rhône basin
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The Rhône, a river
shaped by man
Known as
The French section of the Rhône, from
Lake Geneva to the River Saône, winds
its way through the mountains of the Jura
and the pre-Alps before it reaches
the Ain plain.
the Rotten in its
upper reaches,
the source
of the Rhône is
meltwater from
At Lyon, the river meets the rocky
obstacle that is the Massif Central, forcing
it to change direction to run down a northsouth axis all the way to its delta, the
Camargue. The Rhône basin is noteworthy
for the diversity of climates - mountainous,
oceanic, continental, Mediterranean influencing how the river functions.
The Rhône is a major communication
channel, engineered to optimise navigability,
work on which started in the first half
of the 19th century. Since 1934, navigability
works, hydro-electricity, and the use
of its waters for irrigation have all
expanded. The Rhône is a river shaped
by man with dykes and channels, deviated
from its natural course long ago.
DID YOU KNOW?
the Furka glacier
in the Swiss
canton of Valais.
It runs for 300 km
before reaching
Lake Geneva.
The Furka glacier, like most other Alpine glaciers,
has retreated a great deal over the last 150 years because
of climate change.
ATLANTIC
OCEAN
The French portion of the Rhône now
features 22 hydro-electric power plants,
16 nuclear reactors and 19 locks enabling
the river to be navigated along some
300 km of its length.
IDENTITY CARD
Source: Furka glacier, Swiss Alps
Mouth: Mediterranean Sea
Length: 810 km (just over 500 miles)
Discharge rate at mouth: 1,700 m3/s
Catchment area: 0.1 million sq. km.
Mouth of the Rhône carrying glacier
sediment into Lake Geneva, on the Swiss
side.
A cut-off (lône) is an abandoned
or secondary branch of the Rhône.
Most of them are the result
of man-made changes to the river’s
direction. They are supplied
with water by groundwater
or directly by the river in times
of flooding.
The rivers Ain, Saône, Isère and Durance, the Rhône’s four major
tributaries, receive 60% of the catchment area’s water.
Confluence of the Rhône (right) and Saône (left) in Lyon.
Countries: Switzerland, France
The temperature of the Rhône and its tributaries has risen
substantially over the last 40 years. These changes are caused
by climate change, a slower rate of flow, and discharges of hot water
from the power plants.
The Rhône discharges 54 billion cubic
metres of water, which is 20% of the river water
that flows into the Mediterranean
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rhône basin
A complex river
The Rhône tributaries show highly
disparate monthly flow rates. Some, supplied
by melting snow, have a strong flow in
summer; others, mainly supplied by
rainfall, have a greater hydrological regime
in autumn and winter. The inflows from these
rivers have different effects on Rhône’s flow
rate, floods and low water levels, depending
on the location and the season.
Different types of flood may occur in the
Rhône basin in winter and autumn, i.e.
“oceanic” towards the north, and “Cévennes”
and “extensive Mediterranean” in the south,
the latter two being extreme and sudden.
If they occur at the same time or a few days
apart, a “general flood” arises, often with
devastating effects, as in 2003.
According to researchers, the impact
of climate change on the Rhône basin
is difficult to assess. Separating the influence
of this factor from others such as human
activities and changes brought about to
the environment is no easy matter.
It is however proven that temperatures
are rising, that evaporation is greater and that
snow is melting earlier.
Owing
to the varying
hydrological
regimes of
the various
sub-catchment
areas and the
RESEARCH
Scientific organisations (IRSTEA – France’s National Research
Institute of Science and Technology for Environment and Agriculture,
CNRS - French National Centre for Scientific Research, France’s
meteorological office Météo-France, universities) have been working
together for years on a whole range of programmes studying water
resources and the impact of climate change. These hydroclimatic
modelling projects, ranging from Gewex-Rhône to the current
“Modelling the Rhône” programme, show the system’s sensitivity
to fluctuations brought about by man-made and natural causes.
various climates
the river passes
through,
the Rhône has
a complex flow
pattern, which
Average monthly flows
can experience
episodes of
Source: banque hydro
The Rhône basin receives heavy precipitation, some 1,100 mm
on average per annum. In the Alps, precipitation of over 3 metres
per annum has been measured, mainly in the form of snow.
The Isère is a tributary supplied by meltwater from snow and glaciers;
the waters of the river Saône are essentially rainwater. The flows of each
river will differ a great deal depending on the season.
flooding or low
water at different
times of the year.
Downstream from Valence, the Rhône
and its tributaries are affected by the
Mediterranean climate, with autumn
downpours resulting in frequent flooding,
as here at les Gardons.
The banks of the Rhône in Lyon in 2003.
This “general flood” caused more than
a billion euros of damage, making it one
of the most costly floods ever to occur
in France.
Researchers anticipate an increase in air
temperature of 1 to 3°C, unpredictable changes
to winter precipitation (from -10% to 10%)
and a 5% drop in summer rainfall. They have
not, however, uncovered any clear trend
in changes to floods.
The Camargue is extremely
vulnerable to Rhône floodwaters
as its topography is flat and low-lying.
It can become flooded if a dyke
is breached, as here in
December 2003.
The river hit a rare
3
of
peak flow 11,500 m /s
in December 2003
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rhône basin
A subdued river
Matter in motion in rivers can be split
between alluvium and clay in suspension,
and sand, gravel and pebbles washed along
the river bed. In the Rhône’s case, the
transport of fine sediment in suspension
and sand has been in decline for a century,
but is still substantial. Gravel and pebbles
being carried along the river bed has almost
stopped. Consequently, only sand, alluvium
and clay shape the plain and currently reach
the mouth of the Rhône.
