LETG - Caen

Impacts of river management on low energy rivers in Normandy (France) over 3000 years,
first results of a geomorphological and geoarchaeological approach.
Contact :
[email protected]
Beauchamp Axel (1), Lespez Laurent (2), Le Gaillard Ludovic (3), Bernard Vincent (4) et Delahaye Daniel (1).
(1) LETG-Caen Geophen, UMR 6554 CNRS, UCBN, CAEN, FRANCE
(2) Laboratoire Géographie Physique (LGP) UMR 8591 CNRS, Université de Paris-Est Créteil, FRANCE
(3) INRAP, Centre de Recherches Archéologiques, BOURGUÉBUS, FRANCE
(4) CReAAH , UMR 6566 CNRS, Université Rennes 1, FRANCE
Réalisation graphique :
Axel BEAUCHAMP
Introduction
- The European Water Framework Directive (WFD), issued in 2000 has the objective of improving the quality of water and aquatic environments. In France, the application of this law requires the dismantling and razing
of structures built across waterways (mill valve, mill dam…) which no longer have any use today. We need today to better understand the history of these structures in long-time standing.
En France, l’application de la directive
européenne cadre sur l’eau (DCE) requière
le démantèlement et l’arasement des
constructions entravant les cours d’eau
(moulins, barrages…) pour lesquelles il n’y
a plus d’usage aujourd’hui.
Les premiers résultats géoarchéologiques attestent que l’aménagement des
cours d’eau bas-normands débute à l’Age
du Fer (800 BC).
Ainsi, depuis 4000 ans, les plaines inondables ont subit une aggradation verticale significative résultant d’une érosion
des sols des bassins versants liée au développement des activités agro-pastorales
L’objectif de ce travail est de mesurer
l’impact de l’implantation des ouvrages
hydrauliques majeurs (moulins, barrages,
fossésdedrainage…)surlefonctionnement
des rivières et de proposer un modèle
d’interaction
Homme/Environnement
sur le temps long pour les cours d’eau
en Basse-Normandie et d’anticiper les
conséquences géomorphologiques liées
à la politique d’arasement des barrages.
- First gearchaeological results in Normandy show evidence of river management since the Iron Age (800 BC.). They also show that during the last 4000 years, floodplains have been affected by a significant vertical aggradation resulting from soil erosion in the catchment related to the development of agro-pastoral activities. However, these results say nothing about consequences of the proliferation of mill dams for hydrosedimentary flow
for low energy rivers and their role in the development of sedimentary stocks in valley beds.
- The aim of this work is to measure the impact of the implementation of major hydraulic structures (mill inlet, mill dam, millrace, mill valve, drainage ditches...) on the rivers functioning in the past millennia to propose a
long term modeling Human/Ecosystem interaction for Lower-Normandy river systems and to anticipate the geomorphological consequences related to dam-removal policy.
Study area
Objectifs & Methodology
Montaigu la Brisette
- Research based on case studies
located throughout the Lower Normandy.
Port-en-Bessin
La Sangsurière
- Determine the role of these developments in the establishment of sedimentary stocks in valley bottom.
Blainville-sur-Orne
- These sites are from several time
period to cover the largest time
scale.
- Complementary studies of two watersheds are done to understand the
cumulative effects of mill dams on
river.
- The issues of this work is to understand how humans have shaped the river and how it influenced the hydrosedimentary dynamics in the last 3000 years.
Colomby
Clinchamps-sur-Orne
Vieux
- For this, geomorphological and geoarchaeological investigations are developed at different scales.
1
Virey
0
50 km
The sedimentary fill of floodplain is renconstructed with a geomorphologic and
stratigraphic analyse due to cores and
trenches which are performed on the
edge of the river upstream, downstream
and at the foot of the structure studied.
Study sites
2
Sedimentological and a micromorphological analyses reinforce stratigraphics interpretations by identifying cycles of erosion and sedimentation which partly depend on hydraulics structures built on the river.
Diagram of investigations
carried out around hydraulic structures
m NGF
South
14
12
12
P
10
10
Merderet
8
8
A. Beauchamp
L. Le Gaillard
Photomicrograph of rounded alluvial papule (P)
and clay microlamination (L) in sediment trapped
behind a roman wall built across the river.
