Who’s right about Nelson’s flood risk - the mapping or the locals?

A dispute over 40 centimetres of predicted sea level rise has sparked a flood mapping debate in Nelson that is now headed to an independent planning panel.

What happened? Glenelg Shire councillors voted unanimously last Tuesday to send unresolved objections to external review after residents challenged the accuracy of the flood modelling behind proposed new planning controls.

What’s the dispute about? At the centre of the disagreement are two future sea level rise scenarios used in the flood study: 0.8 metres and 1.2 metres by the year 2100.

• Some residents argue the higher scenario is too extreme and could wrongly place properties inside flood overlays, potentially affecting land values and their ability to build on their land.

• Council and flood authorities, however, say the modelling follows state guidelines and is designed to plan for future risk, not just current conditions.

The background: The flood study, first flagged in 2017, looks at land along the Glenelg River, from north of Dartmoor to the Nelson river mouth.

• The planning scheme amendment was authorised by the state government in October 2025 and went to public consultation between December to February. Five objections were received. 

• Because the dispute between objectors and council centres on technical evidence, the matter must now be tested through an independent planning panel.

Significant concerns: Councillor Mike Noske said the key issue raised by Nelson residents was whether the land height data used in the modelling was accurate.

• “There are significant concerns about the methodology of the flood study amongst the Nelson community,” he said.

• “There are also significant concerns that there is a differentiation between survey height of land and and the aerial height of land that was fed into the modelling,” he said. 

• “The hydrology can’t be perfect, but if the model says the land is a metre lower than it really is, then it's going to show it as being underwater compared to what reality might be.”

An expensive exercise: Councillor Michael Carr said he was frustrated the matter had reached the planning panel stage, which will cost the council about $25,000, but said it was the only path forward.

• “Applying a 1.2 metre level versus the mandated, legislated 0.8 metres, it's [74] years away. We're potentially devaluing these people's land right here, right now,” he said.

Now what? The panel will meet on May 4 and June 15 before reporting back to council, which will then decide whether to adopt the flood overlays.