River Processes and
Morphology
A Case Study of the Souteyran
valley
1
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
3
Specific Information:


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

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:
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:
Transpiration
Evaporation
KEY:
Inputs
Storage
Transfers
Outputs
Precipitation
Interception
Throughfall
Surface Storage
Surface
Runoff
Infiltration
Vegetation
Storage
Soil water storage
Throughflow
Percolation
Groundwater Storage
Baseflow
Channel
Flow
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.
Storm Hydrograph
(3rd – 6th October 2001)
20
18
16
14
12
10
8
6
4
2
0
0.25
Peak Discharge
Lag Time
0.2
0.15
0.1
Peak Rainfall
0.05
0
09-00 19-00 20-00 21-00 22-00 23-00 24-00 09-00 09-00 09-00
(03-10- (03-10- (03-10- (03-10- (03-10- (03-10- (03-10- (04-10- (05-10- (06-1001)
01)
01)
01)
01)
01)
01)
01)
01)
01)
Rainfall (mm)
Discharge (m3/s)
17
/1
0/
20
18
01
/1
0/
20
19
01
/1
0/
20
20
01
/1
0/
20
21
01
/1
0/
20
22
01
/1
0/
20
23
01
/1
0/
20
24
01
/1
0/
20
25
01
/1
0/
20
26
01
/1
0/
20
27
01
/1
0/
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28
01
/1
0/
20
29
01
/1
0/
20
30
01
/1
0/
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01
01
/1
1/
20
01
Storm Hydrograph
(Souteyran 17th – 30th October 2011)
1
140
0.9
120
0.8
100
0.7
80
0.6
0.5
60
0.4
40
0.3
0.2
20
0.1
0
0
Rainfall (mm)
Discharge (m3/s)
The Results of the Storm!
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12
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Aims:

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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
Study
Sites:
Key:
- Study Site
- River
Site
No.
Altitude
(m)
1
Distance
Downstream
(km)
0
2
0.8
1340
3
1.05
1310
4
1.95
1220
5
2.2
1200
6
3.75
1060
7
3.75
1060
8
3.8
1050
9
4.45
1020
10
6.2
910
1440
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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
Present
Flow
Depth
Bank
Full
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
Slowest flow at the
bottom due to friction
from bed and banks
How will velocity 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
The lower course:
More angular bedload
Higher discharge
Larger bedload
Higher velocity
Steepest gradient
Higher hydraulic radius
Greatest cross sectional
Concave
area
Profile
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