engineering?

Man made, physical structures to help when flooding.

Soft engineering?

Natural process that helps when flooding, usually not man made.

Mitigating?

- Acting ahead

- Previous preparation

- Reduces impact of events

Adaptation?

- Happens after

- Helps in future events

- Fixing of damage

Catchment management?

The managing and improvement of an area, this used plans of flood risk and improvement on protection before flooding.

Discharge (m3/s)?

Volume of water per second.

Lag time?

Time difference between the peak of the rain storm and the peak flow of river (peak rainfall and peak discharge).

Rising limb?

Section on graph where discharge rate rises.

Falling limb?

Section on graph where discharge rate falls.

Base flow?

Dotted line on graph that goes under and between the rising and falling limb.

Peak discharge?

Highest volume of water on the graph (the point).

Basin log time?

Section between the start of the rising limb and the peak discharge.

Where is the start of the storm on a graph?

At point (0,0).

Flashy (flat)?

Heavy rain, big storm, steep hills, previous rainfall, concrete floor, high peak discharge.

Flat (flashy)?

Gentle slopes, average rainfall, dry dirt ground, smaller slopes, more calm peak discharge.

Surface runoff?

When water flows over the land into rivers (increases flood risk).

Infiltration?

When water soaks into the ground (slower on impermeable rock).

Storm hydrograph?

A graph that shows how river discharge changes over time after a rainfall event.

What's the source and the mouth?

Source: the starting point of a river or stream

Mouth: the point where a river leaves the drainage basin and enters the sea

Tributary definition?

A smaller stream or river that joins a bigger stream or river.

Confluence definition?

The point where two rivers/streams meet/join.

Watershed definition?

Highland or hill that separates one drainage basin from another.

What is a drainage basin?

An area of land drained by a river and its tributaries.

An area of land drained by a river and its tributaries.

The action of water wearing away rocks and soil at times of flood and on steep gradients. There are four key processes of erosion.

Soil creep?

Individual particles of soil slowly move down a slope due to gravity.

Slumping?

Bottom of valley slope erodes valley sides. Material above slides rotates after heavy rainfall, saturating rock and soil making it heavier.

Flood risk of increased population?

More housing. Building on the cheaper land of the flood plain has put 2.3million houses at risk of flooding.

Flood risk of land use changes?

With urban developments = more impermeable surfaces which increases surface run-off.

Flood risk of changes in weather patterns?

Linked to climate change making extreme weather more likely as a result of the changes in the behaviour of the jet stream. Storms that once occurred every 100yrs are now more likely to happen every 80yrs in southern UK

How does the Environment Agency manage flood risk?

Environment Agency makes Catchment Management Plans, manages rivers and land use, controlling developments in flood plains, building flood defences and help people prepare, giving warnings.

Why is the flood risk in the UK increasing?

Flooding is a natural occurrence but since 1998 severe flooding has occurred somewhere in the UK every year sometimes twice in a year. The main reasons for this are: Increased population, Land use changes and Changes in weather patterns.

How is flooding reduced through Catchment Management Plans?

The EA works out the chances of a flood happening and plan how to continue, the plan would then include the following:

1. reduce run-off - improve land use and restore flood plains

2. prevent bad developments on flood plain

3. improve flood defence in urban areas and protect vulnerable buildings

4. work with natural flood processes where few people live.

How do Human and physical processes interact to cause flooding? Case study Tewkesbury, 2007?

2007 saw heavy rainfall in June/July with river levels at their highest for over 100yrs. Rainfall doubled the average for these months and reached 140mm on one day, 20th July in just a few hours caused by a series of depressions and a strong jet stream. Antecedent weather conditions led to immediate run-off over saturated soils into already swollen rives. Has confluence at two tributaries, along the Severn and Avon. It’s Abbey flooded for the first time in 250 years.

How can flooding be reduced by hard engineering = Embankments?

P = Stop overflowing, covered in grass can blend with environment.

N = Can burst under pressure, water can flow over the top.

How can flooding be reduced by hard engineering = Flood walls?

P = Prevent water spreading in high impact areas e.g. housing

N = Expensive, cause flooding downstream, look unnatural

How can flooding be reduced by hard engineering = Demountable flood barriers?

