RIVER ENVIRONMENTS

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  • Created by: elliel97
  • Created on: 19-03-14 20:51

SLOPE PROCESSES

SLOW MOVEMENT

SOIL CREEP:

1) Individual soil particles are pushed to the surface by wetting, heating or freezing of water.

2) They move at right angles to the surface as it is the zone of least resistance.

3) They fall under the influence of gravity once the particles have dried, cooled or the water has thawed.

  • Net movement is downslope.
  • Rates are slow 1mm/year in the UK.
  • up to 5mm/year in the tropical rainforest.
  • They form small terracettes such as the Manger in the Vale of the White Horse, Oxfordshire.
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SLOPE PROCESSES

SLOW MOVEMENT

RAIN-SPLASH EROSION:

  • FLAT SURFACES: Rain drops compact the soil and dislodge particles equally in all directions
  • STEEP SLOPES: The downward component is more effective than the upward motion due to gravity so erosion downslope increases with slope angle. 

SOLIFLUCTION:

  • The movement of water-saturated sediment due to recurrent freezing and thawing of the ground, affected by gravity. Occurs in periglacial environments.
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SLOPE PROCESSES

SLOW MOVEMENT

SOLIFLUCTION:

  • The movement of water-saturated sediment due to recurrent freezing and thawing of the ground, affected by gravity. Occurs in periglacial environments.
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SLOPE PROCESSES

FLOW MOVEMENT

SURFACE WASH:

  • Occurs when the soil's infiltration capacity is exceeded.
  • Can lead to the formation of gullies (small narrow valley, formed by rain flowing down the side of a hill)
  • Commonly occurs in Britain in the winter when water drains across saturated or frozen ground, following prolonged or heavy downpours or the melting of snow. 
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SLOPE PROCESSES

FLOW MOVEMENT

SHEET WASH:

  • The unchannelled flow of water over a soil surface.
  • Sheetwash is divided into areas of high velocity seperated by areas of lower velocity.
  • It is capable of transporting material dislodged by rain-splash.
  • Occurs on footpaths and moorlands in the UK.
  • Boscastle floods 2004sheetwash from the shallow moorland peat caused steep, narrow gullies to form.
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SLOPE PROCESSES

FLOW MOVEMENT

THROUGHFLOW:

 1) Water moving down through the soil. 

 2) It is channelled into natural pipes in the soil.

 3) This gives it sufficient energy to transport material. This added to the solute load may amount to a considerable volume. 

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SLOPE PROCESSES

FAST MASS MOVEMENTS:

SLIDES:

  • Sliding material mantains its shape and cohesion until it impacts at the bottom of a slope and leads to large, slumped terraces.
  • Can be small-scale - lead to road closures.
  • Can be large-scale - kill thousands. Vaiont Dam in Italy = over 2000 died on 9th October 1963.
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SLOPE PROCESSES

FAST MASS MOVEMENTS:

FALLS:

  • 1) Initial cause of the fall may be weathering such as freeze-thaw or disintergration or erosion prising open lines of weakness.
  •  2) Once the rocks are detached they fall under the influence of gravity. If the fall is short, it produces relatively straight scree.
  • Scree = slope of loose rock debris at the base of a steep incline or cliff.
  • If fall is long it forms concave scree.
  • Rock falls occur on steep slopes.
  • Wastwater in the Lake District = falls and scree.
  • Falls lead to scree slopes and large slumped terraces.
  • In upland ares falls and slides are an important sediment source for rivers.
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FACTORS AFFECTING SLOPES

CLIMATE 

ASPECT 

ROCK TYPE AND STRUCTURE

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WEATHERING

MECHANICAL

Freeze thaw: 

  • Occurs when water in joints and cracks freezes at 0 degrees c and expands by 10% and then exerts a pressure up to 2100kg/cm2 and it can only withstand a pressure of up to 500kg/cm2.

Disintergration:

  • Mechanical weathering of rocks resulting in smaller fragments of the same type. Found in hot desert areas where there is a large diurnal temperature range. Rocks heat up by day and contract by night. As rock is a poor conductor of heat, stresses take place on the outer layers causing peeling or exfoliation to occur.

