A project to review the river flood protection schemes got underway this week with the help of a drone flying the upper reaches of the Waihopai River.
Environment Southland policy and planning manager Lucy Hicks said the Climate Change Impact Assessment Report for Southland released earlier this year indicated that Invercargill could experience an increase in rain volume and intensity. “Because of this, we need to be sure that the flood banks, which protect people, property and livelihoods, are up to scratch.”
“Environment Southland has information on the Waihopai flood banks throughout Invercargill city, so this assessment is to ensure we have a more detailed picture of the flood banks from between the Waihopai detention dam and upstream of Kennington.”
Flood banks and detention dams are monitored three-monthly by Environment Southland’s catchment team and more detailed evaluations typically occur annually after their construction.
As part of the broader study, contractors are carrying out the survey and WSP senior surveyor Quenton Stephens is a Part 102 CAA accredited drone operator. He says this information will tie together what we have for above and below the dam, giving us more robust data.
The survey involved flying a drone in cross sections all the way up the river, with about 25 metres between. This provides a 70-75% overlap in the images that are captured by the drone, meaning the resolution is extremely high.
“In addition to assisting with planning for future climate impacts, the information from the survey will help determine the overall condition of the flood banks. Further analysis of the data will enable us to confirm that the flood scheme design continues to be fit-for-purpose,” Lucy says.
A final report will be presented to Environment Southland’s council in early 2020, and this method could be used as an efficient way of assessing other flood banks when they require detailed review and assist with future identification and reduction of hazard risks.
