Bigger Gunnedah floods to come

It is encouraging to see a combination of local government, non-government support agencies and emergency service putting on a Get Ready and Resilience Expo event, in relation to recent flooding 2021-22

I hope that the event does not use the flooding episodes of 21/22, to celebrate that Gunnedah may have seen what mother nature has to offer in relation to floods. Another 1 metre to 1.35 metres of extra flood height, and considerable extra floodwater volume, is highly likely on the cards, with longer periods of at flood peak. At a date soon to arrive in the future. Looking at historical statistical information. So yes, it is prudent to “Get Ready”, but consider all flood scenarios.

My experiences a few years back, as a local landholder representative member, of the Carroll to Boggabri Floodplain Management Plan Committee, as well as recently a member of the Keepit Dam Airspace Reference Panel (KARP), has provided access to historical factual information, that is indeed a bit scary compared to the recent floods. Attached from the Floodplain Plan is a chart of 135 years of historical Gunnedah Namoi River-Cohens Bridge gauge height flood data, up to year 2000. This statistical information tells the story. As against recent flooding of around 8.5 metres/ 11 previous floods have been higher, some much higher! With land use changes and climate change, the Annual Recurrence Interval probability of more major extensive flooding is increasing. Also interesting is a snapshot of the operations of Keepit Dam, in the recent 2022 events September – November. Keepit Dam is primarily an irrigation dam, some management of airspace is possible before the start of the irrigation season, this can and did, mitigate flood flow volume at Gunnedah by 22-90 per cent, over five of those 2022 events. However, in larger floods, very little or no achievable flood mitigation measures are effective due to the huge water volume and many river tributaries that flow past Gunnedah. As example, the storage volume of Keepit Dam is 425,000 megalitres and the 1955 flood saw volumes of 800,030 megalitres per day/peak flow at the Gunnedah Namoi River Gauge.

So with no consistent pattern to flooding in the Gunnedah area, best to “Get Ready”, deal with some of the shortcomings that arose from recent events. But very much also consider what could be just around the corner. Plan for how best to handle that? It will be interesting to see what is put forward on “Get Ready Day” May 4, by local government and emergency services on how the many major floods to come, will be managed.

Geoff Hood, former member Carroll to Boggabri Floodplain Management Committee, member Keepit Airspace Reference Panel