Poster Australian Marine Sciences Association 2022

Seagrass Wrack Transport and Fate: A Case Study of Berkeley Vale, Tuggerah Lake. (#472)

Shivanesh Rao 1 , Rebecca Swanson 1 , Angus Ferguson 1
  1. Water Wetlands and Coastal Sciences, Science Economics Insights, Department of Planning and Environment, NSW Govt, Sydney, NSW, Australia

The shoreline along Berkeley Vale in the southern basin of Tuggerah Lake is a known area of black ooze accumulation and poor water quality. Preliminary studies found the stormwater treatment zones along the foreshore were highly degraded zones containing high concentrations of dissolved inorganic nutrients and a significant source of groundwater discharge. These factors contributed to the sustained seagrass growth and decay leading to sea wrack and finally black ooze accumulation. This seagrass barrier, 100 meters offshore, also attenuates the current flow strength in the nearshore region, increasing the residence times. During warmer months, the frequent north-easterlies compound the problem further by increasing the seagrass breakage and drift towards the Berkeley Vale shoreline.

A wind-forced hydrodynamic model is developed to examine the characteristics of the offshore seagrass barrier and its role in the flushing of the nearshore region. The model is verified against surface drifters (drogues) and ADCP observations. The model is used to examine possible scenarios (such as channels through seagrass barrier) that can improve the nearshore flushing during different wind directions and lake water levels.