Abstract
In several studies it is necessary to determine the magnitude of extreme flows in a river. Having an adequate register of observed discharge it is possible to adjust a probability density function (fdp) that allows estimating events associated with a high return period (i.e. 100 years). In ungauged basins, such as the majority of basins in the world are, other methodologies are used, such as the Synthetic Unity Hydrograph proposed by the United State Soil Conservation Service (UH-SCS). The UH-SCS model was evaluated in watersheds of the Norte de Santander department (COL), in its capacity to estimate extreme flows, and to explore its possible regionalization. The evaluation is done by comparing estimates of Q100, using the Frequency Factors method and the UH-SCS model. Discharge and precipitation time series were obtained from the IDEAM network, selecting 19 basins based on their drainage area, climatological stations density and records length. Geomorphology was characterized using ArcMap™ on the ASTER-GDEM digital elevation model. Using information available on geology, soils, vegetation cover, and assuming a wet antecedent moisture condition (AMC-III), values of the median of relative Q100 error (ε-Q100) of + 507% and + 406% were obtained for the fdp Gumbel and Log-Pearson. Using dry antecedent moisture condition (AMC-I) ε-Q100 low to + 36% and + 17%. It was possible to minimize ε-Q100 by calibrating the Curve Number (CN) parameter. A satisfactory regionalization function for CN was not found. Applying SCS-HU under AMC-III condition, Q100 is greatly overestimated. It is possible to minimize the error by considering AMC-I and reduce CN, a counter-intuitive situation since extreme flows are associated with wet weather conditions (i.e. Año Niña). Improvements in the characterization of rainfall and soils in Norte de Santander should be investigated.
Highlights
Water resources management is essential for the planning and sustainable management of the environment in a country like Colombia that has a high biodiversity in much of its geographical extension
In the process of designing hydraulic works and road infrastructure, a fundamental requirement is the determination of the magnitude of hydrological events that may occur with certain frequency for extreme or maximum values during a given period, for example: The Q100, which corresponds at maximum flow for a return period of one hundred years, and is the most widely used in hydrological design
By not having historical flow data in most of the country’s river watersheds (Non-Instrumented Watersheds), these flows can be deduced through hydrological models, which have been developed, through empirical formulation, referred to as synthetic unit hydrographs, which estimate surface runoff based on the morphometric characteristics of the watersheds under study
Summary
Water resources management is essential for the planning and sustainable management of the environment in a country like Colombia that has a high biodiversity in much of its geographical extension. By not having historical flow data in most of the country’s river watersheds (Non-Instrumented Watersheds), these flows can be deduced through hydrological models, which have been developed, through empirical formulation, referred to as synthetic unit hydrographs, which estimate surface runoff based on the morphometric characteristics of the watersheds under study These models consist of the relationship of the parameters of the method, with the hydrological processes that occur in the basin; These models have been calibrated in the geography of the countries where they were developed, to establish their parameters, for this reason there is uncertainty in the application of these hydrological models in the region, because the values of the parameters are chosen subjectively
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