Media Release - Unprecedented Flash Flood Event in Port Lincoln
- Media Release
Unprecedented Flash Flood Event in Port Lincoln
On Friday 31 January 2020 at approximately 2pm, Port Lincoln experienced an extreme rainfall event resulting in flash flooding throughout the entire city. The event was caused by a weather pattern that included a monsoonal trough extending from the Northern Territory that was picked up by a cold front passing through South Australia. The thunderstorm pattern was very isolated with many areas on the Eyre Peninsula recording little or no rain.
Port Lincoln experienced the brunt of this rainfall event. The information on the rainfall intensity and duration suggests that the majority of the rainfall occurred within a ½ hour to hour long period between 2 and 3pm. Additional showers were experienced through to approximately 4.30pm. Rainfalls of 50-60mm within this period were reported by numerous residents. The best available data suggests that approximately 60mm of rain was recorded within the hour and up to 75mm in 1.5 hours.
Rainfall intensities of this nature are very rare and impossible to forecast with warnings at best, available only 30 minutes in advance, if at all. Analysis of the anecdotal evidence on rainfall intensities recorded throughout the event suggests that the event experienced in Port Lincoln was in a 1 in 2000 Annual Exceedance Probability (AEP), that is less than a 1 in 2000 chance (or 0.05%) of the event occurring in any given year.
In comparison to the floods experienced in Liverpool St in 2015 (estimated as a 2% annual exceedance probability, 50-year average recurrence interval) and 2016 (estimated as a 1% annual exceedance probability, 100-year average recurrence interval).
The newly constructed stormwater pump station system in Eyre Street has a design capacity approximately equivalent to the 2% annual exceedance probability (50-year average recurrence interval), before flood levels exceed any floor levels.
Clearly this is an unprecedented event and many locals have stated that they have never witnessed flooding to such an extent or depths in Port Lincoln.
Port Lincoln Stormwater System
Council’s stormwater network and pumping system capacities were exceeded across the city. However, all pump systems were operational during the event, including the new Eyre Street pump station. The combined operation of the Liverpool Street Pump Station and Eyre Street Pump Station resulted in the Liverpool St catchment discharging volumes greater than the 2015 and 2016 flooding events. This minimised the impacts of the flood substantially.
Based on the catchment area of approximately 880 hectares draining to the main Port Lincoln foreshore area, there was around 350ML of stormwater discharged to the sea (based on the rain recorded) or equivalent to around 140 Olympic swimming pools.
Data from this extreme event is still being collected and analysed to enable Council to determine the effectiveness of the response and what additional actions can be taken to improve systems and strategies. This information will be used to refine the newly constructed Eyre Street Pump Station to optimise performance for future rainfall events. However, it must be stressed that none of Council’s systems have been designed to cater for such an event as experienced on Friday. This is not a deficiency of the Council’s infrastructure rather the severity of the event is beyond current industry design standards.
Mr Stephen Rufus Chief Executive Officer said, “Council staff and local contractors, along with Emergency Services responded quickly and acted to restrict access to roads and respond to call outs for assistance. The assistance of neighbouring Councils was greatly appreciated”.
Community behaviour during flood events
During the event Council staff, emergency responders and local contractors were disappointed to see a small number of community members disregarding directions to avoid contact with floodwaters. There were properties within millimetres of inundation that were being impacted by bow waves generated by vehicles that continued to drive at pace through floodwaters. Floodwaters typically contain pollutants including pathogens from overflowing sewage systems. Unnecessary primary contact should not occur as there are serious potential health consequences. Council recommend that commercial trade by flooded premises should cease as soon as practical and members of the public are requested to stay out of floodwaters. Stormwater pit lids were lifting off through pressure and suction draughts created under floodwaters could result in serious accidents.
Health warnings, clean-up and recovery
As the event now moves towards the clean-up and recovery stage, Council urges all members of the community to remain vigilant in terms of health and hygiene.
Floodwater can be contaminated by sewage from overflowing sewers or septic systems. As a precaution, all items exposed to flood water including cars, clothing, food and other materials should be treated as contaminated.
Sandbags used during the flood should also be treated as contaminated as well as all other materials used during the clean-up such as mops and buckets. Where sandbags have been used, community members are advised to tip the sand from the bags onto their garden and then place the hessian bag in their waste bin as they will need to go to landfill.
Friday’s record storm event has also impacted the marine and beach environment.
The water quality in Boston and Proper Bays will be impacted by stormwater leaving discoloured and contaminated water and silt, especially around drain outfalls.
SA Health has advised that due to the unprecedented nature of this event people should not swim in discoloured or murky water and to avoid swimming after rain events for 72 hours. The water can contain germs that cause gastrointestinal illnesses. Please avoid contact with stormwater drainage outfalls until coastal rectification works can be undertaken, they are a safety hazard.
Council’s Environmental Health Officers will be visiting food and flood affected businesses over the coming days to emphasise the importance of hygiene practices after a flood event and to assist the community with any public health related queries.
Anyone that has suffered damage to their house or contents are encouraged to contact their insurance provider in the first instance.
If you need emergency flood assistance, call the SES on 132 500. For life-threatening emergencies, call Triple Zero (000). For information on what to do after a flood event visit https://www.ses.sa.gov.au/site/flood.jsp
Statistics on the number of flood affected properties and infrastructure assets are still being collected and collated.
All media enquiries to be directed to the undersigned on 8621 2325 or via email firstname.lastname@example.org.
Chief Executive Officer
Release Date: 3rd February 2020
Updated 4 February 2020 to correct SES information