P = Put up and taken down, replace ugly permanent defences

N = Risk of timing issues, can only be used where deployed

How can flooding be reduced by hard engineering = Flood barriers and storm surge barriers?

P = Protect large areas, used at high tide/storm surge forecast

N = High construction costs and regular maintenance needed

How can flooding be reduced by soft engineering = River restoration (rivers original course including meanders)?

P = More attractive for recreation, creates natural habitats

N = Some flood banks often still needed.

How can flooding be reduced by soft engineering = Flood plain retention (land use according to flood risk?)

P = Low risk areas are used for building, high risk land is used for parks/recreation.

N = Poor public accessibility to some areas.

How do climate, geology and slope processes affect different river landscapes? Case study: River Severn = Gradient?

Decreases: Steep-source (hills) Gentle-mouth due to a shift from vertical to lateral erosion.

How do climate, geology and slope processes affect different river landscapes? Case study: River Severn = Velocity and discharge?

Both increase due to tributaries feeding more water into main channel and reduced friction.

How do climate, geology and slope processes affect different river landscapes? Case study: River Severn = Channel width/depth/roughness?

Becomes wider/deeper/smoother and more efficient with less friction.

How do climate, geology and slope processes affect different river landscapes? Case study: River Severn = Sediment/load?

Smaller: Source =boulders/cobbles then pebbles/sand finally mouth= silt/clay due to abrasion and attrition. Capacity increases downstream.

What decisions are made before building flood defences?

Flood defences are so expensive so the EA works out which would be most effective with limited environmental damage by conducting an impact assessment (residents, business, transport, wildlife and habitats) and a cost benefit analysis.

Interlocking spurs?

At the source rivers have less power and flow around valley slopes (spurs) instead of eroding them. The spurs then interlock from one side to the other.

Waterfalls?

Occur where water flows over bands of rock with differing resistance. Weaker rock erodes quicker due to increased velocity creating a step in the river bed gradually undercutting the more resistant rock. Continued abrasion and hydraulic action creates overhang and plunge pool is created at the base from abrasion and the force of falling water. Eventually overhang will collapse and make the waterfall steeper. Repetition causes waterfall to retreat upstream forming steep-sided gorge.

How is delta made?

- Deposition occurs as river loses velocity when it enters the sea.

- Heaviest material is deposited first and the lightest last.

- Distributaries form as main river channel splits to smaller channels.

- Delta is built up in layers.

Deltas?

Water speed decreases near the sea. Material is deposited. Over time this builds up to create an area of new land = a delta, because river is now flowing slowly the channel fills up with sediment and river splits into different streams, distributaries.

Flood plains?

The area of land at the side of a river in the lower course. Lateral erosion on the outside bend causes meanders to migrate across valley floor so valley floor becomes wide and flat. During floods, rivers deposit sediments called alluvium.

Levees?

Levees are natural embankments formed by the deposition of sediment at times of flood. Large sediment is dropped first as the river floods onto the floodplain and loses velocity. Smaller sediment is deposited afterwards and when this process is repeated the banks get higher forming Levees.

Oxbow lake?

When a meander grows its neck narrows then at times of flood the river simply cuts straight through it leaving an old meander cut off (horseshoe-shaped lake). Deposition blocks up the old bend.

Meander?

Large bends that swing from side to side (sinuosity) on the floodplain. Faster flowing water erodes outside of bend through lateral erosion creating a steep bank (river cliff) whilst inside of bend due to slower shallower water deposition takes places creating a gently sloping bank (slip-off slope).

Formation of a waterfall?

- Harder more resistant rock

- A plunge pool forms, an over deepened area is created by erosion such as hydraulic action of the softer rock

- The overhang collapses as it is weakened by erosion/weathering, and is pulled down by gravity

- Collapsed rocks used as abrasive erosion tools

- The waterfall retreats back upstream to create a gorge

Give an example of a harder more resistant rock?

Granite

Formation of an oxbow lake?

- Narrow Neck of the Meander is gradually being eroded.

- Water now takes quicker route.

- Deposition takes place, sealing off the old meander.

- The Meander neck has been cut through completely.

- Oxbow lake left behind when meander is completely cut off.

Whats the longest river in the UK?

River severn

Where is the source and mouth of the river severn?

Source = Welsh mountains

Mouth = Bristol channel