When there is too much water, the flow capacity of creeks or rivers (known as waterways) become overwhelmed and burst their banks, flooding areas which are not normally under water. This is called riverine or main channel flooding.
An example of riverine type flooding occurred along the Ovens River in 1993 as illustrated in the photography below:
In urban centres, many concrete lined urban stormwater drains were formerly creeks and they can also flood in this way. An example of a concrete lined creek is shown below where its capacity is almost reached.
Riverine flooding is a natural and necessary process. It creates a problem for people when the water enters buildings, damages infrastructure or cuts roads. Despite the negative impact caused by floods they are part of nature. Floodwaters replenish and support wetland ecosystems, and replenish agricultural land following prolonged periods of drought. Refer to Floods and the Environment on this website for further reading.
The size of the flood, how far it spreads and how long it stays up will depend on how much rain has fallen, how big an area is draining into the creek or river, how steep the creek or river is and how flat the land is on either side of the creek or river.
The shorter and steeper the creek or river the smaller the flood and the quicker it will go up and down. In the mountainous parts of Victoria floods can come and go in one or two days while in the north of the state where the land is very flat the water can sit around for weeks, even months. In small urban catchments flooding might only last a few hours.
In many of the larger catchments the Bureau of Meteorology is able to use rainfall and stream flow data to forecast flood rises and issue specific flood warnings for locations along rivers.