Nearshore Flushing in Tuggerah Lakes

(Brian Sanderson 2013, bxs@eastlink.ca)

Nearshore flushing in the southern portion of Tuggerah Lake

The next three movies show results from the high-resolution nested model in the southern section of Tuggerah Lake. (The model coordinate system has been rotated by 30 degrees.) Initially the tracer concentration is set 1 for surface-layer cells that are adjacent the shoreline, zero elsewhere. The movies show the evolving concentrations in the surface-layer (top 0.3 m) under the three most common wind conditions.
Simulation of the dispersion of material from adjacent the coastline under the action of a 5 m/s wind blowing from 40 degrees True.
  • Seagrass drag substantially reduces the rate of nearshore flushing at most locations where seagrass extends into the surface layer.
  • Chittaway Bay has less seagrass in shallow waters and the nearshore surface layer is relatively well-flushed compared to Tuggerah Bay.
  • Additionally blocking wind stress where seagrass reaches the surface causes little change from the case with seagrass drag.
  • Even without seagrass drag, nearshore flushing is poor at: south of Chittaway Point, at the saltmarsh in Tuggerah Bay (near Tuggerah Wharf Ruins), and south of Wyong Point.
Simulation of the flushing of material from adjacent the coastline under the action of a 5 m/s wind blowing from 190 degrees True.
  • Seagrass drag substantially reduces the rate of nearshore flushing at most locations where seagrass extends into the surface layer.
  • Chittaway Bay has little seagrass extending into the surface layer and the nearshore is relatively well-flushed compared to Tuggerah Bay.
  • Additionally blocking wind stress where seagrass reaches the surface causes little change from the case with seagrass drag.
  • Even without seagrass drag, nearshore flushing is poor adjacent lee shores.
Simulation of the flushing of material from adjacent the coastline under the action of a 2.5 m/s wind blowing from 290 degrees True.
  • Without seagrass drag, nearshore flushing is very poor adjacent lee shores.
  • Seagrass drag substantially reduces flushing at windward shorelines.
  • Additionally blocking wind stress where seagrass reaches the surface causes little change from the case with seagrass drag.

Nearshore flushing in the northern part of Budgewoi Lake.

The next three movies show results from the high-resolution nested model in the northern section of Budgewoi Lake. The initial concentration is 1 for surface-layer cells that are adjacent the shoreline, zero elsewhere. (The model coordinate system has been rotated by 30 degrees.)
Simulation of flushing of material from adjacent the coastline under the action of a 5 m/s wind blowing from 40 degrees True.
  • Even without seagrass, the nearshore is poorly flushed in the vicinity of the Golf Course.
  • Seagrass drag substantially reduces flushing near the Golf Course and at other locations.
  • Additionally blocking wind stress where seagrass reaches the surface causes little change from the case with seagrass drag.
Simulation of the flushing of material from adjacent the coastline under the action of a 5 m/s wind blowing from 190 degrees True.
  • Even without seagrass, the nearshore is poorly flushed at several locations, including in the vicinity of the Golf Course.
  • Seagrass drag substantially reduces flushing near the Golf Course and at some other locations.
  • Surprisingly, seagrass drag acts to increase flushing in the small embayments either side of Green Point.
  • Additionally blocking wind stress where seagrass reaches the surface causes little change from the case with seagrass drag.
Simulation of the flushing of material from adjacent the coastline under the action of a 2.5 m/s wind blowing from 290 degrees True.
  • Even without seagrass, the nearshore is poorly flushed at several locations, including in the vicinity of the Golf Course.
  • Seagrass drag substantially reduces flushing near the Golf Course and at most other locations.
  • Surprisingly, seagrass drag acts to increase nearshore flushing in the southwest corner of Munmorah Lake.
  • Additionally blocking wind stress where seagrass reaches the surface causes little change from the case with seagrass drag.