Geography: River Landscapes (Topic 3)

2.1 river processes and distinctive landforms

a. drainage basin terms: watershed, confluence, tributary, source and mouthsmall.png

  • Watershed – Boundary of a drainage basin – this separates one basin from another
  • Confluence – point where two rivers meet
  • Tributary – Small stream and where the river joins another river
  • Source – Starting point of a river, often a spring or lake
  • Mouth  – Point where a river leaves its drainage basin, entering the sea.

b. The impact of weathering, erosion and mass movement on river landscapes

Weathering: The breakdown/decay of rocks by natural processes

Physical weathering – Freeze thaw / frost wedging

  • This happens when rainwater enters the cracks/gaps in a rock – freezes when temperatures drop below 0 degrees c, the water expands, exerting enough pressure on the rock to break and shatter

Chemical weathering – Acid rain, salt crystal growth

  • All rain is slightly acidic – air is polluted by factories and vehicles. When the rain falls on the rocks, acid reacts with weak minerals, causing them to dissolve rocks and decay
  • Salt crystal growth – chemical reaction between the seawater and rock

Biological weathering

  • Roots of plants, especially trees, grow into cracks in rock, splits it apart.
  • Water gets through the cracks
  • Animals past waste containing seeds

 

Erosion – wearing away/removal of material by chemical/physical means

  • Hydraulic action – This results from the force of water hitting the riverbed and banks, wearing them away, especially during high velocity flow
  • Abrasion – Caused by river picking up stones and rubbing them against the bed and banks of the channel in the flow – wearing the bed and banks away
  • Attrition  – Material carried along the river – eg. stones will become smaller and rounder as it travels downstream, colliding with other particles (like sand paper rounding of harsh edges)
  • Corrosion – Dissolving of rocks and minerals by river water flowing over them

Mass movement – Downslope movement of material due to gravity

  • Soil creep  – Individual particles of soil move slowly down rope (either by moisture of gravity) and collects at valley sides, river erodes this material
  • Slumping  – Bottom of valley side is eroded by the river, makes the slope steeper – valley side material slides down in a rotational manner, often triggered by saturation by rain. This lubricates the rock, making it heavier.

c. changes in characteristics from source to mouth of a river and its valley

 

Characteristic Definition Change from source to mouth
Width Distance from one bank to another Increases
Depth Distance from the surface of the water to the river bed Increases
Velocity How fast the water is flowing Increases
Discharge The rate at which water is moved through the river channel Increases
Gradient Steepness of the land Decreases

Upper course features:

  • Atmosphere – mushy, damp, windy and moist
  • Terrain – often moor land, exposed and mountainous. Higher rainfall and snow-relief rainfall
  • Fast flowing, high capacity for deposition, vertical erosion
  • Interlocking spurs, v-shaped valleys, waterfalls
  • Large rocks

Midcourse features:

  • Atmosphere – Hospitable for humans, usually domesticated for farming
  • Terrain – flat and manageable
  • Meanders – deposition (shallow – inside bend) Erosion (steep – outer band, aka river cliff)
  • Subject to flooding
  • Oxbow lakes

Lower course features:

  • Atmosphere – most hospitable
  • Terrain – flat, if urbanised, covered by impermeable rock for industry)
  • Dominant land use – farming (fertile land), primary housing, industry

d. formation of interlocking spurs, waterfalls, meanders, river cliffs, oxbow lakes, floodplains and levees

Interlocking spurs – upper course860b1d857a88b55171ebe33d3248e8e5fba5e8e2.gif

  • As water twists around obstacles, for example rocks and boulders because there is not enough velocity to cut through the obstacle, erosion undercuts outward bends in a zigzag formation
  • From lower down, the interlocking of the spurs of land creates bends and locks the view of the valley.