Grey silt
Silty clay
Coarse gravel
Silty peat
Gravel and sand
Red Trias sand
East
Overview of Roman wall
blocking the river and
the associated sedimentary fill
West
Altitude NGF
12 m
3
10 m
C3
Radiocarbon analyses are
used to date the sediment.
They are accompanied by
historical archives and / or
archaeological research to
date hydraulic structures.
These chronostratigraphy
allow to understand the
impact of human activities
on sedimentation in the
floodplain.
Mills
Organic sand
Overbank silt
Topsoil
Stratigraphic section of the Merderet's valley bed
with the location of the medieval millrace at Colomby's site.
L
Archives departementales
du Calvados
C1
8m
C2
Orne
1797 - 1891 cal AD.
4331 - 4220 cal. BC.
6m
1513 - 1601 cal. AD.
4m
2m
A. Beauchamp
0m
10 m
20 m
30 m
40 m
Top soil
Silty clay with paleosol
Organic sandy clay
Sand and gravel (Weichselian)
Overbank silt
Silty peat
Hydromorphic sandy silt
Sand and gravel (Saalian)
Wet leaf matter
Hydromorphic clay
Bedrock (Brioverian schists)
Brown silty clay
50 m
Stratigraphic section of the
Orne's valley bed downstream a mill dam at
Clinchamps-sur -Orne with C14 dating
Datations C14
Preliminary results
Impacts de l’aménagement
des cours d’eau à faible
énergie en Basse-Normandie
depuis 3000 ans
LETG - Caen
North
Medieval millrace
Road map from the eighteenth century
with the location of mills on the Seulles river
Basse-Normandie •Géoarchéologie
Géomorphologie • Aménagement
des cours d’eau • DCE • Barrage
A. Beauchamp
14
First results from the ancient site Montaigu-la-Brisette shows that
the multiplication of hydraulic structures on the small river in antiquity, have a great impact on the evolution of the fluvial landscape.
The site is an small roman town with hydraulic stuctures (mill) and
roman baths installed on the river edges.
Geomorphological trenches were conducted regularly in the valley between the archaeological structures. A micromorphological analysis completed the stratigraphic analysis of sediments from the floodplain.
ming
dam
Water
m NGF
90
Actual top soil
Archeological sediment
3rd century AD.
Alluvial sediment,
first half of 2d century AD
Ground level,
2d century AD
Ground level,
second half of 3rd century AD
Alluvial sediment,
second half of 3rd century AD
Alluvial sediment,
4th century AD
Paleochannel,
first half of 3rd century AD
90
89
89
88
88
87
87
A. Beauchamp
Bedrock
Drainage ditch,
2d century AD.
Alluvial sediment, la Tène period.
Paleochannel, Iron Age.
Millrace, 2d century AD.
Drainage ditch,
2d century AD.
ne
ntai les
Fo
es
x Pr
au
The bottom unit correspond to organic
sand and silt deposited until the Iron
Age. Then, overbank silts were deposited intercut with ancient ground levels.
Micromorphology assign this sedimentation to soil erosion from land clearing
for forestry and agriculture during early
roman occupation.
Chronostratigraphic section n°2 of the Fontaine-aux-Presles
river at Montaigu-la-Brisette's site.
6
Perspectives
Other case studies on other structures will be implemented for better knowledge about the impact of hydraulic structures on low
energy rivers in Lower Normandy. This work will offer a better understanding of the role of this hydraulic equipment in the establishment of sedimentary stocks in valley bottom and more globally, it will show the place of human activities in the establishment of the
today rivers and floodplains.
Contacts :
Axel Beauchamp, doctorant au laboratoire LETG-Caen Géophen UMR 6554 CNRS
[email protected]
Thermae
Housing
Housing
1
Warehouse
2
Mill
4
Pool
Palaestra
Warehouse
5
3
River system
Roman river system
Roman urban area
Housing
60m
Roman structures
Roman roads
Trenches
A. Beauchamp
The archeological site of Montaigu-la-Brisette and
location of geoarcheological threnches
This sedimentation is amplified by a series of structures
built across the channel which had a sediment dam effect.
Leading to a fast siltation of floodplain and a long-lasting
fixation of channel until today.