Tributary Flood study for Puntei Creek Catchment

Comments are due by 5pm Wednesday 28 July. https://shape.lakemac.com.au/lake-tributary-flood-studies

The Puntei Creek Catchment is 1.52 km2, collecting rainfall and stormwater runoff from Kilaben Bay, Carey Bay, and Toronto. The upper-mid catchment is heavily vegetated and the creek crosses Jarrett St via a boxed-culvert, the lower catchment contains the commercial and residential properties, the creek flows into Lake Mac under Excelsior Pde at Carey Bay.

Of the eight catchments studied in the report, the average annual tangible flood damages for Puntei Creek were the second most costly with projected figures of $814,000/yr. This measure is used to estimate flood damages over a range of flood events and represents the equivalent average damages that would be experienced by the community on an annual basis, by taking into account the probability of a flood occurrence over the long term.

The Tributaries Flooding report states the residents at the bottom of Puntei Creek are highly vulnerable to sea level rise. In flood events Puntei Creek runoff will produce significant inundation across Excelsior Pde. In the mid-lower catchment there are a significant number of properties subject to flooding, overland flow will occur through properties on Jarrett Street between the creek and Oakhampton Ct when the capacity of the Jarrett Street culverts is exceeded. The commercial/industrial properties on Excelsior Pde that back onto the creek, which are low lying, will also experience relatively frequent overland flow inundation. Some of the residential properties in the lowest part of the catchment, bounded by Ambrose St., Excelsior Pde. and Laycock St. are below 1.5 m Annual Height Datum, and will be affected by both Lake Macquarie flooding and local catchment flooding and may no longer be habitable with a rise of more than 0.5 m of the average lake level.

This timely report is using historical data and as we are all too well aware the increasing development of the catchment is underway, reducing vegetation and increasing hard surfaces, resulting in more and faster runoff...and on top of that the compounding impacts of climate change make commenting on this report a high priority.

Comments from the report include;

• (p5) “Some communities around the lake edge are highly vulnerable to sea level rise, notably those residents situated at the bottom of Puntei Creek...”.
• (p19) “The road crest (Excelsior Pde) is very low-lying …It is likely that Puntei Creek runoff will produce significant inundation across the road, particularly if there are coincident elevated water levels in the Lake Macquarie waterway downstream. Some of the houses in the downstream part of this catchment have floor levels less than 1.5 m Annual Height Datum (AHD).”
• (p77-78) The catchment summary 
• ”Puntei Creek…in the mid- to lower-catchment there are a significant number of properties subject to flooding. 
• Overland flow will occur through properties on Jarrett Street between the creek and Oakhampton Ct when the capacity of the Jarrett Street culverts is exceeded, as the low point in the road crest is not aligned with the creek. Water that overtops the road will flow through these properties and return to the open grass swale further downstream.
• The commercial/industrial properties on Excelsior Pde that back onto the creek are low lying and will experience relatively frequent overland flow inundation, with above floor inundation likely in a 1% Annual Exceedance Probability (AEP) event.
• Some of the residential properties in the lowest part of the catchment, bounded by Ambrose St., Excelsior Pde. and Laycock St. are below 1.5 m AHD, and will be affected by both Lake Macquarie flooding and local catchment flooding. Some of these properties will be inundated above floor level more frequently than a 10% AEP event. Flood risks for these properties will be exacerbated even further by Sea Level Rise, and may no longer be habitable with a rise of more than 0.5 m of the average lake level.
• The Puntei Park Dog Exercise Area is subject to low hazard flooding in the 1% AEP, escalating to high hazard in the Probable Maximum Flooding (PMF). A combination of rising access and unpopularity for use during intense rain means risks to life are low.
• The Paradise Palms Caravan Park is subject to low hazard flooding (H3 and below) in a 1% AEP event, escalating to high hazard (H4) during a PMF event. Rising egress is available from most locations in the site, so evacuation on foot will be feasible for mobile occupants. Occupants with limited mobility will be vulnerable to being trapped in hazardous flow in a PMF event”

The report states it is imperative that actions are taken to visit, interview and photograph immediately following any event (or collect from residents who have taken pictures during the event) debris marks or similar that could be used for model verification. Perhaps we could set up a citizen science project...Flood Watch?