Cover Letter, DA Form 1, Plans, Owners Consent, Coastal Environment Assessment · OPW21/0049

Noosa Spit Coastal Protection Environmental Assessment                                                      17
Potential Impacts




5.3     Disturbance of acid sulfate soils
        Acid sulfate soil testing was undertaken of sand in proximity to Dogs Beach prior to the 2013 dredging
        campaign (Coffey, 2011). This identified that Actual Acid Sulfate Soils (AASS) and Potential Acid
        Sulfate Soils) were present in some boreholes at lower depths (i.e. From -3.5m AHD) at very low
        levels. As dredge material will only be taken to -3.0m AHD, it is considered unlikely that any AASS
        or PASS will be encountered. Nevertheless, testing of material will be undertaken during dredging.
        If acidic material is encountered, dredging of that area will cease and sand will be taken from
        elsewhere.

5.4     Changes to Coastal Processes
        The material that is dredged is being placed nearby therefore it is not removing the sediment from
        this system, and is acting to stabilise an eroding shoreline.

        The modelled impacts as part of the SEMP for this project design include:

        • A minor reduction (~0.1 to 0.2m/s) in peak flood current magnitude within the Dog Beach channel.
          This is balanced by increases to current magnitude at the edges and over the crest of each sand
          plug. This suggests that over the time the plugs will be gradually modified by the flood tide currents
            with sediment eroded from the crest and likely deposited in the adjacent channel area. This could
            be described as a gradual ‘smoothing’ of the constructed sand plugs.

        • During peak ebb conditions the impact to currents is widespread with a significant reduction in
          magnitude at the Dog Beach channel and shoreline, and an increase in magnitude through the
            central channel.

5.5     Noise and Interference from Physical Presence of
        Plant/Personnel
        It has been identified dredging activities will generate a level of activity and disturbance (e.g. vessel
        movements, machinery noise and human movement). Noosa River is already subject to frequent
        disturbance from recreational users.

        Dredging will form an intermittent source of underwater noise. Such noise may be generated by
        mechanical means (vessels engines, propellers and other machinery), or by water movements on
        the vessel hull. While dredging machinery-generated noise is normally unlikely to occur at levels
        which cause acute hearing damage to marine fauna, it may cause subtle but possibly more
        widespread increases to ambient noise levels. This may include for example, masking of biologically
        important sounds (e.g. vocalisations), which may lead to some temporary avoidance of an area by
        marine species whilst machinery is in operation.

        Specific knowledge on the relative contributions of various noise sources to ambient noise levels is
        limited, as is information on the effects of noise on marine megafauna in an Australian context.
        Marine megafauna will avoid areas where noise levels are high. However, the zone of noise impact
        is expected to be small. Additionally, the project area and surrounds already receive recreational
        boat traffic and the dredging is not likely to significantly increase background underwater noise levels
        already experienced. Nevertheless, vessel staff will be trained in spotting marine fauna, and
        observations zones will be put in place during dredging (Refer to Section 6).

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