Jurien Bay Boat Harbour
With on-going data collection methods and trialing practical options, DoT is currently using computer modelling, which simulates the floating seagrass and seaweed (wrack) transported into the harbour from Jurien Bay.
The collection of oceanographic data as part of ongoing investigations into environmental issues in the local area also continues.
During winter 2018, a trial saw two separate deployments of a bubble curtain:
- Across the harbour entrance in an effort to exclude wrack from the harbour.
- Inside the harbour in an effort to improve oxygen levels in the water.
Results from the deployments will be compiled and provided to DoT for review.
Have your say: Jurien Bay Boat Harbour maintenance dredging campaigns
The Department of Transport (DoT) is seeking feedback from the community and users of Jurien Bay Boat Harbour in relation to an offshore placement area for future maintenance dredging campaigns.
Sand and seaweed from the offshore marine environment are transported into Jurien Bay Boat Harbour via natural coastal processes and accumulate within the entrance channel and basin. Maintenance dredging is the process undertaken to manage and redistribute accumulated marine sand and seaweed in order to:
- restore navigable depths for vessels;
- provide ongoing access and operational use of the harbour
- remove decomposing seaweed and maintain harbour water quality; and,
- restore natural tidal flushing.
Jurien Bay Boat Harbour maintenance dredging campaigns are completed approximately every two years and previously material generated has been placed in the dune system north of the harbour. DoT is seeking a long-term sustainable solution with the material now proposed to be returned to the offshore marine environment into a natural seabed depression.
The proposed offshore area is preferred due to its close proximity to the harbour, and because it has fewer marine flora and fauna compared with the surrounding areas. Water quality and marine flora and fauna around the proposed placement area will be closely managed to ensure there are no long-term impacts.
Have your say
DoT is working closely with Department of Biodiversity, Conservation and Attractions to obtain the required environmental approvals for the proposed campaigns and is committed to minimising its environmental impact.
DoT values community input in project planning and feedback on the proposed offshore material placement area is being sought until 4 September 2019. Feedback can be provided via the contact details below.
|Street address||Postal address||Telephone||Fax|
|(08) 9435 7604|
|Jurien Bay Boat Harbour maintenance dredging offshore placement||Kb|
The results from the bubble curtain trial will allow DoT to assess the effectiveness of this method as the collection of oceanographic data continues.
In summer 2016-17, dredging removed 62,000m3 of material from the harbour entrance channel and sand trap areas, and seaward of the northern breakwater.
About the project
The Department of Transport (DoT) is working to develop and implement strategies to address ongoing environmental issues in the Jurien Bay Boat Harbour.
Figure 1: Jurien Bay Boat Harbour bubble curtain trial location.
As part of the bubble curtain trial in winter 2018, n May 2018, DoT installed and anchored a line of tubing to the seafloor between the two breakwaters. With compressed air pumped through the tubing, bubbles escape through a series of holes and rise to the surface. The trial operated during storm events, with the expectation the wall of streaming bubbles would generate currents that re-direct floating wrack, preventing it from floating into the harbour during northerly conditions.
A temporary Notice to Mariners 2018-76 was in place for the duration of the trial.
History of the project
Figure 2 (above): Jurien Bay Boat Harbour.
Jurien Bay Boat Harbour opened in 1988 and the facility has a history of problematic seagrass wrack and sand accumulation, contributing to water quality issues. Previous initiatives to address these issues have included weed trawling and maintenance dredging within the harbour.
A wrack trawling exercise in late 2013 was successful in addressing navigation problems and subsequently water quality improved. A further round of pre-emptive wrack trawling of the harbour entrance was completed in July 2014.
DoT completed sand excavation works in September 2014, to remove over 8000 m³ sand from inside the harbour.
Maintenance dredging programs were undertaken in 2015-16 and 2016-17 to deliver an improved harbour environment and to restore navigational depths in the entrance channel. Over the two campaigns approximately 140,000m3 of sand and wrack were removed from the harbour and adjacent Jurien Bay waters.
Figure 3 (right): Jurien Bay.
Investigative study and data collection
Recent data collection and environmental studies
The Department of Transport undertook extensive data collection in 2014-17. The data set included:
- A directional wave rider buoy deployed in Jurien Bay at a depth of 42 m to measure off shore wave parameters including wave height, period and direction.
- Three acoustic wave and current devices (AWACs) were placed outside the harbour to measure inshore waves and currents. AWACs record current speed and direction at different levels of the water column and also record wave parameters.
- A current meter (Aquadopp) was located in the harbour entrance to measure current speed and direction at different levels in the water column.
- Three pressure sensors were mounted in the harbour basin close to the harbour bed to measure water levels at one second intervals. The data assisted investigations into long-period wave condition in the harbour and is also used to validate numerical modelling.
- A tide gauge is installed in the harbour and measures water levels every five minutes.
- Regular aerial photography of the harbour and adjacent beaches.
- Fixed point telemetered photography (from 2017).
Wind direction and speed
- An anemometer (wind data station) was been installed to better understand weather associated with seagrass and sand transport at the harbour.
- Regular hydrographic surveys were undertaken to monitor seabed changes.
In addition to the data set collection a university study into the impact of wrack degradation on the water quality of Jurien Bay Boat Harbour was undertaken in 2016 and 2017. More is now known about wrack transport into the harbour including when the largest masses of wrack arrive, its composition, the impact of wrack age on decomposition rates and the subsequent demand for the consumption of dissolved oxygen from the water column. All these factors impact on the environmental health of the harbour.
Current data collection
DoT actively monitors events and changes in the harbour and undertakes and continues its data collection program. Tide and offshore wave data monitoring equipment continue to provide information on local conditions including wind, waves, ocean currents and water levels. Current instrumentation includes:
- Wave buoy deployed offshore in Jurien Bay.
- Two AWACs in the nearshore marine environment.
- Current meter in the nearshore marine environment.
- Tide gauge measures water levels in the harbour.
- Water quality monitoring in the harbour.
- Hydrographic surveys in the Jurien Bay Boat Harbour and adjacent, nearshore areas.
- Site photographic records from fixed time lapse cameras and regular aerial photography.
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Jurien Bay Boat Harbour project related links
- Jurien Bay boating facilities
- Safety, navigation and data - coast cams
|Media statement 07/05/2018: Bubble curtain trial at Jurien Bay Boat Harbour|
|06/05/2014: High-tech monitoring gear for Jurien Boat Harbour|