In this issue



   - In this Edition



Hydraulic Hazard

-  What is it?



Frequently Asked Question

-  Subsoil Drainage Issue



Wrap Up

   - See you next month



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Hello everyone and welcome to 2017! We hope you had a well-deserved break over the Christmas period and are fresh and ready for the new year!

This is the January edition of “Keep Things Flowing”, the monthly newsletter presented by Storm Water Consulting.

Coming up in this month’s newsletter, we explain “hydraulic hazard” and we answer another frequently asked question.


Hydraulic Hazard

Brisbane City Council’s Flood Overlay Code refers to hydraulic hazard in Items 7, 8, 11, 14 & 17. But what is hydraulic hazard?

Brisbane City Council’s Flood Planning Scheme Policy states:

“Hydraulic hazard is defined as the engineering classification of flood hazard with respect to the velocity-depth product and maximum flood depth to define safe and unsafe conditions with respect to people, vehicles and structures”.

The velocity–depth product is the number resulting from multiplying the depth of flow by the velocity of flow. Example: Overland flow across a property is 0.4m deep and flowing at a velocity of 1.5m/s. The velocity-depth product is 0.4m x 1.5m/s = 0.6m2/s.

The Flood Planning Scheme Policy defines three different flooding conditions which are considered unsafe as listed below:

·         >0.4m2/s velocity-depth product for publicly accessible areas, pathways, driveways, parking or private open space, or where the risk to life is reasonably foreseeable;

·         >0.6m2/s velocity-depth product for public roads, drains and flow paths through private property or communal open space areas;

·         >600mm flood depth at any velocity.

It should be noted that unsafe flooding conditions differ to the conditions listed above when relating to properties with vulnerable uses.

Brisbane City Council’s interactive mapping provides different flood planning areas for the Brisbane River and Creeks and Waterways. The flood planning areas are specified based on various degrees of flood hazard. The flood hazard ratings can be viewed using the following links.

Interactive Mapping

Flood Hazard Ratings

The overland flow flood planning areas are not split into different categories relating to flood hazard. As hydraulic engineers we often see that properties are sterilised from development due to the unsafe hydraulic hazard at the access to the property. If you require assistance with identifying whether a property can achieve a safe hydraulic hazard at the access location please contact our office.


Frequently Asked Question


My property is on a hill and the land has been cut away to provide a level area for my slab on ground house. I’ve noticed that one of the walls on the side of the house facing the excavated areas is damp all the time, in particular following rainfall events. What can I do to fix the issue?


Without knowing much more information about the location of the property it is hard to determine what the cause of the damp wall is. Contacting our office to determine whether the dwelling is located within an overland flow path or flood prone area is a good start. For this example let’s assume that the dwelling is not in a flood prone area. It would appear that the next likely cause of the damage is from the soil in contact with the exterior wall of the dwelling. Water soaking into the ground during a rainfall event drains through the soil and eventually comes into contact with the dwelling. We would recommend consulting a geotechnical engineer for further assistance with the problem. 


Wrap Up

We hope you enjoyed this edition of Keep Things Flowing. Feedback on articles presented is always welcomed and for further information on any of the articles presented please don’t hesitate to contact our office.

As always, Keep Things Flowing!

The Storm Team