Abstract
ABSTRACT Design hydrographs are widely used in practical hydrologic engineering problems. Typical applications adopt event-based (EBM) methods, using rainfall-runoff models to convert design hyetographs into design hydrographs. Uncertainties include the definition of antecedent conditions and the assumption of equivalence between hyetograph and hydrograph return periods. An alternative is to use continuous simulation (CSM) methods, by forcing a rainfall-runoff model with long precipitation series, and directly analyzing the output discharges. To better understand uncertainties in the EBM method and differences between CSM and EBM ones, we applied a hydrological model in the Itajaí-Açu river basin to compare a CSM method with 730 different simulations of an EBM one, considering different basin antecedent conditions and design hyetographs (10- and 50-years). Results indicated that the EBM method leads to a large range of design discharges depending on the antecedent condition. CS-based 10- and 50-years maximum discharges corresponded to percentiles between 30% and 50% of the EBM estimates. Higher discharge variation occurred in sub-basins with larger maximum soil water storage. Our conclusions agree with the literature, which points towards CSM-based methods to estimate design discharges.
Highlights
Estimating maximum discharges is a major topic in hydrology, being fundamental for many engineering applications as design of reservoirs and other hydraulic structures and flood control measures and flood risk mapping
As an alternative to the event-based approach, several authors suggested that design hydrographs and maximum discharges could be obtained by continuous rainfall-runoff simulation (BOUGHTON; DROOP, 2003; LAWRENCE et al, 2014)
We address the uncertainty in the predefinition of antecedent conditions in event-based methods
Summary
Estimating maximum discharges is a major topic in hydrology, being fundamental for many engineering applications as design of reservoirs and other hydraulic structures and flood control measures and flood risk mapping. Uncertainties exist in this event-based approach, including the definition of antecedent (initial or pre-event) soil moisture state and the hyetograph design itself This method assumes an equivalence between return periods of the adopted precipitation and the resulting hydrograph, what may not be always the case (GRIMALDI et al, 2012; HABERLANDT; RADTKE, 2014). As an alternative to the event-based approach, several authors suggested that design hydrographs and maximum discharges could be obtained by continuous rainfall-runoff simulation (BOUGHTON; DROOP, 2003; LAWRENCE et al, 2014) In this case, a continuous model is forced with a long period precipitation (observed or synthetic) to yield a long term discharge series (CALVER; LAMB, 1995; BOUGHTON; DROOP, 2003). An interesting alternative when long precipitation records do not exist is to use a weather generation algorithm to stochastically generate rainfall series, and run the continuous model with it (e.g., BLAZKOVA; BEVEN, 2002)
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