Modelling catchment sediment transfer

Report
Modelling catchment sediment transfer:
future sediment delivery to the Carlisle urban area
Tom Coulthard
Jorge A. Ramirez
Paul Bates
Jeff Neal
Blue, flood outline before, Red flood outline after....
Project Aims/Summary
• To model sediment delivery from the
Eden catchment and how this can
affect flooding in Carlisle
• Using CAESAR, to model morphological
change in the Eden river catchment
and Carlisle reach
• Use different climate & discharge
records to simulate impact of climate
and land cover change
• Transfer updated DTM to Bristol for
hydraulic modelling
What is CAESAR?
• Catchment or Reach based
cellular model
• Models Morphological Change
• Hydrological model
– Adaptation of TOPMODEL
• Hydraulic model
– Simple 2d steady state flow model
• Sediment transport
– Bedload, 9 fractions using Wilcock
& Crowe eqtn.
– Suspended sediment, multiple
fractions
• Slope Processes
– Slope failure (landslips)
– Soil Creep
Main Tasks
• Two modelling tasks:
– 1. Model sediment and water from catchments
draining into Carlisle
– 2. Model morphological changes in Carlisle reach
1. CAESAR catchment scale tasks
• Produce sediment output
for the Eden river at
Carlisle
– Existing climate
– Climate scenarios
– Land cover change
Eden river sub-catchments
Petteril
50m spatial resolution
• 6 sub-catchments
• Divisions coincide
with flow gauges
•
Irthing
Carlisle
Caldew
Lower Eden
Upper Eden
Eamont
25
Km
Linking sub-catchments
Carlisle
Carlisle
Deposition
Erosion
Discharge
Sediment
Initial conditions: grain size distribution
• 40 sites visited
• 173 photographs taken of
sediment on channel edge
Initial conditions: grain size distribution
Photo analysis technique
utilized to estimate individual
grain sizes
Finer
Sediment
20%
Adjusted grain size
Grain
size distributions
distributions
to add
per
all
records
catchment/reach
unmeasurable
small
grain sizes ( < 0.3mm )
Initial conditions: grain size distribution
Grain Size (mm)
Proportion
Size 1
.063
0.10
Size 2
.25
0.10
Size 3
1
0.12
Size 4
2
0.24
Size 5
4
0.21
Size 6
8
0.13
Size 7
16
0.06
Size 8
32
0.02
Size 9
128
0.02
Climate change: What
we wanted to do...
• Use UKCP09 weather
generator to predict future
rainfall
• Use rainfall predictions as
divers for the CAESAR
morphological model
• Generate sediment yields
(and updated DEMs) for
futures.
Eamont
Lower Eden
Irthing
Petteril
Caldew
100000
200000
0
100000
Upper Eden
0
Cumulative rainfall, mm
200000
Climate
0
200,000
400,000
600,000 0
200,000
400,000
Time, hours
600,000 0
200,000
400,000
600,000
Catchment simulations
• 75 year simulation
• 13 years of hourly rainfall repeated and
amplified by climate factor
– 13 years chosen as only continuous period across
all catchments/raingauges
– Climate factor increased by 10, 20 and 30%
• Record DEM’s and sediment outputs
Eamont
Lower Eden
Irthing
Caldew
Petteril
1000000
0
1000000
Upper Eden
0
Cumulative sediment, m3
Catchment Sediment output
0
200,000
400,000
600,000 0
200,000
400,000
Time, hours
600,000 0
200,000
400,000
600,000
2. CAESAR reach scale tasks
• Produce future bed elevations for the Eden
reach at Carlisle:
• Determine how this affects flood inundation
30000000
Hourly Discharge
Caldew 11%
Eden
10000000
20000000
Petteril 5%
Caldew
Petteril
0
Cumulative Discharge ( m3/sec)
Water inputs
0
200,000
400,000
Time, hours
600,000
Eden 84%
Lower Eden
Petteril
1000000
Caldew
0
Cumulative sediment, m3
Sediment inputs
0
200,000
400,000
600,000 0
200,000
400,000
600,000 0
200,000
Time, hours
Hourly
lumped sediment
83%
Eden
12% 5%
Caldew Petteril
400,000
600,000
Changes in bed elevation
Baseline
+10%
+20%
+30%
6m(Erosion)
-6m(Deposition)
LISFLOOD-FP
reference DTM
• Model formulation
with inertia (Bates
et al., 2010)
• 2D channel and
floodplain.
• Normal depth at
boundary with
slope 0.0006 mm-1
(Horritt et al.,
2010)
+30%
Depth, m
11
0
Bed elevations affect on flood levels
Baseline
+20%
+10%
+30%
∆ max water
depth, m
3 (more flooding)
Difference in maximum water elevation (new – original)
- 2 (less flooding)
Previous trial runs (increasing sediment input)
-50%
Baseline
+50%
+100%
5m(Erosion)
-6m(Deposition)
Conclusions
• Morphological changes in the channel can have profound
influences on inundation levels
– relative to changes in flooding caused by climate change?
• Changes in flood level directly linked to
erosion/deposition
– Incision/aggradation alters conveyance
• Changes in channel pattern (cutoff) have a fairly profound
affect on inundation patterns
• Relationship between discharge increase and changes in
sediment yield is very site specific..
– Hard to apply a generic rule to all reaches
Aggradation in urban areas..

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