Quality of long flow records for New Zealand rivers

Residual mass curves for several long records from nearby recorders can be compared to identify discrepancies in data. For New Zealand, four of six rainfall records and two of nine discharge records extending from 1930 or earlier are shown to probably contain error. Outflows for a lake in the central North Island are shown to be inconsistent with long rainfall records; this is attributed to the works at the lake outlet to divert water to an early power station that no longer exists. Comparison of inflows for seven adjacent South Island lakes indicated serious discrepancies in the Lake Pukaki data. Corrections are suggested which reduce the estimated mean inflow for 1927-1992 from 132 mVs to 124 m³/s. Standard time series analysis methods suggest that the series show no evident trends or multi-year cycles.