08/07/2015
Deltas of the Anthropocene
‘Man-made deltas’
Deltas of the Anthropocene
‘Anthropogenic Transformation’
Lessons from the Rhine
‘Sinking deltas’
‘Deltas under pressure’
• Lessons from the Rhine delta history: a nutshell story
Hans Middelkoop
Department Physical Geography, University of Utrecht – The Netherlands
o
Heavily modified by humans
o
Detailed record of forcings and impacts
o
How, where, when have humans affected it?
o
Various options of sustainable management are tested
• What way to go for future deltas
Digital database of the palaeogeography of the Rhine-Meuse delta
Back-barrier delta
present
Age of river courses
1 BC/AD
East
West
3000 BC
6000 BC
10000 BC
Sea-level rise
Delta figure Cohen (& Hijma?)
50 km
K.M. Cohen, E. Stouthamer, H.J. Pierik, A.H. Geurts (2012)
https://easy.dans.knaw.nl/ui/datasets/id/easy-dataset:52125
Enhanced trapping of fines
Cohen & Hijma 2013
Historic load
Changes start after 3500 BP
Upstream changes – recorded in the delta
Mton/yr
Natural situation
Humans: upstream
deforestation
Modern
load
Peat wetland
3500 yr BP
Peat wetland
Peat wetland
Reconstructed trapping
Actually preserved deposits
Holocene: Erkens & Cohen 2009
Modern: Ten Brinke 2000, Middelkoop et al. 2012
Erkens & Cohen 2009
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08/07/2015
Humans in the delta
Enhanced clay deposition from upstream
Prehistoric time
6000 – 2000 BP
1500 yr BP
Adaptation
Delta services:
• Food
• Land
• Transport network
Erkens & Cohen 2009
Source: Arnoldussen & Van Zijverden, 2013
Adapted occupation: Roman Limes
Adaptation
Delta services:
• Food
• Land
• Transport network
• Defense line
Land reclamation: drainage
•
•
•
•
•
Local measures
Pressure on land
Organisation - governance
Power / money
Knowledge and system understanding
People and windmills to do the work
Drainage: subsidence!
Van Dinter et al., 2013
Peat mining, resulting in lakes
Lidar delta elevation: artificial surface
+5 m
~1400 – 1800 AD
Sea level
•
•
•
•
-5 m
Economic development
Urban growth
Need for fuel
Over-exploitation
Peat disappeared
Lakes formed
Now 5 m -SL
Eroded clay from Germany,
Reclaimed after 1000 AD,
Now 2 m -SL
www.ahn.nl/viewer
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08/07/2015
Longitudinal section delta wedge
West
Clay deposition
Peat excavation
Embanked rivers in the delta
East
Oxidation
• Disruption of channel – floodplain connection
• No more natural avulsions
• Sediment deposition only along rivers and in estuary
Embanked floodplains:
1250 - present
Sea-level rise
Delta figure Cohen (& Hijma?)
Compaction
Present surface
20th century engineering: sediment
Man-made channel-belt architecture
• Upstream weirs trap sediment
• Excessive gravel dredging
• Result = reduced sediment delivery
to the delta
Contamination
Accretion
Sand+gravel budget Rhine,
mid-Germany, 1985-2006
(Frings et al. 2014)
‘Confined’ pointbar
Fixed banks
Compaction
Incision
Dredged sediment in the Waal
Weir at Iffesheim – Germany
Sediment dynamics
Impacts across scales
5000
Natural delta
Present Rhine
Total deposition
suspension load
2 – 3 Mton/yr
2.5 Mton/yr
Main depo zones
Flood plain
Channel
Avulsions
Large-scale shifts in
deposition areas
No change
Pacing in
sediment
dynamics
Channel belt life cycles
Erosion, deposition
reworking
Flood pulses only
Residence/
preservation
Downstream increase
Half lives: 102 – 105 yr
Waal before normalisation:
~90% reworked
‘Reworking’ to date:
Floodplains = clay excavation
Channels = dredging
Basin activities
LU change
3000
0
1000
1250
1500
1750
1800
1850
1900
1950 present
Upstream
Channelization
Dams & weirs
Delta impacts
Nat. floodplain
Channel geom.
Channel sed.
aggradation
Delta
Delta activities
Land recl.
Embankment
Channelization
Delta impacts
Nat. floodplain
subsidence
Unintended impact
Emb. floodplain
Channel geom.
Channel sed.
lateral confinement
silting-up
incision
Long-term legacy / impact
coarsening
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What happened – the challenge
Solutions? - Pilots in the Rhine delta
Opening polders
NatureCoast
Delta functioning………….degradation
Ecosystem
services
ESS Hazard
Village
Exploitation,
Destruction
Agriculture
Drainage
subsidence
Soil subsidence…?
Raising
private
Human expansion …… pressure
property
time
Find a new balance for future deltas
Room for
the Rivers
Scientific challenges
Understand the physical system:
Thank you!
• Causes and mechanisms underlying the problem
• Longer-term and larger-scale impacts of measures
• Options for sustainable restoration
Understand the societal system:
• The problem is ‘new’ and not well incorporated in current
governance / legislation
• Who has the problem, who caused it, who solves it?
• Conflicting interests across spatial scales and time
• Identification of adaptation capacity and options
Integrate natural and human sciences
Apply this to deltas of the world
1000
1250
1500
1750
1800
Synthesis – Rhine delta
1850
1900
1950 present
5000
Basin activities
LU change
Channelization
Channelization
Dams & weirs
Dams & weirs
Delta impacts
Nat. floodplain
aggradation
Channel geom.
Land recl.
Embankment
Channelization
Delta impacts
Nat. floodplain
Emb. floodplain
Channel geom.
Channel sed.
Delta - management
Delta activities
Delta - reclamation
Channel sed.
subsidence
lateral confinement
Industrial revolution
Basin activities
LU change
Delta impacts
Nat. floodplain
Channel geom.
Channel sed.
Delta activities
Land recl.
Embankment
Channelization
Delta impacts
Nat. floodplain
silting-up
incision
coarsening
Emb. floodplain
Channel geom.
Channel sed.
3000
0
1000
1250
1500
1750
1800
1850
1900
1950 present
Upstream
aggradation
Delta
subsidence
Industrial revolution
0
River management
3000
Delta reclamation
5000
Agriculture
Synthesis – Rhine delta
Long-term legacy / impact
silting-up
lateral confinement
incision
coarsening
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08/07/2015
Natural delta
High-stand sediment trapping
3.0 Mton/yr
Trapping of fines
Break down
• 500 year time slices
• Spatially explicit
2.5
2.0
Upstream changes – recorded in the delta
Natural situation
Humans: upstream
deforestation
1.5
1.0
0.5
5500- 5000- 4500- 4000- 3500- 3000- 2500- 2000- 1500- < 800
5000 4500 4000 3500 3000 2500 2000 1500 800 Cal BP
0
Erkens (2009)
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