A two-stage decision support tool for restoring tidal flows to flood mitigation drains affected by acid sulfate soil: case study of Broughton Creek floodplain, New South Wales, Australia
William Glamore A C and Buddhima Indraratna BA Water Research Laboratory, University of New South Wales, NSW 2000, Australia.
B Division of Civil and Environmental Engineering, University of Wollongong, NSW 2522, Australia.
C Corresponding authour; email: W.Glamore@wrl.unsw.edu.au
Australian Journal of Soil Research 42(6) 639-648 https://doi.org/10.1071/SR03166
Submitted: 3 December 2003 Accepted: 16 March 2004 Published: 17 September 2004
Abstract
A 2-stage flood estimation and water quality decision support tool (DST) was developed, calibrated, and applied to a field site in south-eastern New South Wales (NSW) to simulate tidal restoration in a flood mitigation drain affected by acid sulfate soils leachate. The first stage of the DST employs a digital terrain map, geographic information tools, and measured water levels to calculate drain water overtopping due to tidal variations. Simulations using the GIS technique at the study site indicated that the primary drainage network can safely contain full tidal flushing (0.91 m AHD or a 58% increase), whereas at the same level the secondary drainage network overtops along relict drainage channels. The second stage of the DST simulates the change in drain water quality using an ion-specific program code written within the open interface PHREEQC program. The results from the water quality model were calibrated against laboratory titration tests. Drain water pH was shown to increase above 6.0, and soluble aluminium and iron concentrations decreased by 73% and 56%, respectively. The extent of water quality change is directly related to the ionic strength of the intruding water and the ion-specific reaction kinetics of aluminium, iron, and sulfate.
Additional keywords: acid sulfate soils, ion association model, saline intrusion, tidal restoration, water quality, acid buffering.
Acknowledgments
We thank the Shoalhaven City Council, Marcus Morgan, Annie Cannon, and local landholders for their support and technical assistance. Funding from the University of Wollongong and the Shoalhaven City Council is gratefully acknowledged.
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