Sediment Research on the Rivers Bandon and Owenabue, Ireland

Dr. J. Harrington

Cork Institute of Technology

Presented at SILTFLUX Workshop, UCD

28th October 2014

Outline of Presentation

• Introduction

• Study Catchments and Characteristics

• Data Collection Programme

• Sediment Fluxes and Yields

• Storm Based Events

• Nutrient Transport

Introduction

• Sediment Research has been underway at Cork Institute of Technology for the past decade

• The focus has been on the nearby Rivers Bandon and Owenabue

• The research work has studied suspended sediment concentrations and loadings based on a field sampling and continuous turbidity monitoring programme

Study Catchments

Study Catchments – Land Use

1

2

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8

9

Forestry Quarry Urban Area

Rain Gauge Hydrometric Station

Study Catchments - Soils

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Bandon Catchment

Owenabue Catchment

Acid Brown Earths, Brown Podzolics Lithosols, Regosols Surface /ground water gleys Peaty gleys Podzols Variable Blanket Peats Made/Built Land Water/Lake (including reservoirs)

River Bandon Catchment

Parameter Detail Parameter Detail

River Details: Station:

Catchment Bandon Station Catchment

Area 424 km-2

Catchment Area 608 km-2 Length to Station 52.55 km

River Length 77 km Station Type Data Logger & Turbidity Probe

Altitude at source 320m OD Body Responsible Office of Public Works & CIT

Average Slope 4.16 m km-1 (from OS maps) Co-ordinates 51.74N, -8.68W

Average Flow Rate 15 m³ s-1 Staff Gauge Zero 6.94 m O.D.

Annual Average Rainfall 1207 mm/year (Cork Airport) Records Available 1975 - Date

Land Use Tillage, pasture, forestry, urban

Turbidity Data

2010 - date

River Bandon – Summary Data

River Bandon Catchment – Some Information

• Relatively large sized catchment in an Irish context (608 km2)

• Primarily agricultural 94% (tillage and pasture)

• Prone to flooding

• Distinguished by engineered works on stretches

• Features a number of special areas of conservation (SAC)

• Exhibits a range of levels of water quality

• Features both suspended and bed load transport

• Dredging undertaken through the town of Bandon (post-2010)

• River improvement works proposed for 2015 and 2016

• River discharge to Kinsale Estuary

River Bandon – Data Collection

Manual Sampling Programme

At the Curranure Hydrometric Station

Samples tested for:

Suspended Sediment Concentration (SSC) since 2004 and turbidity since 2007

Range of Nutrient Parameters

- Nov. 2009 to 2012

Additional suspended sediment and bed sediment samples have been collected at a number of locations along the river since April 2012.

Automatic sediment sampler installed in September 2014

Continuous Monitoring Programme

Turbidity data at 15 minute resolution

(February 2010 – date)

Campbell Scientific OBS 3+ probe

River stage/flow rate data at 15 minute resolution

River Owenabue Catchment

Parameter Detail Parameter Detail

River Details: Station:

Sub-Catchment (of the

Lee) Owenabue

Station Catchment

Area 103 km-2

Sub-Catchment Area 105 km-2 Length to Station 19.05 km

River Length 22.71 km Station Type Data Logger & Turbidity Probe

Altitude at source 110m OD Body Responsible Office of Public Works & CIT

Average Slope 6.34 m km-1 (from OS maps) Co-ordinates 51.82N, -8.42W

Average Flow Rate 2.294 m³ s-1 Staff Gauge Zero 11.29 m O.D.

Annual Average Rainfall 1207 mm/year (Cork Airport) Water Level Records

Available 1956 - Date

Land Use Tillage, pasture, forestry, urban Turbidity Data 2009 - Date

River Owenabue – Summary Data

River Owenabue – Some Information

• A smaller scale catchment (105 km2)

• Primarily agricultural (97%) - tillage and pasture

• Moderate to poor water quality status

• Catchment hill slopes are quite steep with quick response to rainfall

• River discharge to Cork Harbour via town of Carrigaline

River Owenabue – Data Collection

Q = 13.6 m3 s-1 (Peak Flow of Event)

SSC = 123 mg L-1 (4 hours after peak)

Manual Sampling Programme At the Ballea Bridge Upper Station Samples tested for: Suspended Sediment Concentration (SSC) since 2004 and turbidity since 2007 - to 2012 Range of Nutrient Parameters - 2007 to 2012 Continuous Monitoring Programme Turbidity data at 15 minute resolution (Sept. 2009 – date) Campbell Scientific OBS 3+ probe River stage/flow rate data at 15 minute resolution