Pressure release:

  • Overlying rock is removed by erosion causing underlying ones to expand and fracture parallel to the surface. The removal of great weight, such as a glacier has the same effect. 
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FACTORS AFFECTING WEATHERING

CLIMATE:

Rate of weathering varies with climate . Climate is related to moisture avaliability and average annual temperature.

Frost shattering increases as number of freeze-thaw cycles increase.

Chemical weathering increases with moisutre and heat.

GEOLOGY:

Rock type influences the rate and type of weathering in many ways due to:

  • Chemical composition
  • The nature of cements in sedimentary rock
  • joints and bedding planes

E.G = Limestone consists of calcium carbonate and is therefore susceptible to carbonation solution. Whereas Granite with orthoclase feldspar is prone to hydrolysis.

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FACTORS AFFECTING RIVER FLOW AND VELOCITY

TURBULENT FLOW

LAMINAR FLOW

CHANNEL SHAPE

CHANNEL ROUGHNESS

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TRANSPORT IN RIVERS

SUSPENSION

SALTATION

TRACTION

SOLUTION

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TRANSPORT IN RIVERS

  • SEDIMENT YIELD
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FACTORS AFFECTING RIVER FLOW AND VELOCITY

HJULSTROM CURVES

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EROSION IN RIVERS

ABRASION

ATTRITION

HYDRAULIC ACTION

SOLUTION

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EROSION IN RIVERS

FACTORS THAT AFFECT RATES

LOAD 

VELOCITY

GRADIENT

GEOLOGY

pH 

HUMAN IMPACT

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DEPOSITION

HAPPENS BECAUSE OF:

a shallowing of gradient which decreases velocity and energy

a decrease in the volume of water in ther iver

an increase in the friction between water and the channel

human obstructions such as dams

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LANDFORMS PRODUCED BY EROSION

V-SHAPED VALLEYS 

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LANDFORMS PRODUCED BY EROSION

GRADED STREAM PROFILES

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LANDFORMS PRODUCED BY EROSION

WATERFALLS

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LANDFORMS PRODUCED BY EROSION

GORGES

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LANDFORMS PRODUCED BY EROSION

POTHOLES

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LANDFORMS PRODUCED BY EROSION AND DEPOSITION

MEANDERS

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LANDFORMS PRODUCED BY EROSION AND DEPOSITION

OXBOW LAKES

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LANDFORMS PRODUCED BY DEPOSITION

BRAIDED CHANNELS

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LANDFORMS PRODUCED BY DEPOSITION

FLOODPLAINS

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LANDFORMS PRODUCED BY DEPOSITION

LEVEES

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LANDFORMS PRODUCED BY DEPOSITION

DELTAS

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WAYS RIVERS CAN BE A MULTIUSE RESOURCE

THE THAMES BASIN

THE COLORADO RIVER - GLEN CANYON DAM

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ISSUES THAT CAN ARISE FROM THE DEVELOPMENT OF RIVE

THE 2007 FLOODS IN SOUTHERN ENGLAND

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ISSUES THAT CAN ARISE FROM THE DEVELOPMENT OF RIVE

BANGLADESH

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MANAGEMENT CHALLENGES ASSOCIATED WITH THE DEVELOPM

MANAGING THE THAMES AT OXFORD

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WEATHERING

CHEMICAL

CARBONATION: This is when rainwater (which naturally contains carbon dioxide) in solution has a carbonic acid. And this weak acid can react with rocks that contain calcium carbonate such as limestone. The limestone over time dissolves as calcium bicarbonate

HYDROLYSIS: When hydrogen in water reacts with minerals in rocks causing the water to combine with the mineral. This decomposes the rock and forms clays.

OXIDATION: When rocks that are exposed to oxygen react with it and become a browinsh color (sort of like rusting!) which weakens the rock and makes it more vunerable.

HYDRATION: When rocks absorb water into their structure causing them to swell and become vunerable to future breakdown.

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MANAGEMENT CHALLENGES ASSOCIATED WITH THE DEVELOPM

BANGLADESH

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