6. Noosa River DMP Ver0 (Combined)

1 Introduction

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1.1 Purpose of Dredging
Noosa Shire Council (Council) propose to dredge two locations within the Noosa River for beach
nourishment purposes:

•       Noosa River Spit at Dog Beach (spit)
•       Adjacent to the Noosa River between Doonella Lake and Weyba Creek (river).

Noosa Spit
The Noosa Spit at Dog Beach is narrowing and is at risk of a breakthrough, primarily driven by channel
migration processes. Works completed in 2013 have only stabilised the western extent of Dog Beach.
The rate of shoreline recession through the middle section has increased and the channel adjacent to
Dog Beach is now commonly used by recreational and commercial vessels. Shoreline recession is
impacting the social and recreational values attributed to the area. Importantly, this beach also forms
part of an artificially constructed river training/coastal defence strategy that protects property in Noosa
Sound and the back of Hastings Street.

Dredging at the Noosa Spit is required to provide material for nourishment at the adjacent Dog Beach.
The importance of maintaining The Spit and avoiding a breakthrough is primarily related to protecting
existing development within Noosa Sound and the back of Hastings Street. The consequence of a
breakthrough includes:

•       Reduced attenuation of the ocean tide and increases to peak high tide water levels in the lower
        Noosa River. This reduces the freeboard for waterfront development and therefore increases the
        likelihood of flooding driven by coastal and/or fluvial processes.
•       Rapid and unpredictable morphological change following a breakthrough and further loss of coastal
        land and open space that shelters existing development.
A Shoreline Erosion Management Plan (SEMP) was developed to quantify the combined dynamics of
the river entrance and Noosa Main Beach investigate impacts of various river mouth alignments,
simulate the impacts of a breakthrough event, and propose erosion mitigation options for Dog Beach
(BMT, 2019).

A number of design options were investigated as part of the SEMP; however it was determined that the
preferred design involved placing sand plugs at either end of Dog Beach. This involves using a small
cutter suction dredge and slurry pipeline to relocate sand from the adjacent Noosa River estuary to the
two locations. Approximately 85,000m3 of sand would be needed to form the two plugs and nourish the
shoreline.

Over 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.

This will relieve erosion pressure at the Dog Beach shoreline and will promote the development of a
central channel. The project will restore and maintain the existing recreational beach and redirect boat
traffic away from the Dog Beach Channel, providing a safer environment for swimmers.




A10342 | 002                                           2                                   01 December 2021