Waterfalls – upper course / mid course

ba40f0b45c5418bca547288fc5fd8cbac6ab380d.gif

River cliffs – mid course

MeanderCross2.jpg

Meanders + oxbow lakes – mid course 027_bitesize_intermediate2_geography_riverforming_meander3steps_546.jpg

Flood plains – mid/lower course e17010d1384476517ef8b30fcff940faefe099ba.png

Levees – Mid/lower courselarge.png

2.2 – flooding and flood prevention

a. the physical and human causes of river flooding

Physical causes of flooding 

  • Intense rainfall – when rainfall is too fast to fully allow its infiltration into the ground, it goes quickly into the channel as it flows across the surface
  • Cloud bursts (Sudden, intense rainfall)
  • Snowfall promotes rapid thawing – frozen rivers and ground, the temperature changes and the snow and ice defrosts. Water gets fed back into the ground and river with no infiltration time
  • Hot weather ‘bakes’ (hardens) the ground, the ground is no longer permeable to water
  • The laying of impermeable rocks like granite doesn’t let water infiltrate the ground – rainwater runs off surface into the channel very quickly
  • Steep valley sides make the water run downhill, water hits the ground and consequently enters the rivers quicker.

Human causes of flooding

  • Deforestation – trees (vegetation) slows down the time it takes for rainfall to reach the ground (lag time). Vegetation collects stores and uses water from the drainage basin. More lag time makes more water reach the channel, more flooding
  • Urbanisation (building on a flood plain) – covering ground with hard, impermeable man made substances speeds up lag time
  • Drainage systems within towns and cities alo water to flow back into the river channel quicker
  • We don’t maintain drains enough, they’re ineffective at increasing lag time
  • Climate change

b. the effects of river flooding on people and the environment

Effects on people

  • Loss of belongings
  • Damage to property
  • Disruption to transport
  • Disease and illness (trench foot, respiritory problems)
  • Stagnant water breeds mosquito and chlorella cells
  • Contamination of water supply
  • Animal, crops, economic and human life loss

Effects on envirnonment

  • Landslides
  • Soil contamination by sewage
  • Vegetation destroyed (herbs and medicinal plants)
  • Drowning animals
  • Soil erosion

 

CASE STUDY: Boscastle Floods, 2004

Causes of the flood:

  • Small drainage basin – large volume of water collects quickly
  • Steep valley sides – surface runoff travels quickly
  • River Jordan passes 100m underground  – ground already saturated with water, new influx of water cannot infiltrate
  • Boscastle situated at the confluence of river Jordan and river Valency – less space to cope with large volume of water
  • Buildings on a floodplain – water can’t infiltrate the floodplain
  • Bridges over rivers – bottlenecks the river channel, increasing the risk of blockage
  • Low drainage density -not enough rivers to drain the area
  • Not enough channels – can’t take the water

Short term effects of the flood:

  • Over 50 cars carried out to sea by 3m wall of water
  • Clean up operation (village + community hall)
  • Large damage to property

Long term effects of the flood:

  • 2 months after the flood, still no public parking
  • Tourist industry greatly affected (Main source of income)

Reduction of effects by future planning:

  • Building on stilts – above ground level, less possessions damaged
  • Electrical sockets to be moved up
  • Making doors out of concrete rather than wood with chemical water proofing
  • Using waterproof plaster in buildings
  • Replacing heavy doors with removable, possibly buoyant ones

c. prediction and prevention of the effects of river flooding by forecasting, building design, planning and education

Forecasting

  • River water levels are monitored by the Environment Agency
  • If levels rise to a dangeorus point, they are to warn and evacuate
  • Online maps show the areas of risk
  • Computer stimilation models

Building Design

  • Ceramic tiles and rugs instead of fitted carpets
  • Raise the height of electrical sockets to about 1.5m above ground
  • Fit stainless steel and plastic kitchens instead of chipboard
  • Position essential parts of heating and ventilation upstairs
  • Fit non-return valves on drains and water inlet pipes
  • Replace wooden windows and door frames with synthetic ones
  • In LICs, build houses onstilts

Planning

  • Land zoning

Education

  • Leaflets, advertisments in newspapers and tv
  • Social media and websites
  • Offering helpline services
  • Drills and exercises

d. the types of hard and soft engineering used to control rivers in the uk and the advantages and disadvantages of these techniques

 

