Geography Physical Case Studies

Carson Desert Basin, Neveda, USA

• High in the mountains of Western USA. (Gauging station is 1,269m above sea level).
• Has an area of 5,610km² and a perimeter of 412km. 
• Rainfall totals for nearby Las Vegas are very low (highest in Jan with 18mm and lowest in May, June and November with 5mm: range of 13mm throughout the year).
• Not much vegetation as desert environment cannot sustain it, although irrigation methods are used to help the desert bloom. Overall, there is not much interception, as many months per year are completely dry. However, if it does rain, it usually does so in spectacular thunderstorms. 
• In the winter months (December, January and February) when temperatures are the coldest, there can be snow in the mountains as they are at such high altitudes, meaning when it melts, rivers swell. 

Stour Basin, Dorest, UK

• Basin area is 1,300km²
• Located in the south of England, where there is a typical maritime climate (there is usually varying levels of rainfall, temperature and vegetation cover in different seasons). 
• There are no dry months in the year, and rainfall is evenly distributed over the Stour basin, meaning the river does not dry up. 
• Droughts have occured when there is a consecutive period of time with below average rainfall, such as in the late 1980s and the mid 1990s when there were 3 years of below average rainfall. 
• The lower part of the Stour Basin is on the coast, and the Stour itself is a typical British river, that floods after a heavy rainfall event, giving adequate time and warning for preparations to occur. 
• Stour Basin lies over chalk, which is a porous material and allows water to easily run though it (throughflow). 
• The fields in the rural area also cultivate crops in summer, meaning there is increased interception of rainfall. 

V-Shaped Valleys Case Study

Heatherhope Valley, Chevoit Hills, Northumberland

• National Park on the English side of the border with Scotland. 
• Contains peaks of over 500m.

Interlocking Spurs Case Study

Valley of Usway Burn, Northumberland 

• 15 mile walk through the valley

Rapids Case Study

Manitou Rapids on the Rainy River, Minnesota

• Discharge of 31905 cubic feet/second.
• Rock type: Igneous intrusions - more resistant; glacial deposits - less resistant

Potholes Case Study

Bourke's Luck Potholes, Blyde River Canyon, South Africa

• Located in the South region of the Canyon.
• Occur at confluences between the Treur River and the Blyde River. 

Waterfall Case Study

Ribbon Falls, Grand Canyon, California, USA

• In the Yosemite National Park.
• 491m tall. 
• Fed by winter snow.
• Tallest, continuous (single drop) waterfall in the US. 

MENTION:

• Gradient 
• Distance 
• Height above sea level

- 4 Waterfalls along its course (1 at source, 3 further on)

- Gradient decreases: Starts off very steep (400-410m), then becomes less steep and gradient decreases to (350m). 

- Concave long profile. 

- Follow the valley (widest in middle course). 

- River flows at roughly 175m above sea level. 

Incised Meanders Case Studies

• Entrenched meander (symmetrical)
  • River Wear in Durham (has isolated parts of Durham except for one joining point).
• Ingrown meander (asymmetrical)
  • River Wye from Tintern Abbey to Symonds Yat. 
    
  • Terraces 300m above the the River Wye itself. 

River Terrace Case Study

• River Thames (isostatic rebound from Scotland). 
  • Taplow Terrace about 15m above the River Thames. 
  • Boyn Hill Terrace is 320m above the River Thames.

Knickpoint Case Study

• Glen Maye, Isle of Man
  • Rushen River rejuvenated due to uplift of West Coast of the island post glaciation (isostatic rebound)

Braided Streams

• Glacial streams around the world. 
• Yellow River in China - 5,464km long flowing in braided streams, meaning that it is liable to bursting its banks and changing course.

Floodplains

All rivers have floodplains. 

• River Nile, Egypt, Africa: made up of fine silt and mud from repeated seasonal flooding. It runs approximately 6,695km and is very fertile. 

Levees

• Mississippi Levee system covers 3,500 miles of land along the river. It is about 7.3m high but up to 50 feet in some places. 

Deltas Case Studies (3 types)

Arcuate 

• Nile River Delta
  • Empties into the Mediterranean Sea
  • The Aswan Dam has been constructed to reduce the width of the delta. 

Cuspate (tooth-shaped)

• River Tiber in Rome
  • Empties into the Mediterranean Sea
  • Marshland of the delta used for agriculture.

Bird's Foot

• Mississippi River
  • Empties into the Gulf of Mexico
  • Southwest Pass longest

Oxbow Lakes 

Found on the River Severn on the Caersws floodplain. 

• Carves out S-Shaped bends

http://www.bbc.co.uk/education/clips/zrhc87h

Death Valley, California

Alluvial Fans form at the mouths of every canyon in Death Valley.

For example: 

• The Badwater alluvial fan
• The Panamint Mountains - covered with alluvial fans.  

Badwater alluvial fan made of boulders, gravel, sand and silt

Flood Management Stategies

Hard Engineering Definition: A controlled disruption of natural processes using man-made structures. 

Soft Engineering Definition: The use of ecological practices to reduce erosion and achieve stabilisation while enhancing habitats and saving money. 

