Merricks Creek is located on the Mornington Peninsula approximately 70 km south-east from Melbourne. The estuary itself is separated from Westernport Bay by a well-vegetated frontal dune (sand barrier). The sand barrier is a site of regional geomorphic significance as it is rare in Westernport Bay and provides a clear example of a multiple barrier system.
Alluvium was engaged by Melbourne Water to undertake an assessment of issues and options in the Merricks Creek Estuary. This investigation sought to identify the processes that had led to the odour production and the other issues of concern, together with options that best address outcomes sought for the estuary by the community and stakeholders. Key to this work was to explore the physical, chemical and biological estuary processes and their relationships with both Westernport and upstream catchments, and to analyse, from a scientific and engineering perspective, the proposed options for odour remediation and advise on the potential for success.
We undertook a range of investigations to understand the physical processes aligned with the state of the estuary mouth. We assessed the catchment condition and biota and noted the sea grass accumulations and black sludge visible in some locations within the estuary. We considered the coastal patterns and concluded the difference between flood and ebb tide flows into Westernport Bay and the Coriolis effect combine to create a net eastward current drift along the Merricks Creek foreshore area.
The persistent odour at the Merricks Creek Estuary was identified as hydrogen sulfide (H2S) and it was concluded that the odour occurring at Merricks Creek Estuary was resulting from both tidal phases of the sulfate reduction process, including anoxic decomposition of contemporary organic material and associated release of H2S when inundated; and the release of legacy H2S and other gases when acid sulfate soils are exposed during low tide.