Error ‘acceptable’

Press, 24 October 1984, Page 5

Error ‘acceptable’

The 5 per cent margin of error which affected data collected by Ministry of Works scientists gauging flows on the Rakaia River and making composite rating curves, was an “acceptable” margin of error, the Planning Tribunal was told yesterday. Mr M. J. Duncan, a scientist with the Ministry of Works Hydrology Centre, Christchurch, told the tribunal this after lengthy cross-examination by Mr J. R. Milligan, counsel for the Environmental Defence Society. Mr Duncan said a rating curve “altered in validity through the passage of time and the passage of water,” and admitted in his evidence that “estimates of flow are not absolute and may change as more data is gathered or if existing data is re-evaluated.” Nevertheless, Mr Duncan said he believed a 5 per cent margin of error was “an acceptable degree of error.” Mr Duncan also said that

the Rakaia Gorege was the only practical place on the entire river to measure the flows. Of the two waterlevel recorders in the gorge, the North Canterbury Catchment Board’s “Gorge” recorder, and the M.W.D. “Fighting Hill” recorder, Mr Duncan felt the latter would best serve the Rakaia Water Conservation Order in measuring water flows. Mr Duncan said in his evidence that although the proposed irrigation use would have a major effect on low river flows, information on low flows was sparse and therefore subject to large errors. Despite this he felt able to predict that if the abstraction demand was 70 cumecs, and the Draft Order minimum was 90 cumecs, applying the order’s sharing rules, the flow required to satisfy the conservation order would be 170 cumecs, and it would be possible to see that abstraction demand could be met 58 per cent of the time. Evidence on the physical

character of the Rakaia River, was given by Mr M.P. Mosley, leader of the Environmental Hydrology Group at the Hydrology Centre in Christchurch. A submission from the National Council of Women was presented to the tribunal by Mrs S. Rind, convener of the Council’s Christchurch Physical Environment Sub-committee. The first speaker of the day was an Ellesmere farmer, Mr K. R. Taylor, whose farm is on the banks of the Rakaia, speaking on behalf of local farmers. The tribunal will continue to meet in the main chambers of the Christchurch Civic Offices this week. The many appeals and submissions on a draft conservation order recommended for the river began on October 1. The hearing is expected to continue until late November. The tribunal comprises Judge Skelton (chairman), Mrs N. J. Johnston, and Messrs H. M. Dodd and R. A. McLennan.