Satellite view shows how the floods damaged the land

Scientists say a break in cloud cover over the North Island has allowed a satellite to photograph last month's flood damage in Tauranga in great detail.

Tauranga had its highest monthly rainfall in more than a century, 634mm, and more than half of this 347mm fell on May 17 and 18, causing widespread flooding.

The cost of the flooding damage has been estimated at $40 million to $50 million, and yesterday Landcare Research scientists said the United States QuickBird satellite had been used to take images of Tauranga for 10 local agencies.

The images looked like aerial photos, but were much more detailed, down to a 0.6-metre resolution, said Landcare Research scientist Murray Jessen.

"They really do provide a snapshot inventory of landslides and sedimentation from floodwaters," he said.

"We can extrapolate other information such as slope and type of soil, and look for causal relationships to answer questions about the safety of land that could be developed in the future."

Similar images acquired by Landcare Research from the French Spot5 satellite last year mapped the extent of the February flood damage to rural Manawatu, Wanganui and Rangitikei.

The image revealed that nearly 20,000ha had been lost to pasture production through some 62,000 landslides.

Satellite images could show factors such as the percentage of impervious areas like paths and buildings in the city.

Predictions for the effects of global warming have shown that New Zealand is likely to have more intensive weather events, including rainstorms, and stormwater management is likely to be a key issue in urban areas.

"No part of the country is safe from receiving the very high intensity rainfalls that are becoming increasingly common," Mr Jessen said.

"The image will be of real use for Tauranga's town planners and engineers, as it provides a geographically accurate picture of the event," said Mr Jessen, a soil scientist with special expertise in the remote collection data, and its use on geographical information systems.

In the case of Tauranga, the satellite imagery could be overlaid on existing maps to aid ground-based investigations. One possibility would be that if another agency had mapped soil types and underlying rock structure, or features such as sinkholes or tomos (steam holes in geothermal areas), they could be seen in the context of where the worst damage occurred.

"Tauranga clearly has sensitive geological features when even moderate slopes can give way as they have," Mr Jessen said.

Agencies such as the Geological and Nuclear Science Institute could use the images to add value to the geology advice they prepared for councils.

Landcare Research staff would discuss with other agencies the range of useful analysis which could be run from the imagery.

Mr Jessen said Landcare Research was increasing its research focus on urban design and said that poor urban planning eventually was "found out" by the climate.

- NZPA