Impairment charges at Westpac New Zealand fell in the half year to March 2010, though that was thanks to the absence of two large provisions that the bank had to make in the preceding half-year period.The bank made impairment provisions of NZ$208 million in the latest half year, compared to NZ$388 million in the preceding September 2010 half.  But if you remove the NZ$199 million provision on two loans made in the September half, impairments continue to show a rising trend.The bank acknowledged that "impairment charges remain elevated from weaker economic growth and improved provisioning cover."The bank treats twenty-one per cent of loans to property developers in New Zealand as stressed.Much of the impairment have has come from the commercial property sector, with Westpac Group's CFO Phil Coffey noting that of the two segments, development property and New Zealand, there's been further deterioration in the latter.The new impairments were driven by higher individually assessed provisions and downgrades that necessitated an increase of NZ$60 million in new collectively assessed provisions. Looking ahead, any drop in such collective provision or release of provision would depend on the health of the property market, Coffey said.The fall in impairments to NZ$208 million from NZ$388 million largely contributed to the rise in net profit to NZ$125 million, sharply up from NZ$34 million in the September half. Net profit, however, fell from NZ$202 million in the same period a year ago.Core earnings fell to NZ$383 million from NZ$430 million. The bank's net interest margin fell significantly, to 207 basis points from 222 basis points, mainly due to increased wholesale and retail funding costs.An alternative measure of "economic profit", which allows for an 11 per cent cost of capital charge, shows Westpac made a loss in New Zealand in the latest half.