Planned Upgrade of NIWA's High Intensity Rainfall Design System (HIRDS)

Statistics of extreme rainfall play a vital role in engineering practice from the perspective of mitigation and protection of infrastructure and human life from flooding. While flood frequency assessments, based on river flood flow data are preferred, the analysis of rainfall data is often more convenient due to the finer spatial nature of rainfall recording networks, often with longer records, and potentially more easily transferable from site to site. Rainfall frequency analysis in New Zealand as a design tool has developed over the years from daily rainfall frequency maps to a web based tool. This paper briefly describes historic methodologies and outlines the planned upgrades for HIRDS Version 4. The aim of the upgrade is to search out and expand New Zealand’s rainfall dataset to improve coverage, include recent storms, and include historic paper records. The proposed upgrade will carry out analysis to extend the average recurrence interval to the 250 year return period, provide areal reduction curves and temporal patterns for design storms. Other features will include the ability to enable engineers to download maps of areas of interest for specified rainfall duration and frequency from a web site, and provide a comprehensive list of the rain gauges used.