Welcome
Hello
everyone and welcome to the August edition of “Keep Things
Flowing”, the monthly newsletter presented by Storm Water
Consulting.
In this
month’s edition we review and discuss the issue of flood free
trafficable access within Brisbane City Council, we provide the
latest update about flood mapping within Brisbane City Council and
we answer another frequently asked question.
BCC Flood Policy
In our July
newsletter we brought you an update that Brisbane City Council were
tightening up on allowing development to proceed on properties that
could not provide flood free trafficable access. Over the past
month this has been the dominant topic of discussion in our office.
We have seen development applications refused, information requests
been issued and numerous development sites sterilised due to the
recent policy enforcement.
The trafficable
access issue relates to Performance Outcomes 11 and 17 of the Flood
Overlay Code. It must be demonstrated that access to a development
site can be provided during a defined flood event. This applies to
overland flow, creek/waterway and Brisbane River flood events. If
trafficable access cannot be provided for the site, preparing a
Flood Emergency Management Plan may be an appropriate means of
addressing the performance outcome solutions.
A Flood
Emergency Management Plan provides a step by step guide to
management and evacuation procedures before, during and following a
flood event. Our experience with the Council thus far has seen that
these plans are generally acceptable when the site is subject to
Brisbane River flooding. Overland flow and creek/waterway flood
events aren’t as well received. This is usually because there is a
lot more warning time for a Brisbane River flood event and
residents/patrons of a property are able to evacuate well before
the flood event occurs. Overland flow and creek/waterway flood
events may only have a couple of hours of warning time and Council
are wary that evacuation may not occur depending on the time and
location of the flood event.
If you’re
looking at a new development site that is subject to flood water,
we would be pleased to provide you with some information about
flood free trafficable access. Please contact our office and we can
assist you.
BCC Flood Mapping
Last week
Lord Mayor Graham Quirk released information that five new creek
catchment studies have been completed and the new flood information
would be used to update the current City Plan flood mapping for
Brisbane.
The new
flood mapping impacts 4500 blocks of land, with 742 allotments to
receive a higher flood risk than the current data and 3738
allotments to receive a lower flood risk than the current data. The
flood data will become available to the public on September 9th.
Property owners affected by the new flood data will be contacted by
mail to inform them of the new changes.
FAQ
Question:
I live in a
home that was built in the 1970’s and we have always had an issue
with water entering my property from the street during and after a
heavy rainfall event. The water enters the ground floor of my home.
What can I do to prevent water from entering my home/property?
Should Council be responsible for fixing the problem? Surely they
can provide larger stormwater pipes to take the water?
Answer:
To determine
what the likely issues are, I first identify whether the property
is located in a Flood Planning Area (assuming the property is
located within BCC) using the interactive mapping website. I’ve
provided the link below.
http://cityplan2014maps.brisbane.qld.gov.au/CityPlan/
For this
example let’s assume the property is located within an overland
flow flood planning area. This means that during/following a heavy
rainfall event, when the stormwater pipes are full, runoff from the
upstream catchment flows across the lowest ground elevation, which
happens to be through the your property. The dwelling was
constructed in the 1970’s well before any sort of detailed mapping
or flooding information was available for the property. The
dwelling design was therefore unlikely to account for any overland
flow inundation. Unfortunately as the dwelling is established
there’s not a lot of mitigation works that could be undertaken
without a significant cost. Non-invasive works that could be
undertaken might include:
·
The
installation of field inlet pits and pipes to redirect flows around
the dwelling;
·
Earthworks
to redirect overland flow around the dwelling;
·
Utilising
water resistant material for the ground level walls;
·
Changing
the use of the ground level to minimise the damage during an
inundation event.
Some of the
more costly and invasive mitigation measures could include raising
or relocating the dwelling. It is not recommended to undertake any
mitigation works without the advice from an experienced stormwater
engineer. Works that create an adverse impact on neighbouring
properties could lead to civil action. We would be pleased to
provide you with advice about which mitigation options would best
suit your property.
Although the
water comes from Council’s road, the Council is not responsible for
fixing the issue. Council do provide stormwater drainage relief for
most areas however the cost associated with upgrading relief
drainage has to be spread across the whole precinct and maintaining
a budget means that Council prioritise the drainage relief works. Increasing
the size of the existing stormwater pipes could also lead to
stormwater issues on properties downstream, where the water
discharges from the pipes. Upgrading stormwater drainage is a
costly and heavily planned process. Planned stormwater upgrades
(for the future) can be viewed on Council’s Cityplan.
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
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