Tauranga stormwater upgrade to cost $52m

More than $52 million is needed to upgrade Tauranga's stormwater systems in the wake of the May floods, says a new report.

The money is in addition to $18.6 million already allocated to improve the city's drainage.

The latest estimate would see spending on stormwater increase to levels well above the $2.5 million to $3 million currently spent on stormwater upgrades each year.

The report says almost $16 million would be needed in 2007 and between $3.5 million and $8 million each year until 2014.

The report is to be presented at a Tauranga City Council monitoring forum today.

The forum is open to the public and will be held at the council chambers on Willow St at 1pm.

The report, written by stormwater engineer John Palmer, says drainage design should take into account national predictions for climate change.

It said mean temperatures for the Bay of Plenty are estimated to be 3.8C higher in 2080 than in 1990, increasing the likelihood of high-intensity rainfall events such as the one on May 18, when 347mm of rain fell in 24 hours.

The report recommended installing pipe systems to dispose of most stormwater and said pipes needed 30 to 40 per cent greater capacity than existing ones.

It found landslides that accompanied the floods were caused by water flowing over vulnerable slopes.

Identifying areas where overland flow paths could be formed to accommodate excess stormwater was recommended.

Eliminating soakholes from hillside areas was also considered a priority.

Soakholes are used by about 4000 houses in Tauranga to drain rain from rooftops into the ground rather than stormwater pipes.

But the report said the council would not pay the cost of redirecting home downpipes from soakholes to the stormwater system.

Instead, owners of affected properties would pay the $3000 to $4000 bill each.

Property owners could not be forced to connect to the stormwater system, but the council would consider tagging property files where a connection had not been made.

The report also outlined plans for upgrading stormwater catchments.

In the Bureta catchment - one of the worst affected by the May 18 floods - creating an embankment at Otumoetai Golf Course to catch flood waters when stormwater drains were unable to cope was considered a possibility.

The latest records of the disaster show 40 houses were deemed a total loss, 399 buildings were flooded, 486 properties (but not buildings) were flooded, and 452 properties were hit by slips.

Estimated cost for stormwater upgrades in areas in Tauranga affected by May floods:

Bureta $13.4m
Pillans Point $12.6m
Otumoetai $11.4m
Mangatawa drain $1m
Matua $1m
The Avenues (Tauranga) $1m
Mt Maunganui (res.) $5m
Mt Maunganui (industrial) $5m
Other areas $2m

Total $52.4m