Types of Flooding
During heavy rainfall flooding can occur in 2 ways:
1. Mainstream flooding where creeks can overflow, break their banks and flood nearby low-lying areas and properties. These flows may be several metres deep in the channels and relatively fast moving. This is also known as riverine or fluvial flooding.
2. Local overland flow where the capacity of stormwater pipes is exceeded and stormwater then flows aboveground following the low areas of the landscape. This is also known as flash or pluvial flooding
Flooding cannot be completely prevented. Flooding is a natural occurrence and will always be a possibility when large amounts of rain fall.
However, human activities often make floods worse and requires:
• additional infrastructure to reduce the impacts and risks of flooding by slowing the water down or stopping it reaching certain areas
• building in a way that makes space for water.
Infrastructure can be designed to reduce the impacts and risks of flooding by slowing the water down, stopping it reaching certain areas, or by building in a way that we make space for water.
Blacktown City has experienced several large floods in the past. The largest flood on record occurred in 1867 in the Hawkesbury Nepean River affecting areas such as Riverstone, Schofields, Marsden Park and Shanes Park. It was the equivalent of a 1 in 500 chance per year event.
The Blacktown local government area is divided into 5 distinct catchments:
1. Wianamatta - South Creek
2. Eastern Creek
3. Cattai Creek
4. Parramatta River
5. Prospect Reservoir.
As each catchment has different characteristics, the type and scale of flooding that occurs within them can vary.
Wianamatta - South Creek, Eastern Creek and Cattai Creek make up part of the greater Hawkesbury Nepean floodplain. Due to the specific characteristics of the Hawkesbury Nepean floodplain, flooding can also occur due to floodwaters ‘backing up’ from a narrowing of the Hawkesbury Nepean river between the Sackville Gorge and the Brooklyn Bridge.
The extent, depth and rate of rise of floodwaters within the Hawkesbury Nepean makes flooding a significant risk to the residents living in the floodplain.