Muddy implications for Ballina?

The big kicker in the CSIRO flood report for Ballina is the trade-off. A new outlet to the sea at Broadwater would reduce flooding. There is no doubt about that and we know that the river did just that in 1890.

At the river it was a mile wide and at the sea it was 400 feet wide according to the newspaper at the time. It closed up again within two months.

If a channel is constructed, to keep it open would require sand pumping just like on the Tweed. That’s $10,000 per day just for electricity but absolutely doable. But, here’s the rub. The channel would drop the tidal exchange at Ballina to about half what it is now.

Anyone who goes over to Mobbs Bay will know about the mud that has accumulated just upstream of where the boats shelter. In fact, you can even look on Google Earth and compare the colours. It is mud and it does come halfway up you shins if you try to walk in it.

The reason it is there is because the water velocity is lower than the main river. In dry times Ballina does not see much water coming down the river. It is the tides going in and out that provide the velocity.

Boundary Creek

The proposed new outlet is near where the tidal exchange stops. The tide goes all the way up to Lismore of course but the actual limit of exchange of water is near Boundary Creek.

If there is a channel at Boundary Creek the water at Wardell will go in and out via that opening, not via Ballina. The tidal velocity at Ballina will become about half what it is now.

Lower tidal velocity means more fine sediment drops to the bottom. In other words, what we see in Mobbs Bay now will be what we see at the sailing club and along the dog beach.

Is it worth it? Do we reduce the chance of flooding and put up with mud on our river beaches? This is a question only each of us can answer. We know our own priorities.