You may be correct, I certainly have no solid data to back my hypothesis.
But it does seem to me that less water goes into the drains on a rainy day.
It's not a big lagoon, and everything that goes into the tanks would have
gone to the wetland previously (council regulations, all drains must go to
the street side of the house). So if each house has a 10k litre tank (most
would have far more than this), that's hundreds of thousands of litres going
astray each rain event. Not much in catchment terms, but for a small
wetland it is possibly significant. Particularly when people can't water
their gardens any other way, so the tanks always need topping up.
On Mon, Aug 25, 2008 at 2:46 PM, Paul Burcher <>wrote:
> Dave et al
> The amount of rainfall "interrupted"" by water tanks in relation to the
> area covered by other hard surfaces (especially roads) that concentrate
> flows to local creeks would be bugger all. At least some of the tank water
> is being returned to the catchment in a moderating way through groundwater
> if used in gardens. Also very few tanks are large enough to capture all the
> water that falls on a roof so a lot ends up as stormwater anyway.
> I suspect the decline in the lagoon in Brisbane had nothing to do with
> tanks but was just a lag effect from evaporation or lack of groundwater