OVERVIEW OF FINE SEDIMENT

RESEARCH – THE LAST 40 YEARS

DES WALLING

College of Life and Environmental Sciences

Workshop on Sediment Fluxes in Irish Rivers, UCD, Dublin, September 28, 2014

System Behaviour cf Modelling

A Personal View

The Department of Geography,

University of Exeter,1968

1969

An Unfashionable Research Area

X

X X

X

√

A New Importance 2014

REASONS FOR STUDYING FINE SEDIMENT?

• SS is a standard water quality determinand

• Sediment-associated transport

- Nutrients (e.g. P)

- Contaminants (e.g. heavy metals, pesticides

and POPs)

- Pathogens (e.g. E.coli )

• Impacts on aquatic habitats and ecosystems

(Physical and chemical)

- Light transmission / turbidity

- Changing substrate and clogging vegetation

- Siltation of fish spawning gravels

• Close links to fish, phosphorus and metals

problems within WFD assessments

HOW MUCH? (QUANTITY)

WHAT HAVE WE LEARNT?

1970 Present TIME

UK – SW England

THE SUSPENDED SEDIMENT

YIELD OF THE HODGE BECK

YORKSHIRE (18.9 km2)

Imeson (1970) Arnett (1979)

488 t km-2 year-1

2.1 t km-2 year-1

A Non-Capacity Load

Supply Controlled

Exhaustion Effects - Hysteresis

SSC

(mg l-1)

Turbidity

(FTU)

River Exe at Thorverton

Source: English Nature

HOW MUCH?

WHAT HAVE WE LEARNT?

WHAT IS IT?

(QUALITY)

100 µm1.201F

0.705SfW

0.700Sf

0.942R

0.993PR

0.767SfC

0.713E

0.645FR

40.37PCr

36.55PC

39.91P

103.39AC

82.77A

13.88Fmax

9.45Fint

8.66Fmin

9.60DA

1.201F

0.705SfW

0.700Sf

0.942R

0.993PR

0.767SfC

0.713E

0.645FR

40.37PCr

36.55PC

39.91P

103.39AC

82.77A

13.88Fmax

9.45Fint

8.66Fmin

9.60DA

100 µm 1.250F

0.695SfW

0.621Sf

0.893R

0.942PR

0.754SfC

0.702E

0.634FR

82.20PCr

71.09PC

85.05P

483.50AC

372.43A

27.13Fmax

18.37Fint

16.71Fmin

18.26DA

1.250F

0.695SfW

0.621Sf

0.893R

0.942PR

0.754SfC

0.702E

0.634FR

82.20PCr

71.09PC

85.05P

483.50AC

372.43A

27.13Fmax

18.37Fint

16.71Fmin

18.26DA

Absolute / discrete Effective / flocculated

Micrographs of suspended sediment

Micrographs of suspended sediment

particles depicting a small floc (above)

and a group of larger flocs (below)

(Source, Ian Droppo/Environment Canada)

0.5 µm

Continuous Flow Centrifuge Time-integrating Trap Sampler

Mean Annual Total-P

Concentration (mg kg-1)

HOW MUCH?

WHAT IS IT?

WHAT HAVE WE LEARNT?

WHERE DOES IT COME FROM?

(SOURCE)

C

O

M

P

A

R

E

Source A

Source D

Source C

Source B

SEDIMENT SOURCE FINGERPRINTING

Sediment

Properties

Source Material

Properties

Composite Fingerprints

Testing Source Discrimination

Multicomponent Mixing Models – goodness of fit

Particle size effects (Selectivity)

