Relações estatísticas entre precipitações intensas e vazões máximas: Método Gradex

Thls work contains a dlscussed bibliographic review of the main principles in whlch the Gradex Method Is based on. This method shows, in a simple way, the statistical relation between runoff and rainfall. A procedure has been developed for this nethod and applied to eighteen watersheds in São Paulo State, ln order to elimlnate the errors due to the method simplificatlons. Once there are no simplificat1ons, a great accuracy on the rainfall volumes determinations is obtained resulting in a better evaluatlon of the "Gradex" parameter. lt allows a better evaluation of the method and its basic hypothesis. There are statlstical relations between storm and maximum discharge that have been got from the accumulated distribution functions paralelism for the Type I Extremal Distribution which is applied to a set of runoff and rainfall volumes. It has been verified, by the studied watersheds. that the basic hypothesis method are valid for impermeable basins and that the groundwater contributions volumes have large influence on the statistical behavior or the maximum discharges. An ascencional tendency has been observed in the Gumbel probabilistic paper for the frequency volumes, that were drawn ln thelr respectively plottlng positions; and, indicated a statistlc populational non-homogenelty from the "effective precipitation" sample. The non-homogeneity occurs due the mixing between the groundwater and runoff contributions volumes, which have different statistlcal behaviors. The use of these sets, assumed as homogeneous, can lead to a underestimation of the discharges or its non-representation by a specific statistical distribution.