Abstract
Flash floods are observed in the Una River Basin, Pernambuco/Brazil. This particular type of flood is a short-duration hydrological event with occurrence of the peak flow within minutes to few hours after the onset of the rainfall, taking place typically in mountainous regions. The objective of the paper was to assess the sub-daily hydrological and hydrodynamic modeling of flood events in 2011 and 2017. Sub-daily precipitation and streamflow were applied to the models Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS). Model evaluation methods such as Nash-Sutcliffe efficiency (NSE), percent bias, and the ratio of the root mean squared error to the standard deviation of measured data (RSR) were used in the calibration process. The maximum infiltration rate and the Snyder peak coefficient estimation were the most sensitive parameters in the hydrological model. The calibration of the HEC-HMS showed good performances (Catende station NSE=0.78 and RSR=0.46; Palmares station NSE=0.68 and RSR=0.57). During HEC-RAS 1D flow simulations, steep regions in the Una River caused numerical instabilities. The 2D solution was needed to overcome this problem, allowing us to represent the water level in the city of Palmares satisfactorily.
Highlights
Several factors can influence the occurrences of flood events such as land-use change, mainly due to increased imperviousness in urban areas, extreme precipitation events and topographic characteristics of the watershed
According to the classification of Moriasi et al (2007), the simulation performance can be considered between good and very good (RSR and Nash-Sutcliffe efficiency (NSE)), which reflects the agreement between the hydrographs simulated and observed after the calibration of the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model
Hydrological HEC-HMS model calibration performance pointed to good efficiency of the Una River flash flood simulations with hourly and sub-hourly (15 minutes) time steps
Summary
Several factors can influence the occurrences of flood events such as land-use change, mainly due to increased imperviousness in urban areas, extreme precipitation events and topographic characteristics of the watershed. Consequences from these events vary for every watershed and depend on a specific analysis for each one. Hydrologic and hydrodynamic studies are necessary for assessments aiming to minimize the impacts of floods on the population. Mitigation of flooding impacts on human activities can be done with techniques to anticipate these events for urban management and planning. Flash floods are rapid events characterized by the occurrence of the peak flow within minutes to few hours after the onset of the rainfall, taking place typically in mountainous regions. Considering cases of steep-slope river basins, for instance, in the Una River Basin in Pernambuco, Brazil, sub-daily runoff predictions are important to flood risk mapping, flood damage assessment and real-time flood forecasting
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