Modelling catchment sediment transfer: future sediment delivery to the Carlisle urban area
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Transcript of Modelling catchment sediment transfer: future sediment delivery to the Carlisle urban area
Modelling catchment sediment transfer: future sediment delivery to the Carlisle urban area
Tom CoulthardJorge A. RamirezPaul BatesJeff 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• 50m spatial resolution• 6 sub-catchments• Divisions coincide
with flow gauges
Km25
Upper Eden
Lower Eden
Eamont
Irthing
Caldew
Petteril
Carlisle
Linking sub-catchments
Carlisle
Discharge Sediment
Carlisle
Erosion
Deposition
Initial conditions: grain size distribution
• 40 sites visited• 173 photographs taken of sediment on channel edge
Finer Sediment
20%
Initial conditions: grain size distribution
Photo analysis technique utilized to estimate individual grain sizes
Grain size distributions per catchment/reachGrain size distributions all records
Adjusted grain size distributions to add unmeasurable small grain sizes ( < 0.3mm )
Initial conditions: grain size distribution
Grain Size (mm) Proportion
Size 1 .063 0.10Size 2 .25 0.10Size 3 1 0.12Size 4 2 0.24Size 5 4 0.21Size 6 8 0.13Size 7 16 0.06Size 8 32 0.02Size 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.
Upper Eden
Climate
Eamont Lower Eden
Irthing Petteril Caldew
0 200,000 400,000 600,000 0 200,000 400,000 600,000 0 200,000 400,000 600,000
Time, hours
Cum
ulati
ve ra
infa
ll, m
m0
1000
0020
0000
010
0000
2000
00
• 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
Catchment simulations
PetterilCaldew
Lower Eden
Irthing
EamontUpper Eden
Catchment Sediment output
0 200,000 400,000 600,000 0 200,000 400,000 600,000 0 200,000 400,000 600,000
Time, hours
0
Cum
ulati
ve se
dim
ent,
m3
010
0000
010
0000
0
2. CAESAR reach scale tasks• Produce future bed elevations for the Eden
reach at Carlisle: • Determine how this affects flood inundation
Water inputsCu
mul
ative
Disc
harg
e ( m
3 /se
c)
Eden
Caldew
Petteril
Time, hours0 200,000 400,000 600,000
020
0000
0030
0000
0010
0000
00
Eden 84%
Caldew 11%
Petteril 5%
Hourly Discharge
Sediment inputsCu
mul
ative
sedi
men
t, m
3
010
0000
0
0 200,000 400,000 600,000 0 200,000 400,000 600,000 0 200,000 400,000 600,000
Time, hours
PetterilCaldewLower Eden
83% 12% 5%Eden Caldew Petteril
Hourly lumped sediment
Changes in bed elevation
-6m(Deposition)
6m(Erosion)
+30%
+10%Baseline
+20%
LISFLOOD-FP
0
11Depth, m
reference DTM
+30%
• 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)
Bed elevations affect on flood levels
3 (more flooding)
- 2Difference in maximum water elevation (new – original)
Baseline
+20% +30%
∆ max water depth, m
+10%
(less flooding)
Previous trial runs (increasing sediment input)
-6m(Deposition)
5m(Erosion)
Baseline -50%
+50% +100%
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..