Geomorphological Processes and Human Impacts in River Basins (Proceedings of the International Conference held at Solsona, Catalonia, Spain, May 2004). IAHS Publ. 299, 2005., 67-74.

The effects over time of an arterial drainage scheme on the flood magnitude–return period relations

KESHAV P. BHATTARAI1,2 & KIERAN M. O’CONNOR1

1 Department of Engineering Hydrology, National University of Ireland, Galway, Ireland

keshav.bhattarai@nuigalway.ie

2 Environmental Change Institute, National University of Ireland, Galway, Ireland

Abstract Arterial Drainage Schemes (ADSs) were implemented on Irish rivers for the purposes of improving the land drainage and reducing the frequency and extent of overland flooding. Such ADSs mainly involved the deepening and widening of the river channels in order to increase their discharge-carrying capacity, thereby, affecting not only the basins’ response to rainfall but also their peak discharge (QT)–return period (T) relation. Earlier Irish studies involving the effects of ADS on a catchment’s QT–T relation found that the post-drainage QT of an ADS-catchment was always larger, for the same T, in comparison to its pre-drainage counterpart. The current study focuses on investigating whether such effects have persisted in the ADS-catchments, or died out with the passage of time. Results of analysis on 16 ADS and 6-non-ADS catchments show that the ADS (post-1945)-catchments have experienced major changes in the QT–T relation over time, whereas such changes are less pronounced in other catchments.

Key words Arterial Drainage Scheme (ADS); flood frequency analysis; GEV distribution; method of L-moments; QT–T relationship