Mr Ross Hardie1
1Alluvium, Cremorne, Australia
The Merricks Creek estuary was subject to a period of unpleasant hydrogen sulfide (rotten egg gas) odour, fish kills and decreasing aquatic recreation opportunities. This study was undertaken to identify the processes that led to these issues, sorting through the history of the estuary and the diversity of opinions presented by an active and engaged community.
Through a series of investigations, including a review of an unsolved murder mystery, the hydrogen sulphide was found to be associated with the decomposition of organic matter in the presence of sea water, in a low oxygen environment, creating a black ooze. The dominant source of the organic matter, feeding the odour production, was identified to be sea grass brought into the estuary through tidal action. However, the reason behind the sea grass accumulation in the estuary was more complex. The investigations revealed the Merricks Creek estuary to be on the margin of two estuary types i.e. wave dominated estuary and tide dominated estuary. Recent (2011/12) construction of a rock revetment wall to protect adjoining properties from estuary scour was identified to have shifted the estuary from a wave dominated estuary, to a tide dominated estuary, and as a consequence reduced the natural closure events at the estuary mouth, increasing the sea grass input to, and loading in, the estuary.
The paper explores these issues and the difficult decisions required to address the management of the Merricks Creek estuary.
Ross is a founding director of Alluvium and responsible for the assessment, design and review of waterway management programs and estuaries projects throughout Australia and South East Asia. Ross specialises in working with clients and stakeholders to develop agreed objectives, and understanding of the processes that impact on these objectives and the development of programs to achieve agreed water and waterway management outcomes.