Hall Contracting to dredge the Mooloolah river mouth

Maritime Safety Queensland recently contracted a local Sunshine Coast contractor, Hall Contracting, to clear a dangerous sandbar at the entrance to Mooloolaba Harbour.

According to Maritime Safety Queensland general manager Kell Dillon, Hall Contracting has been tasked to dredge the entrance in February 2022, as part of routine scheduled activity.

“One of Hall’s smaller dredges has been on stand-by in the Mooloolah river since February, but due to the severe weather it was too unsafe to use the vessel until now,” said Dillon.

Dillon also added that depending on weather and sea conditions, the larger dredger named Port Frederick could be brought up from Cabbage Tree Creek to Moreton Bay. If this happens the dredge will be used in conjunction with the smaller dredge to clear the bar.

“A bigger dredge requires deeper water in the first place, it’s more susceptible to damage because of the swell lifting the barge up and down and dropping it onto the sand and also the tidal windows in which you can work are narrower,” concluded Dillon.

The dredged sand will be pumped onto Mooloolaba Beach by the pipeline that runs under the beach. The pipeline was installed in 2013 along the eastern breakwater wall and runs across the channel anchored on the riverbed. This makes dredging more efficient with less impact on boaties accessing the harbour.

The Mooloolaba harbour and entrance training walls were built in the late 1960’s. Since that time, sand shoaling events have occurred regularly in the entrance channel.

Maintaining a safe navigable entrance here is crucial for all boaties. The main aim is to keep the entrance clear to a design depth of at least -2.5m Lowest Astronomical Tide (LAT) at all times.

During a shoaling event, sand accretes to form a shoal (like a sand bar). The shoal decreases the water depths making navigation more hazardous.

To improve safety, dredging removes the sand shoal by pumping the sand onto Mooloolaba Beach. The dredge stays in position and continues to remove sand until safe depths are reached. The 2020–2021 shoaling event required almost continuous dredging from September 2020 to November 2021.