River flood frequency approaches for ungauged sites

This paper discusses how research findings in continuous simulation methodologies are best used in practice for quantifying river flood frequencies: these are currently-developing next-generation methods. The work relates to the UK where current practice largely uses the 1999 Flood Estimation Handbook methods(both statistical peak analyses and unit hydrographs), and where recent research initiatives for nationwide systems have also involved the continuous time-base modelling of catchment flood generation responses. This national continuous simulation research has explored parameter-sparse hydrological modelling using a range of regression and site-similarity approaches for the spatial transference of flood characteristic information to ungauged river sites. Recommendations for best use of these parameter-sparse modelling methods are based on tests on over 100 UK catchments. In addition to numerical outcomes, other factors affecting choice of practical method include ease of use and ability to update methods.