Clutha-Taieri area response manager Senior Sergeant Al Dickie said if riverbanks surrounding Mosgiel were breached by floodwaters residents could be trapped in the township as every escape route would be blocked.
A plan was needed on finding ways to evacuate residents, he said.
The Dunedin flood in June exposed weaknesses in the emergency response in Mosgiel.
''The last flood identified where things needed to be shored up and improved and [made apparent] the need for plans.''
Snr Sgt Dickie had begun working with several organisations to create plans, which would included a list of resources, such as generators and sandbags, so the operation centre and health centre could continue to operate after a natural disaster.
Mosgiel residents needed to take the potential flooding risk seriously.
''I think some people are a bit complacent.''
Mosgiel could flood in a similar way to Dunedin Airport in 1980. It nearly did in 2006, when western Mosgiel was evacuated, when floodbanks were nearly breached.
If a flood isolated Mosgiel, the biggest concern would be evacuating the elderly.
The group was working with rest-homes in Mosgiel to co-ordinate evacuation points.
''If they all rush to the same place it could become a mess.''
Southern District Health Board emergency management manager Paul McNamara was working with the group to identify vulnerable people who would need help in an evacuation.
Otago Regional Council engineering, hazards, and science director Dr Gavin Palmer said the council had identified areas in Mosgiel most prone to flooding and supplied topographical maps to help create a plan. Mosgiel residents could be prevented from leaving Mosgiel by floodwater, he said.
The Silver Stream could block the northern exit and Owhiro Stream could block the southern exit.
Snr Sgt Dickie said if people were trapped in Mosgiel and had to be evacuated, the ''high points of Mosgiel'' needed to be identified.
''There are not many of them, so the ORC has been assisting us with finding the safest places in town,'' Snr Sgt Dickie said.
He was working on an emergency response plan with a group including Mosgiel Taieri Community Board chairman Bill Feather.
Mr Feather said the group had been meeting monthly and included representatives from Police, Fire, St John, Neighbourhood Support, Community Patrol, East Taieri Church and medical centres in Mosgiel.
''We need a plan to keep our people safe,'' Mr Feather said.
Saddle Hill Community Board chairman Scott Weatherall was creating a plan with Snr Sgt Dickie in case a natural disaster hit the Saddle Hill area.
Snr Sgt Dickie said Outram also needed an evacuation plan because its residents could be physically isolated in a natural disaster. Outram Volunteer Fire Brigade members were developing a plan to deal with serious flooding in their area.
Dunedin city councillor Mike Lord, of Henley, said he was working on a strategy to evacuate residents and animals from the Taieri Plains.
The strategy would include a way to efficiently alert farmers of the evacuation so as to minimise fatalities.
Farmers would be called upon next year to help create the plan, he said.
''It's about getting the people out, and the cows out, with minimal loses of animals and people.''