Hard Engineering Technique Description Advantages Disadvantages
Embankments (Levees) Raised river banks
  • Can be sued as pathways
  • Effective at stopping bank erosion
  • Earth embankments provide habitats
  • Concrete embankments are ugly
  • If flood water goes over capacity, it will cause greater damage
Channelisation Deepening/widening/straightening of a river channel
  • Effective and long lasting
  • Unnatural, looks bad
  • Greater damage downstream
Flood relief channels Extra channels built next to/away from rivers, diverting floods away from settlements
  • Can be used for water sports
  • Relief channels can take the excess water so the river won’t overflow it’s banks
  • Requires a large amount of land
  • Extremely expensive
  • Unsightly
Dams Built along the course of a river to control the discharge. Water is held back and released later in a controlled way
  • Water stored in a reservoir – hydroelectric power source
  • Recreational use
  • Highly expensive
  • Settlements and agricultural land loss
  • Sediment trapped behind a dam wall leads to further erosion downstream
Floodwalls Vertical barrier usually made from fabricated concrete
  • Can be used in areas where space is limited
  • Easily constructed
  • Has to be assembled well so water doesn’t get into the joints
Storage areas Man made washland
  • Natural
  • Doesn’t damage the environment
  • Needs a large area
  • Can only be utilised when the river has flooded

Soft Engineering Technique Description Advantages Disadvantages
Floodplain zoning Authorities allocate areas of land to different uses according to level of risk
  • Cheap way of reducing flooding
  • Sustainable
  • No surface run off – less likely to cause flooding
  • Enforcement is hard to control in LICs
  • Resistance to the restriction on where to build
Washlands Areas on the floodplain naturally allowed to flood
  • Cost effective
  • Potential site for birds and plants
  • Silt will enrich the soil
  • Productive land could be wasted and turned into marshland
  • Large areas can’t be built on
Flood warning systems Rivers are carefully monitored – if alarm rises downstream residents will be notified
  • Cheap, electronic
  • Gives people a way to prepare and evacuate
  • Sirens have to be tested annually
  • Might not have enough time to prep
Afforestation Planting trees in the catchment area to intercept rainfall
  • Relatively low cost option
  • Improves quality of environment
  • Sustainable
  • Coniferous trees make the soil acidic
  • Dense tree population spoils natural landscapes
  • Bushfire risk may increase

2.3 – river management

a. how a river is managed in a named location

CASE STUDY: River Nene, Northampton

  • River Nene frequently floods
  • Heavy rain, April 1998 caused the river Nene and Grand Union Council to overflow, causing the death of 2 people
  • 2002, the Environment Agency completed a £6.8 mil project to protect the hardest hit areas of Northampton, followed by 2003, 2007 where further works were carried out

Weedon, Northampton

  • 2002, £2mil 450m clay flood embankment across the river valley (upstream of NH)
  • Flood storage area behind embankment, regulated by a culvert
  • Embankment landscaped for aquatic plants and animals

Upton Square

  • Upperclass housing estate built above the level of the floodplain – making it safe to flood

Four Cotton, St. James

  • 2003, flood warning systems upgraded
  • 2 hours warning via text
  • Within 2 hours, residents can move valuables and furniture and rugs upstairs, as well as pick a designated spot to go.

Billing

  • Flood retention reservoir nearby the aquadrone

Foot Meadow

  • 4m high walls installed to protect housing industry and inns
  • Wash land created (an open area for the river to flood to, diverts the flow away from properties on the other side of the river)
  • Debris cleared so river velocity can increase –> Rainwater taken away quicker
  • Gabion baskets protect riverbanks

Upton, Sixfields

  • 2007, £8mil spent developing a washland – effective diversion from the river Nene to reduce the risk of flooding downstream
  • Major road – upton way – A45, built on embankments 6m high
  • Upton Way embankment joins up to specially built floodgates to an area where 1.2 mil cubic meters of water can be stored
  • River channel capacity increase – building earth embankments 10m from the river, aesthetically improved by planting trees

 

CASE STUDY: Blandford Forum

  • River stour, Dorset, England
  • 1979, May, 30 damaged properties. December, 110 damaged properties

Causes of the flood 

  • Floods from West –> east
  • Upstream – town covered in impermeable clay
  • Dense network of streams causes water level to rise quickly
  • Deforestation increases lag time
  • Narrow floodplain
  • 5cm of intense rainfall over 24 hours

Schemes:

  • Total cost: £1.45mil ,saving them from £1.6 mil worth of damage
  • 2.5m flood wall
  • 1m deep relief channel
  • Southside flood bank protects a brewery, industry and housing
  • Washland on the south allows water to flood with minimal impact
  • Pumping station at Langton meadows directs water further downstream
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