Incorporating Uncertainty into the final result

POTENTIAL SEDIMENT SOURCES

• Channel banks / subsurface sources

• Surface soil from cultivated areas

• Surface soil from pasture areas

• Surface soil from woodland areas

Time-Integrating trap samplers

Suspended Sediment Sources in the Wye and Hampshire Avon Catchments, UK

The Wye

The Hampshire Avon

Potential fingerprint property

H-value P-value

Al 17.622* 0.001*

C 40.143* 0.000*

Ca 1.815 0.612

Cd 37.662* 0.000*

Co 1.031 0.794

Cr 25.788* 0.000* 137Cs 52.171* 0.000*

Cu 22.305* 0.000*

Fe 9.542* 0.023*

K 37.820* 0.000*

LOI500 59.472* 0.000*

LOI850 0.891 0.828

Mg 12.692* 0.005*

Mn 39.571* 0.000*

N 60.952* 0.000*

Na 22.822* 0.000*

Ni 10.000* 0.019*

IP 12.696* 0.005*

OP 7.450 0.059

TP 14.067* 0.003*

Pb 10.446* 0.015* 210Pb 18.172* 0.000* 226Ra 8.228* 0.042*

Sr 2.302 0.512

Zn 11.183* 0.011*

Step Fingerprint property selected

% Source type samples

classified correctly

1 137

Cs 55.7

2 Mn 67.9

3 Cd 75.5

4 Ni 81.1

5 IP 84.0

6 Cr 86.8

7 N 86.8

8 Al 87.7

9 Cu 89.6

10 K 90.6

11 LOI500 93.4

Statistical Testing of Source Discrimination

UK Sediment Source

Tracing Studies

70-75

25-30

HOW MUCH?

WHAT IS IT?

WHAT HAVE WE LEARNT?

WHERE DOES IT COME FROM?

WHERE DOES IT GO? (Short and Longer-term Storage)

Bed Sediment Storage

Measurement using a re-suspension technique

Channel Storage of Fine Sediment in English Groundwater Fed River Systems

(LOCAR)

• Three rivers

• Periodic measurements at selected sampling points – estimate Δ storage

• Extrapolate to entire catchment

Comparing Δ Storage with Catchment

Suspended Sediment Yields

River Load Δ Storage Δ St./Load

(t year-1) (t year-1) (%)

River Pang 500 400 80

River Lambourn 1080 300 28

River Tern 1750 1200 69

FLOODPLAIN STORAGE

Quantifying Floodplain Sediment

Storage

MEAN ANNUAL FLOODPLAIN SEDIMENTATION RATES ESTIMATED FOR

REPRESENTATIVE SITES ON 21 BRITISH RIVERS USING Cs-137 AND

EXCESS Pb-210 MEASUREMENTS

River and location

1 River Ouse near York

2 River Vyrnwy near Llanymynech

3 River Severn near Atcham

4 River Wye near Preston on Wye

5 River Severn near Tewkesbury

6 Warwickshire Avon near Pershore

7 River Usk near Usk

8 Bristol Avon near Langley Burrell

9 River Thames near Dorchester

10 River Torridge near Great Torrington

11 River Taw near Barnstaple

12 River Tone near Bradford on Tone

13 River Exe near Stoke Canon

14 River Culm near Silverton

15 River Axe near Colyton

16 Dorset Stour near Spetisbury

17 River Rother near Fittleworth

18 River Arun near Billingshurst

19 River Adur near Partridge Green

20 River Medway near Penshurst

21 River Start near Slapton

Past 33 years

0.95

0.21

1.22

0.15

0.86

0.46

0.88

0.39

0.51

0.70

0.60

0.56

0.45

0.35

0.51

0.04

0.11

0.39

0.51

0.15

0.51

Sedimentation rate (g cm-2 year-1) Past 100 years

1.04

0.46

1.42

0.28

0.95

0.66

1.01

0.33

0.64

0.93

0.65

0.43

0.42

0.32

0.40

0.04

0.14

0.48

0.71

0.23

0.45

Trend*

Stable

Decrease

Decrease

Decrease

Stable

Decrease

Decrease

Increase

Decrease

Decrease

Stable

Increase

Stable

Stable

Increase

Stable

Decrease

Decrease

Decrease

Decrease

Increase

*Increases and decreases are identified as cases where recent (33 year) sedimentation rates deviate by more than ±10% from the 100 year value

Mean

0.50 g cm-2 year Mean

0.57 g cm-2 year

River Ouse, Yorkshire, UK

River Conveyance Loss

Swale 31%

Ure 34%

Nidd 50%

Total Ouse 40%

Wharfe 49%

Floodplain Conveyance Loss?

River Ouse

Yorkshire

Sediment Flux

HOW MUCH?

WHAT IS IT?

WHAT HAVE WE LEARNT?

WHERE DOES IT COME FROM?

WHERE DOES IT GO?

(STORAGE)

THE SEDIMENT BUDGET

AS A MANAGEMENT TOOL

The Pang & Lambourn Catchments (LOCAR)

Catchment Sediment Budgets

The Lambourn at Hunts Green

(166 km2 ) (234 km2 )

Key to Management

SEDIMENT QUANTITY

SEDIMENT QUALITY

SEDIMENT SOURCE

SEDIMENT STORAGE

FLUVIAL GEOMORPHOLOGY

ENVIRONMENTAL ISSUES

CATCHMENT MANAGEMENT

1970

THE PRESENT

Acknowledgements

THANK YOU