future sediment delivery to the Carlisle urban area

kayakjokeΜηχανική

22 Φεβ 2014 (πριν από 3 χρόνια και 7 μήνες)

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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



50m spatial resolution



6 sub
-
catchments



Divisions coincide

with flow gauges

Km

25

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/reach

Grain 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

0.10

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.

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

Cumulative rainfall, mm

0

100000

200000

0

100000

200000


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

Petteril

Caldew

Lower Eden

Irthing

Eamont

Upper 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

Cumulative sediment, m
3

0

1000000

1000000

2. CAESAR
reach

scale tasks


Produce future bed elevations for the Eden
reach at Carlisle:


Determine how this affects flood inundation


Water inputs

Cumulative Discharge ( m
3
/sec)

Eden

Caldew

Petteril

Time, hours

0

200,000

400,000

600,000

0

20000000

30000000

10000000

Eden 84%

Caldew 11%

Petteril 5%

Hourly Discharge

Sediment inputs

Cumulative sediment, m
3

0

1000000

0

200,000

400,000

600,000

0

200,000

400,000

600,000

0

200,000

400,000

600,000

Time, hours

Petteril

Caldew

Lower 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

11

Depth, 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)

-

2

Difference 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..