Flood Mapping is a Great Idea....Right?

Global Information System (GIS) mapping has grown in popularity in conjunction with the technological world. GIS mapping is now commonly used within Local Authorities as a means to accurate track significant event and/or public assets on a larger scale.

All the Local Authorities within the Southeast QLD region rely on GIS mapping to determine potential risks as a result of a particular flood event. They do this by incorporating flood mapping into the development application process in the form of a ‘flood level overlay’, which is essentially the flood mapping data overlayed on a map of the region. This allows Local Authorities assessing the Development Application to determine if it would be adversely affected by a particular flood event.

In theory, this is a great way to highlight a potential risk before the development has commenced; however the information in the flood level overlay is only as accurate as the information that is entered into it. Many flood level overlays can be triggered by postcode regions, suburb names and/or elevation levels of the terrain. In many cases (70% - 80%) this information is enough to highlight an area that may be subject to flooding. However the remaining cases (20% - 30%) are generally flagged as being within the flood level overlay, but will not be affected by expected flood levels. This can be due to environmental conditions unable to be determined by the data (i.e. A high-set house, natural terrain formations, retaining structures) or due to inaccurate flood mapping data (i.e. pixelated flood mapping data, inaccurate rainfall data.

Figure 1: An Example of Pixelated Data

Figure 1: An Example of Pixelated Data

Flood mapping, as a technology, is in its infancy. As with any other technology, usage and time will ‘sort out the bugs’ so that, sometime down the track, the technology will be excellent. Dealing with a technology in its infancy requires that users appreciate its current limitations. Technologists inherently understand this. Non-technologists need to be aware, and understand the effects of those limitations in their specific case. Additional Local Authority fees throughout the development and the development’s end sale price can be affected by inaccurate Flood Mapping Data.

J.C. Engineers are regularly engaged by developers to provide Flood Assessment Reports and/or professional advice to support their development. Whether your development has been incorrectly triggered in a flood level overlay or it has been correctly triggered and you are seeking advice on control measures for your development, give our team a call to discuss your needs.