Surface Salinity: animate_entrance_surf_salB4

This movie shows the limited flushing of the lakes by ocean water through The Entrance. Ocean water (red, high salinity [saltiness]) comes into the lake twice per day on high tides and lake water leaves with the out-flowing tide. Surface salinity changes greatly at The Entrance with the tides but not in other parts of the lake.

During this month of very low rainfall, the lake salinity barely changes which shows that flushing is quite slow. In fact, only 1% of the total lake volume is flushed each day.

The salt water from The Entrance seems to disappear at the edge of the tidal delta. The next movie shows you where the salty water goes.

Salinity Iso-Surface: entrance_movieB2

This movie shows the flow of incoming ocean water in relation to the topography (shape of the sea floor) of The Entrance and nearby regions of the lake (land is dark red, lake depth is blue). The movie only shows the region of Tuggerah Lake between The Entrance, Wyong River and Ourimbah Creek.

The tide comes in and out of The Entrance in each second of movie time.

The Entrance area is a broad shallow plateau that is cut by three slightly deeper channels. The shallow entrance region is bounded by a relatively steep drop off into the deeper waters of Tuggerah Lake. The salty water from The Entrance is heavier than the "less salty" lake water. The salty water falls over the shelf edge into deeper waters on the inflowing tide and spreads as a thin layer along the bottom of the lake. Wind-driven currents cause the bottom layer to slop around and mix with the lake water above.

Flushing Material from Tuggerah Lakes: animate_C2009B7

This movie shows how pollutants from the catchment are retained in the lakes for a long time. Initially the concentration of pollutant is set to 1 (red) throughout the lakes and zero in the ocean (blue). Catchment discharge (eg stormwater) is given a pollutant concentration of 1. The movie simulates the dilution of the pollutant over time.

The 8-month period (April-November 2009) was characterized by relatively low catchment discharge (low rainfall). The catchment discharge was effectively zero for 2 months and the pollutant was hardly diluted by ocean water during this time, except near The Entrance.

This simulation shows what happens to a pollutant in the lake during a low rainfall period. Under wet climatic conditions, the catchment discharge would make concentrations higher as more pollutants are washed into the lake with each rainfall event!

Wrack Simulation in Tuggerah Lakes: wrack_animationA5

This movie shows a computer simulation of floating seagrass leaves ("wrack") being washed around the Lakes and accumulating against the shoreline or amidst nearshore seagrass meadows. The two plots have different scales; concentrations of floating wrack (left plot) are much lower than for the accumulated wrack. A wind vector (yellow arrow) shows the speed and direction of the wind. In this example, surface currents are simulated over several weeks using a three-dimensional hydrodynamic model and a wave model. Seagrass leaves are broken free from the bottom due to agitation by waves. As you can see, most of the wrack is trapped near its origin, but some is swept across the lake.

Information about videos in HTML5

I have confirmed that the above videos can be viewed using Note, people using Internet Explorer 9 can add software to support webm. I will download this software to do the appropriate test shortly.

Of the various video formats, it seems that webm is particularly compact. Hopefully, all web browsers will eventually support webm. Present projects by Google Inc are making webm work within Internet Explorer and Apples Safari.