SSC – Turbidity Relationships

1

R² = 0.9646

0

20

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120

140

0 20 40 60 80

SS

C (

mg

Lˉ¹

)

Turbidity (NTU)

(a) R² = 0.8709

0

100

200

300

400

500

600

700

0 100 200 300 400 500S

SC

(m

g L

ˉ¹)

Turbidity (NTU)

(b)

Sediment Flux Analysis

Ls= 𝑸𝒕 𝑺𝑺𝑪𝒕 dtt2t1

where

Ls = load over a time period (t2 - t1),

Qt = flow rate at time t

SSCt = suspended sediment concentration at time t

Ref: Harrington, S.T., Harrington, J.R., ‘An assessment of the suspended sediment rating curve approach for load estimation on the Rivers Bandon and Owenabue, Ireland’, Geomorphology 185 (2013) 27-38.

Monthly Suspended Sediment Fluxes

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Susp

ende

d Se

dim

ent L

oad

(ton

nes)

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1200

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1800

Susp

en

de

d S

ed

ime

nt

Load

(to

nn

es)

Suspended Sediment Flux and Yield

SS Flux (tonnes/year) SS Yield (tonnes/ha/year)

Feb. ’10 –

Feb. 11 Feb. ’10 –

Feb. 12 Feb. ’10 – Feb.

11 Feb. ’10 –

Feb. 12

River Bandon 6012 4128 0.142 0.097

SS Flux (tonnes/year) SS Yield (tonnes/ha/year)

Sept. ’09 –

Sept. 10 Sept. ’09 –

Sept. 10 Sept. ’09 –

Sept. 11 Sept. ’09 –

Sept. 11

River Owenabue

2636 1822 0.256 0.177

Storm Based Events

• Disproportionate delivery of suspended sediment flux on infrequent high flow events

• Approximately 75% of the suspended sediment load is transported on flow rates above the 10% exceedance level.

• Storm events identified and analysed

• Suspended sediment rating curves analysed (high degree of variability found in the Q-SSC relationship)

Storm Based Events

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Ave

rage

Dai

ly S

SF (

ton

ne

s)

Ave

rage

Dai

ly D

isch

arge

(1

06

m³)

Avg. Daily Q

Avg. Daily SSF

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Ave

rage

Dai

ly S

SF (

ton

ne

s)

Ave

rage

Dai

ly D

isch

arge

(1

06

m³)

Avg. Daily Q

Avg. Daily SSF

Storm Based Events – River Bandon

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140

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SSC

(m

g Lˉ

¹)

Flo

w R

ate

(m

³ sˉ

¹)Event 6

Flow Rate

SSC

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140

0 20 40 60 80 100 120

SSC

(m

g Lˉ

¹)

Flow Rate (m³ sˉ¹)

Event 6Peak 1 CL

Peak 2 CL

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0

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SSC

(m

g Lˉ

¹)

Flo

w R

ate

(m

³ sˉ

¹)

Event 8Flow RateSSC

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25

0 10 20 30 40 50 60SS

C (

mg

Lˉ¹)

Flow Rate (m³ sˉ¹)

Event 8Peak 1 CL

Peak 2 CL

Peak 3 CL

Storm Based Events – River Owenabue

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SSC

(m

g Lˉ

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Flo

w R

ate

(m

³ sˉ

¹)Event 3

Flow RateSSC

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350

0 5 10 15 20

SSC

(m

g Lˉ

¹)

Flow Rate (m³ sˉ¹)

Event 3Peak 1 CL

Peak 2 CL

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SSC

(m

g Lˉ

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Flo

w R

ate

(m

³ sˉ

¹)

Event 12Flow RateSSC

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0 2 4 6 8 10 12 14

SSC

(m

g Lˉ

¹)

Flow Rate (m³ sˉ¹)

Event 12Peak 1 CL

Nutrient Transport

• Dissolved and particulate nutrient behaviour investigated

• Wide variability in nutrient concentrations

• Discharge and SSC influence concentrations

• Turbidity found to be a suitable surrogate for some phosphorous parameters (TP and PP) but nitrogen parameters were not well correlated

Ref: Harrington, S. T. and Harrington, J. R.: Dissolved and particulate nutrient transport dynamics of a small Irish catchment: the River Owenabue, Hydrol. Earth Syst. Sci., 18, 2191-2200, doi:10.5194/hess-18-2191-2014, 2014.

Acknowledgements

• Funding Sources

IOTI Technological Sector Research Programme

Office of Public Works

Byrne Looby PHMcCarthy

• River Data

Office of Public Works

EPA

• Postgraduate Research Team

Sean Harrington, James Hickey, John Gamble, Kevin Motherway,

John Clancy