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

sschmieg@bechtel.com