Scientists helping to create safer communities

New information on how rivers will flood during extreme weather will soon be available to help communities become safer and reduce the costs of natural disasters.

A new project being carried out by scientists at the National Institute of Water and Atmospheric Research (NIWA) will see more than two decades of new data incorporated into New Zealand's flood frequency estimation system. This system includes data collected by about 650 river flow recorders monitored by NIWA and regional councils along New Zealand's rivers. Information from another 250 recorders that are no longer operational will also be used.

NIWA hydrologists, in collaboration with regional council staff involved in river and hazard management, are updating the system with 25 years of new data. The system was last updated in 1989 using data available up to 1987.

The information will improve understanding of flood risks across the country and help New Zealand become more resilient to extreme weather. It will also underpin a nationally consistent assessment of flooding risk recently called for by the Insurance Council of NZ.

NIWA hydrologist Roddy Henderson says since the previous study the amount of data available for analysis has more than doubled.

"This is because there are now longer records at flow sites used in the last study, and there are newer sites that will now have sufficient data to be included," he said.

The data is particularly useful for regional councils which use the information to learn how people living near a river may be affected by severe flooding and to help make decisions on projects such as where and how high to build new bridges.

The project has been supported by councils because flood estimation is a critical part of their responsibilities.

Tasman District Council hydrologist Martin Doyle, regional council liaison for the project, said the system was particularly important to councils.

"Flooding is the natural hazard which occurs most frequently in New Zealand, and is one of the most costly to the nation. The information from this study will be used
extensively by all councils for design and planning purposes on behalf of the communities they serve.

"We also have a strong interest in ensuring that other organisations correctly identify the risks associated with flooding. The extra data which is now available, combined with NIWA's work to develop an authoritative analysis methodology will greatly help to provide consistent and accurate data about flood significance for all regions in New Zealand."

Mr Henderson said the results of the project would be available on NIWA's website through an existing system for providing other important information about rivers to planners and engineers.

"The last time this was done the results were published in a book, so this represents a step forward in making the information as up-to-date and user-friendly as possible.

"We also expect to expose a number of questions in the process that we will then seek to answer. One example is the need for complete flood volume information rather than just a peak flow. This is important when considering the potential extent of flood inundation when rivers exceed the flow for which stopbanks have been designed."

The project is being funded by the Ministry of Business, Innovation and Employment's EnviroLink Fund and NIWA core funding and is  expected to take two years to complete.

NIWA is also undertaking other research programmes looking at how climate change may affect flood risk.