Influences on flood frequency distribution in Irish catchments

This study explores influences which result in shifts of generalized extreme value (GEV) flood frequency distributions in Irish rivers. Data from 139 gauging stations from 100 Irish rivers was analysed using the Hosking algorithm to determine whether Type I, II or III distributions are valid. Results indicate that hydrological data for 89 sites followed Type I distributions. Another 12 and 38 stations followed Type II and Type III distributions respectively. Type I distributions are spatially well represented throughout the country. The majority of Type III distributions appear in four clusters in geographical areas where attenuation influences from floodplains and lakes are influential. Type II distributions appear in a single cluster in a region in the west of the country characterised by a Karst landscape. Type II distributions in this area reflect the finite nature of Karst storage and the effects of saturation when storage is no longer available.