IPWEA SWQ Conference presentation:
Dude, Where’s My Yard? – A Forensic Assessment of Flood Model Results
Being able to undertake a detailed analysis of flood model results is an arrow in the quiver of every talented floodplain engineer. But how do you begin to analyse model results when you already know the answer? Following the 2011 flood event west of Brisbane, a series of waterway crossings were upgraded within the moderately large local catchment of an unnamed creek. In 2013, a rural property in close proximity to these upgraded crossings was devastated by flooding associated with ex-Tropical Cyclone Oswald. Although no significant property damage was incurred, a large portion of viable agricultural land was eroded. Given the close proximity of the property to the crossings, the landowner alleged that these works were responsible for a change in flood behaviour and, subsequently, resulted or at least contributed to the erosion of a significant volume of land.
Prior to the 2011 flood event, the unnamed creek was traversed in numerous locations by small causeways. Although suitable in low flow conditions, these causeways proved problematic following minor and severe flood events with significant damage to several causeways occurring as a result of the 2011 flood event. Widespread improvement and modification of these structures were undertaken with a standard box culvert arrangement adopted at three crossings in the immediate vicinity of the property.
What does a ‘flood model’ have to do with it?
This paper provides insight into the forensic analyses undertaken within this specific reach of the unnamed creek. Of particular interest was the impact blockage of culverts had on flow behaviour and how altered flow paths resulted in a fundamental shift in flood behaviour during the 2013 flood event. Given that numerous iterations reflecting blockage did not readily result in a fundamental change in water level, an assessment of change in velocity and bed shear stress was undertaken. The findings of this assessment indicated that not only did blockage of the culverts result in a redirection of flows but the change in bed shear stress and velocity contributed to significant channel avulsion adjacent to the property and the damaged agricultural land.
Andrew Thompson will be presenting this paper on Thursday 7th March at IPWEA SWQ Branch Conference.
If you would like to know more about this presentation, please call Andrew on 07 3105 1460.