Flow estimation in an unstable river illustrated on the Rakaia River for the period 1958-1978

• Published in: Journal of hydrology (Amsterdam) Vol. 18; no. 2; pp. 88 - 108
• Main Author: Ibbitt, R P
• Format: Journal Article
• Language: English
• Published: 01.01.1979
• Subjects: Rakaia River, New Zealand
• ISSN: 0022-1694

The application of improved data checking techniques to the hydrological data for the Rakaia River at the Gorge Bridge station is described. Inadequacies in the existing data are demonstrated. Use of computer techniques to display gaging data permitted rating change points to be identified. By grouping together consistent sets of gagings, a single-type curve was developed. All ratings are obtained by moving the type curve parallel to the water level axis. In this way, small groups of gagings can be used to fix the position of a rating. Where there were no gaging data, rating changes were based upon differences in the water level hydrograph recession levels. To validate these rating changes, the annual flows, calculated with them were compared with annual means from one other flow station and seven rainfall stations. High correlations were established with West Coast rainfall stations, and a more detailed check of the flow data was made by using the Hokitika rainfall record. The accuracy of the flow values, calculated by using the new ratings, is assessed, and the 95% confidence limits are shown to vary between plus or minus 3 and plus or minus 11%. The upper limit is associated with three months of record where there were no gaging data and obvious silting problems in the water level record. As a consequence of the work, the long-term mean flow value was reduced by 5%.