Unit Hydrographs and Regionalisation of United Kingdom River Flows: Comments on Some Estimation Uncertainties

Two types of unit hydrograph (UH) are discussed, with an emphasis on uncertainties. The paper reviews the 1-parameter triangular unit hydrograph (UH) employed to assist with systematic design flood hydrograph estimation for ungauged United Kingdom catchments. A 6-parameter rainfall-runoff model that incorporates a 3-parameter UH is also discussed. The precision and accuracy of characteristic decay times for dominant quick and slow response UHs, derived from the 6-parameter model, are examined in the context of uncertainty in flow regime regionalisation. On the basis that, as argued in the paper, the full potential of the 3parameter UH has yet to be exploited for regionalisation of flow regimes, there are plans for further work along these lines during the International Association of Hydrological Sciences (IAHS) Prediction in Ungauged Basins (PUB) Decade (2003-2012).