Soft Engineering Management Strategies 

Forecasting and Warning 

This enables predictions, preparations and protection to occur.

For Example:

• The Met Office monitor trends and patterns in rainfall, discharge and cloud cover. They estimate that forecasting saves tens of thousands due to their predictions of weather. 

Afforestation 

Planting trees in river drainage basins, to increase interception and water storage, reduce surface run off and overall reduce the river's discharge during periods of high rainfall to reduce the chance of flooding. 

For Example: 

• Afforestation in New York of 58% of a watershed has reduce peak flows by between 16-66% between spring and winter. 

Soft Engineering Strategies 

Wetland and Riverbank Restoration 

Wetland conservation or re-establishment. They store floodwater to reduce impacts of floods.

For Example: 

• London Wetlands Centre (WWT) is a conservation charity that protects wetlands, emphasising their use in storing and providing water for both people and wildlife. 

Floodplain Zoning (Land use management)

Prevents people from building on floodplains, to allow the floodplain to absorb the impact of the flood, with virtually no impermeable surfaces. This reduces surface run-off and river discharge. 

For Example: 

• Flood zoning and careful land use management prevented 1,300 homes from being destroyed in Maidenhead during periods of heavy rainfall in 2009.

Soft Engineering Strategies 

River Restoration 

Allowing the river to flood naturally upstream to prevent greater scale flooding downstream, reducing the impact in urban areas. This can be done by removing artificial levees for instance.

For Example: 

• The River Crane Restortion Project in Twickenham, London has partnered with WWT and Thames Water (who have pledged £400,000) to restore the river and its habitats, as well as halt unsustainable development projects. 

Hard Engineering Stategies

Dams

Giant walls built across a river channel to slow or stop its flow. A resevior is formed behind the dam, which stores water and releases it again in a steady flow to regulate discharge downstream.

For Example:

• 3 Gorges Dam in China has reduced the risk of flooding downstream from 1 in 10 to 1 in 100.

River Straightening 

Meanders are removed by building artificial "short cuts" which water will naturally follow (fastest course), so the velocity of the river increases to remove water from areas of high discharge.

For Example: 

• A 530km stretch of the Mississippi River has been shortened to 300km. 

Hard Engineering Strategies 

Levees and Embankments 

Levees artificially build up the sides of banks, so that the bankfull level is increased, so the river can hold more water before overflowing, thus floods less often. 

For Example: 

• On the Mississippi River there are concrete mattresses reinforced with steel on either bank - (25mx8m). Tallest is St Louis Levee at 15.8m high. 

Diversion spillways 

Artificial channels that a river can flow into if discharge increases. The channels "divert" water when an area is at risk of flooding, either back to itself further downstream or into another river. 

For Example:

• Mississippi Bonnet Carre Floodway - 9km long spillway, diverted into the Gulf of Mexico.

BANGLADESH (JULY-SEPTEMBER 2004)

Human causes: 

• Deforestation - caused soil erosion so land could not absorb water
• Country's poverty - in 2006, over half the population were said to be below the poverty lineBuildings on the floodplain increased surface run-off
  • No early warning systems (only had 4-5 hours)
• Irrigation for farming meant river channels filled with silt - smaller capacity for water

Physical Causes: 

• 35cm of rain fell in one day on 13th September
• Global warming increases monsoon periods of rainfall and causes increased snow melting in the Himalayas
• Bangladesh supplied water from 4 major rivers. Because all these flooded, impact was widespread. 

BANGLADESH (JULY-SEPTEMBER 2004)

Social impacts: 

• 30 million Bangladeshis affected in one way or another
• Water borne diseases
• Death tolls were over 750
  • 600 people directly killed by the floods
• Famine due to crop failure

Economic impacts: 

• Damage to schools and hospitals put at $7 billion
• 40% of the capital (Dhaka) submerged
• Airports, roads and railways were flooded and bridges destroyed - loss of infrastructure

Environmental impacts: 

• Crop failure (rice)
• Loss of habitats- reduced biodiversity & cattle killed. 

BOSCASTLE FLOODS - 16th AUGUST 2004

Human Causes: 

• Urbanisation on floodplain - increased surface run-off
• Human development e.g. bridges at several points across the rivers meant that floodwaters were blocked in receding

Physical Causes:

• 6cm of rain fell in 2 hours
  • 3m high wall of water
• Due to previous rainfall, ground was already saturated and waterlogged. High tide so water could not recede into the mouth of rivers into the sea
  • High water table
• Settlement on the confluence of the River Jordan and River Valency 

BOSCASTLE FLOODS - 16th AUGUST 2004

Social Impacts:

• Mental trauma (many elderly and retired residents)
  Heavy property damage (including heirlooms as well as new commodities)
  • Stress and anxiety as people could not reutrn home nor save their possessions. 

Economic Impacts: 

• Cornwall already estimated to be UKs poorest rural community
  Loss of tourism - further loss of income
  • Heave economic losses - estimated £15,000-£30,000 in property damage
• Destruction of infrastructure
  • Water, electricty and gas supplies were cut off so needed urgent repairs

Environmental Impacts: 

• River channel changed shape (River Jordan taller in height above sea level)
• Much of the land is covered in alluvium deposits - very fertile