Abstract
Rainfall Intensity formula and design rainfall distribution are fundamental information to design new sewer systems or renew the existing aging ones. The paper applied the multiple-samples selection method recommended by GBJ14-87 (1998) and introduced a case study of frequency analyses, rainfall IDF curves, rainfall intensity formula and design rainfall distribution. Catchment information and data (1991-2000) from Risvollan gauge station in Norway were applied for the case study. When the recurrence interval is over 10 years, however, those results show a methodological reference and may have high uncertainty. The results should be used carefully and modified when observation data are available in a long period.