Big Swamp Rehabilitation Project: Hydrologic Study Will Glamore, PhD - - PowerPoint PPT Presentation

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Big Swamp Rehabilitation Project: Hydrologic Study Will Glamore, PhD - - PowerPoint PPT Presentation

May 30, 2023 230 likes •866 views

Big Swamp Rehabilitation Project: Hydrologic Study Will Glamore, PhD Water Research Laboratory, School of Civil and Environmental Engineering University of New South Wales Introduction Definitions: Big Swamp Pipeclay Canal

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Big Swamp Rehabilitation Project: Hydrologic Study

Will Glamore, PhD

Water Research Laboratory, School of Civil and Environmental Engineering University of New South Wales

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Introduction

Definitions:

  • Big Swamp
  • Pipeclay Canal
  • Cattai Creek

Technical Terms:

  • Hydrology
  • Hydrodynamics
  • Groundwater
  • Hydraulic Head
  • Acidity (pH)
  • Modelling
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Introduction

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Logic of Study and Report

  • 1. How did we get here?
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Conceptual Understanding

  • Manning River catchment

is 8,420 km2

  • Big Swamp-Pipeclay

catchment is 113 km2 or ~1% of total.

  • Average annual rainfall at

Moorland gauge is 1,436 mm but seasonal.

  • ~2000 hectares below 0 m

AHD (mean sea tide)

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Conceptual Understanding

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Conceptual Understanding

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Conceptual Understanding

Drainage History

  • 1899 Big Swamp Drainage

Scheme Approved

  • 1905 completed
  • Designed to pass upland

catchment directly to Cattai Creek

  • Big Swamp drainage was

secondary issue

  • Expanded in 1960s and 90s.
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Conceptual Understanding

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Tide, Drains and Acid Sulfate Soils

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DRY Conditions

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Flood Conditions

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Draining Conditions

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Conceptual into Actual What happens at Big Swamp?

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Field Data Collection

June Sept Feb

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Field Data Collection Program

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Field Data Collection Program

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Elevation Data Check

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Cross-Sections and Culverts

  • 33 Cross-sections taken

from upstream of Pipeclay canal to bridge near Harrington.

  • Plus every known

culvert/structure

  • All based on high precision

RTK-GPS positioning.

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Field Data Collection Program

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New Instruments Installed

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Cattai Creek Logger

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Upper Pipeclay Canal Logger

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RESULTS: Dry Conditions

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Wet Conditions- Flooding on Big Swamp

  • Levee Bank at 1.8m AHD
  • 1% ARI = 3.1 m AHD
  • A 100 year event is

required to flood Big Swamp over the levee banks from local catchment runoff

  • Levee banks overtop from

back-flooding of Manning River at ~10 yr event.

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Flooding

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Flood Event: March 1978 (1.3% AEP)

2000 4000 6000 8000 10000 12000 10 20 30 40 50 60 70 80 Flow (m3/s) Time (hrs) Killawarra Hydrograph: March 1978 Flood Pipeclay Creek Hydrograph: March 1978 Flood

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Flood Event: May 1977 (15% AEP)

1000 2000 3000 4000 5000 6000 20 40 60 80 100 120 Flow (m3/s) Time (hrs) Killawarra Hydrograph: May 1977 Flood Pipeclay Creek Hydrograph: May 1977 Flood

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>200 mm of rainfall was recorded at the site in 3 days in late Jan 2013

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Wet Conditions: Jan-Feb 2013

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On-ground Impacts

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Remediation Options What can we do?

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Priority Assessment

  • Developed Method to

determine which areas are highest priority and should be remediated.

  • Based on:
  • Groundwater/Soil
  • Acidity
  • Surface water
  • Total discharge
  • Areas 1/7 and 0/6 were

highest priority

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Restoration Options

  • Objective is to remediate

acid problem by:

  • Dilution
  • Neutralisation
  • Reduction
  • Aim is to:
  • Improve water quality
  • Reduce acid ponding
  • Improve ecology
  • Decrease acid discharges

from soil

  • On-ground works:
  • Encourage neutralisation at

source by removing floodgates and levee sections

  • Prevent further acid creation

by infilling drains and keeping wet

  • Reduce acid transport by

removing floodgates and filling drains

  • Encourage reduction of

existing acid

  • Ensure no impact to flooding

and limit stagnant water.

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Computer Model

  • Computer model

developed using the field data to:

  • Assess conceptual model
  • Simulate existing scenaro
  • Modify model to test:
  • No floodgates anywhere
  • Selected restoration
  • ptions
  • Dry versus wet scenarios
  • Plan for on-ground works
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Computer Model

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Model Results

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Existing Site Drainage

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Scenario: No Floodgates

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S-W Remediation Options

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S-E Remediation Option

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Restoration Options

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Summary

  • Restoring S-W and S-E

areas will remove large high priority acid zones.

  • The S-E zone will not be

fully restored as it still requires drainage.

  • The remediation works will

not impact flooding elsewhere.

  • Any overland inundation

will be shallow and intermittent.

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Recommendations

  • On-ground works
  • Floodgates
  • Levees
  • Drain modification and

construction

  • Land grading
  • Future Monitoring
  • Continuous sampling
  • Before-After sampling
  • Photo points
  • Proceed with Additional

Restoration Sites

  • Proceed with Plan of

Management

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Acknowledgments

  • Greater Taree City Council
  • Mr Dave Hopper
  • Various field support staff
  • Wetland Care Australia
  • Various stakeholders and

volunteers

  • Landholders for Access to

Monitoring Stations