Hidrograma de Projeto em Pequenas Bacias
Keywords:
flood hydrograph, regionalization, Scarce dataAbstract
The estimation of the design hydrograph for small basins (< 2,000 km2) is a challenge due to the lack of flow data. The model usually used in this case is the NRSCS (NRSCS, 1975), where one of the main parameters is the CN, which estimates the amount of surface water in the basin. The CN value is estimated based on land use and type, but it brings with it many uncertainties due to the subjectivity of the choice of the CN parameter, leading to uncertainties in the estimated flows.
The proposed procedure uses the maximum average daily flow for the chosen risk (return time), obtained by regionalization of the maximum flows observed in the region, and the precipitation with the same risk to estimate the CN parameter, seeking to minimize the uncertainties of its estimate.
This methodology was applied in the Camboriu River basin (SC) with a drainage area of 127 km2 and a concentration time of 6 hours. The maximum average daily flow for each return time was obtained by regionalization by the Index Flood method (NERC, 1975) based on the data measured from the region. The estimated CN value was obtained based on the referred flow and precipitation for the same risk. This result was compared with the conventional procedure where the CN is obtained by the reference tables of the literature based on its land use. The result obtained based on the maximum regionalized flow tends to be more reliable, since it is based on flow data from the region. This methodology is not recommended when regionalization is unreliable. This can occur for basins smaller than 20 km2 that do not have data and extrapolation by regionalization has uncertainties.
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