The “Girardon” engineering structures
designed to increase the depth of the navigable
channel, together with large reservoir dams,
hold back a large proportion of the sediment
in suspension and the sand. The inflow
of pebbles and gravel from tributaries
is stopped by large-scale extraction of
aggregates. With the scarcity of gravel inflows
and the channelling of the river, it is now
subdued and sluggish, its bed and banks
no longer change and no longer rebuild
themselves.
The river’s managers are currently working
on dismantling the Girardon structures
so as to limit the level of floods, increase
the sediment carried by the river, and boost
ecosystems by rehabilitating the Rhone’s dead
offshoots, the “lônes”, and adjoining
land environments.
From Lyon
onwards, the
Rhône has been
gradually altered
to improve flood
protection and
navigability,
and generate
RESEARCH
The Rhône Sediment Observatory (OSR) is a multi-partner research
platform, aiming to generate cross-disciplinary scientific knowledge
over the long term delivering better understanding of the river system’s
dynamics and improved information for public operators. Partners
include the Rhône Basin Long-term Environmental Research Observatory
(ZABR), Rhône Valley Environmental Observatory (OHM-VR), river
management bodies, government departments, French Water Agency,
Compagnie Nationale du Rhône, EDF (electricity generating company),
local governments of regions through which the river passes,
and research institutes.
Digues basses longitudinales
Epis plongeants
Accumulation des galets
hydro-electric
power. These
alterations have
changed the river’s
transport
of sediment,
its geometry,
and how the river
Digue basse
Fine sediment carried through Arles is estimated at 10 million tonnes per annum,
compared with 20 million in the 1950s and perhaps 30 million tonnes per annum
at the end of the 19th century.
The Camargue coast is retreating because
river’s load of solid matter is taken directly
out to sea by the outer branches of the delta,
the Camargue being contained by dykes
and isolated.
Tributaries’ inflows of solids have been
divided by 5, mainly from the removal
of aggregates, especially at their mouths,
certain HEP facilities, and the reduction
of flow speed, which reduces the amount
the river can carry.
works in general.
Put in place between 1880 and 1920, the Girardon system,
consisting of groynes, cross members and low dykes,
reduced the river’s width while making it deeper. The
consequence of these engineering works was not only
to lengthen the period when navigation was possible,
but also to cut substantially into the river bed, reduce
the diversity of depths, increase deposits of alluvia
and sand on the banks, worsen the effects of floods
and to cut off the Rhône’s secondary branches.
At Saintes-Maries de la Mer, in the Camargue,
the German bunker originally built at the top
of the beach is now submerged, which provides
a measure of how far the coastline has retreated.
The Génissiat dam is holding
back over 12 million m3
of various types of sediment
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rhône basin
Back to the source
After more than a century of development
work, the Rhône has changed from a multiplecourse system to a channelled river.
The remediation work has a number of aims,
including to reintroduce and improve
the transport of larger sediments, to reconnect
and re-supply the cut-off branches (the
“lônes”), increase the flow in short-circuited
sections, rehabilitate river habitats, and
to restore fish migration routes.
of habitats that is typical of alluvial plains.
Other branches of the “old Rhône” river bed
now receive just a fraction of the water
they used to. The flow in these short-circuited
sections has been increased to improve the
ecological system and make a Rhône a “swift
flowing” river once again. These measures
are helping to re-establish ecological
continuity and encourage fish to spread
over a wider area of the basin.
The “lônes”, cut off from the main river
by dykes and flow regulators, fill with sand
and silt, leading to the formation of separate
bodies of water, ponds and ditches. Dredging
the beds and removing some of the dykes
improves water flow, recreating the diversity
It is essential to monitor and analyse
the effects of this restoration work to extend it
to other sites in the Rhône basin, while taking
account of the effects of human activities
and climate change on these newly-created
habitats.
RESEARCH
RhônEco (the scientific monitoring of the Rhone rehabilitation
work) is a programme run by the aforementioned ZABR as part of
the wider Rhône Plan. RhônEco focuses on ecological monitoring
of the “Old Rhône” and its rehabilitated offshoots. It is a long-term
research programme that aims to analyse the ecological impact
of the rehabilitation, assess their predictability, and in so doing
help to determine the river’s ecological potential.
Before
Since 1995,
a hydraulic
and ecological
remediation
programme has
been underway,
to recreate
habitats and
to attempt
to restore
the biodiversity
that is
characteristic
of major central
European
After
rivers
(Rhine, Rhône
and Danube).
Since the increase in reserved flow speed from 10 to 100 m3/s in 2000
in the Old Rhône around Pierre-Bénite, the relative abundance of some
fish species (common bleak, beaked carp, dace) has increased
significantly (42% on average).
The flow in the old Rhône was cut (by 80
to 98%) to supply water to hydro-electricity
plants through diversion channels. Old Rhône
at Chautagne on the right, diversion channel
on the left.
The cut-off branches (“lônes”) are remediated by dredging sediment and
opening the channel downstream, and sometimes upstream. Before and
after pictures of the Ciseland Iône in the Pierre Bénite area, south of Lyon.
Engineering structures and dams
on the river have fragmented the water
space. The travel of migratory fish is curbed,
as in the shad of the Rhône. The Migratory
Fish Management Plan implemented
in 1993 allows the progressive reopening
of migration routes.
The zingel asper, the only species endemic
to the basin, is no longer recorded in the Rhône
itself, being found only in a few tributaries.
The remediation of the Old Rhône
is helping to safeguard hundreds
of other animal and plant species
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