Shifting sands

[Big Shed]

Just been reading an article (http://www.theage.com.au/news/national/dredge-to-raise-bay-level-garrett/2008/01/10/1199554804555.html) on the channel dredging in Port Phillip Bay.

In it Peter Garrett, our rockstar turned Environment (but not ALL the Environment!) Minister , claims that this dredging will raise the water level in the Bay by up to 3.5cm.

I know I am only a simple chemist, but I find that hard to believe. Say you have an aquarium and you shift sand on the bottom from the middle to the sides to make it deeper in the middle, does this raise the water level in the aquarium?:no:

Am I missing something here?

[Pusser]

The article talks about the high tide level not the volume. If the mouth of the bay is deepened then more water can rush into the bay at high tide thereby increasing the amount of water and rasing the high tide level. It is like putting water into the aquarium with a bigger pipe for a given time. More will rush out as the tide turns as well so you could get lower low tides and a more powerful rip.

[AlexS]

Don't know the hydraulics of Port Phillip Bay, but under some circumstances it is possible that changes can cause amplification, where the tidal range inside the waterway is greater than that outside. Or it could be as simple as lessening the damping, as described by Pusser.