Scheme 'would degrade streams'

Lake Ellesmere and Canterbury's lowland streams will be further degraded by the revised $135 million Central Plains Water (CPW) irrigation scheme, independent experts say.

Commissioners considering CPW's scheme to irrigate a further 30,000 hectares of farmland have hired their own consultants to report on contamination and effects on waterways.

Report co-author Ned Norton, a National Institute of Water and Atmospheric Research scientist, yesterday told a resumed hearing into the project that there was little doubt contamination would increase because of the scheme.

Environmental aims would not be met without a significant reduction in current nutrient loads, he said.

"Adding the effects of CPW will make things worse by making the restoration job more difficult and future attainment of these objectives less likely."

"Pockets" of streams could remain unaffected by increased nitrates, but intensive irrigation could spell the end for those sensitive aquatic ecosystems.

"That's why we have guidelines."

Commissioners needed to balance environmental negatives against positives such as increased habitat for trout in lowland streams, a proposed environmental fund and catchment-wide farm-management plans, he said.

Co-author Dr Vince Bidwell, of Lincoln Ventures, said the thickness and extent of the contaminated groundwater plume would increase.

More shallow bores could be affected by high-nitrate concentrations because of the scheme, he said.

A predicted rise in nitrate-nitrogen concentrations from CPW and existing land use would be significantly toxic for aquatic plants and animals in lowland streams.

"It is clear from the information available that Te Waihora [Lake Ellesmere] is already a highly disturbed ecosystem and additional pressure from intensified land use will add to existing cumulative effects," the report said.

Hydrologist Peter Callander, for the Christchurch City Council, told commissioners the revised scheme did not pose a threat to aquifers that supply the city's drinking water.

However, the scheme could raise groundwater levels in rural areas west of Christchurch, including gravel-extraction pits, and lead to a higher water table in areas around Lake Ellesmere, he said.

The hearing continues today.

- © Fairfax NZ News