6. Noosa River DMP Ver0 (Combined)

                                                                Noosa River - Sediment Sampling Report
                                            BMT (OFFICIAL)




1 Introduction

  ̶
1.1 Background
Existing dredge operations have been in place since 2006 and were designed around the erosion
hotspots of the time. These initial sites are no longer problem sites due to the mobility of sand bars and
the river channel, however other sites along the river have become problematic.

The new dredge permits for the Noosa River foreshore are intended to allow Council flexibility to adapt
the annual dredge program to target areas that are currently eroding, and therefore allow council to
protect existing assets and maintain the foreshore as needed. There is no intention to increase dredge
volumes overall in this area, but to apply the nourishment volume in the most effective areas as needed
at the time of the campaign.

Previous sediment investigations carried out by Soil Surveys Engineering Pty Ltd adjacent to Gympie
Terrace and Weyba Road indicated that material (to 4m depth) along this stretch of the river consisted
of fine to medium grain alluvial sand with some coarse shell. No actual acid sulfate sols were present.
Potential acid sulfate soils were present however Acid Neutralising Capacity (ANC) testing indicated
that the material had sufficient buffering capacity to neutralise any acid formation.

1.2 Sampling and Analysis Rationale
The assessment of sediment contamination for land-based re-use was undertaken in accordance with
relevant requirements set out in the National Environment Protection Measures (NEPM). NEPM
investigation levels are based on the Health-based Investigation Levels (HILs) for public open space
(HIL – C).

As some material will also be placed below the Highest Astronomical Tide (HAT), samples were
compared against screening levels set out in the National Assessment Guidelines for Dredging (NAGD)
(Commonwealth of Australia, 2009). Furthermore, as NAGD represent good practice for sampling and
assessment of marine sediments, these guidelines informed the study design (i.e. site selection,
sampling effort, derivation of contaminant list) and sampling and analysis methodology.

Other guidelines are referred to including the National Acid sulfate soils guidance: Guidelines for the
dredging of acid sulfate soil sediments and associated dredge spoil management (Simpson et al. 2018).

1.3 Proposed Dredging
Council proposes to undertake an ‘adaptive’ approach to nourishment within the proposed dredge and
placement area. Previous campaigns have focussed on erosion hotspots, however these are no longer
problematic due to mobility of sand bars and the river channel. Indicative cross sections as per previous
dredge design are shown in Table 1.1 for reference. For future campaigns, works of a similar design
and extent will be undertaken within the proposed dredge and placement extent, to protect existing
assets and maintain the foreshore as needed.

The proposed seaward extent of the dredge area has been extended to -2.5m (AHD), or up to 50m
from the adjacent Fish Habitat Area – Management Area A (whichever comes first).

On an annual basis, typically a total of 5000 - 7000 m3 will be dredged and placed within the proposed
dredge area. The placement areas typically range from the Lowest Astronomical Tide (LAT) (-0.42m
AHD) to + 1m AHD. Dredge material will be taken from areas below LAT (-0.42m AHD) to a maximum
dredge depth of -2.5m AHD (or as stated above to within 50m of the adjacent FHA).


A10342 | 005 | 01                                   5                                          14 April 2022