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.
City Council’s Flood Overlay Code refers to hydraulic hazard in
Items 7, 8, 11, 14 & 17. But what is hydraulic hazard?
City Council’s Flood Planning Scheme Policy states:
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”.
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.
Planning Scheme Policy defines three different flooding conditions
which are considered unsafe as listed below:
velocity-depth product for publicly accessible areas, pathways,
driveways, parking or private open space, or where the risk to life
is reasonably foreseeable;
velocity-depth product for public roads, drains and flow paths
through private property or communal open space areas;
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.
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
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
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
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.
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.
Keep Things Flowing!
The Storm Team