A common term used when assessing river or creek flooding is “flood storage.” But what does it mean and when is it important?
Flood storage refers to the volume of stagnant, or very slow moving floodwater that spreads across low-lying areas during a flood event. It typically occurs when a river or creek breaks its banks and inundates the surrounding floodplain.
When the flood storage volume in an area is reduced, local flood levels usually rise. As an example, imagine a bathtub full of water, if you sit in it, you displace a certain volume of water and the water level in the bathtub rises. The same happens on a floodplain—remove storage space and water has to go somewhere else, typically upward and outward.
Most councils require flood storage on a development site to be maintained.
Suppose a development site lies in a flood storage area and Council mandates a flood-immune floor level. The developer has two choices:
If the site is filled, the lost flood storage volume must be compensated by excavating elsewhere on the property—so the amount of earth removed equals the volume displaced by fill.
A flood-storage area may also have other hydraulic roles, such as flow conveyance (carrying fast flowing water). Those functions can further restrict where and how you fill or excavate. In many cases the design must balance both storage and conveyance requirements to meet Council approval.
Whenever earthworks change the natural floodplain, you must replace lost flood storage—otherwise nearby flood levels can rise, increasing hazard and the risk of damages to neighbouring properties.
Ready to build smarter and safer? Talk to our flood-engineering team today and make sure your project keeps its flood storage—and your neighbours—out of harm’s way.
If you have any flood storage questions, Storm Water Consulting Pty Ltd can help assess your flood risk to develop a more timely development.
