Design hydrograph estimation in small and ungauged watersheds: continuous simulation method versus event-based approach

The proper assessment of design hydrographs and their main properties (peak, volume and duration) in small and ungauged basins is a key point of many hydrological applications. In general, two types of methods can be used to evaluate the design hydrograph: one approach is based on the statistics of storm events, while the other relies on continuously simulating rainfall-runoff time series. In the first class of methods, the design hydrograph is obtained by applying a rainfall-runoff model to a design hyetograph that synthesises the storm event. In the second approach, the design hydrograph is quantified by analysing long synthetic runoff time series that are obtained by transforming synthetic rainfall sequences through a rainfall-runoff model. These simulation-based procedures overcome some of the unrealistic hypotheses which characterize the event-based approaches. In this paper, a simulation experiment is carried out to examine the differences between the two types of methods in terms of the design hydrograph's peak, volume and duration. The results conclude that the continuous simulation methods are preferable because the event-based approaches tend to underestimate the hydrograph's volume and duration. Copyright (c) 2011 John Wiley & Sons, Ltd.