REGIONAL FLOOD FREQUENCY ANALYSIS FOR SMALL NEW ZEALAND BASINS: 1. MEAN ANNUAL FLOOD ESTIMATION

One hundred and forty New Zealand basins with areas of less than 100 square kilometres were used to investigate regional methods for estimating mean annual floods for small ungauged basins. Besides the usual sample estimate of mean annual flood, data on slope, soil and hydrogeology were processed from the New Zealand Land Resources Inventory for each basin. Other variables used in the prediction of mean annual flood were basin area, and three rainfall statistics for each basin: 1-hour and 24-hour 5-year return period intensities, and mean annual totals. Multiplicative regression models using catchment characteristics were less precise than McKerchar and Pearson specific mean annual flood contour maps.