In this issue

 

Welcome

†† - Whatís to Come

 

 

BCC Flood Policy

†† - Trafficable Access

 

 

BCC Flood Mapping

†† - Updates

 

 

Frequently Asked Questions

-  Mitigating Existing Flooding Problem

 

 

Wrap Up

†† - See you next month

 

 

Visit our website:

www.stormw.com.au 

 

 

Phone:

07 3398 4992

 

Welcome

Hello everyone and welcome to the August edition of ďKeep Things FlowingĒ, the monthly newsletter presented by Storm Water Consulting.

In this monthís 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 arenít 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 youíre 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 1970ís 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. Iíve provided the link below.

http://cityplan2014maps.brisbane.qld.gov.au/CityPlan/

For this example letís 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 1970ís 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 thereís 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 Councilís 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 Councilís 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 donít hesitate to contact our office.

As always, Keep Things Flowing!

The Storm Team