Rain a gauge of building needs

Years of research into heavy rainfall patterns should result in roads, bridges and stormwater systems that can better cope with extreme weather.

The National Institute of Water and Atmospheric Research (Niwa) has developed a web database so engineers know how much rain they should allow for when designing structures across New Zealand.

The system shows how frequently a site might experience torrential rain, and its likely intensity.

With funding from the Foundation for Research, Science and Technology, Niwa scientists looked at rain-gauge site data and how to calculate rainfall patterns between sites.

Niwa engineering hydrologist Graeme Horrell said it would be impossible to have rain gauges at every site where new roads and bridges were built.

There would never be complete rain-gauge site coverage, which made computer models essential for design engineering.

Engineers can select a location using Google Maps, and the web-based system works out storm rainfall for periods ranging from 10 minutes to 72 hours at average intervals from once a year to once every 100 years.

The model also allowed engineers to account for possible average temperature rises from climate change, Horrell said.

"It's pretty handy for figuring out, say, culvert dimensions, or how high you might need to build that bridge over a river," he said. "If you haven't got that information, you're flying blind.

"There's also interest from insurance companies too.

"They quite often, after a flood event, want to know the return period of it before they decide whether they will pay out."

The system is at niwa.co.nz/our-services/online-services/hirds.

- © Fairfax NZ News