River Processes and Morphology

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River Processes and Morphology

• A Case Study of the Souteyran valley

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General Information

• The Massif Central, contains a landscape of
  enormous variety characterised by a number of
  distinctive landforms.
• Water is an important and dynamic component of
  this landscape system.
• The physical geography of the Massif Central
  means that the region forms a vast watershed from
  which rivers flow to the Mediterranean, and the
  Atlantic coasts.

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General Information (Cont)

• The Massif is well watered. Lozère has more than
  2700 km of water courses.
• River management is an important aspect of water
  control and conservation in the Massif.
• Much of the management in the Cévennes is
  entrusted to the National Park
• Good management can only be achieved by gaining a
  full understanding of the physical processes
  acting within river channels

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Specific Information

• The Souteyran Valley lies along the southern
  slopes of Mont Lozère.
• It contains two rivers, the Souteyran and
  Rieumalet. Both of these flow into the Tarn at Le
  Pont de Montvert.
• The rivers are characteristic of upland streams
  which drain a granite and peat area.
• Both rivers are important to the valley
  communities The Eagle's Nest relies upon them
  for its water supply as do Finiels and Prat
  Souteyran.
• Both rivers flow continuously and much of this
  flow can be attributed to a slow release from
  stores held high up on Mont Lozère. These are
  peat bogs that play an important role in the
  basin hydrological cycle.

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The Hydrological Cycle
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What is a Drainage basin??

• An area of land drained by a river and its
  tributaries.
• It is the catchment area from which a river
  system obtains its supplies of water.
• It can be described as an open system with
  inputs, transfers, storage and outputs.

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Drainage Basin System
KEY
Inputs
Storage
Transpiration
Evaporation
Precipitation
Transfers
Interception
Outputs
Throughfall
Surface Runoff
Surface Storage
Infiltration
Vegetation Storage
Channel Flow
Soil water storage
Throughflow
Percolation
Groundwater Storage
Baseflow
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In Summary

• The dominant movement of water down the valley
  slopes on Mont Lozère is at or just below the
  surface.
• The soil is saturated quickly and large volumes
  of water go rapidly into the river channel at the
  valley floor.
• Therefore this area is prone to dramatic flooding.

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Storm Hydrograph(3rd 6th October 2001)
Peak Discharge
Lag Time
Peak Rainfall
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Storm Hydrograph(Souteyran 17th 30th October
2001)
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The Results of the Storm!
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Aims

• To Investigate the downstream changes within the
  river channel and to account for the changes
  which take place.
• To investigate if the river Souteyran is a
  model river.

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Map of StudySites

• Key
• - Study Site
• - River

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WHAT CAN WE MEASURE

• ?

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Cross Section Measurements

• Channel Width (Present flow and bank full) (m)
• Channel Depth (Present flow and bank full) (m)
• Wetted perimeter (m)

Bank Full Width
Present Flow Width
Bank Full Depth
Present Flow Depth
What will happen to these channel variables as
you move downstream and why?
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Velocity (m/s)

• How do we measure velocity?

Greatest velocity where friction is least (away
from bed, banks and surface
Less fast on surface due to wind resistance
0.4
0.3
0.2
0.1
How will velocity change as you move downstream?
Slowest flow at the bottom due to friction from
bed and banks
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What else can we measure?

• Conductivity (ppm) material in solution
• pH
• Gradient ()
• Sediment Shape (Powers scale)
• Sediment Size (cm)
• How will these variables change as you move
  downstream?

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What can we calculate?

• Cross Sectional Area (A) Width (W) x Depth (D)
• A (m²) W x D
• Discharge (Q) Velocity (V) x Area (A)
• Q (m³/s) V x A
• How will these two variables change as you
  move downstream?

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Hydraulic Radius Area/Wetted perimeter

• A measure of channel efficiency expressed as a
  ratio.

Stream B
Stream A
2m
2m
Area 40
5m
5m
Area 40
20m
8m
WP 558 18
WP 2022 24

• Both streams have the same area but different
  wetted perimeter

Hydraulic Radius of stream A 40/18 2.22m
Hydraulic Radius of stream B 40/24 1.66m
Stream A has a higher hydraulic radius meaning
that it has less water in contact with the bed
and the banks. This creates less friction, which
reduces energy loss and increases velocity
How will Hydraulic Radius change as you move
downstream?
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Changes in river characteristics downstream
Hypotheses
Friction
Channel Roughness
Velocity
Channel Width
Channel Depth
Cross Sectional Area
Discharge
Sediment Size
Angularity of Bedload Conductivity
Channel Gradient
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In Summary
A model river should have the following
characteristics but will the Souteyran show these
characteristics?
The upper course More turbulence More
friction More angular bedload Larger bedload
Steepest gradient
The lower course Higher discharge Higher
velocity Higher hydraulic radius Greatest cross
sectional area
Concave Profile
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Health and Safety!

• During this investigation there will be a number
  of hazards, some more obvious than others.
• Do not take off your footwear.
• Do not jump from rock to rock. (the rocks will be
  slippy so use the wellies provided and walk
  through the water).
• Do not drink from the river!!