George A Griffiths

Temporal patterns for design hyetographs in New Zealand

ABSTRACT Temporal patterns for design hyetographs are estimated by the average variability method for the main regions of New Zealand based on the records from regional clusters of at least five rain gauges with 30 year records. An asymmetric hyperbolic tangent function is used to model non-dimensional cumulative hyetographs for durations from one to 72 h. Results from this reconnaissance study indicate that the largest hyetograph peaks occur near the middle of a storm of 12 or 24 h duration. Slightly lower peaks occur marginally earlier for 1, 6 and 48 h duration peak. Both the 48 and 72 h durations have the lowest but similar peak sizes and the latter occurs latest in a storm for all durations. There is little difference between the cumulative hyetographs for all durations and regions between the North and South Islands and no apparent influence of return period on the results. Considerably more data from more locations are required to make substantive progress in empirical estimation of temporal rainfall patterns, to better understand the influence of return period and to define patterns for durations less than one hour. Hyetographs presented in this study should only be used as a guideline in design.