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..