protecting mangroves during site development using integrated design and land improvement practices
DESCRIPTION
Presented by: Sara SchmiegTRANSCRIPT
Sara Schmieg, Environmental Engineer
International Conference of Women
Engineers and Scientists
Protecting Mangroves During
Site Development Using
Integrated Design and Land
Improvement Practices
CIVIL
GOVERNMENT SERVICES
MINING & METALS
OIL, GAS & CHEMICALS
POWER
The Challenges
I. Coastal regions of Queensland, Australia have a tropical climate with a thriving ecology and biodiversity dependent on mangroves
II. Acid sulfate soils are common in coastal mudflat zones of Queensland
III. Erosion of the acid sulfate soils causes the surrounding water and soils to become acidic
IV. Maintaining the biodiversity requires preventing erosion of the acid sulfate soils and preserving the coastal mangroves
The Solution
Site Development
– Erosion control
– Managing acid sulfate soils
Site Hydrology
– Estimating volumetric flow rate of runoff
Site Ecology
– Protecting mangroves
“The exposure of acid sulfate soils
to oxygen (e.g. by drainage,
excavation or filling) results in
production of sulfuric acid and toxic
quantities of aluminium and other
heavy metals…the acid corrodes
concrete and steel infrastructure
and, together with the metal
contaminants, can kill or damage
fish, other aquatic organisms,
native vegetation and crops.”
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2FeS2 (pyrite) + 7O2 + 2H2O 2Fe+2 + 4SO4-2 + 4H+
Site Development
Queensland State Planning Policy 2/02
Site Development
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• Careful consideration is taken during planning and design phases to protect mudflats and mangrove areas (preserve ecosystems)
• Site development eliminated or minimized in areas with acid sulfate soils
• Disturbed acid sulfate soil is treated and contained on site
• Grading site in manner to not disrupt natural flow channels
Design outfalls for site drainage in areas with natural
channels
Site Hydrology
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• Grading site in manner to not disrupt natural flow channels
• Design and plan for appropriate Annual Recurrence Interval (ARI)
Reviewed low tide conditions for 100 yr flood
• Design outfall(s) capacity to handle increased flow
• Prevent disruption and erosion of acid sulfate soils
Q =
𝐀 𝐑𝟐/𝟑𝐒𝟏/𝟐
𝐧
Site Ecology
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• Characterize the mangroves to understand the impact they have on site flows
Identify parameters to determine mangrove roughness or
Manning’s n
• Estimate site flow velocities for assessing erosion potential
• Protect and preserve mangroves and biodiversity of the coastal region
n = 𝐀 𝐑𝟐/𝟑𝐒𝟏/𝟐
𝐐
Identify Mangrove Parameters
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Five parameters were considered:
• Vegetation species and maturity
• Vegetation density and volumetric occupancy
• Vegetation effective length and flow depth
• Reynolds number and flow velocity
• Vegetation drag and roughness factor
Vegetation Species and Maturity
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Sources: • Husrin, S., and Oumeraci, H. 2009. Parameterization of coastal forest
vegetation and hydraulic resistance coefficients for tsunami modeling. • Husrin, S., Strusinska, A., and Oumeraci, H. 2012. Global and local processes
of tsunami attenuation by mangrove forests-laboratory test results.
Vegetation Density and Volumetric Occupancy
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Sources: • Mazda, Y. Wolanski, E.J., King, B.A., Sase, A., Ohtsuka, D. and Magi, M. 1997. Drag force due to vegetation in mangrove swamps. • Latief, H., and Hadi, S. (2006). “The role of forests and trees in protecting coastal areas against tsunamis,” Proceedings of Regional Technical
Workshop. Khao Lak, Thailand.
Vegetation Effective Length and Flow Depth
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Source: McIvor et al., 2012. Reduction of wind and swell waves by mangroves. NCP Report 2012-01.
Reynolds Number and Drag
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Source: Mazda, Y. Wolanski, E.J., King, B.A., Sase, A., Ohtsuka, D. and Magi, M. 1997. Drag fore due to vegetation in mangrove swamps.
Conclusions
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• Identifying and evaluating the mangrove parameters allowed for the site outfall velocities to be determined
• The outfalls were designed to control and manage site flows to protect mangroves and prevent erosion of soils
This meant increasing riprap sizing of the outfall
channel and changing outfall channel lengths to
decrease velocities
• Manning’s n or mangrove roughness was estimated to be between n = 0.05-0.2 (depending on mangrove parameters)
References
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Husrin, S., and Oumeraci, H. 2009. Parameterization of coastal forest vegetation
and hydraulic resistance coefficients for tsunami modeling.
Husrin, S., Strusinska, A., and Oumeraci, H. 2012. Global and local processes of
tsunami attenuation by mangrove forests-laboratory test results.
Latief, H., and Hadi, S. (2006). “The role of forests and trees in protecting coastal
areas against tsunamis,” Proceedings of Regional Technical Workshop. Khao Lak,
Thailand.
Mazda, Y. Wolanski, E.J., King, B.A., Sase, A., Ohtsuka, D. and Magi, M. 1997.
Drag fore due to vegetation in mangrove swamps.
Mazda, Y. Wolanski, E.J., King, B.A., Sase, A., Ohtsuka, D. and Magi, M. 1997.
Drag fore due to vegetation in mangrove swamps.
McIvor et al., 2012. Reduction of wind and swell waves by mangroves. NCP Report
2012-01.
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Contact Information:
Sara Schmieg
Bechtel National Inc.
Geotechnical and Hydraulic Engineering Services