That's the frightening statistic which has led the Corangamite Catchment Management Authority to make works on Ballarat's Yarrowee River and Canadian Creek a priority.

Studies conducted since the early 1990s have cited one of the major problems being confluence of waters from the Canadian Creek into the Yarrowee River, which meet just south of the CBD.

A Corangamite CMA floodplain strategy report released last year shows hundreds of properties over 365ha in Ballarat are being affected by flooding of the Yarrowee catchment every year, at an estimated annual cost of $1.5 million.

"The Yarrowee River, Gnarr Creek and Canadian Creek through Ballarat are of major concern due to the restriction of their effective flow area by channelisation and building development ...

"As a result, over 900 properties would be affected by flooding from a major flood event in Ballarat," the report says.

But experts say 350 is a more reasonable number of properties that could be affected.

A new study is now a high priority for the CMA to again look at possible flooding impacts.

Hopefully this will be completed before the end of the year.

Ballarat has for a long time been susceptible to flooding, the most recent being in December 1992, when a downpour caused havoc in many CBD streets.

While significant, that event was not at levels expected of a one-in-a-hundred year event.

Ballarat Mayor David Vendy believes there have not been enough works aimed at alleviating the risk.

"If it (one in a 100-year flood) did happen we haven't done a great deal of works," Cr Vendy said.

"Because we are catching more water, I think we would be in trouble if it did happen.

"Even if the 1992 flood was a one in 50-year flood, if we had a one in a 100-year flood I would say a lot of people's floor levels would be tested."

Ballarat City Council parks and environment manager Hedley Thomson said a number of studies had been conducted into the Yarrowee catchment during the past 20 years.

Mr Thomson said there was great awareness of the potential problems since the floods on New Year's Eve, 1992, when large parts of the central business district was under substantial amounts of water.

Water retarding basins on the Gnarr Creek and Yarrowee River have been established during the past 10 years, but as yet none have been constructed on the Canadian Creek.

Council has received State and Federal Government funding for a wetlands project and retarding basin along the Canadian Creek. It is one part of a potential residential subdivision which will soon go before council.

At a recent meeting to discuss the subdivision and creek works, consultant Tim Fletcher told residents that 350 houses in the central business district could be affected and that lives, too, could be endangered in event of a severe flood.

Corangamite Catchment Management Authority floodplain and drainage manager Tony Jones said the Yarrowee catchment was the authority's major priority.

Mr Jones said another study would be conducted this year which would look at the potential impacts of a substantial flood.

In regards to the Yarrowee Creek/Canadian Creek problems, Corangamite CMA has placed a high priority on:

* Conducting works on a retarding basin near Kinnersly Av, Canadian;

* Reviewing flood mapping for the Canadian Creek and Yarrowee River;

* Providing a flood preparedness plan for the Canadian, Gnarr, Redan and Yarrowee tributaries.